48 EFFECTS OF FORESTS ON HUMIDITY. 



ation, and what has first to be established is the possible production 

 of clouds in a transparent sky. The case of a Bengal storm has been 

 cited ; but as evidence of the case in question it may be considered 

 insufficient, I therefore supplement it with more explicit testimony. 



At the Cape of Good Hope, again and again, I have seen the 

 heavens gather blackness where shortly before the sky was cloudless, 

 the first manifestation of a change being the appearance of clouds 

 the size of a man's hand, not blown thither, but there appearing as if 

 formed there, and the progress and completion of the change resemb- 

 ling somewhat the dissolving view represented by a magic lantern. The 

 clouds were neither blown thither bodily nor attracted, but were formed 

 there, apparently by an intermixture of currents of air of diflferent 

 temperatures. And again, the whole cloudland structure — bold in 

 its outline as the smoke belching forth from the cannon's mouth at 

 the moment of discharge, and magnificent as a realization of Fancy's 

 dream of Ossa piled on Pyleon, and Pyleon-like mountains on Ossa 

 again — passed away like the deposition of vapour breathed upon the 

 polished steel, passed away as if it had never been, leaving not a 

 wreck behind. And the corresponding phenomenon I have seen when 

 according to the local phrase, the Devil lays his table-cloth on Table 

 Mountain. To this I have already had occasion to refer. 



At these times the summit of the mountain is covered with a dense 

 mass of beautiful white fleecy cloud in constant 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, notwithstanding 

 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 cloud, which, as it reaches at 

 lower level to leeward, a locality with a higher temperature, the 

 moisture is again absorbed and the air loaded with it is again trans- 

 parent, as is all the air around, and as it was itself before passing 

 over Table Mouutwu in its course. 



