To
the Reader Concerning the Hypothesis of This Work
Since the novelty of the hypothesis of this work has already
been widely reported, I have no doubt that some learned men have taken serious
offence because the book declares that the earth moves, and that the sun is at
rest in the center of the universe; these men undoubtedly believe that the
liberal arts, established long ago upon a correct basis, should not be thrown
into confusion.
But if they are willing to examine the matter closely, they
will find that the author of this work has done nothing blameworthy. For it is
the duty of an astronomer to compose the history of the celestial motions
through careful and skillful observation. Then turning to the causes of these motions
or hypotheses about them, he must conceive and devise, since he cannot in any
way attain to the true causes, such hypotheses as, being assumed, enable the
motions to be calculated correctly from the principles of geometry, for the
future as well as for the past.
The present author has performed both these duties
excellently. For these hypotheses need not be true nor even probable; if they
provide a calculus consistent with the observations, that alone is sufficient. Perhaps
there is someone who is so ignorant of geometry and optics that he regards the
epicycle of Venus as probable, or thinks that it is the reason why Venus
sometimes precedes and sometimes follows the sun by forty degrees and even
more. Is there anyone who is not aware that from this assumption it necessarily
follows that the diameter of the planet in perigee should appear more than four
times, and the body of the planet more than sixteen times, as great as in the
apogee, a result contradicted by the experience of every age? In this study
there are other no less important absurdities, which there is no need to set
forth at the moment. For it is quite clear that the causes of the apparent
unequal motions are completely and simply unknown to this art. And if any
causes are devised by the imagination, as indeed very many are, they are not
put forward to convince anyone that they are true, but merely to provide a
correct basis for calculation.
Now when from time to time there are offered for one and the
same motion different hypotheses (as eccentricity and an epicycle for the sun’s
motion), the astronomer will accept above all others the one which is the
easiest to grasp. The philosopher will perhaps rather seek the semblance of the
truth. But neither of them will understand or state anything certain, unless it
has been divinely revealed to him.
Let us therefore permit these new hypotheses to become known
together with the ancient hypotheses, which are no more probable; let us do so
especially because the new hypotheses are admirable and also simple, and bring
with them a huge treasury of very skillful observations. So far as hypotheses
are concerned, let no one expect anything certain from astronomy, which cannot
furnish it, lest he accept as the truth ideas conceived for another purpose,
and depart from this study a greater fool than when he entered it. Farewell.