174 THE ELEMENTS DOWN TO PLATO’S TIME 
Vitruvius tells us that one Agatharchus was the first to paint 
stage-scenes at Athens, at the time when Aeschylus was 
having his tragedies performed, and that he left a treatise on 
the subject which was afterwards a guide to Democritus and 
Anaxagoras, who discussed The same problem, namely that of 
painting objects on a plane surface in such a way as to make 
some of the Things depicted appear to be in the background 
while others appeared to stand out in the foreground, so that 
you seemed, e.g., to have real buildings before you; in other 
words, Anaxagoras and Democritus both wrote treatises on 
perspective. 1 
There is not much to be gathered from the passage in 
the Rivals to which Proclus refers. Socrates, on entering the 
school of Dionysius, finds two lads disputing a certain point, 
something about Anaxagoras or Oenopides, he was not certain 
which; but they appeared to be drawing circles, and to be 
imitating certain inclinations by placing their hands at an 
angle. 2 Now this description suggests that what the lads 
were trying to represent was the circles of the equator and 
the zodiac or ecliptic; and we know that in fact Eudemus 
in his History of Astronomy attributed to Oenopides the dis 
covery of ‘ the cincture of the zodiac circle ’, 3 which must mean 
the discovery of the obliquity of the ecliptic. It would prob 
ably be unsafe to conclude that Anaxagoras was also credited 
with the same discovery, but it certainly seems to be suggested 
that Anaxagoras had to some extent touched the mathematics 
of astronomy. 
Oenopides op Chios was primarily an astronomer. This 
is shown not only by the reference of Eudemus just cited, but 
by a remark of Proclus in connexion with one of two proposi 
tions in elementary geometry attributed to him. 4 Eudemus 
is quoted as saying that he not only discovered the obliquity 
of the ecliptic, but also the period of a Great Year. Accord 
ing to Diodorus the Egyptian priests claimed that it was from 
them that Oenopides learned that the sun moves in an inclined 
orbit and in a sense opposite to the motion of the fixed stars. 
It does not appear that Oenopides made any measurement of 
1 Vitruvius, De architectura, vii. praef. 11. 
2 Plato, Erastae 132 A, B. 3 Theon of Smyrna, p. 198. 14. 
4 Proclus on Eucl. I, p. 288, 7-8.