April 2: Francesco Maria Grimaldi

Francesco Maria Grimaldi

April 2, 1618 - December 28, 1663

Francesco Grimaldi was an Italian mathematician and physicist who taught at the Jesuit college in Bologna. Between 1640 and 1650, working with Giovanni Battista Riccioli, he investigated the free fall of objects, confirming that the distance of fall was proportional to the square of the time taken.

In astronomy, he built and used instruments to measure geological features on the Moon, and drew an accurate map or selenograph which was published by Riccioli.

Later physicists used his work as evidence that light was a wave, and Isaac Newton used it to arrive at his more comprehensive theory of light.

He was one of the great geometer-physicists of his time and was an exact and skilled observer, especially in the field of optics. He was the first to make accurate observations on the diffraction of light (although by some accounts Leonardo da Vinci had earlier noted it), and coined the word 'diffraction,' which means "breaking up." He laid the groundwork for the later invention of the diffraction grating. He was one of the earliest physicists to suggest that light was wavelike in nature. He formulated a geometrical basis for a wave theory of light in his Physico-mathesis de lumine (1666). It was this treatise which attracted Isaac Newton to the study of optics. Newton deals with the diffraction problems of Grimaldi in Part III of his Opticks (1704), after having first learned of Grimaldi's diffraction from the writings of another Jesuit geometer, Honoré Fabri.

The astronomical work of Francesco Grimaldi was closely related to the astronomical work of another Jesuit, Giovanni Battista Riccioli who wrote the Almagestum Novum. In 1640 Grimaldi conducted experiments on free fall for Riccioli, dropping weights from a tower and using a pendulum as timer. He found that the square of the time is proportional to the distance of free fall from rest. Riccioli praised especially Grimaldi's ability to devise, build, and operate new observational instruments. Grimaldi's contributions included such measurements as the heights of lunar mountains and the height of clouds. 

Francesco Grimaldi is responsible for the practice of naming lunar regions after astronomers and physicists, rather than after ideas such as "tranquility". With Riccioli he composed a very accurate selenograph, a copy of which adorns the entrance to the National Space Museum in Washington. 

The crater Grimaldi on the Moon is named after him.