DOUGLASS 
Ss Oare 
PLATE 11 
. Periodogram of standard 5-year period. 
. Periodogram of mixed periods. 
. Periodogram of sunspot numbers, 1610-1910. 
. Periodogram of Flagstaff 500-year record, to show cycles 
between 4 and 15 years of length. 
. Periodogram of same continued to 25 years. 
