Chapman, Robert L., author
London Pan Books 1988
Buku Referensi
Reifer, Mary, author
Philosophical Library, 1955
Buku Referensi
Geddes & Grosset, 2000
Buku Referensi
edited by. Frank Gaynor
New York, Philosophical library, 1951
Buku Referensi
Collins Clear-Type Press, 1960
Buku Referensi