Wichman, K., author
New York, David Mckay Company
Buku Referensi
Wessely, J.E., author
Chicago dsb. Pollett Publ. 1946
Buku Referensi
Wichman, Karl, author
Philadelphia, David McKay Company, 1944
Buku Referensi
Breul, Karl, author
Boston D.C. Heath 1936
Buku Referensi
Oxford , Clarendon Press
Buku Referensi