ARC IN AIR BETWEEN CARBON ELECTRODES 37 



differed so decidedly as to a small residual E.M.F. is hard 

 to understand. 



Lecher, 1 Luggin, 2 Corbino and Liga 3 concluded that 

 there was no residual E.M.F. Strenger 4 concluded that 

 if there was one it was small compared with 10 volts. 

 Hertzfeld 5 thought at first that he had found one, but 

 afterwards concluded that the observed effects were due to 

 thermo junctions outside the arc. Le Roux 6 found a 

 residual E.M.F. but did not give its magnitude. 



Arons 7 thought that the vapor remaining between the 

 carbons after the impressed E.M.F. was removed was not 

 conducting for small voltages, and that it was necessary to 

 apply 1 8 volts in order to get any current through it. 



Granqvist 8 showed that Arons' failure to get a current 

 with lower voltages was due to using a non-sensitive galva- 

 nometer. Granqvist himself was able to pass a current 

 from one Daniell cell. His method was similar to Ed- 

 lund's, except that he used a rotating switch which closed 

 the galvanometer circuit 0.0009 second after the main cir- 

 cuit was broken. He also assumed Ohm's law to hold, but 

 his voltages were much smaller than Edlund's, so that the 

 error which was introduced in his calculations was much 

 smaller. He found a residual E.M.F. of 0.23 volt in the 

 opposite direction to that of the impressed E.M.F. 



Blondel, 9 using a method almost identical with that of 



1 Wien. Sitzungsber., 95, 2 A, 992; .1887. 



2 Wien. Sitzungsber., 98, 2 A, 1192; 1889. 



3 Monash, Der Elektrische Lichtbogen, p. 134. 



4 Wied. Ann., 45, 33; 1892. 



6 Wied. Ann., 62, 435; 1897. 



6 Lum. Elec., 3, 285, and C. R., 92, 709; 1881. 



7 Wied. Ann., 57, 185; 1896. 



8 Beib., 22, 243; 1898. 



9 Lond. Elec., 39, 615; 1897. 



