



Modification of Ohm's Law. 67 



the wire in air as unity, the conductivities in the vapours 

 tested were approximately as follows : — 



Alcohol vapour -99949 



Chloroform vapour . '99830 



Gasoline burning gas . . '99820 



Sulphuric ether vapour '99750 



Carbon bisulphide vapour, approximately . . 1 



Rarefied air, less than 1 



Some of the phenomena observed made it seem probable 

 that only that part of the dielectric in direct contact with the 

 wire was concerned in this change of resistance. For example, 

 when the petroleum was poured out of the tube and a measure- 

 ment made before it had drained off and evaporated, the 

 resistance observed was the same as when the tube was filled, 

 with petroleum,, and it was only after the tube had been care- 

 fully drained out and dried that the resistance returned to its 

 former value in air. In the case of sulphuric ether vapour 

 this phenomenon was very marked. It was only after the 

 tube had been washed out with alcohol one or more times, and 

 had been dried out by drawing a current of air through it for 

 several hours, that the resistance returned to its former value. 



I am now engaged in investigating the same phenomenon, 

 using a silver wire of the same size as the copper wire used 

 in last year's experiments. In general, the difference in 

 resistance with the dielectrics above mentioned is less marked 

 than in the case of the copper wire formerly used, but it 

 is still noticeable. As in the case of the copper wire, the 

 greatest variation yet noticed was when the tube was filled 

 with sulphuric ether vapour, but with the silver wire the re- 

 sistance is decreased in the ether vapour, while with the copper 

 wire it was increased. The same difficulty in removing the 

 effect of the ether vapour also appears with the silver wire, 

 in which case it was only after repeated washings with alcohol 

 that the resistance of the wire returned to its former value. 



I have thus far been unable to find with what other properties 

 of the dielectrics these phenomena are correlated, but it seems 

 clear that hereafter Ohm's Law will have to be so modified as 

 to take account of the dielectric surrounding a conductor, as 

 well as the nature and temperature of the conductor itself. 



The measurements upon which the above conclusions are 

 based are given in full in a paper entitled " Some Observa- 

 tions upon the Conductivity of a Copper Wire in various 

 Dielectrics," which is now being published by the Leland 

 Stanford Jr. University. 

 Palo Alto, California, 



F2 



October 26, 1892. 



