40 



I>ecre3.s.e. 



Indicitien. 



Stratus de- 

 scribed. 



Jnditalion, 



THE NATURAL HI8TOEY OF CLOUDS. 



hemispherical form is raised; which floats along, presenting 

 its apex to the zenith, while the base, or rather the lower 

 surface of the baseless fabric, continues parallel to the 

 horizon. 



When these clouds are of considerable magnitude, they 

 remain at proportionably great distances. When smaller, 

 they croud the sky by a nearer approacli to each other. In 

 each case the baj.es range in the same plane; and the increase 

 of each keeps pace \vith that of its neighbour, the inter- 

 vening spacts remaining cle'ar. 



The cumulus often arrives at its greatest magnitude early 

 in the afternoon, when the temperature of tHe day is at its 

 maximum. Ae the sun declines, it giadually decreases, re- 

 taining its character till towards sun-set, when it is more or 

 less hastily Taroken up, and evaporates, leaving the sky clear, 

 as in the early part ofthe morning. Its tints are often vivid, 

 and pass through the most pleasing gradation during this 

 ]ast hour of its existence. 



The preceding phenomena form the history of the pure 

 cumulus, as it may be ter.ned, when no other modification 

 appears along with it. They are both the accompanimentai 

 (^l^nd prognostics of the fairest weather. 



Of the Stratus, 



The stratus has a moderate degree of density. It is the 

 lowest of the modifications, being formed in contact with the 

 earth or water. It comprehends those level creeping mists, 

 which, in calm evenings, spread like an inundation from the 

 valleys, lakes, and rivers, to the higher ground. 



Unlike the cumulus, which belongs to the day, and 

 rarely survives the setting sun, this cloud accompanies the 

 shades of night, and commonly vanishes before the ascending 

 luminary. The evaporation comrncnc es from below. At 

 the moment of the separation of the stratus fronn the Earth, 

 its character is changed, and it puts on the appearance of 

 the nascent cumulus. 



The nocturnal visits of the stratus have been always held 

 a prejsage of fair weather. Thus Virgil: 



" At nebulae magis iraa petunt, campoque recumbunt." 

 Then mists the hills forsake and shroud the plain. 



