The sunspot period
(with one plate)
by H. Helm Clayton.

APA Citation

Clayton, H. Helm. (1939). The sunspot period: (with one plate). Washington: Smithsonian Institution.

MLA Citation

Clayton, Henry Helm, 1861-1946. The Sunspot Period: (with One Plate). Washington: Smithsonian Institution, 1939.

Warning: These citations may not always be complete (especially for serials).