Riding the wave

Gian (Gio) Domenico Cassini
(Perinaldo 1625-Paris 1712)

Perinaldo probably derives its name from Rinaldo or Rainald, Earl of Ventimiglia, who built a castle at the beginning of the 11th century.

By mid-13th century the Castle and surrounding lands were purchased by the Doria family, three centuries later overwhelmed by the Grimaldi of Monaco. Their dominance, however, ceased with the conquest of the village by the Duke of Savoy, who put it under the county of Nice, conquered in order to give the House of Savoy an outlet to the sea.

Giovanni Domenico Cassini was born in Perinaldo in August 1625, as he himself states in his autobiography, attached by Father Angelico Aprosio to his work Della Biblioteca Aprosiana kept in Genoa, at the Biblioteca Durazzo-Giustiniani. According to tradition, the Cassini home was the castle which still dominates the hillside, today known as Maraldi castle.

The lobby of the University of Genoa,
once a Jesuit college

The plaque on the door of Maraldi Castle recalls the three astronomers who give prestige to Perinaldo: Gian Domenico Cassini, his nephew Giacomo Filippo Maraldi and the latter's grandson, Gian Domenico Maraldi.

The family, certainly important, came from Siena, as stated by one of his descendants, though Gian Domenico Cassini's handwritten autobiography and the attached documents and correspondence - now in Bologna, at the Biblioteca Comunale dell'Archiginnasio - do not have any reference in this regard.

He attended the prestigious Jesuit College at Genoa probably between 1638 and 1646, where he first developped his interest in astrology and astronomy, studying the theories of Copernicus, Kepler, Galileo.

Between 1646 and 1649 he refined his studies in astronomy under the guidance of Giambattista Baliani, a Genoese nobleman and a scholar of physics and mathematics, in close relationship with many Italian and foreign astronomers. He probably put Cassini in touch with Cornelio Malvasia, senator of Bologna and a lover of astronomy, who played a decisive role in the life of Cassini, opening to him the doors of the University of Bologna, where he was given the chair of the Theory of Planets .

At the end of 1652 there appeared a comet, and Cassini studied its course, issuing the following year the results of his observations, with his theories on the origin of comets. Later on he elaborated the project of a sundial in the church of San Petronio, who met the full approval of the Jesuit mathematician Giovanni Battista Riccioli (the latter's fundamental text De hidrographia et Geographia reformata is present at the Library of the Italian Navy Hydrographic Institute).

Bologna, San Petronio Basilica : Cassini's sundial inside the church. The detail shows the stretch facing the projection of the hole on the floor, which indicates the summer solstice. The brass line marks the exact path of the sun at midday, and it lies between the two series of marble slabs carved with the signs of the Zodiac.
From the biography of the scientist, by Anna Cassini, 1994.

In 1657 he started developing new ephemerides, a fundamental instrument for the purpose of navigation, while his chair at the University of Bologna was renewed until 1659.

In that same year he was tasked by the government in Bologna and by the Vatican to study the old dispute about the course of the Po and of the Rhine between the cities of Bologna, Ferrara and Ravenna, which were regularly damaged by the floods of the rivers, whose course had been altered by the construction of canals.

Therefore, his fame grew within the Vatican and with the nobility, particularly with the powerful Chigi family which included the Pope Alexander VII. By the Pope's brother, Prince Mario, in 1663 Cassini was appointed to direct the expansion of the " Urbano Fortress", close to the border between the Vativan State and the Duchy of Modena, in view of the expected French invasion.

Later on he had to adjust the course of the river Chiana, on the border with the Grand Duchy of Tuscany, in collaboration with Vincenzo Viviani, but in 1664, resumed the study of celestial bodies due to the appearance of two comets in the course of the year.

He then led a landmark study about Jupiter and its satellites - proceeding on the line of research begun by Galileo and his followers - which quickly found practical application for the determination of longitude. Jupiter Satellites - that Galileo had called "Medicean stars" in honor of Cosimo de'Medici, Grand Duke of Tuscany - were given names derived from mythology, such as Pallas, Juno, Temide, Ceres.

A fascinating and fully documented biography, reconstructing the public and private life of this versatile scientist is entitled Gio Domenico Cassini: uno scienziato del Seicento, by Anna Cassini (Perinaldo, 1994) who in spite of her name, is not related to the astronomer, whose descendants died away in the nineteenth century.

