HEAT OF WATER, WITH EXPERIMENTS BY A NEW MEITIOD. 
*) 
•J 
experimental results. Tliis was undertaken by J. M. Gray (‘ Proc. Inst. Meclr 
Eng’./ 1899) who found that the data given l)y Kkgnault did not i]i all cases agree 
with liis calculated results, the discrepancies occasionally reaching 2 or 3 per cent. 
It appeared, from measurements of the original apparatus, that in all these cases the 
recorded quantity of water exceeded the total capacity of the calorimeter. Gray' 
concluded that IIegnault’s calculations were probably correct, and that the dis¬ 
crepancies arose from deficient information or erroneous entries in the data columns. 
Adopting this assumption, it is possible to recalculate Regnault’s observations, 
allowing for the known variation of the specific heat from 0° C. to 30° C., and to 
express his results for the mean specific heat from 0° G. to t° C. in terms of the 
specific heat at 20° C. The separate observations, reduced in this manner, are 
represented l)y the small crosses in fig. 1. The large crosses surrounded by circles 
indicate the means of each group. The general effect of this reduction is to Indiig the 
results on the average about 2 parts in 1,000 below Pi,egnault’s original formula. 
The correction is fairly certain, and is less than the discrepancies between the 
observations in any one group. 
The probable errors of Regnault’s thermometers remain to be considered. These 
have not been included in the reduction, as being much less certain, because the 
original thermometers cannot now l)e recovered and tested. It appears from recent 
observations on the absolute expansion of mercury, and on the pressures of steam 
between 100° C. and 200° C. that Regnault’s temperature scale over this range did 
not differ materially from that given* by formula (l). It is certain, however, that 
Regnault was ignorant of the phenomenon of the temporary depression of zero of a 
mercury tliermometer when heated, and that he was unable to detect any systematic 
B 2 
