PAPERS ON BIOLOGY AND AGRICULTURE 



187 



Examining the annual figures for precipitation only nine 

 or ten years out of the whole sixty-eight show marked vari- 

 ation from the normal. The years 1863, 1864. 1874, 1889, 

 1895 (possibly), 1897, 1899, 1901 (with a total annual pre- 

 cipitation of only 19.7 inches, which is phenomenally low in 

 a region where normally there is around 30 to 35 inches) 

 and 1910 are the ones with low annual precipitation. 



The statement has been made that "since 1885 the rain- 

 fall has decreased" in the Rock River watershed as, a 

 whole.* To test this for the northern part of Illinois the 

 figures for annual precipitation have been added for five 

 year periods both before and after 1885, the data furnishing 

 six of each, and the average annual precipitation for each 

 of such periods calculated. These data are as follows : 



Period 



1856—1860 

 1861—1865 

 1866—1870 

 1871—1875 

 1876—1880 

 1881—1885 



1886—1890 

 1891—1895 

 1896—1900 

 1901—1905 

 1906—1910 

 1911—1915 



Average Annual Precipitation Totals 

 35.9 inches 

 32.9 

 36.9 



29.7 214.4 inches 



41.1 

 37.9 



30.3 

 33.3 

 30.9 

 32.7 

 31.2 

 33.2 



191.5 inches 



22.9 inches 



This would indicate that there had, indeed, been a slight 

 decrease in the total annual precipitation since about 

 1885. But an examination of the figures for the separate 

 years shows that the year 1876, which falls, of course, 

 within the first period — that before 1885 — had a most 

 phenomenally high annual precipitation, a total for the 

 year of 72.8 inches. If the difference between this and an 



•Schwarz, G. F.: The diminished flow of the Rock River in Wisconsin and 

 niinois. U. S. DepU Agric. Bur. of For. Bui. 44, 1903, Page 8. 



