4 Meldkum, Development of t lie Atomic Theory. 



considering how his own ideas had arisen was uncongenial 

 to him, and he never devoted his mind to it. 



As the result of his studies, Debus conckided that 

 Dalton was greatly influenced, during the development of 

 his atomic theory, by the supposition that the particles of 

 different gases under similar conditions are of the same 

 size. This doctrine, which is usually known as Avog- 

 adro's hypothesis, Debus calls the " Dalton -Avogadro" 

 hypothesis. 



Debus first advanced this belief of his in a pamphlet 

 entitled, " Ueber einige Fundamentalsatze der Chemie, 

 insbesondere das Dalton-Avogadrosche Gesetz " (1894, 

 Cassel). His opinion having been controverted by 

 Roscoe and Harden, in their " New View of the Origin 

 of Dalton's Atomic Theory," he replied, and a controversy 

 ensued, in which G. W. A. Kahlbaum also took part. 

 The series of papers is as follows : — Debus, Zeitsch. 

 physikal. Cliem., vol. 20, p. 359, 1896 (or PJiil. Mag., 

 vol. 42, p. 350, 1896); Roscoe and Harden, Zeitsch. 

 physikal. Chem., vol. 22, p. 241, 1897 (or Phil. Mag., 

 vol. 43, p. 153, 1897); Debus, Zeitsch. physikal. Chem..,. 

 vol. 24, p. 325, 1897; vol. 29, p. 266, 1899; Kahlbaum, 

 Zeitsch. physikal. Chem., vol. 29, p. 700, 1899; Debus, 

 Zeitsch. physikal Chem., vol. 30, p. 556, 1899. 



Debus can justify his belief in two ways : — (i) Dalton 

 certainly stated in 1808 that he once had a sort of belief 

 in the hypothesis in question. " At the time I formed 

 the theory of mixed gases, I had a confused idea, as 

 many have, I suppose at this time, that the particles of 

 elastic fluids are all of the same size ; that a given volume 

 of oxygenous gas contains just as many particles as the 

 same volume of hydrogenous ; or if not, that we have no. 

 data from which the question could be solved. But .... 



