TRANSACTIOXS OF SECTION B. 559 



of the chemistry of to-day, liave been little more than the discoverer of the law of 

 multiple proportions. If that cannot be maintained, what, then, becomes of this 

 conception of chemistry as dealing with the minute ? So far as comparison can 

 be made between the opsrations of the astronomer and the chemist, it is the 

 former and not the latter who, as a matter of fact, deals with the almost infinitely 

 minute. For if, indeed, the chemist often worlis upon comparatively small amounts 

 of substances, and, consequently, with very sensitive balances, that is, as we all 

 know, only for reasons of economy of time, materials, and apparatus; otlierwise 

 he works on the largest possible scale, with the object of attaining to the highest 

 degree of accuracy and perfection. The astronomer, on the other hand, has, per- 

 force, to deal with the smallest visible things in nature, the nearest approach there 

 is to geometrical points, those fixed points of light in the heavens which are only 

 known through scientific investigation to be other tlian what they seem to be. It is, 

 therefore, only as interpreted by the atomic hypothesis that chemistry can be said 

 to deal with the minute. 



When the atomic theory is expounded in the usual way it is commonly and 

 correctly stated that, on the assumption that substances consist of minute indi- 

 visible particles having weights or masses bearing the ratios of the combinino' 

 numbers assigned to them, the laws of chemical combination by weight neces- 

 sarily follow, and are thereby explained. But then the converse is not true — that 

 because chemical combination obeys the well-known laws, substances consist of 

 discrete particles. Nor does the assumption of the truth of the atomic hypothesis 

 afford any real explajiation of the facts expressed by the laws of chemical combina- 

 tion, or more comprehensively by the atomic theory, when that theory is given in 

 non-hypothetical terms. It is just as difficult to see why the atoms should possess 

 the weights on chemical grounds assigned to them, as to see why substances interact 

 in the proportions that they do ; that they do do so is, in either case, an ultimate 

 fact, for which no explanation has presented itself. The atomic hypothesis masks 

 this ignorance and deadens inquisitiveness. Notwithstanding all this, which is 

 incontrovertible, it is certainly a common opinion that in chemistry we investigate 

 the minute and intimate constitution of things. 



But if, after all, chemistry does not deal with the minute or, rather, if it has no 

 concern with the magnitude of single bodies or their molecules; if the atomic 

 hypothesis is not the foundation of, or necessary to, the atomic theory, then it is 

 certainly most desirable and important that the theory of chemistry, which, with 

 all its modern developments, I take to be indisputably the atomic theory of Dalton, 

 should be held and expounded without any reference to the physical constitution 

 of matter, in so far as that remains unknown. The opinion that chemical theory 

 should be developed without reference to the atomic hypothesis has indeed all 

 along been held by many eminent chemists ; but then the dilemma appears to 

 have presented itself to them, that either the atomic hypothesis must be granted, 

 or the atomic theory must be dispensed with, since it falls with the hypothesis. 

 That dilemma I do not recognise, and the practice of chemists .shows beyond doubt 

 that it is always ignored. Investigators use the theory, whether they admit it or 

 not ; teachers of the science find it indispensable to their task, however much they 

 may deprecate, and rightly so, unreserved acceptance of the atomic hypothesis astrue. 



Refusing to commit themselves to belief in the hypothesis, chemists have 

 thought from the first to escape the adoption of the atomic theory by putting 

 Dalton's discovery into something like these words: Numbers, called proportional or 

 combining numbers, can be assigned to the chemical elements — one to each — which 

 will express all the ratios of the weights or masses in which substances interact 

 and combine together. Perhaps the atomic theory is here successfully set aside 

 by expressing what is an actuality as an unaccounted-for possibilitj'. But then those 

 who use any such mode of expressing the facts, without reference to the theory, 

 never fail also to adopt the doctrine of equivalents, and thus, by this double act, 

 implicitly give in their adherence to the theory. 



Divested of all reference to the physical constitution of matter, the atomic 

 theory is that the quantities of substances which interact in single chemical changis 

 are equal to one another, — as truly equal in one way as equal masses are in another,— 



