edited by John A. Wolter and Ronald E. Grim
Library of Congress, 1977
Buku Referensi
edited by Edward Friedman
Sage, 1982
Buku Teks
Cipolla, Carlo M., author
Penguin, 1974
Buku Teks
McNally, Rand, author
Rand McNally & Co, 1957
Buku Referensi
Hodges, Henry, author
Penguin Press, 1970
Buku Teks