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Honoré Fabri, S.J. (1607 to 1688)
and his post-calculus geometry

Honoré Fabri, S.J.

Honoré Fabri, S.J. was born in Dauphine and died in Rome. He wrote more than thirty works, some of which were reviewed in the Philosophical Transactions. Fabri was the first of many famous professors produced by the Jesuit Collège de la Trinité: his students included Pierre Mousnier, Francois de Raynaud, Jean-Dominique Cassini and Philippe de La Hire. He was the leader of a circle of mathematicians, which led him into friendship with Gassendi, Leibniz, Mersenne, Descartes and two Huygenes (father and son), Claude Dechales and Berthet. The foci of Fabri's tremendous activity were almost all urgent scientific questions of his day: heliocentrism, Saturn's rings, the theory of the tides, magnetism, optics, and kinematics. In mathematics, infinitesimal methods and the continuum problem were more prominent. Fabri attempted an explanation of tidal phenomena based on the action of the moon. Fabri was also considered the best expert on the errors of Jansenism. Among his close friends was a fellow Jesuit and his classmate at Collège de la Trinité, Père Lachaise, after whom is named the famous cemetery in Paris.

Honoré Fabri tried to unify all physics along the lines of geometry. This effort was described in the Philosophical Transactions of the Royal Society, "Concerning his method he hath comprehended the whole of Physics in a geometrical method." Capillary dispersion was discovered by Fabri who also gave the first reasonable explanation of why the sky is blue, basing his reasons on dispersion of light. He quickly applied the newly invented calculus to the physical world and he was the first to give a cogent reason for Galileo's experiment showing that bodies fall equal distances in equal time. Galileo, in turn, had gotten interested in the problem in the first place because of the writings of another Jesuit, Niccolo Cabeo, S.J.

Fabri, by the way, spoke of another of Galileo's problems, the motion of the earth around the sun. He stated his opinion that the Catholic Church would adopt a figurative meaning to the offending biblical passages if it was shown that the earth does indeed move around the sun, His observations, however, came at an awkward time. Apparently something different was expected of Fabri since he belonged to the Holy Office. The TRS quotes him and then comments on his courageous statements concerning the movement of the earth.
It hath been more than once asked whether they had a demonstration for asserting the motion of the Earth? They durst never yet affirm they had; wherefore nothing hinders but that the Church may understand those scripture-places, that speak of this matter in a literal sense, and declare they should be so understood as long as the contrary is not evinced by any demonstration; which, if perhaps it should be found out by you (which I can hardly believe it will) in this case the Church will not at all scruple to declare, that these places are to be understood in a figurative and improper sense." Whence this Author concludes, that the said Jesuit [Fabri] assuring us that the inquisition hath not absolutely declared, that those Scripture places are to be understood literally, seeing that the Church may make a contrary declaration, no man ought to scruple to follow the Hypothesis of the Earth's motion, but only forbear to maintain it in public, till the prohibition be called in.

His statement about the Galileo case brought Fabri 50 days in prison under Pope Alexander VII, and he was released only by the intervention of Leopold II. He still put a chapter in his Dialogi physici (1665) entitled "de motu terrae" ("concerning the earth's motion").
Fabri's ingenious quadrature of the cycloid inspired young Gottfried Leibniz. Issac Newton claimed that he first learned of Grimaldi's teaching of the diffraction of light from the writings of Honoré Fabri.


