Kull, Irving S.
Rutgers University, 1952
Buku Teks
Voice of America Forum Lectures, 1967
Buku Teks
Malin, James C.
The American Philosophical Society , 1942
Buku Teks
Adams, James Truslow, author
1946
Buku Referensi
editor Thomas C. Cochran, Wayne Andrew
Charles Scribner's Sons , 1962
Buku Referensi