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First editions, very rare, of Cassini's two publications on the comets of 1664-5, which were observed by many astronomers across Europe (including Newton as a student). The discussions about the flight paths of these comets can be regarded as the turning point in the battle between Kepler's elliptical heliocentric model of the cosmos and the Tychonic geo-heliocentric model. Cassini (1625-1712) observed the comets from the palace of Prince Mario Chigi, the Pope's brother, and from the residence of Queen Christina of Sweden (to whom the first work is dedicated), who was then in Rome. "This [first] work is very important because it is the first that reports a precise sequence of observations and the entire path of a comet, also supported by mathematical calculations. Cassini, for the first time in history, tried to determine with the best possible accuracy the cometary movement, and, in this attempt, he employed the same laws used for the planets. The importance of this attempt should not be underestimated. It has to be remembered, in fact, that, according to the Aristotelean and Ptolemaic models, comets did not belong to the heavens, but they rather had a terrestrial origin" (Bernardi, Giovanni Domenico Cassini, 2017). Cassini "formulated a new theory (in agreement with the Tychonian system) in which the orbit of the comet is a great circle whose center is situated in the direction of Sirius and whose perigree is beyond the orbit of Saturn" (DSB). The large engraved plate depicts the course of the comet in the southern celestial hemisphere from December 13, 1664 through the middle of January of 1665. It also shows the appearance and direction of the comet's tail in a series of nightly dated observations. Cassini's detailed observations were made with a powerful new telescope made by Giuseppe Campani, which he describes in the preface to the first work. "Through his friendship with the famous Roman lens-makers Giuseppe Campani and Eustachio Divini, Cassini, beginning in 1664, was able to obtain from them powerful celestial telescopes of great focal length. He used these instruments very delicate and extremely accurate for the time with great skill, and made within several years a remarkable series of observations" (DSB). The comets were also observed by Adrien Auzout (1622-91) in Paris, and by Johannes Hevelius (1611-87) in Danzig. Auzout agreed with Cassini that comets were stable cosmic objects endowed with regular and predictable motions, but he did not subscribe to Cassini's hypothesis on the orbit of the comet. Hevelius, who published his observations in 'Prodromus cometicus' (1665), considered comets to be ephemeral phenomena with elusive spiral trajectories. In the second offered work, addressed to the abbot Ottavio Falconieri, (1646-76), Cassini presents further observations on the comet, and comments on those made by Auzout and Hevelius. RBH lists two copies: Bolaffi 2022, EUR 32,500 (bound with other works in a later binding) & Bolaffi 2014, EUR 21,250 (modern binding). I: Grassi p. 139; Lalande, p. 261; Riccardi I 276; OCLC gives Brown (lacking plate); II: Grassi p. 139; Lalande, p. 258; Riccardi I 277; OCLC: Brown, Cornell, and Ohio State. Two vols in one, folio (350 x 245mm), pp, [iv], 60 [recte 62], [2]; [1-2], 3-22, [1], with woodcut diagrams and one large folding engraved plate in first work, uncut (occasional light browning and foxing). Contemporary carta rustica backed with (18th century?) marbled paper (a bit soiled and stained). Seller Inventory # ABE-1706716334460
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