290 MEMOIR OF DR. DALTON, AND 



No theory can entirely get rid of Dynamics, but it would 

 only introduce confusion into the historical account, if we 

 said more of it than the promoters themselves. 



The old theories were after all exceedingly indefinite, not- 

 withstanding the appearance of exactness. The Daltonian 

 theory is remarkable chiefly for its idea of quantity. It 

 defines composition and combination by quantity. It is 

 mechanical, because it unites pieces of matter in a mason- 

 like style ; it fits every part and breaks none, but it is not 

 merely mechanical. Force is required, and this is of a dif- 

 ferent kind with every species. It is polyhylic. It unites 

 therefore more qualities than previous theories. There has 

 never been any progress made in ascertaining in what essen- 

 tially consists the peculiarity of the forces in each element. 

 That remains for future inquiry. The inquiry has chiefly 

 had relation to weight, and for that reason I have called 

 Dalton's the quantitative atomic theory. Mr. Joule's dis- 

 coveries in heat, although not purely chemical, have begun to 

 introduce into chemistry, through physics, forces that can be 

 exactly calculated other than weight. 



I think it of importance that Dalton's theory as adopted ^ 

 by chemists should have a distinct adjective to express it. 

 The term quantitative atomic connects itself with analysis 

 which in every case leads us to the use of the theory, although 

 the most convenient term for general use, by which also we 

 do honor to the originator, is the Daltonian theory. It re- 

 presents the mode of discovery by weighing and calculating, 

 and the greatest fact treated of with regard to atoms, as viewed 

 by chemists, that they are comparative quantities measurable 

 by the balance : it represents also the state of chemistry since 

 the theory was propounded, a wonderfully elaborate collection 

 of orderly arrangements of bodies distinguished principally 

 by their quantities. I have left out as unnecessary to this 

 history such of the characters of atoms as Dalton held more 

 as hypothetical than theoretical. 



