THE SUNSPOT PERIOD 



By H. HELM CLAYTON 

 (With One Plate) 



PREFACE 



The objects of this paper are: 



i. To show that the smoothed plus and minus annual departures 

 from normal pressure observed in the earth's atmosphere are dis- 

 placed in position in unison with variations in intensity of sunspot 

 maxima. 



2. To show that the annual sunspot numbers may be resolved into 

 a number of regular periods of constant length and amplitude which, 

 when combined, make the irregular sunspot period and permit fore- 

 casting, with reasonable accuracy, the dates of maxima and minima 

 of sunspots and the intensity of the maxima. 



ATMOSPHERIC PRESSURE AND THE SUNSPOT PERIOD 



Atmospheric pressure is subject to large fluctuations of short period, 

 especially in high latitudes. In order to study long-period oscillations 

 like those of sunspot numbers, it is necessary to smooth out the short- 

 period fluctuations, just as it is necessary to smooth out the wind- 

 driven waves in the ocean in order to study the tides. 



This smoothing is frequently done by numerical averaging. Such 

 averages block out the oscillations of short period but do not eliminate 

 long-period trends in the data nor oscillations much longer than the 

 ones it is desired to study. Smoothing by harmonic formulas is there- 

 fore believed to be the best method, because by such smoothing one 

 can eliminate oscillations which are much longer as well as those which 

 are much shorter than those which it is desired to study. 



The type of harmonic formula used for this purpose is as follows : 



Let l , l x , lo, l 3 /„_! be observed values which are associated with 



equidistant values of some argument, say time ; then the single 



Smithsonian Miscellaneous Collections, Vol. 98, No. 2 



