54 M. POUILLET ON SOLAR HEAT, 
substance of the sun itself, a source destined to produce heat, 
to repair in some manner, by chemical, electrical or other ac- 
tions, the losses of calorific rays which take place every instant ; 
or whether, if these losses recurring incessantly without any 
reparation, there results, from century to century, a progressive 
diminution of temperature in which the globe of the earth must 
participate. | 
According to what we have just seen, each square centimetre 
of the sun loses in I! a quantity of heat v= 84888 unities ; in m 
number of minutes it loses m v; and the entire sun loses 
4nrR?.mv. 
Now, if we suppose that the mass of the sun has a perfect 
conductibility for heat, so that its temperature is the same 
throughout,—if we represent its mean density by d and its mean 
capacity for heat by ¢, it is evident that, to be lowered 1°, the 
entire mass of the sun must lose a quantity of heat expressed by 
+. Rxde, 
since in m number of minutes it loses 42 R? mv; it follows that 
during this time it decreases by a number of degrees given by 
the relation Sian 
The radius of the sun expressed in centimetres is 70 billions ; 
the mean density d of the sun, as compared with water, is 1°4 ; it 
is deduced from the mean density of the earth 5°48,from the mass 
of the sun, which is 355 thousand times that of the earth, and 
from its volume, which is 1384 thousand times that of the earth. 
Taking, moreover, for m the number of minutes which cor- 
respond to a year, namely 526000, and substituting for v its 
value 84888, this relation becomes 
4 
3c 
This is the number of degrees which the mass of the sun must 
cool each year, on the hypothesis of a perfect conductibility ; if 
to this first hypothesis we add a second with relation to specific 
heat,—if, for example, we suppose that it is 133 times the spe- 
cific heat of water, we find that the entire mass of the sun would 
then cool 
1 
io ofa degree per annum, 
or 1 degree in a century, 
or 100 degrees for 10 thousand years. 
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