Archivum Historicum Societatis Iesu ( AHSI ) Rome: Institutum Historicum
Bangert, William A History of the Society of Jesus. St. Louis: St. Louis Institute, 1972uis, 1810
Boyer, Carl A history of mathematics. New York: Wiley, 1968
Gillispie, Charles. C. ed., Dictionary of Scientific biography. 16 vols. New York: Charles Scribner and Sons, 1970
{Reference to Honoré Fabri in the Dictionary of Scientific Biography is found in vol. 4 p505-506, Vol. 5 p544, vol. 8 p267.}
Oldenburg, Henry ed. Philosophical Transactions of the Royal Society. vols. 1-30. London: 1665-1715
{Articles by Honoré Fabri or concerning his work are found in the Philosophical Transactions of the Royal Society of London in v 1 p325-327, v 1 p69-73, v 2 p626, v 4 p925-928, v 5 p2055-2057, v 5 p2057-2059, v 5 p2082-2083, v 9 p78-83, v 16 p314-323.}
Reilly, Conor "A catalogue of Jesuitica in the Philosophical Transactions of the Royal Society of London" in A.H.S.I. vol. 27,1958, p. 339-362
Sarton, GeorgeThe study of the history of mathematics. Cambridge, Mass: Harvard, 1936
Sommervogel, Carolus Bibliothèque de la compagnie de Jésus. 12 volumes. Bruxelles: Société Belge de Libraire, 1890-1960
{31 entries about Honoré Fabri are found in Sommervogel; some examples are the following:
Theses de universa mathematica (Lyons, 1646)
Philosophis Universa (Lyons, 1646)
Opusculum geometricum (Rome, 1659)
De Homine (Lyons, 1666)

Adventures of Some Early Jesuit Scientists

José de Acosta, S.J. - 1600: Pioneer of the Geophysical Sciences
François De Aguilon, S.J. - 1617: and his Six books on Optics
Roger Joseph Boscovich, S.J. - 1787: and his atomic theory
Christopher Clavius, S.J. - 1612: and his Gregorian Calendar
Honoré Fabri, S.J. - 1688: and his post-calculus geometry
Francesco M. Grimaldi, S.J. - 1663: and his diffraction of light
Paul Guldin, S.J. - 1643: applications of Guldin's Rule
Maximilian Hell, S.J. - 1792: and his Mesmerizing encounters
Athanasius Kircher, S.J. - 1680: The Master of a Hundred Arts
Francesco Lana-Terzi, S.J. - 1687: The Father of Aeronautics
Francis Line, S.J. - 1654: the hunted and elusive clock maker
Juan Molina, S.J. - 1829: The First Scientist of Chile
Jerôme Nadal, S.J. -1580: perspective art and composition of place
Ignace Pardies, S.J. - 1673: and his influence on Newton
Andrea Pozzo, S.J. - 1709: and his perspective geometry
Vincent Riccati, S.J. - 1775: and his hyperbolic functions
Matteo Ricci, S.J. - 1610: who brought scientific innovations to China
John Baptist Riccioli, S.J. - 167I: and his long-lived selenograph
Girolamo Saccheri, S.J. - 1733: and his solution to Euclid's blemish
Theorems of Saccheri, S.J. - 1733: and his non Euclidean Geometry
Christopher Scheiner, S.J. - 1650: sunspots and his equatorial mount
Gaspar Schott, S.J. - 1666: and the experiment at Magdeburg
Angelo Secchi, S.J. - 1878: the Father of Astrophysics
Joseph Stepling, S.J. - 1650: symbolic logic and his research academy
André Tacquet, S.J. - 1660: and his treatment of infinitesimals
Pierre Teilhard de Chardin, S. J. - 1955: and The Phenomenon of man
Ferdinand Verbiest, S.J. - 1688: an influential Jesuit scientist in China
Juan Bautista Villalpando, S.J. - 1608: and his version of Solomon's Temple
Gregory Saint Vincent, S.J. - 1667: and his polar coordinates
Nicolas Zucchi, S.J. - 1670: the renowned telescope maker

Influence of Some Early Jesuit Scientists

The 35 lunar craters named to honor Jesuit Scientists: their location and description
Post-Pombal Portugal opinion of Pre-Pombal Jesuit Scientists: a recent conference
Seismology, The Jesuit Science. a Jesuit history of geophysics

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Jesuit history, tradition and spirituality

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