8 Meldrum, Developwcut of the Atomic Theory. 



particular mechanism by which he accounted for diffusion 

 proved specially vulnerable/" 



The most eager critic of the mechanical explanation 

 was Gough. He wrote numerous letters and essays 

 against it, which were answered by Dalton, and on one 

 occasion by Henry. One of his criticisms was acute. 

 If, as Dalton supposed, the particles of oxygen in the 

 atmosphere have no action on the particles of nitrogen, 

 and vice versa, this must affect the transmission of sound. 

 Gough said the oxygen must transmit one sound wave 

 and the nitrogen another, each with its own velocity, so 

 that at a sufficient distance a sound should be heard 

 double. 



Berthollet, in his " Essai de Chimie Statique," shows 

 himself a whole-hearted believer in the chemical theory. 

 " It appears to me incontrovertible, that it is a true 

 chemical action which produces the solution of liquids in 

 gases, and evaporation."" He was unfavourably im- 

 pressed by the diagram appended to the " Mixed Gases " 

 Essay, in which Dalton exhibits particles of oxygen, 

 nitrogen, water and carbon dioxide existing in the 

 atmosphere independently of one another. ^^ " A diagram 

 in which Dalton has attempted to show how different 

 gaseous molecules may be disposed in the same space, is... 

 only a figment of the imagination."^" 



Thomas Thomson's interest was roused to a high 

 pitch by Dalton's theory. Whilst expressly withholding 

 his assent to it, he noticed it in edition after edition of 



1" As a matter of fact, Dalton did for years believe that " portions of gas 

 of different kinds behave to each other in a different manner from portions 

 of gas of the same kind . . . whereas there is no difference between the two 

 cases." Clerk Maxwell, " Theory of Heat,"' loth ed., pp. 28-29. 



1* Op. cit., § 164. 



^^ Manchester Memoirs, [i], vol. S, p. 602, 1802. 



i« Op. «Y.,§244. 



