THE MECHANICAL EQUIVALENT OF HEAT. 
495 
The values of J deduced from the two groups of Series I. and the middle group of 
Series II. are dependent upon the value of the water equivalent deduced from the 
highest and lowest weights of Series II. The agreement in the results is a sufficient 
proof of the accuracy of the value assigned to that equivalent. 
The coefficient of increase in the specific heat of the calorimeter may appear large. 
Tomlinson (‘Hoy. Soc. Proc.,’ 1885), gives the following as the specific heat of copper 
and zinc :— 
Specific heat of copper^ = '09008 + '000065 0^, 
,, „ zinc = '09009 + '000075 0^, 
and he quotes the values given by BI:de as 
Copper = '0892 + '000065 d,, 
Zinc = '0859 + '000084 0^. 
Expressing the mean of these results in the same form as that given to the expres¬ 
sion for the water equivalent, we get 
Specific heat of copper = '0896 (1 + '00071 0^), 
„ „ zinc = '0876 (l + '00091 0^). 
Tomlinson states that when reducing his observations, he used Regnault’s expres¬ 
sion for the capacity for heat of water, viz., 1 + '00004 0^ + '0000009 0i^. 
Unfortunately the account of these experiments given in the ‘ Proceedings ’ does not 
supply us with sufficient data to estimate the changes in the coefficient of 0^ that 
would be caused by assuming our expression for the specific heat of water. We are, 
therefore, unable to say how far our rate of increase in the water equivalent agrees 
with the above determinations. We are, however, enabled to state that the values of 
the specific heats at 0° C. would be reduced by about 6 parts in 1000, on the assump¬ 
tion that our formula holds over so large a range. 
Our calorimeter may be regarded as a mixture of copper, zinc, gold, glass, and 
mercury, and the coefficient of increase of such a mixture can only be obtained by 
( direct experiment. 
Howland, in order to compare his results with those of Joule, expressed both in 
I kilogrammetres at Baltimore {g = 980'05), and gave the numerical value of J in terms 
of water at differing temperatures, assuming his own value of the specific heat of water. 
In order to make a similar comparison we give our results in the same form. The 
following Table is extracted from the Appendix to Howland’s paper, with the excep¬ 
tion of the last column, which we have added. 
* Tomlinson’s paper (Table II., p. 497) contains an obvious mispi’int in the coefficient of 
