THE MECHANICAL EQUIVALENT OF HEAT. 
499 
done, the ground upon which we based the above statement. Joule himself, in 
1879, made a careful comparison of his thermom-eter with one which had been 
standardized by Rowland (Baudin’s Therm., No. 6166). The results were pub¬ 
lished as an appendix to Rowland’s paper in the ‘ Proceedings of the American 
x4.cademy’ for March, 1880. A considerable correction in the values obtained by 
Joule was then found to be necessary. Again, Joule had assumed Regnault’s 
expression for the specific heat of water, and a correction for the capacity for heat of 
the calorimeter was also rendered necessary by the changes in the thermometry. As 
the appendix above referred to appears to be but little known in this country, I give 
one example (p. 44, ibid.) to indicate the nature of the various corrections. 
Joule’s result in 1878 (friction of water). 774’6 
Correction for thermometer.-f 3’7 
,, ,, capacity for heat.+ '2 
,, „ latitude (to Baltimore).-f- '9 
,, ,, vacuum.— '9 
Corrected value (at 12°’7 C.) . . . 778 A 
As these corrections were published in 1880, it appears probable that, had they not 
met with Joule’s approval, he would have signified his dissent, but 1 can find no 
record of any such expression of opinion on his part. 
As previously stated, Rowland attached what appear to me to be curiously arbitrary 
values to certain of Joule’s experiments. If we accept his verdict as to their respec¬ 
tive merits, the mean of the selected experiments, as corrected by Rowland (but 
reduced by me to temperature 15°, and to latitude Greenwich), is 776*75 ft.-lbs, ; but 
if we assign equal value to all Joule’s published results, the corrected mean becomes 
779*17 ft.-lbs., and it was on these numbers that our statement was based. 
It is extraordinary that, although these results (or rather the corrections by which 
they are deduced) were published as far back as 1880, we still find that our modern 
books of reference continue to give 772*55 as the number resulting from Joule’s own 
experiments.] 
3 s 2 
