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Leonardo, and from the dates of the manuscripts from which the texts
on astronomy are taken, it seems highly probable that Leonardo
devoted his attention to astronomical studies less in his youth than
in his later years. It was evidently his purpose to treat of
Astronomy in a connected form and in a separate work (see the
beginning of Nos. 866 and 892; compare also No. 1167). It is
quite in accordance with his general scientific thoroughness that he
should propose to write a special treatise on Optics as an
introduction to Astronomy (see Nos. 867 and 877). Some of the
chapters belonging to this Section bear the title "Prospettiva"
(
see Nos. 869 and 870), this being the term universally applied
at the time to Optics as well as Perspective (see Vol. I, p. 10,
note to No. 13, l. 10).
At the beginning of the XVIth century the Ptolemaic theory of the
universe was still universally accepted as the true one, and
Leonardo conceives of the earth as fixed, with the moon and sun
revolving round it, as they are represented in the diagram to No.
8
97. He does not go into any theory of the motions of the planets;
with regard to these and the fixed stars he only investigates the
phenomena of their luminosity. The spherical form of the earth he
takes for granted as an axiom from the first, and he anticipates
Newton by pointing out the universality of Gravitation not merely in
the earth, but even in the moon. Although his acute research into
the nature of the moon's light and the spots on the moon did not
bring to light many results of lasting importance beyond making it
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