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.

阿米尔•艾克塞尔（Amir D. Aczel）

数学家、专业作家，1975年毕业于加州大学伯克利分校，1976年获自然科学硕士学位。曾先后任教于加利福尼亚、阿拉斯加、意大利和希腊的大学讲授数学，出版过两本教科书以及若干数学与自然科学方面的非技术类著作，其中包括曾入围“洛杉矶时报年度好书奖”的《费马最后定理》（Fermat’s Last Theorem，1998）；另有《爱因斯坦的方程式》（God’s Equation，2001）。2004年成为约翰•西蒙•古根海姆纪念基金会研究员（Fellow of the John Simon Guggenheim Memorial Foundation），现为哈佛大学数学史系访问学者。