14 MELDRU^r, Development of the Atomic Theory. 



for a time as being too complicated. The union of two 

 atoms of one kind with three of another must have 

 appeared at that stage of thought to be very complex. 

 Dalton did not adopt such a formula till October. On the 

 1 2th of that month, as a summary of his views, he gives 

 tables of binary compounds, of ternary, of compounds of 

 4 atoms, and compounds of 5. Alcohol and nitrous acids 

 were the only compounds of 5 atoms. Alcohol is ether 

 and water united, or 2 oxygen, 2 carbon, and i hydrogen. 

 Nitrous acid is 3 oxygen and 2 nitrogen. 



The objection of Roscoe and Harden, however, must 

 'be final, but for one circumstance : the objection ignores 

 the physical theory. The experiments with nitric oxide 

 ■and air must have received lengthy consideration had it not 

 been for the fact that Dalton had an atomic theory already 

 in his mind. As it was, these experiments simply served 

 to give the impulse needed to set his mind working. 

 Under that stimulus he ma.de a beginning with the 

 adaptation of the physical theory to chemical purposes. 



Nothing more was needed. Larmor, in his Wilde 

 Lecture on the " Physical Aspect of the Atomic Theory," 

 represents that the doctrine of combination of atoms in 

 the proportion i : i must forthwith lead to other cases 

 such as I : 2. 



" Once it is postulated that only one kind of aggrega- 

 tion into molecules occurs, e.g.., that in water there is only 

 one way in which the hydrogen attaches itself to the 

 ■oxygen, the laws of definite and multiple proportions are 

 self-evident."'" 



Earlier in this paper, the author has pointed out how 

 the doctrine of i : 1 arose logically from the physical 

 theory. There are here, therefore, all the elements of a 

 fair account of the origin of Dalton's chemical theory. 



^^ Manchester Memoirs, vol. 52, no. 10, p. 9. 1908. 



