92 M. J. Ivory on the Constitution of the Atmosphere. 



librio will have more acquired heat than the ascending mass 

 when it comes to occupy the same place ; and the difference 

 will be moi*e considerable when the velocity is greater. Now 

 the pressures being the same in both cases, it follows that, in 

 the former case when more heat is acquired, the elasticity, 

 which in a state of rest balances the external pressure, will be 

 greater than tlie elasticity in the latter case. Wherefore the 

 elasticity of the ascending mass of air is less than the external 

 pressure; and the difference of these two forces opposing the 

 ascent, the velocity will be continually lessened and finally de- 

 stroyed. The reverse of all this will take place when a mass 

 of air moves downwards. In descending it will lose heat ; its 

 elasticity will decrease faster than the pressure augments; 

 and the velocity will be extinguished when these two forces 

 are reduced to an equality. It thus appears that an atmo- 

 sphere constituted as we have supposed, contains a principle 

 of stability, by means of which vertical motions upwards or 

 downwards excited accidentally in the air will be destroyed. 



In reasoning on this subject, if we confine our attention to 

 the powers really existing in nature, that is, to the actual heat 

 of the atmosphere and the different ways of distributing it by 

 the valuation of pressure and density, the atmospheres we have 

 already considered are all that can possibly be admitted. A 

 full enumeration of all the cases that can be imagined would, 

 indeed, lead us to another class of atmospheres, in which the 

 temperature lost in ascending is greater than the heat ab- 

 sorbed by the rarefaction. But it seems impossible to con- 

 ceive in what manner the loss of temperature can be carried 

 beyond the heat of combination merely by transference be- 

 tween the contiguous air, and without assuming hypothetically 

 some exti'aneous source of cold. It is the less necessary to 

 dwell on this point because the real atmosphere cannot be in- 

 cluded in this class, which possesses properties quite opposite 

 to the class already mentioned. In an atmosphere of this 

 kind, a mass of air in ascending would lose heat, and the 

 elasticity would decrease faster than the pressure ; in descend- 

 ing, it would acquire heat, and the elasticity would increase 

 faster than the pressure ; in both cases there would be an aug- 

 mentation of velocity. Motion upwards or downwards once 

 begun, would be accelerated, instead of being retarded and de- 

 stroyed. .. 



It has been shown that, in fact, the temperature lost in as- 

 cending in the atmosphere is less than the heat absorbed by 

 the rarefaction of the air. We have proved tliat this is the 

 only constitution of an atmosphere which is stable, that is, 

 which contains a principle capable of destroying motions up- 

 wards 



