DOUGLASS PLATE 9
A. Periodogram of the sunspot numbers, 1755-1911. Corrugations show periods. The
B. Differential pattern used in making the periodogram, consisting of the sunspot curve
C. Same pattern photographed out of focus to show discontinuities in the vertical lines.
D. Sweep of sunspot numbers, 1755-1911.
E. Differential pattern of sunspot numbers made by the periodograph process.