l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



This forecast is evidently more accurate than simply projecting each 

 maximum and minimum 1 1 years ahead as it occurs. 



A still more accurate forecast probably can be made by a separate 

 combination of all the periods. This combination will be tried when 

 the amplitude and phase of each period are determined with the 

 greatest accuracy possible from existing data. 



In view of the fact that the sunspot period is becoming important 

 in numerous fields of scientific activity, much significance attaches to 

 the forecasting of the time and intensity of the maxima and minima. 



Prof. S. P. Fergusson made the necessary adjustments and modi- 

 fications of the instruments illustrated in plate i, and Miss M. I. 

 Robinson assisted in the computations needed in the preparation of 

 this treatise. 



