Marin Mersenne

Who Counted A Musical Note · Friar & Natural Philosopher · 1588–1648

The friar whose Paris cell was the post office of European science, and who turned a musical note into a NUMBER by counting the vibrations of a string slow enough to see.

Who was Mersenne?

Marin Mersenne was born in Maine in 1588, educated at the Jesuit college of La Flèche alongside Descartes, and entered the Order of Minims in 1611. His cell at the Place Royale in Paris became the meeting place of the new natural philosophy in France, and his correspondence — with Descartes, Galileo, Fermat, Roberval, Gassendi, Torricelli, Pascal and the young Huygens — did the work that learned journals did later. He held that a discovery kept private was not a discovery, and he copied out and forwarded whatever reached him. His own great work is the Harmonie universelle of 1636, on sound and music. In it he set out what determines the pitch of a stretched string: the frequency falls as the string is lengthened, rises as it is tightened, and falls as it is made thicker — relations still taught under his name. Crucially, he found a way to attach a number to a pitch. A string long and heavy enough vibrates slowly enough to be counted by eye, and by scaling from such a string to shorter ones he could say how many vibrations a second an audible note corresponds to. He also measured the speed of sound in air, by firing a gun at a known distance and timing the delay with a pendulum, obtaining a figure close to the modern value; and he heard, in a single plucked string, the higher tones we call harmonics.

Major achievements

• Established the laws relating a string's pitch to its length, tension and thickness
• Made pitch a number by counting the vibrations of a slow string and scaling up
• Measured the speed of sound in air with a gun and a pendulum, close to the true value
• Identified the harmonics audible in a single plucked string
• Translated and defended Galileo in France when doing so carried a risk

Life in brief

• 1588 — Born in Maine: Educated at La Flèche alongside Descartes.
• 1611 — Enters the Minims: The order he never left.
• 1620s — The cell at the Place Royale: The correspondence network begins.
• 1634 — Translates Galileo: The mechanics published in France.
• 1636 — Harmonie universelle: The laws of the string, and pitch as a number.
• 1640s — The speed of sound: A gun at a distance, timed by pendulum.
• 1648 — Dies at Paris: The circle in his cell becomes the Académie.

Explore the life of Mersenne — five chapters

1. From La Flèche to a Religious Order — A labourer's son who took vows and never left
2. The Cell at the Place Royale — Europe's science, copied out by hand and sent on
3. Making Pitch a Number — Harmonie universelle, 1636
4. A Gun, a Distance and a Pendulum — The first good measurement of the speed of sound
5. The Primes, Galileo, and What Came After — A translation that carried risk, and a circle that became an institution

Read the five-chapter life of Marin Mersenne →

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