Stout, Hiram Miller
The University of North Carolina Press, 1938
Buku Teks
Bennett, Martyn
Routledge, 2000
Buku Teks
England. Cabinet Office
Her Majesty's Stationery Office, 1989
Buku Referensi
England. Cabinet Office
Her Majesty's Stationery Office, 1988
Buku Referensi
editor, Andrew Massey
Edwar Elgar, 2011
Buku Teks