René Descartes (1596-1650) and Marin Mersenne (1588-1648), two of the greatest 17th century French minds, carried on a regular correspondence. In this lengthy 1640 letter to Mersenne, Descartes ranges widely, discussing a dispute with Pierre Bourdin, a Jesuit who had advanced a number of objections to Descartes’ Meditationes de Prima Philosophia, then circulating in manuscript form:
[H]enceforth I shall take what comes from one of them as coming from the whole Society … [I]t may happen that Father Bourdin, not to have the shame of retracting, and of allowing the denial to remain with him, will be very glad to send me objections, however bad they may be, in order to gain time and make me lose it. But when they see that the honor of the whole Society is at stake, I think they will prefer to make him hold his tongue, because I know very well he has nothing good to say.
Descartes then turns to a question of physics, with a small explanatory diagram in the margin:
You ask how I know that the bullet coming from D towards B returns to E, rather than continuing towards B. I learn this from the knowledge of the laws of nature, one of which is that “whatever is, remains in the same place in which it is, unless it be changed by some external cause,” thus … what is once in motion is always in motion until something stops it.
Houghton also holds a 1647 letter from Descartes to Mersenne, and it too has been digitized.
This post is part of a weekly feature on the Houghton Library blog, “You’ve Got Mail,” based on letters in Houghton Library. Every Friday this year a Houghton staff member will select a letter from the diverse collections in the Library and put that letter into context. All posts associated with this series may be viewed by clicking on the You’veGotMail tag.
[This post was contributed by John Overholt, Acting Curator of the Donald and Mary Hyde Collection of Dr. Samuel Johnson and Early Modern Books and Manuscripts.]
