Rainfall and the Crops 49 



divided by the area included between the curve and the 

 straight line indicating the mean value of the observa- 

 tions. In the equation to the compound cycle describ- 

 ing the typical curve with which we shall have to deal, 

 the first term gives the mean value of the observations, 

 and the remaining four harmonic terms trace the area 

 about the horizontal line drawn at a distance from the 

 base line equal to the mean value of the observations. 

 The reason for adopting this complex coefficient K is 

 that the curves whose relative degrees of fit are in 

 question apply to qualitatively different things. From 

 the method of calculating K, it follows that the smaller 

 the value of K, the better is the degree of fit of the curve 

 to the observations. 



Passing now to the calculations referring to the 

 representative crops, we find, 



For potatoes, the correlation of the yield per acre 

 with the rainfall of its critical period — July and Au- 

 gust — is r = .666. The measure of the fit of the com- 

 pound cycle of thirty-three years and eight years with 

 their semiharmonics is, in case of the yield per acre, 

 K = 1.97, and in case of the rainfall of the critical period 

 of growth, K = 1.30. 



For hay, the correlation of the yield per acre with 

 the rainfall of its critical period — March, April, May, 

 June — is r = .620. The measure of the fit of the com- 

 pound cycle to the data is, in case of the yield per acre, 

 K = 1.57, and in case of the rainfall of the critical season, 

 # = 1.63. 



For corn, the correlation of the yield per acre with 