A portrait of Giovanni Domenico Cassini, by Anonymous, sec. XVII (Ventimiglia, Civic Library Aprosiana)

A wide variety of unending governmental tasks distracted Cassini from his favorite studies, while his reputation grew within the Curia - where Cassini was a privileged guest of the Pope - and in the Roman literary and scientific circles, where scholars, intellectuals and lovers of astronomy seeked the company of the learned professor of the Archiginnasio of Bologna, now famous throughout Italy.

His studies on the "spots" and rotation of Mars attracted the attention of French and British astronomers, while he also started pursueing medical research, in his attention to the progress of scientific experimentation.

His activity roused the attention of the French Government, since Colbert was convening at Court the best European scientists: in 1668 he was invited to join the Academie des Sciences, which was not only a great honor but also guaranteed full political and financial support to his research.

Finally, after further studies and publications, including the new ephemeris, in February 1669 the Vatican and the University of Bologna allowed Cassini to move to Paris.

He was given a prestigious apartment in the Gallery of the Louvre, at the time a magnificent royal palace still under construction, and immediately set to reorganising the Astronomical Observatory, poorly designed, which in 1671 became the largest and best equipped in Europe.


The Paris Observatory in an engraving of the nineteenth century, in the book Da Brera a Marte, namely the history of the Astronomical Observatory of Brera in Milan, edited by the Nuovo Banco Ambrosiano (published by Ist. Geogr. De Agostini, 1983)

After various diplomatic and personal vicissitudes he obtained from Rome consent to permanently reside in Paris, while having undertaken the study of sunspots and developed research projects so that "astronomy could serve the improvement of geography and navigation."

In October 1671 he discovered a satellite of Saturn - named after the mythical Titan, son of Heaven and Earth - and a year later identified a second one, which he called Rhea, the mythical wife of Saturn and mother of Zeus, Poseidon and Pluto.

Meanwhile he was studying atmospheric phenomena and refining astronomical tables, to improve the accuracy of nautical charts and solve the problem of calculating longitude. To this end, several expeditions were conducted to determine the longitude of different places of the earth and distances of the earth from other celestial bodies, under Cassini's supervision at the Paris Observatory.

He was also the manufacturer or the inventor of ingenious instruments, including an astrolabe designed to instantly calculate the motion of Jupiter and its moons; also, a silver celestial planisphere representing the constellations visible at the latitude of Paris, and a celestial globe which he entrusted the construction of to Nicholas Bion, a famous mathematician and engineer of the King.

Research spurred the improvement of optics and astronomy, but instruments were becoming increasingly cumbersome and unwieldy, till Cassini invented an armor for telescopes with a timing device, which he called "machine parallatique".

In 1673 he married Genevieve de Laistre and on that occasion, the king granted him French naturalization so that he became a French citizen in all respects. On his marriage, Cassini acquired the castle of Thury, in the county of the same name, which was eventually inherited by his youngest son Jacques, who then had the title of Count of Thury.

Thury Castle today, from Cassini's biography by Anna Cassini, 1994.

In the following years he was totally absorbed by his astronomical studies and published a map of the Moon, which remained unsurpassed until the advent of photography in the late nineteenth century. In particular, he proceeded with the observation of the comets and of the planets Venus and Saturn, defined the ring structure of the latter and that specific characteristic that is still known as "Cassini division", and discovered two satellites of the planet, which he called Tethys and Dione.

Meanwhile he collaborated to the Neptune François, ou Atlas Nouveau des Cartes Marines , which was published in 1693 and immediately forged and reprinted in Amsterdam by the Dutch publisher Pierre Mortier.

His name is also linked to the map of France, known as the "Chart of Cassini". Colbert, attaching primary importance to the road-system for the economic development of the Country, had commissioned the Académie the survey of the national territory and Cassini, since his arrival in Paris, had contributed to geodetic measurements. He gave a fundamental contribution in determining the longitudes of various places using the eclipses of Jupiter's moons, the system which he himself had created. Various events slowed the map-making, and the chart was completed by Cassini's successors: by his son Jacques in collaboration with his cousin Giacomo Filippo Maraldi, both skilful astronomers; and by his grandson César-François de Thury (Cassini III) with his cousin Gian Domenico Maraldi, so that the chart - 182 sheets faithfully representing the whole of France - could be presented to the Constituent Assembly by his great-grandson Cassini IV in 1790.

At Perinaldo a museum has been dedicated to the scientist, and an observatory is named after him, open to the public and to schoolchildren.
The postmark dedicated to Cassini during the event known as "Vele d'epoca" - Imperia 2004

Additional biographical info at the site www.castellomaraldi.com

By
Paola Presciuttini (May 28, 2005, updated September 20, 2005)
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