Oji the Theorx) of Mixed Gases. 419 



vapour through a bed of air always appeared 

 to me repugnant to the mechanical philosophy; 

 and my objections to the hypothesis shall be 

 stated in their proper place. In the mean 

 time, the context of the quotation, more espe- 

 cially the happy and familiar elucidation of 

 water descending through pebbles, shews Mr. 

 Dalton to have once imagined, that the par- 

 ticles of air oppose an insuperable resistance to 

 the impulse of vapour of low temperatures. 

 Hut the conviction of experiment has van- 

 quished this favourite opinion ; and the author 

 of it seems desirous of concealing an important 

 change of sentiment, by charging his readers 

 with a want of penetration. My friend ac- 

 knowledges, that vapour of less than 212' does 

 enlarge the pores of air ; this is his present 

 notion ; and by way of defence he asks, why 

 a force, inferior to the weight of the atmo- 

 sphere, cannot increase the distance of two 

 gaseous particles in a small degree ? My 

 reasons for rejecting the substance of this ques^ 

 tion will appear in the next pai*agraph j and 

 {perhaps they may be considered to furnisii a 

 refutation of M. De Luc's hypothesis, with all 

 the corrections that can be given to it. 



A maxim in Pneumatics has been already 

 qiioted from Mr. Dalton *s letter-; which would 

 irtiall' probability have been delivered nearly 

 3g 



