Mr. J. Ivory on the Constitution of the Atmosphere. 89 



proportional to w and equal to A x w ; and upon this suppor 

 sition he has found that the coefficient A must be equal to 

 116° in order to make the computed velocity of sound agree 

 with the observed quantity. .Now if we make w = ^, in the 

 formula 116° x w, the result is 58°, not much different from 

 61° the quantity already found. 



Conceive an atmosphere such as Dalton supposed, in which 

 a given mass of air, wliatever be its height, retains the whole 

 of its absolute heat. As every parcel of air has the source of 

 its temperature entirely within itself, neither communicating 

 heat nor receiving any, it follows that its elasticity will be the 

 same whether it be in motion or at rest. Wherefore, the at- 

 mosphere being in equilibria, if a velocity in any direction be 

 communicated to a mass of air in it, the elasticity would at 

 every instant balance the external pi'essure, and there would 

 be no force tending to alter in any respect the velocity im- 

 pressed. Motion once begun, would, in such an atmosphere, 

 be perpetual. 



What has just been said applies equally to an atmosphere 

 in every part of which the same constant temperature prevails. 

 For in this hypothesis also the elasticity and the pressure of a 

 mass of air would constantly balance one another, whether in 

 a state of motion or of rest. In the case of intestine motion 

 accidentally excited, there is no means provided, in either of 

 the atmospheres we have mentioned, of bringing back the air 

 to a state of rest. 



It may be observed that the two atmospheres we have been 

 considering are not mere theoretical fictions, with regard to 

 which it may be doubted whether they can possibly exist or 

 not. Both of them are physically possible : and they may 

 both be constructed by means of operations that can be per- 

 formed with air. If we have a close vessel containing air of 

 which the density is unit, and enlarge the dimensions of the 

 vessel till the density is reduced to 1 — w, at the instant of the 

 rarefaction, and before any heat is received through the me- 

 dium of the containing vessel, the elasticity of the confined air 



will be equal to (1 — w)^, and the function for temperature 



to (1 — oiY. In this state the dilated air retains the whole of 

 its absolute heat, the temperature lost being identical with the 



heat absorbed. Now if we put (1 — w)^ for p in the equations 

 (H), we shall determine the lieight x, or the place in the at- 

 mosphere of air having the density 1 — «;. By repeating like 

 operations for every degree of dilatation, it is evident that the 

 entire atmosphere may be constructed by the guidance of 

 Vol. G6. No. 328. Au". 1825. M nature 



