204 Literary and Philosophical Society, 



his pocket, and was not content to have made only one. 

 A man like this would have brought fame to a city and to 

 a nation even if he had ceased to write after giving us the 

 one work. 



It was when examining the air that Dalton was led to 

 consider the condition of watery vapour amongst inconden- 

 sible gases, proving that vapour rises from liquids with the 

 same force ' at equal distances above or below the several 

 temperatures at which they boil in the open air : and that 

 force is the same under any pressure of any other elastic 

 fluid as it is in vacuo' The force of aqueous vapour he 

 showed to be the same at the same temperature whether 

 air was present or not. This was the establishment of the 

 separate action of fluid bodies so far, and he then passed 

 on to the separate action of all gases in a mixed state, thus 

 accounting for the fact that they do not separate according 

 to their specific gravities as they ought to do, the heavy 

 gases falling down to the earth if they did not act indepen- 

 dently. For this purpose he supposes the particles of each 

 gas to repel the particles of its own kind, but not those of 

 another gas. For example, ' the particles of A meeting with 

 no repulsion from those of B farther than that repulsion 

 which as obstacles in the way they may exert, would in- 

 stantaneously recede from each other as far as possible in 

 their circumstances, and consequently arrange themselves 

 just the same as in a void space.' 



The same would take place with the particles of B. 

 ' Thus the two gases become rarefied to such a degree that 

 their united forces only amount to the pressure of the 

 atmosphere.' 



We find here that he causes repulsion to do the work 

 which primordial motion does in the hypothesis of David 



