Page:Climatic Cycles and Tree-Growth - 1919.djvu/134

 several maxima at about 8.5-year intervals. Pattern E gives the Vermont 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, however, gives information as to how and when that change took place.

Changes in the 11-year tree-cycle of Arizona—A careful examination of an early differential pattern of the Flagstaff tree record gave the following probable history of the 11-year variation in Arizona:

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: