118 Dr. E. J. Mills onit& Atomic Theory. 



Sinne," has tacitly shown the weakness of tkV> atomic interpreta- 

 tion of isomerism. - 



Those who consider isomerism explained by such methods as 

 have just been discussed, must understand by an explanation 

 something different from the scientific meaning of that term. A 

 phenomenon is explained when it is shown to be a part or in- 

 stance of one or more known and more general phenomena. 

 Isomerism is not, therefore, explained by assertions about indi- 

 visibles, which have neither been themselves discovered nor 

 shown to have any analogy in the facts or course of nature — nor 

 by explicit statements about a "structure" which has never 

 been seen — nor by the use of a phrase to which no clear defini- 

 tion has been, or can be, attached. 



Before isomerism had acquired the importance it now pos- 

 sesses, the great argument in favour of the atomic theory was 

 that the law of multiple and that of definite proportions unde- 

 niably represent facts which can be explained only by the exist- 

 ence of atoms. Here the inadequate and idle notion of an 

 "explanation" recurs. I have already (p. 115) exposed the fal- 

 lacy of supposing that the equational method of arriving at 

 formulae is any thing more than the arithmetical process of taking 

 the least common multiple — and pointed out the imaginary 

 nature of Dalton's rules (p. 114); and formulae that have 

 been obtained by these means, in order to affirm the law of mul- 

 tiple or definite proportions, are condemned accordingly. But 

 the exact point of this argument, so far as it has not been alluded 

 to already, lies in the following considerations. Supposing an 

 aqueous solution of hydric chloride be mixed with successive 

 small quantities of sodic hydrate. Several actions occur; but 

 consider for a moment only that one whereby the hydrogen of 

 the hydric chloride is exchanged for sodium. It is quite evi- 

 dent that, on each addition of the sodic hydrate, anew compound 

 ought to be produced containing, say, the whole of the sodium, 

 in the form H^ Na y C\ z ; and as the quantity of the sodium may 

 be varied infinitely at pleasure, an infinite variety of hydrosodic 

 chlorides must, if matter be infinitely divisible, be the result of 

 the process. But not only does such a variety not arise, there 

 is a perfect absence of any hydrosodic compound ; for the sole 

 product of the reaction in every case is sodic chloride, Na CI. 

 Hence it is inferred that matter cannot be infinitely divisible — 

 that there has been a saltus — in short, that atoms exist. 



Now this is a question of a constant ratio considered as ex- 

 isting between sodium and chlorine when brought together 

 under conditions which need not be constant. As the mixture 

 is made, the sodium and chlorine are unquestionably divided by 

 being dissolved in a larger quantity of liquid than before. If 



