World of Scientific Discovery on Francesco Maria Grimaldi

Francesco Grimaldi was an Italian physicist and Jesuit priest who is best known as the first person to describe the diffraction of light. Apart from his optical research, Grimaldi also conducted experiments on human physiology and made careful observations of the surface of the Moon.

Grimaldi was born in Bologna, Italy, in 1618. While his family was fairly wealthy, his father died when Francesco was rather young; his mother tended the family business while he and his brother entered the Society of Jesuits in 1632. For thirteen years Grimaldi studied theology and philosophy and, in 1645, was finally awarded his degree. He required just two more years to obtain his doctorate, at which time he was appointed to a professorship at the Jesuit College in Bologna in the philosophy department. Grimaldi's health began to decline, however, and within a year he was appointed to a less stressful position, that of professor of mathematics. He took the vows of priesthood in 1651 and remained a professor at the Jesuit College until his death.

While still a student, Grimaldi served as a research assistant to another Jesuit professor, Giovanni Riccioli. Riccioli was obsessed with astronomy and, in particular, the Moon. In the early 1640s Grimaldi helped Riccioli in conducting experiments on free-fall, timing the speed of falling weights with a pendulum. For the observation of the heavens Grimaldi constructed a number of new instruments, including a telescope with an extremely precise micrometer. Using such a telescope he constructed an amazing map, or selenograph, of the Moon. This lunar map consisted of hundreds of drawings pieced together to produce a composite view of the Moon's surface. Grimaldi and Riccioli set about naming the different regions of the Moon, and Grimaldi is often given credit for starting the practice of naming these regions after astronomers and other scientists. Appropriately enough, Grimaldi himslef has a crater on the Moon now named after him.

Grimaldi's most enduring work was in optics. Using a beam of sunlight, he was the first scientist to note the effects of light diffraction. This was accomplished by allowing the light rays to pass through a pair of narrow apertures: the light would pass through the first slit, then the second, then onto a blank screen. Grimaldi was surprised to see that the light on the screen was significantly wider than the last aperture. This phenomenon seemed to indicate that, as it passed through the second slit, the light was bent outward.

This was a major discovery, since light could only bend around objects if it traveled in waves. During the time of Grimaldi's research, it was generally accepted that light was corpuscular (that is, it consisted of particles). Nevertheless, Grimaldi accepted his findings as absolute proof of the wave nature of light. He named his phenomenon "diffraction," a word previously reserved for the behavior of water as it flowed around an obstacle.

As he experimented, Grimaldi began to notice a fringe of color at the edges of his diffracted beam. He carefully described and recorded the appearance and positions of these colored streaks but never truly understood the process by which they were created; this was left to Joseph von Fraunhofer, nearly 150 years later.