HERACLIDES. ASTRONOMICAL DISCOVERIES 317
the circular motion of the stars round the earth, but by the
rotation of the earth about its own axis; several passages
attest this, e. g.
‘Heraclides of Pontus supposed that the earth is in the
centre and rotates (lit. ‘ moves in a circle ’) while the heaven
is at rest, and he thought by this supposition to save the
phenomena.’ 1
True, Heraclides may not have been alone in holding this
view, for we are told that Ecphantus of Syracuse, a Pytha
gorean, also asserted that ‘ the earth, being in the centre
of the universe, moves about its own centre in an eastward
direction ’ 2 ; when Cicero 3 says the same thing of Hicetas, also
of Syracuse, this is probably due to a confusion. But there
is no doubt of the originality of the other capital discovery
made by Heraclides, namely that Venus and Mercury revolve,
like satellites, round the sun as centre. If, as Schiaparelli
argued, Heraclides also came to the same conclusion about
Mars, Jupiter and Saturn, he anticipated the hypothesis of
Tycho Brahe (or rather improved on it), but the evidence is
insufficient to establish this, and I think the probabilities are
against it; there is some reason for thinking that it was
Apollonius of Perga who thus completed what Heraclides had
begun and put forward the full Tychonic hypothesis. 4 But
there is nothing to detract from the merit of Heraclides in
having pointed the way to it.
Eudoxus’s theory of concentric spheres is even more re
markable as a mathematical achievement; it is worthy of the
man who invented the great theory of proportion set out
in Euclid, Book V, and the powerful method of exhaustion
which not only enabled the areas of circles and the volumes
of pyramids, cones, spheres, &c., to be obtained, but is at the
root of all Archimedes’s further developments in the mensura
tion of plane and solid figures. But, before we come to
Eudoxus, there are certain other names to be mentioned.
1 Simpl. on De caelo, p. 519. 9-11, Heib.; cf. pp. 441. 31-445. 5, pp. 541.
27-542. 2; Proclus in Tim. 281 E.
2 Hippolytus, Refut. i. 15 (Vors. i 3 , p. 840. 31), cf. Aetius, iii. 13, 3
('Vors. i 3 , p. 341. 8-10).
3 Cic. Acad. Pr. ii. 39, 123.
4 Aristarchus of Samos, the ancient Copernicus, cli. xviii.
