as flat, but it must be understood that this 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 Hipparchus and Ptolemy, it did not find a
single important champion for more than a thousand years after the time
of the last great Alexandrian astronomer.

The first man, seemingly, to hark back to the Aristarchian conception
in the new scientific era that was now dawning was the noted cardinal,
Nikolaus of Cusa, who lived in the first half of the fifteenth century,
and was distinguished as a philosophical writer and mathematician. His
De Docta Ignorantia expressly propounds the doctrine of the earth's
motion. No one, however, paid the slightest attention to his suggestion,
which, therefore, merely serves to furnish us with another intere