252 ILLINOIS STATE HORTICULTURAL SOCIETY. 



Again, elevation above the sea is an important factor in determining the annual 

 amount of rainfall. More rain falls on the summits of mountains 2,000 or 3,000 feet 

 in height than at the base. From April to September, on the southern slope of the 

 Himalaya Mountains, there was a fall of 610 inches, more than 50 feet. At Vera Cruz, 

 278 inches fell in one year; in Oregon, 90 inches; in Western Europe, 40 inches; in 

 Central Europe, 20 inches; in Russia, 15 inches; in Northern Asia, less than 15 inches. 



It may be interesting to know the annual fall of rain in the various States of the 

 Union. For many of these facts I am largely indebted to Prof. Loomis. He says the 

 annual fall in Alabama and Louisiana is 56 inches; Oregon, 49; Florida, Virginia, the 

 Carolinas, Tennessee, Kentucky, 48; Georgia, 44; Arkansas and Missouri, 42; Mary- 

 land and Pennsylvania, 41 ; Ohio and New England, 40; New York, 37; Michigan 

 and Wisconsin, 32 ; Iowa and Kansas, 31; Texas, 29; California, 18; New Mexico, 

 13. From these data I have estimated the annual fall in Illinois and Indiana from 30 

 to 35 inches. 



Influence of Forests on Rainfall. — We have seen that the atmosphere by its currents 

 is the great distributor of rain. We have seen, also, that the annual fall is modified by 

 elevation, latitude, proximity to mountains, the course of the wind. There are other 

 causes, likewise, which have a tendency to increase or diminish the annual amount. 

 Whatever prevents the water from running off from the surface of the earth into the 

 rivers has the effect to increase the annual fall. The more the atmosphere is saturated 

 with vapor, the greater will be the deposition of rain. The dry atmosphere of the last 

 six months necessarily prevents rainfall. Hence forests, tall prairie grass, vegetable 

 mould, will increase the annual amount of rain. Remove the stately forests, cut close 

 the beautiful herbage that covers the land, turn the vegetable mould beneath the surface, 

 and you will find the annual amount of rain has been sensibly diminished. On the 

 other hand, plant forests of trees, let our valleys and our hill-sides be covered with tall 

 waving grass, and thereby the early and the later rains will appear. Hence in every 

 portion of the earth where there is a dearth of forests, of verdure, there you will find 

 barren wastes and trackless deserts. If a correct statement of the annual amount of 

 rain in Illinois could be given at the time when the Indian hunter pursued the panting 

 deer and "wooed his dusky mate," when the tall prairie grass "nodded" to every pass- 

 ing breeze, and the forests along our streams had never resounded to the echoes of the 

 woodman's axe, you would find, I think, the annual rain much greater than at present. 

 During the last seventy-five years there has been a gradual diminution of rainfall 

 throughout New England. As a proof this, brooks that were once broad and deep 

 have now dwindled to very insignificant streams. Many of these mountain rills and 

 brooks which, in my boyhood, were difficult to pass, can now be crossed at a single 

 bound. The same is true of many portions of New York and Pennsylvania. The 

 "oldest inhabitant" not unfrequently calls attention to the fact that the brooks are 

 drying up. 



The French as a nation seem to take the lead in almost everything. The influence 

 of forests on rainfall has been brought before the French Academy of Sciences and 

 warmly discussed. Becquerel held that forests increased the amount of rain, while 

 Marshal Valiant as confidently maintained the opposite ground. M. Mathieu, connected 

 with the School of Forestry, proposed to himself the following problem: "To deter- 

 mine the amount of rain-water received by the soil of two neighboring districts, one of 

 them covered with timber and the other arable land; and to find out whether, in conse- 

 quence of the covering of trees which intercepts the rain-water, the soil of the woodland 

 is as abundantly watered as that of the open." The conclusion was that the soil of the 

 woodland was more abundantly watered than the open country. 



M. Dausse says: Rain is formed when a warm and humid wind comes in contact 

 with a stratum of cold air; and since the air of forests is colder and more humid than that 

 of the open land rain must fall there in greater abundance. 



In 1874 a Frenchman performed an experiment twenty feet above a group of oaks 

 and hornbeams and in the adjacent open country, in order to ascertain the comparative 

 amount of rainfall and the degree of the saturation of the air. The following is the 

 summary of this experiment : For the month of February, the amount of rainfall to 

 that of ihe open country is in the ratio of i83^ to 18; March, 15 to w)^; Apiil, 27^ 



