THE NATURAL HISTORY OF CLOUDS. ©q 



The duration of this cloud varies according to its staton Its duradoric 

 in the atmosphere, and the presence or absenpe of other 

 clouds: it is long, extfending sometinies to thirtyrsix hours, 

 when it appears alone, and at its greatest elevation j but 

 shorter^ or even very transient, when formed Ipvver, and in 

 the vicinity of the cumulus. 



By an inexperienced observer the cirrus would be pro- Its motion, 

 pounced absolutely motionless. On comparison with a fixed 

 object, however, it is sometimes found to havt- a consider- 

 sible progressive motion. The propagation of the cirrus, it, connexion 

 and the variable directions of its flexures, merit attentive ^''^ ^**^^''i"*^' 

 observatioi}, as being intimately connected with the varia- 

 tions of the wind, although undoubtedly not produced by 

 the mere motion of the air. 



The general principles, which the imperfect notice hi?- 

 therto bestowed on it seems to point out, are the following : 



J, Its appearance is a general indication of wind; and Indications 

 jt is most conspicuous and abundant before storms. ^''"^ ^** 



2. It is often a leeward cloud; or, when a group of cirri 

 (appears on the horizon, it seems to invite a current towards 

 it: and the wind very often shifts into that quarter towards 

 which the points are directed, 



3. Horizontal sheets of the cirrijs, more particularly those 

 which carry streamers pointing upward, are among the iur 

 dications of rain approaching, while the fringe-like depend- 

 ing ones are found to precede fair weather. 



Of the Cumulus, 



Clouds in this modification are commonly of dense Cunylus de- 

 structure. They are formed in the lower atmosphere; and '^uocd. 

 move with the wind, or more properly with that current 

 which flows next the Earth. The phenomena of the cumu- 

 lus are usually these: In the latter part of a clear morning, j^^ fo„na(ign. 

 a small irregular spot appejars suddenly at a moderate ele- 

 vation. This is the mccleus, or commencement of the cloud, 

 the upper part pf vrhich soon becomes convex and well de- 

 fined, while the lower continues irregalarly plane. On the 

 convex surface the increase visibly takes [)lace, one heap op 

 protuberance succeeding another, and again losing itself 

 }a a 9ubse(^vient pn^e, until ;i pile qf jclond of an irregular 



hemispherical 



