,
1/9.92d. In our Earth and her moon, whose mean distance from one another
amounts to 207,200 miles, we find that the differences of mass* and diameter
between the two are much less considerable than are usually observed to
exist between the principal planets and their attendant satellites, or
between bodies of different orders in the solar system.
[footnote] *If, according to Burckhardt's determination, the Moon's radius
be 0.2725 and its volume 1/49.00th, its density will be 0.5596, or nearly
five ninths. Compare, also, Wilh. Beer and H. Madler, 'der Mond', 2, 10,
and Madler, 'Ast.', 157. The material contents of the Moon are, according
to Hansen, nearly 1/34th (and ??dler 1/40.6th) that of the Earth, and its
mass equal to 1/87.73d that of the Earth. In the largest of Jupiter's
moons, the third, the relations of volume to the central body are 1/15370th,
and of mass 1/11300th. On the polar flattening of Uranus, see Schum,
'Astron. Nachr.', 1844, No. 493.
While the density of the Moon is five ninths less than that of the Earth, it
would appear, if we may sufficiently depend upon the determinations of their
magnitudes and masses, that the second of Jupiter's moons is actually denser
than that great planet itself. Among the fourteen satellites that have been
investigated with any degree of certainty, the system of the seven
satellites of Saturn presents an instance of the greatest possible contrast,
both in absolute magnitude and in distance from the central body.
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