Tiscali Quicklinks. Please visit our Accessibility Page for a list of the Access Keys you can use to find your way around the site, skip directly to the main navigation, to the page content, or to more links within reference.
Newton's greatest achievement was to demonstrate that scientific principles are of universal application. Using these principles, scientists could predict the results of their experiments when carried out in controlled conditions, enabling the more rapid development of new ideas. He clearly defined the nature of mass, weight, force, inertia, and acceleration.
In 1679 Newton calculated the Moon's motion on the basis of his theory of gravity and also found that his theory explained how the planets, including the Earth, orbited the Sun. The laws of planetary motion had been worked out by German astronomer Johannes Kepler on the basis of observations of the planets; Newton provided the scientific evidence to back up Kepler's theory.