104 



CLIMATIC CYCLES AND TREE-GROWTH. 



the curve a little but not enough to change the pronounced fluctuations 

 amply shown in recent analysis. This 200-year record showed a very 

 clear combination of the double and triple sun-spot periods. This 

 was illustrated at the time in a drawing which is largely reproduced 

 in figure 35. Curve No. 1 is a triple solar cycle 32.8 years in length; 



/ //J7/7T. 



FIG. 34. Correlation curves in the 11-year cycle. 



No. 2 is a double cycle 21.2 years long, and the third curve is a simple 

 combination of the two. The fourth curve is the tree-growth, showing 

 fluctuations which admirably combine these two periods. All sub- 

 sequent analysis of these trees has entirely supported this result, as 

 shown in the periodograph work below. When the length of curve was 

 extended from 200 years to 500 years, the double solar period was 

 found to prevail through almost the entire length, but the triple period 

 does not appear to have affected the tree-growth in the earlier 300 years. 

 Two other plain examples of the double solar type are illustrated in 

 figures 36 and 37. The former gives the double cycle shown in a scat- 



