XVT.] RETROSPECT AND SUMMARY. 369
marked advance in geographical knowledge was the latter half
of the fourth century before our era. It was at that time that Alex-
ander carried his victorious arms as far eastward as Bactria and
India, and explored the shores of the Indian Ocean; while in the
opposite direction Pytheas was investigating the western coasts of
Europe and the wonders of the northern sea. The task of enlarging
the field of knowledge now passed into the hands of the Romans,
and we have seen how the campaigns of Lucullus and Pompey in
Armenia and Iberia, the progressive subjugation of Spain, Gaul,
and Britain, and finally the expeditions that were undertaken
against Germany and other countries to the northward of the
Alps, revealed to view large areas, about which before that time
only vague rumours had prevailed. The facts that were thus
brought to light were diligently harvested by learned men
amongst the Greeks. The Augustan age formed the culmi-
nating point of these discoveries, and it w_as during that period
that the sum of the information which had~thus been acquired
was once for all brought together, and diligently sifted and
arranged, in the comprehensive work of Strabo.
We have also traced side by side with the growth of this
part of the subject the gradual development of andof Scien.
scientific enquiry about the earth and its com- tificGeo-
ponent elements. In the domain of physical grap y'
geography it has been seen how the early observation of earth-
quake movements and volcanic phenomena by the Greeks led
up to the speculations of Aristotle on the causes which pro-
duced them, and afterwards to the examination and comparison
of them by travellers like Posidonius; and how the tides of the
ocean were made known to the dwellers about the Mediter-
ranean, and the causes of their recurrence were explained, by
Pytheas and other voyagers. In mathematical geography the
process of development has been even more apparent There
we have noticed the early introduction of the gnomon as an
instrument of measurement, and the primitive attempts at map-
making and the division of the world into continents. At the
same time the Homeric conception of the earth as a circular
plane, which was still maintained by the Ionian school of
philosophers, and was not wholly exploded in Herodotus1 time,
T. 24