MR. BIRT'S ARRANGEMENT OF CLOUDS. 



15 



a sheet of cloud extended over the heavens : to point out this spreading 

 or extending of the cloud, I have employed the term F. stratus ; it 

 embraces three modifications, which I have distinguished by the Greek 

 letters. Another variety of this class consists of short thin lines or 

 fibres : these, I conceive, may be sufficiently pointed out by the term 

 F. linealis. The next variety may be described as very beautiful 

 feather-like clouds, sometimes of considerable size ; to these I have 

 applied the term F. plumatus. In addition to these, we have a 

 curled variety, commonly known by the name of mares' tails ; these, 

 I conceive, may be appropriately designated F. crispatus. The last 

 variety of this class consists of clouds that appear as bundles of fibres : 

 to point out these I have employed the term F. fasciformis ; the 

 variety includes three modifications, expressive of the size of the clouds 

 and their influence on the weather. 



The third division embraces all those clouds that differ from the pre- 

 ceding classes, in their structure being hairy : the appearance they 

 present to the eye is that of hairs or fibres, having a very irregular or 

 confused arrangement. As this structure can be clearly traced through 

 the whole class, perhaps the generic term Crinis may be appropriately 

 employed. The clouds composing it occupy the middle region of the 

 atmosphere, while those of the class Fibrus are generally observed in 

 the upper. The appearance of the clouds of Crinis differ according to 

 their elevation ; and I have noticed five distinct series of them, which 

 I have designated by the terms primus, secundus, tertius, quartus, 

 and quintus, commencing with those that occupy the lowest station. 

 These series generally include four varieties, which I have termed te- 

 nuis, compactus, cumulatus, and serratus ; the first expresses that the 

 cloud exists in its earliest stage, and is so thin that its structure is 

 readily perceptible ; the second points out that the cloud has obtained 

 an accession of vapour, which gives it a compact appearance, and 

 obscures its structure in the middle : the third that the cloud has 

 put on a heaped appearance ; and the fourth, that it has become 

 so accumulated as to present a fine notched or serrated edge : this 

 variety is very conspicuous in showery weather. In the upper series 

 the term sphcericus is substituted for that of compactus, as the variety 

 then assumes a more globular figure. In the series secundus, I have 

 noticed an additional variety, which, on account of its rough and 

 shaggy appearance, I have termed hirtus. The teyiuis of the fifth series 

 approximates very closely to the class Fibrus, especially the variety 

 plumatus ; to point out this connexion, I have suggested the term 

 fibratus instead of tenuis. 



