YELLOW PINES AND SEQUOIAS OF THE SOUTHWEST. 121 



period of about twenty-three years was a more satisfactory means of 

 tracing the vicissitudes of the solar period. When these conditions 

 were observed the same result was obtained as before from Arizona. 

 The twenty-three-year period, in fact, begins to show change about 

 1635 instead of 1645 ^^^ continues on a ten-year cycle to the neigh- 

 borhood of 1712, when the double sunspot period is resumed. Prob- 

 ably more and more evidence will be brought to bear on this point. 

 Almost at the time of writing it is noticed that the Vermont hemlocks 

 show a ten-year period from their beginning in 1654 to well on in 

 the middle of the next century. The eleven-year period begins to 

 show at about 1700 and becomes dominant in the latter part of that 

 century. Modifications will doubtless be made in historical review 

 of evidence in the trees of the prolonged dearth of solar influence at 

 that time, but the evidence, so far as it goes, is wholly in favor of a 

 pronounced effect in the growth of trees. 



This correlation found in response to Professor Maunder's note 

 therefore led to two results. First, it seemed to confirm strongly the 

 idea that the cycles in the trees are not merely real, but they are 

 related to weather elements and to cosmic causes ; and, second, it gave 

 added weight to the provisional history of solar variation derived 

 from a study of the 3,200 years of sequoia growth. There has not 

 been enough time yet to review that large mass of measures and 

 derive a satisfactory history, but in conclusion a brief memorandum 

 upon that point will be of interest. It is probable that from 1300 

 B.C. to well after 1000 B.C. the sunspot cycle was well developed; 

 then it slowly decreased. From 300 B.C. on, it was increasing and 

 was very conspicuous during the first two centuries of our era. 

 Then it decreased and from 400 to 650 A.D. was only occasionally 

 evident. From 650 to 850 or 900 it seems fairly continuous. Then 

 it appears only occasionally until about 1250, when it again became 

 fairly continuous with the changes in the seventeenth century above 

 noted. 



Thus there seem additional grounds for regarding the trees as 

 supplying useful historic data and giving us long ranges of time over 

 which to study the vagaries of our fickle climate. 



In summarizing one notes a strong topographic effect in the trees 

 of the Southwest, as expected; the maximum growth in well-watered 



