Mr. Lubbock on the Heat of Vapours, fyc. 



467 



n = l- 78. The experiments of Bessel give for these two cases, 

 1-95 and 1*63. 



I do not consider the above solution of value for the nume- 

 rical results to which it leads, so much as because it serves to 

 establish the principles to be adopted in the treatment of 

 another problem (perhaps the most important that could be 

 proposed in the present state of physical science), the solu- 

 tion of which has hitherto been unattempted, viz. if a minute 

 spherical atom were subject to the mechanical action of the vi- 

 brations of a very elastic medium, like those which take place 

 in air, would it, in addition to a vibratory motion, receive 

 also a permanent motion of translation ? I propose at a fu- 

 ture opportunity to state my reasons for considering this an 

 important question, and to advance some ideas respecting the 

 method in which I conceive it may be answered. 

 Cambridge Observatory, Nov. 16, 1840. 



LXIX. On the Heat of Vapours and on Astronomical Re- 

 fractions. By John William Lubbock, Esq., Treas. 

 U.S., F.R.A.S. and F.L.S., Vice- Chancellor of 'the University 

 of London, fyc. 



[Continued from p. 280.] 



On the Conditions of the Atmosphere, and on the Calculation 

 of Heights by the Barometer. (Resumed.) 



A S the expression which has served to calculate the tem- 

 '*•-*• peratures evidently represents the state of the atmo- 

 sphere far within the limits of the applicability of this or any 

 other formula founded upon a state of repose to an atmo- 

 sphere continually agitated by currents, it must of course 

 serve to eliminate the density and to obtain an expression for 

 the height in terms of the pressures and temperatures at the 

 extremities of any atmospheric column. 



If z be the altitude of the place above any fixed point, 

 a the distance of the fixed point from the centre of the earth, 

 g the force of gravity, 



dp 



9 



ga 



{a+zy 



d z, 



and putting the expression for %', at vol. xvi. p 



k{\ + afl)(/-ff)dj9 ' _ g a" d z' 



pi (pit -E) " («+*7 



2 H2 



. 4-40, 



