45 



as to whether the temperature of the carbon terminals is 

 the same under all conditions. Some have believed that 

 it is the temperature at which carbon vaporizes and 

 consequently is always the same. Others have believed 

 that they have found changes in the temperature. Wilson l 

 examined the luminosity of the anode with different pres- 

 sures of the surrounding gas and found that with higher 

 pressures it was less luminous. At 20 atmospheres it had 

 fallen to a dull red. He concluded that the temperature 

 of the crater depended on how much it was cooled by the 

 surrounding gas. 



Later experiments by Wilson and Fitzgerald 2 led them 

 to believe that this decrease in the luminosity was due to 

 the formation of NO 2 , which became so abundant at the 

 higher temperatures as to decrease the amount of light 

 appreciably. They were, therefore, unable to tell whether 

 the temperature of the carbons decreased or not. 



Waidner and Burgess in the course of their work varied 

 the current from 15 to 30 amperes, and concluded that 

 the temperature of the positive anode increased about 

 70 degrees. 



On the other hand Reich 3 using a Wanner pyrometer 

 found the temperature of the cathode to be 3140 degrees 

 absolute, with currents varying from 3 to 12 amperes. 

 He found the temperature of the anode to be 3700 degrees 

 absolute, which was also independent of the current. He 

 believed that the change observed by Waidner and Burgess 

 may have been due to the increased brilliancy of the gases 

 in the arc with larger currents. He found, however, that 



1 Proc. Roy. Soc., 58, 174; 1895. 



2 Proc. Roy. Soc., 60, 377; 1897. 



3 Phys.ZS., 7, 73; 1906- 



