110 TRANSACTIONS OF THE ILLINOIS 



THURSDAY AFTERNOON. 



Music — Cornet duet, with piano accompaniment. 



DEOUTH AND TEEES. 

 BY PROF. T, J. BURRILL, CHAMPAIGN. 



Much has been written upon forests and rainfall, and much 

 more of observation and discussion upon the relations of these is 

 needed, but in the present paper, attention will only be given to some 

 studies upon the drouth itself and its relations to growing vegeta- 

 tion. 



In the first place let us ask: What is the cause, or what are the 

 causes of drouth? Upon such a question we are very apt to seek 

 for an answer close at hand, and to make explanations from very 

 slender data. Thus more than once has it been suggested during 

 the season in public prints, that drain-tile should be directly charged 

 with the deplorable condition into which man is forcing our rich 

 heritage of freighted air and fertile soil. The destruction of forests 

 is wider in its reach and older in its discussion; but before we confi- 

 dently settle upon any particular or specific cause of climatic change, 

 surely the actual changes which have been known to occur in the 

 past ought to be well studied. Tables are published in the twenty- 

 fourth volume of the Srnitlisonian Contrihutions to Knowledge, show- 

 ing the aqueous precipitation by months and years from 1820 to 

 1865, throughout the United States. These are compiled from the 

 records of a very large number of observers under instructions, and 

 equipped with reliable apparatus. 



Taking the region from Western Pennsylvania to Eastern Mis- 

 souri for illustration, and compiling the records of thirty-four ob- 

 servers, aggregating two hundred and forty-nine years, the average 

 rainfall is 40.88 inches. Using this as the mean, and computing the 

 percentages above and below, we find the amount of fluctuation is 

 really very great. One per cent, of forty inches is four-tenths of 

 an inch, and this means twelve thousand gallons of water per acre. 

 What must it be for the entire area? But when we observe that 

 the fluctuation is fifteen per cent, above the mean and alike amount 

 below, i. e., a variation from year to year of thirty per cent., we 

 shall have to reckon by millions of tons, and then probably fail to 

 appreciate the stupendous difference in the annual unloading of the 

 clouds over our favored and comparatively equitable land. There are, 

 however, other important lessons for us in the tables and figures. 

 From 1832 to 1837 there is an almost regular decrease in the annual 

 precipitation; then from 1837 to 1847 there is a still more regular 

 annual increase, reaching from fifteen per cent, below, to fifteen 



