Page:Popular Science Monthly Volume 43.djvu/750

730 coils in place. It has the mechanical advantage of presenting a smooth exterior surface which can be turned true, and of holding the winding in such a way that it can not become displaced, as is possible with coils wound over the core and bound in place by a wrapping of wire. Electrically it has the advantage of materially diminishing the air gap—the space between the face of the armature and the field poles—and hence allowing the coils to move in an intenser magnetic field. The armature core is carried by a cast-iron spider weighing over fifteen tons which is keyed directly to the shaft of the driving engine. The brush holders, of which there are twelve sets, corresponding to the number of field poles, are mounted upon a yoke supported at one side of the field magnet frame. They are moved into position by means of a shifting gear operated by a hand wheel and are readily accessible from a stairway passing over the shaft. The machine is designed to run at seventy-five revolutions a minute and furnish a current under a pressure of six hundred volts. It has an electrical capacity of fifteen hundred kilowatts, and is claimed to have an efficiency of ninety-six per cent. This ponderous machine was found to be much too large and heavy to be shipped in its complete form, and was accordingly forwarded from the factory in parts and assembled upon its present foundation.

An appreciation of its size and capacity may be gained by remembering what the standards of size were only ten years ago when the Edison "Jumbo" was put to work in the first New York Central station. This machine, which created a veritable sensation at the Paris Exposition of 1881 on account of its immense size, required only a hundred and twenty-five horse power to drive it when working at its normal load. It had a capacity of less than one hundred kilowatts, which is but a fifteenth of that of the present "Jumbo," and weighed very much more in proportion to its output. It is to be seen in the exhibit of the General Electric Company, where it is rightly given a place of honor as the precursor of the race of modern direct-connected dynamos.

While a motor car will answer admirably for the lighter forms of electric traction, the invasion of the domain of the steam railroad, which electricians are already contemplating, will necessitate the design and construction of special electric locomotives. These have already been used quite largely in mine work, and a number of electrical constructors have designed and built such machines of moderate power, but the first one of any considerable size and designed for high speed is one built at the Lynn shops of the General Electric Company and shown in the Transportation Building at the Fair. It is a thirty-ton locomotive intended for a normal speed of thirty miles per hour, and is of sufficient