particles, whatever these may be, the simple properties of matter: at most we can thus follow out into corpuscles as artificial as the corpus—the body itself—the actions and reactions of this body with regard to all the others. This is precisely the object of chemistry. It studies bodies rather than matter; and so we understand why it stops at the atom, which is still endowed with the general properties of matter. But the materiality of the atom dissolves more and more under the eyes of the physicist. We have no reason, for instance, for representing the atom to ourselves as a solid, rather than as liquid or gaseous, nor for picturing the reciprocal action of atoms by shocks rather than in any other way. Why do we think of a solid atom, and why of shocks? Because solids, being the bodies on which we clearly have the most hold, are those which interest us most in our relations with the external world; and because contact is the only means which appears to be at our disposal in order to make our body act upon other bodies. But very simple experiments show that there is never true contact between two neighbouring bodies[1]; and besides, solidity is far from being an absolutely defined state of matter.[2] Solidity and shock borrow, then, their apparent clearness
