Chapter 5

An electrical exhibition on a comparatively small scale was opened in Paris, March 22, 1885, with considerable eclat, the President of the Republic being present. Engines to the extent of 200 H.P. are employed to work the lights. Among the exhibits is the Cruto light. _Engineering_ says: At the first glance it presents the same appearance as an Edison lamp, having the same form of globe, and apparently a similar luminous filament. But this latter is made in an entirely different manner. A platinum wire is employed, 1/100 of a millimeter in diameter. This is obtained by the Wollaston process, that is to say, a piece of coarse platinum wire is covered with a stout coating of silver, and drawn down till the outside diameter is 1/10 millimeter. The silver coating is then dissolved in a bath of nitric acid, and the platinum wire is left behind. This wire is then cut into lengths, bent into a U form, and placed in a glass globe, in which circulates a current of bicarbonated hydrogen obtained by the action of sulphuric acid on alcohol. This gas, previously purified, circulates around the platinum filament, through which an electric current is passed sufficient to bring it to a red heat. This decomposes the gas, and a thin coating of absolutely pure carbon is deposited on the wire. The operation is continued until a sufficient thickness of carbon has been deposited for each type of lamp, and the method of regulating the amount of deposit is effected very simply, and, in fact, almost automatically. Indeed, one of the most interesting features of the process is its great simplicity, although it is somewhat more costly than the ordinary methods of producing incandescence lamps. After having been subjected to the action of the gas for two or three hours, the filament is taken from the glass globe, its diameter is carefully measured, the length is calibrated, and it is set on a platinum support, to which it is soldered by a very ingenious process. The filament is then introduced into a second glass globe charged with bicarbonate of hydrogen; it is placed between pincers that hold the carbon near its union with the platinum, and the platinum some millimeters below. These pincers are then thrown into circuit, and a powerful current is passed through the part which is to be soldered. The platinum and carbon become incandescent, the bicarbonate is decomposed, and a fresh deposit of carbon solders the filament to its support. The system thus mounted is placed within the permanent globe, and a vacuum is obtained in the ordinary way, while the testing and finishing details present nothing of special interest. The finished lamp is then photometrically tested, and placed on a support something like the Edison mounting. Upon it are engraved the working constants. As an ordinary practical result, these lamps, working with 50 volts and 1.15 amperes, give a luminous intensity of 20 candles, or the equivalent in luminous spherical intensity of 1.1 Edison A lamps. This result is interesting, especially as the life of the lamp ranges from 900 to 1,100 hours, as was demonstrated by various careful tests made with some 250 lamps; the most valuable trials having taken place at the Turin Exhibition. After prolonged use, a diminution in the fall of potential is produced, to a more marked degree than in the Edison lamp, and the light can be maintained constant by increasing the strength of the current in a proportion that can be determined by means of resistances. The Cruto filament examined under the microscope appears to be uniformly magnetic, and is very regular, except at the curved parts where the diameter is slightly diminished, and it is here that rupture generally takes place. The great structural regularity of the filament probably accounts for its high durability, and from the fact that it may be worked with a higher current than probably any other form of incandescence lamp. M. Desroziers in a series of experiments obtained as much as 250 carcel spherical luminous value per horse-power; this characteristic is one likely to be of great value in electric lighting by incandescence of high intensity. At present only 20-candle lamps are made on the Cruto system. The carbon filament, when properly prepared, is gray in hue and of metallic appearance; it is built up in very fine laminae indicating the mode of manufacture. The results obtained with these lamps vary as much as 25 per cent., according to the care bestowed in producing the filament. If traces of air exist in the globe, they very quickly manifest themselves by the surface of the glass becoming blackened, while an increased energy is required to maintain the brightness of the light.

In the early days of this lamp it was thought necessary to remove the delicate platinum wire which forms the core of the filament, by raising the strength of the current sufficiently to destroy it in the course of manufacture. This, however, was given up, and the platinum now remains either as a continuous wire or as a series of small separated granules.

* * * * *

ELECTRIC LIGHT APPARATUS FOR MILITARY PURPOSES.

In the first period of the siege of a stronghold it is of very great importance for the besieged to embarrass the first progress of the attack, in order to complete their own armament, and to perform certain operations which are of absolute necessity for the safety of the place, but which are only then possible. In order to retard the completion of the first parallel, and the opening of the fire, it is necessary to try to discover the location of such parallel, as well as that of the artillery, and to ply them with projectiles. But, on their side, the besiegers will do all in their power to hide their works, and those that they are unable to begin behind natural coverts they will execute at night. It will be seen from this how important it is for the besieged to possess at this stage of events an effective means of lighting up the external country. Later on, such means will be of utility to them in the night-firing of long-range rifled guns, as well as for preventing surprises, and also for illuminating the breach and the ditches at the time of an assault, and the entire field of battle at the time of a sortie.

