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Francesco M. Grimaldi, S.J.
(1613 to 1663)
and his diffraction of light

Francesco M Grimaldi, S.J. was born and died in Bologna and was professor of mathematics and physics at the Jesuit college in Bologna for many years. He was one of the great geometer-physicists of his time and was an exact and skilled observer, especially in the field of optics. He discovered the diffraction of light and gave it the name diffraction, which means "breaking up." He laid the groundwork for the later invention of the diffraction grating. He was one of the earliest physicists to suggest that light was wavelike in nature. He formulated a geometrical basis for a wave theory of light in his Physico-mathesis de lumine (1666). It was this treatise which attracted Isaac Newton to the study of optics. Newton deals with the diffraction problems of Grimaldi in Part III of his Opticks (1704), after having first learned of Grimaldi's diffraction from the writings of another Jesuit geometer, Honoré Fabri.

Grimaldi's discovey of diffraction

Grimaldi's experiments and discovery is described by Florian Cajori in his History of physics (New York: Macmillan, 1898, p. 88). He introduced a pencil of light into a dark room. The shadow cast by a rod held in the cone of light was allowed to fall upon a white surface. To his surprise he found the shadow wider than the computed geometrical shadow; moreover, it was bordered by one, two, and sometimes three colored bands. In 1665 Grimaldi published his results:

When the light is incident on a smooth white surface it will show an illuminated base IK notably greater than the rays would make which are transmitted in straight lines through the two holes. This is proved as often as the experiment is tried by observing how great the base IK is in fact and deducing by calculation how great the base NO ought to be which is formed by the direct rays. Further it should not be omitted that the illuminated base IK appears in the middle suffused with pure light, and at either extremity its light is colored.

Single slit diffractionDouble slit diffraction

Issac Newton and later Robert Young only referred to Grimaldi's experiments but repeated and improved upon the experiments. Apparently prompted by Grimaldi's observation of color effects, Newton compared the widths of the luminous patches produced by the lights of different portions of the spectrum, and noticed that the bands of red lights were largest while the blue were least with the green of middle size. Newton used the term "inflection" but Grimaldi's word for this new phenomenon "diffraction" has survived.

The astronomical work of Francesco Grimaldi was closely related to the astronomical work of another Jesuit, Giovanni Battista Riccioli who wrote the Almagestum Novum. In 1640 Grimaldi conducted experiments on free fall for Riccioli, dropping weights from a tower and using a pendulum as timer. He found that the square of the time is proportional to the distance of free fall from rest. Riccioli praised especially Grimaldi's ability to devise, build, and operate new observational instruments. Grimaldi's contributions included such measurements as the heights of lunar mountains and the height of clouds.

Francesco Grimaldi is responsible for the practice of naming lunar regions after astronomers and physicists, rather than after ideas such as "tranquility". With Riccioli he composed a very accurate selenograph a copy of which adorns the entrance to the National Space Museum in Washington.

Grimaldi's selenograph


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 Grimaldi in the Dictionary of Scientific Biography is found in v 3 p100, 528, v 4 p506, v 5 p 542, v 6 p 195, 545, v 9 p485, v 10 p59, v 11 p411, v 14 p461.}
Oldenburg, Henry ed. Philosophical Transactions of the Royal Society. vols. 1-30. London: 1665-1715
{Articles about Grimaldi's work are found in the Philosophical Transactions of the Royal Society of London in v 6 p3069-3070, 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
Sommervogel, Carolus Bibliothèque de la compagnie de Jésus. 12 volumes. Bruxelles: Société Belge de Libraire, 1890-1960
{2 entries are found in Sommervogel; an example is the following: Physico-mathesis de Lumine (Bologna, 1665)}

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

Another menu of Jesuit Interest

Jesuit history, tradition and spirituality

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