A history of Greek mathematics - Wilbourhall.org

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XVII
TRIGONOMETRY:
HIPPARCHUS, MENELAUS,
PTOLEMY
We have seen that Sphaeric, the geometry of the sphere,
was very early studied, because it was required so soon as
astronomy became mathematical ; with the Pythagoreans the
word Sphaeric, applied to one of the subjects of the quadrivium,
actually meant astronomy. The subject was so far advanced
before Euclid's time that there was in existence a regular
textbook containing the principal propositions about great
and small circles on the sphere, from which both Autolycus
and Euclid quoted the propositions as generally known.
These propositions, with others of purely astronomical interest,
were collected afterwards in a work entitled Sphaerica,
in three Books, by Theodosius.
Suidas has a notice, s. v. QeoSocnos, which evidently confuses
the author of the Sphaerica with another Theodosius,
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a Sceptic philosopher, since it calls him Theodosius, a philosopher
', and attributes to him, besides the mathematical works,
'
Sceptic chapters ' and a commentary on the chapters of
Theudas. Now the commentator on Theudas must have
belonged, at the earliest, to the second half of the second
century A.D., whereas our Theodosius was earlier than Menelaus
{fi.
about A. D. 100), who quotes him by name. The next
notice by Suidas is of yet another Theodosius, a poet, who
came from Tripolis. Hence it was at one time supposed that
our Theodosius was of Tripolis. But Vitruvius x mentions a
Theodosius who invented a sundial ? for any climate '
; and
Strabo, in speaking of certain Bithynians distinguished in
their particular sciences, refers to Hipparchus, Theodosius
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2
and his sons, mathematicians . We conclude that our Theo-
1
Be architectura ix. 9.
2
Strabo, xii. 4, 9, p. 566.