The Complete Paintings of Leonardo da Vinci by Angela Ottino della Chiesa, Published by Penguin Books.

The Sacred Science of Numbers by Corinne Heline, Published by De Vorss & Co., Publishers.

The Notebooks of Leonardo da Vinci Compiled and Edited by Jean Paul Richter, Volumes 1 & 2, Published by General Mills Publishing Co.

The Secret Teachings of All Ages by Manly P. Hall, Published by the Philosophical Research Society, Inc.