v. When a mass of metal moves in the vicinity of a magnet it cuts the

lines of force emanating from its poles, thereby producing currents in its mass; as the production of these currents absorbs energy a damping effect is produced upon the movements of the mass.

Magnetic Gear. Friction gear in which electro-magnetic adherence is employed to draw the wheels together. (See Adherence, Electro-magnetic--Electro-magnetic Friction Gear.)

Magnetic Inclination. The inclination from the horizontal of a magnetic needle placed in the magnetic meridian. (See Magnetic Element--Inclination Map.)

Synonym--Magnetic Dip.

Magnetic Induction. The force of magnetization within an induced magnet. It is in part due to the action of the surrounding particles of polarized material; in part to the magnetic field. (See Magnetic Induction, Coefficient of.)

In a more general way it is the action of a magnet upon bodies in its field of force. In some cases the magnetism induced causes the north pole of the induced magnet to place itself as far as possible from the north pole of the inducing magnet and the same for the south poles. Such substances are called paramagnetic or ferromagnetic. They lie parallel or tangential to the lines of force. In other cases the bodies lie at right angles or normal to the lines of force. Such bodies are called diamagnetic.

Some bodies are crystalline or not homogeneous in structure, and in them the lines of magnetic induction may take irregular or eccentric paths. (See AEolotropic.)

Synonym--Magnetic Influence.

Magnetic Induction, Apparent Coefficient of. The apparent permeability of a paramagnetic body as affected by the presence of Foucault currents in the material itself. These currents act exactly as do the currents in the coils surrounding the cores of electro-magnets. They produce lines of force which may exhaust the permeability of the iron, or may, if in an opposite direction, add to its apparent permeability.

Magnetic Induction, Coefficient of. The number, obtained by dividing the magnetization of a body, expressed in lines of force produced in it, by the magnetizing force which has produced such magnetization, expressed in lines of force producible by the force in question in air. It always exceeds unity for iron, nickel and cobalt. It is also obtained by multiplying the coefficient of induced magnetization by 4 PI (4 * 3.14159) and adding 1. (See Magnetic Susceptibility--Magnetization, Coefficient of Induced.)

347 STANDARD ELECTRICAL DICTIONARY.

The coefficient of magnetic induction varies with the material of the induced mass, and varies with the intensity of the magnetizing force. This variation is due to the fact that as the induced magnetism in a body increases, the magnetizing force required to maintain such induction, increases in a more rapid ratio. The coefficient of magnetic induction is the same as magnetic permeability, and in a certain sense is the analogue of conductivity. It is also termed the multiplying power of the body or core magnetized. It is the coefficient of induced magnetization (see Magnetization, Coefficient of Induced) referred to a mass of matter. For diamagnetic bodies the coefficient has a negative sign; for paramagnetic bodies it has a positive sign.

Synonyms--Permeability--Multiplying Power--Magnetic Inductive Capacity.

Magnetic Induction, Dynamic. The induction produced by a magnetic field which moves with respect to a body, or where the body if moving moves at a different rate, or where the body moves and the field is stationary. In the case where both move, part of the induction may be dynamic and part static. (See Magnetic Induction, Static.)

Magnetic Induction, Static. Magnetic induction produced by a stationary field acting upon a stationary body.

Magnetic Induction, Tube of. An approximate cylinder or frustrum of a cone whose sides are formed of lines of magnetic induction. (See Magnetic Induction, Lines of.) The term tube is very curiously applied in this case, because the element or portion of a magnetic field thus designated is in no sense hollow or tubular.

Magnetic Inertia. A sensible time is required to magnetize iron, or for it to part with its magnetism, however soft it may be. This is due to its magnetic inertia and is termed the lag. Permanent or residual magnetism is a phase of it. It is analogous to self-induction of an electric circuit, or to the residual capacity of a dielectric.

Magnetic Insulation. Only approximate insulation of magnetism is possible. There is no perfect insulator. The best ones are only 10,000 times less permeable than iron. Hence lines of force find their way through air and all other substance, being simply crowded together more in paths of iron or other paramagnetic substance.

348 STANDARD ELECTRICAL DICTIONARY.

Magnetic Intensity. The intensity of the magnetization of a body. It is measured by the magnetic lines of force passing through a unit area of the body, such area being at right angles to the direction of the lines of force.

Magnetic Lag. In magnetism the tendency of hard iron or steel especially to take up magnetism slowly, and to part with it slowly. (See Magnetic Inertia.) The lag affects the action of a dynamo, and is a minor cause of those necessitating the lead of the brushes.

Synonym--Magnetic Retardation.

Magnetic Latitude. Latitude referred to the magnetic equator and isoclinic lines.

Magnetic Leakage. The lines of force in a field magnet which pass through the air and not through the armature are useless and represent a waste of field. Such lines constitute magnetic leakage.

Magnetic Limit. The temperature beyond which a paramagnetic metal cannot be magnetized. The magnetic limit of iron is from a red to a white heat; of cobalt, far beyond a white heat; of chromium, below a red heat; of nickel at about 350° C. (662°F.) of manganese, from 15° C. to 20° C. (59° to 68° F.)

Magnetic Lines of Force. Lines of force indicating the distribution of magnetic force, which is due presumably to whirls of the ether. A wire or conductor through which a current is passing is surrounded by an electro-magnetic field of force, q. v., whose lines of force form circles surrounding the conductor in question. A magnet marks the existence of a similar electro-magnetic field of force whose lines form circuits comprising part of and in some places all of the body of the magnet, and which are completed through the air or any surrounding paramagnetic or diamagnetic body. They may be thought of as formed by the Ampérian sheet of current, and analogous to those just mentioned as surrounding a conductor.

Fig. 223. MAGNETIC LINES OF FORCE, DIRECTION OF.

A magnetic line of force may be thought of as a set of vortices or whirls, parallel to each other, and strung along the line of force which is the locus of their centres.

If as many lines are drawn per square centimeter as there are dynes (per unit pole) of force at the point in question, each such line will be a unitary c. g. s. line of force.

349 STANDARD ELECTRICAL DICTIONARY.

Magnetic Mass. A term for a quantity of magnetism. Unit mass is the quantity which at unit distance exercises unit force.

Magnetic Matter. Imaginary matter assumed as a cause of magnetism. Two kinds, one positive and one negative, may be assumed as in the two fluid theory of electricity, or only one kind, as in the single fluid theory of electricity. Various theories of magnetic matter have been presented whose value is only in their convenience.

[Transcriber's note: See "magnet" and Edward Purcell's explanation of magnetism using general relativity.]

Magnetic Memory. The property of retaining magnetism; coercive force; magnetic inertia; residual magnetism.

[Transcriber's note: Small ferrite magnetic donuts were used as computer main memory from 1950 to 1970.]

Magnetic Meridian. A line formed on the earth's surface by the intersection therewith of a plane passing through the magnetic axis. It is a line determined by the direction of the compass needle. The meridians constantly change in direction and correspond in a general way to the geographical meridians.

Magnetic Moment. The statical couple with which a magnet would be acted on by a uniform magnetic field of unit intensity if placed with its magnetic axis at right angles to the lines of force of the field. (Emtage.) A uniformly and longitudinally magnetized bar has a magnetic moment equal to the product of its length by the strength of its positive pole.

Magnetic Needle. A magnet with a cup or small depression at its centre and poised upon a sharp pin so as to be free to rotate or oscillate in a horizontal plane. The cup is often made of agate. Left free to take any position, it places its magnetic axis in the magnetic meridian.

Magnetic Parallels. Lines roughly parallel to the magnetic equator on all parts of each of which the dip of the magnetic needle is the same; also called Isoclinic Lines. These lines mark the places of the intersection of equipotential surfaces with the earth's surface. They are not true circles, and near the poles are irregular ellipses; the magnet there points toward their centres of curvature. They correspond in a general way with the Geographical Parallels of Latitude.

Magnetic Permeability. The specific susceptibility of any substance, existing in a mass, for magnetic induction. (See Magnetic Induction, Coefficient of, synonym for Magnetic Permeability and Magnetization, Coefficient of Induced.)

Synonyms--Magnetic Inductive Capacity--Multiplying Power--Coefficient of Magnetic Induction.

350 STANDARD ELECTRICAL DICTIONARY.

Magnetic Perturbations. Irregular disturbances of the terrestrial magnetism, as by the aurora and in electric storms.

Magnetic Poles. The points where the equipotential surfaces of the terrestrial field of force graze the earth's surface; the points toward which the north or south poles of the magnetic needle is attracted. Over a magnetic pole the magnetic needle tends to stand in a vertical position. There are two poles, Arctic or negative, and Antarctic or positive. Magnetic needles surrounding them do not necessarily point toward them, as they point to the centres of curvature of their respective magnetic parallels. The poles constantly change in position. The line joining them does not coincide with anything which may be termed the magnetic axis of the earth.

Magnetic Poles, False. Poles on the earth's surface other than the two regular magnetic poles. There seem by observation to be several such poles, while analogy would limit true magnetic poles to two in number.

Magnetic Potential. The potential at any point of a magnetic field is the work which would be done by the magnetic forces of the field upon a positive unit of magnetism as it moves from that point to an infinite distance. (Emtage.)

Magnetic Proof Piece. A piece of iron used for testing magnets and the distribution of magnetism in bars, by suspending or supporting above or near the magnet, by detaching after adherence, and in other ways.

Magnetic Proof Plane. An exploring coil used for testing the distribution of magnetism. It is connected in circuit with a galvanometer, and exposed to alternation of current, or to other disturbing action produced by the magnet or field under examination. This affects the galvanometer, and from its movements the current produced in the coil, and thence the magnetic induction to which it was exposed, are calculated.

Synonym--Exploring Coil.

Magnetic Quantity. The magnetism possessed by a body; it is proportional to the action of similar poles upon each other, or to the field produced by the pole in question. It is also called the strength of a pole.

The force exercised by two similar poles upon each other varies with their product and inversely with the square of the distance separating them; or it may be expressed thus (m * m) / (L^2). This is a force, and the dimensions of a force are ML/(T^2). Therefore, (m^2)/(L^2) = ML/(T^2) or m = (M^.5)*(L^1.5)/T.

351 STANDARD ELECTRICAL DICTIONARY.

Magnetic Reluctance. The reciprocal of permeance; magnetic resistance; the relative resistance to the passage of lines of force offered by different substances. The idea is derived from treating the magnetic circuit like an electric one, and basing its action on magneto-motive force acting through a circuit possessing magnetic reluctance.

Magnetic Reluctivity. The reciprocal of magnetic permeability, q. v.

Synonym--Magnetic Resistance.

Magnetic Retentivity. The property of steel or hard iron by which it slowly takes up and slowly parts with a magnetic condition--traditionally (Daniell) called coercitive force.

Magnetic Rotary Polarization. If a plane polarized beam of light is sent through a transparent medium in a magnetic field its plane of polarization is rotated, and this phenomenon is denoted as above. (Compare Refraction, Electric, and see Electro-magnetic Stress.) This has been made the basis of a method for measuring current. A field of force varies with the current; the polarization produced by such field is therefore proportional to the current. (Becquerel & Rayleigh.)

A plane polarized beam of light passing through the transparent medium in the magnetic field by the retardation or acceleration of one of its circular components has its plane of polarization rotated as described. The direction of the lines of force and the nature of the medium determine the sense of the rotation; the amount depends upon the intensity of the field resolved in the direction of the ray, and on the thickness and nature of the medium.

Magnetic Saturation. The maximum magnetic force which can be permanently imparted to a steel bar. A bar may be magnetized beyond this point, but soon sinks to it. The magnetism produced in a bar is prevented from depolarization by the retentivity or coercive force of the bar. The higher the degree of magnetization the greater the tendency to depolarization.

It is also defined as the maximum intensity of magnetism produced in a paramagnetic substance by a magnetic field as far as affected by the permeability of the substance in question. The more lines of force passed through such a substance the lower is its residual permeability. It is assumed that this becomes zero after a certain point, and then the point of saturation is reached. After this point is reached the addition of any lines of force is referred entirely to the field and not at all to the permeability of the substance. But such a zero is only definable approximately.

Magnetic Screen. A box or case of soft iron, as thick as practicable, for protecting bodies within it from the action of a magnetic field. The lines of force to a great extent keep within the metal of the box on account of its permeability, and but a comparatively few of them cross the space within it.

Such screens are used to prevent watches from being magnetized, and are a part of Sir William Thomson's Marine galvanometer.

A magnetic screen may be a sphere, an infinite or very large plane, or of the shape of any equipotential surface.

Synonym--Magnetic Shield.

352 STANDARD ELECTRICAL DICTIONARY.

Magnetic Self-induction. The cause of a magnet weakening is on account of this quality, which is due to the direction of the lines of force within a magnet from the positive towards the negative pole. "A magnet thus tends to repel its own magnetism and to weaken itself by self-induction." (Daniell.)

Magnetic Separator. An apparatus for separating magnetic substances from mixtures. Such separators depend on the action of electro-magnets. In one form the material falls upon an iron drum, magnetized by coils. Any magnetic substance adheres to the drum and is thereby separated. They are used by porcelain makers for withdrawing iron particles from clay, by machinists to separate iron filings and chips from brass, and for similar purposes.

Fig. 224. MAGNETIC SEPARATOR.

Magnetic Shell. A theoretical conception of a cause of a magnetic field or of a distribution of magnetism. If we imagine a quantity of very short magnets arranged in contact with their like poles all pointing in the same direction so as to make a metal sheet, we have a magnetic shell. Its magnetic moment is equal to the sum of the magnetic moment of all its parts. If the shell is of uniform strength the magnetic moment of a unit area gives the strength of the shell; it is equal to the magnetic quantity per unit of area, multiplied by the thickness of the shell.

If its strength is uniform throughout a magnetic shell is called simple; if its strength varies it is termed complex.

Emtage thus defines it: A magnetic shell is an indefinitely thin sheet magnetized everywhere in the direction normal to itself.

Magnetic Shell, Strength of. The magnetic quantity per unit of area of the shell multiplied by the thickness of the shell.

353 STANDARD ELECTRICAL DICTIONARY.

Magnetic Shield. In general a magnetic screen, q. v. Sometimes a strong local field is made to act as a shield, by its predominance overcoming any local or terrestrial field to which the needle to be protected may be exposed.

Magnetic Shunt. The conception of a magnetic circuit being formed, the shunt is a corollary of the theory. It is any piece of iron which connects points of a magnet differing in polarity, so as to divert part of the lines of force from the armature or yoke. The shunt is especially applicable in the case of horseshoe magnets. Thus a bar of iron placed across from limb to limb a short distance back from the poles would act as a shunt to the armature and would divert to itself part of the lines of force which would otherwise go through the armature and would weaken the attraction of the magnet for the latter. In dynamos a bar of iron used as a magnetic shunt has been used to diminish the lines of force going through the armature and hence to weaken the field and diminish the electro-motive force. By moving the shunt nearer or further from the poles the dynamo is regulated.

In the cut the projections between the yoke and poles of the magnet shown act as a shunt to the yoke, taking some lines of force therefrom.

Fig. 225. MAGNETIC SHUNT.

Magnetic Storms. Terrestrial magnetic disturbances sometimes covering very wide areas, and affecting the magnetic declination and inclination. One such disturbance was felt simultaneously at Toronto, Canada, the Cape of Good Hope, Prague and Van Diemen's Land. (Sabine.)

354 STANDARD ELECTRICAL DICTIONARY.

Magnetic Strain. The strain produced by magnetic lines of force in substances exposed to their action. It is observed in substances placed between the poles of a strong electro-magnet, and evinces itself in the alteration of the optical properties of transparent substances.

Magnetic Stress. The stress produced by magnetic lines of force on substances through which they pass, evidenced in alteration of the optical properties of transparent bodies thus treated.

Magnetic Susceptibility. The specific intrinsic susceptibility of any material for magnetic induction. It refers to the particle of matter, and not to the mass, as in the latter its own particles react on each other and bring about what is termed permeability, q. v. (See also Magnetization, Coefficient of Induced, and Magnetic Induction, Coefficient of.)

Synonym--Coefficient of Induced Magnetization.

Magnetic Tick. When a bar of iron is suddenly magnetized or demagnetized it emits a slight sound, called the Page sound, or the magnetic tick. This has been utilized in a telephone by Reiss. The telephone will receive sound, but is very weak. It consists of a bar surrounded with a coil of insulated wire. Variations in current produce sounds, which may be articulate if the currents are produced by a telephonic transmitter.

Magnetic Twist. A bar of iron held in the magnetic meridian and pointing to the pole and twisted becomes to some extent permanently magnetized. Conversely a bar when magnetized seems to have a twist set up in it. The latter is magnetic twist.

Magnetic Variations. Changes in the value of magnetic declination or inclination. (See Magnetic Elements.)

Magnetism, Ampére's Theory of. A theory accounting for magnetic phenomena by assuming the existence of currents circulating around the molecules of permanent magnets. If such currents so circulate and all in the same direction, the result is the same as if the body of the magnet was enveloped in currents representing those of an electro-magnet or solenoid. This is because in the interior the current around one molecule would counteract the current around its neighboring ones in part, so that the only virtual currents left would be represented by those on the outer surfaces of the outer shell of molecules, and these virtually resolve themselves into one general current sheet, surrounding the magnet and coinciding with its surface.

The theory assumes that such currents permanently circulate around the molecules of paramagnetic substances. Under ordinary conditions there is no coincidence in their direction and no resultant current is produced. When magnetized or polarized the molecules are brought into order, so that the direction of their current coincides and the body becomes a magnet.

355 STANDARD ELECTRICAL DICTIONARY.

Fig. 226. AMPÉRIAN CURRENTS IN MAGNETS.

At the north pole of the magnet the direction of the Ampérian currents is the reverse of that of a watch when the observer faces the pole; the reverse obtains for the south pole.

The attraction of opposite and repulsion of similar poles is explained by the actions of the Ampérian currents upon each other. If north and south pole are placed together these currents will coincide in direction and hence will attract each other. If two like poles are put together the currents will have opposite directions and will repel each other.

No energy is supposed to be required to maintain currents around or in a single molecule.

Fig. 227. NORTH AND SOUTH POLES OF A MAGNET SHOWING DIRECTION OF AMPÉRIAN CURRENTS.

Magnetism, Blue. A term arising from the two fluid theory of magnetism; the magnetism of the south pole of a magnet. (See Magnetic Fluids.) The magnetism of the north pole is termed red magnetism. Both terms originated presumably in the painting of magnets, and are little used.

Synonym--South Magnetic Fluid.

356 STANDARD ELECTRICAL DICTIONARY.

Magnetism, Components of Earth's. The magnetic force of the earth acts in the plane of the magnetic meridian and in direction generally lies oblique to the plane of the horizon. It can be resolved into two components, one vertical, which has no directive effect upon the magnetic needle, the other horizontal, which represents the directive element for the usual compass needle. For the dipping needle, q. v., the vertical component is the only active one. A magnetic needle mounted on a universal joint at its centre of gravity would be acted on by both components.

Magnetism, Creeping of. The gradual increase of magnetism when a magnetic force is applied with absolute steadiness to a piece of iron. It is a form of magnetic lag. It may last for half an hour and involve an increase of several per cent. of the total magnetism.

Synonym--Viscous Hysteresis.

Magnet, Iron Clad. A magnet with a casing of iron connected at one end to the core. The term is generally applied to electromagnets of this form.

Synonyms--Tubular Magnet--Jacketed Magnet.

Magnetism, Decay of. The gradual loss of magnetism by permanent magnets, due to accidental shocks, changes of temperature, slow spontaneous annealing of the iron and other similar causes.

Magnetism, Discharge of. The loosing of magnetization. Thus in a shunt-wound dynamo there is a critical resistance for the outer circuit, below which the field ceases to be magnetized, as enough current ceases to be shunted into it to magnetize it. The machine is said to unbuild itself, and a discharge of magnetism occurs from the field magnet.

Magnetism, Ewing's Theory of. Ewing found by a model consisting of a number of pivoted magnetic needles that the observed phenomena of magnetization could be represented thereby. Thus there would be no need of assuming internal frictional forces of Maxwell, nor the closed rings or chains of Hughes. The theory retains the notion, however, of paramagnetic matter, consisting of an assemblage of molecular magnets. The loss of energy by hysteresis is represented in the model by the energy lost by the needles in beating against the air.

357 STANDARD ELECTRICAL DICTIONARY.

Magnetism, Free. The magnetism or magnetic field outside of a magnetic circuit. It is due to escape of lines of force and to the magnetic leakage through the air. The lines of force are never, under the most favorable circumstances, confined to the metallic circuit of the magnet and armature. In a simple magnet without armature all the lines of force have to follow an air path, and the field is at its strongest. As the magnetism is strongest at the surface near the poles, the term is sometimes understood as applying to the surface attraction. In such case it is defined as the distribution, on a magnetized bar or mass, of magnetic lines of force as they emerge from its surface.

Synonym--Surface Magnetization.

Magnetism, Hughes' Theory of. A theory accounting for magnetic phenomena by assuming that each molecule is a magnet, and that in a polarized or magnetized body they are all arranged with their poles in the same direction, while in an unmagnetized body their poles, alternating in direction, neutralize each other.

Magnetization consists in a partial rotation of the molecules so as to make them agree in position, thus, as a resultant developing north and south poles at the ends of the bar.

The theory is in a certain sense simpler than Ampere's theory, but is not so generally adopted.

Magnetism, Lamellar Distribution of. The distribution of magnetism in thin and uniform or "simple magnetic shells," q. v. A given distribution is termed lamellar if the substance in which it exists can be divided into simple magnetic shells, which either form closed surfaces, or have their edges in the surface of the substance. In lamellar distribution the polar area is very large compared with the distance between opposite poles.

Magnetism of Gases. Faraday experimented on this point by coloring gases with a little vapor of iodine or other colored gas, and letting them flow between the two poles of a powerful electromagnet. In this way he found some are repelled, some attracted, and in the case of oxygen, it is attracted at one temperature and repelled at another. At ordinary temperatures a cubic yard of oxygen possesses the magnetism of 5.5 grains of iron and when liquefied it is strongly attracted.

Magnetism or Magnetization, Temporary. When a mass of iron is magnetized by a current, when the current ceases the portion of its magnetism which disappears is the temporary magnetism; the portion retained is the residual or permanent magnetism.

Magnetism, Red. A term arising from the two fluid theory of magnetism; the magnetism of the north pole of a magnet. (See Magnetic Fluids.) The magnetism of the south pole is termed blue magnetism. Both terms originated in the painting of magnets. They are but little used.

Synonym--North Magnetic Fluid.

358 STANDARD ELECTRICAL DICTIONARY.

Magnetic Remanence. The residual magnetism left in a bar of steel or other paramagnetic material after the application of a powerful magnet. It is distinguished from coercive force, as the latter is the amount of negative magnetizing or of demagnetizing force required to reduce the remanent magnetism to zero.

Synonym--Remanence--Residual Magnetism.

Magnetism, Solenoidal Distribution of. The distribution of magnetism in such a way that the poles are very far apart in proportion to their area. The magnetization of a long thin bar of steel illustrates solenoidal distribution.

Magnetism Sub-permanent. The magnetism of a paramagnetic substance which presents a considerable degree of permanency, but which gradually disappears, leaving the permanent magnetism present. It is noticeable in iron or steel ships whose magnetism gradually reduced in quantity, eventually becomes fully permanent.

Magnetism, Weber's Theory of. The molecules of a magnetizable material by this theory are supposed to be magnets with their poles lying in every direction, and hence neutralizing each other. By magnetization these are supposed to be turned with their similar poles in the same direction, and their axis parallel, hence acting like a group of magnets. It is practically identical with Hughes' theory.

Magnetism, Terrestrial. The magnetism of the earth. (See Magnetic Elements.)

Fig. 228. MAGNETIZATION BY DOUBLE TOUCH.

Magnetization by Double Touch. The process of magnetizing a steel bar by simultaneously stroking it with two poles of a horseshoe magnet or with two opposite poles of two bar magnets. The poles must be close but not touching. A block of wood may be placed between the ends if single magnets are used. The poles are placed on the middle of the bar and carried back and forth to one end, then to the other, and so on, ending at the middle of the bar in such direction as to give each end the same number of strokes. The poles must be close together or consequent poles will be produced. If bar magnets are used they may be held inclined at an angle of 15º to 20º with the horizontal bar to be magnetized. The ends of the latter may rest on poles of two other magnets, each end on a pole of the same name as that of the magnetizing magnet on its side. (See Magnetization, Hoffer's Method.)

359 STANDARD ELECTRICAL DICTIONARY.

Magnetization by Separate Touch. A method of magnetization. Two magnets are used. Held in an inclined position two opposite poles are touched to the bar near its centre, and are drawn off to the two ends. They are returned through the air and the process is repeated.

Magnetization by Single Touch. A method of polarizing or magnetizing steel bars, by stroking them always in one direction with one pole of a magnet, returning it through the air. The stroking is best done on both sides. The stroking may begin at one end and end at the other, or it may be commenced in the center of the bar and be carried to one end with one pole, and the same done for the other half with the other pole.

Magnetization by the Earth. The earth imparts magnetism to iron masses. If a rod of steel is held parallel to the inclination and in the magnetic meridian it exhibits polarity, which by jarring or hammering, can be made to some extent permanent. A piece of soft iron held vertically, or still better in the line of the dip as above, and which is twisted when in that position, becomes magnetized with some degree of permanence. Many other instances are cited, such as fire-irons, lamp-posts, iron gates, lathe turnings, all of which often exhibit polarity, having been magnetized by the earth's field.

[Transcriber's note: The earth's magnetic field is believed to originate it electric currents in the moving molten core.]

Magnetization, Coefficient of Induced. The coefficient (q. v.) expressing the relation between the specific intensity of magnetization of a particle and the magnetizing force. The magnetizing force is measured by the lines of force it can produce in a field of air. The coefficient of induced magnetization is the factor by which the intensity of a magnetizing field must be multiplied to produce the magnetization imparted by it to a particle of any substance. This coefficient varies for different substances, and is also called magnetic susceptibility. It is distinguished from permeability as referring only to a particle isolated from influence of a mass of surrounding particles of its own kind. It is definable as the intensity of the magnetization assumed by an exceedingly long and exceedingly thin bar placed in a unit field. If a mass of metal were placed in such a field all its particles would become affected and within the mass no unit field could exist. Hence magnetic susceptibility (another name for this coefficient) does not apply to the case of large cores of electro-magnets and dynamo-armatures, but is really a theoretical rather than a practical figure.

The sign of the coefficient of diamagnetic bodies is negative; of paramagnetic bodies is positive.

Synonym--Magnetic Susceptibility. \

360 STANDARD ELECTRICAL DICTIONARY.

Magnetization, Cycle of. A cycle of positive or of positive and negative magnetization represents the application of a magnetizing force beginning at a fixed value, generally zero, rising to a maximum, or to a value of maximum distance from the initial and then returning to the original basis. It is virtually a full wave of magnetization and may extend on both sides of a zero line giving positive and negative values.

Cycles of magnetization apply especially to transformers and other apparatus of that character used with the alternating current system.

Magnetization, Hoffer's Method. For horseshoe bars an armature is placed against the poles of the magnet bar to be treated. The poles of a strong horseshoe magnet are stroked over it from poles to bend and returned through the air, or vice versa. In the first case the poles will be the same as those of the inducing magnet; in the second case they will be opposite. A maximum effect is produced in ten strokes. The stroking should be applied to both sides. An electro-magnet may be used as inducer as shown, but an armature should be used; in the cut it is omitted.

Fig. 229. MAGNETIZING A HORSESHOE MAGNET.

Magnetization, Intensity of. The amount of magnetism induced in or present in a body. It is expressed in Magnetic Lines of Force, q. v., per cross-sectional area.

Magnetization, Isthmus Method of. A method used by Ewing in a research on the magnetization of iron in very strong fields. He used samples of iron turned down in the centre to a narrow neck, and thus concentrated the lines of force greatly.

Magnetization, Elias' Method. The bar to be magnetized is surrounded by a magnetizing coil, q. v. A strong current is passed through it, and the coil is moved back and forth a few times.

Magnetization, Jacobi's Method. For horseshoe bars. The bar is placed with its poles against those of a horseshoe magnet. A bar of soft iron, long enough to reach from outside to outside of the legs, is laid across near the junction and is drawn along towards the bend of the new bar and away from it. This is repeated a few times on both sides.

361 STANDARD ELECTRICAL DICTIONARY.

Magnetization, Limit of. As the induction of magnetizing force increases, magnetization of paramagnetic metals tends towards a limit, the increase in magnetization being continually less and less as the metal becomes more highly magnetized. In diamagnetic substances no limit is discernible.

Synonym--Maximum Magnetization.

Magnetization, Specific. The magnetic moment per gram of a substance.

Magnet-keeper. A bar of iron connecting the two poles of a permanent magnet. Often the same bar serves as armature and keeper.

Magnet, Lamination of. It is advantageous to make magnets of laminated construction, or of thin plates of steel. The thin metal can be better tempered or hardened than thick metal. A slight separation of the plates is advantageous from some points of view. If in actual contact there is some danger that the weaker members will have their polarity reversed by the stronger ones. This is counteracted to some extent by separation.

Magnet, Long Coil. A high resistance electro-magnet; one whose coil is of thin wire of considerable length.

Magnet, Natural. The lodestone, q. v.; a variety of magnetite or magnetic oxide of iron, exhibiting permanent magnetism, attracting iron, and possessing north and south poles.

Magnet, Neutral Line of. A line at right angles to the magnetic axis of a magnet, q.v., and nearly or quite at the centre, so situated with reference to the poles on either end that it marks the locus of no polarity. It has been called the equator of the magnet. It is defined by the intersection of the plane of no magnetism with the surface of the bar.

Synonym--Magnetic Equator.

Magnet, Normal. A bar or compound bar magnet, magnetized to such an extent that the curves of the lines of force run into each other in the middle, is thus termed by Jamin.

Magneto. Abbreviation for Magneto-electric Generator. (See Magneto-electric Generator.)

Magneto Call Bell. A call operated by current from a magneto-electric generator. It is very generally used in telephone systems.

362 STANDARD ELECTRICAL DICTIONARY.

Magneto-electric. adj. Relating to induced electric effects due to the cutting of true magnetic lines of force by, or equivalent action of or upon a conductor. These effects are identical with electro-magnetic effects and are only distinguished from them by the field being due to a permanent magnet instead of an electromagnet.

Magneto-electric Brake. A device for bringing to rest an oscillating galvanometer needle. It consists essentially of a coil in circuit with a key and with the galvanometer. On opening the circuit an inverse current is established by induction, tending to bring the needle to rest.

Magneto-electric Generator. A current generator operating by maintaining a potential difference at its terminals, by reactions in a field of force, which field is established by a permanent magnet.

The cut, Fig. 230, shows the general principle of construction of a direct current generator. The armature is rotated between the poles of a permanent magnet. Any of the regular types of dynamo armature can be used. From its commutator the current is taken by brushes.

Fig. 230. MAGNETO-ELECTRIC GENERATOR.

Fig. 231. MAGNETO-ELECTRIC GENERATOR.

363 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 231, shows an alternating current machine. In it a pair of bobbins, wound in series, and both either right-handed or left-handed, are rotated between permanent magnet poles. The current may be taken off by two brushes bearing on two collecting rings on the axis of the bobbins, the ends of the wire being connected thereto. Or if a shocking current is desired, one of the brushes or springs may strike a series of pins forming virtually a broken or interrupted collecting ring. This gives a current for medical purposes.

Synonyms--Magneto-dynamo--Magneto-electric Machine.

Magnetograph. An apparatus for recording variations in magnetic elements. One type includes a magnetic needle to which a concave mirror is attached. The light ray from the mirror is reflected upon sensitized paper where its movements are photographically reproduced. The movements of the spot are due to the movements of the needle and act as the record of the same.

Magneto-Inductor. An instrument for use with a ballistic galvanometer to reproduce a definite current impulse. Two magnets are fastened together in one straight line, the north poles almost touching. This is mounted at the end of a rod like a pendulum, the axis of the magnets transverse to the rod. The magnets are carried by a frame and oscillate at the end of the rod, back and forth within a fixed coil, which is one-half the length of the double magnet. A bob is attached to the bottom of the frame by which the whole can be swung. As the magnets are of fixed value, their time of oscillation constant, and the coil fixed in size, the apparatus provides a means of getting a definite instantaneous current of identical value whenever needed.

Fig. 232. MAGNETO-INDUCTOR.

364 STANDARD ELECTRICAL DICTIONARY.

Magnetometer. (a) A reflecting galvanometer, with heavy magnetic needle, dampened by a copper frame. It was devised by Weber.

(b) An apparatus for measuring the intensity of magnetic force. It may consist of a magnet suspended by bifilar or by torsion suspension. A reflecting mirror and scale as in the reflecting galvanometer may be used to act as indicator of its motions. It is used in investigations of the intensity of the earth's field.

If the motions of the spot of light are received on a moving strip of sensitized paper and are thereby reproduced photographically, the instrument is self-recording. Such an apparatus is used in the Kew Observatory, Eng., for recording the terrestrial magnetic elements.

Magnetometry. The determination of the magnetic moment of a magnet.

It involves the determination by experiment of--( a) the product of the magnetic moment, M, of the magnet by the horizontal component, H, of the earth's magnetism; (b) the quotient of M divided by H. Knowing these two quantities, M is given by the formula M = SquareRoot( )M * H) * (M/H) ) and if desired H is given by the formula H = SquareRoot( (M*H) / (M/H)).

M*H is determined by the method of vibrations. A very long, thin magnet suspended by a torsion filament is caused to oscillate, and its period is determined. Calling such period T and the moment of inertia of the magnet I, we have the formula T= 2* PI * SquareRoot( I / (H*M) ) (a), whence H*M is calculated, I of course being known or separately determined.

Fig. 233 END-ON METHOD.

Fig. 234. BROADSIDE METHOD.

M/H is determined by the End-on deflection method, or the Broadside deflection method. In both cases the deflection of a compass needle by the magnet in question is the basis of the work.

In the end-on method AB is the magnet under examination; DE the compass needle; a the angle of deflection; d the distance between C and the middle of AB, which should be considerable compared with the length of DE; 2l, the length of AB. We then have the formula tan a = (M/H) * (2d / (d^2 - l^2)^2), which if 2l is small compared to d reduces to tan a = M/Hd 3

(b), which gives M/H, a and d being known.

365 STANDARD ELECTRICAL DICTIONARY.

In the broadside method the line d is the magnetic meridian, and the diagram shows the relative positions. We then have the formula tan a = (M/H) / (d2 + l2)^1.5; which if 1 is relatively small reduces to tan a = M/(H * d3 )(C.)

[Transcriber's note: The image of the above paragraphs is included here.]

a and c or a and b can be combined giving M and H in C.G.S. measurement.

Magnetometer, Differential. An apparatus, invented by Eickemeyer, for testing the magnetic qualities of different samples of iron. It is very similar in construction and principle to the magnetic bridge, q. v.

Magneto-motive Force. The force producing a magnetic field or forcing lines of force around a magnetic circuit. It is usually applied only to electro-magnets and is expressible in turns of the wire winding multiplied by amperes of current, or in ampere-turns.

Magnet Operation. A term in surgery; the use of the electro-magnet or permanent magnet for removing particles of iron from the eye.

Magnetoscope. An apparatus for detecting the presence of magnetism, without measuring its intensity. A simple magneto-scope consists of a magnetized bit of watch-spring suspended in a vertical glass tube by a fine filament. A bit of unmagnetized soft iron wire may be used in the same way. The first has the advantage of indicating polarity; the latter merely shows magnetic attraction. A cork may be used as base of the instrument.

Fig. 235. MAGNETOSCOPE.

366 STANDARD ELECTRICAL DICTIONARY.

Magnet, Permanent. A bar of steel charged with residual magnetism. Steel possesses high coercive force in virtue of which when once magnetized it retains part of the magnetization.

Permanent magnets are generally straight bars or U shaped; they are termed bar magnets, magnetic needles, horseshoe magnets, machine magnets and otherwise, according to their shape or uses.

Magnet Pole. The part of a magnet showing strongest polarity; the part which attracts iron the most powerfully, and acts as the starting point for lines of force.

Magnet Poles, Secondary. Magnet poles are often not situated at the ends. Owing to inequality of the material or other causes they may occupy intermediate positions on the magnet. Such poles are called secondary poles.

Magnet Pole, Unit. A unit magnet pole is one which exerts unit force on another unit pole placed at unit distance from it. Unit force is the dyne; unit distance is one centimeter.

Magnet, Portative Power of. The power of sustaining a weight by attraction of its armature possessed by a magnet. In general terms the adherence of the armature of a magnet to the pole varies with the square of the number of lines of force which pass through the point of contact. Hence an increased adherence of the armature to a horseshoe electro-magnet is sometimes obtained by diminishing the area of contact of one pole which concentrates the lines of force. Steel magnets were frequently made with rounded ends to increase the portative power.

Magnet, Simple. A magnet made of one piece of metal, or at least magnetized as such; the reverse of a compound magnet, which is magnetized piece by piece and then fastened together.

Magnet, Solenoidal. A magnet which is so uniformly magnetized and is so long in proportion to its other dimensions that it virtually establishes two magnetic poles, one at either end. It is a long thin bar so magnetized that all its molecules would, considered as magnets, be absolutely equal. (Daniell.) It acts like a solenoid, except that it is longer in proportion than the solenoid generally is constructed.

Magnet, Sucking. A magnet coil with movable or loose axial bar of soft iron.

The whole is usually mounted vertically. When a strong enough current is passed the bar is drawn up into the coil as if by suction, whence the name.

367 STANDARD ELECTRICAL DICTIONARY.

Magnet, Unipolar. No such thing as a unipolar magnet is possible. The name is given to poised or suspended magnets, one of whose poles lies in the axis of suspension. It is obvious that such a magnet will act, as far as its directive tendency and rotatory movements are concerned, as if it had only one pole. As shown in the cut, the pole s in both magnets lies in the axis of suspension or directly under the filament by which they are suspended, while the other pole n is the active pole in causing rotation or directive tendency; c c are counterweights or counterpoises.

Fig. 236. UNIPOLAR MAGNETS.

Magnetophone. An apparatus for producing a loud sound, involving the principles of the telephone. A rapidly alternating or make and break current being produced by any means and being transmitted through the telephone gives a loud note of pitch dependent on the current producing it. Sometimes a perforated metallic disc is rotated in a magnetic field, and produces the requisite type of current.

Magnus' Law. A law of thermo-electricity. In a homogeneous circuit, however, the temperature varies from point to point; there is no current.

Whatever potential differences may be established by the variations in temperature it is evident that they must counteract each other and reduce to zero.

Mains, Electric. The larger conductors in a system of electric light or power distribution.

Make. v. To complete a circuit, as by closing a switch.

Make and Break Current. A current which is continually broken or interrupted and started again. It is applied only where the "makes" and "breaks" succeed each other with great rapidity, as in the action of an induction coil or pole changer, etc. It has had considerable importance in litigation affecting the Bell telephone patents, the courts holding that the original Bell patent (No. 174,465, of 1876,) covered the undulating current, for the transmission of speech. Many efforts have been made by litigants to prove that specific telephones have transmitted articulate speech by the make and break current, but without success. If this could have been proved the assumption is that the courts would have sustained the use of such device as not infringing upon the claims of the Bell patent.

Malapterurus. A fish, sometimes called the thunder fish, an inhabitant of African rivers, occurring in the Nile and Senegal. It possesses considerable electric power, similar to that of the gymnotus and torpedo, although inferior in amount.

368 STANDARD ELECTRICAL DICTIONARY.

Fig. 237. MALAPTERURUS.

Man-hole. The cistern-like depression in the ground for giving access to the ends of tubes in electric conduits. (See Conduit, Electric Subway.)

Marked End or Pole. The north pole or north seeking pole of a magnet, so called because it is usually marked with a notch or scratch by the maker. The south pole is called the unmarked end.

Mass. The quantity of matter in a body. The C. G. S. unit of mass is the quantity of matter in a gram. While weight varies with latitude and other circumstances, mass is invariable.

The unit of mass is also defined as the quantity of matter which in a balance will counterpoise a standard mass, the gram or pound. As the gram is intended to be the mass of one cubic centimeter of water at 3.09º C. (39º F.), the C. G. S. unit of mass is really 1.000013 gram.

As a primary unit its dimensions are indicated by M.

Mass, Electric. A term for quantity of electricity. The unit mass is such a quantity as at unit distance will act with unit force.

Matter, Electric. The imaginary substance constituting electricity; a conception used purely as a matter of convenience.

[Transcriber's note: The electron was discovered five years after this publication.]

Matter, Radiant. Matter in the ultra-gaseous or so-called fourth state. In the gaseous state the molecules of a gas are in perpetual kinetic motion, colliding actually or virtually with each other, rebounding from such approach, and striking also the walls of the containing vessel. But except for these deflections, which are of enormous frequency, the paths of the molecules would be perfectly straight.

In the radiant state matter exists in so high a vacuum that collisions of the molecules rarely occur, and the molecules simply beat back and forth in straight lines from side to side of the containing vessel.

A layer of gas in this condition is termed a Crookes' layer, from Prof. William Crookes, who discovered and investigated these phenomena.

369 STANDARD ELECTRICAL DICTIONARY.

Luminous streams of the molecules are produced by electric high potential discharges between electrodes. The course of the discharge is normal, in general terms, to the surfaces of the electrodes, and reaches from one to the other in a curve or straight line, as the case may be.

These luminous streams are deflected by a magnetic field; if brought to a focus can heat refractory material in that focus to a full white heat, and can develop phosphorescence. The latter is termed electric phosphorescence. A great variety of experiments have been devised to illustrate the phenomena of radiant matter. The vacuum is generally produced in a hermetically sealed glass vessel into which the electrodes are sealed, and which contain the phosphorescent substances or other essentials for the experiments. The vessels are termed Crookes' Tubes.

[Transcriber's note: Crookes reported on "radiant matter" in 1879. It is actually electrons, but he failed to distinguish them from ordinary atoms. Thompson properly described electrons in 1897.]

Matteueci's Experiment. An experiment for showing the inductive effect of the discharge of a Leyden jar. Two glass plates are supported on standards in a vertical position. Flat coils of wire are wound or coiled and secured to one surface of each plate. One plate has much finer and longer wire than the other. Metal handles are connected to the ends of the coarser wire coil. The plates are placed with their coils facing each other. A Leyden jar is discharged through the coarser coil, while the handles are grasped by a person. The shock of the discharge is felt by him.

Matting, Electric Floor. Matting or floor covering underlaid with burglar alarm contacts, so arranged as to be closed by anyone walking on the matting. The contacts are connected to a burglar alarm system. The object is to provide an alarm if a burglar enters a house, in case he should enter a door or window without sounding the bell. The latter can be done by cutting out the window or part of the door instead of opening it.

Maxwell's Theory of Light. A theory of light. It is due to J. Clerk Maxwell.

It supposes the phenomena of electric induction to be due to the ether, q. v. It supposes the condition of the ether when conveying light to be the same as if exposed to the induction of rapidly alternating currents or discharges (in this case synonymous). It therefore is an electro-magnetic effect if the theory is correct.

An electric stress such as one due to the induction of an electrostatically charged body is not a wave-creating element or factor, but is a simple stress. But let this stress be stopped and renewed and at once it appears as a wave-forming agency.

This stoppage and renewal represents evidently a discharge succeeded by a charge, or if repeated is equivalent to an intermittent current or an alternating one.

370 STANDARD ELECTRICAL DICTIONARY.

Again the electrostatic stress kept constant may by being carried through space carry with it a wave, just as a moving projectile carries a wave of air in advance of itself.

Admitting this much the following consequences follow:

Since in non-conductors the displacement produces a restitution force, which varies as the displacement which is requisite or is a criterion for the propagation of waves, while in conductors no such force is manifested and the electric energy appears as heat, it follows that light vibrations are not possible in conductors, because electro-magnetic waves do not exist in them when they are in circuit, and conductors should be opaque, while the reverse is true for non-conductors. (Daniell.)

This is carried out often enough to make a striking evidence in favor of Maxwell's theory.

The velocity of propagation of an electro-magnetic disturbance in a non-conductor should be equal to that of light. This constant is proved by mathematical considerations, to be approximately the same as the ratio of the electrostatic to the electromagnetic unit of intensity or quantity. This ratio is 3E10 (30,000,000,000), which is almost exactly the velocity of light.

It also follows from what has been said that if an electrostatically charged body were whirled around a galvanometer needle at the rate of 3E10 revolutions per second it should affect it like a circulating current. This rate of rotation cannot be attained, but Rowland has made manifest the effect of a rotating statically charged body upon a magnetic needle.

The above is the merest outline of Maxwell's theory. The full development must be studied in his own and succeeding works.

Mayer's Floating Magnets. An experiment due to Prof. Mayer. A number of sewing needles are magnetized and thrust into bits of cork, almost all the way through, with their like poles projecting. They are floated in a basin of water and take, under the effects of attraction and repulsion, when approached by a magnet pole, regular geometric positions, marking out the positions of angles of polygons.

Measurements. The determination of the value of quantities; determination of the factor by which the unitary value must be multiplied to produce the quantity under examination. Such are the measurement of the voltage of a galvanic battery, or of the ohms of resistance of a conductor. Electricity has been termed the science of measurement.

Meg or Mega. A prefix, meaning one million times. A megohm is one million ohms; a megerg is one million ergs; a megadyne is one million dynes.

371 STANDARD ELECTRICAL DICTIONARY.

Fig. 238. MAYER'S FLOATING MAGNETS.

Mercury. A metal; one of the elements; symbol, Hg; atomic weight, 200 ; equivalent, 200 or 100; valency, 1 and 2. It is a conductor of electricity. The following data are 0º C. (32º F.) Relative Resistance, 62.73 Specific Resistance, 94.32 microhms. Resistance of a wire, (a) 1 foot long, weighing 1 grain, 18.51 ohms. (b) 1 foot long, 1/1000 inch thick, 572.3 " (c) 1 meter long, weighing 1 gram, 12.91 " (d) I meter long, 1 millimeter thick 1.211 " Resistance of a 1 inch cube, 37.15 microhms. Percentage increase of resistance per degree C. 1.8° F. at about 20° C. (68° F.), .72 per cent. Electro-chemical equivalent (Hydrogen = .0105), 2.10 mgs. 1.05 "

372 STANDARD ELECTRICAL DICTIONARY.

Mercury Cup. A cup of iron, wood or some material that does not amalgamate or is unattacked by mercury, which is filled with mercury and made an electrode of a circuit. By dipping the other terminal of the circuit into the mercury a very good contact is obtained. It is well to cover the mercury with alcohol. The cup may be filled so that the mercury rises in a meniscus or semi-globule above its edges.

For some purposes this form is useful, as for contacts with the end of a swinging wire or pendulum, because in such cases the contact can be made without the contact point entering the cup. The point swings through the projecting meniscus without touching the edges of the cup. A mercury cup and contact constitute a mercury break.

Meridian, Astronomical. The great circle passing through the north and south poles of the celestial sphere. It lies in a plane with the corresponding geographical or terrestrial meridian.

Meridian, Geographic. The true north and south meridian; the approximate great circle formed by the intersection of a plane passing through north and south poles of the earth with the earth's surface.

373 STANDARD ELECTRICAL DICTIONARY.

Fig. 239. SCHALLENBERG'S ALTERNATING CURRENT METER.

Meter, Alternating Current. A meter for measuring alternating current, as supplied to consumers, from an alternating current system. Like most commercial meters its only function is the measurement of quantity; the potential difference is maintained at a constant figure by the generating plant.

The cut shows the Schallenberg meter. It is simply an alternating current motor (see Motor, Alternating Current), with air vanes mounted on its spindle. A main coil passes all the current. Within this is a second coil complete in itself, and not touching or connecting with the other. The latter is built up of copper rings. Within the two coils, and concentric with both is a disc of copper carried by a vertical spindle. The same spindle carries air vanes, and is free to rotate. As it does so it moves the indicating machinery.

The current in the outer coil induces one in the inner coil. Owing to lag, the current in the inner one differs in phase from that in the outer one, and a rotatory field is produced. The copper disc acquires induced polarity, and rotates with speed which normally would be in proportion to the square of the current. But the object of the meter is to register the current only. The air vanes effect this. The resistance of the air to their motion causes the rate of rotation to vary directly as the speed.

