Marin Mersenne

French scientist and mathematician

• Born: September 8, 1588
• Birthplace: La Soultière, France
• Died: September 1, 1648
• Place of death: Paris, France

Mersenne is best known as the priest-scientist who facilitated the cross-fertilization of the most eminent minds of his time. He is widely commemorated for helping to establish modern science by promoting the new ideas of Nicolaus Copernicus, Galileo, and René Descartes and by attacking what he believed to be the pseudo- sciences of alchemy, astrology, and natural magic.

Early Life

Marin Mersenne (mah-rahn mehr-sehn) was born in a small town about 120 miles southeast of Paris. His mother and father, both laborers, were devout Catholics, and their son was baptized on the day he was born and received the unusual name Marin because his birth date fell on the feast of the Nativity of Mary. From his earliest years of schooling, Mersenne showed a disposition for piety and study. His parents, despite their modest condition, were able to send him, first, to the Collège de Mans, where he studied Latin, Greek, and grammar, and, later, to the new Jesuit college at La Flèche, where he went through the already famous course of studies of the Society of Jesus, with its emphasis on the humanities, rhetoric, and philosophy. At this school, Mersenne also studied Aristotelian physics, mathematics, and astronomy. The philosophy he learned was Scholasticism. René Descartes was also studying at La Flèche at this time, but they did not become close friends until 1623.

After finishing his studies at La Flèche in the summer of 1609, Mersenne went to Paris, where he spent two years studying theology. There he came into contact with the Minims, a mendicant order of friars founded in 1435 by Saint Francis of Paola. Their rule, modeled on Saint Francis of Assisi’s, emphasized humility, and they were encouraged to regard themselves as the least (minimi) of all religious persons. Mersenne, impressed by their piety and asceticism, decided to enter the order. He became a Minim friar in 1611, and after a short novitiate he professed his vows of poverty, chastity, and obedience at the age of twenty-four. He returned to Paris and was ordained soon afterward, celebrating his first mass in 1613.

The provincial of the Minims assigned Mersenne in 1614 to teach philosophy to young friars at the convent at Nevers. During his five years there, he became interested in mathematics and science. Religious reasons were inextricably bound up with the development of this interest, because he saw the contemporary proliferation of the occult arts of alchemy, astrology, and magic as a danger both to science and to religion. Followers of the occult arts were sometimes called naturalists, because they believed that nature had a soul. Modern scholars call them Hermeticists, because their inspiration was Hermes Trismegistus, the legendary author of works on astrology, alchemy, and magic. Mersenne fought this animistic world with every weapon at his disposal, because to him it was false religion and false science. According to Saint Thomas Aquinas and other Catholic theologians, God created a hierarchical world, from angels through human beings to animals, plants, and the inanimate world. Hermeticists attacked this system. For them the world existed on a single level, and therefore religious and natural facts were blended, a pantheistic view that Mersenne found abhorrent. In the Hermeticists’ system, the causality that was once assigned to God or spirits became the province of plants, animals, metals, and especially stars. Certain stones could provoke storms, the position of the Sun in the zodiac at a person’s birth could determine his or her character and destiny, and the like. Because physical contact was no longer necessary for one thing to have an effect on another, occult influences could be multiplied endlessly.

Life’s Work

By the time he began to teach philosophy at the Priory of the Annunciation in Paris in 1619, Mersenne had taken up his life’s task to oppose the superstitions of the Hermeticists. He lived at the Minim convent near Place Royale, which would remain his home, except for travels to the Netherlands, Spain, Italy, and the south of France, for the rest of his life. A contemporary engraving depicts him in friar’s robes, his face lightly bearded, his high forehead capped by a receding hairline, and his widely separated eyes in a gaze both piercing and kindly.

