and of the Planetary Spaces. 63 



we call to mind the almost infinite velocity of radiation, that 

 time enough has elapsed for the different layers of the earth, in 

 passing to a solid state, to have lost all the heat developed during 

 their change, and which escaped, by radiation, through the supe- 

 riour layers, still in a state of vapour ; so that long prior to the 

 present period, the last trace of this heat, however great it may 

 have been, had disappeared. An effect similar to that we are 

 now considering would result, for example, if we produce a hori- 

 zontal cylinder, of great length, closed at the ends, and filled 

 with steam at the temperature of the exteriour, and at the inaxi- 

 mum of density. In this position of the cylinder, the weight of 

 the fluid would exercise no influence, and the pressure would be 

 the same throughout the mass ; but if we place this cylinder in a 

 vertical position, the weight of the various layers of the fluid 

 would produce a pressure, increasing in the direction of gravity, 

 that of each being added to the preceding ; and in this manner 

 the several layers would become condensed to a liquid, in regu- 

 lar succession. The movement of each layer, during its descent, 

 it would be difficult to determine, but, the time of its duration 

 would certainly be sufficient for the latent heat of the liquefied 

 vapour to escape, by radiation, if we suppose the sides of the cyl- 

 inder, or even only its top to oppose no obstacle to radiation, or 

 to be permeable to radiant heat ; and in this manner the water 

 of which the vapour had been composed would not become 

 heated, but would preserve the temperature of the exteriour. 



In discarding, then, the opinion that the observed increase of 

 temperature of the earth, with the increase of depth from its 

 surface, is attributable to the original heat our globe may have 

 had, I have proposed another explanation of this phenomenon, 

 founded upon a cause of which the existence is certain, and 

 which may certainly produce an effect similar to that which we 

 observe. This cause is the inequality of heat in the regions of 

 space traversed by the earth, in its movement therein, with the 

 sun and all the planetary system. (6) The temperature of any giv- 

 en point of space, or that which would be indicated by a thermo- 

 meter placed at that point, is produced by the radiant heat from 

 the stars, which traverses space in all possible directions. These 

 stars form, around each point of space, an immense circumfer- 



(6) Has such a movement been recognized ? 



