Halley told the Royal Society of Newton's work on orbits
On this day · 10 December 1684
On December 10, 1684, Edmond Halley reported Newton's tract De Motu to the Royal Society—the seed that grew into the Principia.
On December 10, 1684, the astronomer Edmond Halley informed the Royal Society that he had visited Isaac Newton at Cambridge, who had shown him “a curious treatise, De Motu.” At Halley’s urging, Newton agreed to send the manuscript to be entered on the Society’s register.
The back-story is one of science’s great prods. Earlier that year Halley had asked Newton what path a planet would trace under an inverse-square force. Newton replied, instantly, that it would be an ellipse—and that he had proved it. The nine-page tract that followed derived Kepler’s laws of planetary motion from a single principle.
An elliptical orbit, Newton showed, follows from an inverse-square force fixed at one focus.
Halley grasped at once that he was holding something epoch-making. His persistent encouragement pushed Newton to expand the tract into the Philosophiæ Naturalis Principia Mathematica of 1687, the book that founded classical mechanics. A short December note thus lit the fuse for modern physics.
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