René Descartes (1596–1650) 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 have made our physical and 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 Descartes’s death, Gottfried Leibniz, inventor of calculus and one of the greatest mathematicians in history, moved to Paris in search of this notebook—and eventually found it in the possession of Claude Clerselier, a friend of Descartes. Leibniz called on Clerselier and was allowed to copy only a couple of pages—which, though written in code, he amazingly deciphered there on the spot. Leibniz’s hastily scribbled notes are all we have today of Descartes’s notebook, which has disappeared.

Why did Descartes keep a secret notebook, and what were its contents? The answers to these questions lead Amir Aczel and the reader on an exciting, swashbuckling journey, and offer a fascinating look at one of the great figures of Western culture.

阿米爾•艾剋塞爾（Amir D. Aczel）

數學傢、專業作傢，1975年畢業於加州大學伯剋利分校，1976年獲自然科學碩士學位。曾先後任教於加利福尼亞、阿拉斯加、意大利和希臘的大學講授數學，齣版過兩本教科書以及若乾數學與自然科學方麵的非技術類著作，其中包括曾入圍“洛杉磯時報年度好書奬”的《費馬最後定理》（Fermat’s Last Theorem，1998）；另有《愛因斯坦的方程式》（God’s Equation，2001）。2004年成為約翰•西濛•古根海姆紀念基金會研究員（Fellow of the John Simon Guggenheim Memorial Foundation），現為哈佛大學數學史係訪問學者。