322 Dulong and Petit on the Measure of Temperatures, [May, 
bodies, which produce so powerful an influence on the radiation, 
occasioned any change in the losses of heat occasioned by the 
contact of fluids. For this it was sufficient to observe the cool- 
ing of our thermometer in a gas of a determinate elasticity and 
temperature, first with its bulb in the natural state, and then 
covered with a leaf of silver. 
Of all the experiments which had this comparison for its 
object, we shall only give the two following. 
In the first, we observed the cooling of the largest of our 
thermometers in the balloon containing air under a pressure of 
0-72 metre, and at the temperature of 20°. 
First Case.—The thermometer being in its natural state. 
Excess of temper-|Total velocities of Naocities or nae Velocity of cooling 
ature of the ther-| the cooling of the pe i rom aia due to the air 
mometer, thermometer. sve Sane PIRCe! ante 
in yacuo. 
200° 14-04° 8°56° 5:48° 
180 11-76 7-01 4°75 
160 9-85 5°68 4:17 
‘aig 8-05 4-54 3-51 
120 - 6:46 3°56 2°90 
100 4-99 2-72 ya 
Second Case.—Bulb of thermometer silvered. 
ees 7 “~— 
ne a ye tees Total velocities of the| Velocity of cooling| Velocity of cooling 
monster: cooling of the therm. in vacuo, due to theair. 
200° 693° 150° 5+43° 
180 6-02 1:23 4-79 
160 519 1-00 4-19 
140 4:32 0-80 3°52 
120 3-50 0:62 2-88 
100 2-80 0:48 2-32 
We see, by comparing the last columns of the two preceding 
tables, that the corresponding numbers deviate so little, that the 
deviation may with propriety be ascribed to errors in the expe- 
riments. Air then, other things being the same, takes away the 
same quantity of heat from vitreous and metallic surfaces. 
The two following tables contain all the elements of a similar 
comparison made with hydrggen gas. The small thermometer 
in these experiments was substituted for the large one. The 
experiments were made at the temperature of 20°, the gas being 
subjected to a:pressure of 0°74 metre. 
