886 ^^ ^^' dalton's principle ap combination. 



the a«unip- to consider how far they substantiate and authorize the con- 

 xxQus. elusions that have been deduced from them. Nothing, as 



I can judge, has been advanced, which has the least reference 

 to the first position, that when only one combination of two 

 bodies can be obtained it must be h'mary. This therefore, 

 which is the foundation of all the arsjutnent, must be re- 

 garded as a mere postulate, unsupported by facts, and not 

 resting immediately either on analogy or induction. The 

 2d position, that only one combination of oxigen and hidro- 

 gen, and only one of hidrogen and azote can exist, rests 

 rather on a different foundation from the preceding. We 

 have never yet been able to produce more than one <ombi- 

 nation with each of these substances, therefore Mr. Dalton 

 concludes, that only one combination can possibly exist. But 

 it is evident that this is not a legitimate way of reasoning ; 

 it amounts to no more tljan a presumption, and that drawn 

 from our ignorance; and is in contradiction to the general 

 analogy of chemical affinities*. From what has been 

 stated I think it will be admitted, that Mr. Dalton's 

 hypothesis fails entirely in its two fundamental positions, 

 that one of them is entirely without support, and that the 

 other is founded upon a presumption which scarcely amounts 

 to a probability. In this state of the case we might perhaps 

 be justified in discarding the hypothesis altogether, or at 

 leabt in requiring the author to bring forward some direct 

 Are the conse- arguments in its favour, before we should pay any farther 



^uences fairly attention to it. I shall, however, pursue a different course, 



Reducible . 



from the pre- and shall examine how far the consequences would fairly 



Htises. follow from the premises, supposing that these were demon- 



strated. Nor is this investigation to be considered as a mat* 

 ter of mere speculative curiosity, because, although the hy*> 



•Although in forming his general conclusions Mr. Dalton assumes, that 

 only one combination of oxigen and hidrogen can exist, and from thfs 

 circumstance argues that water is a binary compound, and hence deduces 

 the weight ©f its atoms, o calculation^ upon which all the details of the hy- 

 pothesis depend, yet ui the 2d part of his system he endeavours to show, 

 that the fluoric, muriatic, oxitnuriatic, and hypctoxmuriaticacids are all 

 compounds of oxigen and hydrogen, and even forms estimates of the 

 number of atoms of each element which enters into their composition. 

 So dangerous is it foe the most acute mind to indulge in merely specula- 



pothesift 



