﻿218 Mr. J. A. Brown on the Potential required 



of a. can easily be read. Such a curve is given in fig. 5 A, 

 this being based on the first determination of a made by 

 Professor Townsend*. More recently, for low pressures, 

 when the effect of j3 must be more strongly felt, it was found 

 that Curve B more nearly expresses the true state of affairs. 



Tier. 5. 















- A 



















B 

























/ 



/ 



























100 



£00 



300 



400 



500 



600 



Consequently for the larger values of -, the quantity read off 



from this may be taken to be more nearly correct, based as 

 it is on results from the simultaneous determination of a 

 and /5, which Professor Townsend points out as being ob- 

 viously the most accurate. But it must be remembered that 

 the curve is only an approximation, better determinations 

 being necessary before it can be definitely given. 



Taking a then as given by this curve, j3 can be calculated 

 from the equation 



and the effects of the positive ions at high pressures and small 



forces can be determined and compared with the curves pre- 



S X 

 viouslv found, connecting — and — . This has been done with 



>' * jj p 



two of the curves given in fig. 4, the values of a being taken 

 as 2\54 and 209 respectively for the two pressures 0*77 mm. 

 and 58 mm. 



A very simple graphical solution gives an easy way of 

 making this calculation. The above equation may be written 



ade~ ad =/3de-^. 



Constructing the graphs of each of the members of this 

 equation to solve for values of ad and /3d respectively, they 



* J. S. Townsend, Phil. Mag. v. p. 389 (1903), 



