  The key sources of Newton's stance on atomism in his published work are Querie 31 of his Opticks, and a short piece on acids (Cohen, 1958, 257–8). Atomistic views also make their appearance in the Principia, where Newton claimed “the least parts of bodies to be—all extended, and hard and impenetrable, and moveable, and endowed with their proper inertia” (Cajori, 1962, 399). If we temporarily set aside Newton's introduction of his concept of force, then Newton's basic matter theory can be seen as a version of mechanical atomism improved by drawing on the mechanics of the Principia. Whereas mechanical atomists prior to Newton had been unclear about the nature and status of the laws governing atoms, Newton was able to presume that his precisely formulated three laws of motion, shown to apply in a wide variety of astronomical and terrestrial settings, applied to atoms also. Those laws provided the law of inertia governing motion of atoms in between collisions and laws of impact governing collisions. Newton also added his precise and technical notion of inertia or mass, another fruit of his new mechanics, to the list of primary properties of atoms. These moves certainly helped to give precise content to the fundamental tenets of mechanical atomism that they had previously lacked.