of Air and the Gases, and the I'eloaty of Sound. 9 



ture, the density, and the elastic force of air in any proposed 

 circumstances, viz. 



/ I f a T 4- « i \ •■' 1 + a T +«' + «'' 



P = {^ l + „, ■; ^, T+lTr ' 



T = T + i + 5. 

 If we suppose that air changes its vohnne while it retains 

 the whole of its absolute heat, without receiving any addition 

 of temperature from other bodies, the elastic force and den- 

 sity will be obtained by making 9 = in the last equations : 



P = \ X+ur ) 



p = ?^- 



The last of these equations has already been published by 

 M. Poisson in an article on the velocity of sound printed in 

 the Conn, des Terns 1826. 



3. Let V denote the original volume of the air when the 

 density is unit, and V its volume when the density is g : then, 



v 



and by substituting this value in the equations (D), we get 



— rr^v— = v X ^• 



From the first of these equations we learn, that when air 

 contracts or enlarges its dimensions, the heat disengaged or 

 absorbed follows the proportion in which the linear distance 

 of the particles is lessened or augmented ; a property which 

 may furnish the means of examining experimentally the truth 

 of this theory. On the other hand, the second equation shows 

 that, when the pressure is constant, the changes of tempera- 

 ture are proportional to the variations of volume, which is a 

 point already established pretty extensively by experiment. 



What has just been said makes it very probable that ^ is 

 the true number, and that the experimental quantities are dif- 

 ferent only accidentally. For, till the fact of the case can be 

 ascertained so as to leave no room for doubt, it is much more 

 reasonable to suppose that the heat of combination follows ex- 

 actly the variation of the linear distance of the particles, than 



V.,1. G6. No. ;r27.J///j/ 182.5. B that 



