XL. The Kinds of Clouds 



1. CIRRUS. Made of slender fibers, in long parallel lines or in 

 feathery, curled, tangled or clotted arrangements. Cirrus clouds 

 change slowly in form; do not appear to move as rapidly as do clouds 

 at lower levels, but as their altitude is commonly 5 to 10 miles above 

 sea-level, their actual velocities may be rapid, from 50 to 2OO miles 

 an hour. Usually drift eastward, but occasionally advance slowly to 

 the west in connection with storms. 



2. CIRRO-STRATUS. True cirrus clouds are sometimes associated 

 with other horizontal cloud layers, as if formed by the matting to- 

 gether of growing filaments. These layers frequently form bands of 

 great length, sometimes in parallel trains, straight or greatly curved; 

 they may reach all across the sky and seem to converge at nearly op- 

 posite points of the horizon, being then called polar bands or " Noah's 

 Ark." These bands are often more or less fibrous, striated, or rippled ; 

 they frequently show a tendency to break up into separate clots (Cirro- 

 cumulus). Cirrus haze is applied to a thin overcasting of the sky at 

 high levels, below which various other clouds float. Cirro-stratus and 

 haze produce halos around the sun and moon ; from this, and from their 

 great altitude, they are known to be composed of ice crystals and not 

 of water drops. Alto-stratus is low, heavy cirro-stratus. 



3. CIRRO-CUMULUS. The separate clots or cloud balls into which 

 lofty cloud layers often break up. They often closely resemble the 

 form taken by the foam in the eddying wake of a steamer. When 

 well-defined and closely grouped, they are called " Mackeral " clouds. 



4. CUMULUS. These are the familiar heavy white clouds of the 

 summer sky, flat-bottomed, and cushion-topped. The flat cumulus, 

 often grouped closely together so as nearly to overcast the sky and 

 common in fair, windy weather, is called strato-cumulus. Its still 

 lower ragged forms, often assumed during the early stages of cloud 

 growth and in storms, are called fracto-cumulus. Higher, smaller 

 forms are called alto-cumulus. 



5. CUMULO-NIMBUS. The large overgrown cumulus clouds that 

 have reached the dimensions of thunder storms, having above the 

 " thunder heads " an outflow of cirro-stratus. The under-surface of 

 these extended overflows is sometimes curiously festooned. 



6. STRATUS. Low-lying fogs, such as form at night or in cold quiet 

 winter weather on lowlands or in valleys; also low foggy cloud sheets 

 floating overhead. The name should not be applied to thin cloud sjheet 



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