Applications of Electricity 



235 



you can readily get the idea of 

 oscillation. Radio employs these 

 Hertzian waves. 



The Sending Station. The 

 sending or broadcasting station 

 uses apparatus which forms 

 Hertzian waves and projects 

 them into space in all directions. 

 In place of the spark, the more 

 modern stations use the vacuum 

 tube to generate the to-and-fro 

 electric discharge which results 

 in waves which go out from the 

 antennae, or wires, high in the 

 air. The vacuum tube gives a 

 more uniform wave than the 

 spark. 



The principal parts of the 

 sending set are the dynamo, 

 microphone, transformer, vac- 

 uum tube, inductance coil, and 

 antenna. 



In broadcasting, the voice of 

 the sender strikes the micro- 

 phone, which is much like a 

 delicate telephone transmitter, 

 and causes a disk to vibrate. 

 This vibration results in varia- 

 tions in resistance which cause 

 the electric current passing 

 through the transmitter to 

 change the sound waves to 

 electrical waves. The trans- 

 former increases the pressure 

 of the current. Under this 

 increased pressure, the current 

 passes into the vacuum tube 



AN EARLY RECEIVING SET 



