120 Proceedings of the Royal Physical Society. 
above that, all those mineral oxides which can be raised into 
vapour at a high heat. Next, there would be the great 
body of waters as a highly rarefied vapour, and forming a 
vast atmosphere enveloping the incandescent globe beneath ; 
and above all, the air would be expanded out into space, 
comparatively speaking, to an almost unlimited extent. 
Heated bodies, when suspended in space, radiate heat in all 
directions, and the earth would do the same. The radiation 
would be assisted by atmospheric currents. Air and watery 
vapour have their specific gravity increased by cold, and 
diminished by heat ; and this law would act as follows ; 
— The strata of vapour in contact with the incandescent 
surface would have their temperature higher than those at 
a greater height above it, and would be pressed upward, and 
carry their heat along with them into the higher regions, 
where it would be lost by radiation into space ; whilst the 
colder and denser strata from above would descend and 
come in contact with the surface in their turn, and become 
heated and be pressed upward in succession. After a time, 
the temperature at the surface would be much reduced, and 
if the materials were good conductors of heat, no crust 
would be formed ; for, as fast as the heat of fluidity was lost 
by radiation, it would be supplied from below, and by this 
process going on until the temperature of the whole mass 
fell to the same standard, it would become solid throughout. 
It is found, however, that the materials which constitute 
the crust of the earth are bad conductors of heat, and this 
would influence the rate of cooling. For the heat lost by 
radiation being greater than that derived from below, a time 
would come when the heat necessary to fluidity would be 
finally carried ofi" from the outer stratum, in consequence of 
which it would become solidified. And now the tempera- 
ture having been reduced, changes would occur in the gas- 
eous envelope. The first of these would be the deposition 
of the metals, mineral oxides, and sulphurets ; and after the 
temperature fell to a little below 212° Fahr., water would be 
formed by the condensation of vapour in the atmosphere, 
and would fall in rain. This would lower the temperature 
at once, because water in passing into vapour absorbs avast 
