COXSTITUTJON OF MIXJSD GASES. IQ\ 



not azote. This afTumption is fairly allowed to be a poftulate 

 byMr. Daltonj and he then proceeds to obfervc, that this 

 being admitted, it follows, that if a meafure of oxigen be put 

 to one of azote, the oxigen finding it, viz. the azote, porous, 

 enters its pores, and vice vcrja, &c. But here a fecond and 

 an eflfential poftiilate is flily introduced into the fyllogifm, un- 

 der the form of an inference ; becaufe no ft rid logician will 

 venture to fay that a body. A, muft be porous of neceffity, 

 becaufe it repels a body B ; on the contrary he muft conclude, 

 that this miftake in his art deftroys the demonftralion, and 

 does not retrieve the dodrine from the imputation of being an 

 hypothelis. The fimile of the philofopher, cottager, and fieve, Mr. D.'s fimile 

 may be calculated to promote ridicule, but it is badly chofen ; '"^^^^^^^^ • 

 for it is impoffible to demon ftrate the propofed problem froai 

 Euclid's Elements, becaufe this work confines its fpeculations 

 to abftra6l figures and magnitudes. But a mathematician 

 might demonltrate the fame to a brother mathematician, from 

 the elements of the mechanical philofophy ; and he ought to 

 have his demonftration ready upon demand, which is not the 

 cafe of Mr. D. in the inftance of his fundamental propo- 

 rtion. 



It is a matter of forae furpHfe, that Mr. D. has drawn his The fecond pof- 



demonftration from the mutual affbaions afcribed by him to ^"^^^^ £''^^^ '" - 



J the m fiance of 



oxigen and azote; feeing I had profefledly attempted to fliew vapour and air. 

 the fallacy of his fecond and eflential poftulate, by afcribing 

 the fame affections to aqueous vapour and the permanent gafes 

 of the atmofphere. This unfortunate choice obliges my oppo- 

 nent to be content with a diflant fide-view of the arguments 

 which have been brought againft him ; whereas a fl;ri6ter ob- 

 fervance of the path* chalked out for him in my Strictures, 

 would have given him an opportunity to confront them, and 

 defend his atmofphere of fteam. The thing however has 

 turned out, for fome reafon or other, as it is here reprefented; 

 and Mr. D. arrives very briefly at the following fingular con- 

 clufion ; that though the demonftration of my propotition re- 

 fpedling air and vapour, be rigid, the previous data are not 

 correftly aflfumed. Now this is the point which I endeavoured 

 to eftablifli in the propofition alluded to above; for his fecond 

 poftulate makes one of the incorred data; in fact, they are all 



* Phil. Journ. Vol. IX. Page 53. 

 Vol. IX,— November, 1804* M bis 



i 



