CASSI'NI. We have now for the second time to sketch tho lives and labours of a family of distinguished men, who, though their con tributions to the stock of knowledge do not rival in extent or value those of the Bernoullis, present nevertheless a succession of talent and industry which rarely occurs. From the date of its establishment in 1670, till the time when the revolution destroyed all hereditary privi leges, the Observatory of Paris passed from one Cassini to another through four generations, as though it had boen transmitted by the law of property.
Jotter DOMINIC Cessisr was born at Perinaldo, in the district of Nice, June 8, 1625, of a respectable family which came from Siena, of which place a Cardinal Cassini was archbishop in 1426. He was educated by the Jesuits at Genoa, and there are some Latin poems of his in a collection of 1616. He attached himself to mathematics and astronomy, and also it is said to astrology, of which he was cured by discovering that a prediction which succeeded had been calculated wrongly. He also read the work of Pico di Mirandola against astrologers. In 1644, at the invitation of the Marquis Malvasia, who was building an observatory, he removed to Bologna, and in the university of that place, after the death of Cavalieri, in 1650, he suc ceeded to the chair of astronomy. He here observed the comet of 1652, on which he published his first work. He made various obser vations with a gnomon and meridian line constructed in a church at Bologna. In 1657 bo was deputed, with another, ambassador to the pope, on a quarrel between Bologna and Ferrara relative to the river Po, and on his return was appointed to the superintendence of the river for the former place. In 1663 he was appointed to repair the works of Fort Urban. He was at this time patronised by Pope Alex ander VII., and afterwards by Clement IX. In 1664.5 he made the first of his more brilliant and useful discoveries, namely, the time of the rotation of Jupiter, which he fixed at 9 hours 56 minutes. Professor Airy, by recent observations, makes it Ob. 55m. 21.3 a. He also saw, for the first time, the shadows of the satellites on the disc. (Cssireisr.] By comparison of his own observations with those of Galileo, be con structed (1665) his first tables of the satellites. In 1066-7 he found the rotation of Mars to be 24 h. 40 m. (it is 24 h. 39 m. 2P3 a.), and in this same year he ascertained that the rotation of Venus, which is difficult to observe on account of her phases, does not differ much from that of Mars (it is 23 h. 21 M. 7 a.) He made the apparent rota tion of the sun to be about 27 days, which is very near the truth. These results show considerable skill and assiduity, and made the name of Cassini very well known throughout Europe.
When Colbert founded the Academy of Sciences, in 1666, and at the same time projected an observatory at Paris, he proposed to Cassini to remove into France, and offered him a pension equivalent to his Italian emoluments. Cassini expressed his willingness to comply if tho consent of the pope (Clement IX.) could be obtained ; which was done on condition that Cassini's absence should not last more than two or three years. Ho arrived at Paris April 4,1669, and began his duties at the observatory September 14, 1671, where his observa tions extend from 1671 to 1633. In 1673 the Bolognese government, which had kept all his appointments open, required him to return; but Colbert succeeded in negociatiog his continued stay in France, and accordingly iu the same year he was naturalised iu his new country, and married a French lady. He never returned to Italy, except for a short time in 1695, but remained at the head of the Paris Observatory. In the latter years of his life he was totally blind. He died September 14, 1712, without disease, and only, as Fouteuelle remarks, "par la mule necessit6 de mourir." His eldest son was killed at the battle of La Hogue; of his seoond we shall have to speak as soon as we have completed the present part of our subject. In 1671.2 he discovered the third and fifth satellites of Saturn, and in 1684 the first and second. His gnomon at Bologna led him to mono correct solar tables than had been in use, and to more exact values of the refraction. He gave a more complete explanation of the lunar libration than either Kepler or Hevelius, particularly iu the determination of the quantities concerned ; and though he did not leave the actual observations, Delambro, who, as we shall see, judges him severely, appears to think that he did establish by observation the coincidence of the nodes of the lunar equator and orbit. He was the first who carefully observed the zodiacal light, which he imagines he discovered. His later tables of the satellites of Jupiter (1668 and 1693) were con siderable improvements ; but though in possession of facts analogous to those which led to the discovery of the motion of light, ho not only did not make that discovery, but rejected it when announced by Roemer. For his arc of the meridian, his observations relative to