On a campaign it will prove none the less useful to be provided with movable apparatus that follow the army. A few years ago. Lieut. A. Cuvelier, in a very remarkable article in the _Revue Militaire Belge_, pointed out the large number of night operations of the war of 1877, and predicted the frequent use of such apparatus in future wars.

The accompanying engraving represents a very fine electric light apparatus, especially designed for military use in mountainous countries. It consists of a two-wheeled carriage, drawn by one horse and carrying all the apparatus necessary for illuminating the works of the enemy. The machine consists of the following parts: (1) A field boiler. (2) A Gramme electric machine, type M, actuated directly by a Brotherhood 3-cylinder motor. (3) A Mangin projector, 12 inches in diameter, suspended for carriage from a movable support. This latter, when the place is reached where the apparatus is to operate, may be removed from the carriage and placed on the ground at a distance of about a hundred yards from the machine, and be connected therewith by a conductor. Col. Mangin's projector consists of a glass mirror with double curvature, silvered upon its convex face. It possesses so remarkable optical properties that it has been adopted by nearly all powers. The fascicle of light that it emits has a perfect concentration. In front of the projector there are two doors. The first of these, which is plane and simple, is used when it is desired to give the fascicle all the concentration possible; the other, which consists of cylindrical lenses, spreads the fascicle horizontally, so as to make it cover a wider space.

The range of the concentrated fascicle is about 86,000 feet. The projector may be pointed in all directions, so as to bring it to bear in succession upon all the points that it is desired to illuminate. The 12-inch projector is the smallest size made for this purpose. The constructors, Messrs. Sautter, Lemonnier & Co., are making more powerful ones, up to 36 inches in diameter, with a corresponding increase in the size of the electric machines, motors, and boilers.

The various powers make use of these apparatus for the defense of fortresses and coasts, for campaign service, etc.

The various parts of the apparatus can be easily taken apart and loaded upon the backs of mules. The only really heavy piece is the boiler, which weighs about 990 pounds.

* * * * *

ELECTRICITY AND MAGNETISM.[1]

[Footnote 1: Introductory to the course of Lectures on Physics at Washington University, St. Louis, Missouri--_Kansas City Review._]

Prof. FRANCIS E. NIPHER.

It was known six hundred years before Christ that when amber is rubbed it acquires the power of attracting light bodies. The Greek name for amber, _elektron_, was afterward applied to the phenomenon. It was also known to the ancients that a certain kind of iron ore, first found at Magnesia, in Asia Minor, had the property of attracting iron. This phenomenon was called magnetism. This is the history of electricity and magnetism for two thousand years, during which these facts stood alone, like isolated mountain peaks, with summits touched and made visible by the morning sun, while the region surrounding and connecting them lay hidden and unexplored.

In fact, it is only in more recent times that men could be found possessing the necessary mental qualities to insure success in physical investigation. Some of the ancients were acute observers, and made valuable observations in descriptive natural history. They also observed and described phenomena which they saw around them, although often in vague and mystical terms.

They, however, were greatly lacking in power to discriminate between the possible and the absurd, and so old wives' tales, acute speculations, and truthful observations are strangely jumbled together. With rare exceptions they did not contrive new conditions to bring about phenomena which Nature did not spontaneously exhibit--they did not experiment. They attempted to solve the universe in their heads, and made little progress.

In mediaeval times intellectual men were busy in trying to set each other right, and in disputing and arguing with those who believed themselves to be right. It was an era of intellectual pugilism, and nothing was done in physics. In fact, this frame of mind is incompatible with any marked success in scientific work.

The physical investigator cannot take up his work in the spirit of controversy; for the phenomena and laws of Nature will not argue with him. He must come as a learner, and the true man of science is content to learn, is content to lay his results before his fellows, and is willing to profit by their criticisms. In so far as he permits himself to assume the mental attitude of one who defends a position, in so far does he reveal a grave disqualification for the most useful scientific work. Scientific truth needs no man's defense, but our individual statements of what we believe to be truth frequently need criticism. It is hardly necessary to remark, also, that critics are of various degrees of excellence, and it seems that those in whom the habit of criticism has become chronic are of comparatively little service to the world.

