FRANCESCO GRIMALDI
Francesco Maria Grimaldi was an Italian physicist, astronomer, and priest. He was born in Bologna, Italy on April 2, 1618. He grew up in a wealthy family; his father was a silk merchant and his mother owned a chemist shop.
When he was fourteen, Grimaldi decided to become a Jesuit. While preparing to become a priest, he found that he enjoyed his scientific education. He worked with Giambattista Riccioli, another priest, who was also interested in science. One of Riccioli’s goals was to refute the findings of Galileo in order to support the Catholic church’s beliefs. To do this, he and Grimaldi performed experiments with free fall; however, they found that the distance an object falls is proportional to the square of the time taken, thereby verifying rather than disproving Galileo.
Grimaldi’s most important contribution to science was in the field of optics: he discovered the diffraction of light. He shined a beam of light through a small opening in a screen and observed that it appeared to take on a conic shape after passing through the hole. Moreover, when he placed an object between the screen and the surface behind it, the object’s shadow was wider than expected. He concluded that the light bent as it passed through the opening in the screen and around the object. Grimaldi called this phenomenon “diffraction”, which was derived from the word for the pattern left in a ship’s wake. This important discovery provided support for the wave theory of light, thereby furthering the debate over the dual nature of light. Grimaldi’s discoveries would influence Robert Hooke and Isaac Newton, among others.
Francesco Grimaldi also observed that when light passed through two small openings and fell on a screen, the region where both beams overlapped was darker than the portions on either side where the screen was lit by only one beam. Grimaldi came up with the somewhat convoluted idea that the addition of light to an illuminated object could make it darker. The principle of interference was what was really behind Grimaldi’s discovery. This principle was later used by scientists such as Young and Fresnel.
Grimaldi also observed the dispersion of light through a prism, but did not fully explain the wave behavior of refraction.
Grimaldi’s work was published after his death in his book, Physicomathesis de lumine, coloribus, et iride, aliisque annexis.
Grimaldi’s contributions to astronomy were mostly related to the moon. With regards to physics and astronomy, Grimaldi was more of an experimentalist than a theorist. He designed and built various astronomical devices, some of which aided him in creating his map of the moon. He used a telescope with a micrometer and crosshairs to complete this map, which was one of the most complete and accurate lunar maps at the time. He was partly responsible for the nomenclature of lunar features, which was mainly devised by Riccioli in his book, Almagestum Novum. This book was primarily a defense of the Catholic church’s stance on certain scientific theories, but in one section Riccioli included Grimaldi drawings of the moon along with this new system of nomenclature, which is still used today. The Grimaldi Crater on the moon is named after Francesco Grimaldi.
In addition to his work regarding the moon, Grimaldi helped calculate Bologna’s meridian line, and he prepared star charts. He also observed that Saturn’s shape was not circular, but elliptical.
