USE OF ARC IN WIRELESS TELEPHONY 153 



necessary to use arcs which not only have steep character- 

 istic curves, but also have such curves for rapid oscillations. 

 Among the different forms of arc which have been used 

 successfully is that with graphite terminals. Austin 1 has, 

 given the following data concerning such an arc. 



Electrodes graphite, ends flat. 



Diameter 12 mm. 



Resistance in series with arc about 50 ohms. 



Arc current 4 amp. 



Voltage across arc 26 volts. 



Voltage open circuit 242 volts. 



Arc length about 0.3 mm. 



Inductance in shunt circuit 0.009 millihenry. 



Capacity 0.4 micro-farad. 



Alternating current in shunt 4 amp. 



He found still better results with the arc in a stream of 

 hydrogen or steam. But the best results which he ob- 

 tained were with the arc between silver terminals in air 

 under a pressure of about 7 atmospheres and with an E.M.F. 

 of 4500 volts. The arc then takes on all the characteristics 

 of a very rapid spark discharge and it is possible to develop 

 a large amount of power in the shunt circuit. 



Applications of the " Whistling " Arc to Wireless Te- 

 lephony. The application of the whistling arc to wireless 

 telephony is a subject belonging to works on that subject 

 and can not be adequately treated here. However, two 

 diagrams are given which show how the arc is connected 

 to the other parts of the transmitting apparatus, so as to 

 send electric waves out into the ether. In order to do this 

 two additions must be made to the device shown in Fig. 52. 

 First it must be changed so that modifications may be made 

 in the electric oscillations which shall correspond to the 



1 Bull. Bureau Standards, 3, 325; 1907. 



