Lewes, George Henry, author
Cambridge University Network, 2012
eBooks
Mayer, Frederick, author
American Book Company, 1951
Buku Klasik
Meijering, E.P.
North-Holland , 1975
Buku Teks
Glenn, Paul J.
B. Herder book co, 1950
Buku Teks
Collins, James, author
The Bruce Publishing Company, 1954
Buku Teks