Magruder, Frank Abbott
Allyn and Bacon, 1939
Buku Teks
Moon, Parker Thomas, author
Macmillan, 1926
Buku Referensi
Sills, Theodore R
Richard D.Irwin,Inc, 1951
Buku Teks
Macmahon, Arthur W.
University of Alabama Press, 1953
Buku Teks
Numelin, Ragnar
Oxford University Press, 1950
Buku Teks