  During most of the eighteenth century the primary challenge the Principia presented to philosophers revolved around what to make of a mathematical theory of forces in the absence of a mechanism, other than action at a distance, through which these forces work.  By the last decades of the century, however, little room remained for questioning whether gravity does act according to the laws that Newton had set forth and does suffice for all the motions of the heavenly bodies and of our sea. No one could deny that a science had emerged that, at least in certain respects, so far exceeded anything that had ever gone before that it stood alone as the ultimate exemplar of science generally. The challenge to philosophers then became one of spelling out first the precise nature and limits of the knowledge attained in this science and then how, methodologically, this extraordinary advance had been achieved, with a view to enabling other areas of inquiry to follow suit.