130 CLIMATIC CYCLES AND TREE-GROWTH 



The triple period, essentially Bruckner 's cycle, has operated in Arizona 

 for the last 200 years and in Norway for 400 at least. Western zone 

 cycles are largely its simple fractions. A hundred-year cycle is promi- 

 nent throughout the 3,000 years of sequoia record, and a cycle of 

 about 150 years shows in the 600 years of yellow pine. It seems fairly 

 probable that the 11-year cycle can be judged by the variations in its 

 double value, which in some cases is more easily traced through long 

 periods. A very incomplete review of the sequoia record suggests that 

 from 1300 b. c to well after 1100 b. c, the 11-year cycle was strongly 

 developed. Near 300 b. c. it was again apparent, though not very 

 conspicuous. During the first two centuries of our era it was again 

 highly dominant. It reappeared from 375 to 475 and from 600 to 650 

 and was operating during much of the ninth century, though mixed 

 with other cycles. Then it appears only occasionally until after 1300, 

 when it again becomes fairly continuous, except for the changes in 

 the seventeenth century (1633 to 1712) above noted. This is a pro- 

 visional report and will, without doubt, receive changes when the 

 sequoia records are minutely examined for the purpose. 



Climatic patterns — From this study of the geographical and his- 

 torical distribution of climatic cycles it is inferred that they are 

 climatic patterns made up of interferences between a number of simple 

 fractions of a few fundamentals, traceable to solar influence. This 

 form of interference seems to produce pseudo-cycles which vary with 

 the phase relationship of the fundamentals and whose resulting tem- 

 porary character has always been a stumbling-block in the way of 

 investigation. 



CYCLOGRAMS 



An analytical review of some of the cycles mentioned in this chapter 

 is given in Plate 9. To one who understands the extent of information 

 in the cyclogram, and, if I may add, the spirit of this information, that 

 is, its frankness in showing its own accuracy or error, these figures 

 visualize the facts in a most compact and convenient way. 



Cycle identity across 200 miles — The first three cyclograms, taken 

 in immediate succession on the same plate, show an analysis at a 

 period of 18.1 years (represented by the thread) of the Flagstaff curve 

 and the two points near Aztec in northwest New Mexico, from 1700 

 to about 1910. The most conspicuous alignment is the 21-year cycle, 

 but 17- and 14-year cycles also usually show. The similarity in general 

 pattern is apparent at once. This is evidence of the reality of the 

 cycles and of their climatic significance (page 118). 



Dearth cycles at A. D. 1700 — The Vermont hemlocks give an analy- 

 sis shown in cyclogram 4. Here the Bruckner cycle dominates from 



