By Leo Daft.

I shall experience one difficulty in addressing you this evening, which is, that although I do not wish to take up your time with purely elementary matter, I wish to make the subject clear to those who may not be familiar with its earlier struggles.

If we begin at the beginning we have to go back to the time when Faraday made the discovery that light could be produced by the separation of two carbon rods conducting a current of considerable tension. That is the historical point when electric lighting first loomed up as a giant possibility of the near future. This occurred about the year 1846. In some experiments he found that although the circuit could not be interrupted by any considerable interval when metallic terminals were used without breaking the current, when carbon was substituted the interval could be largely increased, and a light of dazzling brilliancy appeared between the points.

This remarkable effect appears to be produced by the rarefaction of the air, due to the great heat evolved by the combustion of the carbon, and also to the passage of incandescent particles of carbon from pole to pole, thus reducing the resistance, otherwise too great for the current tension.

That was the beginning of electric lighting; and perhaps it will be well to bridge the long and comparatively uninteresting interval which elapsed between this discovery and the equally important one which alone gave it commercial value - I refer to the production of suitable currents by mechanical means. That is to say, the substitution of energy obtained from coal in the form of steam power reduced the cost to a fraction of what it necessarily was when the galvanic elements were used. Here is the point; the cost of zinc today is something over fifty times that of coal, while its energy as a vitalizing agent is only about five times greater, leaving a very large margin in favor of the "black diamonds." This is not the only advantage, for the resulting impulse in the case of mechanical production is much more uniform in action, and therefore better suited to the end in view, while the amount of adjustment and attention required is beyond comparison in favor of the latter means.

The machines adopted were of the magneto variety, and many ingenious machines of this class were operated with more or less success, being, however, quickly abandoned upon the introduction of the dynamo-machine, which gave currents of much greater electromotive force from the same amount of material, the advantage being chiefly due to the large increase of magnetic intensity in the field magnets. At this period lights of enormous power were produced with ease and by the use of costly lamps. With complicated mechanism a new era in artificial illumination seemed close at hand, but a grave difficulty stood in the way - namely, the proper distribution or subdivision of the light. It was quickly found that the electric difficulty of subdividing the light, added to the great cost of the lamps then made, was an apparently insurmountable obstacle to its general adoption, and the electric light was gradually taking its place as a brilliant scientific toy, when the world was startled by the introduction of the Jablochkoff candle, which may fairly claim to have given a greater impetus to the new light than any previous invention, a stimulus without which it is even probable that electric lighting might have slumbered for another decade.

The Jablochkoff candle embodies a very beautiful philosophical principle, and though its promises have not been fulfilled in general practice, we must not forget that we owe it much for arousing scientific men from a dangerous lethargy.

Up to this time the light had always been produced by approximation of carbon rods with their axes in the same plane; but the Jablochkoff candle consisted of like rods arranged parallel to each other and about one-eighth of an inch apart, the intervening space being filled with plaster of Paris, and the interval at the top bridged by a conducting medium. The object of the plaster, which is a fairly good insulating material at ordinary temperatures, is to prevent the passage of the current except at the top, where the conducting material just referred to assisted the formation of the arc at that point, and the resulting intense heat maintained the plaster in a moderately conducting state until the whole carbon was consumed. Here, then, was literally an electric "candle," which could be operated without the costly and unsteady lamps, and fortunately its birthplace was Paris - then the center of philosophical research; from that period the future of electric lighting was assured.

When we reflect that owing to the greater disruptive energy of the positive terminal, the carbon so connected to an ordinary dynamo machine is consumed very much faster than the negative - sometimes in the ratio of 3 to 1 - it will be clear that some other means of consuming the Jablochkoff candle had to be used, since the arc would cease to exist in a very short time by reason of the unequal consumption of the carbons, and the subsequent increase of the intervening space beyond the limit of the current tension.

This difficulty M. Gramme overcame with characteristic ingenuity by adding to the ordinary system a "distributer" capable of delivering plus and minus currents alternately, thus equalizing the consumption, besides being able to supply a large number of candles on the multiple circuit system, each circuit supporting four or five lamps. Thus it will be seen that a result was attained which at least gave such men as Siemens, Gramme, and their peers, if such there be, confidence in the future and a courage which quickly placed the new science safely beyond the limits of the laboratory. I will not occupy your time by stating the apparent reasons why the Jablochkoff candle has not fully sustained its brilliant promise - it will, perhaps, be sufficient to state that it is now superseded practically, though it must always occupy an honorable place in scientific annals.