Climate of South Africa. 249 
temperature in atmospheric columns, and uniformity of hygro- 
metric condition of atmospheric strata. The column of air has 
a different degree of heat, according to local circumstances, and 
particularly the radiating influence of the base from which it 
rises. Humidity, as it diffuses itself, tends to the same altitude 
for equal degrees of moisture. Vapour, then, is manifested 
wherever an atmospheric stratum, containing the proportion of 
moisture, condensible by a certain temperature, is intersected 
by a column of air which has that temperature at the elevation 
of the stratum. 
Clouds at rest, while the wind is blowing with violence, are 
frequently to be seen over False-Bay, and likewise over the 
isthmus, or Cape-downs, precisely similar to clouds suspended 
over peaks. Generally, during a south-east wind, the sky is 
clear between Hanglip and Table-Mountain. But now and 
then a small silvery cloud suddenly appears above the sea, or 
the shore, grows, changes shape, without change of place, 
(though the wind meantime continues to blow most violently,) 
wastes, and vanishes. The phenomenon is singularly beautiful, 
when the tints of the setting sun play on the evanescent clouds. 
It often arrested and riveted my attention. 1 have observed it 
when the cloud has been low, and at no great distance from the 
spot where I stood, and I could distinctly perceive the fleeting 
nature of it. 
By analogy with these, and with clouds at rest above moun- 
tains, 1 conclude that the fibrous and fleecy clouds, which are 
highest in the sky, are as changeable in substance as persistent 
in place. It is remarked that the mare’s-tail and macherel-backed 
sky (as they are familiarly named), and other less noted modifi- 
cations of cérrhus and cirrhostratus, which occupy the most ele~ 
vated position. in the sky, alter their shape continually, and 
exhibit much internal commotion, every speck seeming to be 
agitated and every part undergoing transformation, while the 
mass or aggregate scarcely changes places. This agrees with 
observed facts concerning the mountain-cloud, the table-cloth 
of South Africa. And detached clouds at rest, near mountains, 
or over them, have likewise the characteristic appearance of 
