288 HISTOEY OF CHEMISTRY. 



Sect. 2. Reception and Confirmation of the Atomic Theory. 



IN order to give a sketch of the progress of the Atomic Theory into 

 general reception, we cannot do better than borrow our information 

 mainly from Dr. Thomson, who was one of the earliest converts and 

 most effective promulgators of the doctrine. Mr. Dalton, at the time 

 when he conceived his theory, was a teacher of mathematics at Man- 

 chester, in circumstances which might have been considered narrow, 

 if he himself had been less simple in his manner of life, and less 

 moderate in his worldly views. His experiments were generally made 

 with apparatus of which the simplicity and cheapness 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. Thom- 

 son's Chemistry, in 1807 ; and in Dalton's own 'System of Chemist r// 

 (1808) the leading ideas of it were very briefly stated. Dr. Wol las- 

 ton's memoir, " on superacid and subacid salts," which appeared in the 

 Philosophical Transactions 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 this 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 cannot but remark here, that 

 the scrupulous timidity of Wollaston was probably the only impedi- 

 ment to his anticipating Dalton in the publication of the rule of mul- 

 tiple proportions ; and the forwardness to generalize, 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 



O 



soon followed Wollaston and Thomson, though Davy for some time 

 resisted. They objected, indeed, to Dalton's assumption of atoms, and, 

 to avoid this hypothetical step, Wollaston used the phrase chemical 

 equivalents, and Davy the word proportions, for the numbers which 

 expressed Dalton's atomic weights. We may, however, venture to say 

 that the term " atom" is the most convenient, and it need net be under- 

 stood as claiming our assent to the hypothesis of indivisible molecules. 



