THE MECHANICAL EQUIVALENT OE HEAT. 
387 
Table I. 
Feb. 13 and 20, 1892. 
Comparison with 
Cavendish Standard. 
(Diff. in 6000 parts.) 
May 1, 1892. 
Comparison with 
No. 31. 
(Diff. in 6000 parts-) 
July 3, 1892. 
Comparison with 
No. 31. 
(Diff. in 6000 parts.) 
Sept. 6, 1892. 
Comparison with 
No. 31.* 
(By potentiometer.) 
31 
+ 1 + 
0 
0 
1-00000 
32 
+ 1 
+ 2 “h 
+ 2 - 
+ -00002 
33 
-f 1 
+1 
0 + 
- -00003 
34 
+ 1 
- 1 ‘ 
- 1 - 
- -00013 
35 
+ 2 + 
-1 
0 
- -oooii 
36 
+ 2 + 
0 
+ 1 
•0 
37 
0 
+ 1 
+ -00001 
38 
0 
+ 1 
+ -00002 
39 
0 - 
+ 1 
+ -00001 
40 
0 
+ 1 
- -00006 
41 
0 - 
0 + 
- -00006 
42 
0 - 
0 + 
— -00007 
43 
+ 2 
+ 3 
+ -00022 
44 
+ 1 
+ 2 
^ -00013 
45 
0 + 
+ 2 -f 
-h -00014 
46 
+ 2 + 
+ 3 
+ -00020 
47 
+ 4 
+ 3 
+ -00014 
48 
+ 3 + 
+ 5 
j 
-i- *00016 j 
, 
49 
0 + 
0 + 
- -ooooi 
50 
+ 1 
+ 1 - 
-0 
51 
- 1 
0 H- 
- -00002 
52 
- 1 
0 + 
- -00009 
53 
0 - 
+ 1 - 
- -00007 
54 
- 1 
0 + 
-0 
Temperature . . 
12°'2 
17°'2 
16°'04 
On May 1 and July 3 the total resistance of the two boxes used was 12,00 Q&j, 
so the numbers given represent the dilferences in 6000 parts. In the comparison 
on September 6 a Clark’s potentiometer (constructed by Messrs. Elliott) was 
used. Readings can be taken with an instrument of this kind, with much greater 
ease and certainty than when using two resistance boxes. 
It may be worth mentioning that on September 6 , the instrument was adjusted 
by one observer and the readings taken by the other, who then moved the handle, 
thereby compelling a fresh adjustment by the first observer. The galvanometer used 
was the high resistance one, G^, previously referred to, and gave a distinct deflection 
for a change of 1 / 10 “® in R. 
Several comparisons were also made at different dates with some cells belonging 
* We have not reduced the potentiometer readings to the same form as that adopted in the previous 
columns, as a difference of '00017 corresponds to 1 in 6000, and the differences shown on September 6 
would only amount to + 1 -f in the most extreme case. 
3 D 2 
