McLaughlin, Andrew C., author
Appleton Century Crofts, 1935
Buku Teks
Alden, John Richard, author
American Book Company, 1960
Buku Teks
Clark, Victor S., author
Carnegie Institution of Washington, 1949
Buku Teks
Bemis, Samuel Flagg, 1891-1973, author
Holt, Rinehart and Winston, 1965
Buku Teks
Curtis, William J.R., author
Prentice-Hall, 1996
Buku Teks