  The success of the research in celestial mechanics predicated on the Principia was unprecedented. Nothing of comparable scope and accuracy had ever occurred before in empirical research of any kind. That led to a new philosophical question: what was it about the science of the Principia that enabled it to achieve what it did? Philosophers like Locke and Berkeley began asking this question while Newton was still alive, but it gained increasing force as successes piled on one another over the decades after he died. This question had a practical side, as those working in other fields like chemistry pursued comparable success, and others like Hume and Adam Smith aimed for a science of human affairs. It had, of course, a philosophical side, giving rise to the subdiscipline of philosophy of science, starting with Kant and continuing throughout the nineteenth century as other areas of physical science began showing similar signs of success. The Einsteinian revolution in the beginning of the twentieth century, in which Newtonian theory was shown to hold only as a limiting case of the special and general theories of relativity, added a further twist to the question, for now all the successes of Newtonian science, which still remain in place, have to be seen as predicated on a theory that holds only to high approximation in parochial circumstances.