The New Encyclopaedia Britannica : volume 19, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi
The New Encyclopaedia Britannica : volume 18, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi
The New encyclopaedia Britannica : volume 20, 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 22, macropaedia knowledge in depth
Encyclopaedia Britannica Inc., 1998
 Buku Referensi