Manchester HTcvioirs, Vo/. h. (191 1), No, 4>. 9 



chemical as it had been of the physical atomic theory. 

 ^' When an element A has an affinity for another B, I see 

 no mechanical reason why it should not take as many 

 atoms of B as are presented to it, and can possibly come 

 into contact with it, . . . except in so far as the repulsion 

 of the atoms of B among themselves are \sic\ more than a 

 match for the attraction of an atom of A. Now this 

 repulsion begins with 2 atoms of B to i of A, in which 

 case the 2 atoms of B are diametrically opposed ; it 

 increases with 3 atoms of B to i of A, in which case the 

 atoms of B are only 120° asunder .... and so on in 

 proportion to the number of atoms. It is evident then 

 from these positions, that, as far as powers of attraction 

 and repulsion are concerned (and we know of no other in 

 chemistry) . . . binary compounds must first be formed 

 in the ordinary course of things, then ternary and so on, 

 till the repulsion of the atoms of B . . . refuse to admit 

 any more."" 



Consequently, Newton's postulate of similar particles 

 which are mutually repulsive, is the basis of both the 

 physical and the chemical atomic theories of Dalton. 



II. The genesis of the ciie^mical theory. 

 The inductive and deductive accounts of the genesis. 



This discussion of principles, however, does not 

 exhaust the subject. Much remains obscure regarding 

 the train of thought which Dalton followed in passing 

 from the physical to the chemical theory. The crucial 

 question is, how he arrived at, what suggested, the doctrine 

 of combination of atoms in multiple proportion? 



Two main accounts of the origin of the theory have 



'^ Nicholson'' s Join ., vol. 29, p. 147, iSii ; see also '' New System of 

 Chemical Philosophy," vol. i, p. 216, iSoS. 



