RADIATION AND ABSORPTION. 5a 
by the effect of its rotation do not appear to have any marked 
influence upon the terrestrial temperatures. 
Let us consider the centre of the sun as the centre of a sphe- 
rical inclosure, the radius of which is equal to the mean distance 
of the earth to the sun: it is evident, that upon this vast inclo- 
sure every square centimetre receives in 1/ from the sun precisely 
as much heat as the square centimetre of the earth, that is to say 
1°7633 ; consequently, the total quantity of heat which it receives 
is equal to its entire surface, expressed in centimetres and multi- 
plied by 1°7633, or to 1:7633 . 4 x D?. 
This incident heat is nothing else than the total sum of the 
quantities of heat emitted in all directions by the entire globe of 
the sun, that is to say by a surface 4 7 R®, R being the radius of 
the sun, Thus each square centimetre emits for its share 
, D? _ 1:7633 
1°7633. we oe 
w being the visual demi-angle at which the sun is seen from the 
earth, that is to say 15’ — 40"; which gives 84888: thus each 
square centimetre of the solar surface emits in 1/ 
84888 unities of heat. 
By transforming this heat into a quantity of melted ice, we ob- 
tain the following result :— 
If the total quantity of heat emitted by the sun were exclu- 
sively employed in dissolving a stratum of ice applied upon the 
globe of the sun, and enveloping it on every side, that quan- 
tity of heat would be capable of dissolving in 1’ a stratum 
11™-80 thick, andin one day a stratum of 16992", or 41 leagues. 
This determination, as will have been seen, does not rest upon 
any hypothesis; it is independent of the peculiar nature of the 
sun, of the matter of which it is composed, of its radiating power, 
of its temperature and of its specific heat; it is simply the im- 
mediate consequence of the principles best established in rela- 
tion to radiating heat, and of the number which we have attained 
by experiment. 
10. This same subject may give rise to a multitude of ques- 
tions ; we will further examine the two following, less with a 
view of solving them than of indicating the number and the na- 
ture of the unknown elements on which their solution depends. 
The first question is to ascertain whether there is, in the very 
