The New Encyclopaedia Britannica : volume 18, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi
The New encyclopaedia Britannica : volume 21, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi
The New encyclopaedia Britannica : volume 24, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi
The New encyclopaedia Britannica : volume 29, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi
The New encyclopaedia Britannica : volume 28, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi