This early station grew and prospered, and continued in successful operation for more than seven years, until January 2, 1890, when it was partially destroyed by fire. This occurrence caused a short interruption of service, but in a few days current was again supplied to customers as before, and the service has never since ceased. Increasing demands for service soon afterward led to the construction of other stations on Manhattan Island, until at the present time the New York Edison Company (the successor to the Edison Electric Illuminating Company of New York) is operating over forty stations and sub-stations. These supply current for about 800,000 customers, wired for 17,000,000 incandescent lamps and for about 1,300,000 horse-power in electric motors. The early success of the first central station in New York led to the formation of new companies in other cities, and the installation of many similar plants. The business has grown by leaps and bounds, until at the present time there are many thousands of central stations spread all over the United States, furnishing electric light, heat, and power, chiefly by use of the principles elaborated so many years ago by Mr. Edison. We ought to mention that this tremendous growth has also been largely due to another invention made by him in 1882, called the "three-wire system." Its value consists in the fact that it allowed a further saving of sixty-two and one-half per cent, of copper required for conductors. This invention is in universal use all over the world. It may be mentioned here that at the opening ceremonies of the Electrical Exposition in New York, on October 11, 1911, the leading producers and consumers of copper presented Mr. Edison with an inscribed cubic foot of that metal in recognition of the stimulus of his inventions to the industry. The inscription shows that the yearly output of copper was 377,644,000 pounds at the time of Edison's first invention in 1868, and in October, 1911, the yearly output had increased to 1,910,608,000 pounds. XVII EDISON'S ELECTRIC RAILWAY It is quite likely that many of our young readers have never seen a horse-car. This is not strange, for in a little over twenty years the victorious trolley has displaced the old-time street-cars drawn by one or two horses. Indeed, a horse-car is quite a curiosity in these modern days, for such vehicles have almost entirely disappeared from the streets. The first horse railroad in the United States was completed in 1827, and it was only seven years afterward that a small model of a circular electric railroad was made and exhibited by Thomas Davenport, of Brandon, Vermont. Other inventors also worked on electric railways later on, but they did not make much progress, because in their day there were no dynamos, and they had to use primary batteries to obtain current. This method of generating current was far too cumbersome and expensive for general use.