Plate 43.
SMALL CUMULUS.
(Cumulus Minor.)
After the foregoing explanation, it is easy to see why at a given time the floating cloudlets should have a common base level. This is the height to which the air must attain before reaching its saturation temperature. Each cloudlet marks an uprising current, and the intervals show the position of the counterbalancing descending streams.
A larger variety is shown in Plate [44]. In this the level base and generally pyramidal shape is shown, and also the hard, rounded upper surface. The thickness of this cloud was about 500 metres. When clouds like these are visible, they may be the beginning of larger ones, and the only way to judge whether they are likely to develop into rain- or shower-clouds is to watch them. If they are seen to be growing larger, and particularly if detached fragments are developing into clouds, further growth is almost certain, and rain is probable.
Plate 44.
CUMULUS.
