Person: Fabri, Honoré
Honoré Fabri was a French Jesuit who worked on astronomy, physics and mathematics.
Mathematical Profile (Excerpt):
- After teaching Fabri for two years in Lyon, Boniel returned to Avignon where he was appointed as Rector of the College.
- After completing his studies of Scholastic Philosophy at Lyon, Fabri taught grammar for two years (1630-32) at the College in Roanne.
- After leaving Arles, Fabri continued teaching in Jesuit colleges.
- For six years from 1640, Fabri was professor of logic and mathematics at the Collège de la Trinité in Lyon.
- Fabri was the first of many famous professors produced by the Collège de la Trinité: his students included Pierre Mousnier, who later edited many of his teacher's lectures; the mathematician François de Raynaud, who became famous through his friendship with Newton; Jean-Dominique Cassini; and Philippe de La Hire.
- In 1648, however, Pierre Mousnier was able to publish Fabri's metaphysical lectures which he had given at Lyon, under the title Metaphysica demonstrativa.
- It is reasonable to ask why his writings were seen to be 'dangerous' by Fabri's superiors.
- The main reasons appear to be Fabri's rejection of Aristotle's physics and his belief that space and time were composed of indivisibles.
- Although when Fabri was sent to Rome it was intended to be a temporary measure, he was soon assigned to St Peter's Penitentiary College which is better known as the Inquisition.
- In Rome Fabri met Michelangelo Ricci and this was to prove helpful to him.
- Despite being a member of the Inquisition, Fabri was unable to avoid religious problems himself and he was accused of believing the philosophy of Descartes.
- We have seen that Fabri worked on astronomy, physics and mathematics and, in particular, we have mentioned his dispute with Huygens over Saturn's rings.
- Fabri did not believe that Saturn had a ring system but rather he postulated in his 1660 work that Saturn had two massive but dark satellites close to the planet and two small but bright satellites farther out.
- Fabri also originally had an incorrect theory concerning the satellites of Jupiter which he believed moved so as to always be behind the planet, arguing that if they crossed in front of the planet, then they should be seen against the disk and also a shadow cast by the satellite should be visible on the surface of the planet.
- Fabri developed a theory of tides which was based on the action of the moon.
- Fabri had a major influence on the development of the calculus through Leibniz.
- Fabri certainly proposed that one had to treat theological matters differently from physical ones, particularly when dealing with Christian ideas such as the Trinity.
- Views of Fabri's importance have varied considerably over time.
- the Accademia del Cimento esteemed Fabri, whose 'candor makes his learning additionally agreeable'.
- However, over the years historians have tended to be critical of Fabri's contributions, seeing him as a defender of traditional theories rather than an advocate for the new physics which was flowering in his time.
- One must, of course, understand the difficult position that Fabri was in, for his views, which are seen as too traditional by many historians, were sufficiently daring to see him continually in trouble with the Church.
- it appears that Fabri was highly unpopular both among the most conservative Jesuits, who saw him as dangerously close to novelties, and among the neoterics and especially Borelli, who saw him as a champion of the old philosophy trying to contrast them on their own ground.
- Michael Elazar had recently done much to restore Fabri's reputation.
- In particular, regarding Fabri's concept of impetus as alien to inertia is simply wrong; for Fabri carefully redefined the concept of impetus, as well as the causal connection between impetus and motion, so as to be able to smoothly assimilate the basic idea behind "inertia", i.e. the tendency of a moving and unhindered object to continue its motion with uniform velocity and along a straight line ad infinitum.
- Fabri, eager to adopt linear conservation of motion - officially and explicitly published only in Descartes' 'Principia' (1644) - achieved this by defining (in 1646) impetus as a formal (rather than efficient) cause of motion, thus evading the argument Koyré would raise (three centuries after Fabri) against the compatibility of impetus and inertia.
- In order to ensure the linearity of the motion conserved, Fabri followed Giovanni Battista Benedetti, against the medieval impetus tradition, in limiting the action of impetus to straight lines.
- Moreover, although Fabri - unlike Descartes before him and Newton after him - did not define linear conservation of motion as a law of nature, nevertheless it was an integral part of what could be described as his "inertial framework", which was expressed also by the analysis of natural phenomena in vacuum, by support for Galileo's claim concerning the universal velocity of fall in the void, and by the abstraction of air resistance from the analysis of motion.
- Fabri actually used linear conservation of motion within the discrete analysis he developed as a "mirror image" of Galileo's (continuous) treatment of free fall, and took pains to prove that this discrete analysis - a product of the seventeenth, not the fourteenth, century - converges (assuming infinitesimal instants) to Galileo's famous "odd numbers" law.
- Fabri is indeed far from being an opponent of vacuum, and contrary to Buridan and many of his contemporaries never denies motion devoid of any resistance, i.e. motion in the void.
- Rather, Fabri claims that the (full) universe is immersed in an infinite vacuum, and passionately defends the scientific validity of the concept of void, both by sharply attacking the "paradoxes" formulated by Aristotle to prove the "absurdity" of the concept of void, and by severely criticizing Descartes' anti-vacuist reduction of matter to extension.
Born 8 April 1608, Le Grand Abergement, Ain, France. Died 8 March 1688, Rome (now Italy).
View full biography at MacTutor
Tags relevant for this person:
Astronomy
Thank you to the contributors under CC BY-SA 4.0! 
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- non-Github:
- @J-J-O'Connor
- @E-F-Robertson
References
Adapted from other CC BY-SA 4.0 Sources:
- O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive
