I50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



He finds well-marked periods of 150 years/ 21 years, and 11. 4 years. 

 The last period, which corresponds to the sun spot period, is gen- 

 erally divided into two shorter periods and has two maxima and two 

 minima. This is particularly the case in the earlier 250 years from 

 about 1420 to about 1670. In the time from about 1670 to about 

 1790 these periods and also the eleven-year periods are less marked. 

 In the time from about 1790 until now there are again two maxima 

 and two minima within the eleven-year period, but the minimum 

 in the middle of the period, that is, at sun spot maximum, is deep- 

 est; so that particularly during this time the growth of trees in 

 Arizona and consequently the precipitation varied oppositely to 

 the sun spots. Prof. Douglass gives also a mean eleven-year curve 

 for the precipitation and for the temperature on the coast of Cali- 

 fornia, which is 500 miles from the Arizona region, for the 50 years 

 1863 to 1912. This curve shows great similarity to the average 

 curve of the eleven-year period for the growth of trees in Arizona 

 during 492 years and also a similarity to the inverted average curve 

 of sun spots for the eleven-year period, with the exceptions that the 

 curves for growth and precipitation show two' well-developed maxima 

 within the eleven-year period. 



By measurements of the yearly rings of growth of thirteen trees, 

 at Eberswalde (in Germany) Douglass obtains a curve for the 

 growth of these trees between 1830 and 191 2 which corresponds 

 well with the sun spot curve. Apparently in this region in Germany 

 the growth of trees and the precipitation vary with the sun spots 

 and not oppositely to them as in Arizona. Only in the sun spot 

 period between 1890 and 1901 there is discordance and the variation 

 goes inversely. In this period, however, we find in other meteoro- 

 logical relations similar discordances. 



Douglass' curve for the growth of trees in Eberswalde shows also, 

 though he does not mention it, a shorter period which agrees in 

 part with the variations of the prominence curves and the magnetic 

 curves. 



Huntingdon in 1914 has also given measurements of the yearly 

 rings of a great many old trees (Sequoias and Evergreen trees) in 

 California and New Mexico in his investigations on climatic varia- 

 tions. His results point to the fact that great variations in preci- 

 pitation occurred during the last 3,000 years. He pays little atten- 

 tion, however, to the periodicity in recent times. 



* See the period of three hundred years of Clough (1905) and of seventy-two 

 years of Hansky (1894). 



