VI. CORRELATION WITH SUNSPOTS. 



Dry-climate tests. In the work of 1907 (published 1909) upon the 

 first group of 25 yellow pines from 1700 to 1900 A. D., several long 

 sequences of variation in a 5 to 6 year period were noted. These were 

 compared with rainfall records at Prescott and in southern California 

 and the crests of rainfall and growth appeared to coincide in date. It 

 was then seen that the temperature curve of southern California had 

 a period and phase corresponding to the rainfall curve, but with the 

 second minimum almost entirely suppressed, and that finally this tem- 

 perature curve resembled in form and phase the inverted curve of sun- 

 spot numbers. In connection with the publication referred to (1909), 

 a set of curves was prepared to show these relationships. This set is 

 partly reproduced in figure 34, page 104. In the original drawing the 

 tree-curve was the least satisfactory, which was to be expected, as no 

 real certainty in the dating of rings existed at that time. After cross- 

 identification the tree-curve was again integrated for the 11-year period 

 and far better results were obtained. This new curve is given in the 

 figure referred to. 



This type of integrated curve gives many facts in a very condensed 

 form. A differential or detailed form of presentation should accompany 

 it, as in figure 25, showing the full series of individual observations and 

 beside it the curve with which it is to be compared. The differential 

 study of the Arizona trees will be taken up in connection with cycles, 

 but can be summarized in the statement that in the last 160 years 10 

 of the 14 sunspot maxima and minima have been followed about four 

 years later by pronounced maxima and minima in the tree-growth. 

 Also, during some 250 years of the early growth of these trees, they 

 show a strongly marked double-crested 11 -year variation. 



Wet-climate reaction. In the very first group of continental trees 

 studied, those obtained at Eberswalde near Berlin, the remarkable 

 fact was recognized at once that 13 trees from one of those carefully 

 tended German forests show the 11 -year sunspot curve since 1830 with 

 accuracy. The variation in the trees is shown in plate 8. The arrows 

 on the photographs are not to call attention to the larger growth, but 

 to mark the years of maximum sunspots. The other trees of that 

 group do not show quite so perfect rhythm as do the marked radii 

 shown, but are like the other parts of these sections, showing strongly a 

 majority of the maxima. Taking the group as a whole, the agreement is 

 highly conspicuous, and the maximum growth comes within 0.6 year of 

 the sunspot maximum. The Eberswalde curves arranged in two groups 

 and compared with the sunspot curve were shown in figure 9, page 38. 



In the group of six sections from south Sweden, which were measured 

 subsequently in Stockholm, a spruce (Picea excelsa) was discovered 

 which shows the sunspot rhythm with the same striking clarity as the 



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