#00 On the existence of a Limit to Vaporization. [1826. 



portionally diminished : when the diminution is such that the 

 elasticity is a force not more powerful than the attraction of 

 gravity, then a limit to the atmosphere must occur. The par- 

 ticles of the atmosphere there tend to separate with a certain 

 force; but this force is not greater than the attraction of gravity, 

 which tends to make them approach the earth and each other ; 

 and as expansion would necessarily give rise to diminished ten- 

 sion, the force of gravity would then be the strongest, and conse- 

 quently would cause contraction, until the powers were balanced 

 as before. 



Assuming this state of things as proved, the air at the limit 

 of the atmosphere has a certain degree of elasticity or tension ; 

 and although it cannot there exist of smaller tension, yet if 

 portions of it were removed to a farther distance from the earth, 

 or if the force of gravity over it could in any other way be 

 diminished, then it would expand, and exist of a lower tension ; 

 upon the renewal of the gravitating force, either by approxima- 

 tion to the earth's surface or otherwise, the particles would ap- 

 proach each other, until the elasticity of the whole was again 

 equal to the force of gravity. 



Inasmuch as gases and vapours undergo no change by mere 

 expansion or attenuation, which can at all disturb the analogy 

 existing between them in their permanent state under ordinary 

 circumstances, all the phenomena which have been assumed as 

 occurring with the air at the limit of our atmosphere may, with 

 equal propriety, be admitted with respect to vapour in general 

 in similar circumstances ; for we have no reason for supposing 

 that the particles of one vapour more than another sxtfree from 

 the influence of gravity, although the force may, and without 

 doubt does, vary with the weight and elasticity of the particles 

 of each particular substance. 



It will be evident also, that similar effects would be produced 

 by the force of gravity upon air or vapour of the extreme tenuity 

 and feeble tension referred to, whatever be the means taken to 

 bring it into that state ; and it is not necessary to imagine the 

 portion of air operated upon, as taken from the extremity of 

 our atmosphere, for a portion of that at the earth's surface, if 

 it could be expanded to the same degree by an air-pump, would 

 undergo the same changes : when of a certain rarity it would 

 just balance the attraction of gravitation and fill the receiver 



