276 WELLS'S NATURAL PHILOSOPHY. 



rents of -warm air ascending from the earth are more buoyant, larger, and ri&o 

 higher, and when condensed, form large masses of clouds, each of which may 

 be considered as the capital of a column of air, whose base rests upon the earth. 

 As the heat of the sun diminishes in the afternoon, the strength of the cur- 

 rents abate, the clouds, which are buoyed up by their force, sink down into 

 warmer regions of the atmosphere, and are either partially or wholly 'dis- 

 solved. 



Fig. 225. 



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jicaJfiBJ 



^^^^.^ 



^^^^■^S^^^te^s^'g?^^^^ 



Cirrus, a; Cumulus, 6; Stratus and Nimbus, c. 



'' The rounded figure of the cumulus has been attributed to its method of 

 formation; for when one fluid flows through another at rest, the outline of 

 the figure assumed by the first will be composed of curved lines. This fact 

 may be shown, and the appearance of the cumulus imitated, by allowing a 

 drop of milk- or ink to fall into a glass of water. The same thing is also 

 Been in the shape of a cloud of steam as it issues from the boiler of a loco- 

 motive. 



