CHAPTER III 



RAINFALL AND THE CROPS 



"It is mere weather . . . doing and undoing without end." 



— William James. 



In the preceding chapter the course of annual rainfall 

 in the great cereal-producing area of the United States 

 has been shown to move in cycles: There is a ground- 

 swell of thirty-three years in length upon which cycles 

 of eight years in duration are superposed. Our object 

 in studying the rhythmic changes in the volume of rain- 

 fall was to bring these changes into relation with the 

 variations in the yield per acre of the crops, and in the 

 present chapter we shall be able to realize our purpose. 

 The actual course of the varying yield per acre of the 

 crops will be shown to have both a secular and a cyclical 

 movement; these two movements will be separated for 

 representative crops; and the cyclical movements will 

 be shown to be dependent upon the cyclical movements 

 in the weather represented by the cycles of rainfall. 



The Secular Trend in the Yield of the Crops 



The state of Illinois was chosen in the preceding 

 chapter to illustrate the general conditions of rainfall 

 in the Corn Belt of the Middle West, and we shall now 

 examine the statistics of the yield of its most important 

 crops. 



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