Wireless Telegraphy and Telephony

6O WIRELESS TELEGRAPHY The carborundum detector also requires a battery al- though its action is somewhat different from that just de- scribed. When a battery is used in connection with a detector, an instrument known as a potentiometer becomes necessary. A potentiometer is simply a device for accurately adjusting the voltage of a battery to a value where it will render the detector the most responsive to the incoming signals. Fig. 75, Diagram showing how potentiometer is connected in circuit. The Tuning Coil is a device for accurately adjusting the oscillation circuits to receive the waves. Its action may be illustrated to a certain extent by press- ing down the loud pedal of a piano and at the same time whistling a note loudly and clearly. Listen carefully and some of the wires in the piano will be heard sounding the note whistled. At each vibration of the note of the whistle a wave of pressure went forth from the lips and reaching the wires gave them all a tiny impulse. The impulses fol- lowed each other rapidly at definite intervals giving each of the wires the same push each time. The wires which are tuned to produce the note on the piano corresponding to that of the whistle will vibrate energetically enough to