56 Economic Cycles: Their Law and Cause 



critical seasons may both be accurately de- 

 scribed by a compound cycle composed of a 

 thirty-three years cycle with its semihar- 

 monic, which summarizes the ground-swell of 

 the movement, and a superposed cycle of eight 

 years with its semiharmonic, describing the 

 shorter rhythmical movements. 



(3) In three of the four representative crops, the 



compound cycles summarizing the changes in 

 the rainfall of the critical periods of growth 

 and the changes in the yield per acre of the 

 crops are so nearly congruent that, consider- 

 ing the high correlation of the yield with the 

 rainfall, one may conclude, with a high degree 

 of probability, that the rhythmical movement 

 in the weather conditions represented by 

 rainfall is the cause of the cycles of the crops. 



(4) The index of the fluctuation of the crops taken 



together, and the index representative of the 

 mean effective rainfall during the critical 

 seasons are highly correlated, r = .584. 



(5) The rhythmical changes in the index of the 



fluctuation of the crops and in the index of 

 the mean effective rainfall are accurately 

 described by a compound cycle which is made 

 up of a thirty-three years cycle and an eight 

 years cycle with their semiharmonics, and 

 these two compound curves are, in their gen- 

 eral characteristics, much alike. 



(6) The investigation of the crops taken singly and 



