[footnote] *Brewster, 'Life of Sir Isaac Newton', 1831, p. 162. "The
discovery of the spheroidal form of Jupiter by Cassini had probably directed
the attention of Newton to the determination of its cause, and consequently,
to the investigation of the true figure of the Earth." Although Cassini did
not announce the amount of the compression of Jupiter (1/15th) till 1691
('Anciens Memoires de l'Acad. des Sciences', t. ii., p. 108), yet we know
from Lalande ('Astron.', 3me ed., t. iii., p. 335) that Moraldi possessed
some printed sheets of a Latin work, "On the Spots of the Planets,"
commenced by Cassini, from which it was obvious that he was aware of the
compression of Jupiter before the year 1666, and therefore at least
twenty-one years before the publication of Newton's 'Principia'.
Actual mesurements,
p 165
made by the aid of new and more perfect analysis, have, however, shown that
the compression of the poles of the terrestrial spheroid, when the density
of the strata is regarded as increasing toward the center, is very nearly
1/300th.
Three methods have been employed to investigate the curvature of the Earth's
surface, viz., measurements of degrees, oscillations of the pendulum, and
observations of the inequalities in the Moon's orbit.
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