Meter Bridge. A form of Wheatstone's bridge in which one lateral pair of arms is represented by a straight wire. The other pair comprise a known resistance, and the resistance to be determined. The galvanometer is connected on one side between the known and unknown resistance. On the other side its connection is moved back and forth along the straight wire until the balance is secured and the galvanometer reads zero.

The relative lengths of wire intercepted between the two ends thereof and the movable galvanometer connection are proportional to the resistance of these parts and give the necessary data with the one known resistance for determining the unknown resistance.

374 STANDARD ELECTRICAL DICTIONARY.

In the original meter bridge the wire was one meter long, whence its name, and was stretched straight. In more recent examples the wire varies in length and in one form is bent into a circle or spiral, so as to make the instrument more compact.

The contact is not a sliding one, but is adjusted by trial. The contact piece is slid along, but not touching the wire, and from time to time is pressed down against the wire. This prevents wear of the wire. The wire may be made of platinum or of platinum-iridium alloy. The latter is very hard and not easily worn out.

Sometimes, as shown in the cut, three parallel wires are stretched along the baseboard of the instrument, and arranged so that a single wire, two wires or three wires in series can be used for the proportional sides of the bridge, thus making it a two-meter or three-meter bridge as desired. On the other hand some are made of restricted length, as a half or quarter meter only.

Fig. 240. METER BRIDGE.

In the cut J K is the wire, traversed by the contact key. By moving the contact C back and forth in the slot it can be brought over any of the three divisions of the wire. H is the handle for depressing the key. S is a flat spring, carrying the contact piece and holding it up from the wires, except when pressed downwards. As shown in the cut, it is in use for calibrating a voltmeter V, by Poggendorff's method, G being the galvanometer and r1 and r2 being resistances.

Synonyms--Slide Bridge--Slide Balance.

Meter Candle. A unit of illuminating power; the light given by one standard candle at a distance of one meter. The ordinary units of illuminating power are altogether relative; this one is definite.

375 STANDARD ELECTRICAL DICTIONARY.

Meter, Chemical Electric. A current meter in which the current is determined by the amount of chemical decomposition which it can effect. In the Edison meter the solution is one of zinc sulphate. Two electrodes of zinc are immersed in it, and a fractional part of the current is passed through it. The gain in weight of one electrode and the loss in the other are proportional to the current. Both electrodes are weighed periodically, one acting as check upon the other.

Meter, Current. An instrument for measuring the quantity of electricity in current form supplied to consumers. It may be of various types. The general principle involved is that in commercial installations for incandescent light and power supply a fixed potential is usually maintained, the multiple arc system being employed. Hence all that is requisite is to measure the coulombs or the ampere-hours to know what quantity of energy has been supplied.

Meter, Electro-magnetic. A current meter in which the current is measured by its electro-magnetic effects.

Meter-millimeter. A unit of resistance. (See Resistance, Meter-millimeter.)

Meter, Thermal Electric. A current meter in which the current is measured by the heat it imparts to a conductor. In one meter a very light helix of mica is poised horizontally over a conductor, and the whole is enclosed in a case. As the wire is heated it causes an ascending current of air which rotates the vane, and the latter moves delicate clockwork which moves indicating hands. The hotter the wire the more rapidly the air ascends, and consequently the speed of the vane is proportional to the current, because the heat of the conductor is proportional thereto.

Meter, Time Electric. An electric meter which measures the length of time during which current is used. It assumes a constant current and potential. It is virtually a clock, which is turned on when the current passes, and is turned off with the current.

Meter, Watt. A combined current and potential meter. It is constructed on the general lines of a Siemens' Electro Dynamometer. If in it one coil is made of coarse wire and is placed in series with the current conductor, and if the other is wound with fine wire and is connected as a shunt from point to point whose potential difference is to be determined, the instrument becomes a watt meter.

Synonym--Energy Meter.

Methven Standard or Screen. A standard of illuminating power. It is the light emitted by a three-inch Argand gas flame through a rectangular aperture in a silver plate carried by a screen. The aperture is of such size and so far distant from the flame as to permit the passage of exactly two candles illuminating power.

Fig. 241. METHVEN SCREEN

376 STANDARD ELECTRICAL DICTIONARY.

Mho. A unit of conductance, not in very general use. It is the reciprocal of the ohm. Thus a resistance of ten ohms is a conductance of one-tenth mho.

Mica. A natural mineral, a silicate of several oxides; muscovite. It is used as an insulator and dielectric. Its resistance per centimeter cube after several minutes electrification at 20º C. (68º F.) is 8.4E13 ohms (Ayrton). Its specific inductive capacity is 5, air being taken at 1.

Mica, Moulded. An insulating material, whose body is made of mica pulverized and cemented together with heat and pressure and some suitable cement. Shellac is often used as the cement.

Micro. A prefix meaning "one-millionth of;" a micro-farad is one-millionth of a farad.

Micrometer. An instrument for measuring small distances or small differences. It generally is based upon an accurate screw which may have a worm wheel for head, actuated by a worm or helix with graduated head, so that exceedingly small advances of the screw may be produced. The pitch of the screw being known its actual advance is known.

Micrometer, Arc. A micrometer for measuring the distance between voltaic arc electrodes.

Micron. A unit of length. It is one-millionth of a meter or four one-hundred-thousandths of an inch.

377 STANDARD ELECTRICAL DICTIONARY.

Microphone. An apparatus which includes a contact of variable resistance; such resistance can be varied in amount by slight vibrations, such as those produced by sound waves. The apparatus in use forms part of a circuit including a telephone and current generator. As the contact is varied the resistance of the circuit and consequently the current intensity changes and sounds are emitted by the telephone corresponding to such changes. If the microphone is spoken to, the telephone will emit corresponding sounds, reproducing the voice.

It has been found in practice that carbon gives the best microphone contact. One of the simplest and earliest forms is shown in the cut. A short rod or pencil of carbon, A, such as used in batteries, is sharpened at the ends and rests loosely in a vertical position between two blocks of carbon, C C, in each of which a hole is drilled to receive one of the points. The blocks are carried on a standard and base D. The blocks are connected with two terminals x, y, of a circuit, including a telephone and battery. There are two contacts to be disturbed.

If delicately adjusted a fly walking over the base-board will disturb the contacts enough to produce sounds in the telephone. These sounds are possibly not due only to sound waves, but in part to absolute mechanical disturbances.

The various forms of telephone transmitter are generally microphones.

Fig. 242. MICROPHONE.

Microphone Relay. A combined microphone and telephone. A microphone is placed close to the diaphragm of a telephone. The slight sound waves emitted by the telephone affect the microphone and are repeated in its circuit. The microphone circuit includes a local battery and telephone.

Microtasimeter. An apparatus for indicating minute changes in temperature or atmospheric moisture.

378 STANDARD ELECTRICAL DICTIONARY.

A button of compressed lampblack is placed in series with a battery and galvanometer. A strip of some substance, affected in its length either by heat or by moisture, is held pressing against the button. A slight change in length of the strip varies the resistance of the button and hence affects the galvanometer. In this way exceedingly slight changes in heat or moisture may be indicated.

For heat indications vulcanite may be used. The heat of the hand held near it is enough to affect the galvanometer. For moisture a slip of gelatine is used. The moisture of a damp slip of paper two or three inches distant is sufficient to affect the galvanometer.

In the cut, Fig. 2, shows the general distribution of the apparatus in circuit with a battery and galvanometer. C is the base of the apparatus, from which the standard, B, with adjusting screw, H, rises. The strip of vulcanite is held between I and G. Within D is the carbon button (F in Fig. 3) pressed between G and E; A is a standard to carry the parts last described. In Fig. I it is shown as part of a Wheatstone bridge, a, b and c being resistance coils; l the tasimeter, and g the galvanometer. If a balance is secured, any variation in the resistance of the tasimeter will disturb the galvanometer.

Synonym--Tasimeter.

Fig. 243. MICROTASIMETER.

379 STANDARD ELECTRICAL DICTIONARY.

Mil. A unit of length; one-thousandth part of a lineal inch.

It is equal to .025399 millimeter; .000083 foot; .001000 inch.

Mil, Circular. A unit of area; employed in designating the cross-sectional area of wires and other circular conductors.

It is equal to .78540 square mil; .000507 square millimeter; 7.8E-7 (.00000078) square inch.

If the diameter of a wire is given in mils, the square of its diameter gives its cross-sectional area in circular mils.

Mil-foot. A unit of resistance. (See Resistance, Mil-foot, Unit of).

Mil, Square. A unit of area; one-millionth of a square inch.

It is equal to .000645 square millimeter; 1.2733 circular mil; .000001 square inch.

Milli. A prefix; one-thousandth. Thus a milligram is one-thousandth of a gram; a millimeter is one thousandth of a meter.

Milligram. A unit of weight ; one-thousandth of a gram, q. v.

It is equal to .015432 grain; .000032 troy ounce.

Millimeter. A unit of length; one-thousandth of a meter.

It is equal to 39.37079 mils; .03937 inch; .00109 yard.

380 STANDARD ELECTRICAL DICTIONARY.

Milli-oerstedt. A proposed but not adopted unit of current; one-thousandth of an oerstedt. It is equal to one-thousandth of an ampere.

[Transcriber's note: oersted: 1. CGS unit of magnetic intensity, equal to the magnetic pole of unit strength when undergoing a force of one dyne in a vacuum. 2. Formerly, the unit of magnetic reluctance equal to the reluctance of a centimeter cube of vacuum between parallel surfaces.]

mm. Contraction for millimeters.

Molar. Referring to phenomena of mass as gravitation. Mechanics generally treats of molar laws and phenomena.

[Transcriber's note: Molar, or mole, often refers to a quantity of a substance containing an Avagadro number (6.02E23) of molecules--a weight equal to the atomic weight of the molecule. For example, a mole of hydrogen (H2) is 2.015 grams; sodium chloride (NaCl) is 58.443 grams.]

Molar Attraction. The attraction of mass for mass; gravitation. Synonyms--Mass Attraction--Gravitation.

Molecular Affinity. The attraction of molecules for each other as seen in the formation of double salts, the combining of water of crystallization with a salt, and in other cases; a phase of affinity belonging to chemistry, although outside of true atomic attraction.

Molecular Attraction. The attraction of molecules; physical affinity. Cohesion, the attraction of similar molecules for each other, and adhesion, that of dissimilar molecules, are examples. This should be distinguished from molecular affinity, a phase of chemical force.

Molecular Bombardment. When a gas contained in a vessel is brought to a sufficient state of rarefaction the molecules cease to be subject to the laws of diffusion, but move back and forth in straight lines from side to side of the vessel. Their courses can be affected by electric discharge, which can cause them to all impinge upon one of the electrodes, the positive one, producing luminous effects. The path, if referred to the negative electrode, tends to be normal to its surface, so that the resultant path may be curved, as the stream of molecules go to the positive electrode. The fanciful name of molecular bombardment is given to the phenomenon, the luminous effect being attributed to the impinging of the molecules against the positive electrode as they are projected from the positive. The course of the molecules is comparable to the stream of carbon particles from the positive to the negative electrode in an arc lamp. (See Matter, Radiant.)

Molecular Chain. The theoretical rows of molecules supposed to extend from anode to cathode in an electrolytic cell (see Cell, Electric--Grothüss' Hypothesis) are called molecular chains.

381 STANDARD ELECTRICAL DICTIONARY.

Molecular Rigidity. The tendency of the molecules of a mass to retain their position in a mass in resistance to polarizing or depolarizing force, the first being the effect of a magnetic field. It is the theoretical cause of coercive force, q. v., and of residual magnetism. (See Magnetism, Residual.)

Molecule. The smallest particle of matter that can exist alone. It is made up of atoms, but an atom can never exist alone, but only, with one or two possible exceptions, combined with one or more other atoms as a molecule. The molecules under present conditions are not in constant contact with each other, but are perpetually vibrating through paths, in solids probably in defined paths, in liquids and gases in perpetually new paths. The molecules collide with each other and rebound. This motion is the kinetic motion termed heat. At the absolute zero--minus 273.72° C. (-460.7° F.) the molecules would be in contact and quiescent. In the gaseous state the molecules of most substances occupy the same volume; those of a few elements occupy one-half and of others twice the normal volume. The mean free path of the molecule of hydrogen is about 1/20,000 mm. (1/508,000 inch) (Maxwell) or twice this length (Crookes), the collisions in hydrogen are about 17,750 millions per second; the diameter is about 8/10,000,000 mm. (8/254,000,000 inch) ; A particle of matter 1/4,000 mm. (1/102,000 inch) contains, it is supposed, about 40,000 molecules. The results of different authorities vary so widely as to deprive the subject of much of its interest. A Sprengel pump, such as used for exhausting Geissler tubes, or incandescent lamp bulbs, may leave only one hundred-millionth (1/100,000,000,) of an atmosphere present, giving the molecules a capability of an average free path of vibration 33 feet long.

Moment. When a force is applied so as to tend to produce rotation around a point, the product of the force by the shortest distance from the point of rotation to the extension of the line of the force. Such distance is the perpendicular to the extension of the line through the point of rotation.

Mordey Effect. A phenomenon observed in dynamo armatures. At full loads the hysteresis decreases. The effect is thus expressed by S. P. Thompson. "When an armature core is rotated in a strong magnetic field, the magnetization of the iron is being continually carried through a cycle, but in a manner quite different from that in which it is carried when the magnetizing force is periodically reversed, as in the core of a transformer. Mordey has found the losses by hysteresis to be somewhat smaller in the former case than in the latter."

Morse Receiver. The receiving instrument formerly universally used in the Morse system. It is now but little employed, the sounder having displaced it. Several types were invented.

It consists of machinery which carries a reel of paper ribbon arranged to be fed over a roller by clockwork. A pencil, inking roller, or embossing stylus (for the latter the roller must have a groove) is carried by an arm with restricted range of vibration just over the paper and roller. The armature of an electro-magnet is attached to the arm. When the magnet is excited the armature is attracted and the marking device is pressed on the paper. If the clockwork is in operation the marker will make a line as long as the armature is attracted. When released no mark will be produced. In this way the dots and dashes of the Morse code are made on a ribbon of paper.

As an inking arrangement a small roller is carried by the end of the vibrating arm. The embosser, or dry point stylus, was very extensively used. The clockwork was generally driven by descending weights.

Synonym--Morse Recorder.

382 STANDARD ELECTRICAL DICTIONARY.

Mortar, Electric. An electric toy which may have various modifications. In the cut a wooden mortar with recess to receive a ball is shown. Two wires enter the base but do not touch. On placing the ball in position and passing a spark from a Leyden jar across the interval between the wires, the heat and disturbance are enough to project the ball. Gunpowder may be used, the discharge being passed through a wet string to prolong the spark.

Fig. 244. ELECTRIC MORTAR.

Motor, Compound or Compound Wound. A motor which has two windings on the field magnets, one in parallel with that on the armature, the other in series therewith, exactly as in a compound dynamo. (See Dynamo, Compound.)

Motor, Differential. A differentially wound motor; with a compound wound field, whose series coil and shunt coil are wound in opposition to each other. It is virtually a compound wound dynamo. (See Dynamo, Compound Wound.)

Motor, Electric. A machine or apparatus for converting electric energy into mechanical kinetic energy. The electric energy is generally of the dynamic or current type, that is to say, of comparatively low potential and continuous or virtually continuous flow. Some electrostatic motors have, however, been made, and an influence machine can often be operated as a static motor.

Electric motors of the current type may be divided into two classes--direct current and alternating current motors.

Direct current motors are generally based on the same lines of construction as dynamos. One of the great discoveries in modern electricity was that if a current is passed through a dynamo, the armature will rotate. This fact constitutes the principle of the reversibility of the dynamo.

383 STANDARD ELECTRICAL DICTIONARY.

Motors built on the dynamo model may be series wound, shunt wound, or compound wound, or of the magneto type, in the latter case having a fixed field irrespective of any current sent through them. The field may be produced by an electro-magnet separately excited and unaffected by the current sent through the motor.

A current passed through a magneto or motor with separately excited field will turn it in the direction opposite to that required to produce the same current from it were it worked as a generator.

A current passed through a series wound motor acts exactly as above.

Both these facts follow from Lenz's law, q. v.

A current passed through a shunt wound motor acts oppositely to the above. The direction of rotation is the same as that required to produce a current of the same direction. This is because the field being in parallel with the armature the motor current goes through the magnet coils in the direction the reverse of that of the current produced in the armature when it is used as a dynamo. Hence this also carries out Lenz's law.

The compound wound motor acts one way or the other according as its shunt or series winding preponderates. The two may exactly balance each other, when there will be no motion at all. The series connections of a compound wound dynamo should therefore be reversed, making both series and shunt work in unison, if the dynamo is to be used as a motor.

The general principles of the electric motor of the dynamo, or continuous rotation type, can only be outlined here. The current passing through the field magnets polarizes them and creates a field. Entering the armature by the brushes and commutators it polarizes its core, but in such a way that the north pole is away from the south pole of the field magnet, and the same for the south pole. Hence the armature rotates. As it does this the brushes connect with other commutator sections, and the poles of the armature are shifted back. This action continues indefinitely.

Another class of motors is of the reciprocating type. These are now very little used. (See Motor, Reciprocating.)

One valuable feature of continuous rotation electric motors is the fact that they absorb energy, to a great extent proportional in amount to the work they have to do. The rotation of the armature in the field of the motor involves the cutting of lines of force by its coils. This generates an electro-motive force contrary in direction to that producing the actuating current. The more rapid the rotation the greater is this counter-electro-motive force. The motor armature naturally revolves faster with diminished resistance to the motion of the armature. This increases the counter-electromotive force, so that less energy is absorbed. When the motor is called on to do work, the armature rotates more slowly, and the counter-electro-motive force diminishes, so that the machine absorbs more energy. (See Jacobi's Law.)

384 STANDARD ELECTRICAL DICTIONARY.

Motor Electro-motive Force. The counter-electro-motive force of a motor. (F. J. Sprague.)

A motor rotates in virtue of the pull of the field magnet upon the poles of the core of its armature. In responding to this pull the windings of the armature cuts lines of force and hence generates a counter-electro-motive force, for which the above term was suggested.

Motor-Generator. A combined motor and generator used to lower the potential difference in a portion of a circuit, e. g., that part within a building.

A motor-generator is a dynamo whose armature carries two commutators, with two separate windings, one of fine wire of many turns, the other of coarse wire of few turns. If the potential of the system is to be lowered, the main current is passed through the fine winding. This causes the armature to turn motor-fashion, and a potential difference is generated by the rotation of the large coils in the field. This potential difference is comparatively low and by properly proportioning the windings may be lowered to as great a degree as required.

The same apparatus may be inverted so as to raise potential difference. It acts for continuous current systems as the induction coil transformer does for alternating current systems.

Synonym--Continuous Current Transformer.

Motor, Multiphase. A motor driven by multiphase currents. It is arranged in general terms for distribution of the multi phase currents in coils symmetrically arranged around the circle of the field. These coils are wound on cores of soft iron. A rotating field is thus produced, and a permanent magnet or a polarized armature pivoted in such a field will rotate with the field, its poles following the poles of the rotatory field.

The cut, Fig. 245, illustrates the principles of action of a four phase current motor, connected to a four phase current dynamo or generator. The generator is shown on the left hand of the cut and the motor on the right hand. In the generator the armature N S is supposed to be turned by power in the direction shown by the arrow. Each one of the pair of coils is wound in the reverse sense of the one opposite to it, and the two are connected in series with each other, and with a corresponding pair in the motor. The connection can be readily traced by the letters A A', a a' for one set of coils and B B' b b' for the other set.

385 STANDARD ELECTRICAL DICTIONARY.

For each rotation of the armature two currents, each in opposite direction, are produced in A A', and the same is the case for B B'. These currents which have an absolutely constant relation of phase, and which it will be seen alternate four times for each rotation of the armature, regulate the polarity of the field of the motor. The resultant of their action is to keep the poles of the field magnet of the motor constantly traveling around its circle. Hence the armature N S of the motor, seen on the right hand of the cut, tends to travel around also its north and south poles, following the south and north poles of the rotatory field respectively.

Fig. 245. FOUR-PHASE CURRENT GENERATOR AND MOTOR.

It is not essential that the armature should be a magnet or polarized. Any mass of soft iron will by induction be polarized and will be rotated, although not necessarily synchronously, with the rotatory field. Any mass of copper, such as a disc or cylinder, will have Foucault currents induced in it and will also rotate. The only components of such currents which are useful in driving the motor are those which are at right angles to the lines of force and to the direction of motion. A very good type of armature based on these considerations is a core of soft iron wound with insulated copper wire in one or more closed coils; and so wound as to develop the currents of proper direction.

Such an armature is used in the Tesla alternating current motor. An efficiency of 85 per cent. has been attained with some of the Tesla motors.

Motor, Prime. A machine used for producing mechanical motion against resistance. It may operate by converting heat or any other form of kinetic or potential energy into mechanical energy of the moving type. A steam-engine and a water-wheel are examples of prime motors.

Motor, Reciprocating. The early type of motor depending upon reciprocating motion, such as the motion of a coil in a solenoid. These were based upon the lines of a steam engine, and have been abandoned except for special purposes where reciprocating motion is especially required, as in the case of rock drills.

386 STANDARD ELECTRICAL DICTIONARY.

Fig. 246. RICORDON'S RECIPROCATING MOTOR.

In the cut, B is an electro-magnet; A is an armature; E a pole piece. The current enters by the springs, b b, and by commutation is supplied and cut off alternately, thus maintaining a reciprocating movement of the armature and rotation of the fly-wheel.

Synonym--Pulsating Motor.

Motor, Series. A motor whose winding on the armature is in series with the winding on the field. It is similar to a series dynamo. (See Dynamo, Series.)

Motor, Shunt. A motor whose winding on the armature is in parallel with the winding on the field magnets. It is similar to a shunt wound dynamo. (See Dynamo, Shunt.)

Fig. 247. MULTIPLE ARC CONNECTION.

Multiple. A term expressing connection of electric apparatus such as battery couples, or lamps in parallel with each other. In the ordinary incandescent lamp circuits the lamps are connected in multiple.

Synonym--Multiple Arc.

387 STANDARD ELECTRICAL DICTIONARY.

Multiple Arc Box. A resistance box arranged so that the coils may be plugged in multiple instead of in series. Such can be used as a rheostat, as the resistance can be very gradually changed by putting the coils one by one into parallel with each other. Thus by adding in parallel with a 10 ohm coil a 10,000 ohm coil the resistance is decreased to 9.999001 ohms, and thus the resistance can be very slowly changed without sudden stops or abrupt changes.

[Transcriber's note: The correct value is 9.99001]

Multiple Series. Arrangements of electric apparatus in a circuit in a number of series, which minor series are then arranged in parallel. The term may be used as a noun, as "arranged in multiple-series," or as an adjective, as "a multiple-series circuit."

Fig. 248. MULTIPLE SERIES CONNECTION.

Multiple Switch Board. A switch board on whose face connecting spring jacks or other devices are repeated for the same circuits, so that different operators have each the entire set of connections repeated on the section of the board immediately in front of and within their reach. This multiplication of the same set of connections, giving one complete set to each operator, gives the title "multiple" to the type of switch board in question. The typical multiple switch board used in telephone exchanges is the best example of this construction. The calling annunciators of the subscribers are distributed along the bottom of the board extending its full length. To each operator a given number is assigned, all within reach of the right or left hand. This gives five or six feet length of board to each, and an operator only responds to those subscribers within his range. But anyone of his subscribers may want to connect with any of the others in the entire central station. Accordingly in front of each operator spring jacks are arranged, one for each of the entire set of subscribers connected in that office. The operator connects as required any of the calling subscribers, who are comparatively few, to any one of the large number served by the central station. Thus the entire set of subscribers' spring jacks are multiplied over and over again so as to give one set to each operator.

388 STANDARD ELECTRICAL DICTIONARY.

Multiple Wire Method for Working Electro-magnets. A method for suppressing sparking in working electro-magnets intermittently. The magnet core is wound with a number (from four to twenty) of separate layers of fine wire. A separate wire is taken for each layer and all are wound in the same direction, from one end to the other of the space or bobbin without returning. The ends are then joined so as to bring all the wires in parallel. The effect of this is that as the coils vary in diameter the time constants of each is different from that of the others, the coefficient of self-induction being less, and the resistance being greater for the coils farthest from the central axis. Thus the extra currents run differently in the different coils, and only a comparatively small spark can be produced owing to the division of forces thus brought about.

Fig. 249. DIAGRAM ILLUSTRATING MULTIPLE WIRE WORKING.

Multiplex Telegraphy. Any system of telegraphy transmitting more than four messages simultaneously over a single wire. Properly it should apply to all transmitting more than one, but conventionally has the above restricted meaning, distinguishing it from duplex and quadruplex telegraphy.

Multiplying Power of a Shunt. When a resistance is placed in parallel with a galvanometer on a circuit the following relation obtains. Let s and g equal the resistances of the shunt and galvanometer respectively, S and G the currents in amperes passing through them, V the potential difference between their common terminals, and A the whole current in amperes. Then we have A = ( (s + g ) / s ) * G and ( (s + g ) / s ) is termed the multiplying power of the shunt, as it is the factor by which the current passing through the galvanometer must be multiplied by to produce the total current.

Muscular Pile. A species of voltaic battery, often termed Matteueci's pile, made up of alternate pieces of muscle cut longitudinally and transversely respectively. The different pieces represent the elements of a battery, and their difference of potential is naturally possessed by the pieces.

Myria. A prefix; one million times. Thus myriavolt means one million volts.

[Transcriber's note: Contemporary usage is mega, as in megavolt.]

389 STANDARD ELECTRICAL DICTIONARY.

N. (a) Symbol for north pole or north-seeking pole of a magnet.

(b) Symbol for the number of lines of force in a magnetic circuit.

Nairne's Electrical Machine. The cylinder electrical machine, q.v.

Napierian Logarithms. A series of logarithms the base of whose system is 2.72818. They are also called hyperbolic logarithms.

Nascent State. An element just separating from a combination possesses at that time higher affinities than after separation, and can effect more powerful chemical changes.

It is sometimes attributed to a differential time of existence in the atomic modification, before the freed atoms have united to form molecules.

Natural Currents. A term for earth currents. (See Current, Earth.)

Needle. (a) A term applied to a bar magnet poised horizontally upon a vertical point, or suspended in a horizontal position by a filament. Thus the magnet in a mariner's compass, which may be a substantial bar magnet, is called a magnetic needle.

(b) An indicator in general shape like the hand of a clock. (Sec Annunciator, Needle- Telegraph, Needle.)

Needle of Oscillation. The magnetic needle poised horizontally, and used for measuring the intensity of the earth's magnetic field, or of an artificial magnetic field, by the method of oscillations. The intensities of the field is inversely as the square of the number of oscillations performed in a given time.

Needle, Telegraphic. The index in needle telegraphy (see Telegraph, Needle), whose motions indicate the characters it is desired to transmit.

Negative Charge. One of the two kinds of electric charges. The other is the positive.

By the double fluid hypothesis this is assumed to be a charge of a particular kind of electricity--negative electricity.

By the single fluid hypothesis it is supposed to be caused by the absence of part of the normal electricity of a surface. The reverse is held by some theorists.

The subject is so purely theoretical that neither of the two hypotheses is accepted as final.

[Transcriber's note: Current is a wire is the motion of negative electrons. Current in a electrolyte is the motion of positive ions and negative ions. Current in a plasma is the motion of electrons and positive ions.]

390 STANDARD ELECTRICAL DICTIONARY.

Negative Electricity. The kind of electricity with which a piece of amber is charged by friction with flannel; resinous electricity. (See Electrostatic Series.)

In a galvanic battery the surface of the zinc plate is charged with negative electricity.

According to the single fluid theory negative electrification consists in a deficiency of electricity.

[Transcriber's note: Negative electrification is an excess of electrons.]

Negative Element. In a voltaic cell the plate not dissolved by the solution; the one which is positively charged; the copper, platinum, or carbon plate in the usual type of battery.

The current is assumed to flow from negative element to positive element (the zinc plate) through the wire or other external conductor.

Nerve Currents. Currents of electricity obtained from nerves. They are much more feeble than those obtained from muscle, but are produced in the same general ways.

Network. Conductors in parallel and crossing each other, with connections at the junctions.

The term is sometimes so loosely applied as to include parallel conductors.

Neutral Line of Commutator. The diameter of a commutator which connects its Neutral Points, q. v.; sometimes termed the diameter of commutation; the diameter approximately at right angles with the lines of force. The commutator brushes are applied at the extremities of this diameter.

Neutral Point of a Commutator. The points of a commutator at which no lines of force are cut; the points at the extremities of a diameter which, except for the lag, would be at right angles to the lines of force; the points at which the brushes touch the commutator.

Neutral Point, Thermo-electric. A temperature marking a point of no thermo-electric difference of potential. If the junctions of a thermo-electric couple are at temperatures, one a little over and the other an equal amount under the neutral point, no current will be developed. At the neutral point the thermo-electric polarities are reversed. Differences of temperature above it give currents of reverse direction to those given by corresponding differences below it. For an iron-copper couple the neutral point is 274.5° C. (526° F.)

Synonym--Neutral Temperature.

Neutral Relay Armature. An unpolarizable armature for use with a relay; an armature of soft iron or iron wire; as distinguished from a polarized armature.

391 STANDARD ELECTRICAL DICTIONARY.

Neutral Wire. The central wire in the three wire system, q. v., of electric distribution; the wire connected to a point between the two dynamos, or otherwise to the central point of the current generator.

Fig. 250. DIAGRAM OF THREE WIRE SYSTEM SHOWING NEUTRAL WIRE.

Neutral Wire Ampere Meter. An ampere meter connected in the circuit of the neutral wire to determine the current passing through it. Such determination is for the purpose of ascertaining how much more work is being done by one of the lateral leads than by the other.

Synonym--Balance Ampere Meter.

N. H. P. Symbol or contraction for "nominal horse power." This is a basis for rating the size of an engine.

Nickel. A metal; one of the elements; atomic weight, 58.8 ; equivalent, 29.4; valency, 2; specific gravity, 8.8. It is a conductor of electricity. Relative resistance, annealed (Silver = 1), 8.285 Specific Resistance, 12.47 microhms. Resistance of a wire (a) 1 foot long, weighing 1 grain, 15.206 ohms. (b) 1 foot long, 1/1000 inch thick, 74.963 " (c) 1 meter long, weighing 1 gram, 1.060 " (d) 1 meter long, 1 millimeter thick, .1587 " Resistance of a 1-inch cube, 4.907 microhms. Electro-chemical equivalent, (Hydrogen = .0105) .3087 mgs.

It is strongly paramagnetic, but loses this quality at 350º C. (662º F.)

It is important as a constituent of German silver, an alloy much used for resistance coils.

Nickel, Bath. A bath for the electro-deposition of nickel. A great many formulae have been given. Metallic nickel is dissolved in 1 vol. sulphuric acid mixed with 2 vols. water. Neutralize with ammonia, and add of ammonium sulphate one-half the weight of metallic nickel originally used; 135 parts of nickel will be enough for a bath of 10,000 parts.

392 STANDARD ELECTRICAL DICTIONARY.

Other formulae are as follows: Double nickel-ammonium sulphate, 4 parts. Ammonium carbonate, 3 " Water 100 " Nickel sulphate, nitrate or chloride, 1 " Sodium bisulphate, 1 " Water, 20 "

Nickel anodes are used in the bath to maintain the strength. Too much care cannot be exercised in the absolute cleanliness of the articles to be plated. A too alkaline bath gives a disagreeable yellow color to the deposit; too acid a bath gives badly adhering deposits.

Night Bell. An alarm bell in a telegraph office, which bell is connected at night to give a loud signal to attract the operator's attention. It is used in telephone exchanges and is connected so as to ring as long as a subscriber remains unanswered after calling.

Nobili's Rings. When a dilute solution of copper acetate is placed on a bright silver plate and a strip of zinc is touched to the silver beneath the copper, a series of rings of copper are formed by electrolysis around the zinc. These are Nobili's rings.

If for the copper acetate a solution of lead oxide in potassium hydrate solution is substituted, and if the polished plate which may be German silver is connected to the positive electrode of a battery, and a platinum wire connected to the negative pole is immersed in the liquid, it determines the formation of beautiful iridescent rings of lead binoxide. The platinum wire is sometimes sealed in glass so that only its point projects.

The colors are due to interference of light, the layers of lead oxide being extremely thin.

The lead binoxide is formed by secondary reaction. Metallic lead is first deposited on the negative pole. The oxygen which goes to the positive pole formed by the polished plate produces lead binoxide which is deposited there in rings. The reaction is comparable to that of a storage battery.

Synonyms--Metallochromes--Electric Rings.

Nodular Deposit. A deposit obtained in electroplating, characterized by irregular thickness; due to too low density of current.

Non-conductor. A material that does not conduct electricity except with great difficulty; a substance of very high resistance.

Synonym--Insulator--Dielectric.

North Pole. (a) The north-seeking pole of a magnet; the pole of a magnet which tends to point to the north, and whence lines of force are assumed to issue on their course to the other pole of the magnet.

(b) The North Pole of the earth. Treating the earth as a magnet, and accepting the above nomenclature the north pole should be termed the south pole. (See Austral Pole--Boreal Pole.)

393 STANDARD ELECTRICAL DICTIONARY.

North-seeking Pole. The pole of a magnet which tends to point to the north; the north pole of a magnet.

Null Method. Any method of obtaining measurements or comparisons, in which the measurement is correct when the deflection of the galvanometer or other indicator is zero, nought or null. The Wheatstone Bridge (see Bridge, Wheatstone) is an example of a null method.

Two obvious advantages attach to null methods in electric galvanometer work. One is that an uncalibrated galvanometer can be employed. The other is that a galvanometer of any high degree of sensitiveness can be employed, there being no restriction as to its fineness of winding or highness of resistance.

"Upper case Omega Graphic". (Greek capital" Omega") symbol for megohm. [Transcriber's note: Now used for ohms.]

"Lower case Omega Graphic". (Greek omega) symbol for ohm. [Transcriber's note: Now used for angular velocity, 2*PI*frequency.]

Occlusion. An absorption of gases by metals. Palladium will, if used as the hydrogen evolving electrode in decomposing water, absorb 980 times its volume of hydrogen, which is said to be occluded. The metal may also be heated in hydrogen and allowed to cool therein, when occlusion occurs. Platinum will occlude 4 times its volume of hydrogen; iron, 4.15 times its volume of carbon-monoxide; silver, 7 times its volume of oxygen. Metals with occluded gases may serve as elements in a galvanic couple. (See Gas Battery.) A metal expands in occluding a gas.

In the storage battery it is believed that occlusion plays a part, hydrogen and oxygen being respectively absorbed by the two sets of plates, and acting as they do in Groves' gas battery.

Oerstedt. Name proposed for the unit of current strength, but not adopted. The ampere is the accepted name.

394 STANDARD ELECTRICAL DICTIONARY.

Oerstedt's Discovery. Oerstedt discovered in 1820 that a magnetic needle tended to place itself at right angles to a current of electricity. This fundamental experiment is the basis of the galvanometer.

Fig. 251. OERSTEDT'S DISCOVERY.

Ohm. The practical unit of resistance; 1E9 C. G. S. electro-magnetic units. The legal ohm is the resistance of a mercury column 1 square millimeter in cross-sectional area and 106 centimeters in length. There has been considerable confusion, owing to inaccuracy in early determinations, in the valuation of the ohm. In this work the legal ohm is used. The different ohms will be found defined in their place. Resistance units of various names may also be consulted.

The following table gives the relative values of the different ohms.

Length of Mercury Board of Column in True B. A. Trade Legal Centimetre. Ohm. Ohm. Ohm. Ohm.

True Ohm, 106.24 1. 1.0128 .9994 1.0022 B. A. Ohm, 104.9 .9874 1. .9868 .9889 Board of Trade Ohm 106.3 1.00050 1.0133 1. 1.0028 Legal Ohm, 106.0 .9977 1.0112 .9971 1.

Ohmage. The Resistance of a circuit expressed in ohms.

Ohm, B. A. The British Association unit of resistance; the resistance of a column of mercury 1 square millimeter in cross sectional area and 104.9 centimeters long; the B. A. Unit of Resistance.

Ohm, Board of Trade. The approximate ohm as recommended by the British Board of Trade on the advice of a committee (Sir W. Thomson, Dr. J. Hopkinson, Lord Rayleigh and others). It is the resistance of a mercury column one square millimeter in section, and 106.3 centimeters long at 0º C. (32º F.)

Synonym--New Ohm.

395 STANDARD ELECTRICAL DICTIONARY.

Ohmic Resistance. True resistance as distinguished from spurious resistance, or counter-electro-motive force.

Ohm, Legal. The practical unit of resistance. The resistance of a column of mercury one square millimeter in cross-sectional area and 106 centimetres long at 0º C. (32º F.) The ohm used previously to 1884 is the B. A. Unit of Resistance, q. v.

One legal ohm = 1.0112 B. A. Units, and I B. A. Unit = 0.9889 legal ohm.

The resistance of a copper wire 1 foot long and 1/1000 inch in diameter is about 10 ohms. The resistance of 1 mile of iron wire 1/3 inch in diameter is about 10 ohms.

Synonym--Congress Ohm.

396 STANDARD ELECTRICAL DICTIONARY.

Fig. 252. THEORY OF OHMMETER.

Fig. 253. OHMMETER.

Ohmmeter. An instrument for measuring directly the resistance of a conductor or of any part of a circuit through which a strong current is passing. It is the invention of Prof. W. E. Ayrton.

It contains two fixed coils at right angles to each other acting on the same needle of soft iron. One coil is of thick wire and is placed in series with the resistance to be measured. The other is of very thin wire and is placed in parallel with the same resistance. One wire acts by the total current, the other by the potential difference between the ends of the resistance. The action on the soft iron needle is due to the ratio of potential difference to total currents, or to the resistance itself. By properly designing and proportioning the coils the angular deflections of the needle are made proportional to the resistance.

In use the thick wire may be kept permanently in circuit. On connecting the binding posts of the thin wire coil to any two parts of the circuit its resistance is at once given by the deflection of the needle.

When no current is passing the needle rests in any position. A current in the thick coil brings it to zero. A current simultaneously passing through the thin high resistance coil brings about the deflection.

The instrument is a commercial rather than a scientific one.

Ohm's Law. The fundamental law expressing the relations between current, electro-motive force and resistance in an active electric circuit. It may be expressed thus:

(a) The current strength is equal to the electro-motive force divided by the resistance.

(b) The electro-motive force is equal to the current strength multiplied by the resistance.

(c) The resistance is equal to the electro-motive force divided by the current strength. All these are different forms of the same statement. Algebraically the law is usually expressed thus, (a) C = E/R. It may also be expressed thus: (b) E = C*R and (c) R= E/C, in which R denotes resistance, C denotes current strength, and E denotes electro-motive force.

Ohm, True. The true ohm is the resistance of a column of mercury 1 square millimeter in cross-sectional area, and 106.24 centimeters long. (See Ohm.)

Synonym-Rayleigh Ohm.

Oil Insulation. Oil insulation has received several applications in electrical work. It has been proposed for use in underground conduits. These it was proposed to fill with oil after the insertion of the conductors, the latter properly wrapped with cotton or other covering. For induction coils it has been very successfully used. Its principal utility depends on the fact that it is liquid, so that if pierced by a spark it at once closes again. A solid insulator if pierced is permanently injured. It is also used in telegraph insulators (see Insulator, Liquid) to prevent surface leakage.

397 STANDARD ELECTRICAL DICTIONARY.

Olefiant Gas. A compound gas; C2H4; composed of carbon, 24; hydrogen, 4; molecular weight, 28; specific gravity, .981.

It is a dielectric of about the resistance of air. Its specific inductive capacity at atmospheric pressure is 1.000722 (Boltzman.)

Synonym--Ethene; heavy carburetted hydrogen.

[Transcriber's note: Also called ethylene. A primary use is polyethylene plastic.]

Open. adj. An electric circuit is said to be open when it is cut or broken so that no current can pass through it. The term may be recollected by thinking of a switch; when open no current can pass through it. The same adjective is applied to magnetic circuits, an air gap implying an open circuit.

Open Circuit Oscillation. An oscillation of current in open circuit so that a spark discharge accompanies it. It is produced by electric resonance in a simple circle or loop of wire with ends placed near together but not touching, if the circuit is of such size that its period of oscillation corresponds with that of the inducing discharge. (See Resonance, Electric.) Its period depends entirely on the self-induction of the circuit.

Ordinate. In a system of plane co-ordinates (see Co-ordinates), the distance of any point from the axis of abscissas measured parallel to the axis of ordinates.

Ordinates, Axis of. The vertical axis in a system of co-ordinates, q. v.

Synonym--Axis of Y.

Organ, Electric. An organ in which the air blast is admitted or excluded from the different pipes by electric mechanism.

The outlines of the system are a series of contacts worked by the keys and stops, which cause, when operated by the organist, a current to pass through electro-magnets, opening the valves of the different pipes. Thus the manual may be at any distance from the organ, and a number of organs may be worked upon the same manual. As many as five in a single cathedral are thus connected to a manual in the chancel.

Orientation of a Magnetic Needle. The acquirement by a magnetic needle of its position of rest, with its magnetic axis in the magnetic meridian.

Origin of Co-ordinates. In a system of linear co-ordinates the point of intersection of the axes; the point whose co-ordinates are both zero.

398 STANDARD ELECTRICAL DICTIONARY.

Oscillating Needle. A small light bar magnet suspended by a filament and employed in determining the intensity of a magnetic field by the oscillations it completes in a given time after a given disturbance.

Oscillations, Electric. In static electricity the sudden and very rapid alternations in the discharge of a static condenser. This discharge of the disruptive order seems a single one, but is really composed of a number of discharges alternating in direction and producing electro-magnetic ether waves, probably identical with light waves except that they are longer and far less rapid.

Oscillatory Electro-motive Force. Electro-motive force rapidly changing in sense or in direction, so that it presents an oscillatory character. The alternating current and the telephone current as used in practice are actuated by this type of electro-motive force.

Osmose, Electric. When two liquids are separated by a porous diaphragm, and a strong current of electricity is passed through from the liquid on one side, through the diaphragm, to the liquid on the other side, the liquid on the side towards which the current is passing rises in level. The process is termed electric osmose. When a liquid is forced through a diaphragm a current is produced; in other words electric osmose is reversible. The current thus produced is termed a diaphragm current.

Oscillation, Electric. The phase of discharge of a static condenser in one direction. It is usually followed by a discharge in the opposite direction constituting a second oscillation, and so on, so that a great number of exceedingly short oscillations are comprised. Thus, in the discharge of the Leyden jar a large number of oscillations of current back and forth are produced, the current alternating like the swings of a pendulum.

These oscillations are supposed to affect the ether, producing waves in it identical with light waves, except that we have not been able yet to produce them short enough to affect the visual organs. The waves thus produced can be reflected or refracted; some substances are transparent for them and others opaque. There is a possibility that man may yet succeed in producing electric oscillations of sufficient frequency to bring about the direct production of light.

Oscillatory Displacement. Hypothetical displacement currents of rapidly alternating direction produced in the oscillatory discharge of a Leyden jar or static condenser.

Oscillatory Induction. Induction produced by sympathetic action of an oscillatory discharge or by electric resonance. (See Oscillations, Electric--Resonance, Electric--Resonator, Electric.)

399 STANDARD ELECTRICAL DICTIONARY.

Outlet. The part of an electrolier or electric light fixture out of which the wires are led for attachment of an incandescent light socket.

Output. The rate of energy delivered or of work done by a machine. In the case of a current generator it is the volt-coulombs per given second, or better the volt-amperes delivered at its outer circuit terminals.

Output, Magnetic. The analogue in a magnetic circuit of the output of an electric circuit. It is the product of the magnetizing force by the induced magnetism.

Output, Unit of. As a unit of output of a dynamo Prof. Sylvanus P. Thompson has proposed 1,000 watts, or one kilowatt. This unit is now frequently used. To completely define the dynamo, however, the amperage or the voltage must also be given, as a 10 kilowatt--110 volt machine, or a 10 kilowatt--99 ampere machine.

[Transcriber's note: 10 kilowatt at 110 volts is 91 amperes.]

Over-Compounding. A proportioning of the series and shunt windings of a compound dynamo, so that the voltage of the terminals rises with the load or output enough to allow for the drop in mains, thus maintaining the potential for full load at distant points in a district. It is carried out by an increase of ampere-turns in the series winding.

Overload. In an electric motor a mechanical load put upon it so great as to prevent economical working. One effect of such a load is to make the armature run so slowly as to unduly reduce the counter-electro-motive force and hence to permit so much current to pass through the coils as to heat them, perhaps injuriously. In this case the production of heat implies the waste of energy.

Overtype Dynamo or Motor. A dynamo or motor whose armature is placed above or in the upper part of the field magnets, the yoke piece of the magnets being in or resting upon the base of the machine.

Ozone. An allotropic form of oxygen. It possesses much more energetic chemical properties than oxygen. It is supposed to contain three atoms of oxygen in its molecule, represented thus: O / \ O---O

It is produced by electric discharges and it is its peculiar odor which is noticed about an electric machine, and sometimes in a thunderstorm near the path of a lightning flash.

In the electrolysis of water some ozone may be produced, thus diminishing the volume of the oxygen or of the mixed gases given off. This is a source of inaccuracy in a gas voltameter.

400 STANDARD ELECTRICAL DICTIONARY.

Pacinotti's Inductor. The Pacinotti or Gramme Ring. (See Pacinotti's Ring.)

Pacinotti's Ring. A ring of iron wire wound with coils of insulated wire at right angles to its circular axis, and used as the armature of a dynamo or motor. A number of connections are taken from the coils to a central commutator.

Fig. 254. PACINOTTI'S MACHINE, WITH RING ARMATURE.

If such a ring with its coils is rotated in a field, current can be taken from points of the commutator on a line at right angles to the lines of force entering the ring.

The ring was discovered in 1862 by Pacinotti, and later was independently discovered by Gramme. It is often known as the Gramme ring.

Pacinotti Teeth. Projections on a cylindrical or drum armature, between which in the grooves formed thereby, the wire is wound. The teeth being of iron tend to diminish the reluctance or magnetic resistance of the interpolar space, or interval between the poles of the field magnet.

Synonym--Pacinotti Projections.

Paillard Alloys. Non-magnetic palladium alloys, invented by Paillard, of Switzerland, used in anti-magnetic watches. The following are given as the compositions of several such alloys:

I. II. Palladium, 60 to 75 parts 50 to 75 parts Copper, I5 to 25 " 20 to 30 " Iron. 1 to 5 " 5 to 20 "

401 STANDARD ELECTRICAL DICTIONARY.

The following are more complex: I. II. Palladium, 65 to 75 parts 45 to 50 parts Copper, 15 to 25 " 15 to 25 " Nickel, 1 to 5 " 2 to 5 " Silver, 3 to 10 " 20 to 25 " Gold, 1 to 2-1/2 " 2 to 5 " Platinum, 1/2 to 2 " 2 to 5 " Steel, 1 to 5 " 2 to 5 "

These alloys are used for balance springs, as well as for the balance wheels and escapement parts of watches. The elasticity of recently produced springs has been found to be very satisfactory.

Page Effect. The sounds produced by magnetizing and demagnetizing a bar of iron or steel; the magnetic tick. The sounds are strong enough to produce a telephonic effect. (See Magnetic Tick.)

Palladium. A metal of the platinum series. It has the highest power of occlusion, q.v., of all metals. It is the characteristic ingredient of non-magnetic watch alloys.

Palladium used as an electrode in the electrolysis of water will occlude 936 volumes of hydrogen, and the hydrogen-palladium alloy will exceed in size the original electrode.

Fig. 255. LUMINOUS PANE.

Pane, Luminous. A pane of glass, one side of which has pasted to it a long zigzag strip of tinfoil. A design is made by cutting through the strip. On discharging a Leyden jar or an electric machine through the strip sparks appear where the tinfoil is severed, thus producing the design in a luminous effect. Many variations can be employed in their construction.

402 STANDARD ELECTRICAL DICTIONARY.

Pantelegraphy. A system of telegraphy for transmitting designs, maps, drawing, and the like by telegraphy. (See Telegraphy, Facsimile.)

