Re: How did Sir Isaac Newton discoveries the law of gravity?

How did Sir Isaac Newton discoveries the law of gravity?

Like many legends, this probably has a kernel of truth. But my copy of Encarta^TM contains the following information:

As an undergraduate student of mechanics, Newton had (or claimed to have) formulated rudimentary ideas of universal gravitation. In 1864, Newton was visited by Edmund Halley, who discussed planetary motion with him. Consideration of this problem led to Newton's development of his three Laws of Motion.

Application of the Laws of Motion to Kepler's Laws of orbital motion led directly to Newton's Law of Universal Gravitation. Only the presence of some force could lead to the observed, curved motion of the planets, and Newton kept at it until everything was consistent, not only conceptually but mathematically. Incidentally, he discovered the calculus in the course of his work in mechanics. (Leibniz, who discovered it at about the same time, was just playing with mathematics, but Newton needed a new tool to handle the physics with which he was wrestling.)

All this was published in 1687 in Newton's monumental Philosophiae Naturalis Principia Mathematica (see also here).