THE 



PHILOSOPHICAL MAGAZINE 

 AND JOURNAL. 



31«' JULY 1825. 



I. On the Laws of the Cotidensafion and Dilatation of Air and 

 the Gases, aiid the Velocity of Sound. Bij J. Ivory, Esq. 

 M.A. F.R.S. 



¥N a letter inserted in this Journal for June 1824' I have al- 

 -*- ready hinted at tlie connexion between the pressure, den- 

 sity, and temperature of air at different elevations in the at- 

 mosphere, and of air which is dilated while it retains all its 

 heat. The two cases have at least this in common, that in one 

 and the other the elasticity and temperature depend entirely 

 upon the density. In an atmosphere in equilibrio, which pre- 

 serves its constitution, there is but one temperature and one 

 pressure for every proposed density ; and when air is dilated 

 without acquiring heat from other bodies, and without dissi- 

 pating any of its own, there is but one temperature and one 

 pressure answering to every increase of volume. A parcel of 

 air finds its place in the atmosphere by enlarging or contract- 

 ing its bulk till its temperature and elasticity are in equilibrio 

 with the surrounding mass. In both the cases compared a 

 change of volume or density is the sole cause of a variation of 

 pressure and temperature. There is thus a great analogy : 

 but we must not hastily conclude, as Mr. Dalton has done, 

 that there is an exact identity. A little reflection will show 

 that there are circumstances in the one case which do not exist 

 in the other. What is the arrangement of air in the atmo- 

 sphere that would be produced by the main cause we have 

 mentioned, and how far that arrangement would be affected by 

 the particular circumstances that modify the operation of that 

 cause, is an interesting subject of research. In the present 

 state of the inquiry into tiie constitution of the atmosphere, the 

 whole power of dynamical science seems to be exhausted ; and 

 we cannot reasonably hope that much further progress will be 

 made, without extending our knowledge of the jiiiysical pro- 

 Vol. U6. No. ;J27. July 1825. A 2 perties 



