ON THE OQCTaiNE OF M1XEI\ GASES. 39 



IV. 



Obfcnations on Mr. Cough's StriSiures on the Doctrine of 

 Mixed Gqfes, 5)C\ Jn a Letter from Mr. J. Dalton. 



To Mr. NICHOLSON. 



SIR, 



Jr ROM the formidable manner in whicli Mr. Gough opens Introduaion. 

 the campaign, I might exped him to bring a hoft oi fa6iii 

 and flr^M.///dn^A' to his affiftance ; ihe faSts^ however, he pru- 

 dently keeps in referve, and it is to be feared feveral of the 

 arguments too, as thofe already drawn out are fcarceiy of 

 forc'e futficient to provoke refiftance. 



Mr. Gough's firll argument is, that the fubje6t in difpute 

 is more properly denominated hypotliefis th^n tlieory. Thia 

 is certainly not worth contending about. 



Mr. Gough's next argument is, that the hjpothefis is not 

 mechanical ; but as this cannot be made good, it feems, 

 without a geometrical difquifition of length much exceeding 

 an ordinary letter, the philofophical world are to w^ait till 

 the fame fliall appear in due courfe. I might therefore, for 

 the prefent, wave any remarks on this head, as a long and 

 equally abllrufe defence might be expefted. But as I think Whether the 

 geometry has nothing to do in the bufinefs, and that all that ^Jj^/cha^^^i^al!** ' 

 can be faid effedually, either for or againft the hypothefis, 

 being confiftent with mechanical principles, may be com- 

 prized in one fliort paragraph, I (hall difcufs the argument 

 here. 



Oxigen repels oxigen, but not azote : This is a poflula- Poftulate. The 



turn: and bein*^ admitted, it follows, that if a meafure ofP^^^^^^S^^ 



' ^ ' ... repel each other, 



oxigen be put to one of azote, the oxigen finding it porous, but not thofe of 

 mult enter the pores, and -vice verfa, till the two gafes feve- other gafes. 

 rally making their way into the interftices of th^ other, at 

 laft obtain a perfed equilibrium, and then prefs with equal 

 force on all the furrounding bodies, and no longer prefs on 

 each other. This is fo plain and obvious an inference, and 

 fo little involves any mechanical confideration, that I ihould 

 have juftly incurred blame for infulting my readers with the 

 appearance of mathematical demonftration in tbe.cafe. As 

 well might I have attempted, from the elements of Euclid, 



to 



