64 M. POUILLET ON SOLAR HEAT, 
Excess of temperature 
of the globe | of the globe of the inclosure 
over 
of 0, of b the inclosure | the lace the euvelada 
t-U. t—U"’. t'—t"” 
0:3 0-7 35-0 535 18°5 
0:3 0:8 45°5 59°5 14:0 
0:3 0:9 57°0 65:0 8:0 
0:4 0°38 38°0 49:0 11:0 
0:4 0:9 49:0 56:0 70 
0:5 0-9 41:0 46:0 50 
0°5 0:95 46:5 49°5 30 
0:0 0-9 78:0 91:0 13-0 
0-0 0-1 91:0 91:0 0:0 
It results, for example, that if the diathermanous envelope 
absorbs only three-tenths of the heat of the inclosure and eight- 
tenths of that of the globe, the temperature of the globe then 
exceeds that of the inclosure by 45°5, and that of the envelope 
by 59°°5, which last is thus 14° below the temperature of the in- 
closure itself. 
There is, however, a limit to the accumulation of heat upon the . 
globe and to the cooling of the envelope, and that limit is 91°. 
This effect of diathermanous envelopes is very remarkable, and 
it becomes perhaps still more striking when we ascend to the 
temperatures themselves instead of stopping at their simple dif- 
ference, since the preceding examples then lead to this result, 
that if an inclosure has its sides kept throughout at the tempe- 
rature of melting ice, a globe suspended in the centre of this in- 
closure, having no other heat but what it receives from it, may_ 
nevertheless, under certain conditions, be raised to the tempe- 
rature of 40° to 50° above zero, that is to say, to a temperature 
considerably higher than that of the torrid zone, and maintain 
this excess of temperature without ever cooling, on condition of 
no longer being in equilibrium of temperature, and consequently 
of being instantly heated again by the rays of the heat of the in- 
closure. For this phenomenon, it is sufficient for the globe to 
be protected by a diathermanous envelope, possessing the double 
property of absorbing only half the heat emitted by the surface 
of the inclosure, and of absorbing on the contrary about nine- 
tenths of the heat emitted by the surface of the globe. 
Lastly, to complete this consequence, with relation to the en- 
velope itself, which is the sole cause of this effect, we must also 
add, that this envelope included between an inclosure at zero 
