174 BOOK OF NATURE LAID OPEN. 



and sets in the west, consequently the air will be 

 heated gradually from east to west, and the wind 

 will blow in that direction." The same cause, this 

 author remarks, will explain " the land and sea 

 breezes in the tropical climates;" and the monsoons, 

 though the theory of them be more complicated, origi- 

 nate in the same cause 



And as it is not only necessary that there be a con- 

 tinual agitation kept up in the ocean, by means of 

 the tides and currents, but, in order to prevent its wa- 

 ters from being contaminated by those numerous 

 loads of filth which are, from all quarters, poured into 

 it, it is also requisite that it be furnished with some- 

 thing of a correcting nature, which it has in its salt- 

 ness. So in the atmosphere, besides the perpetual 

 motion kept up in it by means of the winds, and the 

 beneficial consequences proceeding from vegetation 

 and the agitation of the waters, there must be also 

 some correcting quality, especially prevalent in the 

 upper regions, where a number of the most noxious 

 particles, and a considerable quantity of vitiated ef- 

 fluvia, must ascend? perhaps beyond the reach of the 

 other purifying agents. This, it is probable, is the 

 chief cause of the electric fluid, which, although it is 

 found to pervade the whole mass of creation, is sup- 

 posed to be much more copious in the upper than in 

 the lower parts of the atmosphere. 



In the lower regions of the firmament, indeed, the 

 tremendous noise of the thunder is heard, and the 

 vivid lightnings are seen to flash ; but these only hap- 

 pen on extraordinary occasions, or where their pre- 



