CASSINI, Giovanni Domenico Theoriae motus cometae anni MDCLXIV pars prima. Ea praeferens, quae ex primis observationibus ad futurorum motuum praenotionem deduci potuere, cum nova investigationis methodo, tum in eodem, tum in comete novissimo anni MDCLXV ad praxim revocata... Rome, Fabio di Falco, 1665 1665
[bound with:] Lettere astronomische di Gio: Domenico Cassini al Signor Abbate Ottavio Falconieri sopra il confronto di alcune osservazioni delle comete di questo' anno M.DC.LXV. [colophon:] Rome, Appresso Fabio di Falco, 1665.
Two vols in one, folio (311 x 211 mm), pp [iv] 60 [recte 62] [2]; 22 [2], with woodcut diagrams and one large folding engraved plate in first work; errata corrected in a contemporary hand, a few leaves browned, fine copies in contemporary vellum, outer margin of vellum on upper cover torn exposing boards, old library stamp on first title. £18,500
First editions of these two exceptionally rare Cassini publications on the comet of 1664-5. Cassini observed the comet 'in the presence of Queen Christina [to whom the first work is dedicated] and 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 who perigree is beyond the orbit of Saturn' (DSB).
Cassini's detailed observations of the comet were made with a powerful new telescope. 'Through his friendship with the famous Roman lensmakers Guiseppe 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...' (ibid). In the preface to the work Cassini describes the telescopes, and the first observations made with them.
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.
The great comet of 1664-5 was observed by many astronomers, including Auzout, Borelli, Fabri, Hooke, Hevelius, and Petit.
The second work, addressed to the archaeologist Falconieri, presents further observations on the comet, and Cassini's remarks about the observations made by Auzout and Hevelius.
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
£18500
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