The great harbinger of the new era was Galileo. There had been prophets before him, and after him came a greater one--Newton. They did nothing of note in electricity and magnetism, but they were filled with the true spirit of science, they introduced proper and reasonable methods of investigation, and by their great ability and distinguished success they have produced a revolution in the intellectual world. Other great men had also appeared, such as Leibnitz and Huyghens; and it became very clear that the methods of investigation which had borne such fruit in the days of Galileo were not disposed of completely by his unwilling recantation; it became very clear that the new civilization which was dawning upon Europe was not destined to the rude fate which had overwhelmed the brilliant scientific achievements of the Spanish Moors of a half century before.

Already in 1580, about the time when Galileo entered Pisa as a student, Borroughs had determined the variation of the magnetic needle at London, and we have upon the screen a view of his instrument, which seems rude enough, in comparison with the elaborate apparatus of our times. The first great work on electricity and magnetism was the "De Magnete" of Gilbert, physician of Queen Elizabeth, published in 1600. Galileo, already famous in Europe, recognized in the methods of investigation used by Gilbert the ones which he had found so fruitful, and wrote of him, "I extremely praise, admire, and envy this author."

Gilbert made many interesting contributions to magnetism, which we shall notice in another lecture, and he also found that sulphur, glass, wax, and other bodies share with amber the property of being electrified by friction. He concluded that many bodies could not be thus electrified. Gray, however, found in 1729 that these bodies were conductors of electricity, and his discoveries and experiments were explained and described to the president of the Royal Society while on his death bed, and only a few hours before his death. If precautions are taken to properly insulate conductors, all bodies which differ in any way, either in structure, in smoothness of surface, or even in temperature, are apparently electrified by friction. In all cases the friction also produces heat, and if the bodies rubbed are exactly alike, heat only is produced.

An electrified body will attract all light bodies. This gutta percha when rubbed with a cat's skin attracts these bits of paper, and this pith ball, and this copper ball; it moves this long lath balanced on its center, and deflects this vertical jet of water into a beautiful curve.

If a conductor is to be electrified, it must be supported by bad conductors. This brass cylinder standing on a glass column has become electrified by friction with cat's-skin. My assistant will stand upon this insulating stool, and by stroking his hand you will observe that with his other hand he can attract this suspended rod of wood, and you will hear a feeble spark when I apply my knuckle to his.

Du Fay, of Paris, discovered what he called two kinds of electricity. He found that a glass rod rubbed with silk will repel another glass rod similarly rubbed, but that the silk would attract a rubbed glass rod. We express the facts in the well-known law that like electricities repel each other, and unlike attract. For a long time the nature of the distinctions between the two electricities was not understood. It was found later that when the two bodies are rubbed together they become oppositely electrified, and that the two electricities are always generated in equal quantity; so that if the two bodies are held in contact after the rubbing has ceased the two electricities come together again and the electrical phenomena disappear. They have been added together, and the result is zero. Franklin proposed to call these electricities positive and negative. These names are well chosen, but we do not know any reason why one should be called positive rather than the other. The electricity generated on glass when rubbed with silk is called positive.

Let us now examine the distinction between positive and negative electricities somewhat more closely, aiding ourselves by two cases which are somewhat analogous.

Two air-tight cylinders, A and B, contain air at ordinary pressure. The cylinders are connected by a tube containing an air-pump in such a way that, when the pump is worked, air is taken from A and forced into B. To use the language of the electricians, we at once generate two kinds of pressure. The vessels have acquired new properties. If we open a cock in the side of either vessel, we hear a hissing sound, if a light body is placed before the opening in A it would be attracted, and before the opening in B it would be repelled. Now this is only roughly analogous to the case of the electrified bodies, but the analogy will nevertheless aid us in our study. If the two vessels are first connected with the air, and then closed up and the pump is set to work, we increase the pressure in B and diminish the pressure in A. To do this requires the expenditure of a quantity of work. If the cylinders are connected by an open tube--a conductor--the difference in pressure disappears by reason of a flow of gas from one vessel to the other.

If we had a pump by means of which we could pump heat from one body into another, starting with two bodies at the same temperature, the temperature of one body would increase and that of the other would diminish. If we knew less than we do of heat, we might well discuss whether the plus sign should be applied to the heat or to the cold, because these names were coined by people who knew very little about the subject except that these bodies produce different sensations when they come in contact with the human body.

Furthermore, we find that whether the hand is applied to a very hot body or to a very cold body, the physiological effect is the same. In each case the tissue is destroyed and a burn is produced. Shall we now say that this burn is produced by an unusual flow of heat from the hot body to the hand, or from the hand to the cold body, or shall we say that it is due to an unusual flow of cold from the cold body to the hand, or from the hand to the hot body?

