Hooke's analysis of circular and elliptic motion.

Hooke based his analysis on three "suppositions." The first supposition was that all celestial bodies exert a gravitating force that attracts others to their centre. He then continues:

"The second supposition is this, That all bodies whatsoever that are put into a direct and simple motion, will so continue to move forward in a streight line, till they are by some other effectual powers deflected and bent into a Motion, describing a Circle, Ellipsis, or some other more compounded Curved Line. The third supposition is, That these attractive powers are so much the more powerful in operating, by how much the nearer the body wrought upon is to their own Centres."

Reference

quoted from Westfall, R. S. (1971) Force in Newton's Physics, the Science of Dynamics in the Seventeenth Century. Macdonald, London.

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