Meanwhile, investigations into the physical mechanism of the planets culminated in 1687 with the publication of Isaac Newton’s Principia’. Although others had made important contributions to the question of the mutual attraction of bodies, Newton was the first to assimilate it all and to derive the exact equations for the fall of a body on Earth and the equivalent fall of a satellite, such as the Moon, in its orbit. After this masterly synthesis of cosmic and terrestrial physics Newton proceeded to calculate the motions of the various members of the Solar System. He included in his calculations the mutual perturbations of the planets on each other, to see if the observed and predicted positions were in close agreement. As with all his endeavours, Newton expected experimental or observational confirmation of his theories, and rejected hypotheses which he believed to be unverifiable.

Newton’s work presented a whole new consistent world view, just as Aristotle’s had done many centuries before. Although this new structure did not materially affect the state of observations, it did mean that a variety of observations which would perfect the constants of Newtonian physics were made. Different philosophical frameworks require different observations. With the concept of a Solar System as a mechanism in which each member influences the motion of every other member in accordance with the law of universal gravitation, the various irregularities in the motions of planets took on new importance.

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