In the third part of AN, chapters 22–40, Kepler deals with the path of the Earth and intends to offer a physical account of the Copernican theory. By so doing he includes the idea that a certain notion of power should be made responsible for the regulation of the differences in velocities of the planets, which in turn have to be established in relation to the planets’ distances. Now, the Copernican planetary theory departs from the general principle that the Earth moves regularly on an eccentric