218 
ASTRONOMY. 
III. All this, however, proceeds upon a supposition of 
the earth having been formed at first an oblate spheroid. 
There is another supposition; and perhaps our limited in¬ 
formation will not enable us to decide between them. The 
second supposition is, that the earth, being a mixed mass 
somewhat fluid, took, as it might do, its present form, by 
the joint action of the mutual gravitation of its parts and 
its rotatory motion. This, as we have said, is a point in 
the history of the earth which our observations are not 
sufficient to determine. For a very small depth below the 
surface (but extremely small, less, perhaps, than an eight- 
thousandthj* part, compared with the depth of the centre) 
we find vestiges of ancient fluidity. But this fluidity must 
have gone down many hundred times farther than we can 
penetrate, to enable the earth to take its present oblate 
form; and whether any traces of this kind exist to that 
depth, we are ignorant. Calculations were made a few 
years ago, of the mean density of the earth, by comparing 
the force of its* attraction with the force of attraction of a 
rock of granite, the bulk of which could be ascertained: 
and the upshot of the calculation was, that the earth upon 
an average, through its whole sphere, has twice the density 
of granite, or about five times that of water. Therefore it 
cannot be a hollow shell, as some have formerly supposed; 
nor can its internal parts be occupied by central fire, or by 
water. The solid parts must greatly exceed the fluid parts; 
and the probability is, that it is a solid mass throughout, 
composed of substances more ponderous the deeper we go. 
Nevertheless, we may conceive the present face of the 
earth to have originated from the revolution of a sphere, 
covered by a surface of a compound mixture; the fluid and 
solid parts separating, as the surface becomes quiescent. 
Here then comes in the moderating hand of the Creator. 
If the water had exceeded its present proportion, even but 
by a trifling quantity compared with the whole globe, all 
passing through A B is not confined to one situation more than another, 
D E may represent any “ one of the longest axes of the spheroid,” and 
will, as well is A B, always be a “ permanent axis of rotation.” But 
if any other c ameter, as G H, is taken, the earth could not continue to 
revolve permanently about it.— Paxton. 
t The “ deep St. John,” one of the deepest mines in the Hartz, was 
found by M. Deluc to sink 1359 feet. This was in 1778, and it may, 
since that time, have been carried lower, but probably not to the depth 
of the mine of Valenciana in New Spain, the bottom of which, according 
to Humboldt, is 1681 feet below the surface. Now the diameter of the 
earth being about 7912 miles, “ the eight-thousandth part of the depth o 
the centre” must be 2611 feet, or nearly half a mile.— Ibid. 
