OF THE MECHANICAL EQUIVALENT OF HEAT. 
383 
The foregoing results are collected in the following Table : — 
Table. 
Number of 
experiments. 
Proportion 
of metallic 
to total 
friction. 
Mean 
rise of 
temperature 
per A. 
Temperature 
of the 
calorimeter. 
Mechanical 
equivalent 
of unit of 
heat. 
1 
17 
1 
45-907 
58°-46 
772-72 
2 
15 
1 
48-803 
54°-76 
774-57 
3 
21 
1 
i o'er 
44-777 
59°-98 
773-136 
4 
6 
i 
4 3 
14-355 
58°-14 
766-97 
5 
1 
12 0 
67-620 
63°-14 
773-99 
The average of the first two gives 773'65 as the equivalent at a temperature of the 
calorimeter 56 0, 61 ; but inasmuch as the metallic friction is as much as of the whole, 
I prefer to use the last three, and to give each its due weight I will multiply the 
squares of the rise by the square root of the number of determinations : — 
For the 3rd series (44777) 3 X ^/2 1 = 9188. 
For the 4th series (14'355) 3 X v /6 = 504'76. 
For the 5th series (67'62) 3 X \/7 =12097 ‘7. 
Then — 
733-136 x 9188 + 766-97 x 504*76 + 773-99 x 120977 ^ 
9188 + 50476 + 120977 ‘ 
is the equivalent at 61°-69 ; or, using Regnault’s law of the increase of the specific 
heat of water with its temperature, 773 f 369 at 60°. 
The latitude of the part of Higher Broughton, Manchester, where the experiments 
were made, is 53° 28^' N. ; its elevation about 120 feet above the sea level. The 
equivalent at the sea level and the latitude at Greenwich will therefore be 773 '492 
foot lbs., defining the unit of heat to be that which a lb. of water, weighed by brass 
weights when the barometer stands at 30 inches, receives in passing from 60° to 
61° Fah. With water weighed in vacuo the equivalent is finally reduced to 772'55. 
3 D 
MDCCCLXXVIII. 
