Discoveries and Inventions of the Nineteenth Century

adopted the incandescent electric lamps, and it is obvious that the system will become universal. In all ocean-going passenger steamers, electric lighting of the saloons and cabins is now the rule. No mode of illumination so readily adapts itself to the production of artistic and decorative effects as the glow lamps: for the covering glasses may be tinted of any required shade, and the lights may be placed in any position. Small glow lamps are occasionally used as personal adornments, when placed, for instance, as part of a lady’s head-dress amidst diamonds, a novel effect of great brilliancy is produced. It need hardly be said that in this application the wearer is not required to carry a dynamo about with her, for the electricity is supplied in a manner much more convenient for this purpose by a device presently to be described. For several years electric incandescent lamps, supplied by the like means, have been in 530action every night in the carriages of the trains running between London and Brighton, and more recently the Company have had electric reading lamps of five candle-power fitted up in the carriages of the main line trains. They are placed at the backs of the seats just above the passengers’ head. When anyone wishes to make use of one of these lamps, he places a penny in a slot, and then, on pressing a knob, the light appears, and at the end of half an hour it is automatically extinguished; but, of course, it can again be made to appear by another penny dropped in the slot, and so on every half-hour as long as may be required. To maintain the electric light (whether arc or incandescent) quite steady, the greatest uniformity in the speed of the dynamo is essential; and if the prime mover by which it is worked, whether steam-engine, gas-engine, water-wheel, or turbine, is not perfectly regular in its action, the lights will fluctuate in brightness, and thus produce an effect which is very unpleasant. This is entirely obviated by the adjunct we have now to describe, which not only is most efficient as a regulator, but is, moreover, of still more importance by also providing the means of storing up the electrical energy in a portable form. The reader will have understood that in a voltaic cell the production of an electric current is the concomitant of a chemical union of substances within the cell (p. 493). Now, in the experiment shown in Fig. 263 (p. 498), it is the reverse of combination—namely, the decomposition of the water that is supposed to be effected under the influence of the current from a galvanic battery, and the poles are so connected that the direction of the current in the liquid while the decomposition is proceeding is from the wire in the O tube to that in the H tube. If the experiment be interrupted by removing the battery, and then putting a galvanometer (Fig. 258) in its place, the galvanometer will immediately indicate a current passing through the apparatus in a direction the reverse of the former one—that is, in the liquid it goes from H to O, and the volumes of the gases will slowly diminish while water is reproduced by imperceptible and gradual re-combination. Batteries can be made by joining up a series of arrangements like Fig. 263, consisting of nothing but strips of platinum surrounded by hydrogen and oxygen gases and the intervening acidified water. Analogous results are obtainable by cells containing other compounds with suitable metallic poles, for when decomposition has been effected through a series of such cells by a sufficiently powerful current from a primary battery, the series of cells will constitute, on removal of the primary battery, a secondary battery, for when the terminals of this are joined, the current will flow in the reversed direction while the separated parts of the original compounds are re-combining within the cells. These secondary batteries are called also polarisation batteries. A form of secondary battery was contrived some years ago (1859) by M. Gaston Planté, in which the current of the primary battery was made to act on plates of lead immersed in dilute sulphuric acid. The effect was to coat one of the lead plates of each pair with lead oxide; and in the action of the secondary battery this was reversed, and the plates gradually returned to their original condition, when, of course, the current ceased. Some improvements were made in the Planté battery by Faure, who coated one of a pair of very thin lead plates at once with a film of red oxide of lead, and used a layer of felt to separate it from the other plate. Such arrangements have been called “accumulators”; another term applied to them is “storage batteries”; but it is not to be supposed that in them electricity is stored or, so to speak, 531bottled up. They consist merely of such an arrangement of materials as that when a current (direct, not alternating) from a dynamo is passing, certain substances are placed in a position of chemical separation in such a manner that in re-combining an equable current of electricity is produced in the conductor externally uniting them. We need not notice some slight modifications of the Faure cells that have been lately introduced, as no new principle is involved. The light of incandescent lamps worked by the Faure accumulator is perfectly free from the fluctuations which may usually be noticed when the lamps are directly connected with the dynamo only. Even if the engine should stop altogether, the light may be maintained for hours. The accumulator has also the advantage of giving out the electric energy that may have been imparted to it days before; so that when a house is fitted up with an independent electric light installation, there is no necessity for running the dynamo all the time the lamps are in use, as two or three days weekly may suffice to charge all the accumulators. Then there is the portability of the accumulator, which permits