THEORY OF DEFINITE PROPORTIONS. 167 



corresponded to the rest of his habits. In 1804, he 

 was already in possession of his atomic theory, and 

 explained it to Dr. Thomson, who visited him at 

 that time. It was made known to the chemical 

 world in Dr. Thomson's Chemistry, in 1807 ; and in 

 Dalton's own System of Chemistry (1808) the lead- 

 ing ideas of it were very briefly stated. Dr. 

 Wollaston's memoir, "on superacid and subacid 

 salts," which appeared in the Philosophical Trans- 

 actions for 1808, did much to secure this theory 

 a place in the estimation of chemists. Here the 

 author states, that he had observed, in various salts, 

 the quantities of acid combined with the base in the 

 neutral and in the superacid salts to be as one to 

 two : and he says that, thinking it likely this law 

 might obtain generally in such compounds, it was 

 his design to have pursued the subject, with the 

 hope of discovering the cause to which so regular 

 a relation may be ascribed. But he adds, that this 

 appears to be superfluous after the publication of 

 Dalton's theory by Dr. Thomson, since all such facts 

 are but special cases of the general law. We can- 

 not but remark here, that the scrupulous timidity of 

 Wollaston was probably the only impediment to his 

 anticipating Dalton in the publication of the rule of 

 multiple proportions ; and the forwardness to gene- 

 ralize, which belongs to the character of the latter, 

 justly secured him, in this instance, the name of the 

 discoverer of this law. The rest of the English 

 chemists soon followed Wollaston and Thomson, 



