Francesco Maria Grimaldi (1618-1663)Today I present yet another Jesuit physicist/astronomer: Francesco Maria Grimaldi. He made a number of contributions in physics and astronomy, many of which in collaboration with another Jesuit: Fr. Giovanni Battista Riccioli S.J. (1598-1671). I will deal with Riccioli in a future post. However, Grimaldi can take full credit for pioneering the study of diffraction of light, and in coining the term, “diffraction.”
Biographical Sketch: Grimaldi was born in Bologna in 1618. His father, a wealthy silk merchant, died when Francesco was still very young. In 1632 (at age 14) he entered the Jesuit order with his brother Vincenzo. After two years as a novice, he studied rhetoric for a year in Novellara. In 1635 he traveled to Parma for philosophy studies at the college of S. Rocco, but after only one year transferred to Ferrara to begin studying physics. He returned to Bologna to finish his philosophy studies. In 1638 he he was missioned to be professor at the Jesuit college of Bologna, where he would spend the next 25 years. He also undertook his theological studies during this period. He was ordained a priest in 1645. He finished his doctorate in 1647, and took final vows as a Jesuit in 1651. He died of a sudden illness in Bologna in 1663, at the age of 45.
He originally met Riccioli in Parma at S. Rocco, where the elder Jesuit taught him theology. When Grimaldi returned to Bologna in 1638, he found Riccioli there, and their scientific collaboration began. Between ca. 1640-50, he served as the assistant to Riccioli in his studies on geodesy, on the physics of falling bodies, and on lunar mapping.
It was after this period that Grimaldi did his work on diffraction.
Scientific Contributions:
Diffraction: Grimaldi was arguably the first to carefully observe the diffraction of light around solid objects. He conducted several experiments on the subject. For instance, a thin rod placed in a narrow beam of light would cast a shadow that was wider than predicted by purely geometric considerations. The wings of the shadow were bordered by colored bands. Also, sunlight passing through two narrow slits would interfere with itself, creating a dimmer result than sunlight passing through just one slit. He coined the term, “diffraction” for these phenomena. From these and other experiments, Grimaldi concluded that light moves analogously to a liquid (i.e. wave) rather than like the movement of solid particles.
Diagrams from Grimaldi’s experiments in diffraction: (A) Experimental setup for illumination from a slit in a window AB with an opaque rod EF casting a shadow. The edges of the shadow are wider than geometric considerations would allow. (B) Pattern of light and dark colored lines at the edge of the shadow observed by Grimaldi. (C) A second experiment with sunlight passing through two consecutive slits. The image of the light extended into the zones IN and OK on the screen, which would have been excluded by geometrical considerations. Source: Grimaldi Physicomathesis de lumine, coloribus, et iride, aliisque annexis, 1665.His work on optics was published posthumously in 1665, in Physicomathesis de lumine, coloribus, et iride, aliisque annexis (A physicomathematical thesis on light, colors, the rainbow and other related topics). Isaac Newton was aware of Grimaldi’s work in this field, and referenced it in his own work, “Optiks” (1704).
Collaboration with Riccioli: Grimaldi assisted Riccioli in several studies. Most of these will be described in greater detail in a future post.
They did experiments of the physics of falling bodies, dropping objects of different weights off Bologna’s Asinelli tower. They timed the fall with a pendulum. (Because some of the balls were light enough to be affected by air resistance, their results did not agree with Galileo’s conclusions.)
In astronomy, they attempted to measure the diameters of stars through a telescope. (In fact, they were measuring the star’s relative brightness.)
They surveyed a meridian line for Bologna.
They developed maps of lunar surface features. It was Riccioli who named the lunar seas (such as Mare Tranquilitatis), but it was largely Grimaldi who named craters after prominent scientists. Several of the craters are also named after Jesuit scientists. Most of these names are preserved in the official IAU nomenclature for lunar features.
Map of the Moon by Riccioli and Grimaldi (from Almagestum Novum, 1651)There is a crater on the moon named after Grimaldi.
