opinion had no champions among men of science during the Middle
Ages. When, in the year 1492, Columbus sailed out to the west on
his memorable voyage, his expectation of reaching India had full
scientific warrant, however much it may have been scouted by
certain ecclesiastics and by the average man of the period.
Nevertheless, we may well suppose that the successful voyage of
Columbus, and the still more demonstrative one made about thirty
years later by Magellan, gave the theory of the earth's rotundity
a certainty it could never previously have had. Alexandrian
geographers had measured the size of the earth, and had not
hesitated to assert that by sailing westward one might reach
India. But there is a wide gap between theory and practice, and
it required the voyages of Columbus and his successors to bridge
that gap.

After the companions of Magellan completed the circumnavigation
of the globe, the general shape of our earth would, obviously,
never again be called in question. But demonstration of the
sphericity of the earth had, of course, no direct bearing upon
the question of the earth's position in the universe. Therefore
the voyage of Magellan served to fortify, rather than to dispute,
the Ptolemaic theory. According to that theory, as we have seen,
the earth was supposed to lie immovable at the centre of the
universe; the various heavenly bodies, including the sun,
revolving about it in eccentric circles. We have seen that
several of the ancient Greeks, notably Aristarchus, disputed this
conception, declaring for the central position of the sun in the
universe, and the motion of the earth and other planets about
that body. But this revolutionary theory seemed so opposed to the
ordinary observation that, having been discountenanced by