Northrop, H. D. (1896). The gem cyclopedia of universal knowledge, being a complete treasury of information for everyday use..: The whole forming a complete guide and self-instructor on scientific, commercial, historical, artistic and all other subjects. H. J. Smith & Simon Pub. Co..
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Northrop, Henry Davenport. The Gem Cyclopedia of Universal Knowledge, Being a Complete Treasury of Information for Everyday Use..: The Whole Forming a Complete Guide and Self-instructor on Scientific, Commercial, Historical, Artistic and All Other Subjects. Chicago: H. J. Smith & Simon Pub. Co., 1896.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Northrop, Henry Davenport. The Gem Cyclopedia of Universal Knowledge, Being a Complete Treasury of Information for Everyday Use..: The Whole Forming a Complete Guide and Self-instructor on Scientific, Commercial, Historical, Artistic and All Other Subjects. H. J. Smith & Simon Pub. Co., 1896.