192 EFFECTS OF FOEEST TEGETATION ON CLIMATE. 



Humboldt's account of the lake was that its waters were 

 lessening, so that beautiful plantations of bananas and sugar- 

 canes had taken the place of water — in some way like the change 

 that has occasionally altered the condition of Lake George in 

 this Colony. 



This falling off was occasioned by the felling of timber, occasion- 

 ing a deficiency of water in the rivers. Twenty-five years 

 afterwards, Boussingault visited the lake and found its dimensions 

 increasing, owing to the War of Independence having occasioned 

 a cessation of clearings, so that less timber was being cut down, 

 and rain fell in greater abundance than before. 



That this is the true explanation was shown by other lakes in 

 the neighbourhood, which had undergone no change of level, the 

 timber on the surrounding mountains having remained in the 

 state of nature. 



The lakes of Neufchatel, Bienne, Morat, and Geneva have been 

 mentioned as examples of similar diminution by Humboldt and 

 Saussure ; and Gasparin has shown that during the last century 

 the annual amount of rain was stationary at Paris, Milan, and 

 other places, leaving the inference that the clearing of forest 

 country had produced greater evaporation. 



The island of Ascension is next quoted as confirmatory ; for 

 the only spring existing in the island was dried up by the removal 

 of the trees, and on the restoration of the timber the lost water 

 returned. 



This conclusion was, however, disputed by Boussingault, who 

 contended that the trees impeded evaporation, because the island 

 is too small to afi'ect the rainfall. But Daubeny says, " It is 

 enough for our purpose to substantiate the fact that by the 

 removal of forests we have it in our power to modify the character 

 of the country with respect to humidity, whether this be brought 

 about in one way or the other ; of which fact I apprehend there 

 is abundance of proof." 



To the instance of Ascension Island I would add that of St. 

 Helena, which in 1506 was discovered to be entirely covered with 

 forests, but when Dr. Hooker visited it a few years since he 

 found five-sixths of the island barren, and the remainder occupied 

 almost entirely by trees, shrubs, and other plants introduced from 

 Euroj)e, Africa, America, and Australia. The destruction in this 

 case was by goats, and by the inroad of the new vegetation, 

 supplanting the young shoots of native trees. In the days of its 

 first occupation abundance of springs were found to rise from 

 the hilly igneous rocks of the interior. But the country had 

 become dry, and in some places waterless. In 184:8, according to 



