1819.] and onthe Laws of the Communication of Heat. 327 
The small irregularities which these corresponding ratios. pre- 
sent in the numbers which represent them, being less than the 
uncertainty of the observations, we have a right to draw from 
them the following conclusions : 
1. The law, according to which the velocity of cooling by the 
contact of air varies with the excess of temperature, continues the 
same, whatever the elasticity of the aar is. 
2. The elasticity of the air varying in a geometrical progres- 
ston, ats cooling power changes likewise in a geometrical progres- 
ston in such a manner that when the ratio of the first geometrical 
progression is 2, that of the second rs 1°366, the mean of all the 
numbers given above. : 
It will be easily seen that the law just announced was not 
recognized till we had made many experiments. But when 
_once verified for air, it was natural to try it on the other gases. 
We shall now give a tabular view of the observations relative to 
each of these. 
Let us begin with hydrogen. 
Velocity off 
cooling due to’ 
the contact of 
hydrogen. 
Ditto. Ditto. 
Pressure | Pressure 
0:09 m. 0°045 m, 
Excess of fem- 
“perature 
above the gas. 
Ditto, Pres-jDitto. Pres- 
sure 0°36 m, | sure 0°18 m. 
Pres. 0°72 m. 
180° 16°59° 12°86° 9°82° 7-Ag° 581° 
160 14:26 10°97 8:37 6°49 4:95 
140 12°11 9-24 Tl 5:AT 4:24 
120 ||, 10°10 7°83 5:99 4°64 3°51 
. 100 Neem sas. 6-23 - 472 3°63 2°80 
80 6:06 4:62 3°58 2°77 2-09 
60 4°21 3°21 2°48 1:88 1°46 
The ratios between the numbers in the second and third 
columns are: 
eae ae, Cob. 129... bee... Fol wo rol 
The ratios between the numbers of the third and fourth 
columns are: 
- 12 1 PAN 1 geo ICE arpa IS Sie 52 aS (8 aa 2 
The ratios between the numbers of the fourth and fifth 
columns are : 
Pores. 1-29 82) P30 Wy 9R9*..6 1-04-29 ee 
The ratios between the numbers of the fifth and sixth 
columns are: 
Bias Ath coc lt QO ic heBR, cp brGO) op. dQ aot 29 
The very near approach to equality in these numbers furnishes 
us with a result analogous to that which is relative to aw. Hence 
