Clark, Victor S., author
Carnegie Institution of Washington, 1949
Buku Teks
Clark, Victor S., author
Peter Smith, 1949
Buku Teks
Hicks, John R., author
Houghton Mifflin , 1946
Buku Teks
Williams, T. Harry, author
Alfred A. Knopf, 1963
Buku Teks
Risjord, Norman K., author
Prentice-Hall, 1985
Buku Teks