refraction, with a multitude of other points too long to notice here, we must refer to Delambre, Hist. d'Astron. Mod.,' voL We have seen that Casaini, as an observer, was no ordinary man. Even if we leave out of view discoveries such as those of the satellites of Saturn, which though brilliant involve no extraordinary sagacity, we have still the continued, systematic, and successful observations of' the satellites of Jupiter. But as a philosopher, and as a reasoner upon the results of his observations, Cassini does not excel. Au obstinato follower of Descartes, we have no evidence that he ever looked into Newton ; probably his mathematical knowledge was not sufficient to enable him to understand the Principia.' A devoted, if not a bigoted adherent of the Church of Rome, be was a Ptolemaist long after the time when Galileo had made the speculation of Coper nicus sound astronomical doctrine; and we cannot give much admi ration to the power of a mind which enslaves itself to a church in a matter of science. His unskilful handling of Kepler's laws, his crude and unsatisfactory notions upon comets, and indeed his method of dealing with almost any subject which involved investigation, are so many points which render the extravagant praises of Fontenelle and Lalande altogether inadmissible. His reputation iu fact was alto gether of a different species from that which it ought to have been. So far as that sort of notoriety is concerned with which the public iu general is most struck, Cassini and William Herschel appear to resemble each other. Nevertheless, take from the latter Uraoua and six satellites, with two of Saturn, and there is left a first-rate repu tation among astronomers; withdraw the similar discoveries of Cassini and he remake a oessameedable and even a remarkable observer, but by no means In his menet rank. And it moat be remarked that Lloyd) is throughout Caselnrs writings • continual tendency, either from ignorance or rusity, to appropriate the discoveries of red& **sore or costemponwies lie speaks of himself as the first who observed the variation of the moods diameter depending upon her 'Retards "Ool," my* Delambre, to one of his parentheses, "le premier apres Kepler, Ausout, et lierellue." The summing up of this marching 1-istorbur Is worth extracting. "But why, we may ask, has easeful eo unirenal • reputation? Why has he bad more praise to his own share tale all astr000mer. together, at least during their lives! neatly, because there was in him much to praise, because he was insluetrioes, because he kept publics attention constantly awake, because he emplaryol for the most part unusual means, such as his gnomon and his long telarropee; and beause, being invited to Franca as a men who could not be done without, the world early became accustomed to *resider him superior to those who had wished him to join them. Ile was a conquest for which the monarch was praised. and all the flogs bestowed open him went indirectly to the king. lie attributed (felesit hommage) all his disoreories to Louis XIV.; he was the favourite astronomer of the court, so that it did not need se much as he bad to scene him more reputation than any other. All the world understood Cessinre discoveries: Jupiter tamed in 9h. 56m., Venus in 21h. 2Orn., Mare in 24h. 40m.; Saturn had four moons, which no one had sew till then, and a medal had been struck to commemorate the latter. lo reality, these phenomena were isolated novelties, infi nitely curious things, which all astronomers are very glad to know, but which could have been omitted without any result in the smallest degree prejudicial to the promo, of real astronomy. If we feel authorised to reproach any on. it Is not Cassini, but his contempo raries." On the other hand, Laborde, an astronomer of real merit bat of great want of judgment, has the following absurd exaggeration:— " (..maini was one of those rare men who seem formed by nature to give a new fa** to the sciences ; astronomy, augmented and perfeoted in all its parts by the discoveries of Cumin!, underwent in his bands a most aatonithlog revolution. This great man was the chief glory of the glary of Louis XIV. in this respect, and the name of Caasiui is almost synonymous in France with that of the creator of astronomy." On which we can only my, may every Lalande find a Delambre I The writings of Dominic Cawini are numerous, and a complete list may be found in Lalende's 'Bibliographie Astronomique.' It is a presumption, so far as it goo', of the accuracy of the character given by Delambre, that none of these writings are now sought after as con taining matter of any lasting value, except only the pure results of observation.