CONSTITUTION OF MIXED GASES. Q$ 



fure, or taken from if, without its difturbing the denfities 

 and fituations of the remaining atmofpheres*. 



The free paflage of gafes through each other was once the Change in Mr. 

 fundamental maxim of my opponent; at which time he main- ' so P mions ' 

 tained, that the variations in the weight of the atmofpheric 

 compound arife from the changeable nature of the aqueous 

 atmofphere, not from the permanent gafes f. This dogma is 

 eflenlial to the fyftem ; it has, however, been abandoned by 

 its author himfelf; for Mr. D. when attempting to explain 

 the obfervation of Mr. Kirwan, is obliged to admit the per- 

 manent gafes to be more abundant in dry than in moift air; 

 that is, the denfities and pofitions of thefe gafes depend upon 

 the ftate of the contained vapour, contrary to the hypothefis. 

 This departure from the primitive maxim is avowed openly 

 in Mr. D/s explanation of the experiment with the moift 

 bottle. Here he is compelled to confefs, that fleam, at low 

 temperatures, diftends the pores of air; and endeavours to 

 preferve the exiftence of his aqueous atmofphere by fomething, 

 which looks like a demonftration from the final Q. E. D. ; 

 but it ought to be remembered, that the particles of a fluid 

 prefs equally in all directions ; confequently, that the cor- 

 pufcles of air would aft with their full force on the contiguous 

 corpufcles of his fuppofed vapour. 



Perhaps Mr. D. will perceive, by this time, that logical 

 precifion has placed him in the circumftances of certain phi- 

 lofophers mentioned in his third efiay, who are unable to de- 

 fend their opinions. In fa6t, Mr. D.'s hypothefis is repug- 

 nant to natural appearances in its primitive form ; for, ac- 

 cording to it, a fhower of rain is a prodigy ; feeing the drops 

 mutt difplace equal bulks of air, and this removal muft be 

 brought about by the inadequate weight of a column of va* 

 pour which has loft part of its fpring, 



JOHN GOUGH. 

 Middkjhaiv, December 13, 1804. 



P. S. Since the publication of my paper on vegetation, I 

 have found, by Dr. Thorn fon's Chemiftry, that M. Ingen- 

 houz had formerly made the fame difcovery. In 1795, I read 



* Manchester Memoirs, Vol. V. p. 546. 

 f Manchefter Men .is, Vol. V. p. 547. 



his 