Mersenne’s literary career began in the 1620’s with the publication of a group of massive polemical works that he directed against the enemies of science and religion—atheists, Deists, skeptics, alchemists, astrologers, and Hermeticists. His first major publication was Quaestiones celeberrimœ in Genesim (1623; the most famous questions of Genesis), a formidable folio of nearly two thousand columns. On the surface, this book seemed to be a biblical commentary, but Mersenne had a broader apologetic intent: He wished to defend orthodox theology against the magical interpretations of the world presented by such Hermeticists as Giovanni Pico de la Mirandola, Tommaso Campanella , and especially Robert Fludd , whom he called an evil and heretical magician.

Mersenne continued his attack on these believers in the occult in L’Impiété des déistes, athées, et libertins de ce temps (1624; the impiety of modern Deists, atheists, and libertines). His purpose was to defend the teachings of the Catholic Church against those who denied the existence of a loving creator. He was particularly disturbed by Giordano Bruno, whom he called one of the wickedest men whom Earth has ever supported. Mersenne’s refutation of Bruno’s doctrines of a plurality of worlds, the infinity of the universe, and the universal soul, as well as his defense of the rationality of nature, attracted the attention of Pierre Gassendi , whom he met in 1624 and who became his closest friend.

By 1625, Mersenne’s defense of religion increasingly involved a defense of science. This approach characterized La Vérité des sciences, contre les sceptiques ou Pyrrhoniens (1625; the truth of the sciences against the skeptics or Pyrrhonists), a long book in the form of a discussion involving an alchemist, a skeptic, and a Christian philosopher. The philosopher argues that a genuine science of nature will develop only after mathematics and experimentation replace the false magical approach of the alchemists, who even propose that the creation of the world can be understood through chemistry. The skeptic tries to convince everyone that nothing is certain. The philosopher, though conceding that some things cannot be known, believes that many things are not in doubt, for example, relationships discovered by the scientists and equations discovered by the mathematicians.

Despite his opposition to the occult sciences, Mersenne was attracted to the modern sciences by their marvelous character. For example, he was more favorably disposed than Gassendi to comets presaging the death of kings. Mersenne could also be gullible, as when he accepted the story of a dog’s giving birth to a puppy with a human head. These lapses aside, Mersenne strongly believed that both religion and science had a rational basis but that it was important to keep religious and scientific facts separate. As time went on, however, science, which first had only influenced his religious thought, gradually came to dominate it. An example of this development was his growing acceptance of the Copernican theory that the Sun rather than Earth was at the center of the universe. In 1623, he had opposed the Copernican theory because sufficient evidence was lacking, but by 1624 he was claiming that this theory was irrefutable.

During these years, Mersenne’s circle of friends and correspondents was widening. He began to exchange letters with Descartes, who became an important influence on his thought. He also had much to do with advancing Descartes’s ideas, particularly after Descartes went to the Netherlands. In the 1620’s, Mersenne’s correspondence increased to such an extent that he was soon playing the role of communication link to a wide variety of European scientists and philosophers. His friendliness, curiosity, and eclecticism made him the ideal intermediary. His religious house in the Place Royale became a meeting place for such eminent thinkers as Pierre de Fermat , France’s foremost mathematician; Girard Desargues, the founder of descriptive geometry; and Gassendi. Because no scientific journals and no international societies existed then, these meetings at Mersenne’s residence and his widely circulated letters helped to create a genuine scientific community that would later be formalized in the French Academy of Sciences. Although his intent in his gatherings and correspondence was still basically apologetic, his visitors and correspondents did not have to be Catholic, for it was becoming increasingly clear to him that the cause of science was the cause of God. He even became friendly with Thomas Hobbes at a time when his work was being viciously attacked for its materialism but which Mersenne interpreted as a genuinely new science of humankind.

The decade of the 1630’s was important in the evolution of Mersenne’s thought. He did significant work in music and mathematics, embraced mechanism (the doctrine that the world can be explained in terms of matter and motion), and came to the defense of Descartes and Galileo, whose works were being attacked by officials of the Catholic Church. In 1634, he published four books on music. His scientific analysis of sound and its effects on the ear and soul began with his demonstration that pitch is proportional to frequency and that the intensity of sound is inversely proportional to the distance from its source. He discovered, in a law that now bears his name, that an increase in mass and a decrease in tension produce lower notes in a string of given length. He went on to discover similar relations for wind and percussion instruments. He offered quantitative explanations for consonance, dissonance, and resonance, and also measured the speed of sound, which he showed to be independent of pitch and loudness, and pioneered the study of the upper and lower limits of audible frequencies.

