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
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).
Fig. 36.—Double sunspot period in tree-growth at inner fjords of Norway; lower curve a 22.8 year cycle.
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