ed, as an
interesting circumstance, that the time at which he discovered the
scheme of the solar system coincided with a remarkable epoch in the
world's history. The great astronomer had just reached manhood at the
time when Columbus discovered the New World.

Before the publication of the researches of Copernicus, the orthodox
scientific creed averred that the earth was stationary, and that the
apparent movements of the heavenly bodies were real movements. Ptolemy
had laid down this doctrine fourteen hundred years before. In his theory
this huge error was associated with so much important truth, and the
whole presented such a coherent scheme for the explanation of the
heavenly movements, that the Ptolemaic theory was not seriously
questioned until the great work of Copernicus appeared. No doubt others
before Copernicus had from time to time in some vague fashion surmised,
with more or less plausibility, that the sun, and not the earth, was the
centre about which the system really revolved. It is, however, one thing
to state a scientific fact; it is quite another thing to be in
possession of the train of reasoning, founded on observation or
experiment, by which that fact may be established. Pythagoras, it
appears, had indeed told his disciples that it was the sun, and not the
earth, which was the centre of movement, but it does not seem at all
certain that Pythagoras had any grounds which science could recognize
for the belief which is attributed to him. So far as information is
available to us, it would seem that Pythagoras associated his scheme of
things celestial with a number of preposterous notions in natural
philosophy. He may certainly have made a correct statement as to which
was the most important body in the solar system, but he certainly did
not provide any rational demonstration of the fact. Copernicus, by a
strict train of reasoning, convinced those who would listen to him that
the sun was the centre of the system. It is useful for us to consider
the arguments which he urged and by which he effected that intellectual
revolution which is always connected with his name.

The first of the great discoveries which Copernicus made relates to the
rotation of the earth on its axis. That general diurnal movement, by
which the stars and all other celestial bodies appear to be carried
completely round the heavens once every twenty-four hours, had been
accounted for by Ptolemy on the supposition that the apparent move