Chamberlain, Neil W. (Neil Wolverton), author
McGraw-Hill, 1980
Buku Teks
Garrett, James M., author
Westview Press, 1989
Buku Teks
Artikel Jurnal
East, Roger, author
Pinter Publishers, 1997
Buku Teks
Shotwell, James T., author
New York, N.Y. MacMillan Co. 1940,
Buku Teks