Page:Jack Heaton, Wireless Operator (Collins, 1919).djvu/173

 deeply in the earth and radiating in every direction from the station. This network of wires extends over, I should say, ten acres, and this, of course, makes a very good ground.

The current for energizing the sending apparatus is taken from the lines of the ; this runs an electric motor of 200 horse power which in turn drives a 100 kilowatt alternating current generator; the current from the latter flows through a transformer which raises the pressure of it to 25,000 volts. Next a battery of compressed air condensers are charged with this high voltage current and this is discharged by a rotating spark-gap. This spark-gap has a wheel, on the rim of which is set a number of metal points, or electrodes as they are called, and around them are an equal number of fixed metal points or electrodes.

When the wheel revolves sparks are made only when the electrodes on the wheel and those that are fixed around it are exactly in a line. Now instead of a few big sparks taking place every second, a thousand smaller ones occur in a second and this makes a whistling sound which is heard by the operator who is listening