Giovanni Domenico Cassini, the first and most famous, was born at Perinaldo, near Nice, on 8th June 1625, and died on 14th September 1712. He was educated by the Jesuits of Genoa, among whom he gained some reputation as a writer of Latin verse. His study of astronomy was introduced by a fancy for astrology; but, notwithstanding the success of several of his predictions, he became convinced of the baseless character of the art, and thenceforth gave himself entirely to the pursuit of the science, in which, at the age of twenty-five, he had made so much progress that he was appointed professor of astronomy in the University of Bologna. Here he made the observations on the comet of 1652 which formed the subject of his first book; in this he denied that comets are free from subjection to law, and explained them as the result of a mixture of exhalations from the earth and from the stars. About this time he gave a good deal of attention to experiments on the transfusion of blood, and on the habits and structure of insects. Five years later he had an opportunity of displaying his ability, as a man of business, on the occasion of a dispute between Bologna and Ferrara caused by the inundations of the Po; and his success was such that he was asked to continue to act as the representative of the Bolognese. He was also, soon after, appointed to take charge of the repairing of Fort Urban; and already he had gained the patronage of the Pope, Alexander VII. Clement IX., too, valued him so highly that it was only on condition that he should return to Italy after two or three years that he would consent to his accepting Colbert’s offer of the directorship of the Observatory at Paris. Cassini, however, became attached to his new situation, was naturalized, and married a French lady. On 14tb September 1671, he commenced his observations; and his discoveries soon made him the best known astronomer in Europe, and gained him a reputation of an extravagant character. See Astronomy, vol. ii.

Jacques Cassini (1677-1756), was the son of Domenico Cassini. After his father’s death he became director of the Observatory at Paris, and was also appointed to the post of maître des comptes. His work, like his father’s, was purely that of an observer, and he does not appear to have had any adequate knowledge of the state of philosophic thought in his own science. Though he had some personal acquaintance with Newton he does not seem to have understood his theories, and he was quite ignorant of the discoveries of nutation and the aberration of light. Nevertheless, largely on account of his father’s fame, he enjoyed a high reputation throughout Europe.

César Francois Cassini or Cassini de Thury (1714— 1781), was son of the preceding, whom he succeeded in both his appointments. Like his father and grandfather, he was a patient and accurate observer, but such work by itself no longer brought renown. He published Elemens cl ’ Astronomie (1740); but his most important work was his topographical map of France, which was completed by his son.

Jacques Dominique Cassini, Count de Thury (1748- 1845), son of the preceding, completed the line of Cassinis, who for a hundred and twenty-two years filled the post of director of the Observatory at Paris. He appears to have held more philosophical views than his predecessors; but his plans to improve the Observatory, by obtaining larger instruments, and by other means, were cut short in 1793. In that year the National Assembly decreed that three of his pupils should be united with him in his office, an arrangement to which he refused to submit. Next year he was in consequence imprisoned for seven months; and after this he abandoned astronomy, and spent the rest of his life in retirement. The chief events of his life as an astronomer were the voyage which he undertook to test the chronometers of Le Roy (1769), and his association with Mechain aud Legendre in the work of connecting the observatories of Paris and Greenwich by means of a chain of triangles (1779).