CASSINI GIOVANNI DOMENICO. Theoriae motus cometae anni 1664 pars prima. Ea praeferens, quae ex primis obseruationibus ad futurorum motuum praenotionem deduci potuere, cum noua inuestigationis methodo, tum in eodem, tum in comete nouissimo anni 1665 ad praxim reuocata. Auctore Ioanne Dominico Cassino … - Roma, Fabio di Falco, 1665. (Unito:) Lettere astronomiche di Gio. Domenico Cassini al Signor Abbate Ottavio Falconieri sopra il confronto di alcune osservazioni delle comete di quest'anno M.DC.LXV. (In fine:) Roma, Fabio di Falco, 1665.

Due opere in un volume in-folio; (Theoriae motus): 2 cc. (titolo e dedica), 60 (i.e. 62) pp., 1 grande tavola ripiegata, 1 c. (indice) - (Lettere): 22 pp., 1 c. (imprimatur). Legatura del ‘900 in tutta pelle. Ex libris di biblioteca privata a timbro sul frontespizio della seconda opera. Rare pagine un poco brunite, tracce di piegatura alla tavola. Bell’esemplare a grandi margini (32 x 22 cm.).

Prime edizioni. Rarissime opere di Giovanni Domenico Cassini dedicate al passaggio della cometa del 1664: l’autore la osservò attraverso il nuovo telescopio, qui descritto nella prefazione, e "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 perigee is beyond the orbit of Saturn. A new and fertile direction now opened up for Cassini’s observation. Through his friendship with the famous Roman lensmakers 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 on the planetary surfaces, which led him to important discoveries. In July 1664 he detected the shadow of certain satellites on Jupiter’s surface and was thus able to study the revolution of the satellites and to demonstrate that of the planet” (DSB).
La grande tavola ripiegata alla fine della prima opera raffigura la posizione della cometa rilevata nell’emisfero sud tra il 13 dicembre 1664 e gennaio 1665.
La seconda opera è una raccolta di lettere indirizzate a Ottavio Falconieri, dove Cassini riporta ulteriori informazioni riguardo alla cometa e molte indicazioni sulle osservazioni compiute da Auzout e Hevelius.

2 works in one vol., folio: (Theoriae motus): 2 ll. (title-page and dedication), 60 (i.e. 62) pp., 1 large folding engraved plate, 1 l. (index) - (Lettere): 22 pp., 1 l. (imprimatur). 20th-century calf. Stamp of private collector to title-page of second work. Some browning and foxing to a few leaves. Excellent, wide-margined copy (32x22 cm).

First edition of Cassini's extremely rare works concerning the comet of 1664.
The author observed the phenomenon through a new telescope described in the preface, 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 whose perigee is beyond the orbit of Saturn. A new and fertile direction now opened up for Cassini’s observation. Through his friendship with the famous Roman lensmakers 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 on the planetary surfaces, which led him to important discoveries. In July 1664 he detected the shadow of certain satellites on Jupiter’s surface and was thus able to study the revolution of the satellites and to demonstrate that of the planet” (DSB).
The large folding plate at the end of the first work depicts the position of the comet in the Southern Hemisphere between 13 December 1664 and January 1665.
The second work is a collection of letters addressed to Ottavio Falconieri, where Cassini provides further information about the comet and makes several remarks on the Auzout and Hevelius’ observations.

DSB III, p. 101. I) Riccardi I, p. 276. Grassi, p. 139. Lalane p. 261. II) Riccardi I, p. 277. Grassi, p. 139. Lalane, p. 258.