s 



Newbery, The Theory of Overvolt age. 



liberation. This method is of course subject to the same 

 limitation as those already given, z\e., it can only be used 

 with very low current densities. Also the fundamental 

 assumption is not correct, for though overvoltage does 

 depend partly on surface tension forces, there are other 

 equally important factors which have to be taken into 

 account. The results Muller obtained were similar to 

 those obtained by Coehn and Dannenberg. 



The following table shows some of the results obtained 

 by these three methods, and will serve to illustrate the 

 great differences of opinion held by different experimenters 

 on this subject : — 





Caspari. 



Muller. 



Coehn and 

 Dannenberg. 



Platinum 



0*005 v0 ^- 



o'oi volt. 



000 volt. 



Gold 



0'02 ,, 



0*06 ,, 



0-05 „ 



Silver 



0-15 „ 



°"o5 » 



°'°7 !J 



Nickel 



0"2I ., 



003 „ 



0-14 „ 



Copper 



0*23 » 



0*03 ,, 



o'i9 ,. 



Palladium 



0-46 „ 



0*24 ,, 



-0*26 ,, 



Lead 



0*64 ,, 



o-35 ■> 



o'3 6 n 



Mercury 



078 „ 



0-42 „ 



0-44 » 



d. Oscillograph method. 



This method was adopted by Le Blanc, Reichenstein, 

 and others. The instrument used by Le Blanc consisted 

 of a very sensitive moving coil galvanometer, having a 

 coil and mirror together weighing only 0*5 mg., and 



