Encyclopaedia britanica: Knowledge in depth. Volume XIV.

Encyclopaedia britanica: Knowledge in depth.Volume XIII.

Encyclopaedia britanica: Knowledge in depth. Volume XV.

Encyclopaedia britanica: Knowledge in depth. Volume XVI.

Encyclopaedia britanica: Knowledge in depth. Volume XVIII.

Encyclopaedia britanica: Knowledge in depth. Volume XVII.

Encyclopaedia britanica: Knowledge in depth. Volume XIX.

Encyclopaedia britanica: knowledge in depth. Volume VIII.

Encyclopaedia britanica: knowledge in depth. Volume VII.

Encyclopaedia britanica: knowledge in depth. Volume X.

Encyclopaedia britanica: knowledge in depth. Volume IX.

Encyclopaedia britanica: knowledge in depth. Volume XII.

Encyclopaedia britanica: knowledge in depth. Volume XI.