Oh the Theory of Mixed Gases. 4 1 5 



' their circumstances, and in the sequel ar- 

 * range themselves just as in a void space.* 

 ** The truth of the inference thus understood is 

 " so obvious from the fundamental principles 

 ** of the theory, that I do not know what can 

 " be said to illustrate it to any one, who un- 

 " derstands the object of my 4th proposition. 



** To return now to your experiment. Vapour 

 " certainly does enlarge the pores of air, and 

 *' that because . it cannot instantli) escape 

 " through them, but must push against the 

 ** particles of air themselves ; but why the ne- 

 " cessity of having the force of 30 inches to 

 " effect this enlargement of the pores ? If 

 " two particles of a gas have a given distance 

 ** of 99, it does not require a force equal to 

 ** their mutual repulsion, to remove them to 

 ** the distance 100, but only t-4^^ of that force ; 

 " why then may not the moderate force of 

 ** vapour enlarge the pores of air in experi- 

 •* ments made at low temperatures ; though it 

 ** is unable to drive the air wholly our ?" 



The first sentence of the precedmg quotation 

 confirms the accuracy of the experiment with 

 the moist bottle, as far as is necessary : for the 

 design of it was to demonstrate, that the 

 presence of water increases the expansion of 

 air of a given temperature ; and the circum- 

 stance has been admitted by the advocate for 



