CYCLES. 99 
conspicuous and general cycles at once apparent in the trees are directly 
related to the solar period. They are as follows: 
5to 6 years approximate half sunspot period. 
“ “ “ 
10to 13. “ full 
Zito 24 “ ‘ double ‘ , 
32to 35 “ triple“ a 
100t0 105“ “ triple-triple “ Y» 
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 1l-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 
