130 Report S.A.A. Advancement of Science. 



of trees are constantly cooler than the surrounding air, and con- 

 dense at times enormous quantities of water vapour, which is returned 

 to the soil. It has been established by the experiments at Nancy that 

 the forest soil receives, at least in general, more water than the 

 adjoining land in spite of the screen of foliage* In the Cordillera, 

 at Bogota, clouds with rain falling from them can be seen hanging 

 over the forests, while near by, over ground which is covered with 

 shrubs, or is used for agriculture, the sky is blue and the sun is 

 shining. It appears, further, that this open country has been de- 

 forested, and that with the change in the covering of the soil the 

 climate has also changed to some extent. f 



Local showers may well be supposed to precipitate some of the 

 moisture evaporated from lake, swamp or forest, that is retained 

 in the neighbouring atmosphere. If this is true, then water storage 

 and extensive evaporation from forest areas should be credited with 

 at least a part of our local showei's. To any one who has seen clouds 

 gathering over a wooded mountain and fading away on the other side, 

 the question must have been suggested. What would happen if they 

 were bare mountains heated by the sun ? The history of such isolated 

 places as Madeira, St. Helena, Mauritius, etc., supplies the answer : for 

 in each case the destruction of forests has been followed by a decreased 

 watei'-supply. The amount of condensation from saturated clouds on 

 Table Mountain, which often presents a remarkable siglit wiien covered 

 with a white " table-cloth " of cloud, has been investigated by Prof. 

 Marloth. The observations consisted in comparing the contents of 

 two 5-inch range-gauges. One was left open in the usual way and tlie 

 other was surmounted with a framework 1 foot high, consisting of 

 four vertical wires and twenty reeds connected at their ends with 

 wire netting. Between the 21st December, 1902, and 1st January, 

 1903, the gauge with the i^eeds had collected 15-22 ins. and the 

 open gauge nothing. On the 11th January the open gauge was again 

 dry and the reed-gauge contained 14-64 ins. Between the 21st 

 December and 15th February tlie total amounts gauged were 4-97 

 and 79-84 ins. re.spectively. At the AVoodhead Reservoir (altitude 

 2496 ft.) during Januar}'^, 1904, the gaugings were 1-83 and 13- 73 ins., 

 and in January, 1905, were 1-45 and 15-86 ins. J Although it 

 may be open to some question whether these results give the actual 

 condensation that takes place in nature, or are partly due to the 

 mechanical interception of particles of water, they are believed to be 

 the first ever recorded, and prove beyond question the enormous 

 influence exercised on precipitation by mountains (•lf)thed with vege- 

 table yrowtli. 



* Econoinie Forest ir re, by (J. Huil'el, pp. l'2-2 if xcip 



t Die CorcUllere von BognUi, I'et. Mitt. 



X Experiment on Tahle Moiuitain for a-icertainlnfi tlie Amount of Moisture 

 deposited from the Soiith-East Clouds, by R. Marloth, Ph.U., M.A. Transnr- 

 tions of the South African PJiilosophicnl Snricttj, \t)I. \iv, pai-t 4, HK)3 ; aiul 

 vol. xvi, part 2, 19(>o. 



