Discoveries and Inventions of the Nineteenth Century

by Robert Routledge

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 it. When the rails are so used they have, of course, to be insulated from the ground and laid with special electrical contact pieces joining their consecutive lengths, and all the carriage wheels have to be insulated, so that the currents shall flow only through the coils of the electro-motor. A railway on this system has been worked at Berlin for some time, and a short tramway on the same plan has lately been opened at Brighton. The Bessborough and Newry Electric Railway (Ireland) uses a single separate conductor three miles long, and the power is supplied at a very small cost from a dynamo station near the middle of the line, where water power is taken advantage of to drive a large turbine. Quite recently electric propulsion has been adopted on some of the short tunnel lines in London, and it is quite probable that ultimately the system will be adopted throughout the whole course of the underground railways, with the view of obtaining a purer and more agreeable atmosphere.

Fig. 280i.—Poles with Single Arms for Suburban, Roads.—The Ontario Beach Railway, Rochester, N. Y.

A very light electric railway has been designed, in which the cars run along rails attached to posts at such a height above the ground as may be required to make the line level, or with only slight gradients. The rails also serve as conductors. This is known as the telepherage system, and it is found to be well adapted for light loads in an undulating country.

Fig. 280j.—The Glynde Telepherage Line, on the system of the late Fleeming Jenkin.

The other plan which makes use of accumulators commends itself for application to ordinary tramway carriages, because no conductors are required along the line, and each car can move independently. The chief objection is the great weight of the accumulators and the space they occupy, although they are usually placed under the seats without much inconvenience. There are at present (January, 1890) six electric tramcars running in London, and the accumulator system would no doubt have been applied largely as the motive power for the ordinary street omnibus, but for the difficulty of controlling them under the momentum of the great mass of the accumulators, etc. The same objection lies against the use of the accumulators and motors for propelling tricycles, although such machines have really been used. But accidents such as occasionally happen to such vehicles would be attended with additional risks of injury from the acids of the secondary battery, etc. But there is one mode of using electric propulsion, that is free from every objection and, indeed, offers great advantages. Only two years ago the first electric boat on the Thames was tried experimentally between Richmond and Henley, and the result was entirely in favour of the electric over the steam launch. The Faure battery, or so-called “storage cells,” are arranged beneath the floor of the boat for most of its length in the smaller boats, and the electro-motor is directly coupled with the screw shaft. The electric launch has these advantages: perfect safety, freedom from dirt and smoke, no thumping or vibrating, no noise of steam discharge, or smell of hot oil, no engineer or stoker is required, and much larger space available for passengers. One of these electric launches, not going full speed, is able to travel sixty miles without having the accumulators recharged. A considerable number of these launches are already in use, and many more are in course of construction. They are made of all sizes, from the smallest to those that will carry quite a large company, and may be used for excursion parties on the river. The description of one of these last states that she is 65 feet in length, and 10 feet across the beam. She can carry sixty passengers, and twenty can dine in the saloon at one time. There are lavatories, pantries, dressing rooms, etc., and a brass railed upper deck, with an awning. At night this boat is lighted up with electric glow-lamps, the current for these also being supplied by the accumulators. The Electric Launch Company has stations with Gramme machines at work to charge cells ready to replace exhausted ones at several places, namely Hampton, Staines, Maidenhead, Boulter’s Lock, Henley, Reading and Oxford. There is every prospect of a general extension of the electric propulsion of boats, and visitors to the Electrical Exhibition at Edinburgh, in 1890, will find electric launches taking holiday makers as far as Linlithgow. The boats will be like those on the Thames, fitted with the Immisch motor. Some electricians are now sanguine enough to believe that even for large vessels electricity will yet be able to compete with steam in special cases.

The modes of using electric propulsion that we have just noticed furnish a very interesting chain of conversions of one form of force into another, with a reversal of the order of transformation at a certain point. Let us begin with the carbonic acid gas that existed in the atmosphere of the carboniferous geological period. The solar emanations were absorbed, and used by the leaves of the plants to separate the two elements of the gas,—the plant retaining the one in its substance and returning the other to the air. The plant becomes coal; and ages afterwards the particles of the two separated elements are ready to re-unite and give out in the form of heat all the energy that was absorbed by their separation. This heat is in the steam-engine converted into the energy of mechanical power. This mechanical power is in the dynamo expended in moving copper wires through a magnetic field. Every schoolboy who has played with a common steel magnet—and what boy has not?—knows that the space immediately round the magnet is the seat of strange attractive and repulsive force, for he has felt their pulls and pushes on pieces of iron or steel. This mysterious space is the magnetic field, and although a person would not be able to perceive that mechanical force is expended when he moves a single copper ring across such a field, he will readily become conscious of the fact when he moves a number at once that form a closed circuit; and he should not omit the opportunity of feeling this for himself if he is allowed to turn the handle of such a machine as that represented in Figs. [275] or [277]. The mechanical power is absorbed in the dynamo because the movement induces an electric current that would of itself produce motion in the machine in the opposite direction. However, the electricity induced by magnetism and motion is made to pass through the Faure cell or accumulator, when it does chemical work by separating oxide of lead from sulphuric acid, leaving these substances in a position to unite together again, when this action produces a reverse current of electricity through an external metal circuit. The coils of the electro-motor form this circuit; the electricity induces magnetism, and the magnetism gives rise to visible motion and mechanical power.