The lighting of large spaces by electricity in a profitable manner may be dated from 1875. The possibility of producing a brilliant light with this fluid had been well known to physicists ever since Sir Humphry Davy's experiments in 1813, but no method of generating the electricity cheaply had hitherto been invented. Utilizing among others the inventions of Dr. C. W. Siemens, Mr. Charles G. Brush, of Cleveland, 0., gave to the world in 1875 his remarkably efficient dynamo or generator, and from that time the illumination of streets and squares by electricity began to be somewhat common. There was, to be sure another difficulty to be overcome, even for lighting on a grand scale, that of maintaining a steady and continuous light. In this the Jablochkoff candle, used in the Paris streets by 1878, was measurably successful. It was a voltaic arc arrangement, in which, by making each of the two carbon pencils alternately positive and negative, their ends were consumed with equal rapidity and so kept perpetually the same distance apart. [Illustration: Portrait.] Thomas A. Edison. [Illustration: Three men watching a train passing through a long tunnel.] The Hoosac Tunnel Lit by Glow Lamps, after the Plan of the Marr Construction Company. But the voltaic light was too brilliant for a small area. How to divide and subdue it so as to render it suitable for house lighting, was still a difficult problem. Farmer, Sawyer, Mann, and Edison, all attacked it at nearly the same time, going back with singular accord from the voltaic arc principle to that of incandescence in a vacuum. Edison, the prodigy of the century in inventive genius, was the most successful. Besides improving the dynamo, he perfected with little difficulty a cheap vacuum-globe. After long experimenting he succeeded in the more arduous task of securing an automatic checking of the current before it became hot enough to consume the incandescent carbon. He also found that a large current could be divided into smaller ones by splitting up the conductor into minor filaments. Triumph in household illumination was thus achieved, and when, in October, 1878, the results of Edison's experimenting were announced to the world, gas fell from twelve to twenty per cent. The alarm was premature, however, since the new illumination did not, after all, prove so satisfactory as to displace the old. It largely did so for streets, factories, and halls, but to no very great extent for residences. [Illustration: Drawing of lamp.] Edison's Platinum Lamp on Carbon Support, 1879. [Illustration: Drawing of lamp.] Edison's Paper Carbon Lamp. [Illustration: Drawing of lamp.] Edison's First Incandescent Platinum Lamp.