  It is scarcely surprising that the unprecedented success of Newton's theory of gravity stimulated interest in the methodology of the Principia. The obvious thought was to emulate this success in other areas by following the same method. But then, even independently of questions about what the method was, one has to consider exactly how it contributed to the success. Viewed in retrospect, Book 2 makes clear that this question has no simple answer. If Newton followed the same method in Book 2, then the failure of his effort on resistance forces — even worse, the failure that he did not recognize — shows that the method was no guarantee of success. The empirical world must cooperate for it to succeed.