236 Our Surroundings 



which produces rapid to-and-fro motions. The inductance coil 

 regulates the length of the electrical waves before they reach 

 the antenna where they pass into space. These electrical waves 

 travel through the air at a rate of about 300,000,000 meters, or 

 186,000 miles, per second, the same speed as light. 



One movement- of the current in each direction through the 

 vacuum tube is called a cycle. 1000 cycles is one kilocycle. The 

 broadcasting stations in the United States vary in the number of 

 cycles per second from 500,000 to 1,500,000, or from 500 to 1500 

 kilocycles. 



Each cycle sends off one wave. The distance a wave travels 

 per second divided by the number of cycles a station sends per 

 second gives the wave length. For example, WEAF at New York 

 may announce that it is operating under a frequency of 660 kilo- 

 cycles, which is 660,000 cycles. 300,000,000 divided by 660,000 

 gives 454.54, the length of a wave in meters. The lengths of 

 waves sent out by stations in the United States vary from 550 

 meters to 200 meters. However, new stations, known as short 

 wave stations, are now appearing. Some of these send out waves 

 less than a meter in length. These short waves have better car- 

 rying quality and do not require so much power. 



The room in which the broadcasting is done is called the 

 studio. It must be carefully constructed since any vibration or 

 reflection of sound will affect the quality of the broadcasting. 

 The early studios were hung with draperies to prevent echo. The 

 more modern ones have walls made of sound-deadening material. 



The Receiving Set. A receiving set is necessary in order 

 to take from the ether the messages of sending sets and turn 

 them back into sound. The essential parts of a receiving set are 

 the antenna, the transformers, the variable condenser, the vacuum 

 tubes, and a source of electric current. The house lighting circuit 

 is used where possible; otherwise batteries furnish the electric 

 supply. 



In receiving, the waves in the ether from the sending set 

 strike the antenna and set up similar electric waves in its wires. 

 The variable condenser and its transformer may be adjusted so 

 that they let through only waves of a certain length, allowing but 



