CLOUDS. 445 



most frequently exhibits the plienomeDaof the solar and lunar halo, and 

 (as inferred from a few observations) also the parhelion and paraselene. 

 Hence the reason of the prognostic of foul weather, commonly drawn 

 from the appearance of halo. The frequent appearance of halo in this 

 cloud may be attributed to its possessing great extent at such times 

 with little perpendicular depth, and the requisite continuity of substance. 

 This modihcation is, on this account, peculiarly worthy of investiga- 

 tion." 



III. — ClREO-CUMULUS, (HOWAKD.) 



Curdled cloud, (illustrations ISTos. YII andVIIT.) — It is sufficient that the 

 cirro-stratus sinks a little, or that the temperature of the region it occu- 

 pies be slightly elevated, in order to give birth to Howard's cirro-cumu- 

 lus. In the first place, the axes of the stricc grow round; theu, by de- 

 grees, the entire stratification becomes so, until it resembles carded cot- 

 ton, which we call frizzled clouds or curdled shy ; in French, when it is 

 completely covered, moutonnes ov immmele ; in Spanish, ciclo empcdrado. 

 On the contrary, if the cirro-cumulus is elevated a little, or the tempera- 

 ture is lowered, it returns to the type of cirro-stratus. 



The cirro-cumulus is more dense and lower than the cirro-stratus, from 

 which it is derived, though generally the edges of the small accumula- 

 tions or of the entire mass of cloud are transformed into cirro-stratus, 

 wherever, from a greater elevation or a lower temperature, the congela- 

 tion is more vigorous. Its motion is also more rapid, its color slightly 

 grayish, and it may be tinged rose-color or rather reddish. 



The cirro-stratus, and especially the cirro-cumulus, is remarkable from 

 a characteristic of the highest importance, which has escaped the sagacity 

 of Howard and his successors, viz, the distribution of congealed aqueous 

 vapor. It exists in the most fantastical combinations, reproducing all the 

 formations of our continents and seas. Here, a deep bay with promon- 

 tories, capes, x)eninsulas, isthmuses, &c.; there, a river, brooks, lakes, 

 &c.; farther on vast continents and open seas. The outlines and the 

 entire mass of each of these are besprinkled with cirro-cumulus, some- 

 times edged with cirro-stratus, whose volumes of little balls diminish and 

 vanish from center to circumference, while in the emjity spaces is 

 the -purest azure of the heavens. (Plate.) Should it be a lake, the 

 water will be represented by the blue sky, and terra firma by the cirro- 

 cumulus which surrounds it. By carefully studying all these transfor- 

 mations, we can observe in them a striking analogy to the phenomena 

 of the precipitation and congelation of dew. There must be at this 

 altitude, in the same stratum, one above the other, portions of the atmo- 

 sphere having different degrees of density and of temperature, in order 

 that the congelation of aqueous vapor should take place in so variable 

 a manner. 



The influence of cirro-cumulus upon the temperature at the surface of 

 the earth is so marked that the human body feels it at once. A curdled 

 sky at the new moon, on a calm night in the tropics, is a sky compara- 



