undulatory theory; other methods will have to be resorted to in order to free this theory from its difficulties.[1]
3. The third proposition of the atomic hypothesis assigns to the atoms, which are said to compose the different chemical elements, determinate weights corresponding to their equivalents of combination, and is supposed to be necessary to account for the facts whose enumeration and theory constitute the science of chemistry. The proper verification of these facts is of great difficulty, because they have generally been observed through the lenses of the atomic theory, and stated in its doctrinal terms. Thus the differentiation and integration of bodies are invariably described as decomposition and composition; the equivalents of combination are designated as atomic weights or volumes, and the greater part of chemical nomenclature is a systematic reproduction of the assumptions of atomism. Nearly all the facts to be verified are in need of preparatory enucleation from the envelops of this theory.
The phenomena usually described as chemical composition and decomposition present themselves to observation thus: A number of heterogeneous bodies concur in definite proportions of weight or volume; they interact; they disappear, and give rise to a new body possessing properties which are neither the sum nor the mean of the properties of the bodies concurring and interacting (excepting the weight which is the aggregate of the weights of the interacting bodies), and this conversion of several bodies into one is accompanied, in most cases, by changes of volume, and in all cases by the evolution or involution of heat, or light, or of both. Conversely, a single homogeneous body gives rise to heterogeneous bodies, between which and the body out of which they originate the persistence of weight is the only relation of identity.
For the sake of convenience, these phenomena may be distributed into three classes, of which the first embraces the persistence of weight and the combination in definite proportions; the second, the changes of volume and the evolution of light and heat; and the third, the emergence of a wholly new complement of chemical properties.
Obviously, the atomic hypothesis is in no sense an explanation of the phenomena of the second class. It is clearly and confessedly in-
- ↑ Cauchy's theory of dispersion is subject to another difficulty, of which no note is taken by Hunt: it does not account for the different refracting powers of different substances. Indeed, according to Cauchy's formulæ (whose terms are expressive simply of the distances between the ethereal particles and their hypothetical forces of attraction and repulsion), the refracting powers of all substances whatever must be the same, unless each substance is provided with a peculiar ether of its own. If this be the case, the assemblage of atoms in a given body is certainly a very motley affair, especially if it be true, as W. A. Norton and several other physicists assert, that there is an electric ether distinct from the luminiferous ether. Rettenbacher ("Dynamidensystem," p. 130, et seq.) attempts to overcome the difficulty by the hypothesis of mutual action between the corpuscular and ethereal atoms.
