Chapter 4

Referring to Fig. 1, A and B are two troughs rectangular in cross section attached to the supports in such positions that their axes are inclined to one another so as to form the letter V, as shown in the figure. Within these troughs slide freely the two carbon pencils, which are of circular cross section, meeting, when no current is passing, at the lower point, E. The carbon-holder, B, to the right of the figure, is rigidly attached to the framing of the lamp, but the trough, A, which carries the negative carbon, is attached to the framing by a pivot shown in the figure, and on this pivot the carbon holder can rock, its motion being controlled by the position of the armature of an electro-magnet, M, the coils of which are included in the circuit of the apparatus. By this means, the moment the current is established through the lamp, the armature is attracted, and the points of the two carbons are separated, thus forming the arc. The positive carbon, B, is held from sliding and dropping through the trough by the gentle pressure against it of the smaller carbon rod, C¹, which also slides in a trough or tube fixed in such a position that the point of contact between the two rods is sufficiently near the arc for the smaller rod to be slowly consumed as the other is burnt away; the latter in that way is permitted to slide gradually down the trough as long as the lamp is in action. The negative carbon-holder, A, is provided with a little adjustable platinum stop, E, which by pressing against the side of the conical end of the negative carbon, holds the latter in its place and prevents it sliding down the trough except under the influence of the slow combustion of the cone during the process of producing the arc. The position of the stop with respect to the conical end is determined by a small adjusting screw shown in the figure. This arrangement of stop is identical in principle with that adopted by Messrs. Siemens Brothers in their "abutment pole" lamp, and is found to work very well in practice on the negative electrodes, but is inapplicable on the positive carbons on account of the higher temperature of the latter, which is liable to destroy the metallic stop by fusion, and it is for this reason that the positive carbon in Mr. Hedges' lamp is controlled by the method we have already described. For alternating currents, however, the abutment stop may be used on both electrodes.

In order to maintain a good electrical contact between the fixed conducting portions of the lamp and the sliding carbons, Mr. Hedges fits to each carbon-holder a little contact piece, F F, hinged to its respective trough at its upper end, and carrying at its lower or free end a somewhat heavy little block of brass grooved out to fit the cylindrical side of the carbon, against which it presses with an even pressure. This arrangement offers another advantage, namely, that the length of that portion of the carbon rods which is conveying the current is always the same notwithstanding the shortening of their total length by combustion; the resistance of the carbon electrodes is, therefore, maintained constant, and, for the reason that the contact piece presses against the rods very near their lower ends, that resistance is reduced to a minimum. In this way very long carbons, such, for instance, as will burn for ten or sixteen hours, can be used without introducing any increase of resistance into the circuit. The length of the arc can be determined by the adjustment of the screw, G, by which the amount of movement of the armature is limited.

Fig. 2 represents a modified form of Mr. Hedges' lamp designed for installation when it is desirable to burn a number of lamps in series. In this arrangement the carbons are separated by the attractive influence of a solenoid upon an iron plunger, to which is attached (by a non-magnetic connection) the armature of an electro-magnet, the coils (which are of fine wire) forming a shunt circuit between the two terminals of the lamp, and so disposed with respect to the armature as to influence it in an opposite direction to that of the solenoid. When the circuit of the lamp is completed with the electric generator the carbons are drawn apart by the action of the solenoid on the plunger, and the distance to which they are separated is determined by the difference of attractive force exercised upon the armature by the solenoid and the magnet; but as the latter forms a short circuit to that of the arc, it follows that should the resistance of the arc circuit increase either through the arc becoming too long or through imperfection in the carbons or contacts, a greater percentage of current will flow through the magnet coils, and the arc will be shortened, thereby reducing its resistance and regulating it to the strength of the current. In other words, the distance between the carbons, that is to say, the length of the arc, is determined by the position of the armature of the electro-magnet between its magnets and the solenoid, which position is in its turn determined by the difference between the strength of current passing through the coil of the solenoid and that of the magnet.

Mr. Killingworth Hedges exhibits also a third form of his lamp, in most respects similar to the lamp figured in Fig. 1, but in which the ends of the two carbons rest against the side of a small cylinder of fireclay or other refractory material, which is mounted on a horizontal axis and can be rotated thereon by a worm and worm-wheel actuated by an endless cord passing over a grooved pulley. In the lamp one of the carbon-holders is rigidly fixed to the framing of the apparatus, and the other is mounted on a point so as to enable the length of the arc playing over the clay cylinder to be regulated by the action of an electro-magnet attracting an armature in opposition to the tension of an adjustable spring.