In his acoustical studies, Mersenne recognized the importance of mathematical and mechanical models. He believed that using mechanical models to imitate the workings of nature could also serve as a weapon against the Hermeticists, because these models revealed that the world was a machine and not an ensouled body. In this way, Mersenne withdrew the soul from the world of the animists and gave it back to the theologians. Mersenne the scientist provided Mersenne the priest with those principles necessary to save the religious values he held most dear. The spread of the mechanical philosophy owed much to Mersenne and Descartes, who relied on Mersenne as a theological consultant.

Despite Galileo’s difficulties with the Church, Mersenne came to see his discoveries as superlative illustrations of the rationality of nature governed by mechanical laws. He was largely responsible for making Galileo’s work known in France through his translations of Galileo’s studies in mechanics into French. Nevertheless, he did not accept Galileo’s ideas and experiments uncritically. He commented on the lack of precision in Galileo’s experiments using inclined planes to investigate the acceleration of falling objects. His doubts about whether Galileo had actually performed these experiments led him carefully to repeat them. He discovered discrepancies and doubted the relationship between the distance traveled by an object under acceleration and the square of the time that Galileo had discovered.

The Roman Catholic Church’s condemnation of Galileo’s Copernicanism occurred in 1633, but this did not stop Mersenne from defending Galileo’s work. This might seem odd for a person of Mersenne’s piety, until one realizes the naïve simplicity with which Mersenne blended his conceptions of faith and science, both of which led to the truth. Nevertheless, the Galileo affair had a profound effect on both Mersenne and Descartes, but whereas Descartes timidly refrained from publishing, Mersenne continued to issue works on Galileo, and in 1634 he even published a summary account of part of Galileo’s Dialogo sopra i due massimi sistemi del mondo, tolemaico e copernicano (1632; Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican , 1661). Mersenne agreed with the Church’s need to preserve Scripture from error, but he saw no conflict between Scripture, which instructed humans on how to go to Heaven, and science, which showed humans how the heavens moved.

Mersenne’s publication of the complete text of Harmonie universelle (1636-1637; universal harmony) marked the culmination of his achievements in music and science. This work, greatly valued by modern musicologists, contains a useful summary of Renaissance knowledge about acoustics and detailed information on a host of musical instruments.

During the last years of his life, Mersenne worked on mathematics. His most important studies were in number theory, especially on prime and perfect numbers. In 1644, he proposed a formula for generating primes, and although his formula produces only some of them, it inspired other mathematicians to devise better ways of finding prime numbers.

Mersenne fell seriously ill at the end of August, 1647. He became worse as a result of the ineptitude of a surgeon, who cut an artery in his right arm, allowing gangrene to set in. Despite his crippled arm, on a warm day at the end of July, 1648, he left to visit Descartes in the Netherlands. He arrived ill and tired at a Theatine monastery on the route and was quickly returned to Paris and confined to bed. The doctors eventually diagnosed an abscess on the lungs. The surgeons made an incision that caused him much suffering, without discovering his malady. Understanding that the end was near, Mersenne ordered his affairs: He gave instructions on his unfinished manuscripts, made a general confession, and arranged for an autopsy to discover the cause of his approaching death. On the first day of September, 1648, at three o’clock in the afternoon, Mersenne died in the arms of his friend Gassendi. At the autopsy, the surgeons found that their incision had been made too low. This knowledge was Mersenne’s last contribution to science.

