ntre of celestial motions, that the
sun, the moon, and the stars revolved around the world which we
inhabit. Not that the Pythagorean hypothesis was totally forgotten.
There were those who believed that the sun, not the earth, is the centre
of the great circle in which the heavenly bodies perform their
evolutions; but the Ptolemaic hypothesis had the ascendency beyond all
doubt; and with this hypothesis Copernicus could not rest satisfied. It
appeared to him beset with insuperable difficulties. True enough, the
rotation of the heavens around the earth seemed to be what the human eye
beheld, as anyone watched sunrise and sunset. But what the senses thus
presented, reason, in its ponderings, was led to contradict. For the
notion of a huge mechanism like the celestial sphere, spinning round the
terraqueous globe as its pivot looked unreasonable. To explain it in any
way on mathematical principles needed a most complicated array of cycles
and epicycles. Symmetry and simplicity were wanting in the theory. _A
priori_ objections started up against it. If the senses pointed to the
earth as a centre, reason pointed to a centre elsewhere. Copernicus
studied the works of ancient philosophers on the question. He examined
mathematical traditions and criticised the opinions of learned
professors. He found accounts of those who had asserted the motion of
the earth. "Though," he says, "it appeared an absurd opinion, yet, since
I knew that in former times liberty had been permitted to others to
figure as they pleased certain circles for the purpose of demonstrating
the phenomena of the stars, I considered that to me also it might be
easily allowed to try whether, by a supposition of the earth's motion, a
better explanation might be found of the revolution of the celestial
orbs. Having assumed," he goes on to say, "the motions of the earth, by
laborious and long observation I at length found that if the motions of
the other planets be compared with the revolution of the earth, not only
these phenomena follow from the suppositions, but also that the several
orbs and the whole system are so connected in order and magnitude, that
no one part can be transposed without disturbing the rest and
introducing confusion into the whole universe." What Copernicus was in
search of was some simple and symmetrical theory of the appearances of
the heavens which would relieve him of the complexity and confusion
attendant on the Ptolemaic system so popular i