10 Dec 1684: Newton shares work on gravity

On this day in 1684, Edmund Halley shared a letter from Isaac Newton with the Royal Society. Coming to be known as De motu corporum in gyrum – “On the motion of bodies in an orbit” – it laid out the principles of gravity.

Portrait of Sir Isaac Newton (1702) by Sir Godfrey Kneller (National Portrait Gallery)

Some more details:

• Newton discovered the force of gravity depended on two characteristics: mass and distance
• the work of German astronomer Johannes Kepler, who advanced the idea of heliocentrism, was a key inspiration
• Newton’s Principia, published in 1687, fleshed out the ideas put forth in the letter
• Voltaire reported Newton’s supposed inspiration by the falling apple
• “Gravity Day” is celebrated on December 25, Newton’s birthday