Grimaldi Biography

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Olivia Letts

Mr. Percival

Astronomy, Per. 3

12 Oct. 2012

Francesco Grimaldi – A Life

            Francesco Maria Grimaldi had the opportunity to become highly educated, being born into a well-respected and well-to-do family in 1618 in Bologna, Italy.  The seventeenth century, generally considered to be the final century of the Italian Renaissance, was a time marked by both great religiosity and fervent intellectuality.  Grimaldi’s life reflected this – by 1632, he and his brother Vincenzo had joined the Society of Jesus (for Jesuits).  He studied philosophy in Parma, Ferrara, and Bologna.  One of his teachers, Giovanni Riccioli, would later assist and be assisted by Grimaldi during some important experiments.  From 1638 to 1642 he taught rhetoric and humanities at the College of  Santa Lucia at Bologna, where he also studied theology after 1642.  By 1647, he was qualified to teach philosophy, but this was a time-consuming course to teach and thus, suffering from tuberculosis, he had to teach something that he found “less strenuous.” He began to teach mathematics and physics, being skilled in all branches. Full vows for priesthood were taken by Grimaldi in 1651. 

From the 1640s until his death in 1663, he focused heavily on his chief interests, astronomy and optics.  He was the first to observe and record the optical diffraction phenomenon; he was also the one to name it (diffractio).  This was discovered after during a specific experiment in which he introduced sunlight into a darkened room through a tiny hole, projecting it only a white surface.  Between 10 and 20 feet from the slit, Grimaldi put a thin, opaque rod into the cone of light so as to cast a shadow on this white surface.  He was surprised to note that the shadow of this cone was far wider than how it was geometrically predicted, and

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also, there were external diffraction bands of different colors bordering the shadow.  The brightness of these colors was more intense near the shadow, in fact.  In 1665 he published these findings.  Grimaldi had conducted other experiments for diffraction, where he discovered internal paired tracks of light and “fringing.”  His findings further proved the fluid nature of light as opposed to rectilinear passage. Grimaldi’s Physico-mathesis de lumine, published in 1666, the geometrical foundations for the wave theory of light were laid.  Later, Isaac Newton would create a set of careful measurements that made it clear that the phenomenon was of a periodic nature.  Yet this great figure himself did not accurately reflect upon Grimaldi’s experiment, as he treated the concept of diffraction like a mode of refraction, and he could not explain the fringes of color that occurred around the shadow.  Grimaldi as well was never able to properly explain why diffraction occurred – his death was sudden and interrupted further experiments with light - this was not accomplished by anyone until Joseph von Fraunhofer could in the 1800s.

            With former teacher Riccioli, Grimaldi carried out another important experiment, in which the two Jesuits dropped weights from a tower and timed the occurrences with a pendulum. They discovered the time of the fall squared was proportional to the distance of free fall source to rest.  Grimaldi was considered vital to Riccioli’s completion of his Almagestum novum, a major work which actually made Riccioli an incredibly important contributor to astronomy and falling bodies.  Riccioli noted Grimaldi’s great skill in devising and building telescopes and other observational instruments, through which the two frequently observed celestial bodies.  Grimaldi is well-known for his lunar measurements, and his famous selenograph of the moon.  There is a copy of this lunar map in the entrance to the National Space Museum in Washington, D.C.  He began a trend of describing lunar regions by naming them after famous astronomers and physicists.  Grimaldi often did not receive proper credit for his findings, and during his lifetime, his works were not published by his name.