58 M. POUILLET ON SOLAR HEAT, 
and for the total quantity of heat emitted by the inclosure, 
sid=s.B.fa’. 
As the body receives only a portion, sin? w, of this heat, its real 
and definitive loss will therefore be 
se—s'sint?w=sBf.a' t!’— J sintw.B. fa’, 
or on account of s’ sin? w = s, 
3. B.f (ait? = a’). 
Such is the quantity of heat lost by the body. 
If now we represent its weight by p and its specific heat by c, 
it is evident that for one unity of heat which it loses, its tempe- 
rature is only lowered a number of degrees denoted by 
1 
cp* 
Consequently, whilst it loses a number of unities of heat ex- 
pressed by 
7B.jla nt — a’), 
it loses in temperature only a number of degrees denoted by 
2 Bd yet a’): 
CP 
this is, properly speaking, its velocity of cooling. 
To make this formula coincide with that of MM. Dulong and 
Petit, it is sufficient to suppose 
Gg he Ba f 
cP 
and it would moreover be necessary that the constant should be 
null, if it had been added to the value of e, as is easy to be seen, 
supposing the body only to be polished ; this demonstrates the 
exactness of the general relation 
oi Byfa Ts ‘sis ac: mie ee 
and it shows, at the same time, the elementary composition of 
the coefficient m, the numerical value of which has been given 
by the experiments of cooling; thus the magnitude of this co- 
efficient is in direct ratio to the surface of the body and its ra- 
diating power, and in inverse ratio to the mass of the body and 
its capacity for heat. 
With respect to the value of the constant B, it may be de- 
duced from the preceding relation, at least very approximately, 
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