10 THE ELECTRIC ARC 



work. In his explanations he was not so fortunate. His ex- 

 planation was that this " apparent resistance" was partly 

 due to a counter E.M.F., which was equal to the current 

 times the m in his formula, and partly to a "true" resist- 

 ance corresponding to the term nl. The counter E.M.F. 

 he found equivalent to 23 Bunsen cells, which is approxi- 

 mately 40 volts. 



Though this explanation was not fortunate in the sense 

 of being correct, it was very fortunate in that it caused 

 much discussion on the part of other scientists and led to 

 many new experiments. These have dealt on the one 

 hand with the accuracy of his formula, and on the other 

 with the truth of his explanation. It is scarcely of value 

 to consider in detail the data given by the different ex- 

 perimenters. If we should do so, we would find that they 

 differ greatly among themselves, and the real significance 

 of their work is that there are rarely two carbons which 

 give the same results. Even when two carbons are ex- 

 actly alike the data observed will not be identical unless 

 the conditions are the same. 1 



For example, it has been shown by Mrs. Ayrton 2 that 

 the voltage of an arc when first started is quite different 

 from what it is after it has reached a steady condition. 

 The time required to reach this state depends largely on 



1 Ayrton and Perry, Proc. Phys. Soc., 5, 197; 1882. 

 Cross and Shepard, Proc. Amer. Acad. Sc., 22, 227; 1886. 

 Frolich, Elektrot. ZS., 4, 150; 1883. 



Nebel, Centralbl. f. Elektrot., 8, 517 and 619; 1886. 

 Uppenborn, Centralbl. f. Elektrot., 9, 633; 1888. 

 Luggin, Centralbl. f. Elektrot., 10, 567; 1888. 

 Granqvist, Beib., 22, 243; 1898. 

 Thompson, Elec. Rev., 27, 262; 1895. 



2 Mrs. Ayrton's " Electric Arc," p. 107, 



