240 



and thus the values of 



Mr. A, A. Robb on the Conduction of Electricity 

 about "45 and '55. 



and 



are respectively 



Ri + R2 I^i H~ R2 



Now Langevin gives e = '27 at 760 mm. pressure and '62 

 at 1550 mm. for the case of air. 



Thus 6 = -45 corresponds to about 1*53 atmospheres, and 

 e='55 to about 1*83 atmospheres. 



Accordingly, for air at these two pressures the equation has 

 the desired form, and may be solved. 



Taking, then, for simplicity n — e (n = 1 — e gives of course 

 the same final result), we have 



This gives 



s 



nd 



e e 



-1)6'' 



0, 



e 2 - 



where Ci and C 2 are constants of integration. 



By reversing the various steps indicated, we may finally 

 obtain y and v in terms of 6 as an auxiliary variable; but 

 it is desirable to introduce a slight change of notation in order 

 that the final result may not contain a third and superfluous 

 constant. 



We accordingly write 



and 



a transformation which is only possible if d be different from 

 zero, and finally obtain y and v in terms of the auxiliary 

 variable <j>. Thus 



d<f) 



!f- 



e(l— 2e) 



y/^ 



+ h 1 



1 



2c(l-e) 



!ej 



> 2 -e'-l 



1_ 



«H-1 J 



K (ii) 



const. 



As may readily be proved by differentiation. 



