in respiration, and in various processes of com- 

 bustion and fermentation, bears a proportion ex 

 tremely minute to the whole volume of the atmos- 

 phere : if every plant during the progress of its life 

 makes a very small addition of oxygene to the air, and 

 occasions a very small consumption of carbonic acid, 

 the effect may be conceived adequate to the wants of 

 nature. 



It may occur as an objection to these views, that 

 if the leaves, of plants purify the atmosphere, towards 

 the end of autumn, and through the winter, and early 

 spring, the air in our climates must become impure, 

 the oxygene in it diminish, and the carbonic acid gas 

 increase, which is not the case ; but there is a very 

 satisfactory answer to this objection. The different 

 parts of the atmosphere are constantly mixed together 

 by winds, which when they are strong, move at the 

 rate of from 60 to 10O miles in an hour. In our win- 

 ter, the south-west gales convey ah% which has been 

 purified by the vast forests and savannas of South 

 America, and which, passing over the ocean, arrives 

 in an uncontaminated state. The storms and tempests 

 which often occur at the beginning, and towards the 

 middle of our winter, and which generally blow 

 from the same quarter of the globe, have a salutary 

 influence. By constant agitation and motion, the 

 equilibrium of the constituent parts of the atmosphere 

 is preserved ; it is fitted for the purposes of life ; and 

 those events, which the superstitious formerly refer- 

 red to the wrath of heaven, or the agency of evil 

 spirits, and in which they saw only disorder and con- 