Paper Filaments. Filaments of carbon for incandescent lamps made from paper.

This is one of the earliest materials practically used. The paper is cut out of proper shape, and is carbonized in a close vessel, while embedded in powdered charcoal or some other form of carbon to absolutely cut off access of air. It is then placed in the lamp chamber and flashed or subjected to the regular treatment.

Parabola. A curve; one of the conic sections. It is approximately represented by a small arc of a circle, but if extended becomes rapidly deeper than a half circle.

If, from a point within called the focus, lines are drawn to the curve and then other lines are drawn from these points parallel to the axis, the angles of incidence will he equal to the angles of reflection as referred to tangents at the points where the lines touch the curve.

[Transcriber's note; The general equation of a parabola is A*x^2 + B*x*y + C*y^2 + D*x + E*y + F = 0 such that B^2 = 4*A*C, all of the coefficients are real, and A and C are not zero. A parabola positioned at the origin and symmetrical on the y axis is simplified to y = a*x^2 ]

Parabolic Reflector. A reflector for a light, a paraboloid or surface of revolution whose section is a parabola. A light placed at its focus has its rays reflected parallel to each other.

Examples of parabolic reflectors are seen in electric search lights and in locomotive head-lights. They are employed in electric search lights. The arc light must be of such construction as to maintain its ignited points always at the same point, the focus of the paraboloid.

Paraffine. v. To coat or saturate with paraffine wax. Paper may be paraffined by dipping in the wax, or by being sprinkled with fragments of wax, subsequently melted in with a hot iron or otherwise. The tops of battery carbons are often paraffined to prevent the acid from rising in the pores by capillary attraction and rusting the connections.

403 STANDARD ELECTRICAL DICTIONARY.

Paraffine Wax. A hydro-carbon composed principally of mixtures of the higher members of the paraffine series C n H2 n + 2. It is made from cannel coal, coal tar, or petroleum by distillation. It is an insulator. Its resistance at 46° C. (114.8° F.) per centimeter cube is 3.4E16 ohms, or about the highest resistance known.

Its specific inductive capacity (for milky wax) is 2.47 (Schiller). For clear wax it is given as follows by different authorities: 1.92 Ayrton. 1.96 Wüllner. 1.977 Gibson & Barclay. 2.32 Baltzmann.

It is extensively used in condensers and other electric apparatus as a dielectric and insulator.

Paragrêles. Protectors against hail; lightning rods used to guard fields against hail; of little or no real utility.

Parallax. The apparent change in position of an object when looked at from two points of view. By looking at an object a few feet distant first with one eye and then with the other, the shifting in apparent position is seen.

In reading the position of an indicator or needle over a scale parallax introduces an error unless the eye is held vertically over the needle. By making the dial of looking- glass and holding the eye so that the reflection of its pupil is bisected by the needle this verticality is ensured.

Parallel. (a) In the nomenclature of electric circuits two or more conductors leading from one point to another, are said to be in parallel.

(b) When two or more conductors connect two main leads of comparatively large size and low resistance they are said to be in parallel or in multiple arc. This order is easiest pictured as the rungs of a ladder in parallel connecting its two sides representing the main leads.

It may be used as a noun as "arranged in parallel," or as an adjective as "a parallel circuit," the opposite of series, q. v.

Paramagnetic. adj. Possessing paramagnetic properties; tending to occupy a position with the longer axis parallel to the lines of force of a magnetic field; having magnetism; attracted by a magnet.

"If a homogeneous isotropic substance is placed in a magnetic field it becomes magnetized at every point in the direction of the magnetic intensity at that point, and with an intensity of magnetization proportional to the magnetic intensity. When the positive direction of the induced magnetization is the same as that of the magnetic intensity the substance is called Magnetic or Paramagnetic; when it is opposite, the substance is called Diamagnetic." (Emtage.)

A paramagnetic substance has high permeability or multiplying power for lines of force, hence in a magnetic field a bar of iron, etc., is in unstable equilibrium unless its longer axis is parallel with the lines of force in order to reduce as much as possible the reluctance of the circuit.

404 STANDARD ELECTRICAL DICTIONARY.

Iron is the most paramagnetic of all substances. Other paramagnetic metals are: Nickel, cobalt, manganese, platinum, cerium, osmium, palladium. Diamagnetic metals are bismuth, antimony, zinc, tin, mercury, lead, silver, copper, gold, arsenic. Bismuth is the most diamagnetic of all metals.

Of gases oxygen is most paramagnetic. Becquerel calculated that a cubic yard of oxygen condensed would act on a magnetic needle as powerfully as 5.5 grains of metallic iron. Liquefied oxygen will adhere to the poles of a magnet.

Changes of temperature and of other conditions may affect a body's magnetism. Thus hot oxygen is diamagnetic, and a substance paramagnetic in a vacuum may be diamagnetic in air.

Of liquids, solutions of iron or cobalt are paramagnetic; water, blood, milk, alcohol, ether, oil of turpentine and most saline solutions are diamagnetic.

Paramagnetism. (a) The science or study of paramagnetic substances and phenomena.

(b) The magnetic property of a paramagnetic substance; that of being attracted by a magnet, and of arranging itself with its longer axis parallel with the lines of force of a magnetic field.

Parchmentizing. If cellulose is treated with a mixture of two parts of sulphuric acid and one part of water perfectly cold, it becomes like parchment. It should at once be washed with water, and then with ammonia and water. The Swan incandescent light fibres are made of parchmentized cotton thread, which is afterward carbonized.

Partial Earth. A fault in a conductor caused by imperfect connection with the earth, where insulation from the earth is desired.

Passive State. A state of a substance in virtue of which it is unattacked by a solvent which ordinarily would dissolve or attack it. Iron in strong nitric acid is unattacked or assumes the passive state. This particular case is supposed to be due to a coating of magnetic oxide, so that there would be properly speaking no question of a passive state, but only one of superficial protection.

The existence of a true passive state of any substance is very doubtful.

P. D. Abbreviation for potential difference or difference of potential, or for electro-motive force.

405 STANDARD ELECTRICAL DICTIONARY.

Peltier Effect. The thermal effect produced by the passage of a current through the junction of two unlike conductors. Such junction is generally the seat of thermo-electric effects, and a current is generally produced by heating such a junction. If an independent current is passed in the same direction as that of the thermoelectric current, it cools the junction, and warms it if passed in the other direction. In general terms, referring to thermo-electric couples, if passed through them it tends to cool the hot and heat the cool junction. The phenomenon does not occur in zinc-copper junctions.

Peltier's Cross. A bar of bismuth and a bar of antimony soldered centre to centre at right angles, being notched or halved there to receive or to set into each other. It is used to demonstrate the Peltier effect, q. v. To one pair of ends are connected the terminals of a battery circuit; to the other pair are connected the terminals of a galvanometer.

The galvanometer by its deflections in one and then in the other direction indicates that the junction is heated when the current passes from antimony to bismuth and vice versa. It thus illustrates the heating and cooling of a thermo-electric junction by a current of electricity. The current from the battery by the Peltier effect either heats or cools the junction, as the case may be. This heating or cooling them produces a thermo-electric current in the galvanometer circuit. The battery has no direct influence on the galvanometer.

Pendant Cord. A double conductor or pair of conductors, insulated from each other and covered with a worsted, silk, or cotton covering and used to suspend incandescent lamps and at the same time to conduct the current to them. It is also used for other similar service, such as acting as conductors for small motors. Often each conductor is composed of a number of thin wires laid together. This gives flexibility to the cord.

Synonym--Flexible Cord.

Pendulum, Electric. (a) A pendulum operated by the intermittent action of an electro-magnet, whose circuit is opened and closed by the pendulum itself. A point at the lower end of the pendulum swinging through a globule of mercury may close and open the circuit. Various other methods of accomplishing the same end are employed ..

(b) A pith ball suspended by a thread from an insulating stand. It is used to show the attraction exercised by a piece of sealing wax or other substance excited by rubbing.

406 STANDARD ELECTRICAL DICTIONARY.

Pen, Electric. A stylus for producing a series of perforations in paper, so that the paper may act as a stencil for the reproduction of a great number of copies of the original matter. Various kinds of electric pens have been invented. One kind, invented by Edison, consists of a handle carrying an electric motor actuating a needle, which is driven in and out of the other end of the handle with high rapidity. It is used by being held vertically on the paper with the needle end downward, and is moved so as to describe perforated letters or designs. The paper is then used as a stencil with an ink roller to reproduce the writing or design ad libitum. A simpler kind dispenses with the motor and depends on the perforations produced by the electric spark. As shown in the cut the stylus is one terminal of an induction coil circuit. The support on which the paper rests is the other terminal and must be a conductor. In use the induction coil is started, and the stylus is moved over the paper; a series of sparks pass through the paper from stylus to the supporting tablet, perforating the paper and producing a stencil to be used for reproduction.

Fig. 256. ELECTRIC PEN.

Pentane Standard, Harcourt's. A standard of illuminating power; in it the combustible substance is a gas made by mixing one cubic foot of air with three cubic inches of liquid pentane, measured at 60° F. or, if measured as gases, 20 volumes of air to 7 of pentane. It is burned at the rate of 0.5 cubic foot per hour from a cylindrical tube one inch in diameter, closed at the top by a disc 0.5 inch thick with a hole 0.25 inch in diameter, through which the gas issues. It gives a flame 2.5 inches high.

The pentane used is the distillate of petroleum which boils at 50° C. (122° F.) ; it has a specific gravity at 15° C. (60° F.) of from 0.628 to 0.631. It is almost pure pentane (C5H12).

As long as the rate of consumption is between 0.48 and 0.52 cubic foot per hour the flame gives practically the same light.

407 STANDARD ELECTRICAL DICTIONARY.

Perforator. An apparatus used in automatic high speed telegraphy for perforating strips of paper. These are then used by drawing between a roller and contact spring for making and breaking the telegraphic circuit for the production of a record, such as the Morse record, at the distant receiving station.

The perforated strip has different classes of holes punched in it to represent dots or dashes. It is fed by machinery very rapidly, so that the message is transmitted with the highest speed. Several operators may simultaneously prepare the paper strips, and thus in conjunction with its rapid feeding in the transmitter, far surpass the time of ordinary direct transmission.

Fig. 257. PERFORATOR FOR WHEATSTONE'S AUTOMATIC TELEGRAPH.

Perforators may be entirely mechanical but are sometimes pneumatic, compressed air being used to operate them. The holes they make are on different levels of the paper strip, as shown in the cut.

Period. The time required for the completion of one complete element of periodic motion. This may be a complete alternation (See Alternation, Complete) of an alternating current, or of an oscillatory discharge.

Periodicity. The rate of succession of alternations or of other fixed phases; the rate of recurrence of phenomena.

408 STANDARD ELECTRICAL DICTIONARY.

Permanency. In electric current conductors the property of possessing conductivity unaffected by lapse of time. Generally the permanency of conductors is very high. In some cases a slow annealing takes place which causes a gradual change with the lapse of time. Annealed German silver wire has been found to increase in conductivity at about .02 per cent. in a year. (Matthiessen.) Wire, whether annealed or not, is left in a strained condition after the drawing operations, and such a change is consonant with this fact. The figure only applies to the samples tested by Matthiessen.

Permanent State. In a telegraph line or other current conductor, the condition when a uniform current strength obtains over the whole line. When a current is started it advances through the line with a sort of wave front gradually increasing in strength. At the further end some time may elapse before it attains its full intensity. When its does the permanent state prevails. Until then the variable state, q. v., exists in the line.

Permeameter. An apparatus for determining the permeability of samples of iron. It consists of a large slotted block of iron. A coil is placed within the slot. A hole is drilled through one end, and a rod of the iron to be tested is passed through this hole and through the coil to the bottom of the slot. The lower end of the rod must be accurately faced off. The current is turned on, upon which the rod adheres to the bottom of the slot. The force required to detach it is determined with a spring balance. The permeation through its face is proportional to the square of the force required.

Fig. 258. PERMEAMETER.

Permeance. The multiplying or the conducting power for magnetic lines of force possessed by a given mass of material. It varies with the shape and size of the substance as well as with the inducing force. It is distinguished from permeability, as the latter is a specific quality proper to the material, and expressed as such; the permeance is the permeability as affected by size and shape of the object as well as by its material.

409 STANDARD ELECTRICAL DICTIONARY.

Pflüger's Law. A law of electro-therapeutics. It states that stimulation of a nerve is only produced by successive appearance of the kathelectrotonic state, and disappearance of the anelectrotonic state.

Phantom Wires. The extra transmission circuits obtained in multiplex telegraph systems. A single line arranged for four separate simultaneous transmissions by quadruplex apparatus is said to establish three phantom wires.

Phase. In wave motion, oscillating motion, simple harmonic motion, or similar periodic phenomena, the interval of time passed from the time the moving particle moved through the middle point of its course to the instant when the phase is to be stated.

Pherope. An apparatus for the electric transmission of pictures. (See Telephote.)

[Transcriber's note: Precursor of the contemporary Fax and scanner.]

Philosopher's Egg. An ellipsoidal vessel mounted with its long axis vertical and with two vertical electrodes, the upper one sliding, and arranged to be attached to an air pump. A discharge through it when the air is exhausted takes the general shape of an egg.

Phonautograph. An apparatus for registering the vibrations of a stylus, which is mounted on a diaphragm and is acted on by sound waves.

It is virtually a resonating chamber, over one of whose ends a parchment diaphragm is stretched. To the centre of the parchment a needle or stylus is attached. A cylinder covered with soot is rotated in contact with the point of the stylus. As the chamber is spoken into the diaphragm and stylus vibrate and the vibrations are marked on the cylinder. It is of some electric interest in connection with telephony.

Phone. Colloquial abbreviation for telephone.

Phonic Wheel. A form of small motor of very simple construction. It consists of a toothed wheel of soft iron. A bar electro-magnet is fixed with one pole facing the teeth of the wheel. By a tuning fork make and break a succession of impulses of rapid frequency and short duration are sent through the magnet. The teeth act as armatures and are successively attracted by the magnet. The regulated speed is one tooth for each impulse, but it may rotate at one-half the speed, giving two teeth for each impulse, or at certain other sub-multiples of its regular speed. It is the invention of Paul Lecour.

410 STANDARD ELECTRICAL DICTIONARY.

Phonograph. An apparatus for reproducing articulate speech. It is not electric, except as it may be driven by electricity.

It consists of a cylinder of wax-like material which is rotated and moved slowly, longitudinally, screw fashion, at an even speed. A glass diaphragm carrying a needle point is supported with the point barely touching the wax. If the diaphragm is agitated, as by being spoken against, the needle is driven back and forwards cutting a broken line or groove following the direction of the thread of a screw in the wax, the depth of which line or groove continually varies.

This imprints the message. If the needle is set back and the cylinder is rotated so as to carry the needle point over the line thus impressed, the varying depth throws the needle and diaphragm into motion and the sound is reproduced.

The cylinder is rotated often by an electric motor, with a centrifugal governor.

[Transcriber's note; Due to T. A. Edison, 1877, fifteen years before this book.]

Phonozenograph. An apparatus for indicating the direction of the point where a sound is produced. It operates by a microphone and telephone in conjunction with a Wheatstone bridge to determine the locality.

Phosphorescence. The emission of light rays by a substance not heated, but whose luminosity is due to the persistence of luminous vibration after light has fallen upon it.

A phosphorescent body, after exposure to light, is luminous itself. Phosphorescence may be induced by rubbing or friction, by heat, by molecular bombardment, as in Crookes' tubes, and by static discharge of electricity, as well as by simple exposure to light.

Another form of phosphorescence may be due to slow chemical combustion. This is the cause of the luminosity of phosphorous.

Phosphorous, Electrical Reduction of. Phosphorous is reduced from bone phosphate by the heat of the electric arc. The phosphate mixed with charcoal is exposed to the heat of the voltaic are, and reduction of the phosphorous with its volatilization at once ensues. The phosphorous as it volatilizes is condensed and collected.

Photo-electricity. The development of electrical properties by exposure to light. Crystals of fluor spar are electrified not only by heat (see Pyro-electricity) but also by exposure to sunlight or to the light of the voltaic arc.

[Transcribers note: Although first observed in 1839 by Becquerel, it was not explained until 1905 by Albert Einstein with the introduction of photons.]

Photo-electric Microscope. A projection, solar or magic-lantern microscope worked by the electric light.

Photo-electro-motive Force. Electro-motive force produced in a substance by the action of light.

411 STANDARD ELECTRICAL DICTIONARY.

Photometer. An apparatus for measuring the intensity of light emitted by a given lamp or other source of illuminating power. They may be classified into several types.

Calorimetric or Heat Photometers act by measuring relatively the heat produced by the ether waves (so-called radiant heat) emitted by the source. The accuracy of the instrument is increased by passing the rays through an alum solution. A thermopile, or an air thermometer, may be used to receive the rays.

Chemical Photometers. In these the light falls upon sensitized photographic paper. The depth of coloration is used as the index of illuminating power.

Direct Visual Photometers. These include Rumford's Shadow Photometer, Bunsen's Bar Photometer, and Wheatstone's Bead Photometer, in which the light is estimated by direct visual comparison of its effects.

Optical Photometers. These include Polarization Photometers, in which the light is polarized; Dispersion Photometers, in which a diverging lens is placed in the path of the rays of light so as to reduce the illuminating power in more rapid ratio than that of the square of the distance.

Selenium Photometers, in which the variations in resistance of selenium as light of varying intensity falls upon it is used as the indicator of the intensity of the light.

Jet Photometers, for gas only, in which the height of a flame under given conditions, or the conditions requisite to maintain a flame of given height, is used to indicate the illuminating power.

The subject of photometers has acquired more importance than ever in view of the extensive introduction of the electric light. (See Candle, Standard--Carcel--Violé's Standard--and Photometers of various kinds.)

Photometer, Actinic. A photometer whose registrations are produced by the action of the light being tested upon sensitized paper or plates, such as used in photography. Some efforts at self-registering photometers have been based on actinic registration of the height of a flame of the gas to be tested.

Photometer, Bar. A photometer in which the two lights to be compared are fixed at or opposite to the ends of a bar or scale of known length, generally 60 or 100 inches. The bar is divided by the rule of the inverse square of the distances, so that if a screen is placed on any part of the bar where it receives an equal amount of light from both sources, the figure on the bar will indicate the relative illuminating power of the larger lamp or light in terms of the smaller. The divisions of the bar are laid out on the principle that the illuminating power of the two sources of light will vary inversely with the square of their distance from the screen.

412 STANDARD ELECTRICAL DICTIONARY.

The screen used is sometimes the Bunsen disc. This is a disc of paper with a spot of paraffine wax in the centre melted thoroughly into the paper or with a ring of paraffine wax surrounding the untouched centre. When this disc is equally illuminated on both sides the spot is nearly invisible. Inequality of illumination brings it out more visibly. Sometimes a Leeson disc is used. This consists of three pieces of paper, two thin ones between which a thicker piece, out of which a star is cut, is laid. When equally illuminated on both sides the star appears equally bright on both sides.

The bar photometer is the standard form. A candle or pair of candles may be burned at one end and an incandescent lamp at the other, or a gas flame may first be rated by candles and used as a standard.

Synonyms--Bunsen's Photometer--Translucent Disc Photometer.

Fig. 259. BAR PHOTOMETER.

Photometer. Calorimetric. A photometer in which the radiant energy, so called radiant heat, is used as the measurer of the light.

In one type a differential air thermometer is used, one of whose bulbs is blackened. On exposing this bulb to a source of light it will become heated, and if lights of the same character are used the heating will be in proportion to their illuminating power quite closely. The heating is shown by the movements of the index. By careful calibration the instrument may be made quite reliable.

Photometer, Dispersion. A photometer in which the rays from one of the lights under comparison are made more divergent by a concave lens. In this way a strong light, such as all arc lamp can be photometered more readily than where only the natural divergence of the beam exists. The law of the variation of the intensity of light with the square of the distance is abrogated for a law of more rapid variation by the use of a concave lens.

The diagram, Fig. 260, illustrates the principle. E represents a powerful light, an arc light, to be tested. Its distance from the screen is e. Its light goes through the concave lens L and is dispersed as shown over an area A1, instead of the much smaller area A, which the same rays would otherwise cover. Calling l the distance of the lens from the screen, f its focus, and c the distance of the standard candle from the screen when the shadows are of equal intensity, we have the proportion.

Illuminating power of lamps: ditto of standard candle:: (l (e-l) + fe)2 : (c f)2

413 STANDARD ELECTRICAL DICTIONARY.

Fig. 260. DIAGRAM OF PRINCIPLE OF THE DISPERSION PHOTOMETER.

The cut, Fig. 261, gives a perspective view of Ayrton's Dispersion Photometer. C is the standard candle, L the concave lens, R the rod for producing the two shadows on the screen S.

Fig. 261. AYRTON'S DISPERSION PHOTOMETER.

The mirror M is fixed at an angle of 45° with the stem on which it rotates. The light of the arc lamp is received by the mirror and is reflected through the lens. The candle holder slides along a graduated bar C, and at D is an index plate to show the angle at which the spindle carrying the mirror is set.

414 STANDARD ELECTRICAL DICTIONARY.

Dr. J. Hopkinson in his dispersion photometer uses a double convex lens. This gives a focal image of the arc-lamp between the lens and screen, whence the rays diverge very rapidly, thus giving the desired dispersion effect.

It is principally for arc lamps that dispersion photometers are used.

Photometer, Shadow. A photometer in which the relative intensity of the two lights is estimated by the intensity or strength of shadows of the same object which they respectively cast.

Fig. 262. RUMFORD'S SHADOW PHOTOMETER.

Fig. 263. RUMFORD'S SHADOW PHOTOMETER ARRANGED FOR TESTING INCANDESCENT LAMPS.

415 STANDARD ELECTRICAL DICTIONARY.

A rod is supported in a vertical position. Back of it is a screen of white paper. The two lights to be compared are arranged in front of the rod and at a little distance from each other. They are shifted about until the two shadows appear of equal darkness. The relative intensity of the lights varies inversely with the square of their distances from the shadows cast respectively by them on the screen.

The cut, Fig. 262, shows the simplest type of the shadow photometer. In the cut, Fig. 263, a shadow photometer for testing incandescent lamps is shown. In it E is the lamp under trial supported by a clamp H. A is an ampere meter in circuit with the lamp, and V is a voltmeter. A candle C can be moved along a graduated scale G G. R is the vertical rod, and S is the screen on which the shadows fall.

Photophore. An instrument for medical examination of the cavities of the body. It includes an incandescent lamp mounted in a tube with a concave mirror and convex lens.

Photo-voltaic Effect. The change in resistance of some substances effected by light. Selenium, of all substances, is most susceptible to this effect. (See Selenium.)

Piano, Electric. A piano whose manual or key-board operates to close electric circuits, whereby electro-magnets are caused to operate to drive the hammers against the strings.

Pickle. An acid solution for cleaning metal surfaces before electro-plating, galvanizing or other deposition of metal upon them.

Picture, Electric. A picture produced by passing a strong discharge through a piece of gold leaf clamped or firmly pressed upon a sheet of paper. The gold leaf is cut out of the desired shape, or else a stencil of paper overlays it. The discharge dissipates the gold, and produces a purple colored reproduction of the design upon the paper. The design is due to the deposition of an exceedingly thin film of metallic gold.

Synonym--Electric Portrait.

Pile. A galvanic or voltaic battery. It is sometimes restricted to a number of voltaic couples connected. It should be only applied to batteries with superimposed plates and no containing vessel such as the Dry Pile, q. v., or Volta's Pile, q. v.

Pilot Transformer. In alternating current distribution a small transformer placed at any part of the system and connected to a voltmeter in the central station, to indicate the potential difference of the leads.

Pilot Wires. Wires brought from distant parts of electric light or power mains, and leading to voltmeters at the central station, so that the potential of distant parts of the system can be watched. The wires can be very small, as they have but little current to transmit.

416 STANDARD ELECTRICAL DICTIONARY.

Pistol, Electric. An experimental apparatus for exhibiting the power of electric incandescence or of the electric spark. A tube is mounted with a handle like a pistol. A plug is provided to screw in and out of its side. The plug carries two wires connected on its inner side by a fine platinum wire, or else disconnected but with their ends brought near together to act as terminals for the production of a spark. To use it the tube is filled with a mixture of air and gas, the latter either hydrogen, hydro-carbon or other combustible gas. The tube when full is corked. The wire is heated to incandescence by a current, or a spark is passed from a Leyden jar or other source of electrostatic excitation. The mixture, if properly proportioned, explodes and expels the cork violently.

Fig. 264. ELECTRIC PISTOL.

Pith. A light and soft cellular tissue forming the central core of exogenous trees and plants. In the older parts of the tree the woody tissue often encroaches in and partly obliterates it.

For electrical pith-balls, the pith of the elder, of corn, or, best of all, of sun-flower stems is used.

Pith-balls. Ball made of pith. They are used in the construction of electroscopes and for other experiments in static electricity.

They are cut out with a sharp knife and their shape may be improved by gentle rolling in the hand or between the fingers.

Pivot Suspension. Suspension poising or supporting of an object on a sharp pivot. This is used for the needle in the ordinary compass. A cavity or inverted cup, which may be made of agate, is attached to the middle of the needle which has a hole for its reception. The centre of gravity of the needle comes below the bottom of the cup.

Pivot suspension is not perfect, as it has considerable friction. There is no restitution force, as with torsion filaments.

417 STANDARD ELECTRICAL DICTIONARY.

Plant. The apparatus for commercial manufacturing or technical works. An electric lighting plant includes the boilers, engines and dynamos for producing the current, and the electric mains and subsidiary apparatus.

Plant Electricity. Electricity manifested by plant life. By means of a galvanometer potential differences are found to exist in different parts of trees or fruits. The roots and interior portions are negative, and the flowers, smaller branches and fruit are positive.

In some cases a contraction of the tissue of plants can be produced by an electric current. The sensitive plant and others exhibit this phenomenon, exactly analogous to the action of muscular tissue.

Plate, Arrester. In a lightning arrester the plate connected to the circuit. Sometimes both plates are designated arrester plates.

Plate Condenser. A static condenser having a flat plate of glass for dielectric. (See Epinus' Condenser.)

Plate Electrical Machine. A frictional electric machine, in which a circular plate of glass is excited by friction with the cushions. It is the most recent type of frictional machine and has superseded the old cylinder machines. In its turn it is superseded by influence machines, really plate machines, but not so termed in practice.

Plate, Ground. In a lightning arrester, the plate connected to the earth.

Plate, Negative. In a voltaic battery, either primary or secondary, the plate which is unattacked by the oxygen or negative radical or element of the fluid. It corresponds to the carbon plate in the ordinary voltaic battery, and is the one charged with positive electricity.

Plate, Positive. In a voltaic battery, either primary or secondary, the plate which is dissolved or attacked by the oxygen or negative radical or element of the fluid. It is the plate corresponding to the zinc plate in the ordinary voltaic battery, and is the one charged with negative electricity.

Plating Balance. A balance or scales to which articles in an electroplater's bath are suspended. A weight exceeding by a known amount that of the article as immersed overbalances the article. When the plating is being deposited as soon as it exceeds the excess of weight of the counterpoise the balance tips, the article descends a little, the electric circuit is broken and the plating ceases. Thus the plating is automatically stopped when a predetermined amount of metal is deposited.

418 STANDARD ELECTRICAL DICTIONARY.

Plating Bath. A vessel of solution for the deposition of metal by electrolysis as used in electro-plating.

Plating, Electro-. The deposition of metal by electrolysis so as to coat the conducting surface of objects therewith. The full details of the many processes are very lengthy and cannot be given here.

The general principle includes a battery or source of electric current. The object to be plated is connected to the negative terminal and is immersed in the solution. Thus with a battery the object is in electrical connection with the zinc plate. To the other terminal a metallic plate is connected. The object and the plate termed the anode being introduced into a suitable bath, the metal whose solution is in the bath is deposited upon the surface of the object.

The bath is a solution of the metal in some form that will lend itself to the electrolytic action. The anode is often a plate of the metal of the bath, so that it dissolves as fast as metal is deposited on the object, thus keeping up the strength of the solution.

The objects to be plated must be scrupulously clean, and great care must be taken to keep the bath uncontaminated.

When the object has a non-conducting surface, it is made conducting by being brushed over with plumbago q.v. In addition iron dust is sometimes dusted over it. This acts by precipitating the metal of the bath directly and thus giving a conducting basis for the metal to deposit on. To avoid getting iron in a bath the object may be dipped in copper sulphate solution. This precipitates copper in place of the iron and leaves the article in good shape for silver or other plating.

Electro-plating, if made thick enough, gives a reverse of the article when separated therefrom. A direct copy can be got by a second plating, on the first plating after separation, or a wax impression can be employed.

Under the different metals, formulae for the baths will be found. (See also Quicking-- Steeling--Plating Balance.)

Platinoid. An alloy of copper, nickel, zinc in the proportions of German silver with 1 or 2 per cent of tungsten. It is used for resistances. It has a specific resistance (or resistance per centimeter cube) of about 34 microhms. Its percentage variation in resistance per degree C. (1.8° F.) is only about .021 per cent., or less than half that of German silver. This is its most valuable feature.

419 STANDARD ELECTRICAL DICTIONARY.

Platinum. A metal; one of the elements; symbol, Pt; atomic weight, 197.4; equivalent, 49.35; valency, 4; specific gravity, 21.5. It is a conductor of electricity. The following data refer to the annealed metal at 0° C. (32° F.) Relative Resistance (Silver annealed = 1), 6.022 Specific Resistance, 9.057 microhms. Resistance of a wire, (a) 1 foot long, weighing 1 grain, 2.779 ohms. (b) 1 foot long, 1/1000 inch thick, 54.49 " (c) 1 meter long, weighing 1 gram, 1.938 " (d) 1 meter long, 1 millimeter thick, .1153 " Resistance of a 1 inch cube, 3.565 Electro-chemical equivalent (Hydrogen = .0105), 0.5181.

The coefficient of expansion by heat is almost the same as that of glass. It can be passed through holes in glass and the latter can be melted about it so as to hermetically seal its place of passage through the glass. It is used in incandescent lamps for leading-in wires and other similar uses.

Platinum Black. Finely divided platinum. It is made by boiling a solution of platinic chloride with excess of sodium carbonate and a quantity of sugar, until the precipitate is perfectly black and the supernatant liquid is colorless. It seems to possess a great power of occluding oxygen gas. When heated to redness it becomes spongy platinum. The negative plates of a Smee battery are coated with platinum black.

Platinum-silver Alloy. An alloy of 1 part platinum and 2 parts silver, used for resistance coils.

Relative Resistance (silver annealed = 1 ), 16.21 microhms. Specific Resistance at 0°C. (32° F.), 24.39 Resistance of a wire, (a) 1 foot long, weighing 1 grain, 4.197 ohms. (b) 1 foot long, 1/1000 inch diameter, 146.70 " (c) 1 meter long weighing 1 gram, 2.924 " (d) 1 meter long, 1 millimeter diameter, 0.3106 " Resistance of a 1 inch cube, 9.603 microhms. Percentage Variation per degree C. (1.8° F.) at about 20° C. (68° F.), 0.031 per cent.

Synonym--Platinum Alloy.

Platinum Sponge. Finely divided platinum obtained by igniting platinum black, q.v., and also by igniting salts of platinum. It has considerable power of condensing or occluding oxygen. It will, if in good condition, set fire to a jet of hydrogen impinging upon it.

Plow. Contact arms projecting downwards from the motors, trucks, or bodies of electric street cars, which enter the underground conduit through the slot and carry contact pieces or brushes, to take the current for driving the motors from the leads within the conduit.

420 STANDARD ELECTRICAL DICTIONARY.

Plücker Tubes. A special form of Geissler tube designed for the production of stratification and for observing the effects produced in the space surrounding the negative electrode.

Plug. (a) A piece of metal with a handle and a somewhat tapered end, used to make connections by insertions between two plates or blocks of metal slightly separated and with grooves to receive it.

(b) A plug or wedge with two metallic faces, insulated from each other with a separate wire connected to each one. It is used in spring-jacks q. v., to introduce a loop in a circuit.

Synonym--Wedge.

Plug. v. To connect by inserting a plug, as in a resistance box.

Fig. 265. PLUGS FOR RESISTANCE COIL BOX.

Fig. 266. PLUG SWITCH.

Plug, Double. A spring-jack plug or wedge with two pairs of insulated faces, one behind the other, so as to simultaneously introduce two loops into a circuit.

Plug, Grid. A piece or mass of lead oxide, inserted into the holes in the lead plates of storage batteries. The holes are often dovetailed or of uneven section to better retain the plugs.

Plug Infinity. In a box-bridge or resistance box, a plug whose removal from between two disconnected discs opens the circuit. All the other discs are connected by resistance coils of various resistance.

Plug Switch. A switch composed of two contact blocks, not touching each other and brought into electrical connection by the insertion of a metallic plug. The latter is usually provided with an insulating handle, and a seat is reamed out for it in the two faces of the contact blocks.

421 STANDARD ELECTRICAL DICTIONARY.

Plumbago. Soft lustrous graphite, a native form of carbon; sometimes chemically purified. It is used in electro-plating to give a conducting surface to non-conducting objects, such as wax moulds. The surface, after coating with plumbago, is sometimes dusted over with iron dust, which precipitates the metal of the bath and starts the plating. It is sometimes plated with copper, silver or gold, and is then termed coppered, silvered, or gilt plumbago. It is gilded by moistening with etherial solution of gold chloride and exposing to the air, and drying and igniting.

Plunger. A movable core which is used in connection with a so-called solenoid coil, to be drawn in when the coil is excited. (See Coil and Plunger.)

Fig. 267 COIL AND PLUNGER WITH SCALES TO SHOW ATTRACTION.

P. O. Abbreviation for Post Office, q.v.

Poggendorf's Solution. An acid depolarizing and exciting fluid for zinc-carbon batteries. The following is its formula: Water, 100 parts; potassium bichromate, 12 parts; concentrated sulphuric acid, 25 parts. All parts by weight. Use cold.

Point, Neutral. (a) On a commutator of a dynamo the points at the ends of the diameter of commutation, or where the brushes rest upon the surface of the commutator, are termed neutral points. At these points there is no generation of potential, they marking the union of currents of opposite direction flowing from the two sides of the armature into the brushes.

(b) In electro-therapeutics, a place in the intra-polar region of a nerve so situated with reference to the kathode and electrode as applied in treatment, that its condition is unaffected.

Synonym--Indifferent Point.

(c) In a magnet the point of no attraction, situated between the two poles, at about an equal distance from each, so as to mark the centre of a magnet of even distribution of polarity.

(d) In thermo-electricity the point of temperature where the thermo-electric powers of two metals are zero; in a diagram the point where the lines representing their thermo-electric relations cross each other; if the metals are arranged in a thermo-electric couple, one end at a temperature a given amount above, the other at a temperature the same amount below the neutral point, no current or potential difference will be produced.

422 STANDARD ELECTRICAL DICTIONARY.

Point, Null. A nodal point in electrical resonators; a point where in a system of waves or oscillations, there is rest, the zero of motion being the resultant of oppositely directed and equal forces. In electrical resonators it is to be sought for in a point symmetrically situated, with reference to the spark gap, or in a pair of points, which pair is symmetrically placed.

The null point in resonators is found by connecting a lead from one of the secondary terminals of an induction coil to different parts of the resonator. The null point is one where the connection does not give rise to any sparks between the micrometer knobs or spark gap, or where the sparks are of diminished size.

The whole is exactly comparable to loops and nodes in a vibrating string or in a Chladni plate as described in treatises on sound and acoustics. (See Resonance, Electrical--Resonator, Electrical.)

Synonym--Nodal Point.

Point Poles. Magnet poles that are virtually points, or of no magnitude. A long thin magnet with little leakage except close to the ends may be supposed to have point poles within itself a short distance back from the ends.

Points, Consequent. In a magnet with consequent poles, the points where such poles are situated.

Points, Corresponding. In bound electrostatic charges the points of equal charges of opposite potentials; the points at opposite extremities of electrostatic lines of force. This definition implies that the bound charges shall be on equal facing areas of conductors, as otherwise the spread or concentration of the lines of force would necessitate the use of areas of size proportionate to the spreading or concentrating of the lines of force. At the same time it may figuratively be applied to these cases, the penetration of the surface by a single line of force including the area fixed by its relation to the surrounding lines.

Points, Isoelectric. In electro-therapeutics, points of equal potential in a circuit.

423 STANDARD ELECTRICAL DICTIONARY.

Points of Derivation. The point where a single conductor branches into two or more conductors, operating or acting in parallel with each other.

Polar Angle. The angle subtended by one of the faces of the pole pieces of the field- magnet of a dynamo or motor. The centre of the circle of the angle lies in the axis of the armature.

Synonym--Angle of Polar Span.

Polar Extension. An addition made of iron to the poles of magnets. Various forms have been experimented with. The pole pieces of dynamo field magnets are polar extensions.

Synonyms--Pole Piece--Polar Tips.

Polarity, Diamagnetic. The induced polarity of diamagnetic substances; it is the reverse of paramagnetic polarity, or of the polarity of iron. A bar of diamagnetic material held parallel with the lines of force in a magnetic field has a like pole induced in the end nearest a given pole of the field magnet, and vice versa. This theory accounts for the repulsion by a magnet of a diamagnetic substance. The existence of this polarity is rather an assumption. It originated with Faraday.

Polarity, Paramagnetic. The induced polarity of paramagnetic substances, such as iron, nickel, or cobalt.

When such a substance is brought into a magnetic field the part nearest a specific pole of a magnet acquires polarity opposite to that of such pole and is thereby attracted.

Another way of expressing it, in which the existence of a pole in or near to the field is not implied, is founded on the conventional direction of lines of force. Where these enter the substance a south pole is formed and where they emerge a north pole is formed.

Such polarity tends always to be established in the direction of greatest length, if the body is free to rotate.

424 STANDARD ELECTRICAL DICTIONARY.

Polarization. (a) The depriving of a voltaic cell of its proper electro-motive force. Polarization may be due to various causes. The solution may become exhausted, as in a Smee battery, when the acid is saturated with zinc and thus a species of polarization follows. But the best definition of polarization restricts it to the development of counter-electro-motive force in the battery by the accumulation of hydrogen on the negative (carbon or copper) plate. To overcome this difficulty many methods are employed. Oxidizing solutions or solids are used, such as solution of chromic acid or powdered manganese dioxide, as in the Bunsen and Leclanché batteries respectively; a roughened surface of platinum black is used, as in the Smee battery; air is blown through the solution to carry off the hydrogen, or the plates themselves are moved about in the solution.

(b) Imparting magnetization to a bar of iron or steel, thus making a permanent magnet, is the polarization of the steel of which it is made. Polarization may be permanent, as in steel, or only temporary, as in soft iron.

(c) The strain upon a dielectric when it separates two oppositely charged surfaces. The secondary discharge of a Leyden jar, and its alteration in volume testify to the strain put upon it by charging.

(d) The alteration of arrangement of the molecules of an electrolyte by a decomposing current. All the molecules are supposed to be arranged with like ends pointing in the same direction, positive ends facing the positively-charged plate and negative ends the negatively-charged one.

(e) The production of counter-electro-motive force in a secondary battery, or in any combination capable of acting as the seat of such counter-electro-motive force. (See Battery, Secondary--Battery, Gas.) The same can be found often in organized cellular tissue such as that of muscles, nerves, or of plants. If a current is passed through this in one direction, it often establishes a polarization or potential difference that is susceptible of giving a return current in the opposite direction when the charging battery is replaced by a conductor.

Polarization Capacity. A voltaic cell in use becomes polarized by its negative plate accumulating hydrogen, or other cause. This gradually gives the plate a positive value, or goes to set up a counter-electro-motive force. The quantity of electricity required to produce the polarization of a battery is termed its Polarization Capacity or Capacity of Polarization.

Polarization of the Medium. The dielectric polarization, q. v., of a dielectric, implying the arrangement of its molecules in chains or filaments; a term due to Faraday. He illustrated it by placing filaments of silk in spirits of turpentine, and introduced into the liquid two conductors. On electrifying one and grounding (or connecting to earth) the other one, the silk filaments arranged themselves in a chain or string connecting the points of the conductors.

Polar Region. That part of the surface of a magnet whence the internal magnetic lines emerge into the air. (S. P. Thompson.) As such lines may emerge from virtually all parts of its surface, the polar regions are indefinite areas, and are properly restricted to the parts whence the lines emerge in greatest quantity.

Polar Span. A proportion of the circle which represents the transverse section of the armature space between the pole pieces of the field magnet in a dynamo or motor; it is the proportion which is filled by the faces of the pole pieces.

425 STANDARD ELECTRICAL DICTIONARY.

Pole, Analogous. The end of a crystal of a pyroelectric substance, such as tourmaline, which end when heated become positively electrified. On reduction of temperature the reverse effect obtains.

Pole, Antilogous. The end of a crystal of a pyroelectric substance, such as tourmaline, which end, while increasing in temperature, becomes negatively electrified. During reduction of its temperature the reverse effect obtains.

Pole Changer. (a) An automatic oscillating or vibrating switch or contact-breaker which in each movement reverses the direction of a current from a battery or other source of current of fixed direction, as such current goes through a conductor.

(b) A switch moved by hand which for each movement effects the above result.

Pole, Negative. (a) In a magnet the south pole; the pole into which the lines of force are assumed to enter from the air or outer circuit.

(b) In a current generator the pole or terminal into which the current is assumed to flow from the external circuit. It is the negatively charged terminal and in the ordinary voltaic battery is the terminal connected to the zinc or positive plate.

Pole Pieces. The terminations of the cores of field or other electro-magnets, or of permanent magnets. These terminations are variously shaped, sometimes being quite large compared to the core proper of the magnet.

They are calculated so as to produce a proper distribution of and direction of the lines of force from pole to pole. As a general rule the active field should be of uniform strength and the pole pieces may be of contour calculated to attain this end.

Pole, Positive. (a) In a magnet the north pole; the pole from which lines of force are assumed to emerge into the air.

(b) In a current generator the pole or terminal whence the current is assumed to issue into the outer circuit. It is the positively charged terminal, and in the ordinary voltaic battery is the terminal connected to the copper or carbon plate, termed the negative plate.

Poles. (a) The terminals of an open electric circuit, at which there necessarily exists a potential difference, produced by the generator or source of electro-motive force in the circuit.

(b) The terminals of an open magnetic circuit; the ends of a magnetized mass of steel, iron or other paramagnetic substance.

(c) The ends in general of any body or mass which show electric or magnetic properties more developed than those of the central sections of the body.

426 STANDARD ELECTRICAL DICTIONARY.

Pole, Salient. In dynamo and motor field magnets, salient poles are those projecting from the base or main body of the field magnet, as distinguished from consequent poles formed by coils wound on the main body itself.

Fig. 268. SALIENT POLES OF FIELD MAGNET.

Poles, Compensating. A device for avoiding the cross-magnetizing effect on the commutator core due to the lead of the brushes. It consists in maintaining a small bar electro-magnet perpendicularly between the pole pieces. This compensates the cross-magnetizing effect.

Poles of Intensity. The locus of highest magnetic force on the earth's surface. One such pole is in Siberia, another is about lat. 52° N., long. 92° W.

[Transcriber's note: 52° N., long. 92° W is about 250 miles Northeast of Winnipeg.]

Poles of Verticity. The magnetic poles of the earth. (See Magnetic Poles.)

Pole Tips. The extreme ends of the expanded poles of a field magnet. In some machines some of the pole tips are made of cast iron, to alter the distribution of the lines of force and resulting magnetic pull upon the armatures. This is done to take off the weight of the armature from its bearings.

Pole, Traveling. A term applied to the poles produced in the action of a rotatory field, whose poles constantly rotate around the circle of the field. (See Field, Rotatory.)

417 STANDARD ELECTRICAL DICTIONARY.

Porous Cup. A cup of pipe clay, unglazed earthenware or other equivalent material used in voltaic cells to keep two liquids separate and yet to permit electrolysis and electrolytic conduction.

They are necessarily only an expedient, as their porous nature permits considerable diffusion, and were they not porous electrolytic action would be impossible.

Synonym--Porous Cell.

Porret's Phenomenon. In electro-physiology, an increase in the diameter of a nerve produced by the positive pole of a voltaic circuit, when placed in contact with the tissue and near to the nerve in question, the other pole being connected to a more or less remote part of the body.

Portelectric Railroad. A railroad worked by solenoidal attraction, the car forming the core of the solenoids. It includes a series of solenoids or hollow coils of copper wire distributed all along the road and inclosing within themselves the track. On this a cylindrical car with pointed ends moves on wheels. Current is supplied to the solenoid in advance of the car, and attracts it. As it advances it breaks the contacts of the attracting solenoid and turns the current into the one next in advance. This operation is repeated as the car advances.

The solenoids are placed close together, each including in the trial track 630 turns of No. 14 copper wire. The car was of wrought iron, 12 feet long, 10 inches in diameter and weighing 500 lbs. It was proposed to employ the system for transportation of mail matter and similar uses.

Position Finder. An instrument for determining the position of objects which are to be fired at from forts. It is designed for use from forts situated on the water.

Fiske's position finder may be thus generally described. On a chart the channel is divided into squares, and the position finder determines the square in which a vessel lies. For each square the direction and elevation of the guns is calculated beforehand. The enemy can therefore be continuously located and fired at, although from smoke or other cause the object may be quite invisible to the gunner.

It comprises two telescopes situated at distant extremities of as long a base line as is obtainable. These telescopes are kept directed upon the object by two observers simultaneously. The observers are in constant telephonic communication. As each telescope moves, it carries a contact over an arc of conducting material. Below each telescope is an arm also moving over an arc of conducting material. These arcs enter into a Wheatstone bridge and are so connected that when the arm and the distant telescope are at the same angle or parallel a balance is obtained. Thus each observer has the power of establishing a balance. A chart is provided for each of them, and over it the arm connected with the distant telescope and an arm or indicator attached to the telescope at that station move so that as long as both telescopes point at the object and each observer maintains the electric balance, the intersection of the arms shows the position on the chart.

The Position Finder is a simplification and amplification of the Range Finder, q. v. In practice the observers may be placed far from the forts, and may telephone their observations thereto. It has been found accurate within one-third of one per cent.

428 STANDARD ELECTRICAL DICTIONARY.

Positive Direction. The direction which lines of force are assumed to take in the air or outer circuit from a positive to a negative region. It applies to electrostatic, to magnetic and to electro-magnetic lines of force.

Positive Electricity. The kind of electricity with which a piece of glass is charged when rubbed with silk; vitreous electricity.

In a galvanic cell the surface of the copper or carbon plate is charged with positive electricity. (See Electrostatic Series.)

According to the single fluid theory positive electrification consists in a surplus of electricity.

[Transcriber's note: "Positive electricity" is a deficiency of electrons.]

Post Office. adj. Many pieces of electric apparatus of English manufacture are thus qualified, indicating that they are of the pattern of the apparatus used by the British Post Office in its telegraph department.

Potential. Potential in general may be treated as an attribute of a point in space, and may express the potential energy which a unit mass would have if placed at that point.

This conception of potential is that of a property attributable to a point in space, such that if a unit mass were placed there the forces acting upon it would supply the force factor of energy, while the body would supply the mass factor. This property is expressible in units, which produce, if the supposed mass is a unit mass, units of work or energy, but potential itself is neither.

Thus taking gravitation, a pound mass on the surface of the earth (assuming it to be a sphere of 4,000 miles radius) would require the expenditure of 21,120,000 foot pounds to remove it to an infinite distance against gravity. The potential of a point in space upon the surface of the earth is therefore negative and is represented by -21,120,000*32.2 foot poundals (32.2 = acceleration of gravity). (See Poundal.) In practice and conventionally all points on the earth's surface are taken as of zero potential.

[Transcriber's note; 21,120,000 foot pounds is about 8 KWh.]

429 STANDARD ELECTRICAL DICTIONARY.

Potential, Absolute. The absolute electrical potential at a point possesses a numerical value and measures the tendency which the existing electric forces would have to drive an electrified particle away from or prevent its approach to the point, if such a particle, one unit in quantity, were brought up to or were situated at that point. It is numerically equal to the number of ergs of work which must be done to bring a positive unit of electricity from a region where there is absolutely no electric force up to the point in question. (Daniell.) Two suppositions are included in this. The region where there is an electric force has to be and only can be at an infinite distance from all electrified bodies. The moving of the particle must take place without any effect upon the distribution of electricity on other particles.

