Page:Popular Science Monthly Volume 15.djvu/479

 in the subdivision of matter. He claims that the line which may be mentally thrust through the minutest particle of matter is not a needle nor a knife—that it is the mathematician's line as immaterial as space—and that the thrusting of such a line can accomplish no division. He claims that, applicable as it may be to space, such logic need not bind the physicist who studies the constitution of bodies which inhabit space.

Therefore, unconcerned about the abstract question of divisibility, the physicist anxiously inquires whether the phenomena of the material world can afford any testimony in regard to the ultimate constitution of bodies. And the molecular theory may be regarded as an induction from a multitude of observed facts—a generalization reached by a careful comparison of many established principles. The object of the present paper is to present the theory in this light. To exhaust the evidence, however, by this method would be to present the science of modern physics complete, a task impossible at a single sitting.

The three fundamental conceptions embodied in the molecular theory are: the existence of molecules, the existence of molecular spaces, and the existence of molecular motions.

Now, there may be phenomena which declare the existence of molecules without touching the question of molecular space or of molecular motion, and proofs both of the existence of molecules and of molecular spaces may be altogether silent on the question of rest or motion. But notice: whatever evidence we have of the existence of intervals between the ultimate parts of a body is equally evidence of the existence of molecules, and whatever phenomena indicate the existence of motion among these interior parts of a body do equally affirm the existence both of molecules and of molecular spaces. If, then, the three classes of phenomena be presented as bearing first upon the molecule, second upon molecular spaces, and third upon molecular motion, the testimony will be continuous and cumulative.

First, then, as to the existence of molecules. We will confine our attention to two sources of evidence—the phenomena of divisibility and of chemical synthesis.

Is it possible, by continued subdivision, to reach a particle the division of which would put an end to the existence of the substance—not in the sense of annihilation, but, in other words, to reach a particle whose division compels a substance to suffer death by yielding up those identifying properties by which alone we distinguish it from other kinds of matter?

A piece of marble may be crushed and reduced to an almost impalpable powder, and yet, on examination, each little grain is found to be an angular block of stone, lacking no property of the original block except its size and form. The same may be said of other solids. Even ice, keep its temperature low enough, may be reduced to microscopic fineness, and each little particle, notwithstanding its minuteness,