that they are joined two and two at their extremities, so as to form four magnetic fields. A collector which is not seen in the figure receives the impulses thus produced, and gives higher tension. The potential of the first lighting machines was about 60 to 70 volts; that of these octagonal machines was as high as 250 or 300 volts. We shall soon see that this was only a first step, and that it was necessary to go much further. However, these machines were serviceable, and we shall see more of them in speaking of the Electric Exhibition and the applications which followed it.

CHAPTER VI.

FIRST APPLICATIONS FOR THE LOCOMOTION OF

CARRIAGES.

THE application which should best pay, perhaps that in which electricity approaches the nearest to perfection, is the locomotion of vehicles. In all the systems in use up to the present the motive agent itself moves with the conveyance it has to draw: the horse goes before the carriage, the locomotive with the train; and then there is not only the motor itself to move-that is to say, properly speaking, the steam-engine-but the boiler to produce the steam, and the coal to furnish the heat, besides the water; all this causes considerable expenditure of force. Certainly, in contemplating some steam-engines, the wonder is, not that they can draw carriages, but that these enormous engines can be made to move themselves. By making use of electricity, the whole motive power is reduced to the electric motor fitted to the carriage, and which may be very light; the production of the force will take place at a distance, at a fixed centre, where the engines can be arranged as desired without inconvenience. The connection between the fixed generator and the moving motor

may be made to act in several ways, but in no case does it interfere with the locomotion.

The first attempts in this line were, however, quite recent; almost all, as we shall see, being due to the German firm of Siemens and Halske.

The combination to be applied had nothing complicated; it is the electric transport of force in its most simple form. What is there to do after all? To set the wheels of a carriage in motion. The dynamo-electric machine is eminently fitted for this purpose; for, applied to produce force, it is in the form of an axis endued with the power of turning by itself. It will suffice, then, to set up at the startingpoint a dynamo-electric machine driven by a suitable motor which will send a current to a similar machine carried by the vehicle to be moved. The system in itself cannot properly be called an invention, there not being many variations in the execution, at least in the principal parts; there are, however, as we shall see, some difficulties in the carrying out, which have required, after all, no small amount of work and ingenuity.

The first application of this kind we meet with was effected by the firm of Siemens and Halske, at the Berlin Exhibition, during the summer of 1879. It was a small model railway, laid down on a very small scale. The length of the line was about 500 metres; it was in the form of an oval, so that the passengers returned to the starting-point. The train was composed of a small electric locomotive and carriages for the passengers. The latter were small

platforms mounted on low wheels, with two rows of seats facing outwards parallel with the lines. The general appearance of the train was that given in the accompanying Fig. 95.

The locomotive was simply composed of one of Siemens's dynamo-electric machines like that represented in Fig. 68. This was laid horizontally on a framework with wheels; the bobbin was placed parallel to the line, the field electro-magnets being perpendicular thereto. Fig. 94 is a cross-section,

FIG. 94.

P

and Fig. 96 a longitudinal section of this apparatus. The latter shows a section of the cog-wheels 1, t, v, and x, by which the rotary movement of the bobbin