135 



much, richer in Ozone than the air of open countries, and especially of 

 towns. Prof. Schlich sums up as follows : — 



(1) Forests supply timber, fuel and other forest produce. 



(2) They offer a convenient opportunity for the investment of 



capital and for enterprise. 



(3) They produce a demand for labour in their management and 



working, as well as in a variety of industries which depend 

 on forests for their raw material. 



(4) They reduce the temperature of the air and soil to a moderate 



extent, and render the climate more equable. 



(5) They increase the relative humidity of the air and tend to 



reduce evaporation. 



(6) They tend to increase the rainfall. 



(7) They help to regulate the water supply, secure a more sus- 



tained feeding of springs, tend to reduce violent floods, and 

 render the flow of water in rivers more continuous. 



(8) They assist in preventing landslips, and silting up of rivers 



and low-lands, and arrest moving sands. 



(9) They reduce the velocity of air currents, protect adjoining 



fields against cold or dry winds, and afford shelter to cat- 

 tle, &c. 



(10) They assist in the production of Oxygen and Ozone." 



Dr. J. Croumbie Brown in his volume on Forests and Moisture cites 

 several cases in which the destruction of trees had been followed by 

 desiccation ; and the planting of trees has been followed by the restor- 

 ation of humidity. In speaking of Mauritius he says : — 



In a history of that Island, embodied my informant believes in 

 Thorton's History of India, the author observes that when we obtained 

 possession of it our countrymen thought it absurd that the beautiful 

 land on the summits and slopes of the mountains should be abandoned 

 to forests and jungle, and so cut them down, upon which the water 

 supply began to fail. Eeflection soon taught the authorities the 

 cause of this failure ; upon which the hills were again planted with, 

 trees, and the rivers and streams resumed their former dimensions. 



Mr. Marsh writes : — " The Island of Mauritius lying in the Indian 

 Ocean is about 20° N*. L., is less than 40 miles long by about thirty in 

 breadth. Its surface is very irregular, and though it consists, to a 

 considerable extent, of a plateau from 1,200 to 1,500 feet high, there 

 are three mountain peaks ranging froni 2,300 to 2,700 feet in height. 

 Hence, though the general climatic influences are everywhere sub- 

 stantially the same, there is room for a great variety of exposures 

 and of other purely local conditions. It is said that the difference of 

 temperature between the highest and lowest stations does not exceed 

 eight degrees F., while, according to observations at thirty-five 

 stations, the rainfall in 1872 varied from thirty-three inches at Grros 

 Cailloux to one hundred and forty-six inches at Cluny. Nature, 

 September 2 If, 1874- This enormous difference in measurement is too 

 great to be explained by possible errors of observation or other acci- 

 dental circumstances, and we must suppose there are, in different parts 

 of this small island, great differences in the actual precipitation, but 

 still much of this variation must be due to causes whose range of in- 

 fluence is extremely limited." 