In the same exhibit will be found specimens of Mr. Hedges' two-way switches, which have been designed to reduce the tendency to sparking and consequent destruction which so often accompanies the action of switches of the ordinary form. The essential characteristic of this switch, which we illustrate in elevation in Fig. 3 and in plan in Fig. 4, lies first in the circular form of contact-piece shown in Fig. 4, and next in the fact that the space between the two fixed contact-pieces is filled up with a block composed of compressed asbestos, the surface of which is flush with the upper surfaces of the two contact-pieces. The circular contact-piece attached to the switch lever can be turned round so as to present a fresh surface when that which has been in use shows indications of being worn, and a good firm contact with the fixed contact-pieces is insured by the presence of a spiral spring shown in the upper figure, and which, owing to an error in engraving, appears more like a screw than a spring. In order to prevent bad connection through dust or other impurities collecting within the joint, the electrical connection between the fulcrum of the switch lever and the circular contact-piece is made through the bent spring shown edgeways in Fig. 3.--_Engineering._

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RAILWAY APPARATUS AT THE PARIS ELECTRICAL EXHIBITION.

_Lartigue's Switch Controller._--The object of this apparatus is to warn the switch tender in case the switch does not entirely respond to the movement of the maneuvering lever.

The apparatus, which is represented in the accompanying Figs. 1, 2, 3, and 4, consists of the following parts:

(1.) A mercurial commutator, O, which is fixed on a lever, B, connected with a piece, A, which is applied against the external surface of the web of the main rails, opposite the extremity of the switch plates;

(2.) A bar, C, which traverses the web of the rail and projects on the opposite side, and which carries a nut, D, against which the switch plate abuts;

(3.) An electrical alarm and a pile, located near the switch lever. As long as one of the two plates of the switch is applied against the rail, one of the two commutators is inclined and no current passes. A space of one millimeter is sufficient to bring the commutator to a horizontal position and to cause the electric alarm to ring continuously. If the apparatus gets out of order, it is known at once; for if the alarm does not work during the maneuver of the switch, the tender will be warned that the electric communications are interrupted, and that he must consequently at once make known the position of his switch until the necessary repairs have been made.

_Pedals for Transmitting Signals to Crossings._--On railways having a double track and doing a large amount of business it becomes very necessary to announce to the flagmen at railway crossings the approach of trains, so as to give them time to stop all crossing of the tracks. On railway lines provided with electro-semaphores there may be used for this purpose those small apparatus that have been styled semaphore repeaters.

Mr. Lartigue has invented two automatic apparatus, by means of which the train itself signals its approach.

1. The first of these, which is generally placed at about 6,000 feet from the point to be covered, consists (Figs. 5, 6, 7, and 8) of a very light pedal fixed to the inside of the rail, and acting upon a mercurial commutator. A spring, R, carried upon the arm, a, of a lever, A, projects slightly above the level of the rail, while the other arm, b, carries a commutator.

The spring, R, on being depressed tilts the box containing the mercury, closes the circuit, and causes an alarm, S, located at the crossing, to immediately ring. In this alarm (Fig. 8) a piece, P, is disconnected by the passage of the current into the electro-magnet, E, which attracts the armature, a, and, a permanent current being set up, the apparatus operates like an ordinary alarm, until the piece, P, is placed by hand in its first position again.

2. The second apparatus, exhibited by the Railway Company of the North, and also the invention of Mr. Lartigue, bears the name of the "Bellows Pedal." It consists (Figs. 9 and 10) of a pedal, properly so called, P, placed along the rail, one of its extremities forming a lever and the other being provided with a counterpoise, C. When a train passes over the pedal, the arm, B, fixed to its axle, on falling closes the circuit of an ordinary electrical alarm, and at the same time the bellows, S, becomes rapidly filled with air, and, after the passage of the train, is emptied again very slowly under the action of the counterpoise. The contact is thus kept up for some few minutes. This apparatus works very satisfactorily, but is cumbersome and relatively high-priced.

