CYCLES. 



105 



tered group of trees of considerable age from the inner fjords and 

 mountains of Norway. The earlier half of the curve includes 6 trees 

 and the later half 8. The cycle beneath makes evident a well-developed 

 rhythm in these trees. Figure 37 shows a very regular double sun-spot 

 rhythm in the sequoias. There are many similar rhythms apparent 

 in the sequoias, but as yet little study has been made of them. This 

 one shows 80 years of the section D-12, whose identification was for a 



noo 



nso 



1850 



1300 



1800 

 Years 



FIG. 35. Early curve of Arizona pines from 1700 to 1900 A. D. (No. 4), compared with double 



and triple sunspot cycles combined (No. 3). 



175O 



1800 



1850 



I9OO 



FIG. 36. Double sunspot period in tree-growth at inner fjords of Norway; 

 lower curve a 22.8 year cycle. 



2 1 



2.80 



300 



10 



20 

 Years 



30 



350 



FIG. 37. Double sunspot rhythm in sequoia, D-12 about 300 A. D. 

 (Material obtained in 1919 shows the dates in this figure to be too large by 27 years.) 



long time uncertain on account of its complacent character and badly 

 compressed rings. The rhythmic character is so evident that no cycle 

 needs to be placed below the curve. The period is estimated at 20 

 to 22 years. 



A triple solar cycle is shown in figure 38, giving the condensed curve 

 of a single 400-year-old Norwegian tree. The upper curve gives the 

 mean growth, and the lower curve is a simple 34-year cycle. The 

 rhythmic character of the growth was clearly seen in the measures 



