80 



NATURE FOR ITS OWN SAKE 



velocity. In afternoon showers it resembles the 

 cumulus ; in driving storms it lies lower to the 

 earth, moves in great, rolling puffs, or flattens 

 out into thin, fast-flying sheets with ragged edges 

 and long, projecting arms like antennae. At 

 times, when a storm is prolonged for days, the 

 forms of the clouds are hardly discernible ; the 

 masses are lying low in the air and spread from 

 one to another with such close connection that 

 they look like one vast stretch of gray across 

 the sky. In thunder-storms these clouds often 

 bank up dark and threatening in the form of 

 an advance-guard. They move forward quite 

 rapidly and carry with them a rushing wind. 

 The first-comers are always the darkest-looking 

 and most violent of the storm, yet they give 

 forth neither lightning nor rain. They seem 

 to be only wind-makers, though it is common 

 knowledge that clouds are not makers of wind, 

 but merely manifestations of wind existent. 

 The gray clouds behind the dark advance-guard 

 are the ones that carry the rain. In tornadoes 

 the darker ones often twist, writhe, and roll 

 over one another as though pulled by a violent 

 under-current of wind ; in cyclones the move- 

 ment is similar, but from an opposite cause. 

 In the latter case the pull is likely to change 



