44 Economic Cycles: Their Law and Cause 



of the critical season of growth is greater than the 

 correlation between the annual rainfall in Illinois and 

 the annual rainfall in the Ohio Valley, there would 

 seem to be excellent ground for believing that the cycles 

 of the yield of the crops would flow congruently with 

 the cycles of rainfall during their respective critical 

 periods. 



Cycles in the Yield of the Representative Crops and the 

 Corresponding Cycles of Rainfall 



The method of bringing the cycles of rainfall for the 

 critical period of growth of the several crops into rela- 

 tion with the cycles of the respective crops is similar to 

 the method that was employed in passing from the 

 cycles of annual rainfall in the Ohio Valley to the 

 corresponding cycles in the state of Illinois. The 

 laborious but direct way of treating the problem would 

 be to compute the periodogram of rainfall for the 

 critical period of growth of each crop, and then to com- 

 pare the results with the corresponding periodograms of 

 the respective crops. It may be that this laborious 

 process may eventually have to be followed. The 

 process that has been adopted in the present investiga- 

 tion makes several assumptions which it is highly 

 desirable to have clear in mind. It is assumed 



(1) That the course of the annual rainfall is the mean 

 course of the rainfall of the parts of the year 

 and that, consequently, by computing the 

 periodogram of annual rainfall, we obtain a 

 general type of curve for describing not only 



