52 CLIMATIC CYCLES AND TREE GROWTH 



depending on the moon's motions. For example, the lunar "tide" in at- 

 mospheric pressure 1 and the allied lunar diurnal variations in the terrestrial 

 magnetic forces 2 are among the very satisfying results. But in the analysis 

 of climatic changes and even in solar variations, harmonic study has produced 

 a large number of unconnected facts, each one of which has been regarded with 

 distrust because it did not match the astronomic cycles in persistence of 

 activity. To these unconnected facts the laws of probability have been 

 applied in the hope of getting something tangible, but little or no encourage- 

 ment has been found. 



The idea of discontinuous periods, that is, of cycles localized within a 

 special part of a time sequence, seems to the writer to open a new field in 

 cycle study which has hardly yet received serious consideration. Previous 

 to the opening of this new field the discovery and careful study of climatic 

 cycles was usually a matter of accident. A common way to search for them 

 was to plot a curve of data and test it by eye without mechanical device of 

 any sort. Faint permanent periods not evident in that way were appropri- 

 ately called "hidden periodicities." If Schuster had merely applied analysis 

 to the sunspot record as a whole he would perhaps not have seen any localizing, 

 in time, of special cycle lengths. However, he did find some evidence of 

 localized cycles by dividing his data from 1750 to 1906 or so into two parts. 

 He thus obtained more detailed values which he displayed in the now famous 

 periodogram. 



In 1914, H. H. Turner in extending a similar study worked out the "points 

 of discontinuity" in the sunspot sequence since 1750. One feels that he was 

 rather specially impressed with discontinuity in amplitude as would be nat- 

 ural in harmonic analysis. At almost the same time (late 1914) the writer 

 obtained his first automatic cyclogram (Ap-J, April 1915, pages 173-4) and 

 found the discontinuities in period laid bare for all who understood the cyclo- 

 gram method. The multiple plot had in 1913 already shown points of 

 discontinuity. 



Clayton encountered a temporary period as long ago as 1884-5 in his 

 studies of short cycles in climate (A Lately Discovered Cycle, Amer. Met. 

 Jour., vol. I, pp. 130 and 528) . Later he formulated the idea of phase reversal 

 and found it frequent in climatic cycles. 3 Arctowski has investigated short 

 cycles of 1 to 4 years in weather elements. Alter, recognizing the idea of dis- 

 continuity, has made extensive and fine use of subdivisions of his data in order 

 to show that each part independently gives the same results. Subdivision 

 aids in localizing cycles and yet it can not be carried far because the fragments 

 of data become too short. Cyclogram analysis carries subdivision to the 



1 S. Chapman, see Bibliography, 1935. 



2 S. Chapman, see Bibliography, 1925. J. A. Fleming, see Bibliography, 1932. 



3 His continental movements of climatic waves are likely to prove of the first im- 

 portance as are his results on terrestrial temperature reactions to changes in solar radi- 

 ation. Abbot and Clayton have contributed to similar studies in North America and 

 especially the former has supplied the fundamental data on radiation. Arctowski has 

 shown the movement of climatic waves. 



