Electrical Conductivity of Atmospheric Air. 703 



curve indicates that the conductivity was tending towards a 

 limiting value, which the reading taken after forty-four hours 

 showed to be about 6*5. 



As a variation in the experiments, a series of tests were 

 made in air confined in a receiver at high pressures. The 

 cylinder in this case was of heavy rolled iron coated with 

 zinc, and was of the same dimensions as that used in the first 

 measurements. 



The results of observations on the conductivity of air con- 

 fined at a pressure of about seven atmospheres are given in 

 column 2, Table I., the scale used being the same as before. 

 The curve representing these values is shown in fig. 3, and 

 exhibits the same characteristics as that for the lower pressure. 

















Fig. 



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" We have again the rapid decrease to a minimum followed 

 by a gradual rise tendino- towards a limiting value. The 

 minimum conductivity in this case was about 6' 6, and was 

 reached in about four hours after the required pressure in 

 the cylinder had been obtained. The time occupied in pump- 

 ing the air was about one hour. 



In seeking for an explanation of the curves shown in 

 fio's. 2 and 3, their two-fold origin as indicated bv the dotted 

 lines, is at once suggested, the conductivity in the initial 

 stage being due to an agent subject to rapid decay, and that 

 in the second to one whose power shows a gradual increase. 



The first of these dotted curves is similar to that given by 

 Rutherford* for the conductivity of the air in a chamber 

 * Rutherford, Phil. Mag. Jan. 1000, p. 0. 



