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 
thythm 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 
SE Ba sey 5 ll 
— rte. ee eet ee eet ee ed ee 
or a et ee, bd 
>= ~~} | _ | i 
NA ] 
7 410.8 
1700 7750 7800 7850 700 * 
Years 
Fic. 35.—Early curve of Arizona pines from 1700 to 1900 A. D. (No. 4), compared with double 
and triple sunspot cycles combined (No. 3). 
IRA RAAR AH 
Fic. 36.—Double sunspot period in tree-growth at inner fjords of Norway; 
lower curve a 22.8 year cycle. 
3 
NR] 
ed 13 
260. 90 300 0 20 30.~«40~*«S SO G0" 
Years 
Fie. 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 