_The Brunot Controller as a Controller of the Passage of Trains._--The Brunot Controller, which has been employed for several years on the Railway of the North, is designed to control the regularity of the running of trains, and to make automatically a contradictory verification of the figures on the slips carried by the conductors. In Fig. 11 we give a longitudinal section of the apparatus. It consists of a wooden case containing a clockwork movement, H, upon the axle of which is mounted a cardboard disk, C, divided into hours and minutes, and regulated like a watch, that is to say, making one complete revolution in twelve hours. The metallic pencil, c, which is capable of displacing itself on the cardboard in a horizontal direction opposite a groove on the other side of the disk, traces, when pressure is brought to bear on it, a spiral curve. The transverse travel of the pencil is effected in ninety-six hours. The displacement of the pencil is brought about by means of a cam. Under the influence of the jarring of the train in motion, a weight, P, suspended from a flexible strip, l, strikes against the pencil, c, which traces a series of points. During stoppages there is, of course, an interruption in the tracing of the curve.

Up to this point no electricity is involved--the apparatus is simply a controller of regularity. Mr. Brunot has conceived the idea of utilizing his apparatus for controlling the passage of trains at certain determined points on the line; for example, at the top of heavy grades. For this purpose it has only been necessary to add to the apparatus that we have just described an electro-magnet, E, connected electrically with a fixed contact located on the line. When the current passes, that is to say, at the moment the circuit is closed by the passage of a train, the armature, A, is attracted, and the pencil marks a point on the cardboard disk. This modification of the apparatus has not as yet been practically applied.

_Electrical Corresponding Apparatus._--The object of these apparatus is to quickly transmit to a distance a certain number of phrases that have been prepared in advance. The Company of the North employs two kinds of correspondence apparatus--the Guggemos and the annunciator apparatus.

1. _The Guggemos Apparatus._--This apparatus serves at once as a manipulator and receiver, and consists of an inner movement surmounted by a dial, over the face of which moves an index hand. Around the circumference of the dial there is arranged a series of circular cases, C, containing the messages to be received, and similar triangular cases, containing the messages to be forwarded, radiating from the center of the dial. Between each of these there is a button, b.

Fig. 13 represents the interior of an apparatus for twenty messages. It consists of a key-board, M, an electro-magnet, B, a clock-work movement, Q, an escapement, s, and an interrupter, F G.

When one of the buttons, b, is pressed, one of the levers of the key-board arrangement touches the disk, M, which is insulated from the other portions of the key-board, and the current then passes from the terminal C to M, and there bifurcating, one portion of it goes to the bobbins of the apparatus and thence to the earth, while the other goes to actuate the correspondence apparatus. The index-hands of the two apparatus thereupon begin their movement simultaneously, and only stop when the pressure is removed from the button and the current is consequently interrupted. H is a ratchet-wheel, which, like the key-board, is insulated from the rest of the apparatus. The button, K, located over each of the dials, serves to bring the index-needles back to their position under the cross shown in Fig. 12. The key, X, serves for winding up the clock-work movement.

_The Annunciator Apparatus._--This apparatus, which performs the same role as the one just described, is simply an ingenious modification of the annunciator used in hotels, etc.

It consists of a wooden case, containing as many buttons as there are phrases to be exchanged. Over each button, b, there is a circular aperture, behind which drops the disk containing the phrase. Between the buttons and the apertures are rectangular plates, P, in which are inscribed the answers given by pressing on the button of the receiving tablet--a pressure which, at the same time, removes the corresponding disk from the aperture. Two disks located at the upper part carry these inscriptions: "Error, I repeat;" "Wait." The tablets on exhibition have eight disks, and can thus be used for exchanging six different phrases. In the interior, opposite each aperture, there is a Hughes magnet, between the arms of which there oscillates a vertical soft-iron rod, carrying a disk. The maneuver "is simple." By pressing upon a button there is sent into the bobbins of the magnet corresponding to this button a current which causes the disk to appear before one of the apertures, while at the same time an alarm begins to ring. The same maneuver performed by the agent at the receiving-post has the effect of causing the disk to disappear. The two contact springs in communication at each aperture with the alarm and the line are connected by a strip of ebonite, M, against the center of which presses the button.

_Electrical Controllers for Water-Tanks._--The object of these apparatus is to warn the person in charge of a water-tank that the latter is full, and that he must stop the engine-pump; or, that the tank is empty, and that he must at once proceed to fill it. The Company of the North has on exhibition two such apparatus--one of them Lartigue's, and the other Vérité's.

1. _The Lartigue Controller_ (Fig. 15).--This apparatus consists of a long lever, A, which carries at one of its extremities a funnel, E, having a very narrow orifice and which is placed under the overflow pipe of the tank. The lever is kept normally in a horizontal position by a counterpoise; but, as soon as the overflow runs into the funnel, the weight of the water tilts the lever, and the mercurial commutator, F, closes the circuit of a pile, which actuates an alarm-bell located near the pump and engine. The two stops, a and _a'_, limit the play of the lever.

