ARC IN AIR BETWEEN CARBON ELECTRODES 39 



perature of the carbons. There is probably a very small 

 area on the cathode which is as hot as the anode, so that 

 when the impressed E.M.F. is first removed the difference 

 in temperature between the electrodes is small. The area 

 of this high temperature on the cathode is small. It will,, 



SO. 3 



\ 



\ 



0.1 



345 



TIME IN SECONDS 

 FIG. 12. 



therefore, cool more quickly than the anode, so that the 

 difference in temperature between the electrodes at first 

 increases. This would correspond to the increase in the 

 residual E.M.F. observed by Becknell. The observed 

 residual E.M.F. is in the direction corresponding with this 

 view, since the anode is hotter than the cathode after the 

 arc is extinguished. 



