80 



CLIMATIC CYCLES AND TREE-GROWTH. 



The original means of 11 trees are given in the upper line of figure 27. 

 In the middle line these are smoothed by Hann's formula and in the 

 lower line is the sunspot curve, displaced three years to the left in the 

 portions since 1810 and one year in the same direction before that date. 

 The tree crests anticipated the solar crests by three years when the 

 trees were large and making good growth, but when small this anticipa- 



1834- etc. 



Sun spots 

 displaced 

 -J years 



Tree Growth 



(Windsor, Vt.) 



Rain 



Suns pots 



FIG. 29. Correlation curves of solar cycle, rainfall, and tree-growth at 

 Windsor, Vermont, 1835-1912. 



tion of the sunspot maximum was considerably less. A correlation is 

 evident, but it is hard to give a satisfactory explanation of the phase 

 displacement. Figure 28 gives details of the time relation between 

 tree-growth, rainfall, and solar activity. In figure 29 the curves of 

 figure 28 have been summated on an 11.4-year period, as was done in 

 figure 25. At the bottom is the sunspot curve from 1834 to 1912 inclu- 

 sive; directly above it is the curve of rainfall for the vicinity of Windsor, 

 compiled chiefly from records at Hanover and Concord and covering 

 1835 to 1912; above that is the tree-growth from 1834 to 1912, and in the 

 upper line the sunspot curve is repeated with a displacement of 3 years. 



