CASSINI, Giovanni Domenico.

Sammelband of three exceptionally rare works. I. Lettera astronomica di Gio: Domenico Cassini al Sig. abbate Ottavio Falconieri. Sopra l’ombre de Pianetini Medicei in Giove. [Colophon:] Rome: Fabio Di Falco, 1665. II. Tabulae quotidianae revolutionis macularum Iovis. Nuperrimè adinventae a Ioanne Dominico Cassino … Rome: Fabio Di Falco, 1665. III. [Drop-title:] Lettere astronomiche di Gio. Domenico Cassini al Sig. Abbate Ottavio Falconieri sopra la varietà delle macchie osservate in Giove e loro diurne rivoluzioni. [Rome: Fabio di Falco, 1665].

Rome: Fabio Di Falc, 1665.

Sammelband containing the first editions of three exceptionally rare works documenting Cassini’s very accurate observations of Jupiter’s spots, which enabled him to determine its rotation period, and including his discovery of the Great Red Spot – all made possible by his new collaboration with the lens makers Eustachio Divini and, most importantly, Giuseppe Campani. “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). “In July 1664 [Cassini] detected the shadow of certain satellites on Jupiter’s surface and was thus able to study the revolution of the satellites” (ibid.). These observations are reported in the first work in our sammelband. “A controversy about the results of these observations started quite soon. First, someone from Rome observed one dark shadow and another less dark one. Cassini clarified that the latter was not the shadow of a satellite but rather a physical spot on the planet. To prove his statement … he observed that it did not follow the movement of any orbiting body, and that it appeared every 9 hours 56 min, which the astronomer attributed to the rotation period of the planet … In support of the statement of the Italian scientist, Abbot Ottavio Falconieri published the letters between Cassini and himself as proof of his past observations, and Cassini made public his predictions on the return of the spot on Jupiter, to dispel any doubts” (Bernardi, p. 53). This was the discovery of the Great Red Spot (although Cassini was unable to discern the Spot’s red colour due to the limitations of his instruments). These letters were printed in the third work in the present volume. This may have been issued with the second work, which contains tables of the ‘revolutions’ of Jupiter’s spots. All of these works are of great rarity. OCLC lists Harvard only, Library Hub adds one copy of each of the three works.

Widely regarded as the greatest observational astronomer of the 17^th century after Kepler and Galileo, Cassini was born in Perinaldo, Republic of Genoa. “Paradoxically, the beginning of his scientific career benefited from the reputation he acquired for his knowledge of astrology. The Marquis Cornelio Malvasia, a rich amateur astronomer and senator of Bologna who calculated ephemerides for astrological purposes, invited him to come to work in his observatory at Panzano, near Bologna. In accepting this position Cassini initiated the first part of his career, which lasted until his departure for France in February 1669. Thanks to the marquis’s aid, he thus made use, from 1648, of several instruments that allowed him to begin his first researches. He was also able to complete his education under the tutelage of two excellent scientists, the Bolognese Jesuits Giovan Battista Riccioli – who was then finishing his great treatise, the Almagestum novum (1651) – and Francesco Maria Grimaldi, who later became famous for his discovery of the phenomenon of diffraction, published in his posthumous work De lumine (1665). Although one cannot exactly determine their influence on the young Cassini, it appears that they convinced him of the importance of precise and systematic observation and of the necessity of a parallel improvement in instruments and methods” (DSB).

“Since the determination of certain essential astronomical data is tied to the movement of the sun (solstices, obliquity of the ecliptic, and so forth) and thus requires the daily observation of the height of that body at the time of its passage to the meridian, astronomers for a long time had tried to increase the precision of these observations by employing high structures – churches in particular – as supports for large sundials, called meridians. Such was the case at the church of San Petronio of Bologna, where an important meridian had been constructed in 1575 by a predecessor of Cassini in the chair of astronomy at the university, Egnatio Danti. Unfortunately, structural modifications necessitated by the enlargement of the church had recently rendered this meridian unusable by blocking the orifice through which the solar rays entered. In 1653, Cassini, wishing to employ such an instrument, sketched a plan for a new and larger meridian but one that would be difficult to build. His calculations were precise; the construction succeeded perfectly; and its success made Cassini a brilliant reputation.

“In 1610, Galileo discovered with his telescope four Jupiter satellites, which he called Medicean stars. The great Pisan, sensing the great importance of an accurate determination of their motions for the problem of the longitudes entrusted his favorite pupil, Vincenzo Renieri, with the task of continuing his work on this subject. This monk, however, died suddenly in Genova in 1647 without having been able to produce the tables with the ephemerides of the Jovian satellites. Probably during his studies in Genova, Cassini, who mentions the name of Renieri in his biography, saw the sketches of the unfinished tables, but he also believed that, in order to finish this very important work, he needed time and, above all, suitable equipment” (Bernardi, p. 49).

“By 1664, … while Cassini was visiting Rome, he wrote that he had been invited by Campani ‘to come with him to Monte Citorio to observe Jupiter with a number of persons of distinction who were to meet there to test his telescopes. It was while making observations on that occasion that Cassini discovered the shadows of the satellites of Jupiter” (Bedini & Zanetti, p. 579). “Using the exact words of the astronomer: ‘While I was kept busy by the assignments of public character, I could make astronomical observations at night with an excellent telescope, which had been given to me by M. Campani, who had communicated to the public the discovery I had made of the shadows of the satellites of Jupiter onto the disc of this planet, which I had engaged other astronomers to observe’” (Bernardi, p. 52). These observations were published in I, which contains three letters to Falconieri sent from Rome and dated 12, 20, and 26 October, 1665.

