Rainfall and the Crops 57 



taken together leads to the general conclu- 

 sions : 



(a) that there is a rhythmical movement 

 in both the yield of the crops and in the 

 rainfall of the critical periods which is 

 summarized in a compound cycle, in 

 which the constituent elements are a 

 ground-swell of thirty-three years and 

 its semiharmonic, and a shorter super- 

 posed cycle of eight years with its 

 semiharmonic ; 



(b) that the cyclical movement in the 



weather conditions represented by rain- 

 fall is the fundamental, persistent cause 

 of the cycles of the crops. 



