146 



METEOROLOGY. 



Mcteorolo- not conscious of having frequently looked, as it were 



gy- , instinctively, to the appearance of the clouds, in order 



"*"Y"* to form some opinion or conjecture respecting the fu- 

 ture state of the weather. At the same time, there 

 are few subjects perhaps on which there exists so great 

 a diversity and vagueness of opinion. Indications 

 drawn from the appearance of the clouds themselves, 

 are exceedingly indistinct, unless when accompanied 

 with other circumstances which render them more de- 

 finite, such as the colour of the sky at sun-rise or sun- 

 set, the settling of clouds on the summit of hills, the 

 appearance of mist or fogs at particular periods of the 

 moon's age, &c. and though there are no doubt certain 

 Necessarily forms and modifications of clouds, which nine perhaps 

 vague and out of ten tvealher-mise persons would, without hesita- 

 indcfJnitc. tion, pronounce indications of rain or snow ; yet, if 

 they were required to assign a specific reason for their 

 opinion, scarcely two of them would be found exactly 

 to agree. This uncertainty arises necessarily from the 

 rapid changes which the clouds undergo, as well as the 

 endless variety of forms which they assume, circum- 

 stances which seem to preclude the possibility of any 

 thing like classification, or accurate description. An 

 attempt, however, to supply this desideratum, was 

 Howard's made a few years ago by Mr. Howard, a philosopher 

 nomencla- to whose ingenuity and researches the science of me- 

 teor lSy i not a l' tl ' e indebted ; and though his sys- 

 tem has been pronounced fanciful, which is perhaps to 

 a certain extent true, it is even in its present state 

 highly deserving the attention of meteorologists, and 

 will in all probability sooner or later become the stand- 

 ard nomenclature of the clouds. As this part of our 

 subject is designed to be strictly popular, we shall ab- 

 stain at present from saying any thing on the origin 

 and formation of clouds, and simply state the charac- 

 ters by which they are distinguished and described in 

 the system referred to. 



Mr. Howard defines a cloud, a visible aggregate of 

 minute drops of water suspended in the atmosphere, 

 and includes in this definition every such aggregate, 

 whatever be its position relatively to the observer. Of 

 course he comprehends under the term cloud, what 

 are commonly called misls or fogs, because at a greater 

 distance or elevation they are found to assume all the 

 appearance, as they possess, according to his defini- 

 tion, all the qualities of clouds. He then proceeds to 

 define the various forms and modifications of clouds, 

 which he arranges under the seven following classes. 



1. Cirrus. A cloud resembling a lock of hair, or a 

 feather. Parallel flexuous, or diverging fibres, unli- 

 mited in the direction of their increase. 



2. Cumulus. A cloud which increases from above 

 in dense, convex, or conical heaps. 



3. Stratus. An extended, continuous, level sheet 

 of cloud, increasing from beneath. 



These three, Mr. Howard denominates simple and 

 distinct modifications, constituting, as will immediate- 

 ly appear, the elements of every other variety. The 

 two next are of what he calls an intermediate na- 

 ture. 



4. Cirro-cumulus. A connected system of small 

 roundish clouds, placed in close order, or contact. 



5. Cirro-stratus.* A horizontal, or slightly inclined 

 sheet, attenuated at its circumference, concave down- 

 ward, or undulated. Groups or patches having these 

 characters. 



Lastly, says Mr. Howard, there are two modifica- 

 tions, which exhibit a compound structure, viz. 



6. Cumulo-stratus. A cloud in which the structure 

 of the cumulus is mixed with that of the cirro-stratus, 



General 

 definition. 



Classes. 



Cirrus. 



Cumulus. 



Stratus. 



Cirro-cu- 

 mulus. 



Cirro- 



Cumulo- 

 tlratuy. 



or cirro-cumulus. The cumulus flattened at top, and Metcoroie. 

 overhanging its base. gy. 



7. Nimbus. A dense cloud, spreading out into a S 7" : v ' 

 crown of cirrus, and passing beneath into a shower. 



We have given these definitions in Mr. Howard's uis.Vr" 1 

 own language, but our limits will afford room only for nimbus. 

 a very condensed abridgment of his illustrations, and 

 we refer our readers to the treatise itself, published in 

 Tilloch's Philosophical Magazine, or Nicholson's Jour- 

 nal, vol. xxx. p. 35. 



The Cirrus, he observes, is always the least dense, Indications 

 and generally the most elevated modification of clouds, of the "r- 

 sometimes covering the whole face of the sky with a rus- 

 thin transparent veil, and at other times forming itself 

 into distinct groups of parallel threads, or flexuous fi. 

 bres. Its height, according to Mr. Dalton, is from 

 three to five miles above the earth's surface. It is ge- 

 nerally found to be an indication of wind. When 

 formed into horizontal sheets, witli streamers pointing 

 upwards, it indicates approaching rain ; with depend- 

 ing fringe-like -fibres, it is found to precede fair wea- 

 ther. 



The cumulus is. generally of dense structure, ap- of the 

 pearing after a clear morning, increasing from above, cumulus. 

 where its surface is convex, and forming, at its greatest 

 magnitude, a pile of irregular hemispherical cloud. 

 This takes place early in the afternoon, about the time 

 of the greatest heat, and gradually diminishes towards 

 evening, when it disappears. In this case it is an in 

 dication of fine weather. 



The stratus is of moderate density, and compre- Of the 

 hends those creeping mists which rise from valleys and stratus, 

 lakes in calm evenings. It frequently disappears in 

 the morning, and is then an indication of the finest 

 weather. 



The cirro-cumulus appears to be formed by the de- Of the cir- 

 scent of the cirrus, the oblique denser tufts of the lat- ro-cumu- 

 ter changing into the spheroidal form, when the cloud '". 

 assumes the appearance of a ball of flax with one end 

 left unwound or flying out. The cirro-cumulus some- 

 times consists of distinct beds, floating at different al- 

 titudes, the clouds appearing smaller and smaller, till 

 they are lost in the blue expanse. It is most frequent 

 in summer, and, when permanent, affords one of the 

 surest indications of increasing temperature, and fine 

 weather. 



The cirro-stratus assumes various appearances, from of ihe cir- 

 its being frequently connected with other modifica- ro-stratiis. 

 tions. By itself it is always an attenuated sheet, or 

 patch, of an uniform hazy continuity when viewed 

 over head, and of great apparent density towards the 

 horizon. In this state it gives rise to the phenomena 

 of halos, mock suns, &c. and indicates depression of 

 temperature, wind, and rain. When it alternates with 

 cirro-cumulus, the prognostic is doubtful. It is fre- 

 quently seen resting on the summit of high hills, and 

 in this state has been long regarded as foreboding rainy 

 weather. 



The cumulo-stratus is that fleecy cloud which is some- Of the cu- 

 times observed to settle on the summit of a cumulus, mulo-stra- 

 while the latter is increasing from beneath. It usually ". 

 prevails in the completely overcast sky, and apparent- 

 ly without any regard to temperature, as it is found to 

 precede either a fall of snow or a thunder-storm. Be- 

 fore the latter, it is frequently to be seen in different 

 points of the horizon, rapidly swelling to a great mag- 

 nitude. Its indication is doubtful, and must be deter- 

 mined by the prevalence of the other modifications that 

 accompany it. or the nim- 



The nimbus generally appears in the form of a dense bus. 





