J^l THE NATURAL HISTORY OP CLOUDS. 



land. In winter it ^Iso visits the plains, in the form of u 

 very wet and durable mist, the drops of which are neverthe- 

 less too sn^all to be visible, and which, unlike the stratus, is 

 moi'e dense on rising grounds than in the valleys. 



The cirro-stratus usually accords with a sinking state of 

 the barometer. 



Of the Cumulo'Stratus. 

 Cumolostra- The formation of the cirro-cumulus, or cirro-stratus, by 

 »u« unrf vtsfoi- conJensed vapour, descending from the higher atmosphere, 

 •cribed. " does not prevent the cumulus from being produced out of 

 the water, which, in the mean time, evaporates from the 

 Earth, and ascends to the middle region. In this case, the 

 two modifications after a while come into contact, and pre- 

 sent to the attentive observer a succession of curious appear- 

 ances. 



While the cumulus is rapidly increasing upward, a deli- 

 /rate fleece, of a structure visibly different, sometimes at- 

 taches itself to its summit, where it reposes as on a moun- 

 tain. This fleece is a cirro-stratus ; and the materials of 

 ivhich it is formed are brought by a superior current over- 

 taking or meeting the cumulus. Frequently, the cumulus 

 in its increase breaks through the cirro-stratus, and appears 

 again above it, but with a visible change in the aggregation, 

 which now beconves rocky, perpendicular, and, finally, over- 

 hanging. If the cirro-stratus fhould itself increase too fast 

 to be swallowed up by the cumulus, the latter after a while 

 extends its protuberances laterally, and attaches itself by 

 ' them to the superior mass of cloud. 



When the cirro-cumulus, in like manner, occupies the 

 superior place, a cumulus rising beneath it is susceptible of 

 the same union by mutual attraction; the result of which, 

 as in the former case, is a large, lofty, and dense cloud, 

 which often subsists through the day; and in the evening 

 undergoes the usual evaporation. 



, It is not, however, absolutely necessary to the production 

 of this cloud, that either of the superior modifications sliould 

 be previously formed. In a favourable state of the atmos- 

 phere, the cumulus itself, after having arrived at a certain 

 Tuagnitudf , su'ddenly begins to overgrow its base, and pro- 



diH4^8 



