planets, the list of which, as known at that time, comprised
Mercury, Venus, the Earth, Mars, Jupiter, and Saturn. The fixed
stars were alleged to be stationary, and it was necessary to
suppose that they are almost infinitely distant, inasmuch as they
showed to the observers of that time no parallax; that is to say,
they preserved the same apparent position when viewed from the
opposite points of the earth's orbit.

But let us allow Copernicus to speak for himself regarding his
system, His exposition is full of interest. We quote first the
introduction just referred to, in which appeal is made directly
to the pope.

"I can well believe, most holy father, that certain people, when
they hear of my attributing motion to the earth in these books of
mine, will at once declare that such an opinion ought to be
rejected. Now, my own theories do not please me so much as not to
consider what others may judge of them. Accordingly, when I began
to reflect upon what those persons who accept the stability of
the earth, as confirmed by the opinion of many centuries, would
say when I claimed that the earth moves, I hesitated for a long
time as to whether I should publish that which I have written to
demonstrate its motion, or whether it would not be better to
follow the example of the Pythagoreans, who used to hand down the
secrets of philosophy to their relatives and friends only in oral
form. As I well considered all this, I was almost impelled to put
the finished work wholly aside, through the scorn I had reason to
anticipate on account of the newness and apparent contrariness to
reason of my theory.