Page:Popular Science Monthly Volume 52.djvu/760

738 has to be reduced by being passed through the machines shown in the illustration, which are called step-down transformers, their office being to reduce the pressure of the current. These transformers in reality do not reduce the pressure of the current; what they do is to generate a second current, by the aid of the energy derived from the first, of a much lower pressure. The power of the substation is to be used for all purposes, for "arc" and incandescent lighting, for driving stationary motors, and for the operation of electric railways.

The Big Cottonwood Power Company has about completed the construction of an important plant to utilize the water power of the lakes in the Wahsatch Mountains, and distribute it in and around the vicinity of Salt Lake City. These lakes, which empty into the Big Cottonwood Canon, lie at elevations above the sea ranging between eleven thousand and thirteen thousand feet; therefore the total amount of power available is very large on account of the enormous fall. The Big Cottonwood Company controls a fall of about one thousand feet, but in the present installation will only use about four hundred feet. The water is confined in a reservoir, as shown in the topographical map on page 737, and is conveyed by pipe line to the power house, as is shown quite clearly in the illustration of the site of the latter on page 739, where the pipe is seen in the background, descending between the mountains. To guard against an accidental giving way of the reservoir, as well as to render it possible to empty it when desired without interfering with the operation of the plant, the pipe line is carried along the bottom to the upper end of the reservoir, where it connects with the main source of supply. By closing one gate and opening another, the water may be drawn from either point, as occasion may require.

The capacity of this plant is about twenty-five hundred horse power, which will be distributed at a distance of about fourteen miles. The water wheels are mounted directly upon the shafts of the electric generators, as can be seen from the illustration of the interior of the power station shown on page 741. The generator in the foreground is not provided with a water wheel; the only part of this apparatus visible is the water pipe under the shaft, between the two bearings. This generator was not completely mounted when the photograph was taken, but the two machines in the background, it will be noticed, are provided with water wheels, which are mounted on the shaft in the space between the two bearings, which in the front generator is uncovered. The simplicity and solidity of this apparatus are very striking, and, being one of the latest installations, show clearly the perfection to which machinery of this class has been carried; and from the fact that the capacity of