Potential, Constant. Unchanging potential or potential difference.

The ordinary system of incandescent lighting is a constant potential system, an unvarying potential difference being maintained between the two leads, and the current varying according to requirements.

Potential Difference, Electric. If of any two points the absolute potentials are determined, the difference between such two expresses the potential difference. Numerically it expresses the quantity of work which must be done to remove a unit of electricity from one to the other against electric repulsion, or the energy which would be accumulated in moving it the other way.

A positively charged particle is driven towards the point of lower potential. A negatively charged body is driven in the reverse direction.

Potential Difference, Electro-motive. A difference of potential in a circuit, or in part of a circuit, which difference produces or is capable of producing a current, or is due to the flow of such current.

It may be expressed as the fall in potential or the electro-motive force included between any two points on a circuit. The current in an active circuit is due to the total electro-motive force in the circuit. This is distributed through the circuit in proportion to the resistance of its parts. Owing to the distribution of electro-motive force throughout a circuit including the generator, the terminals of a generator on closed circuit may show a difference of potential far lower than the electro-motive force of the generator on closed circuit. Hence potential difference in such a case has been termed available electro-motive force.

Potential, Electric Absolute. The mathematical expression of a property of a point in space, measuring the tendency which existing electric forces would have to drive an electrified unit particle away from or prevent its approach to the point in question, according to whether the point was situated at or was at a distance from the point in question.

Potential is not the power of doing work, although, as it is expressed always with reference to a unit body, it is numerically equal to the number of ergs of work which must be done in order to bring a positive unit of electricity from a region where there is no electric force--which is a region at an infinite distance from all electrified bodies--up to the point in question. This includes the assumption that there is no alteration in the general distribution of electricity on neighboring bodies. (Daniell.)

In practice the earth is arbitrarily taken as of zero electric potential.

430 STANDARD ELECTRICAL DICTIONARY.

Potential, Fall of. The change in potential between any two points on an active circuit. The change in potential due to the maintenance of a current through a conductor.

The fall in potential multiplied by the current gives work or energy units.

The fall of potential in a circuit and its subsequent raising by the action of the generator is illustrated by the diagram of a helix. In it the potential fall in the outer circuit is shown by the descent of the helix. This represents at once the outer circuit and the fall of potential in it. The vertical axis represents the portion of the circuit within the battery or generator in which the potential by the action of the generator is again raised to its original height.

In a circuit of even resistance the potential falls evenly throughout it.

A mechanical illustration of the relation of fall of potential to current is shown in the cut Fig. 269. A vertical wire is supposed to be fixed at its upper end and a lever arm and cord at its lower end, with weight and pulley imparts a torsional strain to it. The dials and indexes show a uniform twisting corresponding to fall of potential. For each unit of length there is a definite loss of twisting, corresponding to fall of potential in a unit of length of a conductor of uniform resistance. The total twisting represents the total potential difference. The weight sustained by the twisting represents the current maintained by the potential difference. For a shorter wire less twisting would be needed to sustain the weight, as in a shorter piece of the conductor less potential difference would be needed to maintain the same current.

Fig. 269. MECHANICAL ILLUSTRATION OF FALL OF POTENTIAL AND CURRENT STRENGTH.

431 STANDARD ELECTRICAL DICTIONARY.

Fig. 270. ILLUSTRATION OF THE FALL AND REDEVELOPMENT OF POTENTIAL IN AN ELECTRIC CIRCUIT.

The fall of potential in a circuit in portions of it is proportional to the resistance of the portions in question. This is shown in the diagram. The narrow lines indicate high and the broad lines low resistance. The fall in different portions is shown as proportional to the resistance of each portion.

Fig. 271. DIAGRAM OF FALL OF POTENTIAL IN A CONDUCTOR OF UNEVEN RESISTANCE.

Potential, Magnetic. The magnetic potential at any point of a magnetic field expresses the work which would be done by the magnetic forces of the field on a positive unit of magnetism as it moves from that point to an infinite distance therefrom. The converse applies to a negative unit.

It is the exact analogue of absolute electric potential.

The potential at any point due to a positive pole m at a distance r is m/r;. that due to a negative pole - m at a distance r' is equal to -m/r';. that due to both is equal to m/r - m/r' or m(1/r - 1/r').

Like electric potential and potential in general, magnetic potential while numerically expressing work or energy is neither, although often defined as such.

432 STANDARD ELECTRICAL DICTIONARY.

Potential, Negative. The reverse of positive potential. (See Potential, Positive.)

Potential, Positive. In general the higher potential. Taking the assumed direction of lines of force, they are assumed to be directed or to move from regions of positive to regions of negative potential. The copper or carbon plate of a voltaic battery is at positive potential compared to the zinc plate.

Potential, Unit of Electric. The arbitrary or conventional potential--or briefly, the potential of a point in an electric field of force--is, numerically, the number of ergs of work necessary to bring a unit of electricity up to the point in question from a region of nominal zero potential--i. e., from the surface of the earth. (Daniell.) This would give the erg as the unit of potential.

Potential, Zero. The potential of the earth is arbitrarily taken as the zero of electric potential.

The theoretical zero is the potential of a point infinitely distant from all electrified bodies.

Fig. 272. DIAGRAM OF POTENTIOMETER CONNECTIONS.

Potentiometer. An arrangement somewhat similar to the Wheatstone Bridge for determining potential difference, or the electro-motive force of a battery. In general principle connection is made so that the cell under trial would send a current in one direction through the galvanometer. Another battery is connected, and in shunt with its circuit the battery under trial and its galvanometer are connected, but so that its current is in opposition. By a graduated wire, like that of a meter bridge, the potential of the main battery shunt can be varied until no current passes. This gives the outline of the method only.

433 STANDARD ELECTRICAL DICTIONARY.

In the cut A B is the graduated potentiometer wire through which a current is passed in the direction of the arrow. E is the battery under trial, placed in opposition to the other current, with a galvanometer next it. Under the conditions shown, if the galvanometer showed no deflection, the E. M. F. of the battery would be to the E. M. F. between the ends of the potentiometer wire, 1 . . . . .10, as 1.5 the distance between the points of connection, A and D of the battery circuit, is to 10, the full length of the potentiometer wire.

Poundal. The British unit of force; the force which acting on a mass of one pound for one second produces an acceleration of one foot.

[Transcriber's note: The force which acting on a mass of one pound produces an acceleration of ONE FOOT PER SECOND PER SECOND.]

Power. Activity; the rate of activity, of doing work, or of expending energy. The practical unit of electric power is the volt-ampere or watt, equal to 1E7 ergs per second. The kilowatt, one thousand watts or volt-amperes, is a frequently adopted unit.

Power, Electric. As energy is the capacity for doing work, electric energy is represented by electricity in motion against a resistance. This possesses a species of inertia, which gives it a species of kinetic energy. To produce such motion, electro- motive force is required. The product of E. M. F. by quantity is therefore electric energy. (See Energy, Electric.)

Generally the rate of energy or power is used. Its dimensions are ( ( (M^.5)*(L^.5) ) / T ) * ( ( (M^.5) *(L^1.5) )/( T^2) ) (intensity or current rate) * (electro-motive force or potential) = (M * (L^2) ) / (T^3), which are the dimensions of rate of work or activity. The practical unit of electric rate of energy or activity is the volt-ampere or watt. By Ohm's law, q. v., we have C = E/R (C = current; E = potential difference or electro-motive force; R = resistance.) The watt by definition = C*E. By substitution from Ohm's formula we deduce for it the following values: ((C^2) * R) and ((E^2) /R). From these three expressions the relations of electric energy to E.M.F., Resistance, and Current can be deduced.

Power of Periodic Current. The rate of energy in a circuit carrying a periodic current. In such a circuit the electro-motive force travels in advance of the current it produces on the circuit. Consequently at phases or intervals where, owing to the alternations of the current, the current is at zero, the electro-motive force may be quite high. At any time the energy rate is the product of the electro-motive force by the amperage. To obtain the power or average rate of energy, the product of the maximum electro-motive force and maximum current must be divided by two and multiplied by the cosine of the angle of lag, which is the angle expressing the difference of phase.

[Transcriber's note; The voltage phase will lead if the load is inductive. The current phase will lead if the load is capacitive. Capacitors or inductors may be introduced into power lines to correct the phase offset introduced by customer loads.]

434 STANDARD ELECTRICAL DICTIONARY.

Pressel. A press-button often contained in a pear-shaped handle, arranged for attachment to the end of a flexible conductor, so as to hang thereby. By pressing the button a bell may be rung, or a distant lamp may be lighted.

Pressure. Force or stress exerted directly against any surface. Its dimensions are force/area or ((M*L)/(T^2)) / (L^2) = M/(L* (T^2)).

Pressure, Electric. Electro-motive force or potential difference; voltage. An expression of metaphorical nature, as the term is not accurate.

Pressure, Electrification by. A crystal of Iceland spar (calcium carbonate) pressed between the fingers becomes positively electrified and remains so for some time. Other minerals act in a similar way. Dissimilar substances pressed together and suddenly separated carry off opposite charges. This is really contact action, not pressure action.

Primary. A term used to designate the inducing coil in an induction coil or transformer; it is probably an abbreviation for primary coil.

Primary Battery. A voltaic cell or battery generating electric energy by direct consumption of material, and not regenerated by an electrolytic process.

The ordinary voltaic cell or galvanic battery is a primary battery.

Prime. vb. To impart the first charge to one of the armatures of a Holtz or other influence machine.

Fig. 273. PRIME CONDUCTOR AND PROOF PLANE.

435 STANDARD ELECTRICAL DICTIONARY.

Prime Conductor. A metal or metal coated sphere or cylinder or other solid with rounded ends mounted on insulating supports and used to collect electricity as generated by a frictional electric machine.

According to whether the prime conductor or the cushions are grounded positive or negative electricity is taken from the ungrounded part. Generally the cushions are grounded, and the prime conductor yields positive electricity.

Probe, Electric. A surgeon's probe, designed to indicate by the closing of an electric circuit the presence of a bullet or metallic body in the body of a patient.

Two insulated wires are carried to the end where their ends are exposed, still insulated from each other. In probing a wound for a bullet if the two ends touch it the circuit is closed and a bell rings. If a bone is touched no such effect is produced. The wires are in circuit with an electric bell and battery.

Projecting Power of a Magnet. The power of projecting its lines of force straight out from the poles. This is really a matter of magnetic power, rather than of shape of the magnet. In electromagnets the custom was followed by making them long to get this effect. Such length was really useful in the regard of getting room for a sufficient number of ampere turns.

436 STANDARD ELECTRICAL DICTIONARY.

Fig. 274. PRONY BRAKE.

Prony Brake. A device for measuring the power applied to a rotating shaft. It consists of a clamping device to be applied more or less rigidly to the shaft or to a pulley upon it. To the clamp is attached a lever carrying a weight. The cut shows a simple arrangement, the shaft A carries a pulley B to which the clamp B1 B2 is applied. The nuts C1 C2 are used for adjustment.

A weight is placed in the pan E attached to the end of the lever D. The weight and clamp are so adjusted that the lever shall stand horizontally as shown by the index E. If we call r the radius of the pulley and F the friction between its surface and the clamp, it is evident that r F, the moment of resistance to the motion of the pulley, is equal to the weight multiplied by its lever arm or to W*R, where W indicates the weight and R the distance of its point of application from the centre of the pulley or r*F = R*W. The work represented by this friction is equal to the distance traveled by the surface of the wheel multiplied by the frictional resistance, or is 2*PI*r*n*F, in which n is the number of turns per minute. But this is equal to 2*PI*R*W. These data being known, the power is directly calculated therefrom in terms of weight and feet per minute.

Proof-plane. A small conductor, usually disc shaped, carried at the end of an insulating handle. It is used to collect electricity by contact, from objects electrostatically charged. The charge it has received is then measured (see Torsion Balance) or otherwise tested. (See Prime Conductor.)

Proof-sphere. A small sphere, coated with gold-leaf or other conductor, and mounted on an insulated handle. It is used instead of a proof-plane, for testing bodies whose curvature is small.

Fig. 275. BOX BRIDGE.

437 STANDARD ELECTRICAL DICTIONARY.

Proportionate Arms. In general terms the arms of a Wheatstone bridge whose proportion has to be known to complete the measurement. There is a different system of naming them. Some designate by this title the two arms in parallel with each other branching at and running from one end of the bridge to the two galvanometer connections. In the cut of the Box Bridge, A C and A B are the proportionate arms. The third arm is then termed the Rheostat arm. (Stewart & Gee.)

Others treat as proportionate arms the two side members of the bridge in parallel with the unknown resistance and third or rheostat arm.

Synonym--Ratio Arms.

Prostration, Electric. Too great exposure to the voltaic arc in its more powerful forms causes symptoms resembling those of sunstroke. The skin is sometimes affected to such a degree as to come off after a few days. The throat, forehead and face suffer pains and the eyes are irritated. These effects only follow exposure to very intense sources of light, or for very long times.

[Transcriber's note: Arcs emit ultraviolet rays.]

Protector, Comb. A lightning arrester, q. v., comprising two toothed plates nearly touching each other.

Protector, Electric. A protective device for guarding the human body against destructive or injurious electric shocks. In one system, Delany's, the wrists and ankles are encircled by conducting bands which by wires running along the arms, back and legs are connected. A discharge it is assumed received by the hands will thus be short circuited around the body and its vital organs. India rubber gloves and shoe soles have also been suggested; the gloves are still used to some extent.

Pull. A switch for closing a circuit when pulled. It is used instead of a push button, q.v., in exposed situations, as its contacts are better protected than those of the ordinary push button.

Pump, Geissler. A form of mercurial air pump. It is used for exhausting Geissler tubes, incandescent lamp bulbs and similar purposes.

Referring to the cut, A is a reservoir of mercury with flexible tube C connected to a tube at its bottom, and raised and lowered by a windlass b, the cord from which passes over a pulley a. When raised the mercury tends to enter the chamber B, through the tube T. An arrangement of stopcocks surmounts this chamber, which arrangement is shown on a larger scale in the three figures X, Y and Z. To fill the bulb B, the cocks are set in the position Z; n is a two way cock and while it permits the escape of air below, it cuts off the tube, rising vertically from it. This tube, d in the full figure connects with a vessel o, pressure gauge p, and tube c, the latter connecting with the object to be exhausted. The bulb B being filled, the cock m is closed, giving the position Y and the vessel A is lowered until it is over 30 inches below B.

438 STANDARD ELECTRICAL DICTIONARY.

This establishes a Torricellian vacuum in B. The cock n is now turned, giving the position X, when air is at once exhausted from the vessel connected to C. This process is repeated until full exhaustion is obtained. In practice the first exhaustion is often effected by a mechanical pump. By closing the cock on the outlet tube c but little air need ever find its way to the chambers o and B.

Fig. 276. GEISSLER AIR PUMP.

439 STANDARD ELECTRICAL DICTIONARY.

Pumping. In incandescent lamps a periodical recurring change in intensity due to bad running of the dynamos, or in arc lamps to bad feeding of the carbons.

Fig. 277. SPRENGEL AIR PUMP.

Pump, Sprengel. A form of mercurial air pump. A simple form is shown in the cut. Mercury is caused to flow from the funnel A, through c d to a vessel B. A side connection x leads to the vessel R to be exhausted. As the mercury passes x it breaks into short columns, and carries air down between them, in this way exhausting the vessel R. In practice it is more complicated. It is said to give a better vacuum than the Sprengel pump, but to be slower in action.

440 STANDARD ELECTRICAL DICTIONARY.

Pump, Swinburne. A form of mechanical air pump for exhausting incandescent lamp bulbs. Referring to the cut, A is a bulb on the upper part of a tube G; above A are two other bulbs C and D. From the upper end a tube runs to the bulb E. Through the cock L, and tube F connection is made with a mechanical air pump. The tube H leads to a drying chamber I, and by the tube J connects with the lamp bulbs or other objects to be exhausted. The tube G enters the bottle B through an airtight stopper, through which a second tube with stopcock K passes. In use a vacuum is produced by the mechanical pumps, exhausting the lamp bulbs to a half inch and drawing up the mercury in G. The bent neck in the bulb E, acts with the bulb as a trap to exclude mercury from F. When the mechanical pumps have produced a vacuum equal to one half inch of mercury, the cock L is closed and K is opened, and air at high pressure enters. This forces the mercury up to the vessel D, half filling it. The high pressure is now removed and the mercury descends. The valve in D closes it as the mercury falls to the level G. Further air from the lamps enters A, and by repetition of the ascent of the mercury, is expelled, through D. The mercury is again lowered, producing a further exhaustion, and the process is repeated as often as necessary.

Fig. 278. SWINBURNE'S AIR PUMP.

Push-Button. A switch for closing a circuit by means of pressure applied to a button. The button is provided with a spring, so that when pushed in and released it springs back. Thus the circuit is closed only as long as the button is pressed. The electric connection may be made by pressing together two flat springs, each connected to one of the wires, or by the stem of the button going between two springs, not in contact, forcing them a little apart to secure good contact, and thereby bridging over the space between them.

441 STANDARD ELECTRICAL DICTIONARY.

Pyro-electricity. A phenomenon by which certain minerals when warmed acquire electrical properties. (Ganot.) The mineral tourmaline exhibits it strongly. It was originally observed in this mineral which was found to first attract and then to repel hot ashes.

The phenomenon lasts while any change of temperature within certain limits is taking place. In the case of tourmaline the range is from about 10º C. (50º F.) to 150º C. (302º F.) Above or below this range it shows no electrification.

The effect of a changing of temperature is to develop poles, one positive and the other negative. As the temperature rises one end is positive and the other negative; as the temperature becomes constant the polarity disappears; as the temperature falls the poles are reversed.

If a piece of tourmaline excited by pyro-electricity is broken, its broken ends develop new poles exactly like a magnet when broken.

The following minerals are pyro-electric: Boracite, topaz, prehnite, zinc silicate, scolezite, axenite. The following compound substances are also so: Cane sugar, sodium- ammonium racemate and potassium tartrate.

The list might be greatly extended.

The phenomenon can be illustrated by sifting through a cotton sieve upon the excited crystal, a mixture of red lead and flowers of sulphur. By the friction of the sifting these become oppositely electrified; the sulphur adheres to the positively electrified end, and the red lead to the negatively electrified end. (See Analogous Pole-Antilogous Pole.)

Pyromagnetic Motor. A motor driven by the alternation of attraction and release of an armature or other moving part, as such part or a section of it is rendered more or less paramagnetic by heat.

Thus imagine a cylinder of nickel at the end of a suspension rod, so mounted that it can swing like a pendulum. A magnet pole is placed to one side to which it is attracted. A flame is placed so as to heat it when in contact with the magnet pole. This destroys its paramagnetism and it swings away from the magnet and out of the flame. It cools, becomes paramagnetic, and as it swings back is reattracted, to be again released as it gets hot enough. This constitutes a simple motor.

A rotary motor may be made on the same lines. Nickel is particularly available as losing its paramagnetic property easily.

442 STANDARD ELECTRICAL DICTIONARY.

Various motors have been constructed on this principle, but none have attained any practical importance. Owing to the low temperature at which it loses its paramagnetic properties nickel is the best metal for paramagnetic motors.

In Edison's motor, between the pole pieces of an electro-magnet a cylinder made up of a bundle of nickel tubes is mounted, so as to be free to rotate. A screen is placed so as to close or obstruct the tubes farthest from the poles. On passing hot air or products of combustion of a fire or gas flame through the tubes, the unscreened ones are heated most and lose their paramagnetism. The screened tubes are then attracted and the armature rotates, bringing other tubes under the screen, which is stationary. Then the attracted tubes are heated while the others cool, and a continuous rotation is the result.

Fig. 279. EDISON'S PYROMAGNETIC MOTOR.

Pyromagnetic Generator. A current generator producing electric energy directly from thermal energy by pyromagnetism.

Edison's pyromagnetic generator has eight electro-magnets, lying on eight radii of a circle, their poles facing inward and their yokes vertical. Only two are shown in the cut. On a horizontal iron disc are mounted eight vertical rolls of corrugated nickel representing armatures. On each armature a coil of wire, insulated from the nickel by asbestus is wound. The coils are all in series, and have eight connections with a commutator as in a drum armature. There are two main divisions to the commutator. Each connects with an insulated collecting ring, and the commutator and collecting rings are mounted on a spindle rotated by power. Below the circle of vertical coils is a horizontal screen, mounted on the spindle and rotating with it.

A source of heat, or a coal stove is directly below the machine and its hot products of combustion pass up through the coils, some of which are screened by the rotating screen. The effect is that the coils are subjecting to induction owing to the change in permeability of the nickel cores, according as they are heated, or as they cool when the screen is interposed. The two commutator segments are in constant relation to the screen, and current is collected therefrom and by the collecting rings is taken to the outside circuit.

443 STANDARD ELECTRICAL DICTIONARY.

Pyromagnetism. The development of new magnetic properties or alteration of magnetic sensibility in a body by heat. Nickel and iron are much affected as regards their paramagnetic power by rise of temperature.

Fig. 280. PYROMAGNETIC GENERATOR.

Pyrometer, Siemens' Electric. An instrument for measuring high temperatures by the variations in electric resistance in a platinum wire exposed to the heat which is to be measured.

Q. Symbol for electric quantity.

Quad. (a) A contraction for quadrant, used as the unit of inductance; the henry.

(b) A contraction for quadruplex in telegraphy.

[Transcriber's note: A modern use of "quad" is a unit of energy equal to 1E15 (one quadrillion) BTU, or 1.055E18 joules. Global energy production in 2004 was 446 quad.]

Quadrant. A length equal to an approximate earth quadrant, equal to 1E9 centimeters. It has been used as the name for the unit of inductance, the henry, q. v.

Synonym--Standard Quadrant.

444 STANDARD ELECTRICAL DICTIONARY.

Quadrant, Legal. The accepted length of the quadrant of the earth, 9.978E8 instead of 1E9 centimeters; or to 9,978 kilometers instead of 10,000 kilometers.

Quadrature. Waves or periodic motions the angle of lag of one of which, with reference to one in advance of it, is 90°, are said to be in quadrature with each other.

[Transcriber's note: If the voltage and current of a power line are in quadrature, the power factor is zero (cos(90°) = 0) and no real power is delivered to the load.]

Qualitative. Involving the determination only of the presence or absence of a substance or condition, without regard to quantity. Thus a compass held near a wire might determine qualitatively whether a current was passing through the wire, but would not be sufficient to determine its quantity. (See Quantitative.)

Quality of Sound. The distinguishing characteristic of a sound other than its pitch; the timbre.

It is due to the presence with the main or fundamental sound of other minor sounds called overtones, the fundamental note prevailing and the other ones being superimposed upon it. The human voice is very rich in overtones; the telephone reproduces these, thus giving the personal peculiarities of every voice.

Synonym--Timbre.

Quantitative. Involving the determination of quantities. Thus a simple test would indicate that a current was passing through a wire. This would be a qualitative test. If by proper apparatus the exact intensity of the current was determined, it would be a quantitative determination. (See Qualitative.)

Quantity. This term is used to express arrangements of electrical connections for giving the largest quantity of current, as a quantity armature, meaning one wound for low resistance.

A battery is connected in quantity when the cells are all in parallel. It is the arrangement giving the largest current through a very small external resistance.

The term is now virtually obsolete (Daniell); "in surface," "in parallel," or "in multiple arc" is used.

Quantity, Electric. Electricity may be measured as if it were a compressible gas, by determining the potential it produces when stored in a defined recipient. In this way the conception of a species of quantity is reached. It is also measured as the quantity of current passed by a conductor.

Thus a body whose surface is more or less highly charged with electricity, is said to hold a greater or less quantity of electricity.

It may be defined in electrostatic or electro-magnetic terms. (See Quantity, Electrostatic--Quantity, Electro-magnetic.)

445 STANDARD ELECTRICAL DICTIONARY.

Quantity. Electro-magnetic. Quantity is determined electro-magnetically by the measurement of current intensity for a second of time: its dimensions are therefore given by multiplying intensity or current strength by time. The dimensions of intensity are ( (M^.5) * (L^.5) ) / T therefore the dimensions of electro-magnetic quantity are ( ( (M^.5) * (L^.5) ) / T ) * T = ( (M^.5) * (L^.5) )

Quantity, Electro-magnetic, Practical Unit of. The quantity of electricity passed by a unit current in unit time; the quantity passed by one ampere in one second; the coulomb.

It is equal to 3E9 electrostatic absolute units of quantity and to 0.1 of the electro- magnetic absolute unit of quantity.

One coulomb is represented by the deposit of .00111815 gram, or .017253 grain of silver, .00032959 gram, or .005804 grain of copper, .0003392 gram, or .005232 grain of zinc.

If water is decomposed by a current each coulomb is represented by the cubic centimeters of the mixed gases (hydrogen and oxygen) given by the following formula. ( 0.1738 * 76 * (273 + Cº ) ) / ( h * 273 ) in which Cº is the temperature of the mixed gases in degree centigrade and h is the pressure in centimeters of mercury column; or by ( 0.01058 * 30 (491 + Fº - 32) ) / (h * 491 ) for degrees Fahrenheit and inches of barometer.

[Transcriber's note: 6.24150962915265E18 electrons is one coulomb.]

Quantity, Electrostatic. Quantity is determined electro-statically by the repulsion a charge of given quantity exercises upon an identical charge at a known distance. The force evidently varies with the product of the two quantities, and by the law of radiant forces also inversely with the square of the distance. The dimensions given by these considerations is Q * Q/(L*L). This is the force of repulsion. The dimensions of a force are (M * L) /(T^2). Equating these two expressions we have: (Q^2)/(L^2) = (M*L)/(T^2) or Q = ((M^.5)*(L^1.5)) / T which are the dimensions of electrostatic quantity.

Quantity, Meter. An electric meter for determining the quantity of electricity which passes through it, expressible in coulombs or ampere hours. All commercial meters are quantity meters.

446 STANDARD ELECTRICAL DICTIONARY.

Quartz. A mineral, silica, SiO2. It has recently been used by C. V. Boys and since by others in the making of filaments for torsion suspensions. The mineral is melted, while attached to an arrow or other projectile. It is touched to another piece of quartz or some substance to which it adheres and the arrow is fired off from the bow. A very fine filament of surpassingly good qualities for galvanometer suspension filaments is produced.

As a dielectric it is remarkable in possessing but one-ninth the residual capacity of glass.

Quicking. The amalgamating of a surface of a metallic object before silver plating. It secures better adhesion of the deposit. It is executed by dipping the article into a solution of a salt of mercury. A solution of mercuric nitrate 1 part, in water 100 parts, both by weight, is used.

R. (a) Abbreviation and symbol for Reamur, as 10º R., meaning 10º by the Reamur thermometer. (See Reamur Scale.)

(b) Symbol for resistance, as in the expression of Ohm's Law C=E/R. (rho, Greek r) Symbol for specific resistance.

Racing of Motors. The rapid acceleration of speed of a motor when the load upon it is removed. It is quickly checked by counter-electro-motive force. (See Motor, Electric.)

Radian. The angle whose arc is equal in length to the radius; the unit angle.

Radiant Energy. Energy, generally existing in the luminiferous ether, kinetic and exercised in wave transmission, and rendered sensible by conversion of its energy into some other form of energy, such as thermal energy.

If the ether waves are sufficiently short and not too short, they directly affect the optic nerve and are known as light waves; they may be so short as to be inappreciable by the eye, yet possess the power of determining chemical change, when they are known as actinic waves; they may be also so long as to be inappreciable by the eye, when they may be heat-producing waves, or obscure waves.

Other forms of energy may be radiant, as sound energy dispersed by the air, and gravitational energy, whose connection with the ether has not yet been demonstrated.

Radiation. The traveling or motion of ether waves through space.

[Transcriber's note: The modern term corresponding to this definition is photons. The modern concept of radiation also includes particles-- neutrons, protons, alpha (helium) and beta (electrons) rays and other exotic items.]

Radicals. A portion of a molecule, possessing a free bond and hence free to combine directly. A radical never can exist alone, but is only hypothetical. An atom is a simple radical, an unsaturated group of atoms is a compound radical.

447 STANDARD ELECTRICAL DICTIONARY.

Radiometer. An instrument consisting of four vanes poised on an axis so as to be free to rotate, and contained in a sealed glass vessel almost perfectly exhausted. The vanes of mica are blackened on one side.

On exposure to light or a source of heat (ether waves) the vanes rotate. The rotation is due to the beating back and forth of air molecules from the surface of the vanes to the inner surface of the glass globe.

Radiometer, Electric. A radiometer in which the motion of the molecules of air necessary for rotation of the vane is produced by electrification and not by heating.

Radio-micrometer. An instrument for detecting radiant energy of heat or light form. It consists of a minute thermopile with its terminals connected by a wire, the whole suspended between the poles of a magnet. A minute quantity of heat produces a current in the thermopile circuit, which, reacted on by the field, produces a deflection. A convex mirror reflecting light is attached so as to move with the thermopile. The instrument is of extraordinary sensitiveness. It responds to .5E-6 of a degree Centigrade or about 1E-6 degree Fahrenheit.

Radiophony. The production of sound by intermittent action of a beam of light upon a body. With possibly a few exceptions all matter may produce sound by radiophouy.

Range Finder. An apparatus for use on shipboard to determine the distance of another ship or object. It is designed for ships of war, to give the range of fire, so as to set the guns at the proper elevation. The general principle involved is the use of the length of the ship if possible, if not of its width, as a base line. Two telescopes are trained upon the object and kept trained continuously thereon. The following describes the Fiske range finder.

The range finder comprises two fairly powerful telescopes, each mounted on a standard, which can be rotated round a vertical axis, corresponding with the center of the large disc shown in the engraving. One-half of the edge of this disc is graduated to 900 on either side of a zero point, and below the graduation is fixed a length of platinum silver wire. This wire only extends to a distance of 81.10 on either side of zero, and is intended to form two arms of a Wheatstone bridge. The sliding contact is carried by the same arm as the telescope standards, so that it moves with the telescope. The two instruments are mounted at a known distance apart on the ship, as shown diagrammatically in the cut. Here A and B are the centers of the two discs, C and D the arms carrying the telescopes, and E and F the platinum silver wires. Suppose the object is at T, such that A B T is a right angle, then AT=AB/sin(ATB).

448 STANDARD ELECTRICAL DICTIONARY.

If the two sectors are coupled up as shown, with a battery, h, and a galvanometer, by the wires, a b and c d, then since the arm, e, on being aligned on the object takes the position c1 while d remains at zero, the Wheatstone bridge formed by these segments and their connections will be out of balance, and a current will flow through the galvanometer, which may be so graduated as to give the range by direct reading, since the current through it will increase with the angle A T B.

Fig. 281. RANGE FINDER.

In general, however, the angle A B T will not be a right angle, but some other angle. In this case AT = AB / sin(A T B) * sin( A B T), and hence it will only be necessary to multiply the range reading on the galvanometer by the sine of the angle A B T, which can be read directly by the observer at B. This multiplication is not difficult, but by suitably arranging his electrical appliances Lieutenant Fiske has succeeded in getting rid of it, so that the reading of the galvanometer always gives the range by direct reading, no matter what the angle at B may be. To explain this, consider the two telescopes shown in the cut in the positions C and D; the whole current then has a certain resistance.

449 STANDARD ELECTRICAL DICTIONARY.

Next suppose them, still remaining parallel, in the positions C1 and D1. The total resistance of the circuit is now less than before, and hence if C1, one of the telescopes, is moved out of parallel to the other, through a certain angle, the current through the galvanometer will be greater than if it were moved through an equal angle out of a parallel when the telescopes were in the positions C and D. The range indicated is, therefore, decreased, and by properly proportioning the various parts it is found that the range can always be read direct from the galvanometer, or in other words the multiplication of A B/sin( A T B ) by sin( A B T ) is to all intents and purposes performed automatically. There is, it is true, a slight theoretical error; but by using a small storage battery and making the contents carefully it is said to be inappreciable. Each telescope is fitted with a telephone receiver and transmitter, so that both observers can without difficulty decide on what point to align their telescopes. It will be seen that it is necessary that the lines of sight of two telescopes should be parallel when the galvanometer indicates no current. It has been proposed to accomplish this by sighting both telescopes on a star near the horizon, which being practically an infinite distance away insures the parallelism of the lines of sight.

Rate Governor. An apparatus for securing a fixed rate of vibration of a vibrating reed. It is applied in simultaneous telegraphy and telephoning over one wire. The principle is that of the regular make and break mechanism, with the feature that the contact is maintained during exactly one-half of the swing of the reed. The contact exists during the farthest half of the swing of the reed away from the attracting pole.

Fig. 282. LANGDON DAVIRS' RATE GOVERNOR.

In the left hand figure of the cut, K is the key for closing the circuit. A is the base for attachment of the reed. V is the contact-spring limited in its play to the right by the screw S. C is the actuating magnet. By tracing the movements of the reed, shown on an exaggerated scale in the three right hand figures, it will be seen that the reed is in electric contact with the spring during about one-half its movement. The time of this connection is adjustable by the screw S.

Synonym--Langdon Davies' Rate Governor or Phonophone.

450 STANDARD ELECTRICAL DICTIONARY.

Ray, Electric. Raia torpedo. The torpedo, a fish having the same power of giving electric shocks as that possessed by the electric eel, q. v. (See also Animal Electricity.)

Fig. 283. TORPEDO OR ELECTRIC RAY

Reaction of Dynamo, Field and Armature. A principle of the dynamo current generator, discovered by Soren Hjorth of Denmark.

When the armature is first rotated it moves in a field due to the residual magnetism of the field magnet core. This field is very weak, and a slight current only is produced. This passing in part or in whole through the field magnet cores slightly strengthens the field, whose increased strength reacts on the armature increasing its current, which again strengthens the field. In this way the current very soon reaches its full strength as due to its speed of rotation.

The operation is sometimes termed building up.

Sometimes, when there is but a trace of residual magnetism, it is very hard to start a dynamo.

Reading Telescope. A telescope for reading the deflections of a reflecting galvanometer.

A long horizontal scale is mounted at a distance from the galvanometer and directly below or above the centre of the scale a telescope is mounted. The telescope is so directed that the mirror of the galvanometer is in its field of view, and the relative positions of mirror, scale and telescope are such that the image of the scale in the galvanometer mirror is seen by the observer looking through the telescope.

Under these conditions it is obvious that the graduation of the scale reflected by the mirror corresponds to the deflection of the galvanometer needle.

The scale may be straight or curved, with the galvanometer in the latter case, at its centre of curvature.

Reamur Scale. A thermometer scale in use in some countries of Continental Europe. The temperature of melting ice is 0°; the temperature of condensing steam is 80°; the degrees are all equal in length. For conversion to centigrade degrees multiply degrees Reamur by 5/4. For conversion to Fahrenheit degrees multiply by 9/4 and add 32 if above 0° R., and if below subtract 32. Its symbol is R., as 10° R.

451 STANDARD ELECTRICAL DICTIONARY.

Recalescence. A phenomenon occurring during the cooling of a mass of steel, when it suddenly emits heat and grows more luminous for an instant. It is a phase of latent heat, and marks apparently the transition from a non-magnetizable to a magnetiz able condition.

Receiver. In telephony and telegraphy, an instrument for receiving a message as distinguished from one used for sending or transmitting one.

Thus the Bell telephone applied to the ear is a receiver, while the microphone which is spoken into or against is the transmitter.

Receiver, Harmonic. A receiver including an electro-magnet whose armature is an elastic steel reed, vibrating to a particular note. Such a reed responds to a series of impulses succeeding each other with the exact frequency of its own natural vibrations, and does not respond to any other rapid series of impulses. (See Telegraph Harmonic.)

Reciprocal. The reciprocal of a number is the quotient obtained by dividing one by the number. Thus the reciprocal of 8 is 1/8.

Applied to fractions the above operation is carried out by simply inverting the fraction. Thus the reciprocal of 3/4 is 4/3 or 1-1/3.

Record, Telephone. Attempts have been made to produce a record from the vibrations of a telephone disc, which could be interpreted by phonograph or otherwise.

Fig. 284. MORSE RECORDER OR EMBOSSER.

452 STANDARD ELECTRICAL DICTIONARY.

Recorder, Morse. A telegraphic receiving apparatus for recording on a strip of paper the dots and lines forming Morse characters as received over a telegraph line. Its general features are as follows:

A riband or strip of paper is drawn over a roller which is slightly indented around its centre. A stylus or blunt point carried by a vibrating arm nearly touches the paper. The arm normally is motionless and makes no mark on the paper. An armature is carried by the arm and an electro-magnet faces the armature. When a current is passed through the magnet the armature is attracted and the stylus is forced against the paper, depressing it into the groove, thus producing a mark. When the current ceases the stylus is drawn back by a spring.

Fig. 285. INKING ROLLER MECHANISM OF MORSE RECORDER.

In some instruments a small inking roller takes the place of the stylus, and the roller is smooth. The cut, Fig. 285, shows the plan view of the ink-roller mechanism. J is the roller, L is the ink well, Cl is the arm by which it is raised or lowered by the electro-magnet, as in the embosser. S S is the frame of the instrument, and B the arbor to which the arm carrying the armature is secured, projecting to the right. A spring is arranged to rub against the edge of the inking roller and remove the ink from it.

The paper is fed through the apparatus by clockwork. At the present day sound reading has almost entirely replaced the sight reading of the recorder.

Recorder, Siphon. A recording apparatus in which the inked marks are made on a strip of paper, the ink being supplied by a siphon terminating in a capillary orifice.

In the cut N S represents the poles of a powerful electro-magnet. A rectangular coil bb of wire is suspended between the coils. A stationary iron core a intensifies the field. The suspension wire f f 1 has its tension adjusted at h. This wire acts as conductor for the current.

453 STANDARD ELECTRICAL DICTIONARY.

The current is sent in one or the other direction or is cut off in practice to produce the desired oscillations of the coil b b. A glass siphon n l works upon a vertical axis l. One end l is immersed in an ink well m. Its longer end n touches a riband of paper o o. The thread k attached to one side of the coil pulls the siphon back and forth according to the direction of current going through the electro-magnet cores. A spiral spring adjusted by a hand-screw controls the siphon. In operation the siphon is drawn back and forth producing a zigzag line. The upward marks represent dots, the downward ones dashes. Thus the Telegraphic Code can be transmitted on it. To cause the ink to issue properly, electrification by a static machine has been used, when the stylus does not actually touch the paper, but the ink is ejected in a series of dots.

Fig. 286. SIPHON RECORDER.

Reducteur for Ammeter. A resistance arranged as a shunt to diminish the total current passing through an ammeter. It is analogous to a galvanometer shunt. (See Multiplying Power of Shunt.)

Reducteur for Voltmeter. A resistance coil connected in series with a Voltmeter to diminish the current passing through it. Its resistance being known in terms of the resistance of the voltmeter it increases the range of the instrument so that its readings may cover double or more than double their normal range.

Reduction of Ores, Electric. Treatment of ores by the electric furnace (see Furnace, Electric.) The ore mixed with carbon and flux is melted by the combined arc and incandescent effects of the current and the metal separates. In another type the metal is brought into a fusible compound which is electrolyzed while fused in a crucible. Finally processes in which a solution of a salt of the metal is obtained, from which the metal is obtained by electrolysis, may be included. Aluminum is the metal to whose extraction the first described processes are applied.

454 STANDARD ELECTRICAL DICTIONARY.

Refraction, Electric Double. Double refraction induced in some materials by the action of either an electrostatic, magnetic or an electro-magnetic field.

The intensity or degree of refracting power is proportional to the square of the strength of field.

Refreshing Action. In electro-therapeutics the restoration of strength or of nerve force by the use of voltaic alternatives, q. v.

Region, Extra-polar. In electro-therapeutics the area or region of the body remote from the therapeutic electrode.

Region, Polar. In electro-therapeutics the area or region of the body near the therapeutic electrode.

Register, Electric. There are various kinds of electric registers, for registering the movements of watchmen and other service. Contact or press buttons may be distributed through a factory. Each one is connected so that when the circuit is closed thereby a mark is produced by the depression of a pencil upon a sheet or disc of paper by electro-magnetic mechanism. The paper is moved by clockwork, and is graduated into hours. For each push-button a special mark may be made on the paper. The watchman is required to press the button at specified times. This indicates his movements on the paper, and acts as a time detector to show whether he has been attending to his duty.

Register, Telegraphic. A term often applied to telegraph recorders, instruments for producing on paper the characters of the Morse or other alphabet.

Regulation, Constant Current. The regulation of a dynamo so that it shall give a constant current against any resistance in the outer circuits, within practical limits. It is carried out in direct current machines generally by independent regulators embodying a controlling coil with plunger or some equivalent electro-magnetic device inserted in the main circuit and necessarily of low resistance. In some regulators the work of moving the regulator is executed mechanically, but under electrical control; in others the entire work is done by the current.

A typical regulator or governor (Golden's) of the first class comprises two driven friction wheels between which is a driving friction wheel, which can engage with one driven wheel only at once. It is brought into engagement with one or the other by a solenoid and plunger.

455 STANDARD ELECTRICAL DICTIONARY.

As it touches one wheel it turns it in one direction. This moves a sliding contact in one direction so as to increase a resistance. This corresponds to a motion of the plunger in one direction. As the driving wheel moves in the opposite direction by a reverse action it diminishes the resistance. Thus the increase and decrease of resistance correspond to opposite movements of the solenoid plunger, and consequently to opposite variations in the current. The whole is so adjusted that the variations in resistance maintain a constant amperage. The resistance is in the exciting circuit of the dynamo.

In Brush's regulator, which is purely mechanical, a series dynamo is made to give a constant current by introducing across the field magnets a shunt of variable resistance, whose resistance is changed by an electro-magnet, whose coils are in circuit with the main current. Carbon resistance discs are used which the electro-magnet by its attraction for its armature, presses with varying intensity. This alters the resistance, decreasing it as the current increases and the reverse. As the connection is in shunt this action goes to maintain a constant current.

Regulation, Constant Potential. The regulation of constant potential dynamos is executed on the same lines as that of constant current dynamos. If done by a controlling coil, it must for constant potential regulation be wound with fine wire and connected as a shunt for some part of the machine.

Regulation of Dynamos. The regulation of dynamos so that they shall maintain a constant potential difference in the leads of their circuit for multiple arc systems or shall deliver a constant current in series systems. Hence two different systems of regulation are required, (a) constant potential regulation--(b) constant current regulation. The first named is by far the more important, as it concerns multiple arc lighting, which is the system universally used for incandescent lighting.

S. P. Thompson thus summarizes the methods of governing or regulating dynamos. Premising that alteration of the magnetic flux is the almost universal way of control, it can be done in two ways; first, by varying the excitation or ampere turns of the field, and second by varying the reluctance of the magnetic circuit. The excitation or magnetic flux may be varied

(a) by hand, with the aid of rheostats and commutators in the exciting circuit;

(b) automatically, by governors, taking the place of the hand;

(c) by compound windings. The magnetic circuit may have its reluctance caused to vary in several ways;

(d) by moving the pole pieces nearer to or further from the armature;

(e) by opening or closing some gap in the magnetic circuit (field-magnet core);

(f) by drawing the armature endways from between the pole pieces;

(g) by shunting some of the magnetic lines away from the armature by a magnetic shunt.

The latter magnetic circuit methods d, e, f, and g, have never met with much success except on small machines or motors. Method e is adopted in the Edison motor, the yoke being withdrawn or brought nearer the cores of the coils. (See Regulation, Constant Current-Regulation, constant Potential.)

456 STANDARD ELECTRICAL DICTIONARY.

Reguline. adj. Having the characteristics of a piece of metal, being flexible, adherent, continuous, and coherent. Applied to electrolytic deposits.

Relative. Indicating the relation between two or more things without reference to absolute value of any one of them. Thus one lamp may be of relatively double resistance compared to another, but this states nothing of the resistance in ohms of either lamp.

Relay. A receiving instrument which moves in accordance with impulses of currents received, and in so moving opens and closes a local circuit, which circuit may include as powerful a battery as required or desirable, while the relay may be on the other hand so delicate as to work with a very weak current.

Fig. 287. RELAY.

The typical relay includes an electro-magnet and armature. To the latter an arm is attached and the lower end of the arm works in pivots. As the armature is attracted the arm swings towards the magnet. When the current is cut off, the armature and arm are drawn back by a spring. When the arm swings towards the magnet its upper end touching a contact screw closes the local circuit. When it swings back it comes in contact with a second screw, with insulated point, and opens the circuit as it leaves the first named screw.

One terminal connects with the arm through the pivots and frame. The other connects with the contact screw through the frame carrying it.

Synonym--Relay Magnet.

457 STANDARD ELECTRICAL DICTIONARY.

Relay Bells. Bells connected by relay connection to a main line for acoustic telegraphy. A stroke on one bell indicates a dot and on the other a dash. The system is now nearly extinct.

Relay, Box-sounding. A relay which is surrounded by or mounted on a resonator or wooden box of such proportions and size as to reinforce the sound. This enables a relay to act as a sounder, its weak sounds being virtually magnified so as to be audible.

Relay Connection. A connection used in telegraphy, including a local battery, with a short circuit normally open, but closed by a switch and a sounder or other appliance. The latter is made very sensitive so as to be worked by a feeble current, and is connected to the main line. A very slight current closes the switch and the local battery comes into operation to work a sounder, etc. When the current ceases on the main line the switch opens and throws the local battery out of action. The switch is termed a relay, q. v. A long main line may thus produce strong effects at distant stations, the intensity of action depending on the local battery.

Fig. 288. RELAY OR LOCAL CIRCUIT.

Relay, Differential. A relay containing two coils wound differentially, and of the same number of turns and resistance. If two equal currents pass through the coils they counteract each other and no action takes place. If there is a difference in the currents the relay acts as one coil preponderates. The coils may be wound for uneven currents with different resistance and number of turns.

Relay, Microphone. A relay connection applied to a telephone circuit. It consists of a microphone mounted in front of the diaphragm of a telephone receiver. In circuit with the microphone is a battery and second telephone receiver. The microphone is supposed to intensify the sounds of the first telephone.

458 STANDARD ELECTRICAL DICTIONARY.

Relay, Polarized. A relay whose armature is of steel, and polarized or permanently magnetized, or in which a permanent magnet is used as the basis for the electro-magnets. In the relay shown in the cut the coils shown are mounted on cores carried on the end of a powerful bent permanent magnet. Thus when no current passes their upper poles are both of the same sign, and the horizontally vibrating tongue is held by the magnetic attraction against one or the other pole piece. If a current is sent through the electro-magnet it gives opposite polarity to the two polar extensions. As the end of the vibrating tongue is of polarity determined by the permanent magnet it is attracted to one pole and repelled from the other. On cessation of current it remains attached by the permanent magnetism. If now a current is sent in the opposite direction the two poles again acquire opposite polarity, the reverse of the former, and the tongue flies across to the opposite side. On cessation of current it remains attached as before by the permanent magnetism.

In its movements to and fro the relay tongue opens and closes a contact, so as to work a sounder or other apparatus. The polarized relay is of high sensibility, and requires little or no change of adjustment.

Fig. 288. POLARIZED RELAY

Reluctance. In a magnetic circuit or portion thereof, the resistance offered to the flow of lines of force. The magnetic circuit as has already been stated is treated like an electric circuit, and in it reluctance occupies the place of resistance in the electric circuit. It is the reciprocal of permeance. S. P. Thompson expresses the law thus:

Total number of magnetic lines = (magneto-motive force) / (magnetic reluctance)

Synonyms--Magnetic Reluctance-Magnetic Resistance.

Reluctance, Unit of. The reluctance of a circuit through which unit magnetizing power (magneto-motive force) can produce a unit of induction or one line of force. This value is very high; the reluctance of ordinary magnetic circuits ranges from 1E-5 to 1E-8 unit of reluctance.

Reluctivity. Specific reluctance; the reluctance of a cube of material whose edge measures one centimeter in length. It is a quality bearing the same relation to reluctance that permeability does to permeance.

It is defined as the reciprocal of magnetic permeability. (Kenelly.) If plotted as a curve for different values of the magnetizing force it is found to be nearly a straight line, a linear function of the magnetizing force, H with the equation a + b H. Reluctivity is the property of a substance; reluctance is the property of a circuit.

