May, 1902.] 



KjN OWL EDGE. 



10< 



}>a86age of a more rapidly -moving air current over a slower 

 one, or of a wave curreut crossint; a luotiouless portion of 

 the air. When two air currents pass over one another at 

 an angle, the particles of clouds tend to fall into different 

 .shapes, hence our mackerel skies. But this cloud (Fig. 7 

 and Fig. 9), although beautiful, is essentially one of 

 warning,* uioi-e especially when the llet^'ks are of a thin, 

 scaly api>earance (resembling the scales of certain fishes 

 so closely that I have called it the scale cloud). Some- 

 times these detached flecks aj^pear in lines, and very 

 striking is the effect produced. 



Fig. 7 and Fig. ;», — C. L. .. .. Stratus Maculosus. 



I. C. A. ... Alto-cumulus. 



M. 0. B. ... Cirro-cumulus. 



TJ. S. H. O. A. Alto-cumulus. 



Fig. 8.-^C. L Cirro-macula. 



,, I. C. A. . . Cirro-cumulus. 



M. 0. B. 



U. S. H. 0. A. 



Fig. 6. — Stratus. 



(4) Cirrus. — The highest form of cloud and the most 

 important as a factor in the science of weather forecasting. 

 Cirrus, ordinarily, appears as wisi)S and feather pieces 

 scattered over the sky, and its significance is then of 

 no import (Fig. 10). 



Fig. lU — Clement Lev Cirrus. 



I.e. A. " , 



M. O. B 



U. S. H. 0. A 



When, however, this cloud takes the form of linos 

 parallel to the horizon, or of lines appearing to radiate as 

 wheel-spokes (Plate lU.) from any one part of the horizon, 

 it should be carefully noted as indicative of approaching 

 weather. Its movement and propagating transition should 

 be observed This cloud is composed of ice-dust or crvstals. 

 Plate III.— Clement Ley ... Cirro-filum. 



Fig. 11. — Clement Lev ... Cirro-velum. 



LC. A. " 



., M. 0. B. .. ... Cirro-stratus. 



U. S. H.O. A. 



^^'^len a cyclonic disturbance is about to pass over an 



observer. Cirrus generally appears first in parallel lines, or 



at a radiant (V) point (Plate III.) ; the threads gradually 



increase and interlace until a complete sheet of Cirro- 



• Fig. 9 preceded a heavy gale by about twelve hours. 



stratus covers the sky, causing a halo (Fig. 11). The 

 cloud further thickens, the halo disappears, all becomes 

 overcast, and rain comes on. The cloud is now known 

 as Nimbus, and after it has endured some time, the wind 



Fig. 7.— Mackerel Sky. 



shifts, the Nimbus clears off, and it is succeeded by a 

 Polar west wind, and the form of cloud shown in Fig. 2. 

 In addition to these forms of clouds, we may often 



Fig. 8.— High Stratus, Mackerel Sky. 



notice, particularly duiing high winds, fragments 

 hurrying across the sky. These are known as 



of clouds 



" scud" : 



