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Cassini, his early studies - N.H. Enzo Gaggero – Founding member « ... Giovanni Domenico Cassini was born in Perinaldo (Imperia) on 8 June 1625. His father, Giacomo, was a land-owner of ancient Sienese extraction, while, his mother, Tullia Crovese, came from a rich family of notaries. Perinaldo, formerly Poggiorinaldo, owed its name to Rinaldo or Rainald, Count of Ventimiglia, that between the XI and the XII century built the small town and surrounded it with walls. In 1625 the town was a dominion of the Doria’s, allies of the Savoia’s. The same town saw the birth of two other astronomers: Giacomo Filippo Maraldi, a nephew of Cassini, and Gian Domenico Maraldi, the grandson of G. Filippo Maraldi. Young Giovanni Domenico Cassini, was eager to learn and quite brilliant. He started his studies with his uncle, Antonio Maria Crovese, a notary and continued, for two years more, with Father Giovanni Francesco Aprosio in Vallebona, a nearby locality. Thanks to the tutelage of the Doria’s, from 1638 to 1646, he attended the prestigious Jesuit College in Via Balbi - Genoa (now the University of Genoa); showing a great liking for arts, philosophy, theology and mathematics. For a short period of time Cassini retired at San Fruttuoso and studied under the guidance of the Abbot Doria. Mathematics was his leading interest. Additionally, he became interested in astronomy, after reading a book of Judicial Astrology, given to him by a clergyman. He, then, dedicated himself to the scientific study of the skies with the help of Giambattista Baliani, a Senator, who had been in correspondence with Galileo and who, in Genoa, was in contact with Vincenzo Renieri, an Olivetan monk, and a former pupil of Galileo. Baliani was also responsible for the build up of the outer circle of walls that surrounded Genoa. Baliani taught
Cassini how to measure the position of the stars, using an instrument (a
predecessor of the sestant) that had belonged to the great astronomer Tycho
Brahe. Enthusiastic, Cassini
decided to dedicate himself to the study of astronomy. His name, thanks
to Baliani, became known beyond the borders of the Republic of Genoa. It
reached the Marquis Cornelio Malvasia, a Senator of Bologna and General
of the Duke of Modena’s troops, who was deeply interested in Astrology
and Astronomy. Cassini
was summoned to his villa in Panzano, near Modena, where he could dispose
of a private observatory and of a rich library.
Panzano and Bologna were quite near. The chair of Astronomy at the University of Bologna was vacant, as the Jesuit Bonaventura Cavalieri (a friend of Galileo), co-inventor of the infinitesimal calculus, had died some years back. On 12 April 1651, the Academic Senate of Bologna confirmed the Chair of Astronomy to Cassini (who was, now, nearly twenty-six) for five years, granting him an allowance of 600 liras. In Bologna, he became acquainted with the Jesuits Riccioli, Bettini and Grimaldi, all astronomers and members of the Santa Lucia Jesuits’ School. At the end of 1652, the transit of a great comet,
allowed Cassini
to study this event in detail. An event Galileo assumed was originated
by a sort of "windiness" released from Earth. On the contrary, Jesuit Father
Ricci, assumed comets were celestial bodies that belonged to the solar
system.
In Bologna, Cassini was asked to restore the Sun-Dial Line of the Basilica of San Petronio, built a century before by Father Danti, who had created an opening in the vault on the Southern side of the Basilica, through which the Sun rays filtered at exactly midday (astronomical time). According to the Sun’s position on the horizon, they illuminated different points, every-day diverse. These points were marked onto a metallic line, stretched obliquely along the floor. Cassini called this dial "Heliometer" and, making use of this great instrument, "certified" the distance Sun – Earth more accurately; the ellipticity of the Earth’s orbit and the inclination of the Earth’s axis. Thanks to Cassini, the truth, conceived for the first time in the 3rd century B.C. by Aristarchus of Samo, that the Earth revolved about the Sun, and that, later on, was re-affirmed by Copernicus (with the Church’s imprimatur) and that, again, was supported by Galileo, who, unfortunately, could not produce any evidence to favour this assumption, became world known. On 26 November 1655, Cassini presented the first drawing of the Sun-Dial line to Queen Christina of Sweden who had stopped in Bologna, during her trip from Stockholm to Rome (her new residence), as, with the help of the Jesuits, she had secretly become a convert to the Catholic Religion.
