Kinmel, Lewis H.
Brookings Institution , 1950
Buku Teks
Painter, William H.
Little,Brown and Company, 1971
Buku Teks
Painter, William H.
Little,Brown and Company, 1981
Buku Teks
Princeton University Press, 1964
Buku Teks
Marsh, Donald Bailey
Jaques Cattel Press , 1945
Buku Teks