"Accordingly, we find in his Optical Queries and in his letters to Boyle, that Newton had very early made the attempt to account for gravitation by means of the pressure of a medium, and that the reason he did not publish those investigations "proceeded from hence only, that he found he was not able, from experiment and observation, to give a satisfactory account for this medium, and the manner of its operation in producing the chief phenomena of Nature." The doctrine of direct action at a distance cannot claim for its author the discoverer [Newton] of universal gravitation. It was first asserted by Roger Cotes, in his preface to the Principia... According to Cotes, it is by experience that we learn that all bodies gravitate. We do not learn in any other way that they are extended, movable, or solid. Gravitation, therefore, has as much right to be considered an essential property of matter as extension, mobility, or impenetrability. And when the Newtonian philosophy gained ground in Europe, it was the opinion of Cotes, rather than than that of Newton that became most prevalent, till at last Boscovich propounded his theory, that matter is a congeries of mathematical points, each endowed with the power of attracting or repelling the others according to fixed laws. In his world, matter is unextended, and contact is impossible. He did not forget, however, to endow his mathematical points with inertia."