Therefore I will not conceal from your holiness that what moved me to consider another way of reckoning the motions of the heavenly bodies was nothing else than the fact that the mathematicians do not agree with one another in their investigations.

In the first place, they are so uncertain about the motions of the sun and moon that they cannot find out the length of a full year.

In the second place, they apply neither the same laws of cause and effect, in determining the motions of the sun and moon and of the five planets, nor the same proofs.

Some employ only concentric circles, others use eccentric and epicyclic ones, with which, however, they do not fully attain the desired end.

They could not even discover nor compute the main thing--namely, the form of the universe and the symmetry of its parts.