62 Temperature of the Terrestrial Globe, 
layers, while, by reason of the mobility of the liquid particles, 
these quantities of heat would be carried to the surface, where 
the whole would be dissipated, by radiation, through the sur- 
rounding space. While thus passing to a solid state, the liquid 
mass would lose all the heat developed by this change. But 
this may be better understood in ascending to the probable cause 
of the primitive fluidity of the planets. 
This we may illustrate by reasoning on the known hypothesis — 
of Laplace, upon the origin of these bodies, namely, that they are 
portions of the sun’s atmosphere, which it has successively aban- 
doned, in concentrating itself around that body. The earth was, 
then, primitively, an aériform mass, of very great volume, rela- 
tively to what it now is, and formed of the different materials, 
solids and fluids, of which it is now composed, which were then 
in a state of vapour, that is of an aériform fluid, of which the 
density could not surpass a given maximum, proportional to its 
degree of heat, and which would become liquid or solid accord- 
ing to the augmentation of the pressure it experienced, without 
changing its temperature. That of the earth would depend, 
then, upon the point it should occupy in space, and upon its dis- 
tance from the sun; and might be more or less elevated. But 
independently of thé attractions aiid repulsions which take place 
only among particles near each other, and which produce the elas- 
tick force of aeériform fluids, equal and contrary to the pressure 
they sustain, the particles of the earth were also subject to their 
mutual attraction, in the inverse ratio of the squares of their dis- 
tances ; and from this force there resulted, upon all the layers of 
the fluid mass, a pressure, nothing at its surface, increasing from 
the surface to the centre, and which, at the centre itself, becomes 
exceedingly great, surpassing 100,000 times, the weight of the 
present atmosphere. It is this increasing pressure, and not an ex- 
teriour temperature much lower than that of the fluid, which has 
successively reduced all the layers to a solid state, commencing 
with those at the centre, and continuing from one to another, 
until nothing remained except the matter composing the oceans 
and the atmosphere of the present day. But this reduction has 
not been instantaneous ; for a certain period of time was neces- 
sary for each layer to fcaxbeck the centre, towards which it was 
urged, by the —— it ean, and which was the exci- 
ting cause of this movement. Now we may readily infer, when 
