ABSTRACT
Isaac Newton, born on Christmas Day 1642, the day of Galileo's death, was in Cambridge at the time of the Great Plague, which drove him, among many others, to retire to country for a while. The law of the inverse square was still unaccepted; in fact, Newton had not apparently published much, if any, of the results of his researches. Halley attacked the problem of elliptic motion without success, starting from principle of the inverse square. By Halley's instrumentality he was induced to send in a memoir to Royal Society, containing some of the propositions afterwards embodied in his "Principia". Newton naturally appealed for more accurate places and elements for planetary orbits, as he was still testing the accuracy of Kepler's numerical third law, in order to apply his new theory to every planet and satellite known in heavens. To prove the universality of Newton's law of gravitation, as it is called, by any direct argument is a practical impossibility.
