Improvements in Science. 221 



some new notions in respect to the source of the earth's 

 heat. He observes, that the spherical form of the earth, 

 and its flattening at the poles, prove that it was originally 

 in a fluid, or perhaps in a gaseous state. After this period, 

 it can only have become solid, either wholly or in part, by 

 a loss of heat, proceeding from the circumstance that its 

 temperature exceeded that of the medium in which it was 

 placed. He conceives, that it has not been demonstrated that 

 the solidification commenced at the surface, and gradually 

 extended to the centre, as those theorists assert who adopt 

 the idea of a fluid centre. The contrary appears to Poisson 

 more probable ; those portions nearest the surface having 

 been cooled first, have descended into the interior, and been 

 re-placed by matter from the interior, which has again de- 

 scended in its turn, and thus the process was repeated until 

 the whole mass was cooled down. But further, the central 

 layers would become solid, in consequence of the immense 

 superincumbent pressure at a temperature equal to, or even 

 superior to that of the layers nearer the surface. Experi- 

 ment has proved that water at common temperatures, when 

 submitted to a pressure of 1000 atmospheres, undergoes a 

 condensation of about £§ of its original volume. Now, if 

 we conceive a column of water equal in height to the earth's 

 radius, and reduce its weight to one half of what it possesses 

 at the surface, in order to render it equal to the mean gra- 

 vity of each radius of the earth, supposing the latter homo- 

 geneous; the inferior layers of this liquid column will un- 

 dergo a pressure of above three millions of atmospheres, 

 or equal to above three millions of times that which reduced 

 the water j$ of its volume. Without any knowledge of 

 the laws of the compression of this liquid, we must still 

 believe, that such an enormous pressure would reduce the 

 inferior layers of the mass of water to the solid state, even 

 when the temperature was very high. 



In order to explain the elevation of temperature which we 

 observe, in proceeding from the surface towards the centre 

 of the earth, he suggests the effect of the inequality of the 

 temperature of the regions of space, which the earth succes- 

 sively traverses, because he considers it very improbable, 

 that the temperature of space is every where the same. 

 The mean temperature of space, may be admitted to differ 



