1826.] On the existence of a Limit to Vaporization. 199 



On the existence of a Limit to Vaporization*. 

 [Read June 15, 1826.] 



IT is well known that within the limits recognized by experi- 

 ment, the constitution of vapourf in contact with the body 

 from which it rises, is such, that its tension increases with in- 

 creased temperature, and diminishes with diminished tempe- 

 rature; and though in the latter case we can, with many sub- 

 stances, so far attenuate the vapour as soon to make its presence 

 inappreciable to our tests, yet an opinion is very prevalent, and 

 I believe general f, that still small portions are produced ; the 

 tension being correspondent to the comparatively low tempera- 

 ture of the substance. Upon this view it has been supposed 

 that every substance in vacua or surrounded by vapour or gas, 

 having no chemical action upon it, has an atmosphere of its own 

 around it ; and that our atmosphere must contain, diffused 

 through it, minute portions of the vapours of all those sub- 

 stances with which it is in contact, even down to the earths and 

 metals. I believe that a theory of meteorites has been formed 

 upon this opinion. 



Perhaps the point has never been distinctly considered, and 

 it may therefore not be uninteresting to urge two or three 

 reasons, in part dependent upon experimental proof, why this 

 should not be the case. The object, therefore, which I shall 

 hold in view in the following pages, is to show that a limit 

 exists to the production of vapour of any tension by bodies 

 placed in vacuo, or in elastic media ; beneath which limit they 

 are perfectly fixed. 



Dr. Wollaston, by a beautiful train of argument and obser- 

 vation, has gone far to prove that our atmosphere is of finite 

 extent, its boundary being dependent upon the opposing 

 powers of elasticity and gravitation . On passing upwards, 

 from the earth's surface, the air becomes more and more atte- 

 nuated, in consequence of the gradually diminishing pressure 

 of the superincumbent part, and its tension or elasticity is pro- 



* Philosophical Transactions, 1826, p. 484. 



t By the term vapour, I mean throughout this paper that state of a body 

 in which it is permanently and indefinitely elastic. 



J See Sir H. Davy's paper on Electrical Phenomena exhibited in vacuo. 

 Phil. Trans. 1822, p. 70. 



Ibid. p. 89. 



