editor in chief, Charles A. Ford
Encyclopedia Britannica Educational Corporation, 1969
Buku Referensi
edited by Jonathan Bate and Russell Jackson
Oxford University Press, 1996
Buku Teks
Wilkes, Peter
Peter Wilkes, 1978
Buku Teks
edited by Peter Hunt
Oxford University Press , 1995
Buku Teks
Richards, Denis
Longman, Green, 1952
Buku Teks