OASES IN THt ATMOSPHERH. 435 



Turface, for any given time, a mean of them would probably 



be 57° or 58®. Now if we may fuppofe the force of vapour It Is on an ave» 



equivalent to that of 55°, at a medium, it will, from ^'e ^^g^^J°;;[^°"« 



table, be = to .443 of mercury ; or, nearly y^j of the whole 



atmofphere. This it will be perceived is calculated to be the 



weight of vapour in the whole atmofphere of the earth. If 



that incumbent over any place at any time be required, it may 



be found as ciireded above. 



3. Of the Weight of the Carbonic Acid Atmofphere. 



From ibme obfervaiions of Humboldt, I was led to exped Dedudtlonofthe 

 about -j-^^ part of the weight of the atmofphere to be car- ^^^^?^^^^ °^j "'J]^^ 

 bonic acid gas : but I foon found that the proportion was im- atmofphere 

 menfely over-rated. From repeated experiments, all nearly j'^""^""^ ^"*"" 

 agreeing in their refults, and made at different feafons of the 

 year, I have found, that if a glafs veffel filled with 102,400 

 grains of rain water be emptied in the open air, and 125 

 grains of ftrong lime water be poured in, and the mouth then 

 ciofed ; by fufficient time and agitation, the whole of the lime 

 water is juft faturated by the acid gas it finds in that volume 

 of air. But 125 grains of the lime water ufed require 70 

 grain meafares of carbonic acid gas to faturate it: therefore, 

 the 102,400 grain meafures of common air contain 70 of car- 

 bonic acid ; or r^-g^ of the whole. The weight of the car- 

 bonic acid atmofphere then is to that of the whole compound a» 

 1:1460; but the weight of carbonic acid gas in a given por- 

 tion of air at the earth's furface, is nearly -j-^'-g-^ of the whole; 

 becaufe the fpecJCc gravity of the gas is \\ that of commoa 

 air. I have fince found that th,e air in an afTembly, in which 

 two hundred people had breathed for two hours, with th^ 

 windows and doors ftiut, contained little more than I percent, 

 of carbonic acid gas. 



Having now determined the force with which each atmo- 

 fphere preffes on the earth's furface, or in other words, its 

 weight; it remains next to enquire into their fpecific gra- 

 7! ties. 



Thefe 



