DETERMINATION OF THE SPECIFIC HEAT OF WATER. 461 
merits. GRIFFITHS finds in this way that the difference between himself and JouLE 
amounts to one part in 350, but, if equal weights are attached to all Joutr’s results, 
the difference is reduced to one part in 4281. Little value can be attached, however, 
to a combination of JouLE’s results which gives equal weights to that obtained in 
1847 and that deduced from his latest and most careful work. There is, moreover, in 
Row anp’s table a misprint or error in the reduction of JouLe’s 1847 result from 
foot-pounds to kilogram-metres, which lowers the value as given by GrirritHs from 
779°2 to about 778. It does not seem to us advisable to go beyond JouLz’s 1878 
results, and the value assigned by him in this latest research should be taken as 
giving his final judgment on the matter. Reducing to the nitrogen thermometer of 
the Bureau International, JouLE’s result is 775 foot-pounds at Greenwich, at a tem- 
perature of 16°°5 C. At the same temperature GRIFFITHS’ number is 779°8. 
Great weight must be attached to Row zanp’s determination, which, at the 
temperature to which JouLE’s number applies, is 777°6, and at 19°°1, 776:1, corre- 
sponding to our 778°5. RowLanp’s value is, therefore, just halfway between our 
own and JovuLe’s result. But it must be taken into consideration that if the 
comparison between RowLanp’s and Joue’s thermometers, as made by the latter, is 
to be trusted, RowLanp’s value referred to the “ Paris” nitrogen thermometer 
would be slightly reduced. At any rate, it seems probable that if his value is 
in error, it is rather in the direction of being too high. We have, therefore, a 
difference of at least three parts in a thousand to account for between our result and 
that of RowLanp, and of nearly four parts in a thousand between GRIFFITHS’ and 
Rowanp’s at a temperature of 19°1. These results are summarised into the 
following table :-— 
Taste XV.—Equivalent in foot-pounds at Greenwich, at 19°°1, referred to “ Paris” 
nitrogen thermometer. - 


ScHUSTER and 
| 
Joute. RowLanb. GRIFFITHS. (Su SSraeN 

774 7761 779-1 778'5 

We now turn to an investigation by Micutescu (‘Annales de Chimie et de 
Physique,’ vol. 27, 1892) in which the mechanical equivalent of heat is measured 
directly by what seems an excellently devised series of experiments. His result 
is 4°1857 X 107. He does not state the exact temperature to which this applies, 
but all his experiments seem to have been made between 10° and 13°, so that we 
may assume 11°°5 to be the mean temperature of his experiments. RRowLAND’s 
value at that temperature is 4199 X 107. We must draw attention to one point in 
MicuLescu’s work, which requires clearing up before we can give to it any decisive 
