Ambrose, James E., author
John Wiley & Sons, 2005
Buku Teks
Shaeffer, R.E., author
Prentice-Hall, 2001
Buku Teks
Laseau, Paul
John Wiley & Sons, 2001
Buku Teks
Laseau, Paul, author
Cahners Books, 1975
Buku Teks
prepared by the Special Publications Division, National Geographic Society, Washington, D.C.
The National Geogarphic Society, 1986
Buku Referensi