60 TRANSACTIONS OF THE ILLINOIS 



angles to the course of the clouds, do not attract rain. Witness the phe- 

 nomena seen day after day at Denver, Colorado. There the storms, 

 which organize upon the mountains to the west, pour rain until the clouds 

 float over the valley, then hold up, and frequently not a drop will fall at 

 Denver ; but by the time the clouds have nearly reached the high ridge 

 (Mera) east of Denver, they begin to pour rain as hard as ever. Why do 

 not the storms approaching the trough of the South Platte act as those 

 approaching the trough of the Mississippi do? The timberless Platte valley 

 and the timbered Mississippi valley furnish the answer. 



Common observation shows that the summer local rains follow timber 

 belts when the belts depart but little from their course, and pouring and 

 depositing increased rain-fall when the belts lay across the storm's course. 

 People who observe see these things, and they conclude, most rationally, 

 that forests do have an influence upon rain-fall, so it is no wonder this 

 has become the popular belief. We have seen it on many a summer day, 

 and many a prairie farmer has felt keenly in sympathy with his parching 

 crops, while he has watched the coveted showers fondly cling to the groves 

 or belts of timber, passing first to the right and then to the left, leaving 

 his fields dry, until a more general storm, perhaps a cyclonic tornado, has 

 given him not only rain but a deluge. 



Unfortunately we have not the data of observations from properly 

 selected points over the whole country, and extending over a long period 

 sufficient to base calculations as to the general rain-fall upon. The frag- 

 mentary observations, adduced as proof, have no value as such except for 

 the points where made, and it happens that those points are just the ones 

 where a lack of rain-fall would not be likely to occur, even though the 

 general rain-fall should decrease. But ocean is just as large as ever, and 

 if we should make a desert of half our land the evaporation of ocean must 

 be deposited somewhere, and thus decreased rain-fall over one area means 

 increased rain-fall over other areas. 



I believe a fair, unprejudiced consideration of all the facts and phe- 

 nomena now known will warrant the belief that the forest denudation in 

 parts of the United States has already affected rain-fall, while it has 

 affected both surface and subterranean water distribution much more ; but 

 yet there is in the interest of science, as well as in the interest of economy, 

 on urgent call for better, more perfect data from which to deduce a knowl- 

 edge of this subject. 



Mr. Riley — I agree with Mr. McAfee in some points. He cites 

 some facts that would lead us to suppose that the coming down of the 

 clouds is more the effect of forests than of any thing else. I could cite 



