Tucker, Caroline, author
Ariel & Books, 1962
Buku Teks
Weaver, John D.
Little, Brown & Co., 1965
Buku Teks
Stanford University Press, 1969
Buku Teks
Klaus, Marshall H.
Mosby Comp., 1982
Buku Teks
Robert Maynard Hutchins, editor in chief
Encyclopaedia Britannica, Inc., 1952
Buku Referensi