660 CLASSIFICATION OF THE CLOUDS. 



Linear Cirrus^ and the transverse lines produce the lieticulated or Curl 

 Cloud. 



At other times the lines of Cirrus become denser, descend lower, and, 

 by uniting or conjoining with others below, produce rain. 



Comoid or Hairy Cirrus, commonly called Mare's Tail, is the proper 

 Cirrus ; it resembles, in appearance, a long lock of white hair, or a bunch 

 of wool pulled out into fine pointed ends. The appearance of Cirrus often 

 indicates wind and rain ; and when the fine tails have a constant direc- 

 tion toward any one point of the compass, it has been frequently observed 

 that the gale has sprung up from that quarter to which they previously 

 pointed. It is often difficult to ascertain the direction of Cirrus, owing 

 to its slowness of motion, but as indicating the difference between the 

 direction of the wind at the earth's surface, and that of the higher regions, 

 it is very important. 



Cirrus is seen far above the highest mountains, and Mr. Glaisher con- 

 cluded from his baUoon observations that its altitude sometimes amounts 

 to over 15 miles. According to Prof. Hildebrandsson's observations at 

 Upsala, in Sweden, its mean altitude is 27,000 feet. 



The Lower Clouds are usually composed of particles of condensed 

 vapour or " bubble-steam," i.e., of water, not of ice ; when they are inter- 

 posed between the sun and the moon, they dim or intercept the light 

 entirely, without giving rise to halos or corona. They may be described 

 as follows : — 



Cirro-stratus and Strato-cirrus differ little in form, bnt much in height, 

 the former having a mean altitude of 27,500 ft., and the latter ranges as 

 lovr as 15,000 feet. 



Cirro-stratus (Cirrus and Stratus), or Wane Cloud, is composed of 

 horizontal or slightly inclined masses of small clouds, attenuated toward 

 a part or the whole of their exterior, bent downward or undulated, separate 

 or in groups, and generally with a sinking barometer, indicating a decrease 

 in temperature, with wind and rain or snow. 



Cirro-stratus is characterised by great horizontal extent in proportion 

 to vertical breadth ; so that when any other Cloud begins to assume that 

 form, it generally ends in Cirro-stratus. Cirrus more commonly becomes. 

 Cirro-stratus than any other Cloud; Cirro-cumulus next; and then Cumulus. 

 Cirro-stratus, once formed, sometimes resumes the modification from which 

 it originated, but more frequently it gradually evaporates or conjoins with 

 some other modification. It seldom remains long in one form, but seems 

 to be constantly declining, and hence the term of Wane Cloud. It is 

 sometimes composed of wavy bars or streaks, connected in the centre and 

 confused, but the streaks more confined at the edges ; this is common in 

 variable weather in summer. The Mackarel Sky, as it is termed, is a 

 variety of this ; another variety consists of one long and plain streaky 

 thick in the middle, and wasting away at its edges ; and a third, con- 

 sisting of small rows of little clouds, curved in a peculiar manner, and a 

 sure indication of stormy weather ; this is more or less regularly formed, 

 and the irregular formation is often produced when a large Cumulus 

 passes under a long line of Cirro-stratus, and is also a sign of stormy 

 weather. 