459 STANDARD ELECTRICAL DICTIONARY.

Remanence. The residual magnetism left after magnetic induction, expressed in lines of force per square centimeter.

Repeater. In telegraphy an instrument for repeating the signals through a second line. It is virtually a relay which is operated by the sender, and which in turn operates the rest of the main line, being situated itself at about the middle point of the distance covered. In the simpler forms of repeater two relays are used, one for transmission in one direction the other for transmission in the other. An attendant switches one or the other in as required.

Thus a common relay is virtually a repeater for its local circuit. If such a relay is placed half way down a line, and if the line beyond it is connected as its local, it becomes a repeater.

Some forms of repeaters are automatic, and repeat both ways without the need of an attendant.

It is the practice to somewhat prolong the signals sent through a repeater.

Replenisher, Sir William Thomson's. A static accumulating influence machine contained in Thomson's quadrant electrometer and used to change the quadrants. The cut shows the horizontal section and construction of the apparatus.

It contains two gilt brass inductors A B, and two eccentric sectors or carriers, C, D, which are mounted on an ebonite spindle, which is spun around by the fingers. The springs s s1 connect each with its inductor; the springs S S1 connect only each other, and touch the sectors as they turn around.

One of the inductors may be always assumed to be of slightly higher potential than that of the other one. When the carriers are in contact with the springs S S1 they are each charged by induction with electricity opposite in sign to that of the nearest quadrant. As they leave the springs S S1 in their rotation, they next touch the springs s s1, but of the recently opposite inductor. They share each a portion of its charge with the inductors building up their charges. The action is repeated over and over again as they rotate.

Fig. 290. THOMSON'S REPLENISHER.

460 STANDARD ELECTRICAL DICTIONARY.

Reservoir, Common. A term applied to the earth, because all electrified bodies discharge into it if connected thereto.

Fig. 289. DIAGRAM OF THOMSON'S REPLENISHER.

Residual Atmosphere. The air left in a receiver after exhaustion by an air pump. The quantity, where good air pumps are used, is very minute.

Residue, Electric. The residual charge of a condenser. (See Charge, Residual.)

Resin. (a) The product obtained by non-destructive distillation of the juice of the pitch pine. It is the solid residue left after the turpentine has been evaporated or distilled. It is a mixture of abietic acid C44 H64 O5 and pinic acid C20 H30 O2. It is an insulator; its specific inductive capacity is 2.55. (Baltzmann.)

Synonyms--Colophony--Rosin.

(b) The name is also generally applied to similar substances obtained from the sap of other trees; thus shellac is a resin. The resins are a family of vegetable products; the solid portions of the sap of certain trees. Common resin, lac, dragons blood, are examples. They are all dielectrics and sources of resinous or negative electricity when rubbed with cotton, flannel, or silk. (See Electrostatic Series.)

461 STANDARD ELECTRICAL DICTIONARY.

Resinous Electricity. Negative electricity; the electricity produced upon the surface of a resinous body by rubbing it; such a body is shellac or sealing wax; flannel and other substances may be used as the rubbing material. (See Electrostatic Series.)

Resistance. (a) The quality of an electric conductor, in virtue of which it opposes the passage of an electric current, causing the disappearance of electro-motive force if a current passes through it, and converting electric energy into heat energy in the passage of a current through it. If a current passes through a conductor of uniform resistance there is a uniform fall of potential all along its length. If of uneven resistance the fall in potential varies with the resistance. (See Potential, Fall of.)

The fall of potential is thus expressed by Daniell. "In a conductor, say a wire, along which a current is steadily and uniformly passing, there is no internal accumulation of electricity, no density of internal distribution; there is, on the other hand, an unequally distributed charge of electricity on the surface of the wire, which results in a potential diminishing within the wire from one end of the wire to the other."

Resistance varies inversely with the cross section of a cylindrical or prismatic conductor, in general with the average cross-section of any conductor, and in the same sense directly with its true or average or virtual length. It varies for different substances, and for different conditions as of temperature and pressure for the same substance. A rise of temperature in metals increases the resistance, in some bad conductors a rise of temperature decreases the resistance.

462 STANDARD ELECTRICAL DICTIONARY.

Approximately, with the exception of iron and mercury, the resistance of a metallic conductor varies with the absolute temperature. This is very roughly approximate.

Except for resistance energy would not be expended in maintaining a current through a circuit. The resistance of a conductor may be supposed to have its seat and cause in the jumps from molecule to molecule, which the current has to take in going through it. If so a current confined to a molecule would, if once started, persist because there would be no resistance in a molecule. Hence on this theory the Ampérian currents (see Magnetism, Ampere's Theory of) would require no energy for their maintenance and Ampére's theory would become a possible truth.

When metals melt their resistance suddenly increases.

Light rays falling on some substances, notably selenium, q. v., vary the resistance.

Longitudinal stretching of a conductor decreases it, it increases with longitudinal compression, and increases in iron and diminishes in tin and zinc when a transverse stress tends to widen the conductor.

(b) The term resistance is used to express any object or conductor used in circuit to develop resistance.

[Transcriber's note: At room temperatures, the thermal motion of ions in the conductor's crystal lattice scatters the electrons of the current. Imperfections of the lattice contribute slightly. At low temperatures superconductivity (zero resistance) can occur because an energy gap between the electrons and the crystal lattice prevents any interaction. At the time of this book, none of this was known. "Jumps from molecule to molecule" is a good guess.]

Resistance, Apparent. Impedance; the virtual resistance of a circuit including the spurious resistance due to counter-electromotive force. It may be made up of true resistance and partly of an inductive reaction, as it represents the net factor, the entire obstruction to the passage of a current, and not merely a superadded resistance or counter-electro-motive force.

Synonym--Impedance.

[Transcriber's note: Impedance can also have a component due to capacitance.]

Resistance, Asymmetrical. Resistance which varies in amount in different directions through a conductor. It implies a compound or composite conductor such as the human system. The presence of counter-electro-motive force in different parts of a conductor may bring about asymmetrical resistance.

Resistance, B. A. Unit of. The British Association Ohm. (See Ohm, B. A.)

463 STANDARD ELECTRICAL DICTIONARY.

Resistance Box. A box filled with resistance coils. The coils are connected in series so that a circuit including any given number has their aggregate resistance added to its own. The terminals of consecutive coils are connected to short blocks of brass which are secured to the top of the box, lying flatwise upon it, nearly but not quite in contact with each other. Plugs of brass are supplied which can go in between pairs of blocks, which have a pair of grooves reamed out to receive them. Such plugs short circuit the coil below them when in position. The cut shows how such coils are connected and the use of plugs to short circuit them. The diagram shows the top of a Wheatstone bridge, q. v., resistance box with connections for determining resistances.

Fig. 291. RESISTANCE BOX.

Resistance Box, Sliding. A resistance box whose coils are set in a circle. Two metal arms with handles are pivoted at the centre of the circle and by moving them around they make and break contacts so as to throw the coils in and out of circuit. The object is to permit an operator to adjust resistance without looking at the box--an essential in duplex telegraphy.

Resistance, Breguet Unit of. The same in origin as the Digney Unit. (See Resistance, Digney Unit of.)

It is equal to 9.652 Legal Ohms.

Resistance, Carbon. A resistance, a substitute for a resistance coil; it is made of carbon, and is of various construction. In the Brush dynamo regulator a set of four vertical piles of plates of retort carbon, q. v., is used as a resistance, whose resistance is made to vary by changing the pressure. This pressure automatically increases as the current strength increases, thus reducing the resistance.

464 STANDARD ELECTRICAL DICTIONARY.

Resistance Coil, Standard. A standard or resistance issued by the Electric Standard Committee of Great Britain. The cut shows the standard ohm. It is formed either of German silver, or of an alloy of silver, 66.6 per cent. and platinum, 33.4 per cent. The wire is insulated and doubled before winding as described before. (See Coil, Resistance.) The two ends of the wire are soldered, each one to a heavy copper wire or rod r. The whole coil is enclosed in a brass case, and is enclosed with paraffine melted in at A. A place for a thermometer is provided at t. By immersing the lower part of the case B in water of different degrees of heat any desired temperature can be attained.

Fig. 292. STANDARD OHM COIL.

Resistance, Combined. The actual resistance of several parallel conductors starting from the same point and ending at the same point. If the individual resistance be a b c d .. and the combined resistance be x then we have x = 1 / (( 1/a) + (1/b) + (1/c) + (1/d) + …)

Synonym--Joint Resistance.

Resistance, Critical. In a series wound dynamo the resistance of the outer circuit above which the machine will refuse to excite itself.

Resistance, Dielectric. The mechanical resistance of a dielectric to the tendency to perforation or to the strains due to electrification. This is a phase of mechanical resistance, and is distinct from the electrical or ohmic resistance of the same substance.

Resistance, Digney Unit of. The resistance of an iron wire, 1 kilometer long, 4 millimeters diameter, temperature unknown.

It is equal to 9.163 legal ohms.

Resistance, Electrolytic. The resistance of an electrolyte to the passage of a current decomposing it. It is almost entirely due to electrolysis and is added to by counter- electro-motive force, yet it is not treated specifically as such, but as an actual resistance. When a current of a circuit of too low voltage to decompose an electrolyte is caused by way of immersed terminals to pass through an electrolyte the resistance appears very high and sometimes almost infinite. If the voltage is increased until the electrolyte is decomposed the resistance suddenly drops, and what should be termed electrolytic resistance, far lower than the true resistance, appears.

465 STANDARD ELECTRICAL DICTIONARY.

Resistance, English Absolute or Foot-Second Unit of. A unit based on the foot and second. It is equal to (( foot / second ) * 1E7) , being based on these dimensions.

It is equal to 0.30140 legal ohm.

Resistance, Equivalent. A resistance equivalent to other resistances, which may include counter-electro-motive force.

Resistance, Essential. The resistance of the generator in an electric circuit; the same as internal resistance.

Resistance, External. In an electric circuit the resistance of the circuit outside of the generator, or battery.

Synonym--Non-essential Resistance.

Fig. 293. RESISTANCE FRAME.

Resistance Frame. An open frame filled with resistance coils of iron, or German silver wire. It is used as a resistance for dynamos and the larger or working class of plant. The coils are sometimes connected so that by a switch moving over a row of studs one or more can be thrown into series according to the stud the switch is in contact with.

Resistance, German Mile Unit of. The resistance of 8,238 yards of iron wire 1/6 inch in diameter. It is equal to 56.81 legal ohms.

466 STANDARD ELECTRICAL DICTIONARY.

Resistance, Hittorf's. A high resistance, often a megohm, composed of Hittorf's solution, q. v. It is contained in a vertical glass tube near whose upper and lower ends are electrodes of metallic cadmium attached to platinum wires. The cadmium is melted in glass tubes, the platinum wire is inserted into the melted metal and the tube is broken after all is solid. The resistance should show no polarization current.

Fig. 294. HITTORF'S RESISTANCE

Resistance, Inductive. A resistance in which self-induction is present; such as a coil of insulated wire wound around an iron core.

Resistance, Insulation. The resistance of the insulation of an insulated conductor. It is stated in ohms per mile. It is determined by immersing a section of the line in water and measuring the resistance between its conductor and the water. The section must be of known length, and its ends must both be above the liquid.

Resistance, Internal. The resistance of a battery, or generator in an electric circuit as distinguished from the resistance of the rest of the circuit, or the external resistance.

Synonym--Essential Resistance.

Resistance, Jacobi's Unit of. The resistance of a certain copper wire 25 feet long and weighing 345 grains.

It is equal to 0.6296 legal ohm.

Resistance, Matthiessen's Meter-gram Standard. The resistance of a pure hard drawn copper wire of such diameter that one meter of it weighs one gram. It is equal to .1434 Legal Ohms at 0º C. (32º F.)

Resistance, Matthiessen's Unit of. The resistance of a standard mile of pure annealed copper wire 1/16 inch diameter, at a temperature of 15.5º C. (60º F.).

It is equal to 13.44 legal ohms.

467 STANDARD ELECTRICAL DICTIONARY.

Resistance, Meter-millimeter Unit of. The resistance of a wire of copper one meter long and one square millimeter in section. It is equal to .02057 ohms at 0º C. (32º F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Mil-foot Unit of. The resistance of a foot of copper wire one-thousandth of an inch in diameter. It is equal to 9.831 ohms at 0º C. (32º F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Non-essential. The resistance of the portion of an electric circuit not within the generator; the same as external resistance.

Synonym--External Resistance.

Resistance, Non-inductive. A resistance with comparatively little or negligible self-induction.

Resistance of Human Body. The resistance of the human body is largely a matter of perfection of the contacts between its surface and the electrodes. It has been asserted that it is affected by disease. From 350 to 8,000 ohms have been determined as resistances, but so much depends on the contacts that little value attaches to the results.

Resistance, Ohmic. True resistance measured in ohms as distinguished from counter-electro-motive force, q. v. The latter is called often spurious resistance.

Synonym--True Resistance.

[Transcriber's note: "True" vs. "spurious" are interesting terms, considering that today we define impedance as a combination of "real" resistance and "imaginary" capacitive and inductive reactance.]

Resistance, Reduced. The resistance of a conductor reduced to ohms, or to equivalent lengths of a column of mercury, 1 square millimeter in cross area.

Resistance, Siemen's Unit of. The resistance of a column of mercury 1 meter long and 1 square millimeter cross-sectional area at 0º C. (32º F.)

It is equal to .9431 legal ohm.

Resistance, Specific. The relative resistance of a substance. It is expressed as the actual resistance of a cube of the substance which is one centimeter on each edge. For metals it is usually expressed in microhms, for liquids in ohms.

The resistances of a specified length of wire of specified diameter of different substances is often given, and is really a particular way of stating specific resistances.

Synonym--Specific Conduction Resistance.

Resistance, Spurious. The counter-electro-motive force, q. v., operating to prevent a current being produced of what should be its full strength were the true resistance and actuating electro-motive force only concerned. Such counter-electro-motive force may be treated as a spurious resistance and such a value in ohms assigned to it as would correspond to its proper effect.

468 STANDARD ELECTRICAL DICTIONARY.

In its effect on opposing a current and in resisting its formation it differs from true resistance. The latter in diminishing current strength absorbs energy and develops heat; spurious resistance opposes and diminishes a current without absorption of energy or production of heat.

[Transcriber's note: "Spurious resistance" is now called reactance, consisting of capacitive reactance and inductive reactance. The combination of reactance and (Ohmic/true) resistance is called impedance. The calculation of impedance requires complex algebra, not just real values used in DC circuit analysis.]

Resistance, Steadying. When arc lamps are connected in parallel or multiple arc a small resistance coil is sometimes placed in series with each lamp for steadying purposes. It reduces the percentage of variation of resistance in each lamp, which may be caused by a change in the position of the carbons.

Resistance, Swiss Unit of. A unit constructed by the "Administration Suisse," based on the same data as the Breguet and the Digney Units. (See Resistance, Digney Unit of)

It is equal to 10.30 legal ohms.

Resistance, Thomson's Unit of. A unit of resistance based on the foot and second.

It is equal to 0.3166 legal ohm.

Resistance, Unit. Unit resistance is that of a conductor in which unit current is produced by unit electro-motive force.

Resistance, Varley's Unit of. The resistance of a standard mile of a special copper wire 1/16 inch diameter.

It is equal to 25.33 ohms.

Resistance, Weber's Absolute Unit. A metric system unit; (meter / second) * 1E7

It is equal to 0.9089 legal ohm.

Resonance, Electric. A set of phenomena known as the Hertz experiments are grouped under this title, which phenomena are incidents of and depend on the propagation of electric waves through wires or current conductors, as well as through the ether. Ordinarily a wire is only a seat of current, and is in its nature inconsistent with wave propagation through its mass. Such waves are virtually confined to the exterior of the wire. The point is that the current-producing force is supposed to enter the wire at all points from without, the current not being produced by an end-push. Hence in rapidly recurring waves which are produced by a rapidly pulsatory or alternating current, no time is afforded for the current-producing force, in this case the wave-producing force, to penetrate into the substance of the wire. In one of his experiments Dr. Hertz surrounded a wire by a glass tube chemically silvered. The coating was so thin as to be translucent. Through this metallic layer a current could be induced in the wire in its interior. Any mechanical layer of metal took up the induction itself, and protected the central wire. This gave a clue to the thickness of metal penetrated by the rapid induced waves used by Dr. Hertz.

469 STANDARD ELECTRICAL DICTIONARY.

Fig. 295. ELECTRICAL RESONANCE EXCITER.

The method used for the production of rapid oscillations is the following. To the terminals of an induction coil two metal spheres AA1 are connected as shown. This apparatus is termed the exciter; in its discharge a series of isochronous discharges takes place, alternating in direction. The period of duration T of a single one is given by the formula T= 2* PI * squareRoot( LC ), in which C is the capacity and L is the self-induction. The spheres may be 30 centimeters (11.8 inches) in diameter, connected each to conductors 0.5 centimeter (.2 inch) in diameter and 40 centimeters (15.7 inches) long each. For the length of an undulation the formula gives for this apparatus 4.8 meters (15.75 feet) as the length of a wave, assuming for them the velocity of propagation equal to that of light. The exciter may have 10,000 times the rate of oscillation possessed by the plain induction coil.

When this apparatus is worked it produces induced waves in every neighboring conductor. The resonance effects appear in the size of the spark induced. Thus a wire bent into a circle with its ends nearly touching will give a spark, but if made of proper electrostatic capacity, corresponding with the particular waves employed, the spark will be very much larger. The ring, with its spark gap is termed a resonator. It is used as an explorer to trace the waves.

Waves thus produced are transmitted by stone walls and nonconductors in general. A plate of zinc reflects part and transmits part. The reflected waves can be traced by the resonator, their angle of reflection being equal to their angle of incidence. They can be received by one parabolic reflector, reflected to another and brought to a focus. They can be reflected so as to produce interference or loops and nodes, and the loops and nodes can be traced by the resonator. By a prism of asphalt they are refracted exactly like light.

From all this it is concluded that an additional proof is furnished of the identity of light and electro-magnetic waves, and a very strong experimental proof of Maxwell's theory of light is furnished.

Synonym--Hertz's Experiments.

470 STANDARD ELECTRICAL DICTIONARY.

Fig. 296. ELECTRICAL RESONATOR.

Resonator, Electric. A small open electric circuit, with ends nearly touching. When exposed to electric resonance, or to a sympathetic electric oscillatory discharge, a spark passes from across the gap. The production of this spark is altogether a matter of the inductance of the resonator. The simplest form is a circle of copper wire with its ends nearly touching. The length of the gap is adjustable by bending. A screw adjustment may also be provided. Another form is shown in the cut, Fig. 296. Here sheets of tinfoil are used to regulate the electrostatic capacity, while at m is shown the finger piece for regulating the size of the spark gap a.

Synonym--Spark Micrometer.

Resultant. The line indicating the result of the application of two or more forces to a point. Its direction and length give the elements of direction and intensity. (See Forces, Resolution of Forces, Composition of Components.)

Resultant Polarity. The magnetic polarity imparted to a mass of iron acted on by two or more separate inducing forces or currents. It appears in dynamos and motors. The final polarity is the resultant of the inducing effect of the field magnet poles and of the windings.

Retardation. In telegraphy a retardation of the rate of transmission of signals. It is due to several causes.

(a) The self-induction of the circuit, especially if it includes many electro-magnets, produces extra currents (see Currents, Extra.) These are opposed to the main current on closing it and hence retard the action. They are in the same direction on opening it and hence again retard the action.

(b) Every line has a certain static capacity. This is affected by the proximity of the lines to the earth. For each signal electricity has to be charged upon the line until the line is charged to its end with a certain proportion of the initial density. This charging takes time and hence introduces retardation.

(c) The cores of the electro-magnets of the relays or sounders are not instantly magnetized and demagnetized. This magnetic lag, q. v., introduces retardation.

471 STANDARD ELECTRICAL DICTIONARY.

Retardation of Phase. The fractional lagging behind of waves or alternating currents; by lagging behind a portion of a wave length the corresponding phases, as of full amplitude, are kept back or retarded. The phase of current intensity may be retarded with reference to the electro-motive force by the introduction of transformers of high capacity with high resistance on open secondary circuits.

[Transcriber's note: Capacitors are used to correct current phase lag.]

Retentivity. Coercitive or coercive force; by virtue of which steel retains its magnetism. It is the more modern name, "coercive force" as a term being rejected by many.

Synonyms--Coercive Force--Coercitive Force.

Retort Carbon. Carbon deposited in coal gas retorts from decomposition of the hydrocarbons. It is a very hard, pure form, and is of graphitic modification. Owing to its great hardness it is little used for electrical purposes, the molded carbons being easier to make. The deposition occurs in the regular gas-making process, and is a disadvantage to the working.

Return. A line or conductor which is supposed to carry current back to its starting point, after it has traversed a line. It may be a wire or the grounding of the ends of a line [or] may make the earth act as a return, termed ground- or earth-return. The best distinction of a return is to so term the portion of a circuit on which no apparatus is placed.

Reversibility. The principal in virtue of which a device for producing a given form of energy can absorb the same and do work. The reversibility of the dynamo is its quality in virtue of which it can act as a current generator, thereby converting mechanical energy into electric energy, or if a current is passed through it, it rotates, doing work, and thereby converting electric energy into mechanical energy. The knowledge of this principle can be traced back to Jacobi in 1850.

Reversible Bridge. A form of Wheatstone's Bridge adapted for reversal of the positions or interchange of the proportionate arms, v., so that the accuracy of the coils can be tested.

Rheochord. An apparatus by means of which variable quantities of wire are thrown into the circuit; a rheostat using wire. (See Rheostat, Wheatstone's.)

Rheometer. A galvanometer. (Obsolete.)

472 STANDARD ELECTRICAL DICTIONARY.

Rheomotor. A source of current; a current generator; a producer of potential difference. (Obsolete.)

Rheophore. The portion of an active circuit capable of deflecting a magnetic needle. This properly includes all of the metallic conductor of a circuit. (Obsolete.)

Rheoscope. A galvanoscope; an instrument for qualitatively detecting potential difference, fall or rise. (See Galvanoscope.)

Rheostat. An adjustable resistance; an apparatus for changing the resistance without opening the circuit. Its action may depend on the introduction of variable lengths of mercury column, of some other liquid, or of wire into a circuit. (See Rheostat, Wheatstone's.)

Rheostat Arm. The third arm of known resistance in a Wheatstone bridge. (See Proportionate Arms.)

Rheostatic Machine. An apparatus for increasing potential difference. It consists of a number of static condensers. They are charged in multiple arc or in parallel, and are discharged in series. Secondary batteries may be used for the charging; thus a static effect is produced from a galvanic battery.

Rheostat, Wheatstone's. This apparatus consists of two cylinders, one, A, made of brass, the other, B, of wood, with a spiral groove. At its end is a copper ring a. A fine brass wire has one end attached to this ring. Its other end is fastened at e, and it is wound as shown; n and o are binding screws connected, one with the cylinder-ring a, the other with the brass cylinder, A. The current entering at o, traverses the wire on B, as there the windings are insulated by the grooves, thence it passes to m and by A, whose metal short circuits all the wire on it, to the binding-post n. The handle, d, is turned one way or the other to regulate the length of the wire through which the current must pass. On each cylinder there is a square head, one of which is shown at c, so that the handle can be shifted from one to the other as required; to A if the wire is to be wound on that cylinder, to B if the reverse is desired.

Fig. 297. WHEATSTONE'S RHEOSTAT.

473 STANDARD ELECTRICAL DICTIONARY.

Rheotome. An automatic circuit breaker, one which rapidly opens and closes a circuit, as in the case of the primary of an induction coil an interrupter. (Obsolete.)

Rheotrope. A pole changer, current reverser, or commutator, g., such as the commutator of an induction coil. (Obsolete.)

Rhigolene. A petroleum product; a hydrocarbon of low boiling point. Its vapor is used in flashing (q. v.) carbon filaments for incandescent lamps.

Rhumbs. In a mariners' compass, the thirty-two points, designated, north, north by east, north north east, etc. (See Compass Mariner's-Compass, Points of the.)

Rhumkorff Coil. The induction coil, q. v.

Rigidity, Molecular. The tendency of molecules to resist rotation or change of position; the assumed cause of magnetic coercive force, or retentivity.

Ring Contact. A contact formed by a terminal clip in the shape of a ring, split or cut at one point so that its ends tend to spring together. The other terminal is a bar which passes into the cut and is tightly pressed by the elastic ring.

Fig. 298. SWITCH WITH RING CONTACTS.

474 STANDARD ELECTRICAL DICTIONARY.

Ring, Faraday. A closed ring of iron used as the core of a transformer or induction coil. The term is derived from Faraday's classic experiment with such an apparatus when he produced a spark by induction in a secondary circuit.

Roaring. A term applied to the noise sometimes produced in a voltaic arc, when the electrodes are close together and a heavy current is passing.

Rocker. In a dynamo the movable piece, mounted concentrically with the commutator, and carrying the rocker-arms and brush-holders. By moving it the brushes are adjusted for proper lead.

Rocker Arms. The arms projecting from a rocker and each carrying one of the brush-holders.

Roget's Spiral. An experimental apparatus for illustrating the mutual attraction of currents going in like direction. A cylindrical helix or spiral of wire is suspended by one end. Its lower end just dips into a mercury cup. An active circuit is connected, one terminal to the upper end, the other terminal to the mercury cup, bringing the apparatus in series into the circuit. The current as it passes causes the coil to shorten, each spiral attracting its neighbors. This breaks the circuit by drawing the lower end out of the mercury cup. The current being cut off the coils cease to attract each other, and the end dips into the mercury cup again. This closes the circuit, the coils again attract each other and the same sequence follows and is repeated over and over again. A bright spark is produced at each break of the mercury contact.

Rotation of Liquids, Electro-dynamic. By passing a current through a liquid, such as dilute sulphuric acid, it rotates if exposed to the induction of a current flowing at right angles to it. The condition resolves itself into a liquid traversed by horizontal currents from centre to circumference or vice versa, rotated by a current passing through a circular conductor below it.

475 STANDARD ELECTRICAL DICTIONARY.

Rotation of Liquids, Electro-magnetic. The rotation produced in a liquid carrying centripetal or centrifugal currents by an electromagnet. It is practically an intensification of electro-dynamic rotation. (See Rotation of Liquids, Electro-dynamic.)

Rubber. In a frictional electric machine the cushion of leather which is pressed against the plate as it rotates.

S. (a) Symbol for second.

(b) Symbol for space, or length; L is preferable.

(c) Symbol for south-seeking pole of a magnet.

Saddle Bracket. A bracket carried on the top of telegraph poles, carrying an insulator for the upper wire.

Safety Device. (a) A device to prevent overheating of any portion of a circuit by excess of current. It generally consists of a slip of fusible metal which if the current attains too much strength melts and opens the circuit. To ensure its breaking a weight is sometimes suspended from the strip. In one form an insulated German silver wire is wrapped around the end of the fusible strip a number of times and its end is connected to it. The other end of the German silver wire connects with the main lead, so that all the current goes through both in series. If the German silver wire becomes heated from excess of current the coil wrapped tightly around the end of the fusible strip melts it and opens the circuit.

(b) Lightning arresters, q. v., may be cited under this heading.

Synonyms--Automatic Cut Out--Safety Fuse, Plug, or Strip.

Fig. 299. COCKBURN SAFETY FUSE.

Safety Fuse. A strip of metal inserted so as to form part of a circuit and of such size that a smaller current [than] would heat the regular wire of the circuit dangerously, so as to cause a conflagration for instance, would melt the fuse and open the circuit. As it sometimes happens that a safety fuse melts without parting a weight is sometimes hung upon it, so as to break it as it softens.

Salt. A salt is a chemical compound containing two atoms of two radicals,. which saturate each other. One atom or radical is electro-positive referred to the other, which is electro-negative. By electrolysis salts are decomposed, the atoms or radicals separating and uniting to form new molecules.

476 STANDARD ELECTRICAL DICTIONARY.

Saturated. adj. A liquid is saturated with a substance when it has dissolved all that it can, while an excess is present in the liquid. It is possible, by dissolving some salts in hot water and allowing the solution to cool without access of air, to obtain a supersaturated solution. On introduction of a crystal of the salt, or often on mere access of air, the solution forms crystals and the liquid left is saturated.

Saw, Electric. A platinum coated steel wire mounted and connected to be raised to incandescence for cutting purposes.

Schweigger's Multiplier. An old term for the galvanometer as invented by Schweigger soon after Oerstedt's discovery.

Scratch Brushes. Brushes for cleaning the surface of articles to be electroplated to give a good metallic surface suitable for deposition. They have often wire instead of bristles.

477 STANDARD ELECTRICAL DICTIONARY.

Fig. 300. WIRE GAUZE ELECTRIC SCREEN.

Screen, Electric. A large plate or a hollow case or cage of conducting material connected with the earth, and used to protect any body placed within it from electrostatic influences.

If within a hollow conducting sphere an electrified body is placed, the inner surface of the sphere will be charged with electricity of opposite kind to that of the sphere, and the outer surface with the same kind as that of the sphere. Thus the sum of the electricities called into action by induction is zero. The two inner charges are bound to each other. The induced charge on the outer surface of the sphere is all that has any effect on objects in the outer air.

If the outer surface is connected to the earth it becomes discharged, and however highly electrified the body introduced into the sphere and the inner surface of such sphere may be, they produce no external effects, as they are bound one to the other.

If the sphere is connected to the earth and an unelectrified object is placed within it, such object will be perfectly shielded from the effects of an outer electrostatic field. Perforated tinfoil or wire gauze has just as good a result. A large plate of metal connected to the earth has the same effect. The screen whether plane or hollow simply retains a bound charge due to the field of force, thereby neutralizing it, and the electricity of the opposite sign escapes to the earth. Thus a true shielding or screening effect is produced.

In the cut an experiment is shown in which an electric screen is carried by a Leyden jar. Pith balls are suspended outside and inside of it. By the approach of an electrified body the outer pith balls will diverge, while no effect is produced upon the inner ones.

Secondary Actions. In electrolysis the direct products of the electrical decomposition are not always obtained at the electrodes, but products due to their reaction on the water and other chemicals may appear. These constitute secondary actions. Thus if a solution of copper sulphate is electrolyzed with platinum electrodes, metallic copper appears at one pole and sulphuric acid and oxygen gas at the other. But the products of electrolysis by the current are copper (Cu) and sulphion (SO4). The latter reacting on water sets free oxygen gas and forms sulphuric acid. The latter is a secondary action.

Secondary Generator. (a) An alternating current converter generating a so-called secondary current.

(b) A secondary battery, q. v., may be thus termed.

Secondary, Movable. The term movable secondaries has been applied to rings, spheres and discs of conducting material, such as copper, whose behavior when near the pole of an electro-magnet traversed by an alternating current, have been studied by Elihu Thomson. Such masses are subjected to very peculiar movements and mutual reactions. As the phenomena are due to induced currents the above term has been applied to the masses in which the currents are induced.

478 STANDARD ELECTRICAL DICTIONARY.

Secondary Plates, Colors of. In a secondary battery of the lead plate type, the color of the plates is a good indication of the condition of the battery. The negative plate should be brown or deep-reddish, the other should be slate-colored.

Secondary Poles. Poles sometimes found in magnets existing in positions intermediate between the end or true poles.

Synonym--Consequent Poles.

Seebeck Effect. The production of a current by heating the junction of two different metals forming part of a circuit, or the thermo-electric production of current, is stated as the Seebeck effect, having been discovered by that investigator.

Selenium. A non-metallic element. It is interesting electrically on account of the changes its electric resistance undergoes when it is subjected to light.

In one set of experiments it was found that diffused light caused the resistance to fall in the ratio of 11 to 9. Full sunlight reduced it to one-half. Of the spectrum colors red was most powerful and the ultra red region still more strongly affected its resistance.

The effect produced by exposure to light is instantaneous, but on removal to the dark only slowly disappears.

A vessel of hot water was found to have no effect, showing that short ether waves are essential to the effect.

Selenium Cell. A selenium resistance box. Vitreous selenium is made by keeping ordinary selenium for some hours at a temperature of about 220º C. (428º F.) after fusing. It is placed in an electric circuit as part of the conductor.

Its resistance can then be determined. It decreases in sunlight to about one-half its resistance in the dark.

The selenium cell is used in the Photophone, q. v. Otherwise it is little more than a subject of experiment.

Selenium Eye. A model eye in which selenium in circuit with a battery and galvanometer takes the place of the retina of the human eye.

Self-repulsion. When a body is electrified each molecule repels its neighbor and the condition in question is thus designated. An electrified soap-bubble expands in virtue of self-repulsion.

Semi-conductors. Substances which conduct static electricity poorly, but quite appreciably and beyond the extent of leakage. The following are examples: Alcohol and ether, powdered glass, flowers of sulphur, dry wood, paper, ice at 0º C. (32º F.)

479 STANDARD ELECTRICAL DICTIONARY.

Sensibility. The measure of the effect of a current upon a galvanometer, or any similar case.

Sensitiveness, Angle of Maximum. Every galvanometer has its angle of maximum sensitiveness, which is the angle of deflection at which a small increment of current will produce the greatest deflection. For every tangent galvanometer 45° is the angle in question. In using a galvanometer for direct reading methods it is an object to have it work at its angle of maximum sensitiveness.

Separately Excited Dynamo. A dynamo-electric machine whose field magnet is excited from an outside source, which may be another dynamo or a battery. Alternating current dynamos are often of this description.

Separate Touch. In magnetism a method of inducing magnetism in a steel bar. The opposite poles of two magnets are applied at the center of the bar to be magnetized, but without touching each other, and are drawn apart to its ends. They are returned through the air and the process is repeated a number of times and on both sides of the bar if necessary.

Separation of Electricities. Under the double fluid theory of electricity the action of electrification in accumulating positive electricity in one conductor and negative on the other of the excited surfaces of two conductors.

Separator. India rubber bands or other forms used in batteries to keep the plates from touching in the cell; especially applied to secondary batteries, where the plates are so near together as to require separators to prevent short circuiting.

Fig. 301. SERIES CONNECTION.

Series. (a) Arranged in succession as opposed to parallel. Thus if a set of battery jars are arranged with the zinc of one connected to the carbon of the next one for the entire number, it is said to be arranged in series. When incandescent lamps are arranged in succession so that the current goes through one after the other they are arranged in series.

The opposite of parallel, q. v., or multiple arc, q. v.; it may be used as a noun or as an adjective.

(b) See Electro-Chemical Series;

(c) Thermo-Electric Series

(d) Electrostatic Series;

(e) Electro-motive Series.

Synonym--Cascade Connection (but little used.)

480 STANDARD ELECTRICAL DICTIONARY.

Series-multiple. Arrangement of electric apparatus, in which the parts are grouped in sets in parallel and these sets are connected in series. It is used as a noun, as "arranged in series-multiple," or as an adjective, as "a series-multiple circuit or system."

Fig. 302. SERIES-MULTIPLE CONNECTION.

Service Conductors. In electric distribution the equivalents of service pipes in the distribution of gas; wires leading from the street mains to the houses, where current is to be supplied.

Serving. The wrapping or winding of a cable composed of small size wire, laid closely and smoothly with a tool called a serving mallet, or serving block, or by machinery. It serves to protect the cable from wear.

Shackle. In telegraph lines a swinging insulator bracket for use where wires make an angle with the pole. A journal box is attached to the pole, like half of a gate hinge. To this a short iron arm is pivoted so as to be free to swing through a considerable angle. At its end an insulator is carried to which the wire is attached. The shackle swings into line with the wire, or takes a position for two wires corresponding to the resultant of their directions of pull.

Fig. 303. DOUBLE SHACKLE

Shadow. Electric. A term applied to a phenomenon of high vacua. If an electric discharge is maintained in a Crookes' tube the glass opposite the negative electrode tends to phosphoresce. A plate of aluminum, used also as the positive electrode, protects the glass directly behind it so as to produce the effect of a shadow.

Synonym--Molecular Shadow.

[Transcriber's note: The effect is due to the "shadowing" of the electrons streaming past the plate.]

481 STANDARD ELECTRICAL DICTIONARY.

Sheath for Magnet Coils. In 1867 C. E. Varley proposed the use of a copper sheath surrounding a magnet core to diminish self-induction. It has since been used by Brush and others. Sometimes metallic foil is laid between the successive coils of wire.

Synonym--Mutual Induction Protector.

Sheath for Transformers. A protective sheath of copper, interposed between the primary and secondary circuits of an alternating current transformer. It is connected to the earth. If the primary coil loses its insulation before it can leak to the secondary it is grounded. This protects the secondary circuit from the high electro-motive force of the primary circuit.

Shellac. A resin; produced as an exudation upon the branches of certain Asiatic trees, such as the banyan (Ficus religiosa). It is due to punctures in the bark of the trees in question, which punctures are made by the female of the insect coccus ficus or c. lacca.

Commercial shellac contains about 90 per cent. of resinous material, the rest is made up of wax, gluten, coloring matter and other substances.

Shellac is soluble in alcohol, and in aqueous solutions of ammonium chloride, of borax and in strong ammonia solution. Long standing is required in the case of the last named solvent. Dilute hydrochloric and acetic acids dissolve it readily; nitric acid slowly; strong sulphuric acid is without action on it. Alkalies dissolve it.

In electric work it is used as an insulator and dielectric. Its alcoholic solution is used to varnish glass plates of influence machines, for the coils of induction coils and similar purposes.

Resistance in ohms per centimeter cube at 28° C. (82.4 F.)--(Ayrton), 9.0E15

Specific Inductive Capacity (Wüllner), 2.95 to 3.73

The same substance in less pure forms occurs in commerce, as stick lac, lump lac, seed lac, button lac.

Shellac Varnish. Solution of shellac in alcohol; methylic alcohol (wood alcohol or wood naphtha) is often used as solvent.

Dr. Muirhead recommends button lac, dissolved in absolute alcohol, and the top layers decanted. For highest insulation he dissolves the lac in ordinary alcohol, precipitates by dropping into water, collects the precipitate, dries and dissolves in absolute alcohol.

Shielded. adj. An electric measuring instrument of the galvanometer type is shielded when it is so constructed that its indications are not seriously affected by the presence of neighboring magnets or by fields of force. Shielding can be effected by using a very strong permanent magnet to produce a field within which the magnetic needle moves and which reacts upon it, or by enclosing the instrument in a thick iron box.

482 STANDARD ELECTRICAL DICTIONARY.

S. H. M. Symbol or abbreviation for "simple harmonic motion."

Shock, Break. A term in electro-therapeutics; the shock received when an electric circuit, including the patient in series, is broken or opened.

Synonym--Opening Shock.

Shock, Electric. The effect upon the animal system of the discharge through it of electricity with high potential difference. Pain, nervous shock, violent muscular contortions accompany it. Of currents, an alternating current is reputed worse than a direct current; intermediate is the pulsatory current.

The voltage is the main element of shock, amperage has also some direct influence.

Shock, Static. A term in electro-therapeutics. The application of static discharges from small condensers or Leyden jars to a patient who is insulated from the ground with one electrode applied to the conducting surface on which he rests, while the other, a spherical electrode, is brought near the body so as to produce a disruptive or spark discharge.

Short Circuit. A connection between two parts of a circuit, which connection is of low resistance compared to the intercepted portion. The term is used also as a verb, as "to short circuit a lamp."

Fig. 304. DIAGRAM ILLUSTRATING SHORT CIRCUIT WORKING.

Short Circuit Working. A method of working intermittently an electro-magnet so as to avoid sparking. It consists in providing a short circuit in parallel with the magnetic coils. This short circuit is of very low resistance. To throw the magnet into action the short circuit is opened; to throw it out of action the short circuit is closed. The shunt or short circuit must be of negligibly small resistance and inductance.

483 STANDARD ELECTRICAL DICTIONARY.

Shovel Electrodes. Large plate electrodes used in a medical bipolar bath. (See Bath, Bipolar.)

Shunt. In a current circuit a connection in parallel with a portion of the circuit. Thus in a dynamo a special winding for the field may have its ends connected to the bushes, from which the regular external circuit also starts. The field is then wound in shunt with the armature. In the case of a galvanometer a resistance coil may be put in parallel with it to prevent too much current going through the galvanometer; this connection is a shunt.

The word is used as a noun, as "a shunt," or "a connection or apparatus in shunt with another," and as an adjective, as "a shunt connection," or as a verb, as "to shunt a battery."

Shunt Box. A resistance box designed for use as a galvanometer shunt. (See Shunt, Galvanometer.) The box contains a series of resistance coils which can be plugged in or out as required.

Shunt, Electro-magnetic. In telegraphy a shunt for the receiving relay consisting of the coils of an electro-magnet. It is placed in parallel with the relay. Its poles are permanently connected by an armature. Thus it has high self-induction.

On opening and closing the circuit by the sending key, extra currents are produced in the shunt. The connections are so arranged that on making the circuit the extra current goes through the relay in the same direction as the principal current, while on breaking the circuit the induced current goes in the opposite direction.

Thus the extra currents accelerate the production and also the cessation of signalling currents, tending to facilitate the operations of sending despatches.

Shunt, Galvanometer. A resistance placed in parallel with a galvanometer, so as to short circuit its coils and prevent enough current passing through it to injure it. By knowing the resistance of the shunt and of the galvanometer coils, the proportion of current affecting the galvanometer is known. This gives the requisite factor for calculation. (See Multiplying Power of Shunt.)

Shunt Ratio. The coefficient expressing the ratio existing between the current in a shunt and in the apparatus or conductor in parallel with it. (See Multiplying Power of/ Shunt.)

Shunt Winding. A dynamo or motor is shunt-wound when the field magnet winding is in shunt or in parallel with the winding of the armature.

Shuttle Current. A current alternating in direction; an alternating current.

484 STANDARD ELECTRICAL DICTIONARY.

Side-Flash. A bright flashing lateral discharge from a conductor conveying a current due to a static discharge.

Sighted Position. In an absolute electrometer (see Electrometer, Absolute) the position of the balanced arm carrying the movable disc or plate, when the disc and guard plate are in one plane. The cross-hair on the lever-end is then seen midway between two stops, or some other equivalent position is reached which is discerned by sighting through a magnifying glass or telescope.

Silver. A metal; one of the elements; symbol Ag.; atomic weight, 108; valency, 1; equivalent, 108; specific gravity, 10.5. It is a conductor of electricity. Relative resistance, annealed, 1.0 Specific Resistance, annealed, at 0° C. (32° F.) 1.504 microhms. Resistance of a wire at 0° C. (32° F.), Annealed. Hard Drawn. (a) 1 foot long, weighing 1 grain, .2190 ohms .2389 ohms. (b) 1 foot long, 1/1000 inch thick, 9.048 " 9.826 " (c) 1 meter long, weighing 1 gram, .1527 " .1662 " (d) 1 meter long, 1 millimeter thick, .01916 " .02080 "

Resistance annealed of a 1-inch cube, at 0° C. (32°F.) .5921 microhms.

Percentage increase in resistance per degree C. (1.8 F.) at about 20° C. (68° F.), annealed, 0.377 per cent.

Electro-chemical equivalent, (Hydrogen = .0105) .1134 mgs.

Silver Bath. A solution of a salt of silver for deposition in the electroplating process.

The following is a typical formula: Water, 10.0 parts by weight. Potassium Cyanide, 5 " " Metallic Silver, 2.5 " "

The silver is first dissolved as nitrate and converted into cyanide and added in that form, or for 2.5 parts metallic silver we may read: Silver cyanide, 3 parts by weight.

While many other formulas have been published the above is representative of the majority. Other solvents for the silver than potassium cyanide have been suggested, such as sodium hyposulphite, but the cyanide solution remains the standard.

Silver Stripping Bath. Various baths are used to remove silver from old electroplated articles. Their composition depends upon the base on which the metal is deposited. Silvered iron articles are placed as anodes in a solution of 1 part potassium cyanide in 20 parts of water. As kathode a silver anode or a copper one lightly oiled may be used. From the latter the silver easily rubs off. For copper articles a mixture of fuming sulphuric acid and nitric acid (40º Beaumé) may be used. The presence of any water in this mixture will bring about the solution of the copper. Or fuming sulphuric acid may be heated to between 300º and 400º F., some pinches of dry pulverized potassium nitrate may be thrown in and the articles at once dipped. These methods effect the solution of the silver, leaving the copper unattacked.

485 STANDARD ELECTRICAL DICTIONARY.

Simple Substitution. A method of obtaining a resistance equal to that of a standard. The standard is put in circuit with a galvanometer and the deflection is noted. For the standard another wire is substituted and its length altered until the same deflection is produced. The two resistances are then evidently identical. The standard can be again substituted to confirm the result.

Sine Curve. If we imagine a point moved back and forth synchronously with a pendulum, and if such point made a mark upon paper, it would trace the same line over and over again. If now the paper were drawn steadily along at right angles to the line of motion of the point, then the point would trace upon it a line like the profile of a wave. Such line is a sine curve. It derives its name from the following construction. Let a straight line be drawn, and laid off in fractions, such as degrees, of the perimeter of a circle of given diameter. Then on each division of the line let a perpendicular be erected equal in height to the sine of the angle of the circle corresponding to that division; then if the extremities of such lines be united by a curve such curve will be a sine curve.

In such a curve the abscissas are proportional to the times, while the ordinates are proportional to the sines of angles, which angles are themselves proportional to the times. The ordinates pass through positive and negative values alternately, while the abscissas are always positive.

Any number of sine curves can be constructed by varying the diameter of the original circle, or by giving to the abscissas a value which is a multiple of the true length of the divisions of circle. If the pendulum method of construction were used this would be attained by giving a greater or less velocity to the paper as drawn under the pendulum.

A species of equation for the curve is given as follows: y = sin( x )

In this x really indicates the arc whose length is x, and reference should be made to the value of the radius of the circle from which the curve is described. It will also be noticed that the equation only covers the case in which the true divisions of the circle are laid off on the line. If a multiple of such divisions are used, say n times, or 1-n times, then the equation should read y = n sin( x ) or y = sin( x ) / n

Synonyms--Curve of Sines--Sinusoidal Curve--Harmonic Curve.

486 STANDARD ELECTRICAL DICTIONARY.

Sine Law. The force acting on a body is directly proportional to the sine of the angle of deflection when--

I. The controlling force is constant in magnitude and direction; and

II. The deflecting force, although variable in its direction in space, is fixed in direction relatively to the deflecting body.

Single Fluid Theory. A theory of electricity. Electricity, as has been said, being conveniently treated as a fluid or fluids, the single fluid theory attributes electrical phenomena to the presence or absence of a single fluid. The fluid repels itself but attracts matter; an excess creates positive, a deficiency, negative electrification; friction, contact action or other generating cause altering the distribution creates potential difference or electrification. The assumed direction (see Direction) of the current and of lines of force are based on the single fluid theory. Like the double fluid theory, q. v., it is merely a convenience and not the expression of a truth. (See Fluid, Electric, and Double Fluid Theory.)

Synonym--Franklin's Theory.

Single Fluid Voltaic Cell. A galvanic couple using only a single fluid, such as the Smee or Volta cell.

Simple Harmonic Motion. Motion of a point or body back and forth along a line; the motion of a pendulum, as regards its successive swings back and forth, is an example of harmonic motion.

Sinistrotorsal. adj. The reverse of dextrotorsal, q. v. A helix with left-handed winding, the reverse of an ordinary screw, such as a wood-screw or corkscrew.

Skin Effect. A current of very brief duration does not penetrate the mass of a conductor. Alternating currents for this reason are mainly conducted by the outer layers of a conductor. The above is sometimes called the skin effect.

Sled. A contact for electric cars of the conduit system. It is identical with the plow, q.v., but is drawn after the cars instead of being pushed along with them.

Slide Meter Bridge. A name for a Slide Bridge one meter long. There are also slide half meter and slide quarter meter bridges and others. (See Meter Bridge.)

S. N. Code. Abbreviation for single needle code, the telegraphic alphabet used with the single needle system.

Soaking-in-and-out. A term for the phenomena of the residual electrostatic charge; the gradual acquirement or loss by a condenser of a portion of its electrostatic charge.

487 STANDARD ELECTRICAL DICTIONARY.

Soldering, Electric. (a) Soldering in which the solder is melted by means of electricity; either current incandescence or the voltaic arc may be used. It is identical in general with electric welding. (See Welding, Electric.)