Significance

Despite his vital role in the scientific revolution of the seventeenth century, Mersenne has been largely neglected and misunderstood. In his study of Mersenne and the birth of mechanism, Father Robert Lenoble did much to rescue Mersenne from oblivion for French scholars, but Mersenne is still remembered principally because of his friendship and correspondence with Descartes, Fermat, and other scientists. In the modern view, these friendships, rather than his ideas, constitute his significance. In contrast to this view, Lenoble sees Mersenne as one of the most important figures in the history of modern thought. Mersenne’s life, which adventitiously placed him on the watershed between the medieval and modern worlds, allowed him to play a pivotal role in the scientific revolution.

Throughout his career, Mersenne’s devotions to religion and to science were in constant interaction. Indeed, his career involved him in several dual roles: priest and scientist, Renaissance man and modern man, naïve believer and skeptic of the occult. Through his vast correspondence and many contacts with the makers of the scientific revolution, Mersenne not only called on specialists in every branch of science to work together but also kept these scientists attuned to religious and moral principles. In this way he did much to foster the new scientific movement and to prevent it from developing initially in an antireligious direction.

Mersenne helped to place science in its modern context. A new type of outlook arose with Mersenne, a science without metaphysics, a science that was verifiable and useful. He was an apostle of this new view, and he had the rare ability to serve the ideas of others. He contributed more than any of his contemporaries to expanding the knowledge of, and interest in, the scientific achievements of his time. Blaise Pascal once said that Mersenne had the very special talent for posing the right questions, and he posed these questions to the right people.

Mersenne believed deeply that false science pulled people away from God whereas true science led people to him. Although his intention was to place religion first in whatever he said and did, he was living in an age that was leaving theology for science, and ironically, in attempting to do the opposite, he encouraged this trend. He fought the Hermeticists, encouraged the mechanists, and was the catalyst for the spread of many important scientific ideas. He did all this for the greater glory of God. From the vantage point of the modern world, one can see that what he actually did was to help separate science from its religious roots.

Bibliography

Boas, Marie. The Scientific Renaissance, 1450-1630. New York: Harper & Row, 1962. Boas presents a valuable summary of a significant period in the evolution of science. She discusses Mersenne’s role in organizing scientists through his extensive correspondence.

Chappelle, Vere, ed. Grotius to Gassendi. New York: Garland, 1992. Collection of essays about sixteenth and seventeenth century philosophers, including Mersenne.

Dear, Peter Robert. Mersenne and the Learning of the Schools. Ithaca, N.Y.: Cornell University Press, 1988. Dear describes how Mersenne developed a mechanistic view of nature, replacing Aristotle’s earlier philosophy of the nature of the schools.

Debus, A. G. Man and Nature in the Renaissance. New York: Cambridge University Press, 1978. An introduction to science and medicine during the early phase of the scientific revolution, from the mid-fifteenth to the mid-seventeenth century.

Holden, Constance. “Another Mersenne.” Science 304, no. 5677 (June 11, 2004). On May 28, 2004, about seventy-five thousand math enthusiasts from around the world announced the discovery of a seven-million-digit prime number. Holden discusses the findings of this group, called The Great Internet Mersenne Prime Search, and its attempts to find a ten-million-digit prime number.

Popkin, Richard H. The History of Scepticism from Erasmus to Descartes. Assen, the Netherlands: Vangorcum, 1964. Explores the influence of skeptical philosophy on the evolution of modern thought. In several of his works, Mersenne attacked skepticism as the enemy of science and religion, and Popkin makes many references to Mersenne.

Simmons, George Finlay. Calculus Gems: Brief Lives and Memorable Mathematics. New York: McGraw-Hill, 1992. This collection of biographies includes a chapter on Mersenne, with a discussion of his theories on prime numbers and cycloids.

Thorndike, Lynn. The Seventeenth Century. Vol. 7 in A History of Magic and Experimental Science. New York: Columbia University Press, 1958. The chapter on Mersenne and Gassendi contains much of interest about the two priest-scientists. Thorndike is not always accurate, and some of his work has been superseded by later scholarship, but his many translations of original materials scattered throughout his presentation make this a valuable and fascinating compendium.