  Mechanical atomism had faced the problem of how to introduce the appropriate kinds of activity into the world relying solely on the shapes, sizes and motions of atoms. They had struggled unsuccessfully to explain elasticity and gravity along such lines and chemistry posed problems of its own. Newtonian forces could readily be deployed to remove these problems. Newton presumed that forces of characteristic strengths (affinities) operated between the least parts of chemicals. What displaces what in a chemical reaction is to be explained simply in terms of the relative strengths of the affinities involved. Elasticity was attributed to attractive and repulsive forces acting between particles of an elastic substance and so on.