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 A 7 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. 



