efforts to perfect his invention. His ideas were evidently far in advance of his time. The Edison lamp differed from those which preceded it in the extremely small section of the carbon strip rendered hot by the current, and in the perfection of the vacuum in which it was mounted. The filament was first made of carbonized paper, and afterwards of bamboo carbon. The modern incandescent lamp has for years past been provided with a filament made by a chemical process. The carbon formed is exceedingly homogeneous and of uniform electric resistance. Edison first exhibited his lamp in his laboratory at Menlo Park, New Jersey, in December, 1879; but before it could be properly utilized an enormous amount of work had to be done. His task was not merely the improvement of an art already existing; it was the creation of a new art. Special dynamo machines had to be invented and constructed for working the lamps; switches were needed for connecting and disconnecting lamps and groups of lamps; meters for measuring the consumption of electric energy were wanted; safety fuses and cut-offs had to be provided; electroliers or fixtures to support the lamp were required; and, lastly, a complete system of underground mains with appurtenances was a requisite for city plants. Even the steam-engines for driving the dynamos had to be remodelled and improved for electric work, and ten years of electric lighting development did more towards the refinement and perfection of steam-engines than fifty years preceding. Steadiness of lights meant the preservation of steady speed in the driving machinery. The Pearl Street station in New York City was the first installation for the supply of current for incandescent lighting in a city district. The constant pressure dynamos were gradually improved and enlarged. The details of all parts of the system were made more perfect, and in the hands of Edison and others the incandescent lamps, originally of high cost, were much cheapened and the quality of the production was greatly improved. Lamps originally cost one dollar each. The best lamps that are made can be had at present for about one-fifth that price. Millions of incandescent lamps are annually manufactured. Great lighting stations furnish the current for the working of these lamps, some stations containing machinery aggregating many thousands of horse-power capacity. Not only do these stations furnish electric energy for the working of arc lamps and incandescent lamps, but, in addition, for innumerable motors ranging in size from the small desk fan of one-tenth horse-power up to those of hundreds of horse-power. The larger sizes replace steam or hydraulic power for elevators, and many are used in shops and factories for driving machinery such as printing-presses, machinery tools, and the like.