Sir Humphry Davy was the first to discover that when the terminal wires of a powerful electric battery were furnished with carbon-points and brought into such a position that they almost touched, the space between them became bridged over with a dazzling arc of light. The excessive cost of producing this light (owing to the rapid consumption of the metal-plates and acids which together form the battery-power) rendered it for a long time almost inapplicable to any other purpose than that of lecture-room demonstration. But it was evident to all that a means of illumination so nearly approaching in its intensity the light of the sun, would, if practicable, be of immense value to society at large. Apart from its cost, there were many other hindrances to its ready adoption. The incandescent carbon-points—which we may here remark are cut from a hard form of gas-coke—were found to waste away unequally. Some plan had therefore to be hit upon of not only replacing them at certain intervals, but also, in view of this inequality of consumption, of preserving their relative distance the one from the other; otherwise the light they gave became intermittent and irregular. These difficulties were met by employing clock-work as a regulator, and more recently by a train of wheelwork and magnets set in motion by the current itself. These arrangements naturally led to complications, which required the constant supervision of skilled operators, and the coveted light was necessarily confined to uses of a special nature where the question of cost and trouble was unimportant.
The use of the battery for the electric light has for some years been almost entirely superseded by the magneto-electric machine. The construction of this machine is based upon Faraday's discovery, that when a piece of soft iron inclosed in a coil of metal wire is caused to pass by the poles of a magnet, an electric current is produced in the wire. The common form of this machine consists of a number of such iron cores so arranged upon a revolving cylinder that in continual succession they fly past a number of stationary horse-shoe magnets placed in a frame round its circumference. By a piece of mechanism called a commutator, the various small streams of electricity thus induced are collected together into one powerful current. This invention forms one of the most advanced steps in the history of the electric light. But although it produces electricity without the consumption of metal involved in the battery system, another element of cost comes into view in the expense of the steam-power necessary to work it; besides which the original outlay is considerable.
In the year 1853 a Company was formed at Paris for producing (by the aid of some large magneto-electric machines) gas for combustion, by the decomposition of water. The Company failed to produce gas, and what was perhaps more to the annoyance of the subscribers, they failed also to shew any dividends, and the expensive machines were voted impostors. However, an Englishman, Mr Holms, succeeded in turning them to better account, and eventually produced by their aid a light of great power. Mr Wilde of Manchester was another worker in the same field; and improved machines were soon introduced to public notice by both gentlemen. A few years after, the South Foreland and Dungeness lighthouses were provided with experimental lights. (The first-named headland had previously been furnished with an oxyhydrogen or lime light, a source of illumination which is also open to the same objections of requiring constant attention and renewal.)
It is a matter of surprise to most visitors to the South Foreland lighthouse to find that a small factory and staff of men are necessary to keep the electric apparatus in working order. The extent of the establishment is partly explained by the fact that, in case of a breakdown of any part of the apparatus, everything is kept in duplicate. Hence there are two ten horse-power steam-engines, and a double set of magneto-electric machines, although only half that number are in actual use at one time. The old oil-lamps are also kept ready, in view of the improbable event of both sets of electrical apparatus going wrong.
Although lighthouses were the first places to which electrical illumination was applied, there are many other purposes for which that species of light is invaluable. One of the chief of these is its use in submarine operations. Unlike other lights, being quite independent of atmospheric air or any kind of gas for its support, and merely requiring an attachment of a couple of gutta-percha-covered wires for its connection with the source of electricity (which may be at a considerable distance from the place of combustion), it is specially applicable to the use of divers. The importance of a means of brilliantly lighting the work of those engaged in clearing wreck or laying the foundations of subaqueous structures cannot be over-estimated. There is another service too in which we may hope some day to see it commonly employed: we mean as a source of light to our miners. For this purpose, the burner could be placed in a thick glass globe hermetically closed; in fact the globe might even be exhausted of air, for experiments prove that the light is in several respects improved when burnt in a vacuum! The danger of fire-damp explosion would by this means be almost altogether obviated; for unless the glass were broken (and abundant means suggest themselves for protecting it), no communication could be made between the light and the gas-laden air of the mine. As a means of night-signalling, the electric light can also be profitably applied. This can be done by an alphabet of flashes of varying duration; the readiness with which the light can be extinguished and rekindled by the mere touch of a wire, rendering it peculiarly adapted for such a purpose; while the distance at which it can be seen is perhaps only limited by the convexity of the earth. Several of Her Majesty's ships are now being fitted with the electric light, which is to serve both for signalling purposes, and as a precautionary measure against the attack of torpedo-boats. For military field operations a brilliant light is often useful; and an electrical apparatus is in actual use by one of the belligerents in the present war. In this case, the light is doubtless worked by an electric battery, as a steam-engine is hardly a convenient addition to the impedimenta of a moving column.
