NO. 2 



THE SUNSPOT PERIOI 



-CLAYTON 



Table 3. — Harmonic terms computed by correlations 



(1) 



Month 



July 



August 



September . . 



October 



November . 

 December . 

 January . . . 

 February . . 

 March .... 



April 



May 



June 



Sums 



(2) 



(3) 



(4) 



(5) 



(6) 



Note. — a = ratio of the observed values to a cosine series having plus unity in July and 

 minus unity in January. 



much greater lengths than the cosine series and shows no consistent 

 period of any length when treating random data. 



For example, if we multiply the monthly mean temperatures at 

 New York City by a cosine series of 12 terms, beginning with any 



-i-o 



Fig. 1. — A cosine series. 



given month, and repeat the process month by month, adding 1 month 

 and dropping 1, taking the mean values in each case, the results will 

 show regular periodic oscillations of 12 months in length. The mean 

 is obtained by dividing the successive sums by hi, n being the number 

 of terms used. The time is taken at the middle of the series. Figure 2 

 shows a plot of the annual period in temperature at New York ob- 

 tained in that manner from 1927-1929. This plot shows that the 



