42 THE ELECTRIC ARC 



puted on the assumption that radiation varies as the 

 square of the temperature, an assumption which is quite 

 incorrect. 



Violle 1 is the only experimenter who has made a de- 

 termination of the temperature of the arc without making 

 use of the radiation from it. He allowed small parts of 

 the heated anode to fall into a calorimeter and measured 

 the heat which they gave out. Assuming that the specific 

 heat of the carbon is the same at the higher temperatures 

 as it is at the lower, the temperature of the arc was com- 

 puted from this amount of heat. This assumption is as 

 reasonable as any made in attempting to solve this problem, 

 but the experimental difficulties of this method are very 

 great. When one remembers that only small pieces of 

 the carbon can be used and that only one surface of these 

 can have the temperature of the anode, it is surprising 

 that Violle's results were as similar to those found by more 

 recent methods as they are. By this method he com- 

 puted the temperature of the anode crater to be 3600 C. 



During the last few years there has been a great advance 

 in our knowledge of the radiation from "black bodies." 

 Such a body would be one which absorbs completely radi- 

 ations of all lengths which impinge upon it. There are four 

 equations concerning the radiation from such a body 

 which have been deduced from theoretical considerations: 

 the Stefan-Boltzmann law, i.e., E = cT*, where E is the 

 total radiation from the black body, T its absolute tem- 

 perature and c a constant; Wien's displacement law, i.e., 

 X m r = const., where Xm is the wave length having the 

 maximum amount of energy; Wien's law for the distri- 

 bution of energy in the spectrum from a black body, i.e., 

 1 C. R., 115, 1273; 1892. Journ. de Phys., (3), 2, 545; 1893. 



