GASES IN THE ATMOSPHERE. 431 



3. To inveftigate th'e proportions of the gafes to each other, —as well ss at 

 fuch as they ought to be found at different elevations above the tj^ns,^" '*' 

 earth's furface. 



To Ihofe who confider the atmofphere as a chemical com- 

 pound, thefe threii objecls are but ont?j others, who adopt my 

 hypothecs, will (ee they are elTentially diftinct. With refpefil 

 to the firft: It is obvious, that, on my hypothefis, the denfity Now each fingle 

 and elaftic force of each gas at the earth's furface, are the pr^gj b"its 

 eifefls of the weight of the atmofphere of that gas folely, the whole weight; 

 different atmofpheres not gravitating one upon another. ^^7^ '*."*'*" 

 Whence the fiii| object will be obtained by afcertaining what fpring and chat 

 fliare of elaftic force is due to each gas in a given volume of**J' iw volume. 

 the compound atmofphere; or, which amounts to the fame 

 thing, by finding how much the given volume is diminifhed 

 under a conft.nnt preffure, by the abftraflion of each of its in- 

 gredients fingly. Thus, if it fhould appear that by extraf^ing Take away one 

 the oxygenous gas from any mafs of atmofpheric air, the "^ 'he gafes and 

 vv' hole was diminiftied f in bulk, ftill being fubject to a preffure vo^,jj,g repre- 

 of 30 inches of mercury; then it ought to be inferred that the fentd its preffUre 

 oxygenous atmofphere prefles the earth with a force of ^x of that^atm'of.' 

 inches of mercury, 8ic. i(her«. 



In order to afcertain the fecond point, it will be farther The weights of 



necelTary to obtain the fpecific gravity of each gas; that is, "^'> fe^" '" 

 '., . . , ,. . , , , n S''*'£" volume 



the relative weights oi a given volume ()t each m a pure liate, haj /f^^ jv,^ 



fubjed to the fame preifure and temperature. For the weight gravity, 



of each gas in any given portion of atmofpheric air, muft be 



in the compound ratio of its force and fpecitic gravity. 



With refpedi to the third objefl, '\X may be obferved, that The proportlona 

 thofe gafes which are fpeciftcally the heavieft muft decreafe f*"^ .'^'^^'"^"^ 

 in denfity the quickefi in afcepding. If the earth's atmofphere tained from the 

 had been a homogeneous elaftic fluid of the fame weigfit it is, progreffion with 

 but ten times the fpecific gravity, it might ealily be de- fa^jg ^^^3^"^'^. ^ 

 monftrated that no fenfible portion of it could have arifen to in computation 

 the fummits of the higheft mountains. On the other hand, an ^^^^^^^f^ 

 atmofphere of hydrogenous gas of the fame weight, would 

 fupport a column of mercury nearly 29 inches on the fummit 

 of Mount Blanc. 



The feveral gafes conftantly found in every portion of at- 



ntiofpheric air, and in (uch quantities as are capable of being 



;^ppreciated, are azotic, oxygenous, aqueous vapour, and 



parbonic aqifd. It is probable that hydrogenous gas alfo is con» 



^ l^antl/ 



