1819.] and on the Laws of the Communication of Heat. 325 
The mere inspection of this table is sufficient to show us that 
the velocities of cooling have remained the same in each of the 
four series for the same excess of temperature. This simple 
law was of too great importance not to endeavour to verify it 
with other gases. The following table exhibits a similar com- 
parison for hydrogen gas, heated successively to 20°, 40°, 60°, 
and 80°. The elasticity in each experiment was 0°72 metre. 
Excessoftemp.|Velocities — of 
of therm. above|cooling due to} y,- A . A i 7 
the surrounding|the contact of No Ae aOr sf, Doto at Gye. Ditto at 80°, 
gas. the gas at 20°, ' 
160° 14;26° 14-08° 14-18° PA 
Tay". 12-11 12°16 12-12 12-08 
120 10°10 10°13 10-20 10°19 
100 7-98 7°83 8-03 8:05 
80 6:06 5°97 6-01 6:00 
60 4-21 4:17 4-18 4-20 
This table leads to the same consequences as the preceding. 
To show that it extends to all the gases, whatever be their 
nature or density, we shall add here a similar set of experiments 
on carbonic acid, under a pressure of 0°72 metre, and on dilated 
air under a pressure of 0°36 metre. 
Velocities o 
Minter: af tem-\cedling) due, tp Ditto temp. 40°, Ditto temp. 60°,| Ditto temp. 80°. 
perature, the —_ carbonic 
; acid ; temp. 20°. 
200° 5*25° 517° _ _ 
180 4°57 4°63 4-52 —_ 
160 4-04 4-06 3°97 4-10 
140 3°39 3°39 | 3°34 3°43 
120 2°82 2°80 2°79 2°83 
100 2°22 2°18 2°21 2°20 
Velocities 0 
Excess of tem-|cooling due to 
Ditto temp. 40°.|Ditto temp. 60°./ Ditto temp. 80°. 
perature. dilated air; 
temp. 20°. | 
200° 4-01° 4°10° —_ — 
180 3°52 3°50 3°55 —_— 
160 3°03 2°99 3°04 3°09 
140 2°62 2°57 2°62 2°66 
120 2°12 2°16 2°14 2-15 
100 1:69 1-71 1:67 1:73 
