NO. 2 THE SUNSPOT PERIOD CLAYTON 1 7 



the yearly sunspot numbers, then these periods are approximately 

 of the length and amplitude given in table 4. 



From scattered observations of sunspots in the past three centuries 

 a table was made at the Zurich Observatory by Wolf and Wolfer 

 giving the approximate time of maxima and minima of spots from 

 1610 to the beginning of regular observations. 



In order to test whether a period of 89.36 years could be used in 

 determining the dates of these maxima and minima, going backward 

 from observed maxima and minima between 1856 and 1933, tables 

 6 and 7 were constructed. Table 6 gives the computed and observed 

 minima of spots, and table 7 gives the computed and observed maxima 

 of spots. 



•880 



>uns pot Numbers 



Fig. 12. — Sunspot numbers forecasted and observed. 



Only a few of Wolfer's estimated dates of minima and maxima of 

 sunspots from 1610 to 1850 differ greatly from the computed values 

 given in the table, and these few were not assigned a weight exceeding 

 2 on a scale of 10 in Wolfer's table. 



The next step was to try how nearly the 89.36-year period could 

 be used in forecasting recent sunspot periods. Beginning with the 

 minimum of 1798, for which a weight of 8 on a scale of 10 was- 

 assigned in Wolfer's table, the sunspot numbers were projected for- 

 ward 89.36 years in time and compared with observed values. This 

 comparison is given in figure 12. It will be seen from this figure that 

 the projected curve, shown by the dotted line, gives a good forecast 

 of the dates of observed maxima and minima of sunspots, shown by 

 the full curve, for the interval of 55 years, 1883-1937, and gives an 

 approximation to the intensity of the maxima, excepting the one in 

 1928. From this showing it is a reasonable inference that a similar 

 accuracy can be obtained for 89.4 years in the future. 



The dotted curve is projected forward to 1950 and indicates the 

 next minimum of sunspots in 1945 and the next maximum in 1949. 



