26 Economic Cycles: Their Law and Cause 



lingers at the minima and the short period during which 

 it flows in the neighborhood of the maxima. 1 



Rainfall in the Corn Belt 



Thus far we have dealt with the law of rainfall only 

 in the Ohio Valley. The object in taking the Ohio 

 data, rather than the data of a state more representa- 

 tive of the leading cereal area, was to make an investiga- 

 tion of a longer meteorological record than is afforded 

 by the data of the central Mississippi Valley. But our 

 purpose in dealing with meteorological records at all is 

 to show the dependence of crops upon the cyclical 

 movement of the elements of the weather. We must, 

 therefore, prove that the cycles of rainfall which we have 



1 1 should like to make clear the method I have followed in the 

 derivation of the equations to the curves. My object was to obtain 

 a summary description of the general course of rainfall in order that 

 I might discover, later on, whether the characteristic general fea- 

 tures of the movement of rainfall are reproduced in the changing 

 yield per acre of the crops. As a first step I tried to detect the real 

 cycles in rainfall and I believe I have shown that, if the 72 years 

 record is sufficiently long to reveal the true cycles, then the most 

 probable lengths of the cycles are, in round numbers, 33 years and 

 8 years respectively. With so short a range of data I regarded it as 

 useless to attempt to calculate the lengths of the periods to a greater 

 degree of precision. I next had to derive the equations to the curves 

 showing the characteristic general course of rainfall, and it seemed 

 to me that, for this purpose, the method described in the text for 

 evaluating the coefficients in a Fourier series might properly be 

 used. If the 33 years cycle were taken as the fundamental cycle, 

 then the 8 years cycle would be approximately the fourth harmonic 

 in the series, and the 4 years cycle would be the eighth harmonic. 



The arithmetical process for computing the coefficients is indi- 

 cated by Professor Schuster in Hidden Periodicities, pp. 13, 14 and is 

 briefly described by Professor Perry in an article on "Harmonic 

 Analysis" in The Electrician, for February 5, 1892. 



