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 off 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 a vast 



