Quote of the Day

There is the story of how [Isaac Newton] informed Halley of one of his most fundamental discoveries of planetary motion. “Yes,” replied Halley, “but how do you know that? Have you proved it?” Newton was taken aback. “Why, I’ve known it for years,” he replied. “If you’ll give me a few days, I’ll certainly find you a proof of it.” As in due course he did.

—John Maynard Keynes, “Newton the Man”