Geology, as illustrated by Chemistry and Physics. 43 



ture towards the centre of the earth, would facilitate the ex- 

 planation of drying of the earth's crust by this means. 



Although we cannot altogether contradict the assumption 

 that the earth was in a pasty condition at the time of its for- 

 mation, still, the existing state of its interior, so far as we are 

 acquainted with it, but little favours such a view. It is diffi- 

 cult to imagine the drying of the earth from the centre to the 

 surface. On the other hand, the opinion that the interior of 

 the earth is still in a pasty state, is opposed by the fact of 

 the high temperatures indicated by hot springs and volcanic 

 phenomena, as well as by the great density of the earth (544 

 or even 5 67), which leads us to infer that its interior must 

 consist of much denser substances than its exterior crust; for 

 any considerable quantity of water in the interior would 

 lessen the density. 



If, therefore, the flattening of the earth at the poles is as- 

 sumed to be a consequence of its former liquid condition, then 

 it is especially the condition of igneous liquidity which is the 

 most in conformity with what we know of its interior. 



But is it possible to entertain any rational doubt of the 

 former liquidity of our earth and the other planets ? If, by a 

 calculation based upon an hypothesis, results are obtained 

 which approximate closely with those obtained empirically, 

 then this hypothesis acquires greater probability in proportion 

 as these results correspond more accurately. Setting out 

 from the assumption that the earth was formerly liquid, 

 Newton obtained for the ellipticity of the earth a value which 

 was somewhat greater than that which the subsequent mea- 

 surement of degrees afforded. Huygens obtained a much 

 smaller number. But these deviations cannot appear strange, 

 since the theory presupposed many conditions which in reality 

 could not have existed. The calculation acquired greater 

 certainty through the theoretical investigations of Maclaurin, 

 Clairaut, Legendre, and Laplace. The latter found the 

 ellipticity 3^5. Finally, Ivory subjected the problem to a 

 thorough investigation, as much as possible free from limit- 

 ing assumptions, and estimated the flattening of the originally 

 liquid terrestrial spheroid at ¥ 1 9 , a result which corresponds 

 as exactly with that obtained by Bessel from the ten most 



