The power and machinery which give vitality to this vast array of lights are to be found in Machinery Hall, and constitute one of the chief electrical exhibits. The most striking feature of this exhibit is the great Westinghouse alternating plant, which supplies the current for the incandescent lamps. It consists of twelve enormous alternating-current generators, each having a capacity of ten thousand sixteen candle-power lamps and requiring a thousand horse power apiece to drive them. They are arranged in two groups, the first six of which are coupled direct to Westinghouse upright engines. Of the remaining six, four are driven separately by different makes of engines, and two are belt-driven in tandem fashion by an Allis-Corliss cross-compound engine nominally rated at two thousand horse power, but which may be worked up to three thousand horse power upon occasion. This engine is one of two of the same type and by the same maker, the other one being stationed in the power house of the intramural railway, and is regarded as a very fine example of modern steam engineering. The alternating generators themselves are of a type only recently devised, in which there is a double row of field poles, and a double set of armature coils, by means of which the machines can supply two separate circuits for the requirements of incandescent lighting, or furnish what is known as a two-phase current for use with alternating-current motors. The current as generated has a pressure of two thousand volts, which is reduced down, at the point of consumption by means of converters, to fifty or a hundred volts.
Besides the "alternators," as these machines are technically termed, there are a large number of direct-current machines in this building supplying the currents to the arc lamps, and the motors scattered through the various buildings. The plan adopted by the Exposition authorities has been to confine the engines and boilers to Machinery Hall, so that all the power required in the Exposition except that for the intramural railway, is generated here and transmitted by electricity through underground conduits to the place where it is to be used. The exhibition is therefore an illustration of the electric transmission of power upon a large scale, and should furnish a basis for the collection of instructive data.
The feature of the Exposition which will command the most interest of any of those in which light plays a prominent part will probably be the electric fountains. Fountains of this character have been features of a number of exhibitions since 188-i, when the first one, designed by Sir Francis Bolton, was shown at the Healtheries in London, but those at Chicago are upon a much greater scale than any heretofore attempted. The principle of operation is that of throwing a powerful beam of light from be-