630 
Proceedings of the Eoyal Society 
the constants may be got from three points (j\ , t x ) . . . (j s , t 2 ), 
where t 1 . . . t s are in arithmetical progression, by means of the 
following equations : — 
a 3 \3?, 
log b = i % 1og zlA z h log zh> 
t i - t l 
e _ lo g (« -ii) - } °g ( a -jj ) 
(h - h) lo s £ 
For the curve in fig. 1, I obtain the following equation by means of 
points between t= 10 and t = 19 — 
j=- 162-*165s-' 1 ^. 
The position of this curve is shown in the figure by means of the 
dotted line. 
Fig. 2 shows the results of another experiment, in which the 
current-density was different. Here the point (*37, 0) is taken as 
origin. The equation to this curve calculated from the points 
corresponding to t — 5, t = 7, .... on the assumption that it is a 
logarithmic curve, is 
/=T16-T01s-' 218 *. 
It will be seen that this curve coincides with that obtained by 
experiment except near the origin. I find that the observed points 
lie very accurately on a curve whose equation is of the form 
j = a - hg-ci+ d e~ et . 
This curve practically coincides with the former for values of t 
greater than 5, so that we may assume a, b, and c to have the same 
values in both. To determine d and e we have the equations 
! & 
log . = ct 
a-J 
log — ” Vf = ct — di~ et , 
°a-j 
where j and / correspond respectively to points on the logarithmic 
