150 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
The double and quadruple master periods of about 46 and 91 years 
seem even more prominent than the 23-year cycle in precipitation. 
In further illustration of the effects of the 23-, 46-, and 91-year perio- 
dicities I give figures 18, 19, and 20. They show, respectively, the 23- 
year period in the growth of trees in California, the 46-year period 
in the precipitation at Bismarck, N. D., and the 23-, 46-, and 91-year 
periods in the level of Lake Huron. It seems probable that large de- 
lie ren les eae 
te ea 
Fi a Pa 
a ee Se 
ACS CIC TNA ir 
OWN TU CHEW — 
WA TT | 
My 
4 188s 6 7 8 9 
PERCENTAGE OF NORMAL PRECIPITATION 
o 
Nh AE 
WAM | VW LT Lee 
pth A a 
SS SS 
eS ale A sa a a 
20 
1930 1 1935 1940 \ 3 1944 
BISMARCK, S.DAKOTA. PRECIPITATION AT EPOCHS SEPARATED 46 YEARS. 
Ficure 19.—The dotted line in the lower curve, from 1937 to 1943, was drawn in 
1937 as a prediction. 
clines in the Great Lakes levels, accompanying great droughts in the 
Northwest, will begin about the years 1975 and 2020. 
THE 14 SOLAR PERIODICITIES REFLECTED INDIVIDUALLY IN 
WEATHER 
There is another method of making long-range weather forecasts 
based on solar variation. With strict attention to the seasonal in- 
fluences on phase already referred to, one may compute from monthly 
