Weale, B.L. Putnam
MacMillan , 1908
Buku Teks
London : Pancy Lund Humpries
Majalah, Jurnal, Buletin
Buss, Claude Albert, author
Macmillan, 1941
Buku Teks
Clyde, Paul H. (Paul Hibbert), author
Prentice-Hall, [date of publication not identified]
Buku Teks
Clyde, Paul Hibbert, author
Prentice-Hall, 1960
Buku Teks