Introduction 7 



the respective amplitudes. It is clear from Figure 2 

 that the cycle with a jieriod in the neighborhood of 

 eight years is by far the most important. The graph is 

 given in Figure 1. The mean annual rainfall in the 

 Ohio Valley is 41.19 inches, and the amplitude of the 

 eight-year cycle is 4.13 inches. The range of the 

 eight-year cycle, which is twice its amplitude, is 8.26 

 inches or twentj^ per cent of the annual rainfall. The 

 tremendous importance of much smaller variations in 

 precipitation is being increasingly emphasized by the 

 findings of the growing science of agricultural meteorol- 

 ogy. 



The cyclical regularity in the variations of the rain- 

 fall in the Ohio Valley for the seventy-two years from 

 1839 to 1910 was first announced ^ in 1914, and as the 

 computations rested upon the records of only three 

 stations, Cincinnati, Portsmouth, and Marietta, there 

 was a very reasonable skepticism as to the reality of the 

 eight-3'ear cycle. One might concede that the measure- 

 ments of rainfall at the three stations show the eight- 

 year cycle for nine consecutive periods in the seventy- 

 two years, and yet deny the economic importance of 

 the cycle on the ground that no evidence has been sub- 

 mitted to show its presence in the whole of the United 

 States. This perfectly legitimate objection must be 

 met, and we shall attempt to meet it by conducting an 

 independent inquiry that will serve as a severe test of 

 the reality and generality of the eight-year cycle. We 

 shall use all available data for the whole of the United 

 States; we shall start with no prejudice with regard to 



^ Economic Cycles: Their Law and Cause, 1914. The data are given 

 in that work, p. 32. 



