CHAPTER VIII. 



USE OF ARC IN WIRELESS TELEPHONY. 



Whispering Arc. The electric arc has been used in 

 two different systems for wireless telephony. The first of 

 these had its origin in a discovery made by Simon in 1898.* 

 While working with an arc, he observed that it gave a 

 chattering noise whenever an induction coil in a neigh- 

 boring room was operated. He found, on examination, that 

 for several feet the feed wires for the induction coil were 



parallel to those running to the 

 arc. With each variation of the 

 current in the induction coil 

 there was an induced current in 

 the arc circuit, and with each 

 fluctuation of the current in the 

 arc circuit there was an expan- 

 sion and contraction of the 

 vapors of the arc which sent out 

 sound waves. 



This suggested to him the idea 

 that instead of the induction coil 

 the transmitter of a telephone 

 could be used and the arc be 

 made to reproduce the sound of 



QTmffiP T 



nrmimn 

 I P 1 



M 



FIG. 51. 



the words spoken into the transmitter, and on trying the 

 experiment this was found to occur. In order to increase 



1 Wied. Ann., 64, 233; 1898. 

 146 



