Grimaldi, Francesco Maria (1618-1663)

Italian physicist who discovered the diffraction of light. In physiology, he observed muscle action and was the first to note that minute sounds are produced by muscles during contraction. Grimaldi was born in Bologna and was professor of mathematics at the Jesuit College there from 1648. He also helped with astronomical observations. Grimaldi let a beam of sunlight enter a darkened room through a small circular aperture and observed that, when the beam passed through a second aperture onto a screen, the spot of light was slightly larger than the second aperture and had coloured fringes. Grimaldi concluded that the light rays had diverged slightly, becoming bent outwards, or diffracted. On placing a narrow obstruction in the light beam, he noticed bright bands at each side of its shadow on the screen. This phenomenon can be explained readily only if light is regarded as travelling in waves - contrary to the then accepted corpuscular theory of light. A description of the experiments was published in Physicomathesis de lumine, coloribus, et iride/Physicomathematical Thesis of Light, Colours and the Rainbow 1665.