49§ 



POPULAR SCIENCE MONTHLY 



•A. The year preceding that of minimum spots. 



5. The } T ear of minimum spots. 



6. The year succeeding that of minimum spots. 



7. An intermediate period of increasing number of spots, — average 



length about l 1 /^ years. 



o 



Q. 



to 



C 



o 



a 



I c 



Years Before e Years After Years Before v> Years After 



Figure 2. Simple Frequency 

 Sayles. 



Figure 6. Simple Frequency 

 Sayles . 



100 



8765432101234567 



Figure 3. Simple Frequency - 

 Jensen. 



Figure 7. Simple Frequency 

 Jensen 



Figure 4. Intensity - Sayles. 



543210123456789 10 



100 



80 

 60 

 40 

 20 

 



Figure 8. Intensity - Sayles. 



Figure 5- Intensity - Jensen. 



Figure 9. Intensity - Jensen. 



Figs. 2-'j. The relative Frequency and Intensity of Seismic and volcanic Phe- 

 nomena at Periods of Sunspot Minima (2-5) and Maxima (6-9). The numeials above the 

 diagrams indicate years, those on the sides, percentages. In the diagrams compiled from 

 Jensen's data the full lines indicate seismic phenomena, and the dotted lines volcanic phe- 

 nomena. 



8. The year preceding that of maximum spots. 



The irregular periods numbered 3 and 7 are necessary because of 

 the variation of the length of the sun-spot cycle. Number 3 may vary 

 in length from 1 to 7 years, and number 7 from to 3. 



