﻿Potential and the Velocities of Electrons. 



589 



between the nickel box and the various plates are shown in 

 Table IV. 



Table IV. 



Metal 



Al (1). 



Zn. 



Brass. 

 -02 



Cu. 



Pt. 



Al (2). 





Contact difference \ 

 of potential. j '" 



•89 



•58 



-•14 



-•20 



1-02 



In fig. 7 (PI. IX.) the first curve for aluminium is 

 shown in the position actually found by experiment. The 

 curve for platinum is also shown in its actual position to the 

 left. From the table we see that the contact difference of 

 potential between aluminium (1) and platinum is 1*09 volts. 

 Thus to reduce the curve for platinum to what it would be 

 if the real values of V, taking into account the contact 

 difference of potential, were the same as in the case of 

 aluminium (1) — we simply shift every point of the platinum 

 curve to the right by an amount equivalent to 1*09 volts. 

 In the same manner the readings for the other curves were 

 all reduced to that for aluminium (1) as a standard. For 

 the sake of clearness, only the curve for aluminium (1) is 

 drawn ; the points determined by the readings taken for the 

 other metals, after being corrected in each case as described, 

 are indicated but not connected together. 



We now have a series of curves which, relatively to each 

 other, are corrected for the contact difference of potential 

 between the metals. It still remains to determine the 

 absolute position of these curves along the axis of V. To do 

 this, w r e refer back to section 4 and fig. 4 (PI. IX.). Here 

 if we calculate, from the amount which each curve is dis- 

 placed for a given number of volts between C and B, what 

 the position of the curve would be with zero volts, we obtain 

 the curve (z), the position the curve should occupy if there 

 were no stray field making itself felt through C. This curve 

 is for a copper-plated box and an aluminium plate D 

 between which the contact difference of potential is 1*02 

 volts. Thus if the curve (i) is shifted to the left an amount 

 equivalent to 1'02 volts, we obtain (A), which cuts the current 

 axis at "46. This calculation was repeated for the other set 

 of curves mentioned but not shown in section 4, and the 

 average of the two results shows that the curve for an 

 aluminium plate should cut the current axis at *39. This, 

 then, is the point at which the current axis is cut by the 

 "''distribution of velocity" curve for electrons from an 



