Artikel Jurnal
edited by Harold C. Gardiner
Devin-Adair Co., 1949
Buku Teks
Robert Maynard Hutchins, editor in chief
Encyclopaedia Britannica, Inc., 1952
Buku Referensi
Keller, Helen Rex
McMillan Company, 1959
Buku Referensi
Campbell, Oscar James
Crofts, 1947
Buku Teks