170. 



The earth* a, is completely 

 surrounded by a transparent 

 body formed of gases and vapours, 

 to the varying conditions of 

 which we owe calms and storms, 

 gloomy days and open sunshine, 

 the changes in the intensity and 

 colours of light, the conveyance 

 of a considerable amount of 

 heat or cold, drought or moisture, 

 from one part of the globe to 

 another, and, to a great extent, 

 the remarkable phenomena of 

 mow, hail, sleet, mist, rain, dew, 



* The size of the eaith in the illustration bears no 

 proportion to the volume of the atmosphere. It must 

 1, " remembered that the diameter of the earth is nearly 

 8000 miles, while the depth of the atmosphere is only 45 

 miles. 



clouds, etc. Clouds are con. 

 stantly forming, floating, and 

 dispersing in the atmosphere, b. 

 There are four primary forms — ' 

 the cirrus c, stratus D, cumulus 

 E, ai^d nimbus E. The cirrus, 

 or curl cloud, flies at the great- 

 est altitude ; the cumulus, or 

 pile cloud next ; the stratus, or 

 streak cloud, next; while the 

 nimbus, or storm cloud, fre- 

 quently rolls like a dark curtain 

 along the surface of the earth. 

 When two or three forms of 

 cloud unite, they take a coin- 

 pound name, according to their 

 characteristics ; thus, o and b 



