108 



CLIMATIC CYCLES AND TREE-GROWTH. 



several maxima at about 8.5-year intervals. Pattern E gives the Ver- 

 mont analysis. The solar cycle shows well for the last 150 years, but 

 is preceded by a 9.2-year cycle for about 50 years, and then by the 

 solar cycle again. This tree curve is shown in figure 27, page 78. 



The Arizona pines are given in pattern F. The double-crested solar 

 cycle shows in the larger part of it, but is best developed in the upper 

 and lower thirds. By sighting along these vertical rows, a dark line 

 in the upper third, indicating the more pronounced minimum, comes 

 in straight line with the lesser dark minimum line in the lower third, 

 indicating a transfer of emphasis from one-half of the 11 -year cycle to 

 the other half in passing the seventeenth century. This was noted 

 above in connection with the analysis of the same record by a series 

 of curves in figure 33, page 103. Further study of this pattern, how- 

 ever, gives information as to how and when that change took place. 



Changes in the 11-year tree-cycle of Arizona A careful examina- 

 tion of an early differential pattern of the Flagstaff tree record gave the 

 following probable history of the 11-year variation in Arizona: 



TABLE 7. Changes in the 11 -year tree-cycle of Arizona. 



Years. 



1395-1550 



1550-1595 

 1595-1661 



1661-1677 

 1677-1770 



1770-1793 



1793-1817 

 1817-1910 



Period. 



11.3 



14.3 

 11.0=t0.5 



16. 0(?) 

 12.5 



9.0 



11.6 



Remarks. 



Double crests throughout, except 1476 and 



1487, where the second crest fails. 

 Heavy double crest. 

 Heavy single crests with trace of double 



diminishing to small variable singles. 

 Possibly 1 long interval. 

 Double crests mostly; going to 10.8 from 



1702 to 1722. 

 Sharp single crest continuing second crest 



of preceding double. 

 Doubtful. 

 Rather broad, heavy crests, sometimes 



double; 1864 has too little and 1875 too 



much crest. 



The interval from 1830 to the present time divides also extremely 

 well on a 21.0-year period, and fairly well in one of 7.3 years. 



In obtaining this result no comparison was made with the sunspot 

 record. So the following is of interest: 



TABLE 8. Changes in tree and sunspot cycles compared. 



