On the homocentric spheres of Eudoxus (Q1385176)

In the 4-th century B. C. Eudoxus and Callippus used sets of rotating homocentric spheres to decompose planetary motions. Critical to their theory is a small motion called by them the hippopede, a ``spherical lemniscate''. Since their original works are lost, different interpretations of their theory are possible. The author takes the view that the theory was only a qualitative tool and he declares that ``the concept of geometrical congruence and similarity are quite precise without being quantitative''. He contests Schiaparelli's and others' earlier quantitative approach.