and ihe Communication of Heat. 
367 
1830 .] 
If we take the ratios of the corresponding’ numbers of the second and third 
columns, we shall find that their values are, commencing at the top, — 
1.37 1,35 1,37 1,34 1,37 1,34 1,37 1,36. 
In the same manner, we have for the ratios between the numbers of the 3rd and 
4th columns, 
1,36 1,35 1,37 1,37 1,35 1,37 1,34 1,37. 
For the ratios of the numbers in the 4th and 5th columns, 
1,34 1,37 1,36 1,36 1,37 1,36 1,37 1,35. 
Finally, we shall have, in dividing the numbers of the 5th column by those 
of the 6th, 
1.38 1,38 1,35 1,37 1,36 1,37 1,35 1,37. 
These ratios differ only as the results of the most careful observations must dif- 
fer; and we are entitled to draw from them the following conclusions : 
1 mo. Whatever the elasticity of the air, the rate of cooling, as affected by the 
sole contact of the fluid, varies after the same law, provided the excess of temperature 
remains constant. . . 
2 do. The elasticity, or tension of the air, varying in geometric progression, its 
cooling power varies also in geometric progression : but in such wise, that when the 
ratio of the terms in the first series is 2, that of the second is 1,366, ( the mean of al 
the preceding numbers.) 
If will be conceded that these laws could not have been established without many 
trials: hut once verified in the case of common air, it was natural to enquire if 
they held good, with regard to the other gases. We shall proceed to give an ac- 
count of our observations with regard to each of them. 
To begin with hydrogen. 
Excess of temp, 
of the therm, 
over that of the 
gas. 
Rates of cooling solely due to the contact of the gas. 
Pressure 
0 m ,72. 
Pressure 
0 m ,36. 
Pressure 
O'M, 18. 
Pressure 
0m,09. 
Pressure 
Oni ,045. 
180° 
16°, 59 
12°, 8b 
9°,82 
7,49 
5°, 81 
160 
14 ,26 
10 ,97 
8 ,37 
6 ,49 
4 ,95 
140 
12 ,11 
9 ,24 
7 ,n 
5 ,47 
4 ,24 
120 
10 ,10 
7 ,83 
5 ,99 
4 ,64 
3 ,51 
100 
7 ,98 
6 ,23 
4 ,72 
3 ,63 
2 ,80 
80 
6 ,06 
4 ,62 
3 ,58 
2 ,77 
2 ,09 
90 
4 ,21 
3 ,21 
2 .48 
1 ,83 
1 ,46 
The ratios between the numbers of the 2nd and 3rd columns are ; 
1,29 1,30 1,31 1,29 1,28 1,31 1,31. 
The ratios between the numbers of the 3rd and 4th columns are ; 
1,31 1,31 1,30 1,31 1,32 1,29 1,29. 
The ratios of the numbers in the 4th and 5th columns are ; 
1,31 1,29 1,30 1,29 1,30 1,29 1,32. 
The ratios of the numbers in the 5th and 6th columns are ; 
1,29 1,31 1,29 1,32 1,30 1,32 1,29. 
The almost perfect equality of these numbers furnishes us with a result analo- 
gous to that which determined for air ; thus : 
1 mo. Whatever the elasticity of hydrogen gas, the intensity of its cooling power 
is represented by the same function of the difference of the temperatures ,* 
2 do. The cooling power of hydrogen gas decreases in a geometric progression , the 
ratio of which is l ,30 1 , when its elasticity is diminished according to a geometric pro- 
gression, the ratio of which is 2. 
We have found the same thing, with regard to carbonic acid and olefiant gas ; 
the truth may he verified by examining the two follow.ng tables, arranged for 
these gases in the same form as the preceding two, for common atrand hydrogen 
gas. 
