446 
LORD RAYLEIGH AND MRS. H. SIDGWICK ON THE 
§ 30. Tables VI., VII., VIII. show the results of most of the comparisons, the 
value of every cell on each day being expressed in terms of Clark No. 1 . It will be 
seen that there are durable differences between cells of the same batch, but that these 
do not much exceed yo^o- There are also changes of small amount in the force of a 
given ceil, part of which is perhaps attributable to a difference of temperature co¬ 
efficient. Moreover the actual temperatures may possibly have differed a few tenths 
of a degree in the case of various cells, many of which stood some feet apart. Clark 
No. 3 does not appear in Table VII., since on January 25 it was found to be short 
circuited. During the later comparisons, Nos. 6 and 7 were unavailable, having been 
diverted to another use. 
The two last batches took a longer time than usual (about three weeks) to reach 
their normal values. It will be seen from Table VIII. that when first set up these 
cells were too strong by as much as 1 or 2 per cent. It was thought that the 
process of settling down might be quickened by closing the circuit occasionally for 
some minutes, through a resistance of 1000 ohms, and the asterisk in the table 
indicates that on the day previous to the comparison the cell in question had been so 
treated for about ten minutes. When once the settling down is completed, further 
short circuiting appear to be without effect. 
Table IX. 
Time. 
Resistance between Poles. 
E. M. F. 
h. m. 
3 35 
00 
4994 
3 47 
00 
4994 
3 53 
Changed from oo to 10,000 
3 56 
10,000 
4851 
3 41 
10,000 
4853 
4 59 
Changed from 10,000 to oo 
5 2 
OO 
4990 
5 15 
00 
4991 
5 47 
00 
4992 
6 3 
Changed from oo to 1000 
6 5 
1,000 
3990 
6 11 
1,000 
3860 
6 13 
Changed from 1000 to oo 
6 19 
CO 
4990 
6 25 
00 
4991 
6 29 
Changed from oo to 500 
6 34 
Changed from 500 to oo 
6 36 
00 
4985 
6 37 
00 
4988 
6 52 
cc 
4991 
§ 31. Some observers having laid great stress upon the importance of guarding 
Clark cells from the passage of sensible currents, we give a specimen of the results of 
some tests to which we have subjected a few of the cells, in order to find out how 
