UAISFALL AND COMMERCE AND POLITICS. i6i 



eerning the number of sheep which can be pastured per square mile 

 with different rainfalls.* 



Such investigations have not been made for the United States, but 

 the data indicate clearly the enormous variations in the food-supply, 

 both vegetable and animal, which attend variations in rainfall; and 

 they suggest how these variations must affect the producer, the trans- 

 porter, the merchant and the consumer. Hence it is easy to imagine 

 the great influence which variations in rainfall may have on com- 

 merce and through this on politics. 



The accompanying table gives the variations in the amount of rain- 

 fall in the Ohio Valley and in the Mississippi Valley which lie about 

 the center of the food-producing area in the United States and include 

 a large part of this area. The data are derived from tables prepared 

 by Professor A. J. Henr}^, of the United States Weather Bureau, and 

 published by the Bureau as Bulletin 'D,' entitled 'Eainfall of the 

 United States,' Washington, 1897. The average rainfall for each dis- 

 trict was made up from a number of stations in the district, the same 

 stations being used so far as the records would permit throughout the 

 period 1830 to 1896. The sharp, irregular fluctuations which charac- 

 terize the rainfall were toned down by Professor Henry by taking the 

 means of several successive years. This process is called 'smoothing' and 

 it renders more evident the long-period oscillations. The average rain- 

 fall for each district was obtained, and the departures of the rainfall 

 for each year from tins mean are given in the accompanying table. The 

 plus sign indicates that the rainfall for the given year was above the 

 mean, and the minus sign that it was below. The figures give the 

 amounts in inches and tenths of inches. The figures for the Mississippi 

 Valley from 1848 to 1857 are derived from the observations at one 

 station only.f 



The t-able also gives the departures from the mean value of the level 

 of the water in Lake Michigan. These data have been carefully col- 

 lected by the engineers on the lakes and were kindly furnished by 

 General John M. Wilson, Chief of Engineers, U. S. Army. The 

 figures show, in feet, the departures of the annual means from the gen- 

 eral average. The lake may be regarded as an enormous rain-gauge. 

 When the rainfall is in excess, the water level rises above the mean; but 



* These facts are largely derived from Hann's 'Climatology,' a standard 

 work on climate. (See Ward's English Translation.) 



t Professor Henry also gives the rainfall for New England. Although the 

 oscillations run roughly parallel to those in the interior valleys the data are not 

 reproduced here, ( 1 ) because Mr. E. B. Weston has shown that the early meas- 

 urements are probably deficient on account of the methods of measuring the 

 snowfall; (2) because New England has largely ceased to be an agricultural 

 region. 



VOL. LX. — 11. 



