Rainfall and the Crops 43 



The critical periods for the other crops are, for oats- 

 May, June, July, r = .290; for hay March, April, 

 May, June, r = .620; for potatoes July and August, 

 r = .666. The critical season for corn, as we found a 

 while ago, is July and August, r = .589. 



The high correlation between the yield of the crops 

 and the rainfall of their respective critical seasons 

 promises well for the theory as to the relation of the 

 cycles of rainfall and cycles of crops. In the last chapter 

 we found that by examining the periodogram of annual 

 rainfall in the Ohio Valley, cycles of eight years and of 

 thirty-three years were discovered; and that by taking 

 periods of thirty-three years and eight years with their 

 semiharmonics, a good fit to the annual rainfall curve 

 was obtained. It was then shown that the annual rain- 

 fall in Illinois is correlated with the annual rainfall 

 in the Ohio Valley, the correlation coefficient being 

 r = .600. Upon the basis of this relatively high correla- 

 tion, it was assumed that the annual rainfall in Illinois 

 passed through similar cycles to the rainfall in the 

 Ohio Valley, and we found that this assumption was 

 justified by the facts inasmuch as the harmonic analysis 

 applied in the same way to the Illinois data afforded as 

 good a fit as when it was applied to the data of the 

 Ohio Valley. Since in two of the four representative 

 crops the correlation between the yield and the rainfall 



exhausted in the above case, nor have we made any attempt to 

 place the critical period for a smaller interval of time than a month. 

 If for any other period a closer relation could be found than r = .589, 

 the conclusions that we draw from our investigation would only be 

 strengthened. 



