240 THE WEATHER 



"feather." These clouds are distinguished by the distinct lines that 

 make them up. The lines may be arranged in many strange forms, 

 such as plumes, hazy streaks, etc. Cirrus clouds are the highest 

 clouds; they are often above five miles high, and consist of minute 

 particles of ice or snow. One arrangement of cirrus clouds is called a 

 "mackerel sky." 



(3) Stratus clouds; these are so called because they occur in layers 

 (cf. 286). Stratus clouds are lower than the other two; usually from 

 half a mile to three miles high. 



(4) Nimbus clouds, so called from nimbus, "a veil." These clouds 

 are cumulus or stratus clouds that are depositing rain or snow. 



270. Rain and Snow. -When the particles of water 

 mist that make up a cloud gather together into drops, 

 they fall into the air below the cloud. If this air is nearly 

 saturated, the drops continue falling until they reach the 

 earth as rain. If the conditions necessary for the forma- 

 tion of raindrops occur below C., snowflakes will be 

 formed (cf. .95, Fig. 76). 



Cloudbursts. If the ascending currents of moist air are very strong, 

 as in thunderstorms and tornadoes (cf. 277 and 278), an enormous 

 quantity of water may be accumulated in the cloud. When this falls, 

 the rain is called a cloudburst. 



271. Hail. Hail is made up of pellets or "stones" of 

 ice and snow in alternate layers. Hailstones probably 

 begin in the freezing of raindrops at lower levels. These 

 are carried upward by ascending currents, are dropped 

 downward, and are then carried upward again ; this treat- 

 ment is repeated many times. Thus the hailstones take 

 on layer after layer of covering, until they become too 

 heavy to be supported longer, and fall to the ground. 

 Hail does a great deal of damage, not only to window 

 panes, but also to fruit trees and crops. 



