CYCLES IN TREE-RING WIDTHS 



By C. G. abbot 



Secretary, Smithsonian Institution 



In my paper " Solar Radiation and Weather Studies " ', I showed 

 that the variation of the sun's emission of radiation since 1920 is 

 the summation of at least 12 periodicities ranging from 7 months to 

 23 years in length. All of them are approximately, perhaps exactly, 

 aliquot parts of 23 years. Hence, 23 years is a cycle wherein we might 

 expect the weather and things dependent on it would show marked 

 recurring features. Furthermore, although hitherto mathematical 

 analysis has not disclosed why the sun's radiation should exhibit a 

 fundamental and many overtones like a violin string, yet since observa- 

 tions show that it does so, it may well be that the fundamental is 

 not 23 years, but 46, 92, or some other multiple of 23 years. 



In my paper just cited I went on to show that all of the solar 

 periodicities are also found in weather records of six stations (one 

 of them, Adelaide, Australia, by the way) during the past century. 

 Moreover, the 23-year cycle is to be found in varves of glacial age, 

 in widths of tree rings in California and the West, in the levels of 

 lakes and rivers, in the weather of the United States, and in other 

 phenomena. It proved also that in many phenomena, and notably so 

 in the levels of the Great Lakes and in the associated droughts in 

 the Northwest, the 46-year cycle is predominant. 



Recently Prof. C. J. Lyon, of Dartmouth College, has published a 

 paper ' on his measurements of widths of tree rings at six localities 

 in Vermont and New Hampshire. My attention was particularly 

 drawn to his figure 3, wherein he plots the average results through 

 the whole range of time they cover. The locality Fairlee, Vermont, 

 has the longest record, extending from 1544 to the present time, 

 almost four centuries. Having graduated a slip of paper in 23-year 

 intervals, I thought I could see in Professor Lyon's diagram a well- 

 marked cycle of variation of this period throughout the entire series. 



Professor Lyon has been so kind as to send me his original observa- 

 tions on the trees at Fairlee, and has graciously consented to let me 



* Smithsonian Misc. Coll., vol. 94, no. 10, 1935. 

 " Ecology, vol. 17, no. 3, July 1936. 



Smithsonian Miscellaneous Collections, Vol. 95, No. 19 



