National Geographic Socity. Special Publication Division & Gray, W. B. (1978). Power of nature. Prepared by the Special Publication Division, National Geographic Society.
Chicago-referens (17:e uppl.)National Geographic Socity. Special Publication Division och William B. Gray. Power of Nature. Washington, DC: Prepared by the Special Publication Division, National Geographic Society, 1978.
MLA-referens (9:e uppl.)National Geographic Socity. Special Publication Division och William B. Gray. Power of Nature. Prepared by the Special Publication Division, National Geographic Society, 1978.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.