edited by Harold C. Gardiner
Devin-Adair Co., 1949
Buku Teks
Mortimer J. Adler, editor in chief
Encyclopedia Britanica, 1994
Buku Referensi
Watt, Homer A., author
Scott, Foresman and company , 1925
Buku Teks
P. F. Collier & Son Corporation, 1959 ; 1969
Buku Referensi
P. F. Collier & Son Corporation, 1969
Buku Teks