Page:Popular Science Monthly Volume 91.djvu/885

 Popular Science Monthly

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��this switchboard, is a panel carrying 300 signal lamps and a. duplicate set of tele- phone terminals. When a feeder is in operation a green lamp shows. This is re- placed by a red lamp when the feeder is not in operation. This makes the location of any trouble in the system an easy mat- ter.

The field frame of these gigantic genera- tors is twenty-one feet high and twenty- six feet across the supporting legs. The weight of each com- plete generator is 105 tons. Five tons of copper are used in its ccnstruction. Owing to their immense size, it was necessary to construct these gener- ators in parts, for the height of the arma- ture alone is greater than the clearance on most railroads at bridges and tunnels. To transport the parts of each generator from Ampere, N. J., to Detroit, Mich., required four freight cars.

Each generator develops 3,750 kilowatts at an electrical pressure of 250 volts and 80 revolutions per minute. This quantity of electrical energy would light 150,000 25- watt lamps, or 7,500 arc lamps. It is equivalent to 5,000 horsepower and the out- put of a single generator would be sufficient to run 300 street cars. Each gener- ator supplies continuously 15,000 amperes of current. The whole plant supplies 260,000 amperes. The total output is one-eight eth of the potential ca pacity of Niagara.

These generators are driven by fourteen 6000-horsepower and one 4000-horsepower reciprocating engines of the gas-steam type and one 1500 horse- power straight steam engine, all of which are direct-connected to the shafts of the genera- tors. The water used

���Here you get an idea of the size of the gen- erator by a simple comparison of the field casting with a four-passenger Ford car

��in cooling cylinders, pistons, valve boxes and bearings of the gas unit leaves the engine at a temperature of 175 degrees Fahrenheit and is utilized for boiler feed and hot water factory supply. The exhaust gases, at a tempera- ture of 1 1 00 degrees Fahrenheit are em- ployed to maintain the temperature of the steam between the high and low pressure cylinders of the steam engines, after which it pre- heats the boiler feed water. The steam engines are of the double expansion Gorliss type. The boilers contain 1800 tubes having an ap- proximate heating surface of 26,000 square feet.

���Germany's spike-studded boards which were left all along the roads when the Hindenburg Line retreated. They were intended to cripple the pursuing Allies but they were discovered in time

��One of the Ways the Retreating Ger- man Army Tried to Prevent Pursuit

WHEN the Germans made what has be- come known as the strategic retreat of the Hindenburg Line they very naturally wanted to prevent the Allies from following them too closely. Various obstacles were put in the path of the pursuers. Those which they counted on to make the most trouble for their enemies were huge spiked boards, shown in the accom- panying illustration.

These wicked-look- ing boards were placed all along the roads and in the trenches. They are constructed of heavy planks thickly studded with spikes. These were covered over with brush, leaves, branches of trees or any other available "camouflaging" device which might be de- pended upon to con- ceal the obstruction from the rapidly ad- vancing troops.

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