’ 
176 Dulong and Petit onthe Measure of Temperatures, (Marcu, 
cooling. There the difficulty of constructing thermometers with 
liquids different from mercury—a difficulty depending upon the 
uncertainty, which still exists, respecting the laws of the dilata- 
tion of these bodies, determined us to observe the cooling of 
these liquids enclosed in the same glass matrass, in the centre of 
which was placed a very sensible mercurial thermometer. We 
even ascertained that the position of the thermometer is indiffe- 
rent, and that at any given instant the temperature of all the 
points of the mass is sensibly the same. This evidently depends 
upon the interior conductibility, which, in liquids, is the result of 
currents, being nearly perfect, at least for masses of the size of 
those which we employed. 
The first of the following tables contains the velocities of the 
cooling of mercury and water compared ; the second exhibits a 
* similar comparison between mercury and absolute alcohol ; and 
the third, between mercury and concentrated sulphuric acid. 
Excess of the tem- 
| 
. . r . 
pemtire of the Velocity of cooling) pitts of water. Ratio of these velo- 
body. of mercury. cities. 
60° 3°03° 1-39° 0-458 
50 2°47 1:13 0°452 » 
40 1:89 0°85 0-450 
30 1:36 0°62 0-456 
Excess of the tem- 
perature of. the Velocity of cooling|/Ditto of absolute|Ratio of these velo- 
body. of mercury. alcohol. cities. 
goo | 89° 150° | «0798 
30 1:36 1:09 0-801 
20 0-87 0-69 0-794 
——— a ae ae em ed 
} 
Velocity of cooling: Ditto of sulphuric. 
Excess of the tem- | 
acid. | cities, 
Ratio of these velo- 
perature of the aR 
body. of mercury. 
60° 3°03° 1-97 0°650 
50 - 2:47 1-59 0-649 
40 1-89 1-22 0-646 
30 P35 | 0-89 0-654 
The ratios, inserted in the last columns of these tables, show us 
that the law of cooling is the same for the four liquids compared; 
for the small irregularities in these ratios proceed evidently from 
uncertainties in the observations; and besides, to make them 
disappear, it would be sufficient to alter the values of the veloci- 
