THE NATURE OF THE INTERIOR OF THE EARTH. 
127 
egg, having a solid shell and yolk separated from one another 
by a molten fluid which represents the white of the egg, is a 
species of hybrid between the first and second theories of the 
earth’s constitution. Evidently intended as a sort of half-way 
compromise between them, it, like most half measures, will not 
probably meet with the approval of the supporters of either of 
the preceding theories. 
If the astronomers have difficulty in reconciling the motions 
of the earth in the heavens, when the earth was imagined to 
possess an entirely fluid interior, it seems probable that still 
greater difficulty will be found in doing so when this view is 
rendered even more complicated by assuming that a sphere of 
solid matter floats, as it were suspended, in the aforesaid liquid 
interior. 
The geologists and others who pin their faith to what they can 
deduce from dii-^ect observation may possibl}^ not make any 
great opposition to such an hypothesis, since the main facts of 
geology are accounted for, if it be only granted that the earth at 
a certain depth below its exterior is in a molten condition ; but 
they will certainly regard this idea of the earth’s interior as 
being unnecessarily complicated, and not be prepared to give it 
any active support until good reasons are brought forward to 
explain why such an internal nucleus is believed to exist. 
The idea of the existence of such a central nucleus is based 
upon the views and before-mentioned experiments of Bunsen, 
who maintained that, owing to the enormous pressure which, 
according to him, would accumulate at the centre of the earth, 
solidification must take place, commencing first at the centre 
and proceeding outwards towards the exterior. 
How far the actual pressure and assumed consolidation at the 
centre would be counteracted by the expansion of the materials 
forming the interior of the earth, by the effects of the laws of 
gravitation, and by the acknowledged increase in temperature 
in depth, are questions which must be answered before such an 
hypothesis can be accepted ; for at present absolutely nothing is 
known of the effects of such enormous pressures as have here to 
be taken into consideration as could warrant the expectation of 
obtaining a correct solution of this problem by arguments built 
upon so uncertain a foundation ; and, as before mentioned, M. 
Delaunay has already given proof of how some of our most able 
mathematicians and astronomers have already been induced to 
advance and support an untenable hypothesis as to the consti- 
tution of the earth, owing to their having based their reasoning 
and calculations upon altogether fallacious premises. 
The fourth and last hypothesis which we have to consider is, 
that the earth consists of an external shell filled with enor 
mously compressed gases. 
VOL. VIII. — NO. XXXI. K 
