# Marin Mersenne

# Marin Mersenne

**1588-1648**

**French Mathematician**

As a mathematician and scientist, Marin Mersenne was far from the equal of his more well-known friends and acquaintances, including Galileo (1564-1642), René Descartes (1596-1650), Pierre de Fermat (1601-1665), Blaise Pascal (1623-1662), and Christiaan Huygens (1629-1695). Yet without Mersenne, the world would know far less about these giants: in a time when there were no scientific journals, Mersenne served as a disseminator of knowledge. An avid correspondent, he also conducted weekly scientific discussions in Paris that became the basis for the French Académie Royale des Sciences. In addition, he inspired investigations into number theory and prime numbers, as well as Huygens's invention of the pendulum clock.

Mersenne was born on September 8, 1588, near the town of Oize in France, and at the age of 23 became a Catholic friar. While in school, he met Descartes, destined to become a lifelong friend. He also became acquainted with Galileo, who he defended against attacks from the church. Eventually Mersenne would be responsible for a "meeting of the minds" between his two distinguished friends. He passed on to Descartes a question from Galileo regarding the path of falling objects on a rotating Earth, and this led to Descartes's suggestion of the logarithmic spiral as the likely path.

Again and again, Mersenne performed this role of bringing great minds together, and both with his correspondence and his weekly meetings, he began creating what a modern person might call a vast database of knowledge. At the meetings, figures such as Descartes, Fermat, and Pascal assembled under one roof to share ideas and argue for opposing theories. Mersenne also had an opportunity to read manuscripts by Descartes and others, in some cases long before they were published.

Though Mersenne wrote widely on mathematical and scientific subjects, he would always be more well-known as a disseminator of works by other thinkers—including ancient Greeks such as Euclid (c. 325-c. 250 b.c.), Archimedes (c. 287-212 b.c.), Apollonius of Perga (262-190 b.c.), and others, whose works he edited. Of his own writings, the most significant was *Cogitata physico-mathematica* (1644), in which he put forth several theorems regarding prime numbers. The theorems turned out to be incorrect, but inspired later investigations into number theories and large primes—sometimes called Mersenne primes.

Mersenne was also the one who suggested that Huygens use a pendulum as a timekeeping device, and this led to the latter's introduction of the pendulum clock in 1656. By then, however, Mersenne was long gone, having died in Paris on September 1, 1648, at the age of 60.

**JUDSON KNIGHT**

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**Marin Mersenne**