437 
made at the close of the experiment is obviously less than the 
truth, for two reasons: Ist. Because it was not taken until m’ 
minutes after the gas was cut off. 2nd. Because, during the 
m minutes that the gas was being absorbed, the copper cylin- 
der was hotter than the surrounding air, and, therefore, con- 
stantly losing heat. After a good deal of reflection on the 
subject, it finally occurred to me to adopt the following method 
of calculating the necessary corrections. 
Having introduced into the copper cylinder, furnished with 
its thermometer, 4.66 cubic inches of water, very nearly the 
quantity used in all the experiments, and raised the whole to 
93.4° (the air being 53.7°), the temperatures were noted at 
intervals of a minute, until the thermometer indicated 66.5°. 
To those I then applied the expression for the velocity of 
cooling, deducible from the Newtonian law, viz. : 
T(h.d.a—hA.l.7) 
ee 
a being the excess of temperature of the cylinder over the air 
at any instant, and r the excess after ¢ minutes, and thus 
obtained the velocities of cooling corresponding to the succes- 
sive values of T separated by intervals of a minute. These 
being reduced to a tabular form, furnish, by mere inspection, 
the means of applying the first of the two corrections already 
indicated, or of ascertaining the temperature which the ther- 
“mometer would show, had it been read at the instant the gas 
was cut off, or m’ minutes previous to the actual time of 
observation. 
‘* But the rise of temperature actually produced is less than 
that which we are in search of, in consequence of the cooling 
power exercised by the joint influence of radiation and atmos- 
pherie contact during the time m. The method I have adopted 
of determining the effect of refrigeration, and which, as far as 
I am aware, has not been previously used, I shall now explain. 
** The velocity of cooling at any instant while the gas is 
2P2 
