FIG. 6. 



the reason of their not falling is this, when the air below 

 the clouds is saturated with moisture it will absorb no more 

 and the rain falls, but when it is warm and dry, and passed 

 in a constantly renewed current, then the vapour is absorbed 

 before it reaches the earth, and is carried off by the wind. 

 Clouds, therefore, although they often appear stationary, 

 are constantly altering their form and size, portions being 

 absorbed while others are being formed. Fogs are the same 

 as clouds, the vapour arising from wet grass, rivers, <fec., 

 being condensed as it ascends, by a current of cold air 

 passing over them. The fogs in London have a brown 

 colour, from admixture of smoke, dust, &c., with which the 

 air is contaminated (fig. 5). Clouds are of various forms 

 and sizes, and indeed of almost every variety, but certain 

 kinds which are frequently seen, have received different 

 names. The " cirrhus " comprises all the feathery white 

 clouds which float high up in the air in fine weather; 

 the " cumulus " consists of the large mountain-like clouds 

 which are generally seen in summer ; the " stratus," those 



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