On the Theory of Mixed Gases. 309 



body of air surrounding the earth, also affords 

 a strong argument for the chemical union of 

 its component fluids s and at the same time 

 discountenances the idea of the compound 

 being a mechanical mixture of any description 

 whatever : for when a number of diaphanous 

 bodies of different specific gravities are mixed 

 together, they form an aggregate w^hich is 

 opaque ^ but the union of the substances by 

 fusion renders the mass transparent in many 

 instances. Now as the atmosphere is diapha- 

 nous, we are obliged by the principles of sound 

 argument to consider it in the light of a com- 

 pound, the ingredients of which are united by 

 a chemical tie. — Whatever may be the condi- 

 tion of the elastic fluids which enter into the 

 composition of common air, one thing is cer- 

 tain from a preceding paragraph of this essay ; 

 namely, no one of them can maintain a sepa- 

 rate equilibrium as long as it makes an indi- 

 vidual of the aggregate; consequently each 

 particle of the compound must be urged by a 

 force resulting from the general action of the 

 mass, not by a pressure occasioned by a par- 

 ticular member of it. \ 



On this account it is impossible for the 



aqueous part of common air to preserve the 



character of a gas at low temperatures /because 



steam cannot support 30 inches of mercury 



Q q 2 



