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syllabus
Aristotle's Cosmos
*Aristotle, Metaphysics
Book XII, Chap 8, gives these figures. The number of spheres
given by Eudoxus (b. ca 390 B.C.) is 27 (including the sphere of the
Fixed
Stars). Callippus (b. ca. 370 B.C.) increases this to 34.
Aristotle
improves on Callippus by including additional spheres to counteract
some
of the motions of the planetary spheres. These additional spheres
are placed between the outermost sphere of a given planet and the
innermost
sphere of the next planet and are one less than the number of spheres
of
the latter (hence the counteracting spheres between Mercury and Mars
number
4, and those between Mars and Jupiter number 3). This is a
significant
modification: Eudoxus and Callippus view their systems as
geometric
models that describe the motions of the planets by reducing them to
uniform
simple motions; arguably, they do not reify these models.
Aristotle,
on the other hand, views the spheres as real existants and realizes
that
they are all literally attached to each other. The motions of the
inner planets will thus affect the motions of the outer planets; hence
the need for counteracting spheres.