OF TIIE MECHANICAL EQUIVALENT OF HEAT. 
373 
In the first seven the average time of transfer is 4 S "57 and the proximate specific 
heat 0 - 091497. In the last three we have 30 s and 0'088302. From these the 
specific heat of the sheet copper at 75° is determined at 0'092094. 
The boxwood piece n, fig. 2, had a brass nut in its centre by which it was screwed 
on the axle of the brass stirrer. Being a bad conductor, and having nearly the whole 
of its surface in contact with the air, only a small portion of its capacity for heat could 
be counted in reckoning the whole capacity of the calorimeter. I determined this 
portion by ascertaining the heat communicated to a can of water when the boxwood 
piece was immersed in it after having been screwed on the calorimeter filled with 
hot water, for different periods of time. Calling the difference between the tem- 
peratures of the air and the calorimeter T, the gain of temperature in the small can t, 
the capacity of this can of water c, and C the modified or virtual capacity of the 
f Q 
boxwood piece, we have C= — • The following results were obtained showing the 
gradual approach of this virtual capacity to a certain limit : — 
Time that the boxwood Virtual 
was screwed on the calorimeter. capacity. 
3™ 45-6 
6 m 57-5 
8 m 63-9 
12 m 67-3 
60 m 76-0 
The virtual capacity of the caoutchouc stoppers was determined 
manner — 
Time. 
Capacity. 
3 m L5-35 
8 m 21-8 
in the same 
30 m 
27-45 
The several capacities making up that of the calorimeter are therefore summed as 
follows* : — 
Brass, 51979 grains X -09047 = 4702-54 
Caoutchouc stoppers . . . 2 7 "45 
Boxwood piece 76 - 00 
Therm ometer 4 4 - 7 8 
Total 4850-77 
I had, therefore, great confidence in employing the value 4842"4, obtained, os 
already described, from experiments with the calorimeter itself. 
* The specific heat of boxwood, which I obtained by immersion in mercury, was 0'417; that of the 
caoutchouc, 0 - 29. 
