competent to account for changes of volume or of temperature. And, with the phenomena of the third class, it is apparently incompatible. For, in the light of the atomic hypothesis, chemical compositions and decompositions are in their nature nothing more than aggregations and segregations of masses whose integrity remains inviolate. But the radical change of chemical properties, which is the result of all true chemical action, and serves to distinguish it from mere mechanical mixture or separation, evinces a thorough destruction of that integrity. It may be that the appearance of this incompatibility can be obliterated by the device of ancillary hypotheses; but that leads to an abandonment of the simplicity of the atomic hypothesis itself, and thus to a surrender of its claims to merit as a theory.
At best, then, the hypothesis of atoms of definite and different weights can be offered as an explanation of the phenomena of the first class. Does it explain them in the sense of generalizing them, of reducing many facts to one? Not at all; it accounts for them, as it professed to account for the indestructibility and impenetrability of matter, by simply iterating the observed fact in the form of an hypothesis. It is another case (to borrow a scholastic phrase) of illustrating idem per idem. It says: The large masses combine in definitely-proportionate weights because the small masses, the atoms of which they are multiples, are of definitely-proportionate weight. It pulverizes the fact, and claims thereby to have sublimated it into a theory.
Upon closer examination, moreover, the assumption of atoms of different specific gravities proves to be, not only futile, but absurd. Its manifest theoretical ineptitude is found to mask the most fatal inconsistencies. According to the mechanical conception which underlies the whole atomic hypothesis, differences of weight are differences of density; and differences of density are differences of distance between the particles contained in a given space. Now, in the atom there is no multiplicity of particles, and no void space; hence differences of density or weight are impossible in the case of atoms.
It is to be observed that the attribution of different weights to different atoms is an indispensable feature of the atomic theory in chemistry, especially in view of the combination of gases in simple ratios of volume, so as to give rise to gaseous products bearing a simple ratio to the volumes of its constituents, and in view of the law of Ampère and Clausius, according to which all gases, of whatever nature or weight, contain equal numbers of molecules in equal volumes.
The inadequacy of the atomic hypothesis as a theory of chemical changes has been repeatedly pointed out by men of the highest scientific authority, such as Grove (Correlation of Physical Forces, in Youmans's "Correlation and Conservation of Forces," p. 164, et seq.), and is becoming more apparent from day to day. I shall have occasion to inquire, hereafter, what promise there is, in the present state
