56 M. POUILLET ON SOLAR HEAT, 
this temperature might be 1761° if the emissive power of the 
sun were analogous to that of polished metals. These numbers 
do not differ much from those which I had determined by other 
principles and by other means of observation in my memoir of 
1822. 
12. Starting from the laws of cooling in vacuo, discovered by 
MM. Dulong and Petit, and developing a particular point of 
view which those able men of science had already indicated in 
their work, I was led to this general theorem. 
The absolute quantity of heat e which is emitted in the unity 
of time by the unity of surface of any body, the temperature of 
which is ¢ + 6, and the emissive power of which is f, is always 
expressed by the relation 
a= (Bisra ts 
B being an invariable constant, which depends solely on the 
zero of the scale and on the unities of time and of surface; its 
value is 1°146, taking the minute and the square centimetre for 
unities. 
To demonstrate this general law of the emission of heat, let 
us consider a spherical body submitted to cooling or to the equi- 
librium of temperature in the centre of an inclosure also spheri- 
cal; let us suppose that the body and the inclosure have, both 
of them, a maximum emissive power, in order to avoid the effects 
of reflexion ; let us designate by e the quantity of heat which is 
emitted by the unity of surface of the inclosure, and let us sup- 
pose that the equilibrium of temperature is established ; the total 
quantity of heat lost by the body in the unity of time is 
eS, 
s being the surface or 477°. 
If we represent by e” the portion of this heat which is received 
and absorbed by the unity of surface of the inclosure, we shall 
have ll gl 
for the total quantity of heat received by the inclosure, s’ being 
its entire surface or 477°". 
Now the quantity lost by the body being equal to that which 
is received by the inclosure, we shall first have 
ca =e 8, 
whence 7 
