THE MECHANICAL EQUIVALENT OF HEAT. 
403 
of the Clark cell at temperature 16°’8 C., hence E.M.F. = 1‘434 volts ;• another set of 
storage cells being used to give the current through the potentiometer. 
Table VI. 
Potentiometer readings. 
Battery. 
E.M.F. 
For battery. 
For Clark cells. 
No. 
1 Leclancbe . . 
. 
32-232 ^ 
32-225 j 
I 
. 33-832 
1-366 
I Storage . . . 
. 
23-915' 
23-936 
I 
. 17-188 
1-994 
2 „ ... 
■ • 
47-735 1 
47-734 j 
2 
. 34-195 
4-004 
3 „ ... 
72-0881 
72-083 
3 
. 51-847 
6-0.39 
4 „ ... 
64-105 
4 
. 45-602 
8-064 
5 „ ... 
• . 
79-8441 
79-857 J 
5 
. 57 029 
10-040 
To determine the internal resistance of the batteries, the current from them was 
sent through the coil and balanced in our usual manner with the mercury rheostat 
(see Section VI.). The temperature being noted, when "the galvanometer was steady, 
the resistance of the whole battery circuit external to the coil, was immediately 
taken; then if x is the internal resistance of the battery, R the resistance of the 
coil approximately corrected for the rise due to the current, then, 
E.M.r. of Clark cell _ K 
E.M.F. of battery II + p -|- .r 
but this ratio was given by the potentiometer comparison, hence we found x, the 
internal resistance of the storages, = •OlSw, and of the Leclanches 2’24(y. 
Hence we have the following results :— 
Table VII. 
Battery. 
E*. 
At end of coil. 
cR. 
I Leclancbe being- 
called 0. 
cR. 
E = -004. 
I Leclancbe 
1-035 
0 
-0016 
1 Storage 
1-90 
-0048 
•C064 
2 „ . . . . 
3-81 
-0208 
-0224 
3 „ . . . . 
5-74 
-0507 
•0523 
4 „ . . . . 
7-67 
-0899 
-0915 
5 „ . . . . 
9-55 
-1485 
-1501 
* It is probable that the values of E are too high, for (as before pointed out) these are the values of 
3 F 2 