Having called our readers' attention to the several special public uses for which the electric light is available, we may now consider how far it can serve us for the more common wants of every-day life. In its crude state as we have described it, governed by such a touchy thing as clock-work, it could not possibly compete with gas for ordinary purposes. But one or two improvements have within the last few months been made, which have led many to hope that the day is not far distant when the light will become common in our streets, if not in our houses.
These improvements are two in number. The one is a plan whereby the electric current can be subdivided so as to serve a number of different lights, and the other is an improvement in the arrangement of the burner. The first-mentioned invention seems most certainly to bring the system more on a par with gas-lighting, only that wires take the place of pipes. But the second offers features of a more novel character. The carbons, instead of being placed point to point, one above the other, as in the old system, are put side by side and made into a kind of candle. The carbons therefore represent a double wick; while the portion of the candle usually made of tallow is made of kaolin, a form of white clay used in the manufacture of porcelain. The points are thus kept at a fixed distance apart; and as they burn, they vitrify the kaolin between them, which both checks their waste and adds, by its incandescence, to the light produced. The old difficulty of keeping the carbons apart by the aid of clock-work, therefore disappears. The invention of this 'electric candle' is due to a Russian engineer, M. Jablochkoff. Another plan which is also credited to the same inventor is that of doing away with the carbon-points altogether, and substituting for them a thin plate of kaolin. The light produced is said to be softer, steadier, and more constant than that obtained by any previous method. Successful experiments with M. Jablochkoff's invention both in France and England have shewn it to be readily applicable to many purposes. It was lately tried at the West India Docks, London, where its power of illuminating large areas for the purpose (among others) of unloading ships by night, was fully demonstrated. Moreover, its portability is such that it can be carried into the depths of a ship's hold. We may mention as a result of these experiments, that the various gas companies' shares have been depreciated to a considerable extent.
Meanwhile, improvements in the magneto-electric machine have not been wanting; Siemens in England and Gramme in France have succeeded in obtaining intense currents from machines far less bulky than those of the old pattern. But still steam-power is required to set them in motion, and until this is obviated, we cannot expect that the electric light can become really available for more general use. The inventors claim that their method of illumination is, for the amount of light obtained, far cheaper than any other known, pleading that one burner is equal to one hundred gas-lights. But we must remember that for ordinary purposes this amount of light is far beyond our needs. In factories where steam-power is already available, and where the light would supersede a large number of gas-burners, it can of course be employed with profit. Indeed we learn that at several large workshops in different parts of France the light is in actual use with the best results. Some of the railway stations both there and in Belgium are also making arrangements for its immediate adoption.
The problem, however, which has now to be solved is, whether the light can be made available for domestic purposes. We fear that the necessary motive-power presents an insuperable objection; for although, as we have explained, one engine will feed a certain number of lights, it will bear no comparison in this respect with the capabilities of a small gas-holder. Besides which, a man would have far more difficulty and expense in starting a steam-engine in his back-garden than he would have (as is commonly done in country districts) in founding a small gas-factory for the supply of his premises. Without losing sight of the benefits which coal-gas has given us, we may hope that it is not the last and best kind of artificial illumination open to us. It blackens our ceilings and walls; it spoils our books and pictures, besides robbing our dwellings of oxygen, and giving us instead a close and unhealthy atmosphere. The combustion of electricity is on the other hand, as we have already shewn, independent of any supply of air; and instead of vitiating the atmosphere, it adds to it a supply of that sea-side luxury ozone, which may truly be said to be 'recommended by the faculty.' Besides these advantages, it can be used without any sensible rise of temperature. Another great advantage which its use secures is its actinic qualities, which would enable artists and all whose work depends upon a correct appreciation of colours, to be independent of daylight.
In conclusion, we may say that, beyond the special uses for the electric light which we have enumerated, and for which it has by experience been found practicable, we see no likelihood of its more general adoption until two requisites are discovered. The one is a substance that will, without wasting away and requiring constant renewal, act as an incandescent burner; and the other is a cheap and ready method of obtaining the electric fluid. For the former we know not where to look, for even the hardest diamond disappears under contact with the electric poles. But with regard to the latter, we cannot help thinking how, many years ago, Franklin succeeded by the aid of a kite-string in drawing electricity from the clouds. Is it too much to hope that other philosophers may discover some means not only of obtaining the luminous fluid from the same source, but of storing it up for the benefit of all?