PRIMARY CONCEPTS OF MODERN SCIENCE. 715 



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 mechani- 

 cal mixture or separation, evinces a thorough destruction of that in- 

 tegrity. 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 re- 

 ducing 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 hy- 

 pothesis. It is another case (to borrow a scholastic phrase) of illus- 

 trating idem per idem. It says : The large masses combine in defi- 

 nitely-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 un- 

 derlies the whole atomic hypothesis, differences of weight are differ- 

 ences 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 dif- 

 ferences of density or weight are impossible in the case of atoms. 



It is to be observed that the attribution of different weights to dif- 

 ferent atoms is an indispensable feature of the atomic theory in chem- 

 istry, 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 

 Ampere 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 scien- 

 tific 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 occa- 

 sion to inquire, hereafter, what promise there is, in the present state 



