CLOUDS, RAIN, SNOW, AND HAIL. 275 



WTiat occasions When clouds are not continuous over the Trhole surface of 

 and broken ap- the sky, various circumstances contribute to give them a 

 pearance of rough and uneven appearance. The rays of the sun faUing 

 upon diflerent surfaces at diflerent angles, melt away one set 

 of elevations and create another set of depressions ; the heat also, which ia 

 liberated below in the process of condensation, the' currents of warm air 

 escaping from the earth, and of cold air descending from above, all tend to 

 keep the clouds iu a state of agitation, upheaval, and depression. Under 

 these influences, the masses of condensed vapor composing the clouds arc 

 caused to assume all manner of grotesque and fanciful shapes. 



The shape and position of clouds is also undoubtedly influenced in a con- 

 siderable degree by their electrical condition. 



_ Clouds are freq uently seen to collect around 



Why do clouds . i i i 



frequently col- mountaiu pcaks, when the atmosphere else- 

 mountain wheie is clear and free from clouds. This is 

 caused by the wind impelling up the sides of 

 the mountains the warm, humid air of the valleys, the 

 moisture of which, in its ascent, gradually becomes coa^ 

 densed by cold, and appears as a cloud, 

 g^^ ^^ 608. Clouds are generally divided into foit» 

 kinds nf clouds great classes, viz. : the Cirrus, the Cumulus, 



are recognized? 07 77 



the Stratus, and the Nimbus. 

 ci^r^us ifoud'?^ '^^® Cirrus* cloud consists of very delicate 



thiQ streaks, or feathery filaments, and is 

 usually seen floating at great elevations in the sky during 

 the continuance of fine weather. 



It is highly probable that the cirrus cloud, at great elevations, does not con- 

 sist of vesicles of mist^ but of flakes of snow. 



Fig. 225, a, represents the appearance of this variety of cloud. 



What is the The Cumulusf cloud consists of large round- 



Cumulus cloud ? J /» • i , • 



ed masses oi vapor, apparently restmg upon 

 a horizontal basis. When lighted up by the sun, cu- 

 mulus clouds present the aj^pearance of mountains oi 

 snow. 



The cumulus is especially the cloud of day, and its figure ia most perfect 

 during the fine, warm days of summer. 



Fig. 225, h, illustrates the appearance of the cumulus cloud. 



These clouds appear in greatest number at noon, on a fine day, but disap- 

 pear as evening approaches. The explanation of this is, that at noon the cur- 



• From thi» Latin word cimix — a lorlc nf hair, or curL 

 t From the Latin word cumulus — a mass, or pile. 



