The Clockwork Universe: Isaac Newton, the Royal Society, and the Birth of the Modern World

by Edward Dolnick

Kepler knew, for example, how long it took each planet to orbit the sun—Mercury, 3 months; Venus, 7 months; Earth, 1 year; Mars, 2 years; Jupiter, 12 years; Saturn, 30 years—but try as he might he could not find a rule to connect