(b) The deposition by electric plating of a metal over the ends of two conductors held in contact. This secures them as if by soldering. It is used in connecting the carbon filament of an incandescent lamp with the platinum wires that pass through the glass. Copper is the metal usually deposited.

Solenoid. The ideal solenoid is a system of circular currents of uniform direction, equal, parallel, of equal diameter of circle, and with their centers lying on the same straight line, which line is perpendicular to their planes.

Fig. 305. EXPERIMENTAL SOLENOID.

The simple solenoid as constructed of wire, is a helical coil, of uniform diameter, so as to represent a cylinder. After completing the coil one end of the wire is bent back and carried through the centre of the coil, bringing thus both ends out at the same end. The object of doing this is to cause this straight return member to neutralize the longitudinal component of the helical turns. This it does approximately so as to cause the solenoid for its practical action to correspond with the ideal solenoid.

Instead of carrying one end of the wire through the centre of the coil as just described, both ends may be bent back and brought together at the centre.

A solenoid should always have this neutralization of the longitudinal component of the helices provided for; otherwise it is not a true solenoid.

Solenoids are used in experiments to represent magnets and to study and illustrate their laws. When a current goes through them they acquire polarity, attract iron, develop lines of force and act in general like magnets.

A solenoid is also defined as a coil of insulated wire whose length is not small as compared with its diameter.

488 STANDARD ELECTRICAL DICTIONARY.

Sonometer, Hughes'. A sound measurer; a modification of a portion of Hughes' induction balance, used for testing the delicacy of the ear or for determining the relative intensity of sounds. (See Hughes' Induction Balance.) It is the arrangement of three coils, two mounted one at each of the ends of a graduated bar, and the third one between them and free to slide back and forth thereon.

Sonorescence. The property of producing sounds under the influence of momentary light radiations rapidly succeeding each other. It is the property utilized in the photophone, q. v.

Fig. 306. MORSE SOUNDER.

Sounder. In telegraphy an instrument consisting of an electromagnet with armature attached to an oscillating bar, the range of whose movements is restricted by adjusting screws. The armature is drawn away from the magnet by a spring. When a current is sent through the magnet the armature is drawn towards the poles and produces a sound as the bar strikes a striking piece or second adjusting screw. When the current ceases the bar and armature are drawn back, striking the first mentioned screw with a distinct sound, the back stroke.

The sounder is used to receive Morse and analogous character messages. The forward strokes correspond to the beginnings of the dots or dashes of the code, the back strokes to beginnings of the intervals. The distinction between dots and dashes is made by observing the interval between forward and back stroke.

Various devices are used to increase the sound. Sometimes a resonance box is used on which the sounder is mounted.

In practice sounders are generally placed on local circuits and are actuated by relays.

489 STANDARD ELECTRICAL DICTIONARY.

Sound Reading. The art or method of receiving telegraph messages by ear. It is now universally used by all expert Morse operators. It can only be applied to telegraph systems producing audible sounds; in some cases, as in needle telegraphy, it may be quite inapplicable.

Space, Clearance. The space between faces of the pole pieces and the surface of the armature in a dynamo. It is really the air gap, but in calculating dynamo dimensions the thickness of the insulated copper wire windings of the commutator are counted in as part of the air gap, because copper is almost the same as air in impermeability. Clearance space is a mechanical factor; the air gap is an electric or magnetic factor.

Synonym--Inter-air Space.

Space, Crookes' Dark. In an exhausted tube, through which an electric discharge is caused to pass, the space surrounding the negative electrode of the tube. This space is free from any luminous effect, and by contrast with the light of the discharge appears dark. The vacuum may be made so high that the dark space fills the whole space between the electrodes. It is less for a less vacuum and varies for other factors, such as the temperature of the negative electrode from which it originates, the kind of residual gas present, and the quality of the spark.

Space, Faraday's Dark. The space in an exhausted tube between the luminous glows about the two electrodes.

Space, Interferric. A term for the air-gap in a magnetic circuit. It is etymologically more correct than air-gap, for the latter is often two-thirds or more filled with the insulating material and copper wire of the armature windings. (See Space, Clearance.)

Spark Arrester. A screen of wire netting fitting around the carbons of an arc lamp above the globe to prevent the escape of sparks from the carbons.

Spark Coil. A coil for producing a spark from a source of comparatively low electro-motive force. It consists of insulated wire wound round a core of soft iron, best a bundle of short pieces of wire. Such a coil may be eight inches long and three inches thick, and made of No. 18-20 copper wire, with a core one inch in diameter. On connecting a battery therewith and opening or closing the circuit, a spark is produced by self-induction, q. v. It is used for lighting gas.

490 STANDARD ELECTRICAL DICTIONARY.

Spark, Duration of Electric. Wheatstone determined the duration of the spark given by a Leyden jar as 1/24000 second. Feddersen by interposing a tube of water 9 millimeters (.36 inch) long in its path found that it lasted 14/10000 second, and with one 180 millimeters (7.2 inches) long, 188/10000 second. Lucas and Cazin for a 5 millimeter (.2 inch) spark, with different numbers of Leyden jars, found the following: Number of jars. Duration of Spark. 2 .000026 second 4 .000041 " 6 .000045 " 8 .000047 "

The duration increases with the striking distance, and is independent of the diameter of the balls between which it is produced.

Spark Gap. The space left between the ends of an electric resonator (see Resonator, Electric) across which the spark springs. Its size may be adjustable by a screw, something like the arrangement of screw calipers.

Sparking. In dynamo-electric machines, the production of sparks at the commutator between the brushes and commutator sections. The sparks are often true voltaic arcs, and in all cases are injurious if in any quantity, wearing out the commutator and brushes.

Sparking, Line or Points of Least. In a dynamo or electric motor the diameter of the commutator determining, or the points on the commutator marking the position of the brushes where the sparking is a minimum. Field magnets powerful in proportion to the armature are a preventative cause. The direction of the line fixes the angle of lead to be given to the brushes.

Sparking, Resistance to. The resistance to disruptive discharge through its substance offered by a dielectric or insulator. It does not depend on its insulating qualities, but on its rigidity and strength.

Spark, Length of. The length of the spark accompanying the disruptive discharge is counted as the distance from one electrode to the other in a straight line. It is longer for an increased potential difference between the two electrodes. If the gas or air between the electrodes is exhausted the length increases, until the vacuum becomes too high, when the length begins to decrease, and for a perfect vacuum no spark however small can be produced. The shape of the conductor which is discharged, the material of the electrodes, and the direction of the current are all factors affecting the length of spark producible.

491 STANDARD ELECTRICAL DICTIONARY.

Spark Tube. A tube used as a gauge or test to determine when the exhaustion of the vacuum chamber or bulb of an incandescent lamp is sufficiently high.

The interior of the tube is connected with the interior of the bulb or chamber of the lamps in process of exhaustion, and hence shares their degree of exhaustion. From time to time connections with an induction coil are made. When the exhaustion is carried far enough no discharge will take place through the vacuum. As long as the tube acts like a Geissler tube the exhaustion is not considered perfect.

Specific Heat of Electricity. The heat absorbed or given out by a fluid in passing from one temperature to another depends on its specific heat. In the Peltier and the Thomson effects. q. v., the electric current acts as the producer of a change of temperature, either an increase or decrease as the case may be. This suggests an absorption of and giving out of heat which amount of heat corresponding to a current of known amount is determinable, and may be referred to any unit of quantity such as the coulomb. This or some equivalent definite quantity of heat it has been proposed (Sir William Thomson) to term the Specific Heat of Electricity.

Spent Acid. Acid which has become exhausted. In a battery the acid becomes spent from combination with zinc. It also loses its depolarizing power, if it is a chromic acid solution or of that type, and then may be said to be spent.

Spent Liquor. The liquor of a plating bath which has become exhausted from use, the metal it contained being all or partly deposited.

Sphygmograph, Electric. An electric apparatus for recording the beat of the pulse, both as regards its rate and strength.

Sphygmophone. An apparatus for examination of the pulse by the microphone and telephone.

Spiders. Core-discs of a dynamo or motor armature are sometimes perforated with a large central aperture, are fastened together with insulated bolts, and the whole mass is secured to the shaft by three- or four-armed spiders. These are like rimless wheels, the ends of their arms being secured to the hollow cylinder constituting the armature core, and a central aperture in their hub receiving the shaft.

492 STANDARD ELECTRICAL DICTIONARY.

Spiral. This term is sometimes used instead of coil, as the primary spiral or secondary spiral of an induction coil or transformer.

Spiral Winding. The winding used on ring armatures. This may diagrammatically be represented by a spiral carried around the ring shaped core. With two field poles it gives two collecting points, positive and negative, with four field poles it gives four collecting points, alternately positive and negative.

Splice Box. A box in which the splices in underground cables and electric lines are contained. The splicing is generally done in the boxes with the cables in place. They may be two-way for straight lines, or be four-way for two side or lateral connections.

Spluttering. A term applied to a sound sometimes produced in a voltaic arc, perhaps caused by impure or insufficiently baked electrodes. (Elihu Thomson.)

Spring Control. Control of or giving the restitutive force to the needle of a galvanometer, core of a solenoid ammeter or moving part of any similar instrument by a spring. As an example see Ammeter, Ayrton's.

Fig. 307. SPRING JACKS.

Spring Jack. An arrangement for effecting, at one insertion of a species of plug, the opening or breaking of a circuit and for the simultaneous connection to the terminals formed by the breaking of two terminals of another system or loop. Thus let a line include in its circuit two springs pressing against each other, thereby completing the circuit. If a plug or wedge of insulating material were inserted between the springs so as to press them apart it would break the circuit and the whole would constitute a spring jack cut-out. If each side of the plug had a strip of brass or copper attached to it, and if the ends of another circuit were connected to these strips, then the insertion of the plug would throw the new line into the circuit of the other line.

493 STANDARD ELECTRICAL DICTIONARY.

Spring Jack Cut-out. A cut-out, of the general construction of a spring jack, q. v., except that a simple insulating plug or wedge is used in place of the metal-faced wedge with its connections of the regular spring jack. The insertion of an insulating wedge opens the circuit, which on its removal is closed. The regular spring jack wedge will operate in the same way, if its connections are kept open.

Spurious Voltage. The voltage in excess of that developed by a secondary battery which is required in the charging process. It is about .25 volt.

Square Wire. Wire whose cross-section is a square. It has been used of iron for building up the cores of armatures for dynamos or motors, for which it is peculiarly suitable, and also of copper as a winding for armatures.

Staggering. adj. When the brushes of a dynamo are set, one a little in advance of the other on the surface of the commutator, they are said to be set staggering. It is used to get over a break in the armature circuit.

State, Electrotonic. A term expressing an abandoned theory. Faraday at one time proposed the theory that a wire had to be in the electrotonic state to produce electro-motive force by movement through an electric field. Any such idea was ultimately abandoned by Faraday.

Static Breeze. The electric breeze obtained by the silent discharge of high tension electricity.

Static Electricity. Electricity at rest or not in the current form ordinarily speaking. The term is not very definite and at any rate only expresses a difference in degree, not in kind. The recognition of the difference in degree has now to a great extent also disappeared.

Station, Central. The building or place in which are placed electrical apparatus, steam engines and plant supplying a district with electric energy.

Station, Distant. The place at the further end of a telegraph line, as referred to the home station.

Station, Home. The end of a telegraph line where the operators using the expression are working.

494 STANDARD ELECTRICAL DICTIONARY.

Station, Transforming. In alternating current distribution, a building or place where a number of transformers are worked, so that low potential or secondary circuits are distributed therefrom.

Steel. A compound of iron with carbon. The carbon may range from a few hundredths of one per cent. up to two per cent. For magnets, tool steel drawn to a straw color or a little lower is good. All shaping and filing should be done before magnetization.

Steeling. The deposition of iron on copper plates by electrolysis. In electrotyping a thin deposit of iron is thus given the relief plates before printing from them. The deposit is very hard and exceedingly thin, so that it does not interfere with the perfection of the impression in the printing process. As the iron becomes worn it can be dissolved off with hydrochloric acid, which does not dissolve the copper, and a new deposit can be given it. Thus the plate may last for an indefinite number of impressions.

The iron bath may be prepared by immersing in a solution of ammonium chloride, two plates of iron, connected as anode and kathode in a circuit. One plate dissolves while hydrogen is given off from the other. The solution thus produced is used for a bath.

The hardness of the deposit, which is really pure iron, gives the name of "steeling."

Synonym--Acierage.

St. Elmo's Fire. Luminous static discharge effects sometimes seen on objects elevated in the air. They are especially noticed on ships' masts. The sailors term them corpusants (holy bodies). They resemble tongues or globes of fire.

Step-by-step Telegraphy. A system of telegraphy in which in the receiving instrument a hand is made to move step-by-step, with an escape movement around a dial. For each step there is a letter and the hand is made to stop at one or the other letter until the message is spelled out. (See Dial Telegraph.)

Step-down. adj. A qualification applied to a converter or transformer in the alternating current distribution, indicating that it lowers potential difference and increases current from the secondary.

Step-up. adj. The reverse of step-down; a qualification of a transformer or converter indicating that it raises the potential and decreases the current in the secondary.

Sticking. The adherence, after the current is cut off, of the armature to the poles of a magnet. In telegraphy it is a cause of annoyance and obstructs the working. It may, in telegraphy, be due to too weak a spring for drawing back the armature, or to imperfect breaking of the contact by the despatcher's key or by the receiver's relay.

495 STANDARD ELECTRICAL DICTIONARY.

Stopping Off. In electroplating the prevention of deposition of the plating metal on any desired portions of the object. It is effected by varnishing the places where no coating is desired. An article can be plated with silver, stopped off in any desired design, and the unvarnished portions may then be plated with gold in another bath. Various effects can be produced by such means.

Storage Capacity. A term for the ampere-hours of electricity, which can be taken in current form from a storage battery.

Storage of Electricity. Properly speaking electricity can only be stored statically or in static condensers, such as Leyden jars. The term has been popularly applied to the charging of secondary or storage batteries, in which there is really no such thing as a storage of electricity, but only a decomposition and opposite combination brought about, which leave the battery in a condition to give a current.

Storms, Electric. Wide-spread magnetic and electric disturbances, involving the disturbance of the magnetic elements and other similar phenomena. (See Magnetic Storms.)

Strain. The condition of a body when subjected to a stress. Various consequences may ensue from strain in the way of disturbance of electric and other qualities of the body strained.

Stratification Tube. A Geissler tube, q. v., for showing the stratification of the electric discharge through a high vacuum.

The stratifications are greatly intensified by the presence of a little vapor of turpentine, alcohol, bisulphide of carbon and other substances.

Stray Field. In a dynamo or motor the portion of the field whose lines of force are not cut by the armature windings.

Stray Power. The proportion of the energy wasted in driving a dynamo, lost through friction and other hurtful resistances.

Streamlets, Current. A conception bearing the same relation to an electric current that lines of force do to a field of force; elementary currents. If evenly distributed the current is of uniform density; if unevenly distributed, as in alternating currents, the current density varies in different parts of the cross section of the conductor. This evenness or unevenness may be referred to the number of streamlets per unit of area of cross-section.

[Transcriber's note: Streamlets per unit of area is redundant with current density.]

Stress. Force exercised upon a solid tending to distort it, or to produce a strain.

496 STANDARD ELECTRICAL DICTIONARY.

Stress, Dielectric. The condition of a dielectric when maintaining a charge; its two extremities are in opposite states of polarity, or are under permanent potential difference. As the two opposite polarities tend to unite a condition of stress is implied in the medium which separates them.

Stress, Electro-magnetic. The stress produced upon transparent substances in an electro-magnetic field of force. It is shown in the modified optical properties of glass and similar substances placed between the poles of a strong electro-magnet.

Stress, Electrostatic. The stress produced upon substances in an electrostatic field of force; the exact analogue of electro-magnetic stress, and affecting transparent substances in the same general way.

Striae, Electric. In Geissler tubes the light produced by the electric discharge is filled with striae, bright bands alternating with dark spaces; these may be termed electric striae.

Striking Distance. The distance that separates two conductors charged with electricity of different potential, when a spark starts between them.

Striking Solution. In silver-plating a bath composed of a weak solution of silver cyanide-with a large proportion of free potassium cyanide. It is used with a strong current and a large silver anode. This gives an instantaneous deposition of metallic silver over the surface of the article which goes to insure a perfect coating in the silver bath proper. After a few seconds in the striking solution, the article is at once removed to the plating bath.

Stripping. The removal of electroplating from an object. It may be effected in several ways. An object whose plating is to be removed is placed in a plating bath of the solution of the metal with which it is coated. It is connected as the anode to the positive plate of the battery or corresponding terminal of the generator. A kathode connected to the other terminal being placed in the bath, the coating is dissolved by electrolytic action. Sometimes simple treatment with acid is employed. Different stripping baths are described under the heads of the different metals.

S. U. Symbol or abbreviation for Siemens' Unit of Resistance. (See Resistance, Siemens' Unit of.)

Sub-branch. A branch or lead of wire taken from a branch lead: a term used in electric distribution.

Sub-main. In electric distribution a conductor connected directly to a main; a branch.

497 STANDARD ELECTRICAL DICTIONARY.

Subway, Electric. A subterranean system of conduits for electric cables. As generally constructed in this country it includes manholes, q. v., at the street corners connected by ducts or pipes. These pipes are large enough to hold a cable. To introduce a cable into a duct, which latter may be two or three inches in diameter, and from two hundred to six or seven hundred feet long, a wire or rope is first passed through the duct. This is done by a set of short wooden rods with screws at the end so as to be screwed together. Each rod must be shorter than the diameter of the manhole. A rod is thrust in, another is screwed to it and thrust in, and thus a set of rods is made to extend as far as desired. In pulling them out a rope is attached and drawn through. This rope or a larger one is used in drawing the cable through the duct. A windlass is employed to draw the rope with cable attached through the ducts.

Sulphating. In storage battery cells, the formation of a hard white basic lead sulphate, Pb2 S05. Its formation is due to over-exhaustion of the cells. As long as the voltage is not allowed to fall below 1.90 volts per cell little of it forms. As it accumulates it is apt to drop off the plate and fall to the bottom, thus weakening the plate possibly, and depriving it of active material, and clogging up the cell. If it carries a film of metallic lead with it, there is danger of short circuiting the cell.

The presence of some sodium sulphate in the solution is said to tend to prevent sulphating, or to diminish it.

Sulphur Dioxide. A compound gas, S O2; composed of Sulphur, 32 Oxygen, 32 Molecular weight, 64 Specific gravity, 2.21.

It is a dielectric of about the same resistance as air. Its specific inductive capacity at atmospheric pressure is: 1.0037 (Ayrton).

Synonyms--Sulphurous Acid--Sulphurous Acid Gas.

Sunstroke, Electric. Exposure to the arc light sometimes produces the effects observed in cases of sunstroke. It is said that, in the case of workmen at electric furnaces, these effects are very noticeable. (See Prostration, Electric.)

[Transcriber's note: Effects are due to ultraviolet light.]

Supersaturated. adj. A liquid is supersaturated when it has dissolved a substance at a temperature favorable to its solubility and its temperature has been allowed to change, the liquid being kept free from agitation or access of air, provided crystallization or precipitation has not taken place. It expresses the state of a liquid when it holds in solution more than the normal quantity of any substance soluble in it.

Surface. A galvanic battery is arranged in surface when all the positive plates are connected together and all the negative plates are also connected. This makes it equivalent to one large cell, the surface of whose plates would be equal to the aggregate surface of the plates of the battery. It is also used as an adjective, as "a surface arrangement of battery."

498 STANDARD ELECTRICAL DICTIONARY.

Surface Density. The relative quantity of an electric charge upon a surface.

Surface, Equipotential. A surface over all of which the potential is the same. In a general sense equipotential surfaces are given by planes or surfaces which cut lines of force at right angles thereto, or which are normal to lines of force. The conception applies to electrostatic and electro-magnetic fields of force, and for current conductors the planes normal to the direction of the current are equipotential surfaces.

The contour of an equipotential surface of a field of force which is drawn or represented by delineations of its lines of force can be obtained by drawing a line normal thereto. This line will ordinarily be more or less curved, and will be a locus of identical potentials.

An electric equipotential surface may be described as electro-static, electro- magnetic, or magnetic; or may be an equipotential surface of a current conductor. Besides these there are mechanical and physical equipotential surfaces, such as those of gravitation.

Surface Leakage. Leakage of current from one part of an insulating material to another by the film of moisture or dirt on the surface.

Suspension. This term is applied to methods of supporting galvanometer needles, balance beams, magnetic compass needles and similar objects which must be free to rotate. (See Suspension, Bifilar--Fibre and Spring Suspension--Fibre Suspension--Knife Edge Suspension--Pivot Suspension--Suspension, Torsion.)

308. DIAGRAM OF BIFILAR SUSPENSION.

Suspension, Bifilar. Suspension by two vertical parallel fibres, as of a galvanometer needle. The restitution force is gravity, the torsion being comparatively slight and negligible. Leaving torsion out of account the restitution force is (a) proportional to the distance between the threads;. (b) inversely proportional to their length; (c) proportional to weight of the needle or other object suspended; (d) proportional to the angle of displacement.

499 STANDARD ELECTRICAL DICTIONARY.

Assume two masses A and B at the end of a weightless rod, suspended by the parallel cords a A, b B. Let the rod be rotated through an angle theta. Consider the cord a A. Its lower end is swung through the angle theta, as referred to the center O; the cord is deflected from the vertical by an angle psi, such that a A tang(psi)= O A 2 sin (theta/2). The component of gravitation tending to restore A to A, acting towards A is equal to m g tan(psi). Its moment around O is equal to (m g tan(psi)) * (O A cos(theta/2). The whole moment of the couple is 2 m g tan(psi). 0 A. cos(theta/2) = 2 m g (O A2/ a A) 2 sin(theta/2). Cos(theta/2) = 2mgl(OA2/aA) sin(theta). The moment of the restoring force is thus proportional to the sine of the angle of deflection, and the oscillations of such a system are approximately simple harmonic. (Daniell.)

If the twisting is carried so far as to cause the threads to cross and come in contact with each other the suspension ceases to be a bifilar suspension, but assumes the nature of a torsional suspension.

[Transcriber's note: This is the image of the first paragraph.]

Swaging, Electric. Mechanical swaging in which the objects to be swaged are heated by an electric current as in electric welding.

S. W. G. Abbreviation for Standard Wire Gauge.

Fig. 309. SIMPLE SWITCH.

Switch. A device for opening and closing an electric circuit.

A simple type is the ordinary telegrapher's switch. A bar of metal is mounted horizontally by a pivot at one end, so as to be free to rotate through an arc of a circle. In one position its free end rests upon a stud of metal. One terminal of a circuit is attached to its journal, the other to the stud. Resting on the stud it closes the circuit, in other positions it opens the circuit.

500 STANDARD ELECTRICAL DICTIONARY.

Switch, Automatic. A switch opened and closed by the electric current. It is used for lighting distant incandescent lamps. It includes one or two electro-magnets operated by two push buttons. In the usual arrangement one button is black and the other white, for extinguishing and lighting respectively. When the white button is pushed it causes a current to pass through one of the electro-magnets. This attracts its armature, thereby making a contact and throwing the lamps into the lighting circuit. Then they remain lighted until the black button is pressed. This excites the other magnet, which attracts its armature, breaks the contact and extinguishes the lights.

The object of the automatic switch is to enable distant lamps to be lighted without the necessity of carrying the electric leads or wires to the place whence the lighting is to be done. A very small wire will carry enough current to operate the magnets, and open circuit batteries, such as Leclanché batteries, may be used as the source of current for the switch, but generally the lighting current is used for the purpose.

A single magnet may do the work. When the lighting button is pressed the magnet is excited, attracts its armature and holds it attracted, until by pressing the black button the current is turned off from it. In this case the lighting current is used to excite the magnet.

Switch Board. A board or tablet to which wires are led connecting with cross bars or other switching devices, so as to enable connections among themselves or with other circuits to be made.

Switch, Circuit Changing. A switch whose arm in its swing breaks one contact and swinging over makes another. It is employed to change the connections of circuits from one dynamo to another.

Synonyms--Changing Switch--Changing Over Switch.

Switch, Double Break. A form of switch in which double contact pieces are provided to give a better contact. One form consists of a hinged bar whose end swings down between two pairs of springs. Both pairs are connected to one terminal, and the bar to the other terminal of a circuit.

Switch, Double Pole. A heavy switch for central station work, that connects and disconnects two leads simultaneously.

Switch, Feeder. A heavy switch, often of double contact type, for connecting and disconnecting feeders from bus bars in central stations.

501 STANDARD ELECTRICAL DICTIONARY.

Switch, Knife. A switch whose movable arm is a narrow, deep bar of copper or brass, and which in making contact is forced in edgeways between two springs connected to one terminal. The bar is connected to the other terminal.

Synonyms--Knife Break Switch--Knife Edge Switch.

Switch, Multiple. A switch which in the swing of its bar connects one by one with a number of contacts so that ultimately the end of its bar is in contact with all at once. It is used to throw lights in and out in succession, and it can, if the multiple contacts connect with resistances, make them operate as a rheostat.

Switch, Pole Changing. A switch for changing the direction of the current in a circuit.

Switch, Reversing. A switch, often of the plug type (see Plug Switch) for changing the direction of current passing through a galvanometer.

Switch, Snap. A switch constructed to give a quick, sharp break. It has a spiral spring interposed between the handle and arm. As the handle is drawn back to open it the spring is first extended, the bar being held by the friction of the contacts, until the spring suddenly jerks it up, thus breaking the contact.

Switch, Storage Battery Changing. A switch for changing storage battery connections from series to multiple and back again.

Switch, Three Way. A switch, so constructed that by turning its handle connection can be made from one lead to either of two other leads, and also so that connection can be completely cut off.

Sympathetic Vibration. The establishment of periodic movement in one body by impulses of the same period communicated to it from another body in motion. Thus if two tuning forks are of the same pitch and one is sounded the other will begin to sound by sympathy, the sound waves communicating the necessary periodic impulses to it.

Sympathetic vibrations are utilized in harmonic telegraphy. (See Harmonic Receiver--Telegraph, Harmonic.)

T. Symbol of time.

Tailings. (a) In high speed transmission of telegraph signals by the automatic system, the definiteness of the signal marks is sometimes interfered with by retardation. Wrong marks are thus produced called tailings.

(b) The prolongation of the current at the distant receiving station of a telegraph line due to the discharge of the line and to self-induction.

Synonyms--Tailing--Tailing Current.

502 STANDARD ELECTRICAL DICTIONARY.

Tamidine. Reduced nitro-cellulose. Nitro-cellulose is dissolved in a proper solvent and is obtained by evaporation as a translucent solid mass. By ammonium sulphide or other reagent it is reduced so as to be virtually cellulose. It is cut into shape for filaments of incandescent lamps, which shapes are carbonized and flashed.

Tangent Law. In a galvanometer the tangents of the angles of deflection of the needle are proportional to the deflecting force--

I. When the controlling force is unaltered in absolute magnitude and direction by the motion of the needle.

II. When the deflecting force acts at right angles always to the controlling force.

These conditions are usually secured by having the actuating coil through which the current passes flat and of large diameter compared to the length of the needle; by using the uniform field of the earth as the control; by having a short needle; by placing the coil with its plane in the magnetic meridian.

For best proportions of tangent galvanometer coils see Bobbins.

Fig. 310. GRAPHIC CONSTRUCTION OF TANGENT SCALE.

Tangent Scale. An arc of a circle in which the number of graduations in any arc starting from zero are proportional to the tangent of the angle subtended by such arc. The system is for use with tangent galvanometers. Thus if for 45° a value of 100 is taken and marked on the scale then for the arc 26° 33' + a value of 50 should be marked on the scale because such are the relative values of the tangents.

Thus the scale instead of being divided into degrees is divided into arcs of varying length, growing shorter as they are more distant from the zero point, of such length that the first division being subtended by a tangent of length 1, the first and second divisions added or taken together as one arc are subtended by a tangent of length 2, and so on.

In the cut a simple method of graphically laying out a tangent scale is shown. In it C is the centre of the arc, and H the radius running to the zero of the instrument. From C a circle is described and on H a vertical line tangent to the arc is erected. Taking any part of the tangent, as the length shown ending at D, it is divided into any number of equal parts. Radii of the circle are now drawn whose prolongations pass through the divisions on the tangent. These radii, where they intersect the arc of the circle, determine equal divisions of the tangent scale, which, as is evident from the construction, are unequal angular divisions of the arc.

503 STANDARD ELECTRICAL DICTIONARY.

Tanning, Electric. The tanning of hides in the manufacture of leather by the aid of electrolysis. A current of electricity is maintained through the tanning vats in which regular tanning liquor is contained. Very extraordinary claims are made for the saving of time in the tanning process. What is ordinarily a process of several months, and sometimes of a year, is said to be reduced to one occupying a few days only. The action of electrolysis is the one relied on to explain the results.

Tapper. The key used in single needle telegraph transmitters. It comprises two flat springs L, E, each with a handle, normally pressed upward against one contact bar Z, and when pressed down by the operator making contact against a lower bar C when messages are to be transmitted. A double tapper, such as shown, is used for each instrument.

Synonyms--Double Tapper Key--Pedal Key.

Fig. 311. TAPPER.

Target, Electric. A target registering or indicating electrically upon an annunciator the point of impact of each bullet.

Taste, Galvanic. The effect produced upon the gustatory nerves by the passage of an electric current, or by the maintenance of potential difference between two portions of the tongue. It is very simply produced by placing a silver coin above, and a piece of zinc below the tongue, or the reverse, and touching their edges. A sour, peculiar taste is at once perceived. It cannot be due to any measurable quantity of current or of electrolytic decomposition, because the couple can do little more than establish a potential difference. With a strong current the taste becomes too strong for comfort, and if on a telegraph line the extra currents produced by the signaling make the operation of tasting the current a very unpleasant one. It is said that messages have been received in this way, the receiver placing one terminal of the line on his tongue, and a terminal attached to a grounded wire below it, and then receiving the Morse characters by taste.

504 STANDARD ELECTRICAL DICTIONARY.

Teazer. Originally a fine wire coil wound on the field magnets of a dynamo in shunt with the regular winding to maintain the magnetism. It was originally used in electroplating machines to prevent inversion of the magnetism, but has since developed into a component part of the winding of the compound dynamo. (See Dynamo, Compound.)

Tee, Lead. A lead pipe of T shape used for connecting branches to electric cables. The tee is soldered by wiped joints to the lead sheathings of the cable and branches after the wires have been connected, and the junctions coated with insulating tape or cement, or both.

It is sometimes made in two halves, and is known as a split tee.

Tel-autograph. A telegraph for reproducing the hand-writing of the sender at the receiving end of the line. To save time a special spelling is sometimes used.

Teleautograph. The special spelling used with the Tel-Autograph telegraph.

Tele-barometer, Electric. A barometer with electric attachment for indicating or recording at a distance the barometric readings.

Telegraph, ABC. This term is applied to alphabet telegraphs indicating the message by the movements of a pointer on a dial marked with the characters to be sent. In England the Wheatstone ABC system is much employed.

Telegraph, Automatic. A telegraph system based on the operation of the transmitting instrument by a perforated strip of paper drawn through it. The perforations made by an apparatus termed a perforator, are so arranged as to give telegraphic characters of the Morse or International Code in the transmitting instrument. (See Perforator.) Bain in the year 1846 was the originator of the system. He punched a fillet of paper with dots and dashes, and drew it between two terminals of the line, thus sending over the line a corresponding series of short and long currents which were received by his chemical receiver. (See Chemical Receiver.) The method was not successful. Its modern development, the Wheatstone Automatic Telegraph, is highly so. The perforated paper by its perforations controls the reciprocating movement of two rods, which pass through each hole in two rows, corresponding to the two rods respectively as the holes come opposite to the ends of the rods. The rods are kept constantly moving up and down. If unperforated paper is above them their upward motion is limited. This gives three positions for the rods, (a) both down, (b) one up and the other down, (c) both up. These positions of the rods work a pole changing key by which dots, spaces, and dashes are transmitted to the receiving instrument, which is an exceedingly delicate ink-printer. The latter can have its speed adjusted to receive from 200 to 450 words per minute.

505 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Dial. A telegraph in which as receiver a dial instrument is used. A pointer or index hand moves around a dial. The dial is marked with letters of the alphabet. The movements of the pointer are controlled by the transmitting operator at a distant station. He by the same actions moves a pointer on a duplicate instrument before him and the two are synchronized to give identical indications. Thus a message is spelled out letter by letter on both dials simultaneously. The motions of the index are generally produced by what is virtually a recoil escapement. The scape wheel is carried by the axle of the index, and a pallet or anchor is vibrated by an electro-magnet whose armature is attached to the stem of the pallet. As the pallet is vibrated it turns the wheel and index one tooth for each single movement. There are as many teeth in the wheel as there are characters on the dial. The two instruments being in duplicate and synchronized, the pallets move exactly in unison, so that identical readings of the dials are given. The pallets may be moved by any kind of make and break mechanism, such as an ordinary telegraph key. The index moves by steps or jerks, so that the system is sometimes called step-by-step telegraphy.

Fig. 312. DIAL TELEGRAPH.

In the cut the make and break transmitter is shown at v v, with its handle and contacts g and t. This mechanism sends impulses of current by F and Z to the receiving magnet l. This attracts and releases its armature K from contact into the position indicated by the dotted lines. This works the rocker n on the pin o, and actuates the double or anchor pawl s r, which turns the pallet or scrape wheel m.

The system is dropping into disuse, being supplanted by the telephone.

Synonym--Step-by-step Telegraph.

506 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Double Needle. A telegraph system in which the message is read by the motions of two vertical needles on the face of the instrument in front of the receiving operator. An identical instrument faces the transmitting operator. By two handles, one for each hand, the needles are caused by electric impulses to swing to right and to left so as to give a telegraphic code. It has been generally superseded by the single needle telegraph.

Telegraph, Duplex. A telegraph capable of transmitting simultaneously two messages over one wire. The methods of effecting it are distinct from those of multiplex telegraphy. This term is used as a distinction from diode multiplex telegraphy, in which the work is done on other principles. There are two systems of duplex telegraphy, the differential and the bridge systems.

Telegraph, Duplex Bridge. A system of duplex telegraphy employing the principle of the Wheatstone bridge. The other or differential system depends on equality or difference of currents; the bridge method on equality or difference of potentials. The cut shows the system known as Steam's Plan.

At the ends of the line wire are two cross connections like duplicate galvanometer connections in a Wheatstone bridge, each including a receiving relay. The rest of the connections are self-explanatory.

When A depresses his key the current splits at the point indicating the beginning of the bridge. One portion goes through the line to B and to earth, the other goes to earth at A through the rheostats indicated by the corrugated lines.

On reaching B's end the current divides at the cross-connection and part goes through the receiving relay shown in the center of that cross-connection.

Thus if A sends to B or B to A it is without effect on the home receiving instrument. Now suppose that both simultaneously are sending in opposite directions. If the connections be studied it will be seen that every movement of the transmitting key will affect the balance of the distant or receiving end of the bridge and so its instrument will record the signals as they are sent.

As shown in the cut the sending keys are on local circuits, and work what are known as duplex transmitters. These are instruments which send line signals without breaking the connection.

Fig. 313. STEARN'S PLAN OF DUPLEX BRIDGE TELEGRAPHY.

In Stearn's plan condensers are introduced as shown. By this plan different receiving instruments can be used. The inventor once worked a Morse instrument at one end of the line, and a Hughes' instrument at the other end.

507 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Duplex, Differential. A system of duplex telegraphy employing the differential action of two exciting or magnetizing coils. The general principles are the following. Suppose that at each of two stations, there is a magnet working as a sounder or relay. Each magnet is differentially wound, with two coils of opposite direction, of identical number of turns.

When the sending key at a station A is depressed two exactly equal currents go through the magnet in opposite directions. One called the compensation current goes to the earth at the stations. The other called the line current goes through the line, through the line coil of the distant station E, thereby actuating the relay or sounder armature.

The instrument of the sender A is unaffected because he is sending opposite and equal currents through its two coils. A special resistance is provided on the compensation circuit for keeping the currents exactly equal in effect. Nothing the sender at A does affects his own instrument.

Now suppose E desires to telegraph back at the same time that A is telegraphing to his station. He works his key. This does not affect his own instrument except by sending the equal and opposite currents through its coils. When his key is depressed and A's key is untouched, he works A's receiving instrument.

508 STANDARD ELECTRICAL DICTIONARY.

When A's key is depressed simultaneously with B's key, the two line currents are in opposition and neutralize each other. This throws out the balance in the instruments and both armatures are attracted by the compensation currents left free to act by the neutralization of the line currents.

Fig. 314. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM

Suppose that B is sending a dash, and it begins while A's key is raised. The line and compensation currents in B's receiving instrument neutralize each other and no effect is produced, while A's receiving instrument begins to register or indicate a dash. Now suppose A starts to send a dash while B's is half over. He depresses his key. This sends the two opposite currents through his magnet. His line current neutralizes B's working current so that the compensation currents in both receiving instruments hold the armatures attracted for the two dashes. Meanwhile A's dash ends and he releases his key. At once his line current ceases to neutralize B's line current, his receiving instrument is actuated now by B's line current, while B's receiving instrument ceases to be actuated by the compensation current.

Two assumptions are made in the above description. The line currents are assumed to be equal in strength and opposite in direction at each station. Neither of these is necessary. The line current received at a station is always weaker than the outgoing line current, and it is the preponderance of the compensation current over the partly neutralized line current that does the work. As this preponderance is very nearly equal to the line current received from the distant station, the signals are actuated by almost the same current, whether it is compensation or line current.

509 STANDARD ELECTRICAL DICTIONARY.

Both line currents may coincide in direction. Then when the two keys are depressed, a line current of double strength goes through both receiving instruments and both work by preponderance of the double line current over the compensation current. In other respects the operation is the same as before described.

Fig. 315. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM.

Fig. 316. DIFFERENTIAL DUPLEX TELEGRAPH CONNECTIONS.

The cut shows a diagram of the operation of one end of the line. R and R are resistances, E and E are earth contacts, and the two circles show the magnet of the receiving instrument wound with two coils in opposition. The battery and key are also shown. It also illustrates what happens if the key of the receiver is in the intermediate position breaking contact at both 1 and 2. The sender's line current then goes through both coils of the receiving instrument magnet, but this time in series, and in coincident direction. This actuates the instrument as before. Owing to the resistance only half the normal current passes, but this half goes through twice as many coils or turns as if the receiver's key was in either of the other two positions.

In actual practice there are many refinements. To compensate for the varying resistance of the line a rheostat or resistance with sliding connection arm is connected in the compensation circuit so that the resistance can be instantly changed. As the electro-static capacity of the line varies sectional condensers are also connected in the compensation circuits.

510 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Facsimile. A telegraph for transmitting facsimiles of drawing or writing. The methods employed involve the synchronous rotation of two metallic cylinders, one at the transmitting end, the other at the receiving end.

On the transmitter the design is drawn with non-conducting ink. A tracer presses upon the surface of each cylinder and a circuit is completed through the two contacts. In operation a sheet of chemically prepared paper is placed over the surface of the receiving cylinder. The two cylinders are rotated in exact synchronism and the tracers are traversed longitudinally as the cylinders rotate. Thus a number of makes and breaks are produced by the transmitting cylinder, and on the receiving cylinder the chemicals in the paper are decomposed, producing marks on the paper exactly corresponding to those on the transmitting cylinder.

Synonyms--Autographic Telegraph--Pantelegraphy.

Telegraph, Harmonic Multiplex. A telegraph utilizing sympathetic vibration for the transmission of several messages at once over the same line. It is the invention of Elisha Gray. The transmitting instrument comprises a series of vibrating reeds or tuning-forks, each one of a different note, kept in vibration each by its own electro-magnet. Each fork is in its own circuit, and all unite with the main line so as to send over it a make and break current containing as many notes superimposed as there are tuning forks. At the other end of the line there are corresponding tuning forks, each with its own magnet. Each fork at this end picks up its own note from the makes and breaks on the main line, by the principle of sympathetic vibration.

To each pair of operators a pair of forks of identical notes are assigned. As many messages can be transmitted simultaneously as there are pairs of forks or reeds.

The movements of a telegraph key in circuit with one of the transmitting reeds sends signals of the Morse alphabet, which are picked out by the tuning fork of identical note at the other end of the line.

511 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Hughes'. A printing telegraph in very extensive use in continental Europe. Its general features are as follows:

The instruments at each end of the line are identical. Each includes a keyboard like a piano manual, with a key for each letter or character. On each machine is a type wheel, which has the characters engraved in relief upon its face. With the wheel a "chariot" as it is termed also rotates. The type wheels at both stations are synchronized. When a key is depressed, a pin is thrown up which arrests the chariot, and sends a current to the distant station. This current causes a riband of paper to be pressed up against the face of both type wheels so as to receive the imprint of the character corresponding to the key. The faces of the wheels are inked by an inking roller.

Fig. 317. ELECTRO-MAGNET OF HUGHES' PRINTING TELEGRAPH.

The most characteristic feature is the fact that the current sent by depressing a key does not attract an armature, but releases one, which is then pulled back by a spring. The armature is restored to its position by the mechanical operation of the instrument. The magnet used is a polarized electro-magnet. Coils are carried on the ends of a strong powerful magnet. The coils are so connected that a current sent through them by depressing a key is in opposition to the magnetism of the permanent magnet so that it tends to release the armature, and in practice does so. This release permits the printing mechanism to act. The latter is driven by a descending weight, so that very slight electric currents can actuate the instruments.

Synonym--Hughes' Type Printer.

Telegraphic Code. (a) The telegraphic alphabet, as of the Morse System. (See Alphabet, Telegraphic.)

(b) A code for use in transmitting messages either secretly, or comprising several words or short sentences in one word, in order to economize in transmission. Such codes are extensively used in commercial cable messages.

512 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Magneto-electric. A telegraph in which the current is produced by magneto-electric generators. It has been applied to a considerable extent in England. The Wheatstone ABC or dial telegraph is operated by a magneto-generator turned by hand.

In this country the magneto-electric generator by which the calling bell of a telephone is rung is an example. The magneto-electric key (See Key, Magneto-electric) is for use in one kind of magneto-electric telegraphing.

Telegraph, Morse. A telegraph, characterized by the use of a relay, working a local circuit, which circuit contains a sounder, or recorder for giving dot and dash signals constituting the Morse alphabet. The signals are sent by a telegraph key, which when depressed closes the circuit, and when released opens it. The two underlying conceptions of the Morse Telegraph system are the use of the dot and dash alphabet, and the use of the local circuit, which circuit includes a receiving instrument, and is worked by a relay, actuating a local battery. It would be difficult to indicate any invention in telegraphy which has had such far-reaching consequences as the one known as the Morse telegraph.

In other places the principal apparatus of the system will be found described. The cut Fig. 318, repeated here gives the general disposition of a Morse system. (See Circuit, Local.)

Fig. 318. DIAGRAM OF MORSE SYSTEM.

513 STANDARD ELECTRICAL DICTIONARY.

The key by which the messages are transmitted is shown in Fig. 319. M is a base plate of brass. A is a brass lever, mounted on an arbor G carried between adjustable set screws D. C is the anvil where contact is made by depressing the key by the finger piece B of ebonite. E, Fl are adjusting screws for regulating the vertical play of the lever. H is the switch for opening or closing the circuit. It is opened for transmission, and closed for receiving. By screws, L L, with wing nuts, K K, the whole is screwed down to a table.

Fig. 319. MORSE TELEGRAPH KEY.

In the United States the simplest disposition of apparatus is generally used. The main line is kept on closed circuit. In it may be included a large number of relays at stations all along the line, each with its own local circuit. There may be fifty of such stations. Battery is generally placed at each end of the line. Very generally gravity batteries are used, although dynamos now tend to supplant them in important stations.

As relays the ordinary relay is used. Its local circuit includes a sounder and local battery. The latter is very generally of the gravity type, but oxide of copper batteries (See Battery, Oxide of Copper) are now being introduced. At main or central offices, the terminals of the lines reach switch boards, where by spring-jacks and plugs, any desired circuits can be looped into the main circuit in series therewith.

In European practise the main line is kept on open circuit. Polarized relays are used to work the local circuits. The currents for these have to be alternating in direction. When the line is not in use its ends are connected to earth at both ends, leaving the battery out of circuit. Each intermediate station has its own main, or line battery for use when it desires to send a message. In the American system as first described, it will be seen that the main batteries are at most two in number.

For the details of the different apparatus, the following definitions may be consulted: Embosser, Telegraphic--Recorder, Morse--Relay--Relay Connection--Sounder.

514 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Multiplex. A system of telegraphy by which a number of messages can be transmitted in both directions over a single wire. The principles underlying the systems are the following:

Suppose that at the two extremities of a telegraph line two arms are kept in absolute synchronous rotation. Let the arms in their rotation, press upon as many conducting segments as there are to be transmissions over the line. A transmitting and receiving set of instruments may be connected to one segment at one end of the line, and another set to the corresponding segment at the distant station. For each pair of segments two sets can be thus connected. Then if the arm rotates so rapidly that the contacts succeed each other rapidly enough each pair of sets of instruments can be worked independently of the others. In practice this rapid succession is effected by having a number of contacts made for each pair during a single rotation of the arm or equivalent.

The multiplex system has been perfected by the use of La Cour's phonic wheel (see Phonic Wheel), and brought into a practical success by Patrick B. Delany, of New York.

Two phonic wheels rotate at each end of the line. They are kept in synchronous motion by two vibrating steel reeds of exactly the same fundamental note, and the axle of each wheel carries an arm whose end trails over the contacts or distributor segments already spoken of. The reeds are adjusted to vibrate at such speed that the trailer is in contact with each segment about 1/500 second. The number of groups of segments required for each working is determined by the retardation of the signals owing to the static capacity of the line. To convert the rapidly recurring impulses of current into practically a single current, condensers are connected across the coils of the relay. One battery serves for all the arms.

Multiplex telegraphy can effect from two to six simultaneous transmissions over one wire. For two or four transmissions the method only distinguishes it from duplex or quadruplex telegraphy. The terms diode, triode, tetrode, pentode and hexode working are used to indicate respectively the simultaneous transmission of two, three, four, five, or six messages over one wire.

It will be seen that the multiplex process really assigns to each transmission separate times, but divides these times into such short and quickly recurring intervals that the work is executed as if there was continuous contact. In no case is there the popular conception of the sending of several messages actually simultaneously over one wire. Each signal in reality has its own time assigned it, divided into short periods of high frequency, and only utilizes the line when it is free.

515 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Over-house. An English term for telegraph lines led over houses and supported on standards on the roofs.

Telegraph Pole Brackets. Arms for carrying insulators, which arms are attached to telegraph poles or other support. They vary in style; sometimes they are straight bars of wood gained into and bolted or spiked in place; sometimes they are of iron.

Telegraph, Printing. Various telegraphs have been invented for printing in the ordinary alphabet the messages at the receiving end of the line.

Representative instruments of this class are used for transmitting different market and stock reports to business offices from the exchanges. The type faces are carried on the periphery of a printing wheel, which is rotated like the hand of a dial telegraph, and against whose face a paper riband is pressed whenever the proper letter comes opposite to it. As each letter is printed the paper moves forward the space of one letter. Spacing between words is also provided for. In the recent instruments two lines of letters are printed on the paper one above the other.

In England, and on the continent of Europe, printing instruments have received considerable use for ordinary telegraphic work. Hughes' type printer and Wheatstone's ABC telegraph meet with extensive use there for ordinary transmission.

Telegraph, Quadruplex. Duplex telegraphy is the sending of two messages in opposite directions simultaneously through the same wire. Duplex telegraphy is the sending of two messages simultaneously in the same direction. The two combined constitute quadruplex telegraphy. [SIC]

The system was suggested by Stark of Vienna and Bosscha of Leyden in 1855; the successful problem was solved by Edison in 1874.

The principle is based on the two orders of difference in electric currents; they may vary in strength or in direction. Thus we may have one instrument which works with change of strength of current only, the other with change of direction only. The two can be worked together if the direction of the current can be altered without alteration of strength, and if strength can be altered without alteration of direction. Double current and single current working are so combined that one relay works by one system of currents and another relay by the other system. A current is constantly maintained through the line. The relay operated by change in direction is a simple polarized relay which works by change of direction of current. The relay operated by change in strength is the ordinary unpolarized relay.

