Trattner, Walter I., author
Free Press, 1979
Buku Teks
Thistlethwaite, Frank, author
Cambridge University Press, 1955
Buku Teks
Adams, James Truslow, author
1946
Buku Referensi
editor Thomas C. Cochran, Wayne Andrew
Charles Scribner's Sons , 1962
Buku Referensi
U.S. Information Service,, 1981
Buku Teks