MECHANICAL ACTION OF GLACIERS. 151 
fired at a target out at sea; and the same thing may be 
seen in the effects of the wind striking the surface of the 
water in a river, in a lake, or in the sea, for rarely, if ever, 
does it blow horizontally or parallel to the surface of the 
water, 
In another volume, entitled Forests and Moisture,* I 
have had occasion to refer to another and different pheno- 
menon occasioned in the same way. It is of frequent 
occurrence at the Cape of Good Hope, and in local phrase 
is spoken of as the Devil’s Table-Cloth on Table Mountain. 
At these times the summit of the mountain is covered 
with a dense mass of beautiful white fleecy cloud in con- 
stant flow over the precipice, and pouring down the almost 
vertical front of the mountain facing Table Bay as if 
threatening to bury in an avalanche the capital of the 
colony at its base; but long ere it reaches the town, not- 
withstanding the continuous flow, it stops; to that line it 
flows on continuously, but beyond it not; there the cloud, 
in unceasing flow, terminates, the spectator sees not why. 
The beautiful and interesting phenomenon is occasioned 
by a south-east wind, which up to the Table Mountain 
range, was undimmed. The wind was strong, but the sky 
blue and serene, though the wind was loaded with vapour 
—vapour dissolved and invisible. 
But, passing over Table Mountain, the elevation of this 
is such that the decrease of temperature, consequent on 
expansion under diminished pressure, bringing this below 
the dew-point, the moisture is deposited by the air in the 
form of a cloud, which, as it reaches, at a lower level to lee- 
ward, a locality with a higher temperature, the moisture is 
* Forests and Moisture ; or, Effects of Forests on Humidity of Climate. In which 
are given details of phenomena of vegetation on which the meteorological effects of 
forests affecting the humidity of climate depend, —of the effects of forests on the humi- 
dity of the atmosphere, on the humidity of the ground, on marshes, on the moisture of 
a wide expanse of country, on the local rainfall, and on rivers,—and of the correspon- 
dence between the distribution of the rainfall and of forests,—the measure of corres- 
pondence between the rainfall and that of forests,—the distribution of the rainfall 
dependent. on geographical position determined by the contour of a country,—the dis- 
tribution of forests affected by the distribution of the rainfall,—and the local effects of 
forests on the distribution of the rainfall within the forest district.—Edinburgh : Oliver 
and Boyd. London: Simpkin, Marshall, & Co. 1877. 