516 STANDARD ELECTRICAL DICTIONARY.

For the following description and the cuts illustrating it we are indebted to Preece and Sivewright. The cut shows the arrangement of the apparatus and connections for terminal offices.

"Sufficient table room is provided to seat four clerks. The apparatus is arranged for the two senders to sit together in the centre, the messages to be forwarded being placed between them. The section on the left of the switch Q is known as the 'A' side, that on the right as the 'B' side of the apparatus.

K1 the reversing key, reverses the direction of the current. K2 is a simple key, known as the increment key; it is used simply to increase the strength of the current.

Fig. 320. QUADRUPLEX TELEGRAPH CONNECTIONS.

The way in which the keys K1 and K2 combine their action is shown by Fig. 321. E1 and E2 are the line batteries, the one having two and one-third (2-1/3) the number of cells of the other, so that if E1 be the electro-motive force of the smaller, that of the whole combined battery will be 3.3 E1. The negative pole of E1 is connected to z and z1 of K1 and the positive pole of E2 to a of K2 through a resistance coil s. A wire, called the 'tap' wire, connects the positive pole of E1 and the negative pole of E2 to b of K2. This wire has in it a resistance coil r2. The springs c and c1 of Kl are connected to the lever L of K2. Now, when both keys are at rest, the negative pole of E1 is to line through z, and the positive pole of E1 to earth through b of K2 and c of K1; the positive pole of E2 being insulated at a of K2.

517 STANDARD ELECTRICAL DICTIONARY.

There is thus a weak negative current flowing to line. When K1 alone is worked, the current of E1 is reversed. When K2 is worked alone, c of K1 is transferred from b to a, and the strength of the negative current going to line is increased through the increase of the electro-motive force from E1 to 3.3 E1 for the whole battery is brought into play. When K1 and K2 are depressed together, then the negative pole of E1 goes to earth through Z1; and the positive pole of E2 to line through a of K2 and c1 of K1 and a positive current, due to the whole electro-motive force 3.3 E1 goes to line. Hence the effect of working K1 is simply to reverse the current, whatever its strength, while that of K2 is to strengthen it, whatever its direction.

The resistance coil s, of 100° resistance, is called a spark coil, because it prevents the high electro-motive force of the whole battery from damaging the points of contact by sparking or forming an arc across when signals are sent; and the resistance r2 is made approximately equal to the combined resistance of E2 and the spark coil, so that the total resistance of the circuit may not be altered by the working of the apparatus.

Fig. 321. QUADRUPLEX TELEGRAPH.

A1 and B1 (Fig. 320) are the relays which are used to respond to the changes in the currents sent by the keys K1 and K2 at the distant station.

A, is a simple polarized relay wound differentially, each wire having a resistance of 200 [omega], and so connected up as to respond to the working of the reversing key K1 of the distant station. It acts independently of the strength of the current, and is therefore not affected by the working of the increment key K2. It is connected up so as to complete the local circuit of the sounder S1 and the local battery l1 and forms the receiving portion of the 'A' side.

B, is a non-polarized relay also wound differentially, each coil having a resistance of 200 [omega]. It responds only to an increase in the strength of the current, and therefore only to the working of the increment key K2 of the distant station.

[Transcriber's note: In current usage upper case omega indicates ohms and lower case omega denotes angular frequency, 2*PI*f.]

518 STANDARD ELECTRICAL DICTIONARY.

The relay spring is so adjusted that the armatures are not actuated by the weak current sent from E by the key K1.

In its normal position this relay completes the circuit of the local battery through the sounder S. This sounder S, called the uprighting sounder, acts as a relay to a second sounder, S2, called the reading sounder, which is worked by another local battery, l2. Of course, normally, the armature of S is held down and that of S2 is up, but when the tongue t moves, as it does when the increment key K2 is depressed so as to send the whole current to line, then the current from l is interrupted, and the circuit of l2 is completed by the rising of the armature of S, causing the reading sounder S2 to work. This is the 'B' side.

R is a rheostat for balancing the resistance of the line, as used in duplex working.

C is a condenser used for compensating the static charge of the line. It is provided with an adjustable retardation coil, R1, to prolong the effect of the compensating current from the condenser.

G is a differential galvanometer, used for testing, and for facilitating adjustment and balancing.

Q is a switch for putting the line to earth, either for balancing, or for any other purpose. There is on the earth wire leading from Q a resistance coil, r1, equalling approximately the resistance of the whole battery, 3.3 E1, and the resistance s.

The connections shown in Fig. 321, are for an 'up' office. At a 'down' office it is necessary to reverse the wires on the two lower terminals of the galvanometer and the two battery wires on the reversing key K1.

The keys K1 and K2 are, for repeaters, replaced by transmitters.

The adjustment of this apparatus requires great care and great accuracy. Its good working depends essentially on technical skill that can only be acquired by patience and perseverance.

Faults in working generally arise from careless adjustments, dirty contacts, loose connections, battery failures, and the ordinary line interruptions, but there are no troubles that are beyond the reach of ordinary skill, and it can be safely said that, within moderate distances, wherever and whenever duplex working is practicable, then quadruplex working is so too."

The above is a typical quadruplex bridge system. There is also a differential system, the full description of which, in addition to what has been given, is outside of the scope of this work.

519 STANDARD ELECTRICAL DICTIONARY.

Telegraph Repeater. An extension of the relay system, adopted for long lines. A repeating station comprises in general terms duplicate repeating apparatus. One set is connected for messages in one direction, the other for messages in the opposite direction. The general operation of a repeating set is as follows. The signals as received actuate a relay which by its local circuit actuates a key, which in ordinary practise would be the sounder, but in the repeater its lever opens and closes a circuit comprising a battery and a further section of the line.

Repeaters are placed at intervals along the line. Each repeater repeats the signals received for the next section of line with a new battery. It represents an operator who would receive and repeat the message, except that it works automatically.

The Indo-European line from London to Teheran, 3,800 miles long, is worked directly without any hand retransmission, it being carried out by five repeaters. This gives an average of over 500 miles for each repeater. [Transcriber's note: … 650 miles for each repeater.]

Repeaters introduce retardation, and each repeater involves a reduction in the rate of working. Yet in many cases they increase the speed of a line greatly, as its speed is about equal to that of its worst section, which may be far greater than that of the whole line in one.

Synonym--Translater.

Telegraph Signal. In the telegraph alphabet, a dot, or dash; the signal or effect produced by one closing of the circuit. A dash is equal in length to three dots. The space between signals is equal to one dot; the space between letters to three dots; and the space between words to six dots.

Telegraph, Single Needle. A telegraph system in which the code is transmitted by the movements of a needle shaped index which oscillates to right and left, the left hand deflection corresponding to dots, the right hand deflection to dashes. The instruments for sending and receiving are combined into one. The needles are virtually the indexes of vertical galvanometers. In one form by a tapper key (see Tapper), in another form by a key worked by a drop-handle (the drop handle instrument), currents of opposite directions are sent down the line. These pass through both instruments, affecting both needles and causing them to swing to right or left, as the operator moves his key.

As galvanometer needle or actuating needle a soft iron needle is employed, which is polarized by the proximity of two permanent magnets. This avoids danger of reversal of polarity from lightning, a trouble incident to the old system.

520 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 322, shows a single needle telegraph instrument of the tapper form. The action of the tapper can be understood from the next cut.

Fig. 322. SINGLE NEEDLE TELEGRAPH INSTRUMENT, DOUBLE TAPPER FORM.

Fig. 323. DOUBLE TAPPER KEY FOR SINGLE NEEDLE TELEGRAPH.

C and Z are two strips of metal to which the positive and negative poles of the battery are respectively connected. E and L are two metallic springs; E is connected to earth, L is connected to the line; at rest both press against Z. If L is depressed so as to touch C, the current from the battery goes to the line by the key L, goes through the coils of the distant instrument and deflects the needle to one side, and then goes to the earth. If the key E is depressed, L retaining its normal position, the direction of the current is reversed, for the other pole of the battery is connected to the earth and the reverse current going through the coils of the distant instrument deflects the galvanometer needle to the other side.

In the drop-handle type an analogous form of commutator worked by a single handle produces the same effects.

521 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Wheatstone, A. B. C. A magneto-electric telegraph of the dial system. An alternating current magneto-generator is turned by hand and by depressing keys its current is admitted to or cut off from the line and receiver's instrument. The message is received by a dial instrument working by the escapement motion described under Telegraph, Dial.

Telegraph, Writing. A telegraph in which the message is received in written characters. The transmitter includes a stylus which is held in the hand and whose point bears against the upper end of a vertical rod. The rod is susceptible of oscillation in all directions, having at its base a spring support equivalent to a universal joint.

The stylus is moved about in the shape of letters. As it does this it throws a series of resistances in and out of the circuit.

At the receiving end of the line the instrument for recording the message includes two electro-magnets with their cores at right angles to each other and their faces near together at the point of the angle. An armature is supported between the faces and through it a vertical rod carried by a spring at its bottom rises. These magnets receive current proportional to the resistances cut in and out by the motions of the other rod at the transmitting end of the line. These resistances are arranged in two series at right angles to each other, one for each magnet. Thus the movements of the transmitting stylus and rod are repeated by the end of the rod in the receiving instrument. A species of pen is carried at the end of the rod of the receiving instrument, which marks the letters upon a riband of paper which is fed beneath it.

Telemanometer. Electric. A pressure gauge with electric attachment for indicating or recording its indications at a distance.

It is applicable to steam boilers, so as to give the steam pressure in any desired place.

Telemeter, Electric. An apparatus for electrically indicating or recording at a distance the indications of any instrument such as a pressure gauge, barometer or thermometer, or for similar work. The telemanometer applied to a boiler comes into this class of instrument.

Telephotography. The transmission of pictures by the electric current, the requisite changes in the current being effected by the action of light upon selenium. The picture is projected by a magic lantern. Its projection is traversed by a selenium resistance through which the current passes. This is moved systematically over its entire area, thus constituting the transmitter, and synchronously with the motion of the selenium a contact point at the other end of the line moves systematically over a sheet of chemically prepared paper. The paper, which may be saturated with a solution of potassium ferrocyanide and ammonium nitrate, is stained by the passage of the current, and by the variation in intensity of staining, which variation is due to variations in the current, produced by the effects of the light upon the selenium, the picture is reproduced.

522 STANDARD ELECTRICAL DICTIONARY.

Telepherage. An electric transportation system, hitherto only used for the carrying of ore, freight, etc. Its characteristic feature is that the electric conductors, suspended from poles, supply the way on which carriages provided with electric motors run. The motors take their current directly from the conductors.

There are two conducting lines, running parallel with each other, supported at the opposite ends of transverse brackets on a row of supporting poles. At each pole the lines cross over so that right line alternates with left, between consecutive pairs of poles.

The cars are suspended from pulleys running on one or the other of the conductors. A train of such cars are connected and the current is taken in near one end and leaves near the other end of the train. These current connections are so distant, their distance being regulated by the length of the train, that they are, for all but an instant at the time of passing each of the poles, in connection with segments of the line which are of opposite potential. To carry out this principle the distance between contacts is equal to the distance between poles. Owing to the crossing over of the lines the contacts are in connection as described and thereby the actuating current is caused to go through the motors.

Cars running in one direction go on the electric conductors on the one side, those running in the other direction go on the other conductor.

A great many refinements have been introduced, but the system has been very little used.

Telephone. An instrument for the transmission of articulate speech by the electric current. The current is defined as of the undulatory type. (See Current, Undulatory.)

The cut shows what may be termed the fundamental telephone circuit. A line wire is shown terminating in ground plates and with a telephone in circuit at each end. The latter consists of a magnet N S with a coil of insulated wire H surrounding one end. Facing the pole of the magnet is a soft iron diaphragm D, held in a frame or mouthpiece T. Any change of current in the line affects the magnetism of the magnet, causing it to attract the diaphragm more or less. The magnet and diaphragm really constitute a little electric motor, the diaphragm vibrating back and forth through an exceedingly short range, for changes in the magnetic attraction.

The principle of the reversibility of the dynamo applies here. If the magnet is subjected to no change in magnetism, and if the diaphragm is moved or vibrated in front of its poles, currents will be induced in the wire bobbin which surrounds its end. If two such magnets with bobbins and diaphragms are arranged as shown, vibrations imparted to one diaphragm will send currents through the line which, affecting the magnetism of the distant magnet, will cause its diaphragm to vibrate in exact accordance with the motions of the first or motor diaphragm. In the combination one telephone represents a dynamo, the other a motor.

If the vibrations of the diaphragm are imparted by the voice, the voice with all its modulations will be reproduced by the telephone at the distant end of the line.

523 STANDARD ELECTRICAL DICTIONARY.

Fig. 324. DIAGRAM OF BELL TELEPHONES AND LINE WITH EARTH CONNECTIONS.

Fig. 325. SECTION OF BELL TELEPHONE.

The above gives the essential features of the Bell telephone. In practice the telephone is used only as the receiver. As transmitter a microphone is employed. To give the current a battery, generally of the open circuit type, is used, and the current in the line is an induced or secondary one.

The microphone which is talked to, and which is the seat of the current variations which reproduce original sound, is termed the transmitter, the telephone in which the sounds are produced at the distant end of the line is termed the receiver.

Fig. 325 shows the construction of the Bell telephone in universal use in this country as the receiver. M is a bar magnet, in a case L L. B B is a bobbin or coil of insulated wire surrounding one end of the magnet. D is the diaphragm of soft iron plate (ferrotype metal), and E is the mouthpiece. The terminals of the coil B B connect with the binding screws C C. The wire in the coil is No. 36, A. W. G., and is wound to a resistance of about 80 ohms.

524 STANDARD ELECTRICAL DICTIONARY.

As typical transmitter the Blake instrument may be cited. It is a carbon microphone. It is shown in section in the cut; a is the mouthpiece and e is a diaphragm of iron plate, although other substances could be used; f is a steel spring, with a platinum contact piece at its end. One end bears against the diaphragm, the other against a carbon block k. The latter is carried by a brass block p, and pressure is maintained between these contacts by the spring g and weight of the piece c, which by gravity tends to press all together. The current passes by way of the spring f, carbon button k and spring g through the circuit indicated.

A battery is in circuit with these parts. If a telephone is also in circuit, and the transmitter is spoken against, the diaphragm vibrating affects the resistance of the carbon-platinum contact, without even breaking the contact, and the telephone reproduces the sound. The heavy piece of metal C acts by its inertia to prevent breaking of the contact. The position of this piece c, which is carried by the brass plate m, is adjusted by the screw n.

Fig. 326. SECTION OF BLAKE TRANSMITTER.

In practice the transmitter and battery are usually on a local circuit, which includes the primary of an induction coil. The line and distant receiving telephone are in circuit with the secondary of the induction coil, without any battery.

Telephone, Bi-. A pair of telephones carried at the ends of a curved bar or spring so that they fit the head of a person using them. One telephone is held against each ear without the use of the hands.

525 STANDARD ELECTRICAL DICTIONARY.

Telephone, Capillary. A telephone utilizing electro-capillarity for the production of telephonic effects. The following describes the invention of Antoine Breguet.

The point of a glass tube, drawn out at its lower end to a capillary opening dips vertically into a vessel. This vessel is partly filled with mercury, over which is a layer of dilute sulphuric acid. The end of the immersed tube dips into the acid, but does not reach the mercury. One line contact is with mercury in the tube, the other with the mercury in the vessel. The arrangement of tube and vessel is duplicated, giving one set for each end of the line. On introducing a battery in the circuit the level of the mercury is affected by electro-capillarity. The tubes are closed by plates or diaphragms at their tops, so as to enclose a column of air. It is evident that the pressure of this air will depend upon the level of the mercury in the tube, and this depends on the electro-motive force. On speaking against the diaphragm the sound waves affect the air pressure, and consequently the level, enough to cause potential differences which reproduce the sound in the other instrument.

Fig. 327. BREGURT'S CAPILLARY TELEPHONE.

Telephone, Carbon. A telephone transmitter based on the use of carbon as a material whose resistance is varied by the degree of pressure brought to bear upon it. Undoubtedly the surface contact between the carbon and the other conducting material has much to do with the action. Many carbon telephones have been invented. Under Telephone the Blake transmitter is described, which is a carbon telephone transmitter. The Edison carbon transmitter is shown in section in the cut. E is the mouth piece and D the diaphragm. I is a carbon disc with adjusting screw V. A platinum plate B B, with ivory button b, is attached to the upper surface of the carbon disc. C C is an insulating ring. The wire connections shown bring the disc into circuit. It is connected like a Blake transmitter. It is now but little used.

Fig. 328. SECTION OF EDISON CARBON TRANSMITTER.

526 STANDARD ELECTRICAL DICTIONARY.

Telephone, Chemical. A telephone utilizing chemical or electrolytic action in transmitting or receiving. The electro-motograph is an example of a chemical receiver. (See Electro-motograph.)

Telephone, Electrostatic. A telephone utilizing electrostatic disturbances for reproduction of the voice. In the cut D and C are highly charged electrophori. The diaphragms A and B when spoken to affect the potential of the electrophorus so as to produce current variations which will reproduce the sound. Dolbear and others have invented other forms of transmitters based on electrostatic action. Receivers have also been constructed. A simple condenser may be made to reproduce sound by being connected with a powerful telephone current.

Fig. 329. DIAGRAM OF EDISON'S ELECTROSTATIC TELEPHONE.

Telephone Induction Coil. The induction coil used in telephone circuits for inducing current on the main line. It is simply a small coil wound with two separate circuits of insulated wire. In the Edison telephone the primary coil, in circuit with the transmitter, is of No. 18 to 24 wire and of 3 to 4 ohms resistance. The secondary in circuit with the line and receiving instrument is of No. 36 wire and of 250 ohms resistance. The Bell telephone induction coil has its primary of No. 18 to 24 wire wound to a resistance of 1/2 ohm, and its secondary of No. 36 wire, and of 80 ohms resistance.

527 STANDARD ELECTRICAL DICTIONARY.

Telephone, Reaction. A form of telephone containing two coils of insulated wire, one of which is mounted on the disc, and the other on the magnet pole in the usual way. These coils react upon each other so as to strengthen the effect.

Telephone, Thermo-electric. A telephone transmitter including a thermo-electric battery, placed in circuit with the line. A plate of vulcanite faces it. When the sound waves strike the vulcanite they move it backward and forward. These movements, owing to the elasticity of the vulcanite, produce minute changes of temperature in it, which affecting the thermo-electric pile produce in the circuit currents, which passing through a Bell telephone cause it to speak. This type of instrument has never been adopted in practice.

Telephote. An apparatus for transmitting pictures electrically, the properties of selenium being utilized for the purpose.

Synonym--Pherope.

Teleseme. An annunciator, displaying on a dial the object wanted by the person using it. It is employed to transmit messages from rooms in a hotel to the office, or for similar functions.

Tele-thermometer. A thermometer with electric attachment for indicating or recording its indications at a distance.

Tempering, Electric. A process of tempering metals by electrically produced heat. The article is made part of an electric circuit. The current passing through it heats it, thereby tempering it. For wire the process can be made continuous. The wire is fed from one roll to another, and if required one roll may be immersed in a liquid bath or the wire between the rolls may be led therein. The current is brought to one roll and goes through the wire to the other. As it does this the wire is constantly fed from one roll to another. The bath may be used as described to cool it after the heating. The amount of heating may be regulated by the rate of motion of the wire.

528 STANDARD ELECTRICAL DICTIONARY.

Ten, Powers of. This adjunct to calculations has become almost indispensable in working with units of the C. G. S. system. It consists in using some power of 10 as a multiplier which may be called the factor. The number multiplied may be called the characteristic. The following are the general principles.

The power of 10 is shown by an exponent which indicates the number of ciphers in the multiplier. Thus 10^2 indicates 100; 10^3 indicates 1,000 and so on.

The exponent, if positive, denotes an integral number, as shown in the preceding paragraph. The exponent, if negative, denotes the reciprocal of the indicated power of 10. Thus 10^-2 indicates 1/100; 10^-3 indicates 1/1000 and so on.

The compound numbers based on these are reduced by multiplication or division to simple expressions. Thus: 3.14 X 10^7 = 3.14 X 10,000,000 = 31,400,000. 3.14 X 10^-7 = 3.14/10,000,000 or 314/1000000000. Regard must be paid to the decimal point as is done here.

To add two or more expressions in this notation if the exponents of the factors are alike in all respects, add the characteristics and preserve the same factor. Thus:

(51X 10^6) + (54 X 10^6) = 105 X 10^6. (9.1 X 10^-9) + (8.7 X 10^-9) = 17.8 X 10^-9.

To subtract one such expression from another, subtract the characteristics and preserve the same factor. Thus:

(54 X 10^6) - (51 X 10^6) = 3 X 10^6.

If the factors have different exponents of the same sign the factor or factors of larger exponent must be reduced to the smaller exponent, by factoring. The characteristic of the expression thus treated is multiplied by the odd factor. This gives a new expression whose characteristic is added to the other, and the factor of smaller exponent is preserved for both,

Thus: (5 X 10^7) + (5 X10^9) = (5 X 10^7) + (5 X 100 X 10^7) = 505 X 10^7.

The same applies to subtraction. Thus: (5 X 10^9) - (5 X 10^7) = (5 X 100 X 10^7) - (5 X 10^7) = 495 X 10^7.

If the factors differ in sign, it is generally best to leave the addition or subtraction to be simply expressed. However, by following the above rule, it can be done. Thus:

Add 5 X 10^-2 and 5 X 10^3. 5 X 10^3 = 5 X 10^5 X 10^-2 (5 X 10^5 X 10^-2) + (5 X 10^-2) = 500005 X 10^-2

This may be reduced to a fraction 500000/100 = 5000.05.

To multiply add the exponents of the factors, for the new factor, and multiply the characteristics for a new characteristic. The exponents must be added algebraically; that is, if of different signs the numerically smaller one is subtracted from the other one, and its sign is given the new exponent.

Thus; (25 X 10^6) X (9 X 10^8) = 225 X 10^14. (29 X 10^ -8) X (11 X 10^7) = 319 X 10^-1 (9 X 10^8) X (98 X 10^2) = 882 X 10^1

529 STANDARD ELECTRICAL DICTIONARY.

To divide, subtract (algebraically) the exponent of the divisor from that of the dividend for the exponent of the new factor, and divide the characteristics one by the other for the new characteristic. Algebraic subtraction is effected by changing the sign of the subtrahend, subtracting the numerically smaller number from the larger, and giving the result the sign of the larger number. (Thus to subtract 7 from 5 proceed thus; 5 - 7 = -2.)

Thus; (25 X 10^6) / (5 X 10^8) = 5 X 10^-2 (28 X 10^-8) / (5 X 10^3) = 5.6 X 10^-11

[Transcriber's note: I have replaced ordinary exponential notation by the more compact and simpler "programming" representation. The last two example would be: 25E6 / 5E8 = 5E-2 28E-8 / 5E3 = 5.6E-11 ]

Tension. Electro-motive force or potential difference in a current system is often thus termed. It is to be distinguished from intensity or current strength, which word it too greatly resembles.

Tension, Electric. (a) The condition an electrified body is brought into by electrification, when each molecule repels its neighbor. The condition is described as one of self-repulsion.

(b) The voltage or potential difference of a circuit is also thus termed.

Terminal. The end of any open electric circuit, or of any electric apparatus; as the terminals of a circuit, dynamo, or battery.

Terminal Pole. In telegraph line construction the last pole of a series; one beyond which the line is not carried. Such pole, as the pull of the wires is all in one direction, requires special staying or support. The regular line poles are free from this strain, as the wire pulls in both directions.

Tetanus, Acoustic. A term in electro-therapeutics. An effect produced on a nerve by very rapidly alternating induced currents. The currents are produced by an induction coil with a vibrator giving a musical note. This is a species of gauge of proper frequency of alternations.

Theatrophone. An apparatus worked by automatic paying machinery by which a telephone connection is made with a theatre or opera by the deposition of a coin in a slot.

Therm. A unit of heat. It has been proposed by the British Association and amounts to a redefinition of the smaller calorie. It is the amount of heat required to raise the temperature of one gram of water one degree centigrade, starting at the temperature of maximum density of water.

530 STANDARD ELECTRICAL DICTIONARY.

Thermaesthesiometer. An electro-therapeutic instrument for testing the sensitiveness of the surface of the body to changes of temperature. Vessels of mercury are provided with thermometers to indicate their temperature. One vessel is surrounded by an electric conductor wound in a number of turns. The temperature is raised by passing a current through this. By successive applications of the vessels to the same spot upon the skin the power of differentiating temperatures is determined.

Thermo Call. (a) An electric alarm or call bell operated by thermo-electric currents. It may serve as a fire alarm or heat indicator, always bearing in mind the fact that differential heat is the requisite in a thermo-electric couple.

(b) See Thermo-electric Call.

Thermo-chemical Battery. A voltaic battery in which the electro-motive force is generated by chemical action induced by heat.

The chemical used generally is sodium nitrate or potassium nitrate. The positive plate is carbon. On heating the battery the nitrate attacks the carbon, burning it and produces potential difference. For negative plate some metal unattacked by the nitrate may be employed.

Fig. 330. POUILLET'S THERMO-ELECTRIC BATTERY.

Thermo-electric Battery or Pile. A number of thermo-electric couples q. v., connected generally in series.

In Nobili's pile the metals are bismuth and antimony; paper bands covered with varnish are used to insulate where required. In Becquerel's pile copper sulphide (artificial) and German silver, (90 copper, 10 nickel) are the two elements. The artificial copper sulphide is made into slabs 4 inches long, 3/4 inch wide, and 1/2 inch thick (about). Water is used to keep one set of junctions cool, and gas flames to heat the other set. In Fig. 331, c, d represent the binding screws. The couples are mounted on a vertical standard, with adjusting socket and screw B, so that its lower end can be immersed in cold water, or raised therefrom as desired.

531 STANDARD ELECTRICAL DICTIONARY.

FIG. 331. BECQUEREL'S THERMO-ELECTRIC BATTERIES.

Fig. 332 shows one couple of the battery. S is artificial antimony sulphide; M is German silver; m is a protecting plate of German silver to save the sulphide from wasting in the flame.

Fig. 332. ELEMENTS OF BECQUEREL'S THERMOELECTRIC BATTERIES.

Clamond's pile has been used in practical work. The negative element is an alloy of antimony, 2 parts, zinc, 1 part. The positive element is tin plate. Mica in some parts, and a paste of soluble glass and asbestus in other parts are used as insulators. They are built up so as to form a cylinder within which the fire is maintained. The air is relied on to keep the outer junctions cool. The temperature does not exceed 200° C. (392° F.)

Sixty such elements have an electro-motive force of 300 volts and an internal resistance of 1.5 ohms. Such a battery requires the consumption of three cubic feet of gas per hour. (See Currents, Thermo-electric. )

532 STANDARD ELECTRICAL DICTIONARY.

Thermo-electric Call. A thermostat arranged to ring a bell or to give some indication when the temperature rises or falls beyond certain points. It may be a compound bar of brass and steel fixed at one end and free for the rest of its length. Its end comes between two adjustable contacts. As the temperature rises it bends one way (away from the brass side) and, if hot enough, touching a contact gives one signal. If the temperature falls it curves the other way, and if cold enough touches the other contact, giving another signal. (See Thermostat, Electric.)

Thermo-electric Couple. If two dissimilar conductors form adjacent parts of a closed circuit, and their junction is at a different temperature than that of the rest of the circuit, a current will result. Such pair of conductors are called a thermo-electric couple. They may be joined in series so as to produce considerable electro-motive force. (See Thermo-electricity and other titles in thermo-electricity.)

The efficiency of a thermo-electric couple according to the second law of thermo-dynamics is necessarily low--not over 10 per cent.

Thermo-electric Diagram. A diagram indicating the change in potential difference for a fixed difference of temperature between different metals at different temperatures. It is laid out with rectangular co-ordinates. On one axis temperatures are laid off, generally on the axis of abscissas. On the other axis potential differences are marked. Different lines are then drawn, one for each metal, which show the potential difference, say for one degree centigrade difference of temperature between their junctions, produced at the different temperatures marked on the axis of abscissas.

Fig. 333· THERMO-ELECTRIC DIAGRAM, GIVING POTENTIAL DIFFERENCE IN C. G. S. UNITS.

Thus taking copper and iron we find at the temperature 0° C. (32° F.) a difference of one degree C. (1.8° F.) in their junctions will produce a potential difference of 15.98 micro volts, while at 274.5° C. (526.1° F.) the lines cross, and zero difference of potential is indicated. Taking the lead line on the same diagram it crosses the iron line a little above 350° C. (662° F.), indicating that if one junction is heated slightly above and the other is heated slightly below this temperature no potential difference will be produced. Lead and copper lines, on the other hand, diverge more and more as the temperature rises.

533 STANDARD ELECTRICAL DICTIONARY.

Thermo-electric Inversion. The thermo-electric relations of two conductors vary at different temperatures. Sometimes at a definite point they have no electro-motive force and after passing this point the positive plate becomes a negative one and vice versa. This is inversion, or reversal. (See Thermo-electric Diagram.)

Synonym-- Thermo-electric Reversal.

Thermo-electricity. Electric energy, electro-motive force or electrification produced from heat energy by direct conversion. It is generally produced in a circuit composed of two electric conductors of unlike material, which circuit must possess at least two junctions of the unlike substances. By heating one of these to a higher temperature than that of the other, or by maintaining one junction at a different temperature from that of the other a potential difference is created accompanied by an electric current.

In many cases differential application of heat to an identical material will develop potential difference. This effect, the converse of the Thomson effect, is not used to produce currents, as in a closed circuit the potential differences due to differential heating would neutralize each other.

Thermo-electric Junction. A junction between two dissimilar conductors, which when heated or cooled so as to establish a differential temperature, as referred to the temperature of the other junction, produces potential difference and an electric current.

Thermo-electric Pile, Differential. A thermo-electric pile arranged to have opposite faces subjected to different sources of heat to determine the identity or difference of temperature of the two sources of heat. It corresponds in use to a differential air thermometer.

Thermo-electric Power. The coefficient which, multiplying the difference of temperature of the ends of a thermo-electric couple, gives the potential difference, expressed in micro-volts. It has always to be assigned to a mean or average temperature of the junctions, because the potential difference due to a fixed difference of temperature between two metals varies with the average temperature of the two junctions. (See Thermo-electric Diagram.)

For bismuth and antimony at 19.5° C. (67.1° F.) it is 103 microvolts per degree Centigrade (1.8° F.). This means that if one junction is heated to 19° C. and the other to 20° C. (66.2° F. and 68.0° F.) a potential difference of 103 micro-volts will be produced.

The potential difference is approximately proportional to the difference of temperature of the two junctions if such difference is small. Hence for large differences of potential the thermo-electric power coefficient does not apply.

As a differential function it is thus deduced by Sir William Thomson, for expressing the E. M. F. in a thermo-electric circuit: If a circuit is formed of two metals with the junctions at indefinitely near temperatures, t and t + dt, and dE is the E. M. F. of the circuit, then the differential coefficient dE/dt is called the thermo-electric power of the two metals for the temperature t.

534 STANDARD ELECTRICAL DICTIONARY.

Thermo-electric Series. The arrangement of possible thermoelectric elements, q. v., in a table in the order of their relative polarity. Bismuth and antimony form a couple in which when their junction is heated the bismuth acts as the positive or negatively charged element and antimony as the negative or positively charged. Between these two extremes according to Seebeck the series runs as follows:

Antimony, Silver, Copper, Arsenic, Gold, Platinum, Iron, Molybdenum, Palladium, Steel, Tin, Cobalt, Cadmium, Lead, Nickel, Tungsten, Mercury, Bismuth. Zinc, Manganese,

A differential temperature of 1° C. (1.8° F.) in a bismuth-antimony couple maintains a potential difference of 103 micro-volts.

Matthiessen gives a different series; it is arranged in two columns; the first column has positive coefficients annexed the second has negative. On subtracting the greater one from the lesser, which, if the two elements are in different columns, of course amounts to adding after changing the negative sign, the relative potential difference due to the combination is obtained. + - Bismuth 25 Gas Coke 0.1 Cobalt 9 Zinc 0.2 Potassium 5.5 Cadmium 0.3 Nickel 5 Strontium 2.0 Sodium 3. Arsenic 3.8 Lead 1.03 Iron 5.2 Tin 1 Red Phosphorous 9.6 Copper 1 Antimony 9.8 Silver 1 Tellurium 179.9 Platinum 0.7 Selenium 290

Thus the relative E. M. F. of a bismuth-nickel couple, as both are in the + column, would be 25 - 5 = 20; that of a cobalt-iron couple, one being in the + column the other in the - column, would be 9 + 5.2 = 14.2. Alloys are not always intermediate to their constituents, and small amounts of impurities affect the results largely. This may account for the discrepancies of different observers. Other compounds could be introduced into the series.

Artificial silver sulphide has been used by Becquerel in a thermo-electric battery.

535 STANDARD ELECTRICAL DICTIONARY.

Thermo-electric Thermometer. A species of differential thermometer. It consists of two thermo-electric junctions connected in opposition with a galvanometer in the circuit. Any inequality of temperature in the two ends or junctions produces a current shown by the galvanometer. It may be used to determine the temperature of a distant place, one of the junctions being located there and the other being under control of the operator. If the latter junction is heated until no current is produced its temperature is evidently equal to that of the distant couple or junction. The heating may be done with hot water or mercury, or other melted metal. The temperature of the water, or other substance, gives the temperature of the distant place.

Thermolysis. Decomposition by heat; dissociation. All compound bodies are decomposable by heat if it is intense enough. Hence at very elevated temperatures there can be no combustion.

Synonym--Dissociation.

Thermometer. An instrument for indicating the intensity of heat. Three scales of degrees of heat are used in practise, the Fahrenheit, Réamur, and Centigrade, each of which is described under its own title. (See Zero, Thermometric-Zero, Absolute.) The ordinary thermometer depends on the expansion of mercury; in some cases alcohol is used. Besides these the compound bar principle as used in the thermostat (see Thermostat, Electric) is employed.

Thermometer, Electric. (a) A thermometer whose indications are due to the change of resistance in conductors with change of temperature. Two exactly similar resistance coils maybe electrically balanced against each other. On exposing one to a source of heat, its resistance will change and it will disturb the balance. The balance is restored by heating the other coil in a vessel of water when the temperature of the water gives the temperature of both coils. The coils are enclosed in water-tight metallic cases.

Synonym--Electric Resistance Thermometer.

(b) A differential thermometer may be made by connecting with a pair of conductors, two thermo-electric couples in opposition to each other, and including a galvanometer in series. On heating the junction of one couple more than that of the other a current at once goes through the galvanometer.

(c) (See Thermometer, Kinnersley's.)

Synonym--Thermo-electrometer.

536 STANDARD ELECTRICAL DICTIONARY.

Fig. 334. KINNERSLEY'S THERMOMETER.

Thermometer, Kinnersley's. A thermo-electrometer. A large glass tube is mounted on a standard and communicates with a small tube parallel to it. Water is poured in so as to rise in the small tube. Two wires terminating in bulbs enter the large tube by its top and bottom. The upper wire can be adjusted by moving up and down through a stuffing box. On discharging a Leyden jar through the space between the knobs on the two wires the water for a moment rises in the small tube. There is little or no accuracy in the instrument. It is allied to the electric mortar (see Mortar, Electric) as a demonstrative apparatus.

Synonyms--Electric Thermometer--Thermo-electrometer.

Thermo-multiplier. A thermo-electric battery including a number of couples. The term is generally applied to a small battery with its similar junctions facing in one direction and used for repeating Melloni's experiments on radiant energy, or so-called radiant heat.

537 STANDARD ELECTRICAL DICTIONARY.

Thermophone. An apparatus for reproducing sounds telephonically by the agency of heat; a receiving telephone actuated by heat. Thus a wire may be attached to the centre of a diaphragm and kept in tension therefrom, and the transmitting telephone current may be caused to pass through it. The wire changes in temperature and consequently in length with the pulses of current going through it and vibrates the diaphragm, reproducing the sound. It is to be distinguished from the thermo-electric telephone which involves the action of potential difference produced by thermo-electric action.

Thermostat, Electric. A thermostat or apparatus, similar to a thermometer in some cases, for closing an electric circuit when heated. It is used in connection with automatic fire alarms to give warning of fire. For this use a temperature of 52° C. (125° F.) is an approved one for setting one at, to complete the circuit. It is also applied to regulation of temperature, as in incubators.

(a) One kind of thermostat consists of a compound bar wound into a spiral and fastened at one end, to which a terminal of a circuit is connected. The bar may be made of two strips of brass and iron riveted together, and wound into a spiral. When such a bar is submitted to changes of temperature it bends in different directions, because brass expands and contracts more under changes of temperature than does iron. A contact point, to which the other terminal is connected, is arranged to make contact with the spiral at any desired degree of temperature, thus closing an electric circuit and ringing a bell, opening or closing a damper, or doing anything else to notify an attendant or to directly change the temperature.

If the brass forms the outside of the spiral, increase of temperature makes the bending of the spiral bring the coils still closer. If the brass forms the inside, increase of temperature makes the spiral tend to become less close. As shown in the cut, the brass should lie along the inside of the spiral.

Sometimes a straight compound bar is used, one of whose ends is fastened and the other is free. As the temperature changes such a bar curves more or less, its free end moving to and fro. Two contact screws are provided, one on each side of its free end. If the temperature falls it makes contact with one of these; if the temperature rises, it makes contact with the other. Thus it may close one of two circuits, one for a fall and the other for a rise in temperature.

It is well to introduce a third bar between the brass and iron ones, made of some material of intermediate coefficient of expansion.

(b) Another kind of thermostat comprises a vessel of air or other gas, which, expanding by heat, actuates a piston or other device and closes an electric circuit. Synonym--Electro-pneumatic Thermostat.

(c) Another form utilizes the expansion of mercury. The mercury is made part of an open electric circuit. As it expands it comes in contact with the other terminal of the circuit, thus completing it, when the current gives an alarm or does as is provided for in the apparatus employed.

Thermostats may be worked on either open or closed circuits; normally the circuit may be open as described and may close on rise of temperature, or it may be normally closed and open as the temperature rises.

Fig. 335. ELECTRIC THERMOSTAT.

538 STANDARD ELECTRICAL DICTIONARY.

Thomson Effect. In an unequally heated conductor the differential heating is either increased as in iron, or diminished as in copper by a current. In lead the phenomenon does not occur. It is termed the Thomson effect. It is intimately related to the Peltier effect.

In a thermo-electric couple a heated junction is the source of electro-motive force, if heated more than other parts of the circuit. The current in a copper-iron junction flows from the copper to the iron across the heated junction. A hot section of an iron conductor next to a cold section of the same is a source of thermoelectricity, in the sense that the hot section is negative to the colder. A current passing from the hot to the cold iron travels against rising potentials, and cools the iron in the cooler parts. As it passes to the hotter parts it travels against falling potentials and hence heats the iron in these parts. In this way a current intensifies differential heating in an iron conductor.

In copper the reverse obtains. In it the thermo-electric relations of hot and cold copper are the reverse of those of iron, and a current tends to bring all parts of a differentially heated copper conductor to an identical temperature.

As a current travels in iron from hot to cold it absorbs heat; in copper traveling from cold to hot it absorbs heat.

The convection of heat by a current of electricity in unequally heated iron is negative, for it is opposed to that convection of heat which would be brought about by the flow of water through an unequally heated tube. In copper, on the other hand, the electric convection of heat is positive. (Daniell.)

The above effects of the electric current upon an unequally heated conductor are termed the Thomson effects. In iron, at low red heat, they are reversed and are probably again reversed at higher temperatures.

539 STANDARD ELECTRICAL DICTIONARY.

Three Wire System. A system of distribution of electric current for multiple arc or constant potential service. It is the invention of Thomas A. Edison.

It includes three main wires which start from the central station or generating plant, and ramify with corresponding reduction in size, everywhere through the district or building to be lighted. As ordinarily carried out when dynamos are used, the dynamos are arranged in groups of two. One lateral lead starts from the negative binding post of one dynamo. The positive terminal of this dynamo connects to the negative of the other. Between the two dynamos the central or neutral lead is connected. The other lateral lead starts from the positive binding post of the second dynamo.

The lamps or other appliances are calculated for the potential difference of a single dynamo. They are arranged between the neutral wire and the laterals, giving as even a disposition as possible to the two laterals.

Fig. 336. DIAGRAM OF THREE WIRE SYSTEM SHOWING NEUTRAL WIRE.

If evenly arranged and all burning or using current, no current goes through the neutral wire. If all the lamps situated on one lateral are on open circuit all the current goes through the neutral wire. In other cases the neutral wire receives the excess of current only.

The advantages of the system are that it uses smaller wire than the two wire system for lamps of the same voltage. If lamps of double the voltage were used the two wire system would be most economical.

540 STANDARD ELECTRICAL DICTIONARY.

Four wire and five wire systems have been more or less used, based on identical considerations, and involving in each case the coupling of three or of four dynamos respectively, or else employing a dynamo with special armature connections to give the requisite three-fold or four-fold division of total potential. In the five wire system the total voltage is four times that of a single lamp, the lamps are arranged four in series across the leads and the central wire is the only one that can be considered a neutral wire. When lamps are burning entirely from three side-leads they constitute a sort of three wire system by themselves, and their central wire may for the time be a neutral wire.

In some of the three wire mains, especially in the larger sizes, the neutral wire is made of much smaller section than that of a lateral conductor, because in extensive districts it is practically impossible that the current should be concentrated in the neutral wire.

Throw. In a galvanometer the instantaneous deflection of the needle when the contact or closing of the circuit is instantaneous, or when the discharge is completed before the needle begins to move. The throw of the needle is the datum sought when the ballistic galvanometer is used.

Synonym--Elongation.

Throw-back Indicator. A drop annunciator, whose shutter or drop is electrically replaced.

Thrust-bearings. Bearings to support the end-thrust or push of a shaft. In disc armatures where the field-magnets attract the armatures in the direction of their axis of rotation, thrust-bearings have to be provided. In ordinary cylinder or drum armatures end-thrust is not applied, as a little end motion to and fro is considered advantageous as causing more even wear of the commutator surface.

Thunder. The violent report which, as we hear it, succeeds the lightning flash in stormy weather. It is really produced simultaneously with the lightning and is supposed to arise from disturbance of the air by the discharge. The rolling noise has been attributed to successive reflections between clouds and earth, and to series of discharges reaching the ear from different distances and through air of varying density. The subject is obscure. By timing the interval from lightning flash to the report of the thunder an approximate estimate of the distance of the seat of discharge can be made. The first sound of the thunder should be timed. An almost concurrence of thunder and lightning indicates immediate proximity of the discharge.

[Transcriber's note: The speed of sound at sea level is about 5 seconds per mile.]

Ticker. A colloquial name for a stock or market report automatic printing telegraph, which prints its quotations and messages on a long tape.

541 STANDARD ELECTRICAL DICTIONARY.

Time Constant. (a) When current is first turned into a circuit of considerable self-induction it is resisted rather by the inductance than by the resistance. It is governed by the ratio of resistance and self-induction and this factor represents the time which it takes for the current to reach a definite fraction of its final strength. This fraction is (2.7183 - 1)/2.7183 or 0.63. 2.7183 is the base of the Napierian system of logarithms. Thus if in any circuit we divide the inductance in henries by the resistance in ohms, the ratio gives the time-constant of the circuit, or it expresses the time which it will take for the current to reach 0.63 of its final value.

(b) In a static condenser the time required for the charge to fall to 1/2.7183th part of its original value.

Time Cut-outs. Cut-outs which automatically cut storage batteries out of the charging circuit when they are sufficiently charged.

Time-fall. In a secondary battery the decrease with use of electromotive force maintained by a primary or secondary battery. As the battery becomes spent its voltage falls. The conditions of the fall are represented by its discharging curve. (See Curve, Discharging.)

Time-reaction. A term in electro-therapeutics; the period of time occupied in the passage of the effects of an electric current from nerve to muscle.

Time-rise. In a secondary battery the increase of electromotive force produced during the charging process. Its rate and conditions are graphically shown in the charging curve. (See Curve, Charging.)

Tin. A metal; one of the elements; symbol, Sn; atomic weight, 117.8; equivalent, 58.9 and 29.5; valency, 2 and 4; specific gravity, 7.3. It is a conductor of electricity.

Relative resistance, compressed, (Silver = 1) 8.784 Specific resistance at 0° C. (32° F.), 13.21 microhms. Resistance of a wire at 0° C. (32° F.), (a) 1 foot long, weighing 1 grain, 1.380 ohms. (b) 1 foot long, 1/1000 inch thick, 79.47 " (c) 1 meter long, weighing 1 gram, .9632 " (d) 1 meter long, 1 millimeter thick, .1682 " Resistance of a 1 inch cube at 0° C. (32° F.), 5.202 microhms. Percentage of variation in resistance per degree C. (1.8° F.), at about 20° C. (68° F.), .0365 Electro-chemical equivalent (hydrogen = .0105), .619 mgs. .310 "

542 STANDARD ELECTRICAL DICTIONARY.

Tinnitus, Telephone. A nervous affection of the ear, of the order of professional cramp; it is attributed to too much use of the telephone.

Tin Sounders. A recent addition to the single needle telegraph. (See Telegraph, Single Needle.) It consists of small tin plates, cut and bent, and so fitted in pairs to the instrument, that the needle as deflected strikes one or the other on its right and left hand movements. The sounders can be made to give sufficiently distinctive sounds to make sound-reading, q. v., possible. Commercial tin plate, which is really tinned iron, seems to give the best results.

Fig. 337. TIN SOUNDERS.

Tissandier's Solution. A solution for bichromate batteries. It is composed as follows: Water, 100 parts by weight potassium bichromate, 16 parts 66° sulphuric acid, 37 parts.

Tongue of Polarized Relay. The German silver extension of the vibrating or oscillating member of a polarized relay, corresponding to the armature of an ordinary relay.

Tongue of Polarized Relay, Bias of. In a Siemens' polarized relay the pole pieces are adjustable so that they may be brought nearer to or withdrawn from the tongue. One of the poles is adjusted so as to be nearer the tongue. This one-sided adjustment is the bias. Its effect is that when the relay is unexcited this pole attracts the armature so that it normally is drawn towards it. This ensures the normal contact of the tongue either with the contact point, or with the insulated stop piece or adjustment screw. Without bias the armature remains in contact with or drawn towards whichever pole it was last attracted to. In its usual use a bias is given it.

Top, Magnetic. A toy illustrating magnetic attraction. It consists of a disc or body of lead or other material, through which a magnetized steel spindle pointed at its lower end is thrust. A number of short pieces of iron wire are used with it. It is spun like an ordinary top upon the point of the spindle and one of the pieces of iron wire is laid by the side of its point. As it turns the magnetic adherence causes the piece of wire to be carried along in one direction by the rotation of the spindle, until the end is reached, when it goes over to the other side of the spindle and travels back again.

By using bent pieces of wire of various shapes the most curious effects are produced. Circles and S shaped pieces give good effects. To increase the mysterious effect covered iron wire (bonnet wire) may be employed.

Fig. 338. MAGNETIC TOP.

543 STANDARD ELECTRICAL DICTIONARY.

Torpedo, Electric. (a) A fish, the Raia Torpedo, which possesses the power of giving electric shocks. (See Ray, Electric.)

(b) An instrument of war; a torpedo whose operations include electrical discharge or other electric function or factor of operation.

Torpedo, Sims-Edison. A torpedo driven by an electric motor, and also steered by electricity. Its motions are all controlled from the shore. The torpedo proper is carried some distance below the surface of the water by a vessel immediately above it, from which it is suspended by two rigid bars. In the torpedo is a cable reel on which the conducting cable is disposed. An electric motor and controlling gear are also contained within the torpedo. In its front the explosive is placed. It is driven by a screw propeller actuated by the electric motor. As it moves it pays out cable so that it has no cable to draw after it through the water, the cable lying stationary in the water behind it. This avoids frictional resistance to its motion. The maintenance of the torpedo at a proper depth is one of the advantages of the system.

