Manchester Memoirs, Vol. Iv. ( 1 9 1 1 ), No. 5- 



V. The Development of the Atomic Theory : (4) Dalton's 

 Physical Atomic Theory. 



By Andrew Norman Meldrum, D.Sc 



{Carnegie Research Fellow). 

 (Communicated by Prof. H. B. Dixon, Af.A., F.R.S.) 



Received October, igio. Read January loth, igii. 



In the opinion of the author, many of those who write 

 about Dalton let their attention be engrossed too much by 

 his chemical work. For, in order to understand even the 

 chemical work, it must be kept in mind that Dalton began 

 his scientific career as a meteorologist, that this led him 

 to become a student of physics, and that he took up the 

 study of chemistry subsequently. 



The following paper shows that Dalton's physical 

 atomic theory was the first great achievement of his 

 career. It was based on his experimental work, and 

 theory and work together, as soon as published, aroused, in 

 his own words, the " attention of philosophers throughout 

 Europe." 



The physical atomic theory, otherwise the theory of 

 " mixed gases," is specially interesting because it marks a 

 stage in the development of Dalton's ideas. Both it and 

 the experiments connected with it arose out of the 

 meteorological observations and studies of his early life. 

 It reveals him as a student of Newton, and as the up- 

 holder of a physical atomic theory years before he formed 

 the chemical one. 



The present paper is divided into three parts : — I. 

 Dalton's theory of " mixed gases "; II. The beginning and 

 course of Dalton's experimental work ; III. The two forms 

 of the physical atomic theory and the dates of their origin. 



March yi/i, igii. 



