AQUEOUS ATMOSPHERIC PHENOMENA. 467 



About a hundred yards below the junction, the temperature of the central part of the 

 Danube was 59, and here the quantity of mist was less. The evening of June 12th was 

 cloudy, preventing radiation, and the temperature of the atmosphere remained till after 

 dark higher than that of the river, when there was not the slightest appearance of mist. 

 Similar observations were made on the Rhine, the Save, the Izonzo, the Po, the Tiber, 

 and on the small lakes in the Campagna of Rome, and in no instance was there the form- 

 ation of mist, but under the circumstances which have been detailed. 



4. Cirrocumulus Sondercloud. This is a form of cloud of an intermediate nature 

 between the cirrus and cumulus, and hence its Latin compound name. The cirrus, after 

 having exhibited itself for a time, frequently passes into this modification, descending at 

 the same time to a lower station in the atmosphere. Its parallel bars are broken into a 

 number of small cumuli, of irregular shape, but generally orbicular, arranged in exten- 

 sive beds, the component parts being quite distinct, or asunder, which explains the Saxon 

 derivative title, the sondercloud. The previous appearance of the cirrus is not, however, 

 necessary to the production of cirrocumulus, which often starts into existence independ- 

 ent of any other modification. The prevalence of this cloud in summer augurs an 

 increase of temperature ; and in winter, the termination of frost. Sometimes its dif- 

 ferent members are of very regular round form, dense structure, in close contact with 

 each other, and arrarged on a curved base, in which state the cirrocumulus is commonly 

 the natural harbinger of thunder-storms. In another variety, the small masses of cloud 

 exhibit no uniformity of shape, and appear of a very light fleecy texture. Bloom field's 

 description of this cloud, 



" The beauteous semblance of a flock at rest," 



aptly pictures its aspect at night in the presence of the moon. 



5. Cirrostratus Wanecloud. These names point to the frequent origin and form of 

 the cloud they indicate. It results from fibres of the cirrus waning or subsiding in the 

 atmosphere, drawing closer to each other, and becoming arranged in horizontal strata. 

 The cirrostratus exhibits several varieties: a series of thin, inclined, and wavy streaks 

 (Jig. 1.) ; a row of short thick patches of cloud (fig. 2.) ; and a long horizontal sheet, very 

 narrow in proportion to its extent, and attenuated at the edges (fig. 3). The appearance 

 and prevalence of this cloud indicate wind, rain, or snow ; and the second arrangement 

 of it generally precedes storms, or occurs in the intervals of them. It is sometimes seen 

 cutting the sun and the moon's disc with a dark line, or hanging over them like a thin 

 hazy veil, one of the surest prognostics we have of a fall of rain or snow. Virgil in his 

 Georgics gives it this interpretation: 



" Or should his rising orb distorted shine 

 Through spots, or fast behind a cloud's dark line 

 Retire eclipsed ; then let the swain prepare 

 For rainy torrents ; a tempestuous air 

 Swift from the southern deep comes fraught with ill, 

 The corn and fruits to waste, the flocks to chill." 



6. Cumulostratus Twaincloud. This is the most magnificent form of cloud, as cirro- 

 cumulus is one of the most beautiful. It is formed either by two or more cumuli uniting 

 together, or a single cumulus increasing laterally, so as to exhibit several vast hemispherical 

 heaps overhanging the base. These mountainous masses form a multiple or twaincloud, 

 and resting upon a common stratum are called cumulostratus. Nothing can be more im- 

 posing than the spectacle occasionally presented by these compound clouds, which the eye 

 is disposed to contemplate as the architecture and home of giant spirits. The formation 

 of cumulostratus takes place under different temperatures, and may precede a tempest of 



