de Peiresc, Nicolas-Claude Fabri
Born Belgentier, (Var), France, 1 December 1580
Died Aix-en-Provence, (Bouches-du-Rhône), France, 24 June 1637
In addition to fostering scientific correspondence, Nicolas Peiresc discovered the Orion nebula and tracked the satellites of Jupiter in order to solve the longitude problem. He was the son of Réginald Fabri, descendant of a Pisan family, and Margareta Bomparia, both of whom represented notable Provencal lineages and connections. After Peiresc attended Jesuit schools in Aix and Avignon, his father and uncle sent him on an extended trip to Italy (1599–1602) to prepare him further for the family post in the parliament of Provence. During his first year in Italy, Peiresc studied in Padua, where he met Galileo Galilei before settling in Montpellier to study law. After finishing his legal studies there, Peiresc attained a doctorate degree in civil law in Aix (1604). When his uncle died on 24 June 1607, leaving open the family parlementposition, Peiresc immediately filled the seat and held it for 30 years until his own death. For much of his adult life, Peiresc was at the center of an important correspondence network as a mediator to whom others looked for diplomatic solutions. For example, when Galilei was put under house arrest, Peiresc warned Cardinal Barberini that the failure to change Galilei’s verdict might yield a comparison with Socrates’ trial and similar condemnation.
Among his many interests and activities, Peiresc dedicated time to astronomical observations. In November 1610, while repeating some of Galilei’s observations published in Sidereus Nuncius, Peiresc and cleric Joseph Gaultier de la Valette (1564–1647) were apparently the first to observe a nebula in the constellation of Orion. Peiresc also observed the moons of Jupiter with the help of Gaultier and mathematician Jean Morin , and subsequently wrote a commentary he never published.
Peiresc’s most important and practical astronomical contribution stems from his work on longitude calculations. The main problem of determining longitude involves finding an accurate timekeeper. In the early seventeenth century, the regular motions in the heavens provided the most accurate clock. Peiresc originally planned to use the satellites of Jupiter as that celestial clock. Between November 1610 and May 1612, Peiresc made regular observations of the Jovian moons. Near the end of this period of observation, Peiresc felt his calculations were adequate enough for testing. He sent his assistant Jean Lombard to make observations of the moons of Jupiter in locations as far away as North Africa, Malta, and the Levant. The local time difference between the appearance of a configuration of Jupiter’s satellites as they appeared in Aix (according to Peiresc’s tables) and the appearance of that same configuration observed in Malta (by Lombard) could be used to calculate the difference in longitude between the two locations. After Lombard’s mission failed due to the difficulty of this technique, Peiresc largely abandoned work in astronomical observations for 16 years.
Between 1616 and 1623, Peiresc lived in Paris, where he met and associated closely with the circle of thinkers surrounding the librarians Pierre and Jacques Dupuy. It was through the Dupuy brothers that Peiresc met Marin Mersenne and others. Peiresc never married; his relationships did not extend beyond the intellectual friendships he had with such men as the Dupuy brothers and Mersenne. In 1618, Louis XIII granted Peiresc the abbacy of a monastery in Guîtres, north of Bordeaux, making Peiresc’s ties to the church stronger and his distance from marriage further. Peiresc returned to Aix in the summer of 1623; in the next year, he took the tonsure in order to regularize his position as abbé of the Guîtres monastery.
By 1628, Peiresc again took up the task of establishing longitude positions from his home in Aix, but with a different plan. He determined to use observations of lunar and solar eclipses made in different cities to establish the separation of longitude between them. To begin this new project, he requested others (among them the Dupuys) to send him observations of eclipses that occurred in January and February of 1628. He later distributed the observed times of the eclipses, which could then be compared to astronomical tables. According to the observations made in Paris and Aix in 1628, Peiresc calculated that the separation in longitude between the two cities was 3° 30′ 2″ greater than the previous standard.
Because of plague and public unrest between 1629 and 1631, Peiresc temporarily abandoned Aix for his country home in Belgentier, where he was unable to continue his astronomical observations. In 1632, Peiresc returned to Aix, where he resumed his telescopic observations and his larger project of gathering observations of eclipses from diverse locations in order to make longitudinal calculations. To aid him in this project, he recruited priests and Jesuits stationed in various locations from Rome to Mount Sinai. Despite the condemnation of Galilei in 1633, Peiresc explained to his recruits that making observations would not bring harm to souls and could even encourage others to follow in their footsteps.
For making eclipse observations, Peiresc stressed the need to use a telescope, but the network of observers he assembled did not always perform as he wished. Complications included letters and instruments lost in the mail, bad weather, sick observers, and faulty clocks - a crucial problem given the importance in determining the precise time of any given observation. These and other difficulties made Peiresc’s task of compiling observations all the more difficult. He was, however, able to find some success with a lunar eclipse on 28 August 1635; it resulted in correcting, and reducing by about 1,000 km, the length of the Mediterranean found on contemporary maps. To further increase the accuracy of such observations, Peiresc, along with the help of Pierre Gassendi and others, established the Provençal school of astronomy, where he could instruct future observers and achieve more uniformity in his project. However, after his death, the school folded, with most of the remaining students and teachers moving to Paris.
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