CLOUDS AND CLOUD FORMS 
69 
the winds. It is visible only where it clings 
to the lee-side of the peak, and it stretches 
out into the air as far as shelter is afforded it 
in the shape of along, thin flag. At a distance 
it looks as though it were something perma- 
nent, whereas it is only a continuous-forming 
cloud cut sharp on its sides by the keen edges 
of the wind. 
But these illustrations are of exceptional 
clouds, and even with them the rising currents 
alone are hardly sufficient to account for their 
being sustained in air. The majority of clouds 
are formed in open space and their air-currents 
have no mountain-sides to protect them. Nor 
are the common clouds subject to such violent 
destruction as the banner clouds. Moist currents 
are rising, clouds are forming and reforming, 
changing, sinking, disappearing ; but they are 
not often slashed into strips by the winds. We 
must seek a third cause for their being sus- 
tained in air, and it has been suggested already 
by the word “renewal.” Clouds after they are 
formed are practically self-renewing. When 
the ascending air-current condenses into cloud 
the heat of the air-current goes upward with a 
tendency to form newer and higher clouds as it 
rises ; but the moisture of the current, robbed 
Clouds 
Sormed in 
open space, 
Self-re- 
newal of 
clouds. 
