66 Mr. F. Sanford on a necessary 



the apparatus being allowed to stand untouched for two weeks 

 to make sure that none of the constants were changing, and 

 in the whole series not a single measurement in either dielec- 

 tric fell upon or beyond the curve made for the other dielectric 

 (see PI. III. fig. 1). The resistance of the wire in petroleum 

 was shown to be about '00006 ohm less than in air ; and as the 

 whole resistance of the tube and wire averaged about '0335 

 ohm, this difference corresponded to about *18 of one per cent, 

 of the whole resistance. 



Regarding the conductivity of the wire in air as unity, its 

 conductivity in the liquid dielectrics tested was as follows : — ■ 



Petroleum . 1*0018 



Mixture of carbon bisulphide and turpentine . 1*0009 



Carbon bisulphide, uncertain, apparently . . 1 + 



Wood alcohol '9998 



Benzine '9994 



Wood alcohol and benzine '9985 



Absolute alcohol '9981 



Wood alcohol and petroleum "9973 



Distilled water, uncertain, apparently . . . 1 — 



It will be seen that when two dielectrics which do not seem 

 to mix with each other were used together the resistance of 

 the wire was greatly increased, as in the case of wood alcohol 

 and benzine, and wood alcohol and petroleum. That these 

 liquids do diffuse into each other was shown by measuring the 

 index of refraction of the two components before and after 

 they had stood in contact with each other, and in every case 

 a change was observed. 



A similar change of resistance was noticed when the tube 

 contained different gaseous dielectrics. This was first observed 

 when the burning gas used in the laboratory was allowed to 

 enter the tube. This gas was made from gasoline by a 

 machine on the ground, and consisted of the vapour of gaso- 

 line mixed with air. A series of measurements was made in 

 this gas and in air, the measurements in air being made both 

 before and after those made in the gas. Of the seventeen 

 measurements with the wire in the gas, only one was as 

 much as "00001 ohm from the curve drawn, while the nearest 

 distance of any gas measurement to the air-curve was '00004 

 ohm, and the average distance of the gas points from the 

 air-curve was '000058 ohm. From these measurements the 

 resistance of the wire in gasoline burning gas was 1*0017 

 times its resistance in air (see fig. 2). 



The other vapours used were those of volatile liquids, a 

 small quantity of the liquid being poured into the tube and 

 allowed to evaporate. Taking, as before, the conductivity of 





