GIOVANNI DOMENICO

CASSINI (1625-1712)  , the first of these, was born at Perinaldo near Nice on the 8th of June 1625 . Educated by the Jesuits at Genoa, he was nominated in 165o professor of astronomy in the university of Bologna; he observed and wrote a treatise on the comet of 1652; was employed by the senate of Bologna as hydraulic engineer ; and appointed by Pope Alexander VII. inspector of fortifications in 1657, and subsequently director of waterways in the papal states . His determinations of the rotation-periods of Jupiter, Mars and Venus in 1665–1667 enhanced his fame ; and Louis . XIV. applied for his services in 1669 at the stately observatory then in course of erection at Paris . The pope (Clement IX.) reluctantly assented, on the understanding that the appointment was to be temporary; but it proved to be irrevocable . Cassini was naturalized as a French subject in 1673, having begun work at the observatory in September 1671 . Between 1671 and 1684 he discovered four Saturnian satellites, and in 1675 the division in Saturn's ring (see SATURN); made the earliest sustained observations of the zodiacal light, and published, in Les Elements de l'astronomie verifies (1684), an account of Jean Richer's (163o–1696) geodetical operations in Cayenne . Certain oval curves which he proposed to substitute for Kepler's ellipses as the paths of the planets were named after him Cassinians." He died at the Paris observatory on the I Ith of September 1712 . A partial autobiography left by Giovanni Domenico Cassini was published by his great-grandson, Count Cassini, in his Memoires pour servir d l'histoire des sciences (181o) . See also C . Wolf, Histoirede l'observatoire de Paris (1902) ; Max . Marie, Histoire des sciences, t. iv. p .

234; R . Wolf, Geschichte der Astronomic, p . 450, &c .