By permission oj Martuni'* H'/ri'/i'.v.v Telegraph Co., Ll.l. 

 THERMIONIC VALVE 



This apparatus is called a " valve " because it permits an elec- 

 tric current to pass in only one direction, and thus enables this 

 current to operate the telephone set in the wireless receiving 

 apparatus. The thermionic valve is fully described in the 

 text. It has revolutionised wireless telegraphy of late. 



C W 



wwv 



From "Fifty Years of Electricity" (The Wireless Press, Lid.). 



A DIAGRAM ILLUSTRATING THE NATURE OF THE APPARATUS FOR CONDUCTING 

 WIRELESS TELEPHONY 



On the left-hand side is the transmitter, by which continuous electric waves (CW) are 

 thrown off from the aerial. These are altered in amplitude or height by speaking to the 

 microphone T. At the receiving station (on the right) the aerial picks up these waves, and 

 they are rectified by a thermionic valve V and heard as speech sounds in the telephone 

 receiver R. 



In the actual apparatus the persistent oscillations in the sending aerial are created by a 

 three-electrode thermionic valve. 



