Editing Marin Mersenne (section)

=== Work ===

''Quaestiones celeberrimae in Genesim'' was written as a commentary on the [[Book of Genesis]] and comprises uneven sections headed by verses from the first three chapters of that book. At first sight the book appears to be a collection of treatises on various miscellaneous topics. However Robert Lenoble has shown<ref>{{cite book |last1=Lenoble |first1=Robert |title=Mersenne ou la naissance du mécanisme |date=1943 |publisher=Vrin |location=Paris}}</ref> that the principle of unity in the work is a polemic against [[magic (paranormal)|magic]]al and [[divination|divinatory]] arts, [[Christian Kabbalah|cabalism]], and [[Animism|animistic]] and [[pantheism|pantheistic]] philosophies.

Mersenne was concerned with the teachings of some Italian [[naturalists]] that all things happened naturally and determined astrologically; for example, the [[Determinism#Nomological_determinism|nomological determinism]] of [[Lucilio_Vanini#Thought|Lucilio Vanini]] ("God acts on sublunary beings (humans) using the sky as a tool"), and [[Gerolamo Cardano]]'s idea that martyrs and heretic were compelled to self-harm by the stars;<ref>{{Cite journal|last=Regier|first=Jonathan|date=2019|title=Reading Cardano with the Roman Inquisition: Astrology, Celestial Physics, and the Force of Heresy|url=https://biblio.ugent.be/publication/8608904/file/8651154.pdf|journal=Isis|volume=110|issue=4|pages=661–679|doi=10.1086/706783|hdl=1854/LU-8608904|s2cid=201272821}}</ref> Historian of science William Ashworth<ref>{{cite web |title=William B Ashworth Jr |url=https://scholar.google.com/citations?user=ebdG_2kAAAAJ&hl=en |website=scholar.google.com}}</ref> explains "Miracles, for example, were endangered by the naturalists, because in a world filled with sympathies and occult forces—with what Lenoble calls a "spontanéité indéfinie"—anything could happen naturally".<ref>"Italian naturalism was considered dangerous to religion because it confused the natural with the supernatural and physics with metaphysics; essentially, it eliminated the boundaries between science and faith." {{cite journal |last1=Ashworth |first1=William B. |title=5. Catholicism and Early Modern Science |journal=God and Nature |date=31 December 1986 |pages=136–166 |doi=10.1525/9780520908031-007|isbn=978-0-520-90803-1 }}</ref>{{rp|138}} 

Mersenne mentions [[Martin Del Rio]]'s ''Investigations into Magic'' and criticises [[Marsilio Ficino]] for claiming power for images and characters. He condemns astral magic and [[astrology]] and the ''[[anima mundi]]'', a concept popular amongst [[Renaissance]] [[neo-platonism|neo-platonists]]. Whilst allowing for a mystical interpretation of the Cabala, he wholeheartedly condemned its magical application, particularly [[angelology]]. He also criticises [[Pico della Mirandola]], [[Cornelius Agrippa]], [[Francesco Giorgio]] and [[Robert Fludd]], his main target.

''Harmonie universelle'' is perhaps Mersenne's most influential work.  It is one of the earliest comprehensive works on music theory, touching on a wide range of musical concepts, and especially the mathematical relationships involved in music.  The work contains the earliest formulation of what has become known as [[Mersenne's laws]], which describe the frequency of oscillation of a stretched string. This frequency is:
# Inversely proportional to the length of the string (this was known to the ancients; it is usually credited to [[Pythagoras]])
# Proportional to the square root of the stretching force, and
# Inversely proportional to the square root of the mass per unit length.

The formula for the lowest frequency is

:<math> f=\frac{1}{2L}\sqrt{\frac{F}{\mu}}, </math>

where ''f'' is the frequency [Hz], ''L'' is the length [m], ''F'' is the force [N] and μ is the mass per unit length [kg/m].

In this book, Mersenne also introduced several innovative concepts that can be considered the basis of modern reflecting telescopes:
* Much earlier than [[Laurent Cassegrain]], he found the fundamental arrangement of the two-mirror telescope combination, a concave primary mirror associated with a convex secondary mirror, and discovered the telephoto effect that is critical in reflecting telescopes, although he was far from having understood all the implications of that discovery. 
* Mersenne invented the [[Afocal system|afocal]] telescope and the beam compressor that is useful in many multiple-mirror telescope designs.<ref>{{citation|title=Reflecting Telescope Optics I: Basic Design Theory and its Historical Development|first=Todd|last=Wilson|publisher=Springer|year=2007|isbn=9783540765813|page=4|url=https://books.google.com/books?id=PuN7l2A2uzQC&pg=PA4}}.</ref>
* He recognized also that he could correct the [[spherical aberration]] of the telescope by using aspherical mirrors and that in the particular case of the afocal arrangement he could do this correction by using two parabolic mirrors, though a [[hyperboloid]] is required.<ref>
{{cite book|title=Mirror Mirror: A History of the Human Love Affair with Reflection| first=Mark|last= Pendergrast| author-link=Mark Pendergrast| year=2003|pages=88–89|publisher=Basic Books|url=https://books.google.com/books?id=T4-GErgSbU0C&pg=PA88|isbn=0786729902}}</ref>

