Cassini, the name of a family distinguished for their services in astronomy and geography.
GIOVANNI DOMENICO CASSINI, born at Perinaldo, near Nice, 8th June 1625, studied at the College of Jesuits, Genoa, and at Bologna, where in 1650 he was appointed to the astronomical chair. His first work related to the comet of 1652. He subsequently devoted himself to the determination of astronomical refraction and of the sun's parallax, &c. In 1664-65 he determined the period of Jupiter's rotation. Subsequently he determined the periods of the planets Mars and Venus, and made a near approximation to the parallax of the sun. He discovered four of the satellites of Saturn, as well as the dual character of that planet's ring, and was the first who carefully observed the zodiacal light; he also demonstrated that the axis of the moon was not (as had been believed) at a right angle to the ecliptic, and explained the cause of the phenomenon known under the name of lunar libration. He had an important share in the Meridian (q.v.) measurement begun in 1669. After a long life devoted to painful observations that ultimately deprived him of sight, he died September 14, 1712, at Paris, whither he had gone in 1669, at the invitation of Colbert, to take charge of the observatory erected by that minister.
JACQUES CASSINI, his son, born at Paris, February 18, 1677, was elected a member of the Academy of Sciences in 1694, travelled in Italy, Holland, and England, where he formed the acquaintance of Newton, Halley, Flamsteed, and others, and was elected a member of the Royal Society. He succeeded his father as director of the observatory at Paris, and died April 16, 1756. He wrote several treatises on electricity, the barometer, and astronomical subjects, &c.—His son, CÉSAR CASSINI (1714-84), was also engaged in scientific pursuits.
Cæsar's son, JEAN DOMINIQUE, COMTE DE CASSINI, born at Paris, June 30, 1748, succeeded to the charge of the observatory, and completed in 1793 the great topographical map of France begun by his father. He subsequently became a member of the Institute. He died October 18, 1845.