171 



The particles composing any fluid mass are subject to 

 various changing influences, in particular of pressure, vrhen- 

 ever tliey are moved from one situation to another. In this 

 way they experience changes of temperature altogether 

 independent of the efiects produced by the radiation or con- 

 duction of heat. When all the parts of a fluid are freely 

 interchanged and not subject to the influence of radiation 

 and conduction, the temperature of the fluid is said by the 

 Author to be in a state of convective equilibrium. The 

 equations of convective equilibrium in the atmosphere investi- 

 gated by the Author are as follows^ IT, T, and W denoting 

 the pressure, temperature, and mass per cubic foot of the air 

 at the earth's surface, and p, t, and p the same qualities of 

 the air at any height x, 



which is the known relation between temperature and 

 pressure. 



the deduced relation between pressure and density ; and 

 » dp^=z — p dx (3) , 



the hydrostatic equation, the variation of gravity at different 

 heights being neglected, and the weight of unit mass (lib) 

 being taken as unit of force. Hence by integration, 



t ^ W.C ^ — 1 n 



^ = 1 — 7—^ Or if, for brevity, we denote — by H, 



t X k—l 



— = 1 — (4) 



T H ^ -^ 



From (4) and (1) it appears that temperature and density 



1*41 

 would both vanish at the verv moderate height — rrxH 



