NO. 2 



THE SUNSPOT PERIOI 



-CLAYTON 



13 



Curve a was obtained from 5 consecutive cosine waves, each cover- 

 ing 10 units of time, curve b from 5 consecutive cosine waves, each 

 covering 11 units of time and curve c from 5 waves each covering 

 12 units of time. 



Each curve shows recurrent maxima and minima at intervals of 

 about 11 months. Hence, it is evident that the length of the cosine 

 series does not have to be exactly of the same length as the hidden 



11 1 i n 1 1 1 1 11 1 ; in 1 1 1 1 1 11 1 in m 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 in 1 



1920 ' I92| I9« 1923 1924 



1 1 1 1 I 1 I 1 I 1 1 1 I 1 I 1 1 1 1 1 n 1 1 1 1 I 1 1 1 1 1 1 1 1 11 it I I I I 1 1 1 I UX 



Fig. 11. — Eight-month period in solar radiation and sunspots. 



period in order to disclose it, but only approximately of the same 

 length. The cosine waves of 10 units of time do not produce a 

 10-months' period, and the series of 12 does not produce a 12-months' 

 period. 



When the monthly sunspot numbers from Zurich are treated in this 

 same manner with an 11-term series, there are found oscillations 

 similar in length and form to those found for solar radiation (see 

 curve &'), but the oscillations are not quite so regular. The maxima 

 of spots occur nearly at the same time as the maxima of solar radiation. 



