National Geographic Socity. Special Publication Division & Gray, W. B. (1978). Power of nature. Prepared by the Special Publication Division, National Geographic Society.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)National Geographic Socity. Special Publication Division و William B. Gray. Power of Nature. Washington, DC: Prepared by the Special Publication Division, National Geographic Society, 1978.
توثيق جمعية اللغة المعاصرة MLA (الإصدار التاسع)National Geographic Socity. Special Publication Division و William B. Gray. Power of Nature. Prepared by the Special Publication Division, National Geographic Society, 1978.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.