CYCLES. . 99 



conspicuous and general cycles at once apparent in the trees are directly 

 related to the solar period. They are as follows: 



5 to 6 years approximate half sunspot period. 

 10 to 13 " " full 



21 to 24 " double " 



32 to 35 " triple " 



100 to 105 " " triple-triple " 



There are few if any periods over 20 years not in this list, but under 

 20 years several are fairly persistent, such as 19-, 14-, 10-, and 7-year 

 periods. There is also a period of about 2 years which causes a frequent 

 alternation of size in successive rings, giving a " see-saw" or " zig-zag" 

 effect in the appearance of the curve. The discussion in this chapter, 

 however, will be confined to the solar group of periods above listed and 

 to a preliminary statement regarding the 2-year period. As the larger 

 of these solar periods are very nearly simple multiples of the 11-year 

 period, it is naturally suspected that they are or should be real multiples 

 of the sunspot period. Hence I feel at liberty to speak of the " double 

 sunspot period" or the " triple sunspot period" without committing 

 myself to its exact length. 



Locality and solar cycles. Compared to the multitudes of meteoro- 

 logical districts about the world, the few isolated localities which have 

 here been investigated seem very insignificant. The wet-climate trees 

 near the Baltic Sea show variations following almost perfectly the 

 curve of sunspot numbers. The Scotch pines just south of the sea have 

 had good care since they were planted about 90 years ago. This care 

 has prevented the excessive competition between individuals which 

 characterize natural forests, and perhaps for that reason they give this 

 remarkable record of external conditions. The trees to the north of 

 the Baltic include spruces as well as Scotch pines, and show the same 

 reaction. Both these groups are in comparatively level country and 

 far from mountains. The group of pines from the Swedish province of 

 Dalarne show the 11-year period somewhat less clearly. They were 

 nearer the backbone of mountains which extends down the Scandi- 

 navian peninsula. The older trees of this group show evidence of a 

 triple sunspot period. The groups growing in the mountains and in the 

 inner fjords of Norway show extensive variations and even reversals. 

 Some of the individual trees exhibit the sunspot period very well, 

 while some show it inverted and some divide it into two crests. The 

 older trees show evidence of an inverted double period. 



The trees near sea-level, both at Christiania, and on the outer coast 

 of Norway, return again to the 11-year period. The former do not 

 cross-identify well and the latter show occasional variations, such as 

 double-crested period, inversion, etc. Variations of this kind were 

 noted in different radii of the same tree. The trees from the south of 



