VI. RELATION BETWEEN TERRESTRIAL AND 

 SOLAR RECORDS 



EARLY RESULTS 



The first measures of tree rings at Flagstaff in 1904 were made for the 

 purpose of finding whether their thicknesses varied from year to year in re- 

 lation to the sunspot cycle. Six trees were used whose dating was not free 

 from small errors. The measures were smoothed by 9-year running means 

 and a comparison with a similar smoothed curve of southern California rain- 

 fall showed some resemblance. This was considered encouraging because the 

 energy used in carrying moisture from the oceans to these forests comes from 

 the sun. In 1906, the ring records of 19 more sections of western yellow pine 

 from locations near Flagstaff were compared with rainfall data in long running 

 means with similar promising results. These comparisons are shown in 

 figure 47. 



i! 



-oO 



1870 1880 1890 1900 



Fig. 47 — Arizona tree growth and California rainfall; curves of 1909. 



Comparisons with rainfall could only reach back to 1898 near Flagstaff, 

 1867 near Prescott, and 1851 in southern California, but correlations with 

 solar records could extend back to the beginning of the latter in 1610. 

 Integrations of sunspot data in a cycle length of 11.4 years were compared 

 with similar integrations of tree records (not yet accurately dated), southern 

 California rainfall and temperature. This set of curves, prepared in 1908, 

 gave the first crude record of the Hellmann cycle in trees, as shown in 

 figure 48. In this correlation diagram, two crests appeared in the Arizona 

 trees, two crests appeared in southern California rainfall; one crest and a 

 possible second are seen in the temperature curve and, of course, only one in 

 the sunspot curve. A maximum of tree growth, rainfall, and temperature 

 came near the minimum of sunspots. 



116 



