AlcuicJicster hfenioirs, J^o/. h: (igii), No. ^. 7 



province both doctrines. Debus, as the author has pointed 

 out elsewhere, has committed himself to the opinion that 

 Dalton could be at one and the same time a believer in 

 the hypothesis and not in the law.'' 



4. Finally, Dalton held this hypothesis without con- 

 sidering that it leads to the conclusion, familiar now to 

 chemists, that the " atoms " of hydrogen, oxygen and other 

 elements are divisible. 



There is no evidence, not the faintest indication, 

 that Dalton had realised the hypothesis before the end 

 of the year 1803, ^^ ^^W o"g of these four ways. It is, 

 therefore, impossible to suppose that the hypothesis — the 

 "confused idea" — had any influence on him whilst he 

 was forming his chemical atomic theory, 



T/ie main principles of Daltuiis system. 



The principles on which Dalton based his theory 

 must have continued the same from 1803 to 1808, simply 

 because his opinions regarding the " atom " of water, of 

 ammonia, etc., remained the same. The general prin- 

 ciples regarding the combination of atoms, which he set 

 out in 1808, are somewhat cumbrous, and some of them 

 superfluous. They can be reduced to two: — (i) That 

 atoms of different kinds tend to combine in the propor- 

 tion I : I rather than in any other, that the next propor- 

 tion to occur is I : 2, then i : 3, and so on ; (2) that when 

 two compounds of the same two elements are gaseous, 

 the lighter is binary and the heavier tertiary. 



It is true that this second principle is not to be found 

 among the set of rules which Dalton gives in the " New 

 System of Chemical Philosophy." He says there that 



« " Avogadro and Dalton — the standing in Chemistry of their hypotheses," 

 1904, pp. 63-66. 



