n the schools. He started
from an _a priori_ point of reasoning--the only one thought of in his
day--but he came to certain conclusions which _a posteriori_ examination
in after times abundantly confirmed.

[Illustration: Copernicus.]

He believed that the earth is spherical; that the earth and the sea
constitute a wonderful globe; that the motions of the heavenly bodies
are circular and uniform, or compounded of circular and uniform motions;
that the earth revolves on its own axis, and also performs a journey
along its own orbit round the sun; that the sphere of the fixed stars is
immensely distant, and that it is impossible to explain the motion of
the planets upon the supposition of the earth being their centre. And he
distinctly remarks: "It does not shame us to confess that the whole
space in which the moon revolves, together with the earth, moves along a
great orbit among the planets, round the sun every year; that the sun
remains permanent and immovable, whatever may be its apparent motion."
It must be kept in mind throughout any careful study of his theory,
that it was an _hypothesis_ framed to remove difficulties connected with
older systems; that he sought to bring conceptions of the universe into
harmony with reason, instead of giving way to impressions made by the
senses, or to the authority of world-honored teachers, either in other
days or in his own; nor can we omit adding that, while he found fault
with the Ptolemaic cycles and epicycles, he constructed similar devices
of his own.

"As the real motions, both of the earth and the planets, are unequable,
it was requisite to have some mode of representing their inequalities;
and accordingly the ancient theory of excentrics and epicycles was
retained so far as was requisite for this purpose." In the case of
Mercury's orbit he makes suppositions which are extremely complex,
although they manifest his apprehension of the difficulties attendant on
the common theory of his own time; but he verified many of his views by
astronomical observations; and his approximations to modern science, and
the light he threw on preceding discoveries, establish the fame of
Nicholas Copernicus.

On a review of the life of Copernicus, and the conclusions he reached,
the mental and moral qualities of the man come out with conspicuous and
extraordinary lustre.

He was a mathematician, thus walking in the footsteps of Roger Bacon.
This science, since the days of Euclid, had bee