CLARK CELL AS A STANDARD OF ELECTROMOTIVE FORCE. 
021 
Cells described in Tables VIII. and IX. 
No. of cell. 
71 
72 
73 
74 
75 
76 
65 
69 
70 
77 
78 
79 
Difference, Dec., 1891 
_2 
1 
0 
-1 
-1 
0 
-2 
-3 
-1 
-1 
- 3 
-3 
„ July 14, 1892.. 
-1 
-1 
-1 
-1 
-3 
-5 
„ „ 21,1892.. 
_2 
-1 
-1 
-1 
-1 
-2 
0 
-3 
-1 
-1 
-1 
-1 
„ 22,1892.. 
-3 
-1 
-1 
-1 
-1 
— 2 
1 
-4 
-1 
-2 
_2 
o 
— o 
Cells described in Tables X. and XV. 
No. of cell. 
42 
43 
44 
45 
46 
47 
82 
83 
Difference, Dec., 1891.. 
-1 
1 
1 
2 
0 
4 i 
-2 
- 3 
,, Jnly, 1892.. 
-9 
-1 
-4 
-2 
-1 
-1 
— 2 
-16 
The results of comparisons made at the end of 1891, and of the latest compari¬ 
sons we have made, are given in Table No. XVIII. The Table shows that, with few 
exceptions, the relative values of the cells remain closely the same as before. 
It will be remembered that Nos. 57 and 58 were known to be unsaturated, while 
No. 59 dropped suddenly in value between May and August, 1891, and has remained 
low ever since. 
The behaviour of No. 76 requires some notice. Some comparisons were made 
on July 13 and it was observed that it w T as then five units too low. This 
continued on July 14; but when the cells were next tested, on July 21, it had 
recovered, and has since remained right, having been frequently re-tested. The cause 
of this is not quite clear, but it is probable that it was due to the following circum¬ 
stance —The binding screw which connected No. 76 to the circuit was allowed by 
accident to fall into the bath; the water was dirty, having been standing for some 
time; and possibly some of the moisture adhered to the screw, and set up a small 
E.M.F. at the junction. It was found by experiment on July 21 that, by wetting 
this binding screw, small changes could be produced in the E.M.F. observed. 
With this exception, the sets Nos. 71 to 76 and 65 to 79 show very steady agree¬ 
ment. These, it will be recollected, are cells set up in accordance with the second 
form of the Board of Trade Memorandum. 
The set Nos. 42 to 47 shows some change. These are the cells from which the 
grey deposit was removed. They were left unsealed for some time, and after the 
treatment to which they have been subjected, can hardly be considered standards. 
