five, the earth of three, the moon of four, and each of the three outer planets of five circles; and even with this complicated machinery the new system did not represent the actual motions in the heavens any better than the Ptolemean did. Copernicus himself said that he would be as delighted as Pythagoras was when he had discovered his theorem, if he could make his planetary theory agree with the observed positions of the planets within 10′.[1] But the accuracy was very far indeed from reaching even that limit.[2] Doubtless the Prutenic tables were better than the Alphonsine ones, but that was simply because Copernicus had been able to apply empiric corrections to the elements of the orbits, and because Reinhold did his work better than the numerous computers at Toledo had done theirs. The Copernican system as set forth by Copernicus, therefore, did not advance astronomy in the least; it merely showed that it was possible to calculate the motions of the planets without having the origin of co-ordinates in the centre of the earth. But of proofs of the physical truth of his system Copernicus had given none, and could give none; and though there can hardly be any doubt that he himself believed in the reality of the earth's motion, it is extremely difficult to say of most of his so-called followers whether they had any faith in that motion, or merely preferred it for geometrical reasons.[3]
It is always difficult to avoid judging the ideas of former ages by our own, instead of viewing them in their connection with those which went before them and from which they
- ↑ Rhetici Ephemerides novæ, 1550, p. 6.
- ↑ Möbius has shown that the use of the mean place of the sun (i.e., the centre of the earth's orbit) instead of the true place might, in the Copernican theory of Mars, lead to errors of 2°. See a note in Apelt's Die Reformation der Sternkunde, Jena, 1852, p. 261.
- ↑ The contemporaries of Copernicus were not aware that the introduction to his book, in which the system is spoken of as a mere hypothesis, was written without the knowledge of the author by Osiander of Nürnberg.
