Parks, Wallace Judson, author
Johns Hopkins Press, 1951
Buku Teks
edited by Allan Nevins and Louis M. Hacker
D.C. Heath, 1943
Buku Teks
Stebbins, Richard P., author
Harper & Row, 1963
Buku Teks
Kemmerer, Donald L., author
Littlefield, Adams, 1956
Buku Teks
Lippincott, Isaac, author
Appleton Century Croffs, 1933
Buku Teks