544 STANDARD ELECTRICAL DICTIONARY.

Torque. A force tending to produce torsion around an axis. An example is the pulling or turning moment of an armature of an electric motor upon its shaft. It is often expressed as pounds of pull excited at the end of a lever arm one foot long.

The expression is due to Prof. James Thompson, then of the University of Glasgow.

"Just as the Newtonian definition of force is that which produces or tends to produce motion (along a line), so torque may be defined as that which produces or tends to produce torsion (around an axis). It is better to use a term which treats this action as a single definite entity than to use terms like 'couple' and 'moment,' which suggest more complex ideas." (S. P. Thompson.)

A force, acting with radius r gives a torque equal to f X r ; f and r may be expressed in any units. S. P. Thompson gives the following equivalents :

To reduce dyne-centimeters to gram centimeters, divide by 981 dyne-centimeters to meter-kilograms divide by 981E5 dyne-centimeter, to pound-feet divide by 13.56E6 pound-feet to meter-kilograms divide by 7.23

In each of these compound units the first unit is the force and the second unit is the radius or lever arm of the torque.

Synonyms--Turning Moment--Moment of Couple--Axial Couple--Angular Force--Axial Force.

Torsion Balance, Coulomb's. Originally an apparatus in which electrostatic attraction or repulsion is measured against the torsion of a filament, often of silk-worm cocoon fibre. It consists in one form of a cylindrical glass vessel in which a light shellac needle is suspended horizontally by a fibre. This needle carries at one end a gilded disc or sphere and is suspended by a fine wire, or filament. A proof plane, q. v., is excited by touching it to the body under trial; it is then inserted in the case. The disc on the needle is first attracted and then repelled. The position finally taken by the needle is noted. The force of torsion thus produced is determined by twisting the filament by the torsion head on the top of the apparatus so as to move the needle a certain distance towards the proof plane. The more the torsion-head has to be turned to carry the needle through a specified arc the greater is the torsion effected or the greater is the repulsion exerted, The torsional force of a wire is proportional to the angle of torsion; this gives the basis for the measurement.

With magnetic needle it is used to measure magnetic repulsion and attraction. The best material for the filament is quartz, but the instrument is not very much used.

Torsion Galvanometer. A galvanometer in which the torsion required to bring the index back to zero, when the current tends to displace it, is made the measure of the current strength or of the electro-motive force. It involves the use of a torsion head, q. v., or its equivalent.

545 STANDARD ELECTRICAL DICTIONARY.

Torsion Head. The handle and disc from whose undersurface the filament depends to which the needle or magnet is attached. It is turned to measure the torsional effect, the edge of the disc being marked or graduated so as to give the angle of deflection required to overcome the effect of the torque of the needle.

Torsion Suspension. Suspension by one or more wires, fibres, or ribands, involving the restitutive force of torsion. Thus fibre suspension, q. v., is a variety of torsion suspension.

Often a single riband of steel stretched horizontally and secured at both ends is used, the suspended object, e. g., a balance beam, being attached at its own centre to the centre of the stretched riband. Quite sensitive balances are constructed on this principle. It is peculiarly available where an electric current is to be transmitted, as absolute contact is secured, as in William Thomson's ampere balances.

Touch. A term applied to methods of magnetization, as "single touch," "double touch," or "separate touch," indicating how the poles of the inducing magnet or magnets are applied to the bar to be magnetized. Under the titles of Magnetization the different methods are described.

Tourmaline. A mineral; a subsilicate; characterized by the presence of boric trioxide, which replaces aluminum oxide. It is notable for possessing pyro-electric properties. (See Pyro-electricity.)

Tower, Electric. The tower used in the tower system, q. v., of arc light illumination.

Tower System. In electric lighting the system of lighting extended areas by powerful arc lamps placed on high towers, generally of iron or steel frame-work. The lights are thus maintained at a high elevation, giving greater uniformity of illumination than if they were lower, but at the expense of considerable light which is lost. Sometimes wooden masts are employed instead of towers.

The principle involved is that the intensity of light at any place given by a source of illumination varies with the square of its distance from the place in question. Hence in using strong arc lights it is an object to have the distances of all parts of the area illuminated at as nearly uniform distances from the light as possible. An approximation to uniformity is secured by placing the lamps at a very high elevation.

546 STANDARD ELECTRICAL DICTIONARY.

Transformer. In alternate current lighting the induction coil by which the primary current with high initial electro-motive force is caused to produce a secondary current with low initial electromotive force.

A typical transformer consists of a core of thin iron sheets. The primary is of comparatively thin wire and often of ten or more times as many turns as the secondary. The latter is of thicker wire. Where the ratio of 10 to 1 as regards number of turns in the primary and secondary obtains, the initial E. M. F. of the secondary is one-tenth that of the primary circuit.

The cores are laminated, as described, to avoid the formation of Foucault currents.

The counter-electro-motive force of the transformer when the secondary circuit is open, prevents any but the slightest current from passing through the primary. In proportion as the secondary is closed and its resistance diminished, as by lighting more lamps in parallel, the counter-electro-motive force of the transformer falls and more current passes through the primary.

Fig. 339. FERRANTI'S TRANSFORMER.

The economy of the apparatus is in the fact that counter-electromotive force reduces current through a conductor without absorbing any energy. A resistance coil cuts down a current, but absorbs energy equal to the current multiplied by the potential difference between the terminals of the coil. This electric energy is converted into heat energy and is wasted. But the counter-electromotive force of a transformer is exerted to reduce current without production of heat and with little waste of energy. This is one of the advantages of the alternating current system of distribution of electric energy.

The object of a transformer being to secure safety to the person or to life by the separation of the high potential primary or street circuit, and the low potential house circuit, any contact of the two circuits in the converter is a source of danger. Special care should be taken to ensure absence of leakage, as it is termed. Mica or other insulation is sometimes employed to prevent the wires from coming in contact by piercing or sparking with the core and with each other.

547 STANDARD ELECTRICAL DICTIONARY.

Transformer, Commuting. A type of continuous current transformer, resembling a dynamo with armature and field both stationary, but with revolving commutator, by which the magnetic polarity of a double wound armature is made to rotate. This secures the desired action, of a change or lowering of potential.

Transformer, Continuous Alternating. An apparatus for transforming a continuous into an alternating current or the reverse. The combination of a continuous current dynamo with an alternating current one is sometimes employed. It is a form of motor dynamo.

Another type is a regular dynamo with ordinary commutator and with, in addition thereto, two, three or four contact rings, connecting to as many symmetrically disposed points in the winding of the armature. This will give out or receive alternating currents of two, three or four phases according to the number of collecting rings. One winding serves for both alternating and continuous currents.

Transformer, Continuous Current. A machine of the dynamo type for changing the potential of a circuit. In one form two armatures are mounted on one shaft in a single field or in separate fields; one is a motor armature driven by the original current; the other generates the new current. This is a motor dynamo. In 1874 Gramme constructed a machine with ring armature with two windings, of coarse and fine wire respectively, and with independent commutators. Such dynamo could transform currents up or down.

Continuous current transformers have attained an efficiency of 83 per cent. at full load, and of 75 per cent. at half load. Owing to the balancing of the self-inductions of the two windings these machines do not spark. As the driven and driving parts are contained in one rotating part their friction is very slight.

Transformer, Core. A transformer wound upon an enclosed core, such as the hedgehog transformer (see Transformer, Hedgehog), or common induction coil.

548 STANDARD ELECTRICAL DICTIONARY.

Transformer, Hedgehog. An induction coil transformer whose iron core is composed of a bundle of iron wires, which after the wire windings are in place have their ends spread out to reduce to some extent the reluctance of the circuit, which at the best is high, as the air acts as the return circuit.

This transformer has a low degree of hysteresis; and its efficiency for very small loads or for no load is superior to that of the closed magnetic circuit transformer.

Fig. 340. SWINBURNE'S HEDGEHOG TRANSFORMER.

Transformer, Multiple. A transformer connected in parallel with others between the two leads of the primary circuit. The term refers to the connection only and not to any peculiarity of the transformer itself.

Transformer, Oil. A transformer with oil insulation. The advantage of this insulation is that if pierced it at once closes, so that no permanent injury ensues. It is a self-healing form of insulation.

Transformer, Series. Transformers connected in series upon the primary circuits. The term, like "multiple transformers," only applies to the connection, not to the transformer. Series transformers are but little used.

Transformer, Shell. A transformer with its iron core entirely outside of and enclosing the primary and secondary winding. It may be made by the use of outer iron wire windings as core.

Transformer, Welding. The transformer used for electric welding. (See Welding, Electric.) It is a transformer with very long primary and exceedingly short and thick secondary. It is used with the alternating current in the primary, and produces in the secondary circuit which includes the bars to be welded a very low potential difference.

Owing to the very low resistance of the secondary circuit this low electro-motive force produces a very strong current, which develops the requisite heat. The same type of transformer is used for brazing and similar purposes.

549 STANDARD ELECTRICAL DICTIONARY.

Transmitter. In general electric phraseology, any instrument which produces signals to be transmitted through a line or circuit is a transmitter. Thus the Morse key in telegraphy or the Blake transmitter in telephony are examples of such.

Transmitter, Carbon. A form of microphone used as a telephone transmitter. (See Carbon Telephone.)

Transposing. A method of laying metallic circuits for telephoning. The wires at short intervals are crossed so that alternate sections lie on opposite sides of each other. It is done to avoid induction.

Transverse Electro-motive Force. Electro-motive force in a substance in which electric displacement is taking place, produced by a magnetic field. It is sometimes assigned as the cause of the Hall effect, q. v.

Trimmer, Brush. A shears for cutting off evenly and squarely the ends of copper dynamo brushes. The brushes when uneven from wear are removed from the brush holders, and their ends are sheared off in the trimmer.

Trolley. A grooved metallic pulley or set of pulleys which runs along an active wire of a circuit, a lead from which trolley goes to earth or connects with another wire, so that the trolley takes current generally for operating a street car motor placed upon the circuit leading from it; a rolling contact with an electric lead.

Trolleys are principally used on electric railroads, and are now universally of the sub-wire system, being at the end of a pole which is inclined backward and forced upward by springs, so as to press the trolley against the bottom of the wire. Thus the trolley does not increase the sagging of the wire, but tends to push it up a little in its passage.

Trolley, Double. A trolley with two rollers or grooved wheels, placed side by side, and running on two parallel leads of wire. It is adapted to systems employing through metallic trolley lines with the motors in multiple arc, connecting or across the two leads.

Trolley Section. An unbroken or continuous section of trolley wire.

Trouvé's Solution. An acid exciting and depolarizing solution for a zinc-carbon battery. Its formula is as follows: Water, 80 parts; pulverized potassium bichromate, 12 parts; concentrated sulphuric acid, 36 parts; all parts by weight. The pulverized potassium bichromate is added to the water, and the acid is added slowly with constant stirring. As much as 25 parts potassium bichromate may be added to 100 parts of water. The heating produced by the acid and water dissolves nearly all the potassium salt. Use cold.

550 STANDARD ELECTRICAL DICTIONARY.

True Contact Force. A species of electro-motive force whose existence is supposed to be proved by the Peltier effect. The lowering in temperature of a contact of dissimilar metals is attributed to a force that helps the current on its way if in the direction of thermo-current proper to the junction and opposing it if in the reverse. The true contact force is taken to explain this phenomenon; thermo-electric force cannot, as there is no heat or cold applied to the junction.

Trumpet, Electric. An apparatus consisting of a vibrating tongue, kept in motion by electricity as in the buzzer, q. v., placed in the small end of a trumpet-shaped tube.

Trunking Switchboard. A telephone switchboard arranged in sections, which sections are connected by trunk lines, through which trunk lines the desired connections are made.

Trunk Lines. In telephone distribution systems, the lines connecting different stations, or different sections of a switch-board and used by anyone requiring such connections; one trunk line answers for a number of subscribers.

Tube, Electric. A tube of glass around which is pasted a series of tinfoil circles, diamonds, or little squares, or other form of interrupted conductor. The pieces generally are placed in the line of a spiral. When a static discharge of electricity takes place along the conductor a row of bright sparks is produced at the breaks in the conductor. These by reflection are multiplied apparently, and a beautiful effect of intersecting or crossing spirals of sparks is presented.

The experiment is in line with the luminous pane and lightning jar, and is used merely as a demonstration, or lecture experiment.

Synonym--Luminous Tube.

Tubular Braid. A braid woven of tissue or worsted, and tubular or hollow. Its object is to provide a covering which can be drawn over joints in covered wires. In making the joint the ends of the wires are necessarily bared, and a short piece of tubular braid is used for covering them. It is drawn by hand over the joint.

Turns. An expression applied to the convolutions of wire in a solenoid, electro-magnet, or other apparatus or construction of that kind. A turn indicates a complete encircling of the core or axis of the object. Thus a wire wound five times around a bar gives five turns.

While this is its primary meaning the term if compounded may refer to virtual turns. Thus an ampere-turn means one ampere passing through one turn. But ten ampere-turns may mean ten amperes passing through ten turns, five amperes passing through two turns, and so on. This use is analogous to a dimension of length in a compound word, as foot-pound.

[Transcriber's note: "But ten ampere-turns may mean ten amperes passing through ONE turn or one ampere through ten turns, and so on."]

There may be a number of kinds of turns qualified by descriptive adjectives, as series-turns, the turns of wire in a series circuit of a compound dynamo. In the same way there are shunt-turns. If series ampere-turns or shunt ampere-turns are meant the word ampere should be included.

551 STANDARD ELECTRICAL DICTIONARY.

Turns, Dead, of a Dynamo. The rotations of a dynamo armature while it is building itself up or exciting itself. The expression is a bad one, as it is likely to be confounded with the dead turns of armature wire.

Turns, Primary Ampere-. The ampere-turns in a primary circuit of an induction coil or transformer. In an electric welding transformer, or in the transformer used in the alternating current system, where efficiency is an important element, the ampere-turns in primary and secondary for an efficiency of 100 per cent. should be equal. In the case of an experimental induction coil other considerations outweigh that of mere efficiency. Insulation, including security from piercing, and the production of as long a spark as possible, are, in these cases, the controlling consideration.

[Transcriber's note: A 100 per cent efficient transformer is impossible, but over 99 per cent is common. At room temperature there is always some lost flux, eddy currents and resistive losses.]

Turns, Secondary Ampere-. The ampere-turns on the secondary circuit of an induction coil or transformer. These depend on the path provided for the current. If of negligible inductance, such as a number of incandescent lamps would provide, the ampere-turns should be equal to those of the primary coil. (See Turns, Primary Ampere.)

Typewriter, Electric. A typewriter in which the work of printing or of pressing the type faces against the paper, or printing ribbon, is done by electro-magnetic attraction. The keys close electric circuits, throwing the electro-magnetic action into play. This involves the use of electricity for what is ordinarily only a mechanical process. The strength of the impression, however, is independent of the touch of the operator. It has not come into very extensive use.

[Transcriber's note: IBM introduced widely used electric typewriters in 1935.]

Ultra-gaseous Matter. Gas so rarefied that its molecules do not collide or very rarely do so.

Experiments of very striking nature have been devised by Crookes and others to illustrate the peculiar phenomena that this matter presents. The general lines of this work are similar to the methods used in Geissler tube experiments, except that the vacua used are very much higher.

When the vacuum is increased so that but one-millionth of the original gas is left the radiant state is reached. The molecules in their kinetic movements beat back and forth in straight lines without colliding, or with very rare collisions. Their motions can be guided and rendered visible by electrification. A tube or small glass bulb with platinum electrodes sealed in it, is exhausted to the requisite degree and is hermetically sealed by melting the glass. The electrodes are connected to the terminals of an induction coil or other source of high tension electrification. The molecules which come in contact with a negatively electrified pole are repelled from it in directions normal to its surface. They produce different phosphorescent or luminous effects in their mutual collisions.

Thus if they are made to impinge upon glass, diamond or ruby, intense phosphorescence is produced. A piece of platinum subjected to molecular bombardment is brought to white heat. A movable body can be made to move under their effects. Two streams proceeding from one negative pole repel each other. The stream of molecules can be drawn out of their course by a magnet.

The experiments are all done on a small scale in tubes and bulbs, resembling to a certain extent Geissler tubes.

[Transcriber's note: These effects are caused by plasma--ionized gas and electrons.]

552 STANDARD ELECTRICAL DICTIONARY.

Unbuilding. The loss of its charge or excitation by a self-exciting dynamo. It is the reverse of building-up. The latter indicates the exciting of the field by the action of the machine itself; the former the spontaneous loss of charge on open circuit or from other cause.

Underground Conductor. An electric conductor insulated and placed under the surface of the earth, as distinguished from aerial conductors.

Underground Electric Subway. A subway for the enclosing of electric telegraph and other conductors under the surface, generally in the line of streets, to do away with telegraph poles and aerial lines of wire. Many systems have been devised. The general type includes tubes called ducts in sets, called conduits, bedded in concrete or otherwise protected. Every two or three hundred feet the sets lead into a cistern-like cavity called a manhole. The insulated wires or cables, generally sheathed with a lead alloy are introduced into the tubes through the man-holes. A rope is first fed through the tube. To do this short rods which screw together are generally employed. One by one they are introduced, and each end one is screwed to the series of rods already in the duct. When the end of the duct is reached the rope is fastened to the last rod, and the rods are then drawn through, unscrewed one by one and removed, the rope following them. By means of the rope a windlass or capstan may be applied to draw the cable into the duct. At least at every second man-hole the cables have to be spliced.

Each cable may contain a large number of conductors of small size for telephoning, or a smaller number for electric light and power. The tendency is now to separate the different classes of wires in important lines, placing the heavier wires on one side of the street and the telephone and telegraph wires on the other. This of course necessitates two separate conduits.

The advantage of underground distribution affects not only the appearance of streets in doing away with unsightly telegraph poles, but it also removes an element of danger at fires. Aerial wires interfere greatly with the handling of ladders at fires, and expose the firemen who attempt to cut them to danger to their lives from shock.

533 STANDARD ELECTRICAL DICTIONARY.

Unidirectional. adj. Having one direction as a "unidirectional current" or "unidirectional leak." The term is descriptive, and applicable to many cases.

Uniform. adj. Unvarying; as a uniform potential difference, uniform current or conductor of uniform resistance per unit of length. The term is descriptive, and its application and meaning are obvious.

Uniform Field of Force. A field of evenly distributed force; one in which the number of lines of force per unit of area of any equipotential surface is the same.

Unipolar. adj. Strictly speaking this term means having only one pole, and is applied to magnets, armatures and the like. In its use a solecism is involved, for there is no such condition possible as unipolar magnetism or distribution of magnetism. An example of its use is shown in unipolar magnets. (See Magnet, Unipolar.)

Unipolar Armature. An armature of a unipolar dynamo; an armature whose windings continuously cut the lines of force about the one pole, and hence whose polarity is unchanged in its rotation.

Unipolar Current Induction. Current induction produced by moving a conductor through a magnetic field of force so that it always cuts the lines in similar relation to itself. Thus it produces a constant current through its own circuit, if a closed one, and no commutator is required. As this case always in practice amounts to the cutting of lines of force in the neighborhood of a single pole the term unipolar is employed to designate the action.

The simplest representation of unipolar induction is the rotating of a conductor around the end of a bar magnet, its axis of rotation corresponding with the axis of the magnet.

Unipolar Dynamo. A dynamo in which one part of the conductor slides on or around the magnet, so as always to cut lines of force near the same pole of the magnet.

Unit. A directly or indirectly conventional and arbitrary quantity, in terms of which measurements of things with dimensions expressible in the chosen units are executed.

Thus for length the c. g. s. unit is the centimeter; the B. E. unit is the foot.

554 STANDARD ELECTRICAL DICTIONARY.

Unit, Absolute. A unit based on the three fundamental units of length, mass and time. These units are the centimeter, gram and second. Each one in itself may be termed a fundamental absolute unit. The system of such units is termed the centimeter-gram-second system.

Unit, Angle. A factor or datum in angular velocity, q. v. It is the angle subtended by a portion of the circumference equal in length to the radius of the circle. It is equal very nearly to 57.29578° or 57° 17' 44.8".

Unit, B. A. This term, while logically applicable to any of the British Association units, is often restricted to the ohm as formerly defined by the British Association, the B. A. Unit of Resistance, q. v.

Unit, Fundamental. The three units of length, mass and time, the centimeter, gram and second, are termed fundamental units. On them is based the absolute system of units, and on multiples of them the practical system of units.

Unit Jar. A Leyden jar which is used as a unit of measure of charge.

It consists of a Leyden jar about 4 inches long and 3/4 inch diameter, with about 6 square inches of its outer and the same of its inner surface coated with tinfoil. It is placed between a source of electricity and a larger jar or battery of jars which is to be charged. The inner coating connects with the machine; the outer coating with the jars to be charged. Short conductors terminating in knobs connect with inner and outer coatings, and the knobs are adjusted at any desired distance apart.

By the charging operation the large jar or battery of jars receives a charge by induction, and the charge of the small jar is at first equal to this quantity. After a while a spark passes from knob to knob, discharging the small jar. This indicates the reception by the large jars of the quantity of electricity represented by the charge of the small jar. The charging goes on, and for every spark approximately the same quantity of electricity is received by the larger jars.

The sparking distance m is directly proportional to the quantity of electricity, and inversely proportional to the area of coated surface, or is proportional to the potential difference of the two coats. This is only true for short sparking distance, hence for accuracy the knobs should be adjusted not too far from each other.

555 STANDARD ELECTRICAL DICTIONARY.

Unit of Supply. A commercial unit for the sale of electric energy, as defined provisionally by the English Board of Trade; 1,000 amperes flowing for one hour under an E. M. F. of 1 volt; 3,600,000 volt-coulombs, or 1,000 watt-hours, are its equivalent. It is equal to 1000/746 = 1.34 electric horse power.

Synonym--Board of Trade Unit.

[Transcriber's note: Now called a kilowatt-hour.]

Units, Circular. A system of units of cross-sectional area, designed especially for use in describing wire conductors. The cross-sectional area of such is universally a circle, and the areas of two wires of different sizes vary with the square of their radii or diameters. Hence if the area of a circle of known diameter is determined it may be used as a unit for the dimensions of other circles. Any other circle will have an area proportioned to the area of the unit circle, as the squares of the diameters are to each other.

In practise the commonest circular unit is the circular mil. This is the area of a circle one mil, 1/1000 inch, in diameter and is equal to .0000007854 square inch. A wire two mils in diameter has an area of four circular mils; one ten mils in diameter has an area of one hundred circular mils.

Thus if the resistance of a given length of wire 1 mil in diameter is stated, the corresponding resistance of the same length of wire of the same material, but of other diameter, is given by dividing the first wire's resistance by the square of the diameter in mils of the wire in question.

As it is a basic unit, most conveniently applied by multiplication, the smaller units are used; these are the circular mil, and circular millimeter.

Units, Derived. Units derived by compounding or other processes, from the three fundamental units. Such are the units of area, volume, energy and work, momentum and electric units generally. In some cases the dimensions of the derived unit may reduce to those of a simple unit as inductance reduces to length, but the unit, as deduced from the fundamental ones, is still a derived unit.

Units, Practical. A system of units employed in practical computation. The absolute units, especially in electricity, have been found too large or too small, and the attempt to make them more convenient has resulted in this system. It is based on exactly the same considerations as the absolute system of units, except that multiples of the original fundamental units of length, mass, and time have been taken as the base of the new system. These basic units are multiples of the fundamental units. They are the following: The unit of length is 1E9 centimeters; the unit of mass is 1E-11 gram; the unit of time remains 1 second.

While this has conduced to convenience in giving better sized units, micro- and mega-units and other multiples or fractions have to be used. The following are the principal practical electric units:

Electrostatic Electromagnetic C. G. S Units. C. G. S. Units. Intensity-Ampere equal to 3E9 1E-1 Quantity-Coulomb " 3E9 1E-1 Potential-Volt " (1/3)* E-2 1E8 Resistance-Ohm " (1/9)* E-11 1E9 Capacity-Farad " 9E11 1E-9

556 STANDARD ELECTRICAL DICTIONARY.

Universal Battery System. A term in telegraphy. If several equal and high resistance telegraphic circuits are connected in parallel with each other from terminal to terminal of a battery of comparatively low resistance each circuit will receive the same current, and of practically the same strength as if only one circuit was connected. This is termed the universal battery system. It is a practical corollary of Ohm's law. The battery being of very low resistance compared to the lines the joining of several lines in parallel practically diminishes the total resistance of the circuit in proportion to their own number. Thus suppose a battery of ten ohms resistance and ten volts E. M. F. is working a single line of one hundred ohms resistance. The total resistance of the circuit is then one hundred and ten ohms. The total current of the circuit, all of which is received by the one line is 10/110 = .09 ampere, or 90 milliamperes. Now suppose that a second line of identical resistance is connected to the battery in parallel with the first. This reduces the external resistance to fifty ohms, giving a total resistance of the circuit of sixty ohms. The total current of the circuit, all of which is received by the two lines in equal parts, is 10/60 = .166 amperes. But this is equally divided between two lines, so that each one receives .083 ampere or 83 milliamperes; practically the same current as that given by the same battery to the single line. It will be seen that high line resistance and low battery resistance, relatively speaking, are required for the system. For this reason the storage battery is particularly available. The rule is that the resistance of the battery shall be less than the combined resistance of all the circuits worked by it.

Unmarked End. The south-seeking pole of a magnet, so called because the other end, called the marked end, is usually marked with a scratch or notch by the maker, while the south pole is unmarked.

V. (a) Symbol for velocity.

(b) Symbol or abbreviation for volume.

(c) Symbol or abbreviation for volt.

557 STANDARD ELECTRICAL DICTIONARY.

V. A. Symbol or abbreviation for voltaic alternatives, q. v.

Vacuum. A space destitute of any substance. The great pervading substance is in general sense the atmosphere. It is the gaseous mixture which surrounds and envelopes the earth and its inhabitants. It consists of a simple mixture of oxygen, 1 part, nitrogen, 4 parts, with 4 to 6 volumes of carbonic acid gas in 10,000 volumes of air, or about one cubic inch to one cubic foot. It presses with a force of about 14.7 lbs. per square inch under the influence of the force of gravity. The term vacuum in practise refers to any space from which air has been removed. It may be produced chemically. Air may be displaced by carbonic acid gas and the latter may be absorbed by caustic alkali or other chemical. The air may be expelled and the space may be filled with steam which is condensed to produce the vacuum. Of course in all cases the space must be included in an hermetically sealed vessel, such as the bulb of an incandescent lamp. But the universal method of producing a vacuum is by air pumps. An absolute vacuum means the entire absence of gas or air, something almost impossible to produce. A high vacuum is sometimes understood to mean one in which the path of the molecules is equal in length to the diameter of the containing vessels, as in Crookes' Radiometer and other apparatus for illustrating the radiant condition of matter. The air left after exhaustion is termed residual air or residual atmosphere.

[Transcriber's note: Dry air is about .78 nitrogen, .21 oxygen, .01 argon, .00038 carbon dioxide, and trace amounts of other gases. Argon was suspected by Henry Cavendish in 1785. It was discovered in 1894 by Lord Rayleigh and Sir William Ramsay.]

Vacuum, Absolute. A space free of all material substance. It is doubtful whether an absolute vacuum has ever been produced.

Vacuum, High. An approximate vacuum, so nearly perfect that the molecules of the residual gas in their kinetic motions rarely collide, and beat back and forth between the walls of the containing vessel, or between any solid object contained in the vessel and the walls of the vessel. The gas in such a vacuum is in the radiant or ultra-gaseous state. (See Ultra-gaseous Matter.)

Vacuum, Low. A vacuum inferior to a high vacuum; a vacuum in which the molecules collide with each other and do not move directly from side to side of the containing vessel.

Vacuum, Partial. A space partially exhausted of air so as to contain less than an equal volume of the surrounding atmosphere. It really should come below a low vacuum, but is often treated as synonymous therewith.

Vacuum, Torricellian. The vacuum existing above the mercurial column in a barometer tube. The principle of this vacuum is applied in the Geissler and other air pumps. (See Pump, Geissler--Pump, Sprengel--Pump, Swinburne.)

558 STANDARD ELECTRICAL DICTIONARY.

Valency. The relative power of replacing hydrogen or combining therewith possessed by different elements; the number of atomic bonds belonging to any element. Thus oxygen has a twofold valency, is bivalent or is a dyad, and combines with two atoms of hydrogen because the latter has a unitary atomicity, is monovalent or is a monad.

Valve, Electrically Controlled. A valve which is moved by or whose movements are regulated by electricity.

In the block system of railroad signaling the semaphores are worked by weights and pneumatic cylinders and pistons. The valves for admitting or releasing the compressed air are operated by coil and plunger mechanism. There are many other instances of the control of valves by the electric current.

Vapor Globe. A protecting glass globe surrounding an incandescent lamp, when the lamp is to be used in an atmosphere of explosive vapor, as in mines or similar places; or when in a place where it is exposed to dripping water which would break the hot lamp bulb if it fell upon it.

Variable Period. The period of adjustment when a current is started through a conductor of some capacity. It is the period of duration of the variable state, q. v., in a conductor. As indicated in the next definition in a cable of high electrostatic capacity a variable period of nearly two minutes may exist. This indicates the retardation in signaling to be anticipated in cables and other lines of high capacity.

Variable State. When an electric circuit is closed the current starts through the conductor with its full strength from the point of closure, and advances with a species of wave front so that some time elapses before it attains its full strength in the most distant parts of the conductor, owing to its having to charge the conductor to its full capacity at the given potential. The state of the line while the current thus varies is called the variable state.

A long telegraph line when a message is being transmitted may be always in the variable state. The current at the receiving end may never attain its full strength.

In the case of such a conductor as the Atlantic cable, 108 seconds would be required for a current to attain 9/10 of its full strength at the distant end, and but 1/5 second to attain 1/100 of its final value. During the period of increase of current the variable state exists.

Variation of the Compass. The declination of the magnetic needle. (See Elements, Magnetic.) As the declination is subject to daily, annual and secular variations, it is unfortunate that this term is synonymous with declination. Thus the variation of the compass means its declination, while there is also the variation of the declination and of other elements. The term variation of the compass is more colloquial than the more definite expression "declination," or "magnetic declination."

559 STANDARD ELECTRICAL DICTIONARY.

Variometer. An apparatus used in determining the relative values of the horizontal component of the earth's magnetic field in different places.

Varley's Condenser. A static condenser whose conducting surfaces are platinum electrodes immersed in dilute sulphuric acid. When the potential difference is 1/50th that of a Daniell's cell, two square inches of platinum have a capacity equal to that of an air condenser whose plates have an area of 80,000,000 square inches, and separated 1/8th of an inch from each other. As the E. M. F. increases the capacity also increases.

Varley's Resistances. Variable resistances formed of discs of carbonized cloth, q. v., piled up, and pressed together more or less firmly to vary the resistance as desired.

Varnish. A glossy transparent coating of the nature of paint, applied as a protective, or ornamental coating to objects.

Varnish, Electric. Alcoholic or etherial varnishes are the best for electrical apparatus. They dry quickly and perfectly, and tend to form surfaces unfavorable to the hygroscopic collection of water. Sealing wax dissolved in alcohol, or shellac dissolved in the same solvent are used for electrical apparatus, although the first is rather a lacquer than a varnish. Etherial solution of gum-copal is used to agglomerate coils of wire. It is well to bake varnished objects to harden the coating.

Varnish, Red. A solution of sealing wax in 90 per cent. alcohol. It is best made thin and applied in several coats, each coat being allowed to dry perfectly before the next is applied. It is often seen on Leyden jars. It is a protector from surface leakage.

Vat. A vessel for chemical or other solutions. A depositing vat is one in which a plating solution is worked, for the deposition of electroplate upon articles immersed in the liquid, and electrolyzed by an electric current.

Velocity. The rate of motion of a body. It is usually expressed in distance traversed per second of time. The absolute unit is one centimeter per second or kine. The foot per second is very largely used also.

The dimensions of velocity are length (L) divided by time (T) or L/T.

Velocity, Angular. Velocity in a circle defined by the unit angle, or the angle which subtends a circular arc equal in length to itself. The radius of the circle traversed by the moving body does not enter into this definition, as the real velocity of the object is not stated. If its angular velocity and the radius of the path it travels are given its actual velocity can be deduced.

560 STANDARD ELECTRICAL DICTIONARY.

Velocity of Signaling. The speed of transmission of electric signals is affected by the nature of the line, as regards its static capacity, and by the delicacy of the receiving instruments, which may need a more or less strong current to be affected. Thus of an original current one per cent. may suffice to operate a sensitive instrument. This might give almost the velocity of light, while if the instrument would only respond to the full current nearly two minutes (see Variable State) might be required for the production of a signal.

Velocity Ratio. A term applied to the ratios existing between the electrostatic and electro-magnetic units. If we take as numerators the dimensions of the different qualities in the electrostatic system, and their dimensions in the electro-magnetic system as denominators, the fractions thus obtained reduce to expressions containing only velocity or V in some form. Thus if we divide the dimensions of the electrostatic quantity by the dimensions of electro-magnetic quantity the quotient is simply V or velocity. A like division for potential, electrostatic and electro-magnetic gives (1/V), and so on.

The value of the velocity ratio is very nearly 3E10 (sometimes given as 2.98E10) centimeters per second. This is almost exactly that of light (2.9992E10 centimeters per second.) This is one of the proofs of Clerk Maxwell's magnetic theory of light. (See Maxwell's Theory of Light.)

[Transcriber's note: The SI metre was defined in 1983 such that the speed of light in a vacuum is exactly 299,792,458 metres per second or about 186,282.397 miles per second.]

Ventilation of Armature. In a dynamo or motor ventilation of the armature is often provided for by apertures through it in order to prevent heating. This heating is caused by Foucault currents. By proper disposition of the interior of the armature with properly disposed vanes and orifices an action like that of a fan blower can be produced, which by creating a current of air cools the machine very efficiently.

Verticity, Poles of. Points upon the earth's surface where the horizontal component of magnetic force disappears, leaving only the vertical component active. The term is derived from the verticity of the dipping needle when over either of them.

561 STANDARD ELECTRICAL DICTIONARY.

Vibration Period. In electrical resonance the period of a vibration in an electrical resonator. The length of this period indicates the quality of the resonator in responding to electrical oscillations by sympathetic vibration. For conductors of small resistance the period is thus calculated. Let T be the period of one-half a full vibration; L the absolute coefficient of self-induction expressed in centimeters or in henries X 10-9; C the electrostatic capacity of the terminals, also expressed in the same unit; v the velocity of light in centimeters per second. Then we have the formula

T = PI * SquareRoot( L * C ) / v

[Transcriber's note: If the inductance is in henries and the capacitance in farads, frequency in hertz = 1/(2 * PI * squareRoot( L * C ) )]

Vibration, Sympathetic. A vibration in a cord or other body susceptible of elastic vibration produced by the vibrations of exactly the same period in a neighboring vibrating body. Thus if two tuning forks are tuned to precisely the same pitch, and are placed near each other, if one is sounded it will start the other into vibration by sympathy.

In electricity its application is found in electric resonance experiments. The resonator has a definite period of electric resonance, and is made to give a spark by the exciter of identical period. This is by what may be called electric sympathetic vibration, and is exactly analogous to the action of the tuning forks upon each other.

Vibrator, Electro-magnetic. The make and break mechanism used on induction coils, or other similar apparatus in which by alternate attractions by and releases from an electro-magnet an arm or spring is kept in motion. In most cases the work is done by a single magnet, whose armature is attracted to the magnet, when the latter is excited, but against the action of a spring which tends to pull it away from the magnet. In its motions a make and break action is produced, to give the requisite alternations of attraction and release. Two electro-magnets may be connected so as alternately to be excited and keep an arm carrying a mutual armature in vibration, or the same result may be attained by a polarized relay. The make and break is illustrated under Bell, Electric--Coil, Induction-- Anvil.

Villari's Critical Value. Magnetization induced or residual in a wire is diminished on stretching, provided that the magnetization corresponds to an inducing force above a certain critical value, known as above; this being (Sir Wm. Thomson) about 24 times the terrestrial intensity. Below that critical value tension increases the magnetization of a magnetized wire. The effects of transverse expansive stress are opposed to those of longitudinal stretching. (Daniell.)

Viole's Standard of Illuminating Power. A standard authorized by the International Congress of 1881. It is the light given by one square centimeter of platinum, melted, but just at the point of solidification. It is equal to 20 English standard candles almost exactly.

It has not been very widely accepted, the tendency among photometrists being to adhere to the old standards, carcel or candle. It is obvious that actual use of the Viole would be very inconvenient and would involve expensive apparatus, difficult to work with.

Synonym--Viole.

562 STANDARD ELECTRICAL DICTIONARY.

Vis Viva. The kinetic energy of a body in motion; "mechanical energy."

Vitreous Electricity. Positive electricity; the electricity produced on the surface of glass by rubbing it with silk and other substances. (See Electrostatic Series.)

The term "positive electricity" should be allowed to supplant it. It is the analogue and opposite of resinous electricity.

Vitriol, Blue. A colloquial or trade name for copper sulphate (Cu SO4).

Vitriol, Green. A colloquial or trade name for ferrous sulphate (Fe SO4).

Vitriol, White. A colloquial or trade name for zinc sulphate (Zn SO4).

Volt. The practical unit of electro-motive force or potential difference. It may be referred to various data.

An electro-motive force of one volt will cause a current of one ampere to flow through a resistance of one ohm.

A condenser of one farad capacity charged with one coulomb will have a rise of potential of one volt.

The cutting of 100,000,000 lines of force per second by a conductor induces one volt E. M. F.

A Daniell's battery gives an E. M. F. of 1.07 volts; about the most familiar approximate standard that can be cited.

It is equal to 1/300 absolute electrostatic unit.

It is equal to 1E8 absolute electro-magnetic units.

[Transcriber's note: The SI definition of a volt: The potential difference across a conductor when a current of one ampere dissipates one watt of power.]

Voltage. Potential difference or electro-motive force expressed in volts; as a voltage of 100 volts. Thus voltage may express the electro-motive force absorbed in a conductor, while electro-motive force is a term generally applied where it is produced, evolved or present in the object. The term voltage of a lamp expresses simply the volts required, but does not suggest the possession of electromotive force.

563 STANDARD ELECTRICAL DICTIONARY.

Voltage, Terminal. The voltage or potential difference at the terminals of an electric current generator, such as a dynamo, as distinguished from the total electro-motive force of the dynamo or generator.

In batteries the distinction is not generally made in practice; the total electro-motive force of the battery is made the basis of calculations.

Voltaic. adj. This adjective is used to qualify a great many things appertaining to or connected with current electricity. It is derived from Volta, the inventor of the voltaic battery, and now tends to displace the term "galvanic," formerly in general use.

Voltaic Alternatives. A term used in electro-therapeutics or medical electricity to indicate an alternating battery current.

Synonym--Alternative current.

Voltaic Effect. The potential difference developed by contact of different conductors. It is the basis of the contact theory, q. v., of electricity, although it may be accepted as the expression for a condition of things by those who reject the above theory. This potential difference is slight when the conductors are separated, but it is calculated that it would be enormous could the metals be so quickly separated as to hold each its own charge.

Thus if a copper and a zinc plate are assumed to be in contact, really 1/20000000 centimeter or 1/50000000 inch apart, they may be treated as a pair of condenser plates. Being so near, their density of charge, which is a strongly bound charge, is enormous. If it were possible to separate them without permitting any discharge, their potential would rise by the separation, on the principle of Epinus' condenser, q. v., to such an extent that they would spark through twenty feet of air. (See Volta's Fundamental Experiment.)

Voltaic Electricity. Electricity of low potential difference and large current intensity; electricity such as produced by a voltaic battery; current or dynamic electricity as opposed to static electricity.

Voltameter. In general an apparatus for determining the quantity of electricity passing through a conductor by measuring the electrolytic action it can perform.

Voltameter, Copper. An apparatus which may be of similar construction with the silver voltameter (see Voltameter, Silver), but in which a copper anode and a solution of copper sulphate are substituted for the silver anode and silver nitrate solution. One coulomb corresponds to .329 milligram or .005084 grain of copper deposited. It is not accepted as of as high a standard as the silver voltameter.

The electrodes should be placed half an inch from each other. Two square plate electrodes may conveniently be used, and not less than two square inches on each plate should be the area per ampere of current.

564 STANDARD ELECTRICAL DICTIONARY.

Voltameter, Differential, Siemens'. A volume or gas voltameter with duplicate eudiometers and pairs of electrodes. It is used for determining the resistance of the platinum conductor used in his pyrometer. A current divides between the two voltameters; in one branch of the circuit the platinum conductor is placed, in the other a known resistance. The current strength varying inversely with the resistance, the resistances of the two conductors are inversely proportional to the gas evolved.

Voltameter, Gas. A voltameter whose indications are based on the electrolysis of water, made an electrolyte by the addition of sulphuric acid. The gases evolved are measured. It may take several forms.

In one form it is an apparatus consisting of a single eudiometer or graduated glass tube with upper end closed and its lower end or mouth open, collecting the mixture of hydrogen and oxygen.

In the form shown in the cut three tubes are connected, the side tubes representing eudiometers. For each side tube there is a platinum electrode. In this apparatus the oxygen and hydrogen are connected in opposite tubes. A is an open tube filled with dilute sulphuric acid. By opening the cocks on B and C they can both be completely filled with acid. As shown in the cut, this operation is not yet completed. The hydrogen alone may in this case be measured.

The mixed gas voltameter has only one eudiometer.

The exact equivalents are only approximately known. The volume of mixed gases per coulomb is given as .1738 cubic centimeters (Ayrton); .172 cubic centimeters (Hospitalier); and other values by other authorities. The hydrogen is equal to 1/3 of the mixed gases almost exactly.

Synonyms--Volume Voltameter--Sulphuric Acid Voltameter.

The gas is measured at 0º (32º F.) and 76 centimeters, or 30 inches barometer.

Fig. 341. GAS VOLTAMETER.

565 STANDARD ELECTRICAL DICTIONARY.

If the gas is measured in cubic inches, the temperature in degrees F., and the barometric height in inches, the following formula may be used for reduction to standard pressure and temperature. It is the volume corresponding to one coulomb. ( .01058 * 30 * (491 + Fº - 32) ) / (h* 491)

For the metric measurements and degrees C. (.1738 * 76 * (273 + Cº)) / (h X 273)

Voltameter, Silver. An apparatus consisting of a platinum vessel containing a solution of silver nitrate into which solution a silver anode dips, whose end is wrapped in muslin to prevent the detachment of any particles. When a current is passed by connecting one terminal to the dish and the other to the rod, securing a proper direction of current, silver will be deposited on the dish and the same amount will be dissolved from the rod. The dish is weighed before and after the test. Its increase in weight gives the silver deposited.

FIG. 342. SILVER VOLTAMETER.

In the cut Ag is the silver anode, Pt is the platinum dish, r is the conducting rod, p is a wooden standard, Cu is a copper plate on which the dish rests and which also serves as a conductor and contact surface, b is a muslin cloth to place over the silver plate to prevent detached particles falling in the dish; s s' are the binding screws.

The weight of silver corresponding to a coulomb is given variously by different authorities. Ayrton and Daniell take 1.11815 milligrams or .017253 grain of metallic silver. Other determinations are as follows: 1.1183 milligrams (Kohlrausch). 1.124 " (Merscart).

The solution of silver nitrate should be from 15 to 30 per cent. of strength. The current should not exceed one ampere per six square inches; or in other words not more than about 3/1000 grain of silver should be deposited per second on a square inch area of the dish. The edge of the silver disc or anode should be about equidistant from the side and bottom of the dish. The latter notes are due to Lord Rayleigh.

566 STANDARD ELECTRICAL DICTIONARY.

Voltameter, Weight. A voltameter in which the amount of decomposition is determined by weighing the products, or one of the products of the electrolysis. The titles Voltameter, Copper, and Voltameter, Silver, may be cited.

Fig. 343. WEIGHT VOLTAMETERS.

In the cuts are shown examples of weight gas voltameters. These are tubes light enough to be weighed when charged. Each contains a decomposition cell T, with its platinum electrodes, and charged with dilute sulphuric acid, while t is calcium chloride or other drying agent to collect any water carried off as vapor or as spray by the escaping gases; c are corks placed in position when the weighing is being executed, so as to prevent the calcium chloride from absorbing moisture from the air.

In use the tubes are weighed. They are then connected to the circuit, after removal of the corks, and the decomposition proceeds. After a sufficient time they are removed, the corks put in place, and they are weighed again. The loss gives the water decomposed.

The water corresponding to one coulomb is .09326 milligram .001430 grain, Ayrton, .092 " Hospitalier, .0935 " Daniell.

567 STANDARD ELECTRICAL DICTIONARY.

Voltametric Law. The law on which voltameters are based. The amount of chemical decomposition produced by an electric current in a given electrolyte is proportional to the quantity of electricity passed through the solution.

Fig. 344. VOLTA'S FUNDAMENTAL EXPERIMENT.

Volta's Fundamental Experiment. The moistened finger is placed on the upper plate of a condensing or electrophorous electroscope. The other hand holds a plate of zinc z, soldered to a plate of copper c. The lower plate is touched with the copper. On removing the cover the gold leaves l diverge and with negative electricity. Hence zinc is supposed to be positively electrified when in contact with copper. The experiment is used to demonstrate the contact theory of electricity.

568 STANDARD ELECTRICAL DICTIONARY.

Volta's Law of Galvanic Action. The electro-motive force between any two metals in an electro-chemical series (see Electro-Chemical Series) is equal to the sum of the electro-motive forces between all the intervening metals.

Volta's Law of Thermo-electricity. In a compound circuit, consisting of a number of different metals, all points of which are at the same temperature, there is no current.

Volt, B. A. The volt based on the B. A. ohm. It is equal to .9889 legal volt.

Volt, Congress. The volt based upon the congress or legal ohm; the legal volt.

Volt-coulomb. The unit of electric work; the watt-second; it is equivalent to 1.0E7 ergs. .24068 gram degree C. (calorie) .737337 foot lbs., .00134 horse power seconds.

Volt Indicator. A form of easily read voltameter for use in electric light stations and for similar work.

Volt, Legal. The legal volt based upon the legal ohm. It is equal to 1.00112 B. A. volt.

Voltmeter. An instrument for determining the potential difference of any two points.

In many cases it is a calibrated galvanometer wound with a coil of high resistance. The object to be attained is that it shall receive only an insignificant portion of current and that such portion shall suffice to actuate it. If connected in parallel with any portion of a circuit, it should not noticeably diminish its resistance.

The divisions into which ammeters range themselves answer for voltmeters. In practice the same construction is adopted for both. The different definitions of ammeters in disclosing the general lines of these instruments are in general applicable to voltmeters, except that the wire winding of the coils must be of thin wire of great length. The definitions of ammeters may be consulted with the above understanding for voltmeters.

In the use made of voltmeters there is a distinction from ammeters. An ammeter is a current measurer and all the current measured must be passed through it. But while a voltmeter is in fact a current measurer, it is so graduated and so used that it gives in its readings the difference of potential existing between two places on a circuit, and while measuring the current passing through its own coils, it is by calibration made to give not the current intensity, but the electro-motive force producing such current.

In use it may be connected to two terminals of an open circuit, when as it only permits an inconsiderable current to pass, it indicates the potential difference existing between such points on open circuit. Or it may be connected to any two parts of a closed circuit. Owing to its high resistance, although it is in parallel with the intervening portion of the circuit, as it is often connected in practice, it is without any appreciable effect upon the current. It will then indicate the potential difference existing between the two points.

569 STANDARD ELECTRICAL DICTIONARY.

Voltmeter, Battery. A voltmeter for use in running batteries. In one form (Wirt's) it is constructed for a low range of voltage, reading up to two and a half volts and having exactly one ohm resistance, thus giving the battery some work to do.

Voltmeter, Cardew. A voltmeter in which the current passing through its conductor heats such conductor, causing it to expand. Its expansion is caused to move an index needle. By calibration the movements of the needle are made to correspond to the potential differences producing the actuating currents through it. The magnetic action of the current plays no part in its operation. It is the invention of Capt. Cardew, R. E.

The construction of the instrument in one of its most recent forms is shown in the cut. On each side of the drum-like case of the instrument are the binding screws. These connect with the blocks m and n. To these the fine wire conductor is connected and is carried down and up over the two pulleys seen at the lowest extremity, its centre being attached to