166 MATHEMATICAL GEOGRAPHY. [CHAP.
course of speculation succeeded in anticipating, though they
could not demonstrate, some of the truths which modern science
has established Thus Heracleides Ponticus, the associate of
Plato, taught the rotation of the earth on its axis, though still
regarding it as the centre of the universe1. But it was reserved
for the master-mind of Aristotle to place these
Impulse
given to it by subjects in their true light according to the know-
Aristotle, ledge that wag then ava{iabiej an(j ty the applica-
tion of a strictly scientific method to establish the principles in
accordance with which the investigation should be pursued. Yet
for the discussion of many of the points in question the informa-
tion which Aristotle possessed was insufficient. Had his Meteoro-
logica, the work in which most of his opinions on mathematical
and physical geography are contained, been composed after,
instead of before, Alexander's Eastern expedition, the case might
have been different; but at the time when he wrote, the know-
ledge that was available concerning the surface of the earth and
the features which it presented was too restricted to admit of
adequate conclusions being deduced from it By means of that
expedition and of the observations of the men of
science who accompanied it, and by the discoveries
of Pytheas in the north and west of Europe, and
the increasing acquaintance with the Indian Ocean and the neigh-
bouring coasts which arose through the explorations set on foot
by the Ptolemies, the enquirers who followed him were in a
position to advance more boldly, and to determine numerous
principles which were of the highest importance both for the
theoretical conception of the globe and for the practical purposes
and by the °^ map-making. Finally, the establishment of the
Museum of Museum at Alexandria provided a central point
Alexandria. . ji.-i.iit , .,
towards which all these researches might converge,
and a great genius who could avail himself of them in the
person of Eratosthenes of Cyrene, who occupied the post of
librarian of that institution for the space of more than forty years
(240—196 B.C.).
The question of the sphericity of the earth is the one which
1 Coraewall Lewis, Astronomy of the Ancients, p. 171.