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



his " System of Chemistry." Dalton's reply to the 

 criticism in the second edition had a notable consequence. 

 Thomson visited Manchester in order to get an explana- 

 tion of the theory from the author himself, and it was 

 on this occasion that Dalton told him about the chemical 

 atomic theory. 



II. The beginning and course of Dalton's 



EXPERIMENTAL WORK. 

 The Beginning. 



Dalton did not begin original experimental work 

 till 1799, when he was thirty-three years of age, and had 

 been six years in Manchester. Up to then he had 

 confined himself to work of observation, chiefly in meteor- 

 ology. The first paper in which his own experiments 

 occupy a considerable space is his memoir on the 

 power of fluids to conduct heat. It was read before 

 this Society on the 12th April, 1799. 



A previous paper of his, read six weeks earlier, is 

 of quite another stamp. The title of this is as follows : — 

 " A paper, containing Experiments and Observations to 

 determine whether the quantity of Rain and Dew is equal 

 to the quantity of water carried off by the rivers and 

 raised by Evaporation ; with an inquiry into the origin of 

 springs." Now, not only are the experiments recorded in 

 this paper hardly worthy of the name, but the subject itself 

 is of the nature of a forlorn hope. Dalton could not have 

 embarked on such a hopeless inquiry as this, if he had 

 been accustomed to experimental research, and had experi- 

 enced the advantages to be gained simply by limiting the 

 scope of an investigation. This paper, therefore, marks 

 the end of the first stage in his scientific career. By 

 April of the year 1799 he was in the full swing of 

 experimental work. 