2. _The Vérité Controller_ (Fig. 16).--This apparatus consists of a float, F, provided with a catch, C, calculated in such a way as to act only when the float has reached a certain definite height. At that moment it lifts the extremity of the weighted lever, E, which in falling back acts upon the extremity, a, of another lever, N, pivoted at the point, O. The piece, P, which is normally in contact with the magnet, A, being suddenly detached by this movement of the lever, N, the induced current which is then produced causes the display, near the pump, of a disk, Q, upon which is inscribed the word "Full." This is a signal to stop pumping.

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THE TELEPHONIC HALLS OF THE ELECTRICAL EXHIBITION.

Telephonic communication between the Opera and the Exhibition of Electricity is obtained by means of twenty conducting wires, which are divided between two halls hung with carpets to deaden external noises. We represent in the accompanying engraving one of these halls, and the one which is lighted by the Lane-Fox system of lamps. As may be seen, there are affixed against the hangings, all around the room, long mahogany boards, to which are fastened about twenty small tablets provided with hooks, from which are suspended the telephones. The latter are connected with the underground conductors by extensible wires which project from the wooden wainscot of which we have just spoken, so that it is very easy for the auditors to put the telephones to their ears.

As the telephones are connected in series of eight with the same couple of microphone transmitters, and as each of these transmitting couples occupies a different position on the stage, it results that the effects are not the same at different points of each hall. Those telephones, for example, which correspond with the foot-lights of the theater are more affected by the sounds of the large instnuments of the orchestra than those which occupy the middle of the foot-lights; but, as an offset to this, the latter are affected by the voice of the prompter. In order to equalize the effects as much as possible, Mr. Ader has arranged it so that the two transmitters of each series shall be placed under conditions that are diametrically opposite. Thus, the transmitter at the end of the foot-lights, on the left side, corresponds with the transmitter of the series to the right, nearest to the middle of the stage; and the arrangement is the same, but in an inverse direction, for the transmitter at the end of the foot-lights to the right. But the series which produces the best effects is, as may be readily comprehended, that which corresponds with the transmitters occupying the middle of the right and left rows. These considerations easily explain the different opinions expressed by certain auditors in relation to the predominant sounds that they have heard, and why it is that some of them who have listened in different parts of the same hall have not had the same impressions. Naturally, the fault has beeen laid to the telephones; but, although these may vary in quality, it is more particularly to the arrangement of the transmitters on the stage that are to be attributed the differences that are noted.

As the Opera does not give representations every day, Mr. Ader has had the idea of occupying the attention of the public on Tuesday, Thursday, Saturday, and Sunday with the telephonic effects of flourishes of trumpets, which imitate pretty well the effects of French horns. These experiments have taken place in the hall in which is installed the little theater, and we must really say that in the effects produced French horns count for nothing.--_La Lumiere Electrique._

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THE ACTION OF COLD ON THE VOLT

When the voltaic arc plays between two metallic rheophores, of copper for instance, each formed of a U-tube traversed by a rapid current of cold water, and placed horizontally opposite each other, the following facts are observed: The luminous power of the arc is considerably weakened; it is reduced to a mere luminous point even when a current of 50 to 75 Bunsen elements of the large pattern is employed. The arc is very unstable and the least breath is sufficient to extinguish it. If a leaf of paper is placed above the arc at the distance of 0.004 to 0.005 meter a black point is produced in a few moments, which spreads and becomes a perforation, but the paper does not ignite. The arc consists of a luminous globule, moving between the two rheophores up and down and back again. The form of this globule, as well as its extreme mobility, causes it to resemble a drop of water in a spheroidal state. If we approach to the voltaic arc the south pole of a magnet the arc is attracted to such a degree that it leaves the rheophores and is extinguished. The same facts are observed in an intense form on presenting the north pole of a magnet to the arc. The quantity of ozone seems greater than when the arc is not refrigerated. It is to be noted that notwithstanding the refrigeration of the rheophores the flame of the arc is slightly green, proving that a portion of the copper is burning. It becomes a question whether the arc would be produced on taking as rheophores two tubes of platinum in which is caused to circulate, e.g., alcohol cooled to -30°.--_D. Tommasi._

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WATCHMAN'S DETECTER.