Francesco Maria Grimaldi

1618-1663

Italian Physicist

Francesco Maria Grimaldi was the first scientist to recognize the tendency of light to bend around objects, a phenomenon he named diffraction. He also constructed one of the most detailed maps of the Moon up to his time, and may have initiated the practice of naming lunar features after scientists. Today there is a crater on the Moon named after Grimaldi.

Born in Bologna, Italy, in 1618, Grimaldi came from a wealthy background. His father died when he was young, and at 14 he and his brother entered the Society of Jesus, or the Jesuit order. He studied theology and philosophy until he was 27, and also taught at the College of Santa Lucia, a school operated by the Jesuits, in Bologna. In 1645 he received his bachelor's degree, and an additional two years of study yielded his doctorate.

During his student years in the 1640s, Grimaldi had an opportunity to work as assistant to astronomer Giovanni Riccioli (1598-1671), who was also a Jesuit professor. Their early work together followed up on experiments made by Galileo (1564-1642) concerning falling weights, the speed of which they timed using a pendulum. For their astronomical work, Grimaldi developed a new and highly precise telescope, which helped him construct an extremely detailed Moon map or selenograph. Actually, the selenograph consisted of hundreds of drawings pieced together by Grimaldi and Riccioli.

Soon after earning his doctorate, Grimaldi gained an appointment as professor in the philosophy department of the College of Santa Lucia. Health problems forced him to give up this position, however, shortly afterward he was appointed to a mathematics professorship. At the age of 33 in 1651, he was ordained as a priest.

Around this time, Grimaldi began conducting his famous experiments with optics, allowing light to pass through a series of two apertures, or slits, and onto a blank screen. He noted that the area covered by the light on the screen was much wider than the last aperture, which indicated that the light had bent outward from the second opening.

Up until that time, scientists accepted the view that light traveled in the form of particles, whereas Grimaldi's research indicated that it actually came in waves, since only a wave could bend around objects. Some three centuries later, scientists would be confronted with the perplexing realization that light can travel either in waves or in particles, and though Grimaldi was incorrect in his conclusion that it only came in waves, his work was important for introducing the wave theory.

In choosing the word "diffraction," Grimaldi was referring to the manner in which water flowed around stones, branches, or other obstacles in its path. As he continued to study diffracted beams, he began to notice colors at the edges of the light beam, but could not figure out how they were created. The latter discovery would have to wait for Joseph von Fraunhofer (1787-1826).

As for Grimaldi, he continued to teach at Santa Lucia, the Jesuit College, for the rest of his life. He died in 1663, at a mere 45 years of age.

JUDSON KNIGHT