308 0;z the Theory of Mixed Gases. 



mon centre of gravity, whether it be at rest or 

 in motion : so that A and B are under the ne- 

 cessity of observing the law^ of their specific 

 gravities, just as if the kindred particles of each 

 fluid w^ere actuated by no reciprocal repulsion 

 nor any other cause of reaction. The doctrine 

 of gases, which are mutually inelastic, is ren- 

 dered indefensible by the preceding arguments; 

 for the hypothesis is thereby exposed to a dif- 

 ficulty which the author of the theory justly 

 remarks, makes a mixture of mutually re- 

 pulsive gases of different specific gravities an 

 improbable conjecture ; so that his own objec- 

 tion ultimately discountenances the leading 

 opinions of that theory which it induced him ta 

 adopt in particular. At the same time, phi- 

 losophers are convinced that the atmosphere is 

 a compound of gases, possessing various degrees 

 of specific weight : they moreover know that 

 different chemical agents perpetually disturb 

 the equilibrium of the compound, as some of 

 them constantly absorb while others unfold the 

 gases of which it is composed. The preceding 

 facts are certain ; consequently the heterogene- 

 neous elements of the atmosphere mu5>t be 

 united by a common tie, which may be deno- 

 ninated a species of affinity, at least while our 

 knowledge of the subject remains in its present 

 imperfect state. The transparency of the great 



