Somewhat Divine

Simon Schaffer

• Isaac Newton: The ‘Principia’ Mathematical Principles of Natural Philosophy translated by I. Bernard Cohen
  California, 974 pp, £22.00, September 1999, ISBN 0 520 08817 4

‘This incomparable author having at length been prevailed upon to appear in public, has in this treatise given a most notable instance of the extent of the powers of the mind.’ This is how the very first review of the Principia began, in summer 1687: from the start, you were forced to admire Newton’s modesty, and his genius. The reviewer, the young astronomer Edmond Halley, knew what he was talking about. Three years earlier, during a visit to Cambridge, he had posed the puzzle which started Newton on the path to his Principia. What is the orbit of a planet under the influence of an attractive force varying inversely as the square of the distance? Halley reminded his readers that the great Kepler had long before identified vital patterns in planets’ motion: their elliptical paths with the Sun at their focus, the mathematical regularities which governed their orbital speeds.