1020] Thermionic Valve in Wireless Telegraphy & Telephony 177 



space which are propagated outwards as an electromagnetic wave. 

 Whether, in view of Einstein's revolutionary theory of Relativity, we 

 have justification for speaking any longer of an electromagnetic 

 medium or of an aether must be left to those who have more know- 

 ledge of that theory than your lecturer possesses, but we may, perhaps, 

 still be permitted to postulate a space-filling medium as a convenient 

 hypothesis. It is certain that wireless telephony is achieved by 

 some kind of undulation propagated through space, and if so, then 

 there must surely be somethiuo- which undulates. 



Fig. 13. — Diagrammatic Sketch showing the Principles of 

 a Wireless Telephone Transmitter and Receiver. 



Ae.t, transmitting aerial. Ae.r, receiving aerial. A, a high 

 frequency alternator or else a generating valve. P, S, oscillation 

 transformer. T, speaking carbon microphone. V, receiving 

 valve. P, receiving telephone. 



We have in the next place to vary the amplitude of these radiated 

 electromagnetic waves by a speaking microphone, and this is done by 

 means of a Control Valve. 



This latter valve has its grid circuit inductively connected by a 

 transformer with a circuit containing a battery and a telephone 

 transmitter. 



Hence, when speech is made to the mouthpiece of the carbon 

 microphone, this varies the electric current through it, and therefore 

 the potential of the grid, in accordance with the wave form of the 

 speech sound. The plate circuit of this control valve is joined in 

 parallel with that of the generating or power valve, and the result is 



Vol. XXIII. (X T o. 1U) n 



