A STANDARD OF ELECTRO-MOTIVE FORCE. 
793 
was no practical uncertainty on this account. The variation of the two cells relatively 
to one another was less than i 0 ooo during the whole month of observation. 
(Table XV.) 
Table XIV.—Value of Cells referred to No. 1. 
Temperature. 
(Fahr) 
Date, 1885. 
(1). 
Ti. 
t 3 . 
W 31 . 
w 50 . 
w 62 . 
M ia . 
O 
47 
Nov. 8 . . . 
1-0000 
•9957 
•9991 
•9991 
•9993 
491 
„ 2 . . . 
1-0000 
•9955 
•9993 
•9999 
•9997 
51 
Oct. 31 . 
1-0000 
•9957 
1-0001 
•9996 
1-0000 
•9997 
564 
„ 28 . . . 
1-0000 
•9957 
1-0003 
57 
„ 27 . . . 
1-0000 
■9957 
1-0001 
1-0000 
1-0000 
581 
Nov. 4 . 
1-0000 
"9954 
•9992 
•9992 
loboo 
•9996 
61 
Oct. 30 . 
1-0000 
•9957 
•9997 
•9993 
•9999 
•9980 
67 
Nov. 27 . . . 
1-0000 
•9951 
•9996 
1-0001 
•9996 
•9997 
1-0000 
69 
July 20 . 
1-0000 
•9957 
•9998 
From the results in Table XIV., reduced to No. 1 as standard, the reader will see 
that there is no distinct difference of coefficient. It is interesting to note that T : 
(which there is every reason to consider supersaturated) keeps its distance from 
No. 1. When I first thought of supersaturation, I regai’ded this agreement of 
temperature-coefficient as an argument on the other side, not at that time recog¬ 
nising the probable occurrence of the lower hydrate. But what will still more arrest 
attention is the agreement of Dr. Alder Wright’s cells with No. 1. There are 
same irregularities, possibly dependent upon imperfect penetration of temperature 
through the masses of paraffin in which the cells are imbedded ; but there is no 
distinct evidence of a lower coefficient, and certainly no such difference as that 
between '0008 per degree Cent, and '0004. The same may be said of M 183 , which I 
received from Dr. Alder Wright. 
§ 53. The absolute variations with temperature of (l), (10), (39), (40) are shown 
in Table XV., in which all the electro-motive forces are expressed in terms of (38) 
at 51° F., a small correction being introduced to allow for the 1° or 2°, by which the 
actual temperature of (38), (35), may have differed from 51°. The coefficients for (1) 
and (10) are almost identical. The observed values for (1) agree pretty well with the 
formula 
•9970{1 — '000425(^ — 57)}, 
as will be seen from the adjoining column calculated therefrom. This is in 
Fahrenheit degrees. The corresponding formula in Centigrade degrees is 
•9970{1 —*000765(« —13*9)}. 
It appears, therefore, that the temperature-coefficient for these cells, including those of 
Dr. Alder Wright, is '00077, and that the observed values are utterly irreconcilable 
with such a coefficient as '0004. 
