66 CLIMATE. 



A corresponding effect has been remarked with regard to 

 the impression of cold, but this is only true to a certain 

 extent, as from the great clearness of the sky in elevated 

 situations the effect of radiation is greatly increased. It 

 has in fact been frequently observed on the hills,' as well as 

 elsewhere, that plants, grass, and other substances near the 

 ground are from this cause, viz. increased radiation, strong- 

 ly frozen, when the circumambient air indicates a tempera- 

 ture some degrees above freezing point. 



These, and the other less important effects of the relative 

 altitude will be more evident when we speak of the various 

 conditions of the atmosphere in detail, to which we will also 

 refer our consideration of the second modifying circum- 

 stance, namely, the situation of the hills between the in- 

 fluence of the two monsoons, and partaking of both ; merely 

 observing, that the sky being covered with clouds during 

 the months of June, July, and August, when the sun is 

 vertical, tends greatly to equalize the temperature, and to 

 obviate the effects which would otherwise be produced on 

 vegetation, and on the human body, by the united power of 

 the sun's rays and the excessive dryness of the atmosphere. 



The third circumstance which we have stated, as naturally 

 influencing the climate of the hUls, and certainly not the 

 least important, is their isolated position at a great distance 

 from land of equal or nearly equal elevation. This will be 

 better understood by comparing them with the subordinate 

 ranges, leaning against the lofty chains of the Pyrenees, the 

 Alps, Caucasus, or Himalaya. In all these situations it is 

 found that the temperature is liable to great, sudden, and 

 rapid variations. The air, when heated in the plains below, 

 rises to a certain height, but instead of passing over the first 

 range, it rests there ; producing a considerable elevation of 



