SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 8q 



group of maxima are here called periods of high solar activity and 

 the second group, periods of moderate activity. It will be noticed 

 that periods of higher and lesser activity have occurred alternately, 



HIGH LATITUDES 



MIDDLE LATITUDES 



MAX. 

 SPOTS 

 Moderate Solar Activity 



MAX. 

 SPOTS 

 Moderate Solar Activity 

 1683 



Moderate Solar Activity 

 1905 



NEvnrORK 

 41 "N 



Moderate Solar Activity 

 1905 



MARSEILLE 

 ' / NEW YORK " 



High^Solar Activity 

 / 19l\ 



(■■ I I /l I I l\l I I I I 



Hiph Solar Activity 

 1917 /\ 

 i-.l I I I /i I 1 I I 



0.0 



Fig. 8. — Smoothed annual means of pressure during the sun-spot period, 

 Northern Hemisphere. 



thus giving rise to a period of 22 to 24 years between similar states 

 of activity. This alternation is found in the records since 1848 but 

 not earlier. 



In figure 8 the smoothed annual means of pressure at Upernivik 

 and at Yakutsk have been plotted for successive periods of sun-spot 



