lo Mrldrum, Development of the Atomic Theory. 



did. While not denying the influence of Richter, he sums 

 up the evidence on the subject as " unequivocally demon- 

 strating the genesis of the atomic theory as a general 

 ph)'sical conception from the study of matter in the 

 aeriform condition, and its first practical application in 

 chemistry to gaseous bodies, and emphatically to such as 

 combine iyi multiple proportions."'^ There is no question 

 here of extraordinary insight and discernment on Henry's 

 part. He has simply considered the use Dalton had 

 made of the physical atomic theory previous to forming 

 a chemical one. 



Roscoe and Harden have not paid sufficient attention 

 to this. They say " It is . . . . well known that 

 Dalton was an ardent adherent of the Newtonian doctrine 

 of the atomic constitution of matter .... It now 

 appears that it was from this physical standpoint that 

 Dalton approached the atomic theory, and that he arrived 

 at the idea that the atoms of different substances have 

 different weights from purely physical considerations."-" 

 There is really not sufficient justification for Roscoe and 

 Harden's suggestion that they had found in Dalton's 

 narrative a new view of the genesis of his atomic theory. 

 The view is to be found in Henry, and might be formed 

 by any person who should read with understanding 

 Dalton's " Essay on the Constitution of Mixed Gases," 

 which was written in i8oi, and published in 1802. 



There is, however, a fundamental objection to Dalton's 

 narrative. It has a deceptive appearance of being historical. 

 Dalton was a pioneer of science, and a pioneer is a man 

 who must make many mistakes and experience many 

 failures. He has taken a number of different scientific 

 movements and marshalled them, so that they are invested 



-•' W. C. Henry, (9/.. at., p. 84. 



■-'-' 1-loscoc and Ihirflen, ()/. cit., p. viii. 



