104 Ort th£ Modifications of Clouds, and 



This modification is on this account more peculiaflf 

 worthy of investioation. Little is yet ascertained of the re- 

 lations of this and the last modification with the barometer, 

 &c. although^ as may be readily supposed, they have been 

 found to accord with opposite indications of those instru- 

 ments. 



Of the Cumulo-stratus. 



The different modifications which have been just treated 

 of sometimes give place to each other, at other times two 

 or more appear in the same sky ; but in this case the clouds 

 in the same modification lie mostly in the same plane of 

 elevation, those which are more elevated appearing through 

 the intervals of the lower, or the latter showing dark against 

 the lighter ones above them< When the cumulus increases 

 rapidly, a cirro-stratus is frequently seen to form around its 

 summit, reposing thereon as on a mountain, while the for- 

 mer cloud continues discernible in some degree through it. 

 This state continues but a short time. The cirro-stratus 

 speedily becomes denser and spreads, while the superior 

 part of the cumulus extends itself and passes into it, the 

 base continumg as before, and the convex protuberances 

 changing their position till they present themselves late- 

 rally and downward. More rarely the cumulus alone per- 

 forms this evolution, and its superior part constitutes the 

 incumbent cirro-stratus. 



In either case a large lofty dense cloud is formed, which 

 may be compared to a mushroom with a very thick short 

 stem. But when a whole sky is crowded with this modifi- 

 cation, the appearances are more indistinct. The cumulus 

 rises throng! i the interstices of the superior clouds, and the 

 whole, seen as it passes oH' in the distant horizon, presents 

 to the fancy mountains covered with snow, intersected with 

 darker ridges and lakes of water, rocks and towers, &c. 

 The distinct cumulo-stratus is formed in the interval be- 

 tween the first appearance of the fleecy cumulus and the 



and tint degree of continuitv of substance which seems requisite to the 

 pli?enomen<)n. There is also probably some additional peculiarity of 

 structure in it not yet attended to. 



The following lines of Virgil seem to relate to an effect of 'the cirro- 

 stratus, which in this country is more often to be observed on the ietting 

 sun : 



lUe ubi nascentem macidis variaverit ormm 

 Conditus in nubem, mn/ioque reftigerit orbe, 

 Swipecti tibi sint imbm : namquc urget ab alto 

 Aiboribusijue smibtjuc ^'eiui, pccoriquc sinister. 



Gear^ic. lib. i. 



commencement 



