30 Economic Cycles: Their Law and Cause 



tion of the observations from this curve is S =4.20. In 

 case of the Ohio curve the root-mean-square deviation 

 was £ = 5.29. But this is a better relative fit for the 

 Illinois curve than we have a right to claim, because in 

 Ohio the mean annual rainfall is 41.19, while in Illinois 

 the mean is 38.53. If we express the relative scatter of 

 the observations about the curve as the ratio of the 

 root-mean-square deviation of the observations to the 

 mean rainfall, we get for Ohio and Illinois, respectively, 

 S 1 = .128; S 1 = .109. 



In Figure 8, the Ohio curve for 1870-1910 is placed 

 upon the same chart as the Illinois curve for the same 

 flow of time, and the degree of correspondence of the 

 two curves is seen to be so close that, with due allowance 

 for the difference in their mean annual rainfall, they 

 seem to be almost congruent. 



We may say, therefore, that the two curves fit their 

 respective data equally well. 



Our problem has now received its solution. Annual 

 rainfall in the chief grain-producing area of the United 

 States has no secular trend, but its mean course is the 

 resultant of causes producing two cycles of 33 years 

 and 8 years respectively. The manner in which these 

 cycles of rainfall produce a rhythmical expansion and 

 contraction in the yield of the crops we shall examine in 

 the next chapter. 



