Brace, Richard M., author
Holt, Rinehart and Winston, 1961
Buku Referensi
Snyder, Louis L., author
D. van Nastrand Company, Inc., 1967
Buku Teks
Brinton, Crane, 1898-1968, author
Prentice-Hall, 1957
Buku Teks
Hoffding, Harold, author
Macmillan, 1955
Buku Teks
edited by G. Goodwin
Cambridge University Press, 1958
Buku Teks