344. Mr. Faraday on the 



These formulae will be found of considerable use to the prac- 

 tical engineer and architect. 



I am aware that the degree of flexure of the specimen will 

 in a small measure affect the result, but too small to deserve 

 attention in practice. Yours truly, 



B. Bevan. 



LIU. On the Existence of a Liinit to Vaporization. By M. Fa- 

 raday, F.R.S. Corresponding Member of the Royal Academy 

 of Sciences at Paris, tyc. fyc* 



TT is well known that within the limits recognised by expe- 

 ■*■ riment, the constitution of vapourf in contact with the body 

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

 increased temperature, and diminishes with diminished tem- 

 perature ; and, though in the latter case we can, with many 

 substances, 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 |, that still small portions are 

 produced ; the tension being correspondent to the compara- 

 tively low temperature of the substance. Upon this view, it 

 has been supposed that every substance in vacuo 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 substances 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 ex- 

 ists 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 ob- 

 servation, 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 Philosophical Transactions, for 1826. Part III. 



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

 body in which it is permanently and indefinitely elastic. 



~\. See Sir H. Davy's paper On Electrical Phenomena exhibited in vacuo. 

 Phil. Trans. 1822, p. 70. § Thil. Trans. 1822, p. 89. 



from 



