Schiphol writes of a long-lost letter by René Descartes to Marin Mersenne that has come to light at Haverford College, in Pennsylvania, where it had lain buried in the archives for more than a century. The discovery could revolutionize our view of one of the 17th-century French philosopher's major works. "[T]housands of treasured documents... vanished from the Institut de France in the mid-1800s, stolen by an Italian mathematician. Among them were 72 letters by René Descartes... Now one of those purloined letters has turned up at a small private college in eastern Pennsylvania... The letter, dated May 27, 1641, concerns the publication of Meditations on First Philosophy, a celebrated work whose use of reason and scientific methods helped to ignite a revolution in thought."