IM'3 



EOROLOQY. 



[TOT CLOCDS. 



lititlion Mwem Cloud* and the II". -''. r.- I 1 . 

 are in the habit of narrowly studying the phen. 



ii li, are enabled to draw con. : :tuli accu- 



racy respecting tin- coming weather. Thus cirro cumuli 

 are for ttie most part indicative of serene, fair weather ; the 



ilence of wind subsequently to the appearance of 

 much-extended aiid higMjr-Ooloimd stratus cloud* if a 

 nee, Theappearaneeot minims 

 i-. proclaim -itofr.iiii ; :md thocirrosti 



Betimes ooli ky as with a veil, all well- 



<1. lined form being absent, is uliiiu.it a sure forerunner of 

 bad weather. 



.lyxiritioM of CUntds. That clouds are composed nf 



water in some condition does not require to be demon- 



strat' .me ox]il:uiution must be given of tlio cir- 



blin,' water, ,-i material so much heavier 



than atmospheric uir, to remain suspended frequently in 



elevated rejjions, where the atmosphere, thin though 

 it lie on the earth's surface, is still more attenuavd. 

 This is a matter which, it must be confessed, is still \ 

 in conoid.- irity ; but, perhaps, the most rational 



explanation of cloud formation is the following : Fi: 

 aqueous vapour is diffused, or rather absorbed, iuv! 

 throughout the air. The laws of the absorption or dif- 

 fusion are perfectly well known. The amount differs, as 

 w- have already seen, for clill'erent temperatures, I 

 proportionate to the temperature. Assuming, then, thai 

 tin- upper regions of the atmosphere at any time are 



ited witli u'niospheric moisture in its invisible 

 dition, let us no.v contemplato the effect of cooling that 

 atmosphere liy any cause. It is not difficult to furnish 



numeron 



varied such as sudden variations of electric condition, 

 sudden variations ill the direction of winds. Jf, then, from 

 any cause, the atmosphere is cooled below its capaci' 

 holding vapour in the invisible form, aqu .ition 



occurs. If this deposition take place on the earth's snr- 



f lie result is dew ; if aloft iii the air, we have a cloud. 

 Thus far the steps of each succeeding change, are 



ut ; but the remaining points of cloud-formation 



are more obscure, the c;rciim*tances of chief difficulty 



nd an explanation of the aerial permanence of 



.. seeing that the material of which they 

 are composed is so much heavier than air. Fro- 

 balily the most consistent explanation is this: 

 Atmospheric moisture, when it changes from the 

 invisible to the visible form, a- physical I- 



cnnditinn of spheroids or vehicles in 

 of water, in point of fact, each bubble lilled with 

 If these vesicles be exposed to the sun's rays, it is 

 ut, from consideration of known laws, that 

 they must become specifically lighter than the 



Hiding medium ; and thus atlected, they 

 would float, for t: i~on that a 



. ;ulst it is yet warm, notwithstanding that 

 tlie air, which it. contains, is heavier than the 



unrounding re, \Ve. w.em, th'-n 



U) account for the up) 



of cloud st; ution noiv to 



the lo.\cr part i.;~ s rational to 



that the vesicles of which they are d.' 

 should descend. 1'i-obahly : : continuing 



descent until b] in contact with an 



atmosphere siillieiently warm to dissolve their aqu 

 n vert their water once more into the \. 

 r invisilile form. Thus it may lie, and most probably 

 i, that a cloud, which loo !. ut to thee;, 



exposed to the continued operation of resolution and re 

 formation: or, rather, that the ' .which 



are hero spoken of as producing active chan 



Ivi-x, and give rise to a condition of equip 

 Althoii : ;h it has hitherto been taken for granted that. 

 clouds ar. : unfrozen water, we know that such 



!y the case. If t , ;,. 



1 sink to freezing poii F. T its coi; 



w is the result Many philos. 

 more especially Kaemtz, arc of opinion 



the cirrus the cloud which soars in th- hi-hest i 



frequently at an elevation not less than 30, 000 feet above 



the earth's surface consists of particles of snow or ice. 

 Assuming this to betho case, it is not easy to advance the 

 such molecules remaining aloft in a medium so 

 sated as is atmospheric air in a position so 

 /'o.tifion of Clovdt It in somewhat remarkable, that 

 every known form of cloud a < the 



horizontal position. Vertical clou 1, and, 



if we choose to except water-spouts, not rccogn; 

 them as cloud.-.. . ry unknown. Tim 



horizontality of cloiiiU, warrants their being a pole. 

 as composed of strata i t are 



very well delined. MM. I 1 Hotlard have care- 



fully examined the thickness of tlie>. u the 



1'vienees, and have found their nvera n to lieho- 



D the limits of S.41K) and l.i Mr. (Ilai- 



fcher, during his lial!i.<.n 



through clouds of about 8,000 feet thickness. In the 

 fifth chapter of this section, the/ reader will find the 



ttions of that meteorologist fully detailed. 

 ll'iijlit <>f Clmiil.i. Several meteorologists, amongst 

 whom liiccioli, \Vrede, Kaeintz, and Ara^'o must lie par- 

 ticularly mentioned, have set them ^ ! ie. task of 

 u-ring tilt; height of clouds. 'J 1 



lions were made have been various. 

 Kiccioli determined their height by placing two 

 a certain and known distance apart; \\redo by makin ; 

 use of their shadows, and then reducing the coi 



ight to the solution of a jiroblem in trigonous 

 -:i stated t!ie maximum height of clouds to 

 ' feet ; and Lambert gave their minimum hei_ht 

 at 13,000: whilst their ma.\imnni height, accordir 

 the same, is from I:.,II:M) to 20,00* ) 



when he acquired in his balloon an elevation of 21, (in > 

 perceived small clouds floating much above him. 

 Kaenitx believed that the usual range of cumulus runs 

 from o.OOO to 10,000 feet; of cirrus, from 10,0<> 

 24,000 feet ; of nimbus, or thunder-cloud, between 1 

 and 5,000 feet. That very accurate physicist, 1'ouillet, 

 as the lesult of certain experiments perlormcd in 1 

 states that he has proved the e- : clouds a; 



:ion from about 22,300 to 38,000 feet : and .Mr. 

 Olaishcr, in 16ii'J-'t;.; i them at those heights. 



. the elevation of clouds, we may arrive at the 

 I, that cirrus does not descend below 2,000 or 

 8 000 feet ; whilst nimbus occasionally descends so low 

 ..roaches the earth within a few hundred feet 

 of surface. The maximum mean elevation of clouds 

 ; to be in low latitudes, evidently on account, of the 



aeity of the atmosphere to absorb and di 

 us vapour. It should here be remarked thai 

 :;on of a cloud cannot bo determined by reference 

 to its apparent place in the sky ; and, except the distance 

 ,er can its actual size. These remarks 

 by the ab. 



the same cloud will be Man, at different tune*, under 



different angles by the sai .bs.-rvcr, :w reference to 



agiea i. BO and liKD ,!! testify, whence the 



height would ditler for two 



