Article abstract: 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 the pseudosciences of alchemy, astrology, and natural magic.
Mersenne was born at Soultière, a small town near Oizé in the region of Maine, 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 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 character and destiny, and the like. Since physical contact was no longer necessary for one thing to have an effect on another, occult influences could be multiplied endlessly.
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 the 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 Father 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 the earth was at the center of the universe. In 1623, he had opposed the Copernican theory because sufficient evidence was lacking,...
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