RADIO COMMUNICATION 



267 



as the simple wireless amateur station. Such sending stations 



are known as discontinuous wave stations because they radiate 



into the ether these series of wave-trains. In such large stations 



the source of power is usually an alternating current dynamo, and 



a high-frequency transformer is used in 



place of the induction coil. The helix may 



consist of many turns of heavy copper wire 



or rod, and the condenser usually is made 



up of many rows of large Leyden jars in 



parallel. (See Field and Laboratory Guide 



in Physical Nature-Study, p. 69.) 



The more modern method of radio trans- 

 mission employs what is known as the con- 

 tinuous wave. As the name indicates, the 

 wave motion which is radiated from the 

 antenna is not broken into a series of wave-trains each of which 

 dies out before the next begins. The continuous wave is one 

 long series of waves of radio frequency, which are sustained, and 

 have the same strength as long as the circuit at the sending 

 station is closed. A simple diagram to illustrate this continuous 

 wave in comparison with a discontinuous wave is shown in 

 Figure 122. 



FIG. 121. A rotary 

 variable condenser. 



FIG. 122. Discontinuous and continuous waves 



The methods employed to produce these continuous waves are 

 of various sorts. Sometimes an arc between a carbon and a 

 copper electrode is used. The arc is placed in a circuit with induc- 

 tance and capacity, and when properly balanced such a circuit will 