Cassini, as a Public Mathematician, was obliged to take into consideration the complicated hydro-geological situation of the Po Valley, crossed by the rivers Po and Rhine. He, patiently, faced this problem, working in unhealthy and uneasy areas. An experience that, afterwards, proved precious, when he started to work in France as a cartographer. In 1664, Cassini moved over to Rome, following the call of Pope Alexander VII (Fabio Chigi) and observed a new comet. He also wrote a treatise, which he dedicated to Queen Christina of Sweden, now exile in Rome. Between 1664 and 1666, Cassini re-approached Galileo’s studies on the satellites of Jupiter and on the rotation of Mars, with the use of the telescopes designed and built by Giuseppe Campani of Spoleto. In 1667, Cassini, while studying how to arrange the course of the rivers flowing through Val di Chiana, carried out important entomological studies on the vital cycle of insects. At the same time, in his residence at Bologna, together with Geminiano Montanari, he carried out experiments on blood transfusion, which, at the time, were performed only on animals. Cassini replaced the metal thin tubes with a hen ‘s quill feather. Its transparency allowed to regulate the flow of the blood. His fame reached the King of France. On 25 February 1669, he was summoned to Paris for a temporary assignment at the Court of King Louis XIV, withholding, however, his post and allowance at the University of Bologna, to which he renounced (on his own account, without anybody forcing him), when he understood his stay in Paris, went beyond all expectations. Leaving Bologna, he stopped at Forte Urbano (near
Modena) guest of the Malvasia’s. He then proceeded toward Genoa and Perinaldo,
where he welcomed his parents and then reached Paris on 4 April 1669.
Cassini, his work in France ... his return to Italy ... In Paris, welcomed by the Court, he helped to set up the Astronomical Observatory (becoming the actual director of it, even though this position was not official). Here he dedicated himself to astronomical studies. Observing Saturn, he was first to discover four satellites of this planet and, additionally, he discovered the dark division between the rings, called the "Cassini Division". He further calculated more accurate Ephemerides noting down the position of the stars and of Jupiter’s satellites. Using his astronomical data he was able to carry out a trigonometric survey of France and of its overseas territories, a task continued by his successors. On 10 November 1673, he married Genevieve de Laistre, who was much younger than him. His two sons were born in the apartment of the Observatory: Jean Baptiste entered the Navy and died in the battle of Cap de La Hague, while Jacques followed his father’s steps. Through marriage Cassini acquired the castle of Thury which, after, became the residence of his successors. On 23 September 1694, the Autunnal equinox, Cassini and his son decided to travel back to Italy, taking with them many scientific instruments. Cassini wanted to meet the Pope, to dispute with him the hydrographic problem of the Po’s delta, never solved, and to decide how the Sun-dial of San Petronio could be restored. During this journey, they carried out accurate measurements of the geographic co-ordinates in the South part of France. They passed through Nizza and stopped in Perinaldo, where Cassini met with his sisters Angela, Caterina and Francesca (his parents, unfortunately, had died already twenty years ago). Around mid November, he left for Genoa
and Portofino,
spots he loved, as in these places he had started his first astronomical
observations. He then passed through Florence,
where he met, once again, his friend Vincenzo
Viviani, an astronomer who, at the time,
was working on the Sun-dial of Santa Maria del Fiore and found time
to collaborate with him. After, he reached Bologna,
where he restored the heliometer of San Petronio.
In his honour, the city struck a medal, created by Ferdinand de Saint-Urbane
of Lorraine.
Cassini, his last works in Italy ... his return to France ... The winter between 1694 – 1695 was extremely biutter. Cassini spent Christmas period guest of the Marquis Monti, but urgency to speak with the Pope, obliged him to leave for Rome. Discussions, however, were disappointing, so Cassini left, once again, for Bologna, where he favoured young astronomers with advices and donations. Among them, Guglielmini, Manfredi and Count Luigi Ferdinando Marsili who put up the Marsiliano Observatory and founded the Science Institute. He also managed to request Paris to send them instruments, books and a precision watch. In 1696, he returned to Paris, (it was now Spring) and, once again took up the systematic topographical survey of France. With the help of his son Jacques and of his grandson Giacomo Filippo Maraldi, he measured the arc of the meridian from Paris to Perpignan and brought forward astronomical and geodetic operations, which were reported to the "Académie". His grandson, Jean Dominique, Cassini IV, presented this cartographic work, in 182 sheets, to the Constituent Assembly in 1790. This work was accomplished after 132 years. Cassini became blind in his old age, and dictated his autobiography. It was published in 1710. He died in Paris on 14 September 1712, at the age of eighty-seven and was buried in the Church of Saint Jacques du Hautpas. A plain memorial stone remembered his name "J. D. Cassini - Astronome". His successors carried on his studies at the "Observatoire". His studies are up to date and in use still today.
"Cassini’s Laws"
are the result of studies carried out on bodies in resonance "rotation/orbit"
[e.g. Moon or Mercury], originating from the tidal inter-action between
the body of reference and the orbiting body.
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