296 MR. E. H. GRIFFITHS ON THE LATENT 
it is evident that by a movement of the connecting rods, the following resistances 
could be taken, viz. :— 
Mtr, MYR +75, ro + B+, 73 +7) 
If N,, N,, N3, and N, are the resulting numbers, we get 
R, = {(N, + Ns) — (Ni + Ny) }/2, 
and there is no necessity that 7, 7, 73, and 7, should be equal. The value of R, was 
always obtained in the above manner, and then expressed in terms of the box ohm at 
17°. A full account is given in Paper J., pp. 407-410, of the comparisons of the 
individual coils of my resistance box with the B.A. Standards, and the values of R, 
were reduced to true ohms in the manner there indicated, with the further corrections 
given in a later communication.* 
In Appendix III. I give an example of an observation together with the reductions. 
It was next necessary to find the increase in R, (6R) due to the rise of temperature 
caused by the current. This was done in substantially the same manner as that 
described in Paper J., pp. 404-407 ; dR was in this case found to be very small—as 
shown by the following table. 
TasBLe VII. 

Potential difference | 
in terms of a ok. 
Clark cell. 

“00076 
00198 
00377 
00630 
HE 0 Doe 




The resulting curve was (as in other similar cases) practically a parabola. 
A further correction was necessary for the heat developed in leads 2 and 4 in the 
portion that passed from the steel to the calorimeter lid. Their total resistance was 
0068. We may assume that half the heat here generated passed into the calorimeter, 
and therefore consider their resistance as ‘(0034 ohm = 7. Now the points kept at a 
constant D.P. were between these wires and the coil, and since JH = E?/R (1+7/R) 4, 
we get the effective resistance = R — 1. 
The following table gives the values (after the application of all corrections) of R, 
at the temperatures at which the L experiments were performed, the potential dif- 
ference being denoted by the suffix. 
* “Roy. Soc. Proc.,’ vol. 55, p. 25. 
