CASSINI, JOHN DommouE, a celebrated French astronomer, was born at Perinaldo, in the county of Nice, on the gth of June, 1625, and was descended from a has ranked among the senatorial families of Sienna since the time of Cardinal Cassini, who was archbishop of that city lb 1426. After receiving the early part of his education under a private tutor, he was sent to the college of Jesuits at Genoa, where he made such a rapid progress in literature, that some of his Latin poems were published when he was only eleven years of age. in consequence of sonic books on judicial astrology having been lent to him by an ecclesiastic, when he was on a visit at the country house of M. caro, the doge of Genoa, his attention was directed to the study of the heavens. He began to predict future events from the aspects of the heavenly bodies, and made numerous extracts from the astrological books which were put into his hands ; but having accidentally read the work of Pic de la Marandi against astrologers, he burned all the extracts which he had made, and aban doned for ever the dreams of astrology. He now devoted himself wholly to astronomy ; and such was the rapidity of his progress, that in the year 1650, when he was only twenty-five years of age, he was invited by the senate of Bologna to the professorship of astronomy, which had been vacant for several years by the death of Cavalleri; a situation in which lie continued for several years, devoting the whole of his leisure time to astronomical observations. From a series of observations on the comet of 1652, made with the Marquis of Alalvasia, who had been instrumental in bringing him to Bologna, he concluded that comets were not of a meteoric nature,. as had been imagined, but that they were guided in their paths by the same laws as the planetary bodies ; and he explains the motion of the comet by a circle described round the earth and beyond the orbit of the moon. These observations were published in his first produc tion, which appeared in 1653, under the title of De Cometa anni 1652 et 1653. Muntinx, fol. In the same year he obtained a solution of the celebrated problem for determining geometrically from the mean and true place of a planet, the eccentricity of its orbit, and the place of its apogee, which had baffled the ingenuity both of Kepler and Bullialdus. In 1653, when the church of St Pe
tronius at Bologna underwent a repair, Cassini obtained permission to draw the famous meridian line, which we have already described in our account of that city. This meridian line, which had been first drawn in 1575 by Egnazio Dante, was renewed in 1695 by Cassini, when a full account of it was published by him, entitled, La Meridiana del tempio di S. Petronia, tirata e nreparata per le osservationi astronomiche l'anno 1655, ri-rista restaurata l'anno 1695. Bologna, fol. In the year 1657, Cassini went to Rome in the capacity of assistant to the Marquis Tanara, had been sent by the senate of Bologna as ambassador to Pope Alexander VIL respect ing certain differences which had arisen between the cities of Bologna and Ferrara, about the inundation of the Po ; and such was the skill and judgment which he displayed on this occasion, that he was chosen superin tendant of the waters of the state of Bologna. Marius Chigi, the Pope's brother, afterwards appointed him in 1663, inspector general of the fortifications of the castle of Urbino, and he was also chosen engineer for all the rivers in the ecclesiastical state. Cassini was employed in settling with M. Viviani the difference which arose between Pope Alexander VII. and the Grand Duke of Tuscany, respecting the waters of the Chiana ; and such was the personal regard which this pontiff entertained for him, that he frequently sent for Cassini to con verse with him upon the sciences, and urged him, in vain, by the promises of preferment,• to enter into the church.
During these occupations, which were rather foreign to the habits of a practical astronomer, Cassini found lei sure to prnseente his favourite study. Ile observed al most all the celestial phenomena which occurred, he discovered the rotation or Mars upon his axis, and he formed tables of the motion of Jupiter's satellites. I lis various observations made in his native country v. ere pub. fished in the following works: 1. Specimen Obscrvationunz Bononiensium YEquinoctii verni, anni 1656. Bonon. 1656, fol.