RADIATION AND ABSORPTION. 63 
Such are the general relations which give in all possible cases 
the differences of temperature required by the conditions of equi- 
librium between the globe and the inclosure, the globe and the 
envelope, the inclosure and the envelope. We see that these 
differences depend essentially upon the relative values of 6 and 
of 0!, that is to say, on the absorbing powers which the diather- 
manous envelope exercises upon the heat of the globe and upon 
that of the inclosure. 
If we first suppose that these absorbing powers are equal, 
that is to say that 6 =0’, it results that 
be & 
t—i" ing 
v Pf 
b 
Thus all diathermanous envelopes which exert equal absorb- 
ing powers on the rays of heat of the globe and the inclosure, 
do not prevent the globe and the inclosure having for the equi- 
librium exactly the same temperature as if the diathermanous 
inclosure did not exist, and vice versd. 
With regard to the temperature of the diathermanous enve- 
lope itself, we see that it can only be equal to that of the globe 
and of the inclosure, under the condition that f" = 6, that is to 
say, that the emissive power of that envelope is equal to its ab- 
sorbing power, which, in fact, is the case with rock-salt and air, 
as I have ascertained by experiment. 
But when these conditions are not fulfilled, when the diather- 
manous envelope exerts unequal absorbing powers on the heat 
of the inclosure and on that of the globe, the principle of the 
equality of temperature ceases to be true, and immediately there 
are then manifested, contrary to the ordinary laws of equilibrium, 
differences more or less considerable between the temperatures 
of the globe, the inclosure and the envelope. The following 
table contains some of the results which are obtained in discuss- 
ing the formule, after having attributed different values to J! 
and to 6. 