Logically these expressions are identical; still we have come to prefer one of them. It is because we have learned that in those bodies which our fathers called hot, the particles are vibrating with greater energy than in cold bodies, that we prefer to say that heat is added and not cold subtracted, when a cold body becomes less cold.

Now to come back to our electrified bodies. Let us suppose that this gutta percha, and this cat's-skin are not electrified. That means that their electrical condition is the same as that of surrounding bodies. Let us also suppose that their thermal condition is the same as surrounding bodies, ourselves included--that is, they are neither hot nor cold. We express these conditions in other words by saying that the bodies have the same electrical _potential_ and the same temperature.

Temperature in heat is analogous to potential in electricity. As soon as adjacent bodies are at different temperatures, we have the phenomena which reveal to us the existence of heat. As soon as adjacent bodies have different electrical potentials, we have the phenomena which reveal the existence of electricity. As soon as adjacent regions in the air are at different pressures, we have phenomena which reveal the existence of air.

Bodies all tend to preserve the same temperature and also the same electrical potential. Any disturbances in electrical equilibrium are much more quickly obliterated than in case of thermal equilibrium, and we therefore see less of electrical phenomena than of thermal. In thunder storms we see such disturbances, and with delicate instruments we find them going on continuously. Changes in temperature occurring on a large scale in our atmosphere, occurring in these gas jets, in our fires, in the axles of machinery, and in thousands of other places, are so familiar that we have ceased to wonder at them.

If we rub these two bodies together, the potential of the two is no longer the same. We do not know which one has become greater, and in this respect our knowledge of electricity is less complete than of heat. We assume that the gutta percha has become negative. If we now leave these bodies in contact, the potential of the cat's skin will diminish and that of the gutta percha will increase until they have again reached a common potential--that of the earth. As in the case of heat and cold, we may say either that this has come about by a flow of positive electricity from the cat's skin to the gutta percha, or by a flow of negative electricity in the opposite direction, for these statements are identical.

In case of our gas cylinders, the gas tends to leak out of the vessel where the pressure is great into the vessel where it is small. The heat tends to leak out of a body of high temperature into the colder one, or the cold tends to go in the opposite direction. Similarly, the plus electricity tends to flow from the body having a high potential, to the body having a low potential, or the minus electricity tends to go in the opposite direction.

* * * * *

[ENGINEERING.]

THE HYDRODYNAMIC RESEARCHES OF PROFESSOR BJERKNES.

BY CONRAD W. COOKE.

We have in former articles described the highly interesting series of experimental researches of Dr. C. A. Bjerknes, Professor of Mathematics in the University of Christiania, which formed so attractive a feature in the Electrical Exhibition of Paris in 1881, and which constituted the practical development of a theoretical research which had extended over a previous period of more than twenty years. The experiments which we described in those articles were, as our readers will remember, upon the influence of pulsating and rectilinear vibrating bodies upon one another and upon bodies in their neighborhood, as well as upon the medium in which they are immersed. This medium, in the majority of Professor Bjerknes earlier experiments, was water, although he demonstrated mathematically, and to a small extent experimentally, that the phenomena, which bear so striking an analogy to those of magnetism, may be produced in air.

Our readers will recollect that in the spring of 1882 Mr. Stroh, by means of some very delicate and beautifully designed apparatus, was able to demonstrate a large number of the same phenomena in atmospheric air of the ordinary density; and about the same time Professor Bjerknes, in Christiania, was extending his researches to phenomena produced by a different class of vibrations, namely, those of bodies moving in oscillations of a circular character, such, for example, as a cylinder vibrating about its own axis or a sphere around one of its diameters; some of these experiments were brought by Professor Bjerknes before the Physical Society of London in the following June. Since that time, however, Professor Bjerknes, with the very important assistance of his son, Mr. Vilhelm Bjerknes, has been extending these experimental researches in the same direction, and with the results which it is the object of the present series of articles to describe.

The especial feature of interest in all Professor Bjerknes experiments has been the remarkably close analogy which exists between the phenomena exhibited in his mechanical experiments in water and other media and those of magnetism and of electricity, and it may be of some interest if we here recapitulate some of the more striking of these analogies.

(1.) In the first place, the vibrating or pulsating bodies, by setting the water or other medium in which they are immersed into vibration, set up in their immediate neighborhood a field of mechanical force very closely analogous to the field of magnetic force with which magnetized bodies are surrounded. The lines of vibration have precisely the same directions and form the same figures, while at the same time the decrease of the intensity of vibration by an increase of distance obeys precisely the same law as does that of magnetic intensity at increasing distances from a magnetic body.