8 Generating Economic Cycles 



the existence of a cycle of definite period ; we shall sim- 

 ply inquire, if there be an important cycle with period 

 between three and twelve years, what the length is; 

 and then we shall compare the findings with those that 

 were obtained for the Ohio Valley. 



In 1922 Professor Alfred J. Henry of the United 

 States Weather Bureau pubhshed ^ an article which for 

 the first time supplied rainfall data relating to the 

 United States as a unit. Professor Henry's object was 

 to show that there is no ground whatever for the recent 

 claim that rainfall in the United States follows the 

 eleven-year sun-spot cycle, and he sought to make his 

 criticism as convincing as possible by arraying against 

 the sun-spot argument the vast material collected by 

 the Weather Bureau. 



The records that were utilized by Professor Henry 

 were drawn from about two hundred individual Weather 

 Bureau stations grouped into twenty climatic districts 

 embracing the whole of the United States. ^ 



1 Monthly Weather Review, March, 1922, p. 130. 



2 These details Professor Henry gave me in a letter of December 

 29, 1922. After Professor Henry puljiished his article he discovered 

 that a number of errors had crept into his data and computations 

 and he very kindly sent to me, in December, 1922, his corrected table 

 of rainfall departures for the forty years from 1881 to 1921. In Table I 

 of the Appendix to this chapter are listed Professor Henry's original data 

 as they appeared in the Monthly Weather Review, March, 1922, p. 130, 

 and his corrected data as they were sent to me in December, 1922. In 

 both cases Professor Henry smoothed the raw data by means of the 

 formula 6 = ]4, {a -\- 2h -{- c) where h was the value of the middle year 

 in each consecutive series of three years. 



The curve in Figure 1 for the rainfall in the whole of the United 

 States was computed from Professor Henry's corrected data. The 

 curve that was published in my paper on "An Eight- Year Rainfall 

 Cycle," which appeared in the Monthly Weather Review, July, 1922, 

 was based upon Professor Henry's uncorrected figures and fitted the 

 data slightly better than the curve that is given in Figure 1. 



