New Researches on Heat. 381 
the sensible qualities are such as to deserve attention ; and the 
name of Dr. Withering ought to be sufficient to give it a place 
in the materia medica. 
NEW RESEARCHES ON HEAT. 
MM. Dulong and Petit have lately given to the world a Me- 
moir on Heat, which gained the prize medal for 1818, of the Aca- 
demy of Sciences. The title of the paper is, “* On the Measure of 
Temperatures, and on the Laws of the Communication of Heat.” 
Law 1. lf the cooling of a body placed in a vacuum termi- 
nated by a medium absolutely deprived of heat, or of the power 
of radiating, could be observed, the velocity of cooling would de- 
crease in a geometrical progression, whilst the temperature di- 
minished in an arithmetical progression. 
2. For the same temperature of the boundary of the vacuum 
in which a body is placed, the velocity of cooling for the excess 
of temperature, in arithmetical progression, will decrease, as the 
terms of geometrical progression diminished by a constant num- 
ber. The ratio of this geometrical progression is the same for 
all bodies, and equal to 1:0077. 
3. The velocity of cooling in a vacuum for the same excess of 
temperature increases in a “geometrical progression, the tempe- 
rature of the surrounding body increasing in an arithmetical pro- 
gression. The ratio of the progression is also 1-0077 for all 
bodies. 
4. The velocity of ccoling due to the contact of a gas is en- 
tirely independent of the nature of the surface of bodies. 
5. The velocity of cooling due to the contact of a fluid (gas) 
varies in a geometrical progression, the excess of temperature va- 
rying also in a Beamer ical progression. If the ratio of the last 
progression be 2, that of the first is 2°35 ; whatever the nature 
of the gas, or whatever its force of elasticity. ‘This law may also 
be expressed by saying, that the quantity of heat abstracted by a 
gas is in all cases proportional to the excess of the temperature 
the body raised to the power of 1.233. 
6. The cooling power of a fluid (gas) diminishes in a geome- 
trical progression, when its tention or elasticity diminishes also 
in a geometrical progression. If the ratio of this second progres- 
sion be 2, the ratio of the first will be for air 1:366 ; for hydrogen 
1301 ; for carbonic acid 1°341; for olefiant gas 1-415. This 
law may be expressed in the following manner : 
The cooling power of gas is, other things being equal, propor- 
tionate to a certain power of the pressure. The exponent of this 
power, which depends on the uature of the gas, is for air 0-45 ; 
for hydrogen 0-315 ; for carbonic acid 0°517 ; for olefiant gas 
0-501. 
7. The 