Because of criticism that he encountered, especially from Descartes, Mersenne made no attempt to build a telescope of his own.

Mersenne is also remembered today thanks to his association with the [[Mersenne prime]]s. The [[Mersenne Twister]], named for Mersenne primes, is frequently used in computer engineering and in related fields such as cryptography.

However, Mersenne was not primarily a mathematician; he wrote about [[music theory]] and other subjects. He edited works of [[Euclid]], [[Apollonius of Perga|Apollonius]], [[Archimedes]], and other [[Chronology of ancient Greek mathematicians|Greek mathematicians]]. But perhaps his most important contribution to the advance of learning was his extensive correspondence (in [[Latin]]) with mathematicians and other scientists in many countries. At a time when the [[scientific journal]] had not yet come into being, Mersenne was the centre of a network for exchange of information.

It has been argued that Mersenne used his lack of mathematical specialty, his ties to the print world, his legal acumen, and his friendship with the French mathematician and philosopher René Descartes (1596–1650) to manifest his international network of mathematicians.<ref>{{cite journal|author=Grosslight, Justin |year=2013|title=Small Skills, Big Networks: Marin Mersenne as Mathematical Intelligencer|journal=History of Science|volume= 51|issue=3|pages=337–374|doi=10.1177/007327531305100304 |bibcode=2013HisSc..51..337G|s2cid=143320489}}</ref>

Mersenne's philosophical works are characterized by wide scholarship and the narrowest theological orthodoxy. His greatest service to philosophy was his enthusiastic defence of Descartes, whose agent he was in Paris and whom he visited in exile in the [[Netherlands]]. He submitted to various eminent Parisian thinkers a manuscript copy of the ''[[Meditations on First Philosophy]]'', and defended its orthodoxy against numerous clerical critics.

In later life, he gave up speculative thought and turned to scientific research, especially in mathematics, physics and astronomy. In this connection, his best known work is ''[[Harmonie universelle]]'' of 1636, dealing with the [[music theory|theory of music]] and [[musical instrument]]s. It is regarded as a source of information on 17th-century music, especially French music and musicians, to rival even the works of [[Pietro Cerone]].

One of his many contributions to [[musical tuning]] theory was the suggestion of
: <math>\sqrt[4]{\frac{2}{3-\sqrt{2}}}</math>
as the [[ratio]] for an [[equal temperament|equally-tempered]] [[semitone]] (<math>\sqrt[12]{2}</math>). It was more accurate (0.44 [[cent (music)|cent]]s sharp) than [[Vincenzo Galilei]]'s 18/17 (1.05 cents flat), and could be constructed using [[straightedge and compass]]. Mersenne's description in the 1636 ''Harmonie universelle'' of the first absolute determination of the frequency of an audible tone (at 84&nbsp;Hz) implies that he had already demonstrated that the absolute-frequency ratio of two vibrating strings, radiating a musical tone and its [[octave]], is 1&nbsp;:&nbsp;2. The perceived harmony ([[consonance and dissonance|consonance]]) of two such notes would be explained if the ratio of the air oscillation frequencies is also 1&nbsp;:&nbsp;2, which in turn is consistent with the source-air-motion-frequency-equivalence hypothesis.

He also performed extensive experiments to determine the acceleration of falling objects by comparing them with the swing of [[pendulum]]s, reported in his ''Cogitata Physico-Mathematica'' in 1644. He was the first to measure the length of the [[seconds pendulum]], that is a pendulum whose swing takes one second, and the first to observe that a pendulum's swings are not [[isochronous]] as Galileo thought, but that large swings take longer than small swings.<ref>{{cite book
  | last = Koyre  | first = Alexander | title = Metaphysics and Measurement | publisher = Taylor & Francis | year = 1992 | page = 100 | url = https://books.google.com/books?id=rJLQyZ4ccMgC&pg=PA100 | isbn = 2-88124-575-7}}</ref>