Finer, S. E.
Clarendon Press Oxford, 1995
Buku Teks
Andrews, William G.
D.van Nostrand Company,Inc., 1968
Buku Teks
Gibson, William M.
Duke University Press, 1948
Buku Teks
Wheare, K. C.
Oxford University Press, 1975
Buku Teks
Maddex, Robert L.
London: Routledge, 1995,
Buku Referensi