Carrel, Alexis
Man the unknown
Penguin Books, 1967
 Buku Teks
De Blij, Harm J.
Geography : realms, regions, and concepts
John Wiley & Sons, 1994
 Buku Teks
De Blij, Harm J.
Geography : realms, regions, and concepts
John Wiley & Sons, 1997
 Buku Teks
Carnegie, Dale, 1888-1955
Lincoln: the unknown/Dale Carnegie
New York :Dake Carnegie & associates, Inc. ,1999,
 Buku Teks
Ireland, David
The unknown industrial prisoner
Angus and Roberson Publishers, 1983
 Buku Teks