680 



Professor J. A. Fleming 



[June 4, 



oscillation detector then enables not merely signals but audible 

 speech to be transmitted. In other words, it can effect wireless 

 telephony. The difficulties, however, in connection with the achieve- 

 ment of wireless telephony are not so much in the receiver as in the 

 transmitter. We have to obtain, first, the uniform production of 

 persistent electromagnetic waves radiated from an antenna : and, next, 

 we have to vary the amplitude of these electric waves proportionately 

 to, and by means of, the aerial vibrations created by the voice 



Fig. 21.- 



-Ernst Ruhmer's High-tension Aluminium Arc for Producing 

 Persistent Oscillations for Radiotelephony. 



speaking to some form of microphone. We cannot employ an 

 intermittent spark generator because each spark would give rise to a 

 sound in the telephone, and these sounds, if occurring at regular 

 intervals, would produce a musical note in the telephone. If, how- 

 ever, we make the sparks run together into what is practically a high 

 voltage arc taking a small current, then, in an oscillatory circuit 

 shunted across this arc, we have set up persistent high frequency 

 oscillations, as first achieved by Mr. Duddell. We can greatly 

 increase the energy of the oscillations by immersing the arc in a 



