made in the application of electricity for the purpose of reaching some sources of energy which would otherwise be lost. If progress in this direction has not been as fast as might be desired, the reason lies in this, that installations of this kind are necessarily of some magnitude, and cannot be undertaken as mere experiments. If a small installation of electric lighting were to turn out a failure in any particular case, the loss to the contractor would not be so very serious. The dynamo, the wire, and the lamps have all their fixed market value, and if they have to be removed from one installation, they can be utilized in another. Not so with the transmission of energy from some hitherto inaccessible source. The dynamo and the motor have to be built specially for each particular case, and the probability that they can be used elsewhere is small. The line and supports are expensive items, which have only value in that particular locality where they have been erected, and the works necessary for transforming the crude energy of nature so as to be applied for driving the generating dynamo, have also only a local value. In such cases the installation must be a complete success, or else most of the plant and work is a dead loss; and it is but natural that capitalists shrink from rushing into enterprises as long as there is the least taint of an experimental nature about them.

Another reason which has, in England at least, operated to delay the electric transmission of energy from natural and inaccessible sources to more convenient places, is that in this country coal is cheap and water-power scarce. In France the case is different, and accordingly we find that the first experiments on a large scale have been undertaken there. Although it is quite incorrect to say, as is frequently stated in French papers, that M. Marcel Deprez has in

vented the electric transmission of energy, or has even invented any special system by which the electric transmission of energy is made practicable, it must be admitted that he has had the courage of his opinion, and has been the first to demonstrate that energy can be transmitted electrically over long distances. All scientists have long been agreed on the necessity of employing for long distance transmission currents of high electromotive force, but M. Marcel Deprez was the first to carry this into practice.

Broadly speaking, there are two purposes for which the electric transmission of energy is of great value. The one comprises all cases where, as has been shown above, hitherto inaccessible sources of natural energy are by its means rendered accessible, and the other comprises all those cases where the source of energy itself is accessible, but where it is desired to distribute it to a number of independent small working centres. In the first case we have to transmit a large amount of energy, so to speak, in one lump from the distant source to the place of operation; and, in the second case, we have to split up the energy of a source close at hand into a number of small fragments, and distribute them within a limited area to do useful work. In this case electric transmission of energy comes into competition with the more mechanical means of belts, shafts, wire-ropes, and pneumatic or hydraulic tubes, and the question whether one or the other of these systems is preferable, depends on the amount of energy transmitted, and the distance over which it is transmitted, as well as on many local circumstances. Electricity has the great advantage of being extremely portable, and capable of having its direction and intensity changed with greatest ease. No mechanical

force can be detected in the conductor carrying the electrical energy such as appears during purely mechanical transmission with shafting, belts, wire-ropes, or in pipes conveying steam, water, or air. The conductor is clean, cold, does not move, and altogether appears inert. It can be bent, moved, or shifted in any manner while transmitting many horse-power. It might be brought round sharp corners, and, having little weight, it can be fixed with greater ease than any mechanical connection. It is thus possible to bring the energy into rooms and places awkwardly situated for mechanical transmission, and there is no noise, smell, dirt, or heat during the transit, nothing to burst or give way. The power is, moreover, under perfect control, and its application exceedingly elastic. The same circuit which may be tapped to give many horse-power can, at the same time, and as conveniently be used to work a sewing-machine, or other small domestic implement, and the power consumed at the generating dynamo is always in proportion to the power obtained from all the motors, so that there is no waste of energy if some of the motors are standing still or are working with less than their full load. In addition to these advantages, electrical distribution of energy has also the merit of being exceedingly economical. The commercial efficiency of dynamos and electro-motors seldom falls below 80 per cent., and is in many cases as high as 90 per cent., so that even if we make a liberal allowance for loss of energy in the conducting wires, 60 per cent. of the power of the prime-mover at the generating station can be recovered from the motors distributed over a limited area. For instance, a steamengine of 100 horse-power, driving a generating dynamo in the centre of a two-mile circuit, could deliver an

aggregate of sixty horse-power in as many separate points within that circuit. Apart from all considerations of nuisance and cost of attendance in the case of sixty separate small steam-engines placed throughout the district, which might be used instead of the sixty electromotors, it is evident that we can generate one hundred horse-power in one single engine at a far less cost of fuel than could be done in small engines, and although the double conversion necessitated by electrical distribution of energy entails some loss, there is still a large margin in the general economy of the system.

In some cases it is found convenient to transmit the energy from the generating dynamo, not directly to the motors, but to interpose between the two a set of accumulators or secondary batteries. This is in reality an extension of the system, and has the double advantage of providing motive power even at those times when the generating dynamo is standing still, and also of giving to the motor a certain amount of portability. Electric transmission of power is thus actually carried beyond the limits of a fixed conductor, or is even effected without the aid of a conductor at all. As a case in point, may be cited the propulsion of street tramcars by means of secondary batteries. Here we have a charging station at some place near the line containing some prime mover and dynamos, the current from which is sent by a pair of cables to the secondary batteries in the car which are to be charged. This is the first stage in the electric transmission of energy. When the cells are fully charged, the cables are detached, and the car is ready to start, and during its journey the second stage of the transmission, viz., that of the energy in the cells into the motor, takes place. By the employment of secondary batteries, we

have thus carried the operation beyond the limits of the cables. If the charging station is so situated that cars can enter it, the process of charging can be accelerated by making each set of cells detachable from the car, and charging them whilst the car, furnished with a duplicate set, is on the line. As each car comes in, its set of exhausted cells is replaced by a set newly charged, and can go out again within a few minutes. In this case the actual transmission of energy between the dynamo and the cells, which are placed in close proximity, is only over the space of a few yards; yet this energy may, later on, be utilized over a very long line.

A similar system is in use for the propulsion of small boats by electricity. It can be most conveniently applied in the case of launches belonging to vessels which are fitted with the electric light; for the same dynamo which works the incandescent lamps at night can be used to charge, or keep charged, the accumulators in the launch during the day-time, so that the latter may at a moment's notice be lowered into the sea, provided with a sufficient store of energy for some hours' run. When the launch is stowed away on deck, its accumulators can also be used for lighting the vessel, if a mishap occurs to the dynamo, or if it be necessary to stop the machinery for some other reason.

Examples of this kind might be multiplied to any extent, but sufficient has been said to show that in the present state of electrical industry the electric transmission of energy is a question of great practical interest. Its application is not only confined to the transmission of power, pure and simple, between two distant points, as commonly understood, but it enters more or less into every application of electricity.