86 ATMOSPHERIC MATTER. 



suffers by combustion is proved by the decom- 

 position of the water out of it. We have the fact 

 proved in a general way, constantly before our 

 eyes, by the depressions which the mercury of 

 the Eplanometer sustains in a storm, and its 

 elevation in a calm, in a wet and in a dry day ; 

 sinking, more especially in tropical climates, 

 where the periodical changes which take place 

 in the atmosphere, are more evident, and con- 

 siderable, than they are in lower latitudes, the 

 mercury sinking from the elevation of 31 to 27 

 inches; and in this country, from 30 2-10 

 to 28. 



The reduction of the expansible force in the 

 atmosphere is observable at night, by the ab- 

 sence of the solar rays, more especially in the 

 summer season, when we behold a large pro- 

 portion of the water which had been during the 

 day, absorbed and gasified, return during the 

 night from gas to vapor, from vapor to mois- 

 ture, or dew. It is owing to the decreased de- 

 grees of expansibility in the atmosphere, in 

 consequence of its increasing dilatation from 

 the surface of the earth, to the more elevated 

 regions, that from being clear and transpa- 

 rent, it is found to terminate in a turbid or 

 foggy state, known by the name of clouds ; so 

 that the transmutations which we often behold 

 clouds and fogs undergo, from dry ness to 

 moisture from levity to weight from suspen- 



