Beer, Samuel H.
Clarendon Press, 1957
Buku Teks
Titmuss, Richard M.
University of Toronto Press , 1962
Buku Teks
Trevelyan, George Macaulay, 1876-1962, author
Longmans , Green, 1948
Buku Teks
Kiralfy, A.K.R.
Sewwt & Maxwell Limited, 1960
Buku Teks
Jackson, David, author
LLoyd's of London Press, 1987
Buku Teks