146 ON ATMOSPHERIC AND BAROMETRIC 



Thus we find, that we have only to trace the 

 effects of the various changes of temperature, 

 arising from the different causes that are known 

 to be in operation on the separate constituents of 

 the atmosphere, to perceive with considerable 

 clearness, how all those alterations in atmospheric 

 pressure, and changes of wind, which appear at 

 the first view so incompatible and contradictory 

 are accomplished. The constituents of the 

 atmosphere, separately, and independently, obey 

 the laws which govern them, and although in so 

 doing, they may impinge upon, and to some small 

 extent disturb each other in their movements, 

 yet the daily fluctuations of temperature, which 

 are the primary disturbing causes, are sufficiently 

 slow to allow each elastic fluid to act nearly in 

 conformity with its own laws. When vapour is, 

 by the slow process of evaporation, discharged 

 into the atmosphere, it penetrates the atmospheric 

 mass, ascends, and also expands laterally, yet 

 rests on the surface of the globe with its own 

 weight alone, that weight being increased or 

 diminished as the vapour becomes more or less in 

 quantity. But, in spreading laterally, the vapour 

 has not sufficient force to impinge upon, and 

 carry along the gases, — it therefore does not, in a 

 direct and mechanical way, produce a wind. 



