1830.] 
and the Communication of Heat . 
365 
the case of solid bodies, and by the continued displacement of the fluid, owing to the 
ascending current. Our method of proceeding, by allowing us to verify the law in 
gases so different in their nature, obviates every doubt which the experiments of 
Mr. Leslie may appear to have left. It is one of those occasions on which some 
opinion may be formed as to the advantages of our method of experimenting. 
The principle we have just established, having been thus verified, we have coi fined 
ourselves in our subsequent experiments, to observing the cooling of the thermome- 
ter with the naked bulb in air, and in different gases. Henceforward, therefore, we 
shall only tabulate the effects due to the contact of the gas ; they have been always 
calculated, as we previously remarked, by subtracting from the total rate of cooling 
that which would have been observed if the thermometer had been cooled in a va- 
cuum. 
We shall now enter upon an examination of the various circumstances which 
might be supposed to modify the energy of elastic fluids in the production of the 
phenomenon we are treating of. We propose to study the influence of eacli of these 
causes; first, in the case of common air, afterwards, in those of hydrogen, of car- 
bonic acid, and of olefiant gas ; the first two have been selected on account of the 
great difference which they present in some of their physical properties. Air and 
olefiant gas again are gases of nearly equal density, but of very different capacities. 
The influence exercised on the cooling process, by the greater or less temperature 
of the surrounding mass, has naturally suggested to us the enquiry. Whether the 
temperature of the gas might not produce some analogous effect on the loss of heat 
occasioned by its contact ? It is scarcely necessary to say that such experiments 
have never yet been attempted those enquirers who have occupied themselves with 
such questions, having supposed that the rate of cooling entirely depended on excess 
of temperature. 
We shall uot stop to give the details of our first attempts, but at once give tables 
of results in which the law i» itself manifest. In the experiments which we made, 
we effected the required change of temperature of the gas, by heating the water 
which surrounded the balloon. But the gas was, at the same time, allowed to 
expand freely, so that the pressure was always the same. The following table 
contains the particulars of such a series made with air. 
Excess of temp, 
of the therm 
over that of the 
surrounding air. 
Rates of cooling due solely to the contact of air. 
Pressure 0 m ,72. 
Temperature 
20°. 
Pressure 0 m ,72. 
Temperature 
40°. 
Pressure 0 m ,72. 
Temperature 
60°. 
Pressure 0m,72 
Temperature 
80o. 
200° 
5° ,48 
5°, 46 
• • • • 
• • • • 
180 
4 ,75 
4 ,70 
4°, 79 
• m • • 
160 
4 ,17 
4 ,16 
4 ,20 
4° ,13 
140 
3 ,51 
3 ,55 x 
3 ,55 
3 ,49 
120 
2 ,90 
2 ,93 
2 ,94 
2 ,88 
100 
2 ,27 
2 ,28 
2 ,24 
2 ,25 
80 
1 ,77 
1 ,73 
1 ,70 
1 ,78 
60 
1 ,23 
i ,19 
1 ,18 
1 .20 
A simple inspection of this table is sufficient to show, that the rate of cooling is 
the same in each of the four series; the excess of temperature being the same. 
This law is too important not to require being verified on other elastic fluids. 
The following table contains the results of a smn'ar comparison made with hydro- 
gen gas which has been raised, successively, to the temperatures of 20°, 40% 60% 
and 80°1 The pressure has been in all t'-ese experiments O m ,72. 
Excess of temp 
of the therm, 
over that of the 
air. 
Rates of cooling due solely to the contact of the gas. 
Pressure 0 m ,72. 
Temp. 20°. 
Pressure 0m,72. 
Temp. 40°. 
Pressure 0 R, ,72. 
Temp. 60°. 
PressureO m ,72. 
Temp. bi)°. 
160° 
140 
120 
100 
80 
60 
14°, 26 
12 ,11 
10 ,10 
7 ,98 
6 ,06 
4 ,21 
14°. 08 
12 ,16 
10 ,13 
7 ,83 
5 ,97 
4 ,17 
14%18 
12 ,12 
lu ,20 
8 ,03 
6 ,01 
4 ,18 
• • • • 
12° ,08 
10 ,19 
8 ,05 
6 ,00 
4 ,20 
