Ren Descartes (15961650) is one of the towering and central figures in Western philosophy and mathematics. His apothegm Cogito, ergo sum marked the birth of the mind-body problem, while his creation of so-called Cartesian coordinates has made our intellectual conquest of physical space possible.But Descartes had a mysterious and mystical side, as well. Almost certainly a member of the occult brotherhood of the Rosicrucians, he kept a secret notebook, now lost, most of which was written in code. After Descartess death, Gottfried Leibniz, inventor of calculus and one of the greatest mathematicians of all time, moved to Paris in search of this notebookand eventually found it in the possession of Claude Clerselier, a friend of Descartess. Liebniz called on Clerselier and was allowed to copy only a couple of pageswhich, though written in code, he amazingly deciphered there on the spot. Liebnizs hastily scribbled notes are all we have today of Descartess notebook.Why did Descartes keep a secret notebook, and what were its contents? The answers to these questions will lead the reader on an exciting, swashbuckling journey, and offer a fascinating look at one of the great figures of Western culture.From the Hardcover edition.