Johnson, Harry G., author
George Allen and Unwin, 1958
Buku Teks
Root, Franklin R., author
Sout-Western, 1966
Buku Teks
Marsh, Donald Bailey
Harcowith, Brace and Company , 1951
Buku Teks
edited by Roy Harrod
Martin Press, 1965
Buku Teks
Viner, Jacob, author
George Allen and Unwin, 1960
Buku Teks