XXXvi REPORT — 1844. 



a third, tliey may combine in the same proportion with each other. In 1787, 

 Dr. Higgins of Dublin had approximated to the Liw of tlie combination of 

 different multiples of the elements of bodies, in the case of sulphur and iron : 

 but these discoveries, considerable as they were, were not generally known, 

 and the laws derivable from them were not formally enunciated ; they had 

 hitherto exercised no influence upon the processes or the results of analytical 

 chemistry; and so little was their authority recognized, that even Berthollet, 

 one of the greatest chemists of his age, continued to maintain that the ele- 

 ments of bodies might combine in variable proportions, a conclusion which the 

 vague forms under which the analyses of bodies, more particularly those of 

 the mineral kingdom, were commonly exhibited, was not a little calculated to 

 favour. 



The atomic theory, however, by the clear conception which it enables us 

 to form of the conditions of the co-existence of the elements of bodies in 

 chemical combinations, by which they acquire permanent and distinctive 

 characters, as different from the results of their indefinite .aggregation and 

 mixture, has totally changed the whole face of the science of cheniisiry. It 

 was by considering thejveights ar. well as the number of the elementary atoms 

 which form the compound atom of the resulting body, that this theory was 

 not merely distinguished from the vague speculations of the atomic philoso- 

 phers of a former age, but became, when it was once admitted and established, 

 the guide as well as the basis of all accurate chemical analysis. The very de- ' 

 finite and comprehensive form in which this law was enunciated by its author 

 was the immediate expression of his primary conception of the constitution of 

 bodies ; and simple, natural and obvious as it may appear to us who are now 

 familiar with the results to which it leads, it was not, on that accoimt, a less 

 important step in the science of chemistry, whose form and language it rapidly 

 changed : the revolution which it effected in our views of the laws and results 

 of chemical combination, was nearly as great as that which was produced in 

 Physical Astronomy by the discovery and enunciation of the law of universal 

 gravitation. 



It has been contended, however, that he only discovers who proves, and 

 that inasmuch as most of the analyses which Dalton made the foundation of 

 his law, were either erroneous or insufficient, he has no suflScient claim to the 

 character of its discoverer. The atomic weight which he assigned to oxy- 

 gen was 7 instead of 8*01, that of hydrogen being 1 ; and his analyses of de- 

 fiant gas and carburetted hydrogen, which he made, in the first instance, the 

 basis of the law of multiple combining proportions, was likewise imperfect: 

 the theory of atoms also, in the form in which he presented it, was not free 

 from very serious objections, as involving assumptions respecting the ultimate 

 constitution of bodies, which are not only removed beyond the range of our 

 experience, but opposed to our primary conception of matter as susceptible 

 of infinite divisibility. But admitting the defects of his analyses, it may be 

 justly contended that they in no respect affect the form in which he ex- 

 pressed the lawof definite proportions ; and what is more important, they were 

 not of such a nature as to affect the form and character of the researches, 

 which, even if his fundamental analyses had been found to be perfectly accu- 

 rate, would still have been necessary for its further and complete develop- 

 ment ; and what is more, that the bearing of such investigations upon the esta- 

 blishment or refutation of the theory had been fully pointed and exemplified : 

 whilst, in reply to the last objection, it might be contended that not only is 

 our conception, of the infinite divisibility of matter, rather geometrical than 

 physical, but likewise that it by no means precludes other modes of exhibiting 



