RELATION BETWEEN TERRESTRIAL AND SOLAR RECORDS 



117 



In 1911 a full total of about 10,000 ring measures had been made when it was 

 proposed to test what seemed a highly improbable relationship; namely, a 

 linear positive correlation between ring thickness and annual rainfall. After 



ll'/3 YEAR 

 PERIOD 



Rain 

 (California) 



in. 

 +8.0 



+4.0 



o 



-4.0 

 -8.0 



°F. 



Temperature 

 (San Diego) ° 



Inverted 

 sunspot curve 



1863 



1874 



Tree growth 

 (Arizona) 



Fig. 48 — First western correlations, 1909. The horizontal scale gives proportionate 

 parts of 11£ years. Rainfall curves are: dotted line — San Francisco; broken line — San 

 Diego; full line— their average, approx. 1850-1900. Tree Growth, 1701-1906. 



adjusting the rainfall year to begin near October of the preceding year, com- 

 parisons were made upon an accurately dated group just collected and the 

 agreement was obvious. In the same year, a group of specimens from Pres- 



