Jaren Callum, son of Dominic, was born at Paris, February 18, 1677, and at seventeen years of age was thought of sufficient promise to be received • member of the Academy of Sciences. He eccom pan'ed his father to Italy in 1605, and afterwards travelled in England and Holland, where be became acquainted with Newton, Flamsteed, he. lie succeeded his father at the observatory, was Maitre des Comptes, and died April 16, 1756. He was proceeding to his estate of Thury, when the carriage was npset, and he became immediately paralytic.
There is not much of brilliancy In the results of the life of James Omeloi as compared with those of his father, whom, on the whole, he much resembled in tht character of his methods of ohsereing and de-lot:log. lie was a better mathematician, and devoted himself for the most part to fundamental points of astronomy, and to tho con struction of talsles. 11s separate writings are not numerous ; some of them on optics by himself and his brother (Afterwards killed as before stated) were published in 1691, being nothing but college exer cise*. The others are, • De Is Grandeur et de la Figure de la Terre, Par* 1720; and ' Chime:is d'Astronomie,' Pali*, 1740.
The first of thee. two works (a mile to the' Mom. Acad. Sci: for 1719) captains the account of the continuation of l'icard's arc of the meridian, begun by Dominic Cassini and La Hire lo 1080, and recom norocel by Dominic and James Cassini in 1700. On the results of this measurement Dominic Cassini concluded that the earth was a spheroid elongated towards the roles, contrary both to theory and other observations. Much discussion was excited at the time. The second work ie an elementary treatise, which seems intended to explain his own and his father'. astronomy. It is accompanied by a volume of table., whielr must be considered sia the joint work of the father and so* This collection was republished when the original edition became meow, but with so many moon of press as to diminish ita value mate rially. The correct edition is that of the Impritnerio ItoyAle, Park, with the deur de-4s in the title-page. From this work we see that Jame. eosin! seems biumd, which is no great matter of surprise In favour of his father, ever to the extent of declaring that the hypothesis of the esconsire propagation of light, whiob all the world knew to belong te Roemer, was in fact started, examined, and rejected by Dominic Cash& He cites the ' Memoir. of the Academy of Sciences,'
width when examined by Delambre were found to contain nothing in support of the assertion, but showed very distinctly that Cassini and Romer were in controversy upon the subject, and that nothing but the rejection of the hypothesis now known by the name of Roemer speoars to Lave belonged to Dominic Cassini. It Appears Also that James Cassini wee rather Copernic:tu in his notions, but not very strongly determined ; that be knew nothing, or next to nothing, of the system and writings of Newton (' Principia; 1637; J. Cassius 'Astronomy,' 1740), which he cites in two pleas—once to endeavour to explain the acceleration of Jupiter's motion. in another for obser vations of a comet lie knows nothing of Bradley's discovory of aberration (1727.23); but Delambre has forgotten when he adds that he knew nothing of that of natation, widish was not published till 1747. lie appears to be, like his father, a follower of Descartes, and also, like him, to prefer graphical method, to calculation. His ideas upon the theory of comets would have been much the better for the study of Newton. Nevertheless, as no observer, J. Cassini was dis tinguished. His determinations of the times of revolution of the five satellites of Saturn then known are very exact: he first observed the inclination of the orbit of the fifth (now the sereuth) of them. He improved the methods and tables of refraction; determined very nearly the variation of the obliquity of the ecliptic, and the length of the year by comparison of a large number of equinoxes of his own and others. lie loft also a great number of good observations. Nevertheless, it is but justice to Picard and Roemer to remember, that both of the Cassinis put together, distingnishcd as they were, did absolutely nothing which can now bring them to the daily remembrance of the astronomer, though their fame has surpassed that of the re-inventor of the micrometer, and the inventor of the transit instrument.