On Climate, fyc. 



of particular situations, is a point which is less frequently 

 considered than the primary one which we have been inves- 

 tigating; but which requires perhaps still more attention. 

 The utmost concentration of cold can only take place in a 

 perfectly still atmosphere : a very slight motion of the air is 

 sufficient to disperse it. A low mist is often formed in meadows 

 in particular situations, which is the consequence of the slow 

 extension of this cold in the air, as before described ; the 

 agitation of merely walking through this condensation is fre- 

 quently sufficient to disperse and melt it. A valley sur- 

 rounded by low hills, is more liable to the effects of radiation 

 than the tops and sides of the hills themselves ; and it is a 

 well known fact that dew and hoar frost are always more 

 abundant in the former than in the latter situations. It is 

 not meant to include in this observation, places surrounded 

 by lofty and precipitous hills which obstruct the aspect of 

 the sky, for in such, the contrary effect would be produced. 

 Gentle slopes which break the undulations of the air without 

 naturally circumscribing the heavens, are most efficient in 

 promoting this action, and it is worthy of remark and consi- 

 deration, that by walls and other fences, we may artificially 

 combine circumstances which may produce the same injurious 

 effect. 



But the influence of hills upon the nightly temperature of 

 the vallies which they surround is not confined to this insu- 

 lation ; radiation goes on upon their declivities, and the air 

 which is condensed by the cold, rolls down and lodges at 

 their feet. 



Their sides are thus protected from the chill, and a double 

 portion falls upon, what many are apt to consider, the more 



