7 h THE POPULAR SCIENCE MONTHLY. 



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, de- 

 terminate weights corresponding to their equivalents of combination, 

 and is supposed to be necessary to account for the facts whose enu- 

 meration and theory constitute the science of chemistry. The proper 

 verification of these facts is of great difficulty, because they have gen- 

 erally 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 system- 

 atic 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 de- 

 composition present themselves to observation thus: A number of 

 heterogeneous bodies concur in definite proportions of weight or vol- 

 ume; they interact; they disappear, and give rise to a new body pos- 

 sessing properties which are neither the sum nor the mean of the prop- 

 erties 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 in- 

 volution 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 re- 

 lation 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- 



1 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 sub- 

 stances. Indeed, according to Cauchy's formulae (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, un- 

 less 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 cor- 

 puscular and ethereal atoms. 



