Wireless Telegraphy and Telephony

130 WIRELESS TELEGRAPHY 2. Means for varying or. modulating the stream of elec- trical waves in accordance with the sound waves. 3. A receiver, continuously responsive and capable of corresponding with sufficient rapidity to the speech har- monics. In order to obtain the desired result, recourse is had to an arc lamp as a generator of undamped high frequency oscillations. When an arc is properly connected with a condenser and Fig. 144.—How the sound waves of the voice are impressed upon undamped oscillations. an impedance coil it will emit a musical note. The note is due to rapid changes in the arc, a very important factor which led to its recognition as a value in wireless telephony. When the condenser and inductance are shunted across an arc supplied with direct current, the condenser immedi- ately becomes charged, and the current through the arc is diminished. The potential difference across the latter is therefore instantly increased, tending to further charge the condenser. This increase of charge reacts on the arc, increasing its current. The condenser discharges, through the inductance coil, and becomes charged in the opposite direction, just like a spring, which released, goes beyond its normal position and then returns. The operation is repeated many times per second (usu-