and of the Planetary Spaces. 61 



after numerous oscillations, arrived at a permanent figure, which 

 was determined in this state of fluidity, and that the liquid sub- 

 sequently preserved this figure while passing to a solid state. 

 The solution of this problem of hydrostaticks requires only a 

 knowledge of the temperature of the liquid ; but now, if we sup- 

 pose that this heat was very great, and much superiour to the 

 temperature of the regions of space surrounding the planet, we 

 see not what exteriour pressure there could have been which pre- 

 vented the liquid from dilating itself to a state of vapour, instead 

 of passing from a liquid to a solid state : and if it was possible 

 that the layers near the surface had commenced, through conden- 

 sation, to assume the solid state, before the interiour layers had 

 lost their primitive heat, we can no more clearly understand how 

 these last, by their tendency to dilation, of which we understand 

 the power, should not burst the solid, exteriour envelope as often 

 as formed. It is farther to be observed that this high temperature 

 of our planet, in the liquid state, is a gratuitous assumption of 

 which it would be difficult to find an explanation. (5) It is true 

 that when a body is at first a liquid, more or less compressible, of 

 which the layers would augment in density, in going from the 

 surface to the centre, and terminate by passing to a solid state, 

 by reason of the pressm'e from without, this condensation and 

 this change of condition would develope a great quantity of heat ; 

 but it is necessary to observe that in this view of the subject the 

 solidification would probably commence at the centre of the mass : 

 the nucleus, thus solidified, would become a focus of heat, which 

 would raise the temperature of the immediately sm'rounding layer, 

 still in a liquid state ; this layer, thus heated, and its density di- 

 minished, would be elevated, and its place supplied by a new 

 layer which, in passing to the solid state, would radiate heat in 

 like manner, and so in succession, until the entire mass should 

 have become a solid. In this manner the solid nucleus, gradually 

 augmenting, would communicate, to the parts still liquid, the 

 quantities of heat successively disengaged from newly solidified 



(5) Some interesting remarks upon central heat occur in Lyell's Geology, Amer- 

 ican edition, 1837, vol. 1, p. 452, and onward. The last English edition, of which 

 this one is a copy, was published during the present year ; yet it is probable the 

 author had not seen M. Poisson's Theory of Heat, as he quotes both Fourier and 

 Cordier, and controverts their theory, but without mention of Poisson. 



