|THE PRIMARY CONCEPTS OF MODERN PHYSICAL SCIENCE.|
III.—The Assumption of the Essential Solidity of Matter.
IT cannot have escaped the notice of the attentive reader of the passage quoted in my last paper from Prof. Tyndall's lecture on "The Use of the Scientific Imagination" that Tyndall urges the theory of the atomic constitution of matter as the only theory consistent with its objective reality. He takes it for granted that the alternative lies between the definite, tangible, solid atom on the one hand, and a shadowy abstraction—a "vibrating, multiple proportion, or a numerical ratio in a state of oscillation"—on the other. There is no doubt that the opinion thus expressed is shared by the great majority of physicists, as well as of ordinary untrained men. To the minds of most persons, as to the mind of Tyndall, the conception of matter involves the notion of definite, tangible, and indestructible solidity. It is the general tacit assumption that, of the three molecular states, or states of aggregation, in which matter presents itself to the senses—the solid, the liquid, and the gaseous—the last two are simply disguises of the first; that a gas, for instance, is in fact a group or cluster of solids, like a cloud of dust, differing from such a cloud only by the greater regularity in the forms and distances of the particles whereof it is composed, and by the fact that these particles are controlled in the case of a gas by their mutual attractions and repulsions, while in the case of the cloud of dust they are under the sway of extrinsic forces. And, while the transition of the three molecular states into each other in regular and invariable order is too obvious to be ignored, it is supposed that the solid is the primary, normal, and typical state of which the liquid and gaseous, or aëriform, states are simply derivatives, and that, if these states are considered as evolved the one from the other, the order of evolution is from the solid to the vapor or gas. In this view the solid form of matter is not only the basis and origin of all its further determinations—of all its evolutions and changes—but it is also the primary and typical element of its mental representation and conception.
While this view of the relation between the molecular states of matter is all but universally prevalent, it is not difficult to show that it is in irreconcilable conflict with the facts of scientific experience. All evolution proceeds from the relatively Indeterminate to the relatively Determinate, and from the comparatively Simple to the comparatively Complex. And (confining our attention, for the moment, to the two extreme terms of the evolution, the solid and the gas, and ig-