80 
NATURE FOR ITS OWN SAKE 
Forms of 
the rain 
cloud, 
Storm 
clouds. 
velocity. In afternoon showers it resembles the 
cumulus; in driving storms it hes lower to the 
earth, moves in great, rolling putts, or flattens 
out into thin, fast-flying sheets with ragged edges 
and long, projecting arms like antenne. 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 
