RADIATION AND ABSORPTION. va 
sphere must lose every day all the heat that they receive. Now 
the quantity of heat received by one of the lower strata, for ex- 
ample, depends upon the absorbing power which is peculiar to it, 
and on the incident heat which reaches it; both from the earth 
below, and also from the sun and from space above. It is the 
same with respect to one of the upper strata: only it is evi- 
dent that this will receive from the sun and from space much 
more incident heat than the lower stratum, since this heat is 
weakened more and more in proportion as it penetrates into 
deeper strata; it is also evident that the lower stratum in turn 
will receive in compensation much more terrestrial heat than the 
upper stratum, because the terrestrial heat is weakened by the 
same cause in proportion as it penetrates into more elevated strata. 
The relation of these received quantities, or rather of the quan- 
tities received and absorbed by any two strata, may be calculated 
approximately, and we find that it does not vary much from 
unity, provided at least that we do not arrive at strata very near 
the limits of the atmosphere: if we assume it equal to unity, 
this signifies that two strata of air, one upper and the other 
lower, very near to or very distant from one another, absorb 
each day equal quantities of heat; but since they both lose all 
that they receive, it results very evidently that they lose in the 
same time equal quantities of heat. Thus, we should have 
Bkmca’=Bkme a’, 
ef 
ce 
This result, which expresses in so simple a manner the law of 
the decrease of the temperature of the air for the equatorial re- 
gion, and which seems to extend nearly to the limits of the at- 
mosphere, requires to be verified by experiment, as much at least 
as these verifications are possible. 
Now we know, by the researches of M. de Laplace and M. 
Poisson, that the capacities of elastic fluids for heat are connected 
with the pressures which these fluids support by a relation of 
the form 
1 
OD i errs 
e \gl Z 
which becomes for dry air 
a (2) 
c p ] 
whence Han gas Lee 
la 
