TY - JOUR T1 - A Photographic Periodogram of the Sun-Spot Numbers JF - The Astrophysical Journal, Y1 - 1914 A1 - Douglass, A.E. KW - Douglass KW - numbers KW - periodogram KW - photo KW - photographic KW - spot KW - sun KW - sun spot VL - XL IS - No. 3 ER -