308 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 19 31 



served through the exact, different cycles appear in the form of 

 interference bands in different directions, according to their length. 

 Thus the cycles are automatically separated. Suitable range is se- 

 cured by interposing a movable mirror between the curve and the 

 lens and the cycle length may be read directly from the position of 

 the mirror. 



The method has great rapidity and flexibility in cycle exploration 

 and in the separation of mixed cycles. On several occasions 42 differ- 

 ent curves averaging 175 units in length have in three hours been 

 analyzed for all cycles between 5.5 and 40 units by one observer. 

 The use of this method has led me to believe that harmonics or in- 

 tegral parts of a fundamental are not suited to the expression of 

 climatic cycles. Nor are we justified in assuming the sine curves 

 that are used in harmonic analysis. 



CYCLES IN MODERN TREE GROWTH 



Some 52,000 measures have been made on 305 modern pines in the 

 western United States. Their growth curves were divided into 42 

 groups and analyzed. In the general summary the cycles appear 

 in a great majority of cases to be simple fractions of two or three 

 times the sun-spot cycle. This result, reached in 1926, was held to 

 be of sufficient importance to make a complete and independent 

 analytical check before publishing. 



Similar expressions have been reached by Abbot, Clayton, and 

 C. E. P. Brooks. Thus, there seems support for the hypothesis that 

 climatic cycles, which have shown such puzzling complexity, are 

 related in a simple manner to the 11-year sun-spot cycle. One might 

 suggest that this curious fractionizing process has something to do 

 with interferences in any given locality between impulses coming 

 from different centers of influence. Some recent evidence (Abbot's 

 work on solar radiation and mine on analysis of monthly sun-spot 

 numbers since 1750) points distinctly toward solar activity as offer- 

 ing a clue to this fractionizing process. That does not lessen the 

 complexity of terrestrial distribution. 



SEQUOIA CYCLES 



The longest tree records were found in the giant sequoias of Cali- 

 fornia, Sequoia gigantea. About a dozen specimens in my laboratory 

 have records that go back to about 200 B. C. At least four carry 

 the record back to 1100 B. C, and one extends it to 1300 B. C. The 

 sun-spot cycle appears to be recognizable in many parts of this 

 record, especially if one searches for the double value of something 

 over 22 years. This subdivides at different times into halves, thirds. 



