10(3 



KNOWLEDGE 



[May, 1902. 



Intoiuational Cloud Atlas ... C'liniuliis 



Meteorological Oflico Book 

 U. S. Hvdrograpliic Atlas ... „ 



(2) Rain Cumulus, of which thort? are two sul)- 

 varietics : — 



(d) Shower-cumulus (Fig. 1), when rain falls from 

 the cloud without increment of wind. The edges 

 of this cloud are not cirrus-topped. 

 (h) Squall-cunuilus. when the rain is accompanied hy 

 wind (Fig. 2 and Plate I.), or by wind with hail 

 and snow falling from this cloud. 



Clement Ley ... Cumulo-Nimbus 

 I. C. A. ..." 



M. O. B 



U. S. H. 0. A. ... 

 In these cases the Cumulus cloud is generally 

 much serrated, having a cirriform edging. In 

 some cases this cirriform edging extends far over 

 the sky and forms halos, particularly at the 

 rear. 

 Two rarer varieties of Cumulus are : — 

 PiUar-cumiihis (Plate II.) generally noticed over the 

 calm belts of the ocean, and distinguishable by its slender 

 forms, which rise to great altitudes. 



Fio. 4. — Cumulus 



1 (!■) 



SO blown along by the wind as to assume the roll forma- 

 tion from which it is named. 



Clement Lev 



LC. A. ...' 



M. B Roll-cumulus 



U. S. H. 0. A Strato-cumulus 



RoU-cumuhis generally accom])anies strong winds, par- 

 ticularly polar west winds, which succeed cyclonic 

 disturbances. Here we have the ordinary Cumulus cloud 



A still rarer form of Cumulus ajDpears in scattered 

 patches over the sky, and is indicative of an electrical state 

 of the atmosphere. 



Cumulus clouds form at a low altitude, but they fre- 

 quently tower upwards to great heights. 



It should be noticed that in these clouds the fine 

 weather form is of soft smooth outline, and has a quiet 

 appearance. In Fig. 1 (a form which indicates rain) there 

 is a harder and more solid appearance, which is still more 

 accentuated in the Squall-cumulus form of cloud. 



Figs. 3 and 4 show i-espectively a horizontal and vertical 

 view of a Cumulus which, later in the day, developed 

 showers. 



Stratus Clouds may be divided into four varieties as 

 follows : — 



(1) Fog (Fig. 5), so well known as not to need 

 description. It is, in fact, a Stratus cloud resting on the 

 earth's surface. 



Clement Ley ... ... ... Nebula 



I. C. A 



M. 6. B. '.'.". '.'.'. ... ... Fot; 



U. S. H. O. A '^ 



(2.) Stratus (Fig. 6), a cloud sheet which covers the 

 whole sky at a moderate elevation. Here and there the 

 cloud is thin, and under surfaces appear as parallel lines 

 all round the horizon. This is the characteristic cloud of 

 anti-cyclonic, or dry fine weather conditions. It may con- 

 tinue to cover the sky for several days in succession. 



Stratus Quietus 

 Strato-cumulus 

 Stratus 

 Stratus 

 all the varying forms of 



Clement Ley 



LC. A 



M. O. B 



U. S. H. 0. A. ... 



(3) HiyJi Stratus, including 

 Cirro-cumulus from the mackerel skies (Fig. 7) to the 

 Cirro-macula (Fig. 8) of Clement Ley. Many beautiful 

 varieties of this cloud of minute cumuliform appearance are 

 caused by the changes taking place in the atmosphere. We 

 notice waves, wavelets, stipplings, and flecks. To it are 

 due the corouae sometimes seen round the svm, as also 

 iridescent clouds occasionally noticed in the same vicinity. 

 The wave-like appearance of the clouds is due to the 