electrical energy to be made use of in situations where dynamos and prime movers would be impossible. It is said that a large Faure cell weighing about 140 lbs. can receive and give out energy equal to one horse power for one hour. In the arrangement for the reading lamps in railway carriages referred to above, accumulators are placed under the seats; and it need hardly be said that when the electric light has been seen in a coiffure, a small Faure cell concealed about the wearer’s person has supplied the current. A very interesting and useful application of the accumulator is the portable electric light lamp for miners made by the Edison-Swan Company. It is simply an incandescent lamp protected by a strong glass cover attached to the side of a cylindrical case containing a four-celled accumulator. This lamp is provided with an ingenious contrivance by which the circuit would be interrupted, if by accident the outer glass cover of the lamp were broken. Let us now see what another new development of the applications of electricity gains by the use of accumulators by turning our attention to the electro-motor. At the Vienna Exhibition of 1873, the Gramme Company showed two of their machines, and it is said that when one of these machines was at rest, a workman connected the ends of two covered copper wires with the other machine, thinking that these were placed to carry the current from that machine when in movement. Everybody was surprised when, without any power from the machinery, the ring was soon in rapid rotation. These wires were in fact joined up to the other Gramme machine which was already in action, and it was the current from this that set the former in motion. There is no reason why this story should not be perfectly true, although there are good reasons for believing that the electro-motor was the result of no such accidental circumstance. The attractions and repulsions between the poles of electro-magnets was soon seen to supply an available source of motive power, and the subject has been already mentioned on page 518. Professor Jacobi, of St. Petersburg, seems to have been the first who constructed an electro-magnetic engine, the exciting power being the current supplied by a voltaic battery. This was in 1834, and in a few years afterwards the Professor applied his engine to a small paddle-wheel boat, 28 feet long, which was electrically propelled for several days, but at a slow speed. The engine in this case was virtually a magneto-electric machine worked backwards, that is, instead of applying power to turn the machine and so produce a current 532of electricity, the current was supplied by the battery and produced power. In 1850, an electro-motor of five horse power was shown by an American, Mr. Page, the principle of which may be illustrated by supposing a reversal of the action represented in Fig. 271, thus: if, instead of producing currents by moving the magnet, C, in and out of the coil, A B, we substitute a battery for D, we can, by alternating the direction of the current through the coil, cause a reciprocating motion of the magnet, C, and this again may be described as a magneto-electric machine worked backward. It was soon recognized that no practical electro-motor was adequate to the production of such high powers as the steam engine supplies, and that the cost must necessarily many times exceed that of steam power. But certain advantages, nevertheless, pertained to the electro-motor in certain positions, as instance in safety, and where a small force only was occasionally required. Now, when the Gramme machine was invented to supply currents of electricity under conditions much more favourable than the magneto-electric machines it superseded, and at a cost vastly less than that of any voltaic battery, it is highly improbable that the relation of the new current generator to the production of electro-motive power would long be overlooked. The electro-motor may, therefore, be considered simply as a dynamo worked backward, and almost any form of dynamo may in this way be used as an electro-motor, that is, a current being supplied either from a battery or from a dynamo, the motor converts the electrical energy into mechanical energy. Any dynamo that supplies a direct and continuous current can thus be used; but there are certain conditions which make it desirable to somewhat modify the proportions and arrangement of the several parts when the machine is for motor purposes. In general, any source of current may be used, but in the applications of the electro-motor there are chiefly two methods in practice of supplying the current. The one takes the current from a dynamo in motion, the other from an accumulator which has previously been “charged” by a dynamo. Both of these methods are used in the familiar and interesting application of the electro-motor to the propulsion of carriages on tramways and railways. For the latter, indeed, an attempt was made half-a-century ago on the Edinburgh and Glasgow railway, to employ the force of an electro-magnetic machine actuated by a battery. This was in 1842, and although this electric locomotive was fitted up completely, it did not attain a speed of more than four miles an hour. The weight with the batteries, carriage, etc., exceeded five tons. But in the recent inventions which have been in practical operation in many places, it is found quite easy to dispense with any current producer on the electric locomotive itself, for the electricity is supplied by a fixed dynamo and the current is transmitted along the line by a conductor from which a sliding contact conveys it to the electro-motor, which is attached to the framework of the carriage and acts on the driving axles of the wheels directly or by toothed gear. In such cases the return current is carried either by another conductor or by the rails themselves. In another arrangement one rail conveys the current to the locomotive and the other returns