Cassini’s observations generated controversy partly because he had seen two kinds of spots on Jupiter: shadows of Jupiter’s moons and at least one spot that was physically on the surface of the planet. However, in June 166, “Huygens, who had been invited to the Observatory in Paris by Minister Jean-Baptiste Colbert, wrote to Prince Leopold, ‘As to what concerns the new observations made by Cassini on the shadows of the satellites of Jupiter, they appear to me to be excellent and fecund, and I have no doubt of his veracity, as I have learned there has been doubt from others, and even less after the same say, September 26^th of the year 1665, when I was able myself to observe clearly the shadow of the third satellite, which Cassini had predicted would appear’” (Bedini & Zanetti, p. 596).

The first observation of Jupiter’s Red Spot has sometimes been ascribed to Robert Hooke in 1664, but Falorni has shown that what Hooke observed was almost certainly the shadow of one of Jupiter’s moons. “As far as Cassini is concerned, it is beyond doubt that he repeatedly observed a spot quite like our modern Red Spot. It seems likely that his first observations were made at Cittá della Pieve, between the summer and the autumn of 1665; a full report was published the same year in the form of letters directed to the Abbot Falconieri [i.e., III]. Cassini’s interest in the spot concerned its use in determining the planet’s rotation period, which at the time was unproven …

“First he took care to single out – by means of computing – which spots were caused by the transit of a satellite or a satellite’s shadow on the planet’s disc. Secondly, Cassini demonstrated that the remaining observable spots had to be located on the true surface of the planet. Among these latter, he finally recognized a spot that was exceptionally conspicuous and permanent, and proved ideal for determining a highly reliable rotation period.

‘To that first light of distinction then followed the other of detecting among the number of the other spots a permanent one which was often seen to return in the same place with the same size and shape. It is the same spot that Yr. Ecc. was able to see just touching the real northern edge of that belt of Jupiter which, among the three obscurer ones, lies more southerly. That one, which among the spots hitherto observed is the greatest, the most conspicuous and the more permanent … appeared to be different in colour, not so dark and black [as the shadows], but quite like that of the obscure belts … different in figure as being, when nearer to the centre, larger in accordance with the line of the belt which it grazes, or narrower when nearer to the circumference” (III, p. 3).

“With these words Cassini described for the first time Jupiter’s Great Red Spot.

“On the basis of his own observations, which amounted to no less than 13 between August 19 and October 30, Cassini compiled a Table of the transits of the Spot [i.e., II], from which he derived a rotation period of 9h 56m. His results were confirmed, on more than one occasion, by two groups of observers in Rome. The groups were headed by the well-known telescope makers and observers Campani and Divini, and Cassini had frequent contacts with them around that period. The fit between the computed and observed times of transit was excellent, and the Table confirmed that a previous observation on July 9 by Divini’s group – when a spot (‘semiumbram’) was seen to accompany the transit of the shadow of the third satellite – as also a Permanent Spot …

“Of all the Spot’s distinctive features, Cassini missed only its red colour, but it is out of the question that he would have been able to distinguish it because of the low light-grasp of telescopes of that time.

“The many observations that Cassini made in Paris from 1672 to 1694 – he had been appointed Director of the newly-built Royal Observatory – do not add anything of importance on the subject” (Falorni, p. 217).

“Continuing the studies begun in Italy, Cassini discovered the Saturnian satellites Iapetus (1671), Rhea (1672), Tethys (1684), and Dione (1684). He also discovered the flattening of Jupiter at its poles (a consequence of its rotation on its axis). In 1672, as part of a concerted effort to determine the size of the solar system more accurately, Cassini sent his colleague, Jean Richer, to South America so that roughly simultaneous measurements of the position of Mars could be made at Paris and Cayenne, French Guyana, leading to a better value for the Martian parallax and, indirectly, for the distance of the Sun. Between 1671 and 1679 Cassini made observations of the Moon, compiling a large map, which he presented to the Académie. In 1675 he discovered the Cassini Division and expressed the opinion that Saturn’s rings were swarms of tiny moonlets too small to be seen individually, an opinion that has been substantiated. In 1683, after a careful study of the zodiacal light, he concluded that it was of cosmic origin and not a meteorological phenomenon, as some proposed.

“In 1683 Cassini began the measurement of the arc of the meridian (longitude line) through Paris. From the results, he concluded that Earth is somewhat elongated (it is actually somewhat flattened at the poles). A traditionalist, he accepted the solar theory of Nicolaus Copernicus within limits, but he rejected the theory of Johannes Kepler that planets travel in ellipses and proposed that their paths were certain curved ovals, which came to be known as Cassinians, or ovals of Cassini. Although Cassini resisted new theories and ideas, his discoveries and observations unquestionably place him among the most important astronomers of the 17th and 18th centuries” (Britannica).

I. Lalande, p. 258; Riccardi I.1, col. 277, no. 13. II. Lalande, p. 258; Riccardi I.1, col. 277, no. 15. III. Lalande, p. 258; Riccardi I.1, col. 277, no. 12. Bedini & Zanetti, Giuseppe Campani, “Inventor Romae,” an Uncommon Genius, 2021. Bernardi, Giovanni Domenico Cassini, 2017. Falorni, ‘The discovery of the Great Red Spot of Jupiter,’ Journal of the British Astronomical Association, vol. 97 (1987), pp. 215-219.

Three works in one volume, folio (317 x 210 mm). I. pp. 7, [1, blank], woodcut initial; II. pp. [4] (title page and 3 pages of tables); III. pp. 12, decorative woodcut initials. The catchword at end of p. 12, ‘Illu-‘, may indicate that the work was originally meant to continue, but all copies have the same collation as ours (moderately browned). Eighteenth-century decorative paper wrappers (a bit worn and rubbed).

Item #6550

Price: $15,000.00