of 'Cumulus, Cirrus, and their Varieties. 363 



are two distinct kinds of cloud, depending on two distinct 

 agents for their formation. I have not, in any instance, seen 

 the cumulus result from any modification of cirrus, which is 

 mostly confined to the higher regions of the atmosphere ; I 

 have, however, on some occasions, observed this cloud in the 

 region of the cumulus, which is generally noticed in that 

 stratum of the atmosphere situated immediately above the 

 vapour plane. When both the cirrus and cumulus are traced 

 from their earliest stages, a most decided difference is per- 

 ceptible : all the varieties of cirrus commence as " thin white 

 lines, or threads, pencilled on the azure sky ; " and they pre- 

 serve this form until cirro-stratus is produced, as is frequently 

 observed. Throughout the whole group of cirro-stratus, the 

 fibrous, or thread-like, character can be well traced ; and in no 

 instance have I observed the least approximation in the cirrus 

 or cirro-stratus to heap. The commencement of the cumulus 

 is decidedly hairy-form, without the slightest tendency to 

 present a thread-like appearance : the best comparison I can 

 give is the appearance presented by steam escaping from a 

 steam-pipe, or smoke issuing from a high narrow chimney : 

 in both cases an expansion takes place upon the escape of the 

 vapour, which gives rise to a hairy-form appearance, similar 

 to that which is observed in the commencement of the cu- 

 mulus. Throughout the whole of the four stages of the lower, 

 or foul weather, cumulus, and the corresponding stages of the 

 upper, or fair weather, cumulus, this hairy-form appearance is 

 distinctly traced ; and, as the thread-like appearance is not 

 exhibited by any modification of the cumulus, nor the heaped 

 appearance by any modification of the cirrus, I think the 

 phenomena sufficient to mark these clouds (the cirrus and 

 cumulus) as perfectly distinct, and depending on different 

 agents for their production. 



But, while the cirrus and cumulus are, under all circum- 

 stances, entirely distinct, and in no instance have they been 

 observed to result from each other (I speak from personal 

 observation), there are two varieties that are frequently seen 

 to interchange, one being resolved into the other. I do not, 

 however consider this change to depend on the augmentation 

 of the masses which cause them to descend into a lower 

 region : the groups I allude to are cirro-stratus and cirro- 

 cumulus. The cirro-stratus, as before observed, results, in 

 many instances, from the cirrus; and the cirro-cumulus, though 

 not resulting from the cumulus, appears to be rather con- 

 nected with it; for the largest masses of cirro-cumulus appear 

 to possess the same characters as the third stage of the upper, 

 or fair weather, cumulus; with this exception,that the masses 



