crosses were placed upon the central ring, which was usually the largest of the group. These crosses are well shown in plate 4, b. Their dates were noted during the measuring. In figure 26 the ordinates give the number of maximum marks found in each date throughout the whole
Fig. 28.—Smoothed quarterly rainfall (upper curve), sunspot numbers (center), and tree growth (lower) at Windsor, Vermont, 1835 to 1912.
80 sections. The more recent dates show higher crests because there are more trees. In the second line is the sunspot curve. The matching of the crests of the two curves is unmistakable. The secondary tree-crest at sunspot minimum is very regular, as would be expected from the inclusion of the three groups of figure 24, some of which are evident reversals. This test is only qualitative, but seems to the writer to offer substantial support to the quantitative relation shown in figure 25.
Windsor (Vermont) correlation. — An interesting sidelight is thrown on this type of correlation by the American curves from Windsor, Vermont.