180 MATHEMATICAL GEOGRAPHY. [CHAP.
more accurate theory was regarded as established; and the prac-
tical application of it was facilitated by the discovery, which had
not yet come to the knowledge of the Greeks in Aristotle's time,
that Syene was on the tropic, and by Pytheas' report that the
arctic circle passed through Thule. Aristotle also maintained
that both the temperate zones were habitable, but did not enter
into the question whether the south temperate zone was actually
inhabited1. The view which prevailed among the ancients with
regard to the whole subject is sketched in outline
Description ky Virgil in a familiar passage of the Georgics, the
leading points in which are borrowed from the
Hermes, an astronomical poem by Eratosthenes. In this it will
be seen that the terrestrial zones are represented as corresponding
to celestial phenomena; and also that both the temperate zones,
but they only, are regarded as habitable. " Five zones there are
which gird the heaven," the poet says, " whereof one ever glows
with the blazing sun and ever is parched with fire; and round it
to right and left sweep the two outermost, stiff with blue ice and
lowering with storms; while two between these and the central
zone are granted by the bounty of the gods to suffering
mortals, and between them a path has been drawn, along
which the procession of the signs of the zodiac might turn in
slanting course*/'
We learn from Strabo that Eratosthenes' primary object in
Eratosthenes' ^ stu^ of S^S^P^Y was to reform the map
Map of the of the world8. It cannot be doubted that before
his time a great advance had been made in the
construction of maps since the days of Anaximander, but we
have little means of knowing in what this progress consisted,
though it is certain that Dicaearchus contributed largely to it. In
the course of the present chapter we have seen how Eratosthenes
determined the dimensions of the globe, the extent of the in-
habited world, and the positions of the chief parallel and the
chief meridian which intersected it. He proceeded to inscribe
1 AT. MeteoroLi a. 5.11, 16.
3 Virg. Georg^ r.1133—9. The passage in the Hermes of Eratosthenes is
given in Conington's note ad loc.
1 Strabo, a. x* a.