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XXXVI. The Genesis of Dalton s Atomic Theory. 

 By Henry Debus, Ph.D., F.R.S.* 



SIR H. E. ROSCOE and Mr. A. Harden Lave lately 

 published a book f entitled ' A New View of the Origin 

 of Dalton's Atomic Theory/ with the following introductory 

 remarks : — 



" It may seem remarkable that, after the lapse of nearly a 

 century, since John Dalton first applied the atomic theory of 

 matter to chemical phenomena, it should be possible to find 

 anything new respecting the genesis of his ideas. The ex- 

 planation is to be found in the unlooked for discovery, in the 

 rooms of the Literary and Philosophical Society of Manchester, 

 where the whole of Dalton's experimental work was carried 

 out, of his Laboratory and Lecture Note-Books contained in 

 a number of manuscript volumes. A careful study of these 

 has led us to conclusions concerning the origin of the atomic 

 theory of Chemistry which differ widely from those which 

 have been generally accepted. It has hitherto been supposed 

 that it was the experimental discovery of the law of combina- 

 tion in multiple proportions which led Dalton, seeking for an 

 explanation of this most remarkable fact, to the idea that 

 chemical combination consists in the approximation of atoms of 

 definite and characteristic weight, the atomic theory being thus 

 adopted to explain the facts discovered by chemical analysis. 

 . . . The actual relations are, therefore, precisely the inverse 

 of those which are usually accepted. It was the theory of the 

 existence of atoms of different weights which led Dalton to 

 the discovery of the facts of combination in multiple pro- 

 portions." 



This view of Roscoe and Harden is not new ! Two years 

 ago 1 published a pamphlet |, wherein it is clearly stated that 

 the atomic theory led Dalton to the discovery of the law of 

 multiple proportions. It is gratifying to me that Dalton's 

 Note-books confirm the view expressed by me in May 1894, 

 In the same essay (p. 58), I have shown that several years 

 before Avogadro Dalton had formed the hypothesis that equal 

 volumes of different gases contain under normal conditions of 

 temperature and pressure an equal number of molecules. 



* Communicated by the Author. 



t ' A New View of the Origin of Dalton's Atomic Theory, a Contri- 

 bution to Chemical History,' by Henry E. Roscoe and Arthur Harden. 

 London : Macmillan & Co. 1896. 



\ * Ueber einige Fundamentalsatze der Chemie, insbesondere das 

 Dalton-Avogadro'sche Gesetz. Eine historische Untersuchung von 

 Dr. Heinrich Debus.' Cassel : Guatav Klaunig, 1894, pp. 44-45. 



