DETERMINATION OF THE SPECIFIC HEAT OF WATER. 459 








TABLE XIV. 
| 10°. 12 14°, 16°. 18°. 20°. Oe. 24°. 
| | 
Correction to nitrogen | 
thermometer. . . .|—000369 | -00337 | -00305 | -00275 | -00247 | -00220 | -00194 | -00170 | 
| | 
| | | | 
| Correction to hydrogen | 
thermometer. . . .| —0°:00418 | 00381 | 00345 | -00313 | :00280 | :00249 | -:00219 | -00190 
| 






In comparing our results with those of other observers, we have in the first place to 
consider the value which Mr. Grirrirus has obtained in his very excellent series of 
measurements. His final result (‘ Proc. Roy. Soc.,’ vol. 55, p. 26; Phil. Trans., vol. 184, 
1893, A., p. 361), is 
J = 4:1982 (1 — 000266 6 — 15) x 107. 
This refers to the nitrogen thermometer. At a temperature of 19°1 the value 
would be reduced to 4°1936, which corresponds to our 41905 at the same tempera- 
ture. GRIFFITHS’ value is to be increased slightly owing to the fact that he really 
measures the difference between the specific heat of water and of air. This would 
increase the value of J by ‘0011 about, so that the value of J at 19°1 would be 
raised to 4:1947 Xx 10’, which is exactly one part in a thousand larger than ours. 
The difference is smali, but must be due to some systematic error, as both GRIFFITHS’ 
value and our own agree so well with each other, that ordinary observational errors 
and accidental disturbance could not have produced so large a difference in ‘our 
result. The least satisfactory part of a calorimetric measurement must always be 
the cooling correction, and we have considered it of great importance to reduce that 
correction as much as possible. The uncertainty of the cooling correction does not 
necessarily depend on its value; thus, we can much diminish it by starting, as we 
have done in our last series, with the initial temperature of the calorimeter about as 
much below that of the water-jacket as the final temperature is above it. Yet the 
uncertainty of the correction does not seem to us to be diminished by that process. 
We may reasonably estimate the uncertainty due to the cooling correction by calcu- 
lating what the error in the observed rate of cooling, either at the beginning or end 
of the experiment, must have been in order to produce a difference of one part in a 
thousand in the final result. We find in our own experiments that the error must 
have amounted to more than 15 per cent. We consider it unlikely that so large an 
error occurred always in the same direction. Apart from the cooling correction, 
however, it is difficult to see how a difference of one-tenth per cent. is produced 
unless by accumulation of a number of small errors. 
3N 2 
