50 Economic Cycles: Their Law and Cause 



the rainfall of the critical season — July and August — 

 is r = .589. The measure of the fit of the compound 

 cycle to the data is, for the yield per acre, i£ = 1.52, 

 and, for the rainfall of the critical season, K = 1 .30. 



For oats, the computation of the equation has not 

 been carried out because no critical period of growth 

 could be found in which the correlation between yield 

 and rainfall was higher than r = .3. The correlations 

 were, for March, r = — .181; for April, r = — .147; for 

 May, r = 120; for June, r = .297; for July, r = .140; for 

 May, June, and July, r = .290. 



Referring now to the Figures 11, 12, 13 and to the 

 calculations that have just been reviewed, we observe 

 that the compound cycles of yield per acre and of the 

 rainfall of the critical seasons flow almost congruently, 

 and that the compound cycle of thirty-three years 

 and eight years with their semiharmonics fits the yield 

 data nearly as well as it fits the rainfall data. 



Cycles in the Index of Crop Fluctuations and in the Cor- 

 responding Index of Mean Effective Rainfall 



Does the cyclical movement of rainfall give a rhyth- 

 mic movement to the fluctuations in the yield of the 

 crops taken all together? The preceding section has 

 treated the relation of the yield of the separate crops 

 to the rainfall of their respective critical seasons; we 

 now inquire whether the yield of all of the crops taken 

 together shows a tendency to conform to the cyclical 

 movement of rainfall. In order to answer this question 

 two preliminary steps must be taken: (1) A method 



