CHYMISTRY APPLIED TO AGRICULTURE. 7 



elasticity, &c It however loses its most important powers 

 of influencing vegetation ; so that all the substances found 

 in the atmosphere are necessary to the production and re- 

 newal of the phenomena which the three kingdoms pre- 

 sent to us. 



Of the four principles of which I have just spoken, as 

 constituting the atmosphere, the aqueous fluid is that 

 which appears to be the least closely united to the others ; 

 since a change of temperature alone is sufficient to pro- 

 duce a change of its proportions ; whilst azote, oxygen, and 

 tarbonic acid preserve, always, nearly the same relative 

 proportions ; nor can they be varied, or disunited; by 

 means of compression or change of temperature. The 

 aqueous fluid does not rise to a great height in the atmo- 

 sphere ; for, according to the reports of those experimental- 

 ists who have arrived at their conclusions by the assis- 

 tance of air-balloons, the higher regions of the atmo- 

 sphere are very dry, so as to produce, by the avidity with 

 which they absorb the moisture from the boat of the bal- 

 loon, a warping and cracking of its boards, as if they had 

 been exposed to a strong heat. This effect is produced 

 by the dryness of the atmosphere and the diminution of 

 its specific gravity. 



The manner in which the atmospheric elements are 

 united is worthy of notice. This union is sufficiently 

 strong to counterbalance the difference in their specific 

 gravities, and not to allow them to be separated by com- 

 pression, or the tumultuous agitation of the air ; and yet 

 it permits the various principles to be decomposed and 

 isolated, by presenting to them bodies for which they have 

 some slight affinity. Thus, if we inclose under a bell- 

 glass any volume whatever of atmospheric air, the aqueous 

 fluid may be extracted from it, by the calcined muriate of 

 lime. The combustion of phosphorus in it will absorb 

 the oxygen gas ; lime-water, or the caustic alkalies, will 

 combine with the carbonic acid ; and nothing will remain 

 but azote, which is the portion that has the least tendency 

 to form combinations. 



This weak state of union among the principles con- 

 tained in the atmosphere is necessary, in order that they 

 may exert their powerful and constant action upon all the 

 various bodies which cover the surface of the globe ; 

 the composition and decomposition of which cannot be 

 effected otherwise than by the means of these agents. 



