MATTER. From a physical point of view, matter is anything that can affect the senses, or that can exert, or be acted on by, force. The existence of matter, in the sense of substance, ha.s been doubted by many philosophers, including some of the great est of experimenters. Indeed, as we can know matter only by the forces it exerts, it is ebvious that the supposition of mere geometric points, capable of exerting force (tech nically called centers of force), will as satisfactorily account for all observed phenomena as any other idea of the ultimate nature of matter. Here, however, we are dealing with a question confessedly beyond the reach of experiment, and belonging to the domain with which metaphysics professes to deal. See PERCEPTION.
Although experiment cannot lead to a knowledge of the ultimate nature of matter, it may lead to important discoveries as to the arrangement of the molecules of different bodies, and their similarity or dissimilarity. Some of the questions to which we may expect an answer, though not a speedy' one, have already been mentioned in the article FORCE, CONSERVATION OF; but in order to render intelligible the short account which we intend to give of some very interesting ideas recently propounded by Graham (q.v.), it will be necessary to repeat some of them.
The old idea of the transmutation of metals (see ALCHEMY) implicitly contains the assumption that all kinds of matter are ultimately one. Far from being a startling assumption, this is the simplest and most easily conceived notion we can entertain on the subject; and it offers a remarkably simple explanation of that extraordinary prop erty of matter which Newton proved by careful experiments, that the weight of a body depends only on the quantity, not on the quality of the matter that composes it. One idea, then, of matter is, that the atoms (or smallest parts, whatever these may be) of all bodies are identical, but that the molecules (each of which is a single atom, or a defi nitely arranged group of atoms) differ from one body to another. Thus (to take an instance merely for explanation, not as at all likely to be correct), if hydrogen be sup posed to consist of the simple atoms of matter oxygen, each niolecule of which is 8 times as heavy as one of hydrogen, may nave each molecule formed of 8 elementary atoms, arranged in a group such as the corners of a die; carbon, 6 times as heavy per molecule, might be composed of 6 simple atoms grouped as at the corners of an octo hedron; and so on. It is obvious that here each atom must be supposed capable of
axerting force on every other. This leads us naturally to speculations as to the medium through which this force, if it be exerted at a distance, is propagated (see FORCE, CON ElERVATION OF); and then we have introduced matter of a more refined character than our supposed elementary atoms. This difficulty has suag.ested to various philosophers the idea that there is no actio in distans, that all pressure,for instance, in a gas is due to incessant impacts of its particles upon each other and upon the containing vessel. But from various experimental results, we know that this species of motion is capable of being transferred from one body to another, of being increased oi diminished by change of temperature, and is, in fact, heat itself, oue form of kinetic energy. This, if there be no ultimate difference between kinds of matter, could never be the cause of their apparent difference. Hence, in Graham's view, though all ulthuate atoms are identical in substance, they have special !notions of their own, by which one is distinguished from another, these motions not being capable of transfer from one atom or group of atoms to another. It is difficult to conceive energy in such a form as not to be trans ferable, so that we refer the reader to Graham's own papers for the further development of his theory—remarking, in conclusion, that no theory of the nature of niatter can be considered as at all complete till it account for the mutual action of separate atoms; for this the existence of a continuous material medium in space would seem to be necessary; and this, in lts turn, would, if accepted, enable us to dispense with the idea of atoms. In connection with this, we may mention that sir William Thomson has shown that more heterogeneity (which we know exists in matter), together with gravitation, is sufficient to explain all the apparently discordant laws of molecular action; matter being sup posed, in this theory, to be continuous but of varying density from point to point.