110 CLIMATIC CYCLES AND TREE-GROWTH. 
rhythm in the long Norwegian and shorter Austrian records, whose 
curves were given in figures 36 and 24 respectively, pages 105 and 77. 
Pattern J shows the 33-year cycle of the 400-year tree, N-2, from near 
the Arctic Circle in Norway. The Vermont hemlocks are shown in 
pattern K. Here is found a good rhythm with a change in phase about 
100 years ago. The Swedish curve shows a good rhythm at 37 years. 
Several intervals of triple solar cycle appear in the 1,000 years of early 
sequoia growth in pattern M. All the 8 patterns G to N are taken 
from special curves prepared on a one-fifth scale, using 5-year sums 
in the plot. 
The 100-year cycle-—Only two tree records are long enough to be 
tested for a cycle of this length. The sequoia gives a very excellent 
alinement at a period of 101 years, shown even better in the upper 
pattern of figure 40. The pattern of the present plate shows an 
increase to about 125 years in the last 600 years, which corresponds to 
the best analysis of the 500-year Arizona curve. This latter is at 120 
years as shown in pattern P. Both of these are made from special 
curves plotted on one twenty-fifth of the usual scale. 
Illustration by the periodograph.—The illustrations of periodograph 
analysis given above are practically the first made with this instrument 
and are therefore crude in many respects. Its advantage in the study 
of simple and obvious cycles such as the sunspot numbers is not at 
once apparent to the eye and its efficiency becomes evident only when 
one tries to select the exact period and state its accuracy. But one can 
foresee a useful application of this instrument in the study of mixed 
periods, such as appear in tree-growth here considered or in rainfall 
and other meteorological elements, a field as yet almost untouched on 
account of its complexity. However, in the brief presentation of its 
work given above, it is evident that the periodograph is found to 
corroborate and extend the results of the previous direct study of 
curves and to confirm the evidence there given of the great extent and 
importance of the solar cycles in the growth of trees. 
~~ ae 
