HEAT OF EVAPORATION OF WATER. 297 








Taste VIII. 
| Temp. Ro. | Rye. Ree. Ry. 
| 
20 103246 i 10:3266 103284 10:3309 
30 10-3482 | 10-3502 10-3520 10-3545 
40. 103720 | 10°3740 103758 10:3783 
50 10-3966 10-3986 10-4003 10-4028 


dR, per 1° C. = 0024. 
This coil has shown no signs of any change throughout its history. 
As Q. = (ne)?/R,J, I have now indicated how the value of Q. could be accurately 
ascertained. 
Had full details of the method not been given in previously published papers, it 
would have been necessary for me to give further particulars as to the various 
measurements. 
There can, I think, be little doubt that the value of Q, could be determined with 
great certainty. 
I have already (see p. 272 supra) pointed out that even if my value of J (4:199 x 107) 
be in error, it is the correct value to use for these experiments, and that even if e 
(the D.P. of a Clark cell) and the units in which R, is measured (7.e., the value of a 
“true ohm ”) are in error, the results are unaffected, provided that no changes have 
taken place in my Clark cells, or the coils of the resistance box since they were used 
for the determination of the value of J. 
[ Note, May 4, 1895.—During the spring of this year my Clark cells were carefully 
re-compared with the Cavendish standard, RI. Comparisons were made at regular 
intervals, and Mr. Skinner was so kind as to take some independent observations. 
The differences are expressed in hundred-thousandths of the E.M.F. of the standard. 
The highest of the thirty cells exceeds R I by 40 such units. The lowest is less than 
RI by 36. The mean value of the whole set is less than RI by 3 such units (7e., 
by 000004 volt). Thus, although the individual cells show larger discrepancies than 
in 1892-4, the mean value is almost exactly that of the Cavendish standard. The 
previous history of that standard shows that it had remained unchanged during the 
interval of eight years which had elapsed between the absolute determination of its 
E.M.F. by Lord RaytercH in 1883, and that by Messrs. GLAzEBROOK and SKINNER 
in 1891. There is no reason to suppose that it has altered since the latter date, and 
this conclusion is borne out by comparison with other standards at the Cavendish 
Laboratory. I think, therefore, that I am justified in assuming that the mean E.M.F. 
of my cells remains practically unaltered. 
Cells 37 to 42 have been compared at Manchester by Professor ScuusTeR with his 
standard. These six have the highest mean E.M.F. of any of my sets. Their mean 
value exceeds RI by 22 units, and they exceed Professor ScuusTER’s standard by 
MDCCCXCV.—A. 2Q 
