The eastward displacement of a freely falling body on the rotating Earth: Newton and Hooke's debate of 1679



In this article I would like to tell the story of the beginning of modern theoretical physics, freed from all kinds of questionable anecdotes which have entered the scientific literature over the centuries. It all began in the seventeenth century when the mathematical theory of astronomy began to take shape. A major step in the history of modern science was taken when a few members of The Royal Society in London realized that the laws ruling the motions of heavenly bodies as manifested in Kepler's three laws are also effective in the dynamics of Earth-bound particle motion. Everything started, not with I. Newton, but with R. Hooke. Not Newton's falling apple (Voltaire's invention), but a far-reaching response by R. Hooke to a letter by I. Newton, dated November 28, 1679, ignited Newton's interest in gravity. That letter contained the famous spiral which a falling body would follow when released from a certain height above the surface of the Earth. Hooke's answer, based on Keplerian orbits, expressed the opinion that the body's trajectory would rather follow an elliptical path. In his spiral sketch Newton, however, predicted correctly that the falling body would be found to suffer an eastward deviation from the vertical in consequence of the Earth's rotation. In the course of time, many a researcher, including Hooke himself, was able to verify this conjecture. But it took until 1803 for the first satisfactory calculation of the eastward displacement of a freely falling body to be performed, and was provided by C.F. Gauss.