44 



THE ELECTRIC ARC 



three different kinds of pyrometers in connection with 

 the same formula found values varying from 3860 to 3720 

 degrees absolute. A comparison of these results is given 

 in the following table, which is taken from the article by 

 Waidner and Burgess. 



a Black body temperature. 



b Pure graphite gives a temperature not over 50 degrees higher. 



They say concerning this: "From this table it will be 

 seen that the photometric methods based on the extrap- 

 olation of Wien's equation show that the 'black body 

 temperature of the arc' (pure graphite) is at least 3750 

 degrees absolute, so that its true temperature must be 

 higher than this; it is not possible to state how much, in 

 the absence of more definite knowledge concerning the de- 

 parture of carbon from black body radiation. In the light 

 of the best evidence that is at present available it would 

 seem that the true temperature of the hottest part of 

 the positive carbon is between 3900 and 4000 degrees 

 absolute." 



Variation in the Temperature of the Arc. There has 

 been a difference of opinion among different experimenters 



