Jean Picard

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Picard's sundial in the courtyard of the Sorbonne

Jean Picard , called Abbé Picard (Abbot Picard), (born July 21, 1620 in La Flèche , † October 12, 1682 in Paris ) was a French astronomer and geodesist .

He is considered one of the founders of geodesy . In 1670 Picard was the first to determine the length of a degree of a meridian arc - and thus the size of the earth - by triangulation with quadrants , which had telescopic sights with crosshair eyepieces to target the celestial body. This achieved a degree of precision that was previously impossible . Isaac Newton used these measurements to verify his theory of gravity .

Life and accomplishments

Little is known about the first decades of his life. He attended the Collège Henri-IV in his birthplace. He later assisted Pierre Gassendi in observing the solar eclipse of August 25, 1645 and in other astronomical events in the two following years. He probably also heard Gassendi's lectures at the Collège Royal . He probably acquired the title of prior of Rillé , a small town near his native town, around 1650 , which gave him a small income. He seems to have continued to work on astronomical observations and became a professor at the Collège de France in 1665 .

He was one of the first members of the Académie Royale des Sciences appointed by Colbert in 1666 .

On June 21, 1667, the day of the summer solstice , Adrien Auzout , Jacques Buot , Bernard Frénicle de Bessy , Jean Picard and Jean Richer , mathematicians and astronomers of the Académie Royale des Sciences, set the meridian of Paris by marking on a stone, over which the Paris observatory was built afterwards . The difference in length to the previously commonly used Ferro-Meridian was usually calculated at 22 ° 30 ′.

Picard's quadrant
Picard's leveling device

In 1667 and 1668 he worked together with Adrien Auzout to equip the previous quadrants with simple sights with telescopic sights and to build cross-hair eyepieces and micrometers into these telescopes . For nighttime observations, the fine threads suspended in the eyepiece could be made visible by a lateral light source. Even if others already had these ideas, it is thanks to Auzout and Picard that they worked hard to develop these devices into ready-to-use precision instruments. He also developed a leveling device that was also equipped with measuring telescopes .

During this time he made use of his influence on Colbert to appoint Cassini as director of the observatory in Paris.

Paris - Amiens meridian arc

In 1668 Colbert informed the members of the academy that he wanted more precise maps of France than the ones that had been used up to that point and asked the academy to prepare the necessary measures. As a first step, David Vivier had a map of the area around Paris made according to the specifications of Gilles Personne de Roberval and Picard. However, it was agreed that mapping the entire country would require a degree measurement using geodetic triangulation and precise astronomical positioning of the larger places.

The first degree measurements of modern times were the 1525 by Jean François Fernel from the revolutions of the wheel of his carriage and the 1615 by Willebrord van Roijen Snell (Snellius) for the first time calculated on the basis of a triangulation .

Picard therefore carried out the first degree measurement in 1669 and 1670, in coordination with the Academy, in which the triangulation was carried out with instruments that had telescopes with crosshair eyepieces and thus had a precision that was previously impossible.

The level measurement found on the route between the south of Paris, nearly at the Paris meridian located Malvoisine (today Champcueil ) and the short distance to the north of Amiens remote Sourdon place later than the meridian arc Paris - was referred to Amiens.

Picard started south of Paris with a roughly 11 km long baseline between Villejuif and Juvisy-sur-Orge , which was measured twice on a largely straight, paved road with wooden 3.9 m long poles, with only 2  feet apart Results. Then he connected the baseline in a triangulation with Malvoisine and Sourdon, which was then extended to Amiens. His instruments allowed him to have triangles with sides averaging 28 km in length. As a control, he finally created a 7.6 km long baseline. As a result, he calculated the length of a degree with 57,060  Toisen or 111.210 km, which corresponds to a radius of curvature of 6,371.9 km.

In his measurements, Picard also noted the different strengths of refraction , which he suspected to be due to differences in temperature and air pressure in the air (but without being able to draw any conclusions about differences in density). As a result, thermometers and barometers were soon taken into account in the measurements.

Trip to Uraniborg

In July 1671, Picard began his journey to Uraniborg on the Öresund island of Ven , which is now part of Sweden , in order to redefine the position of Tycho Brahe's observatory so that his observations of the fixed stars and planets from the years 1580 to 1597 could be used for astronomical research in Paris close.

On the way he made a stop in Holland , where he compared the Rhenish foot , which was the basis of Snellius' triangulation, with the Paris foot , and found slight differences from the measurements he had used in Mesure de la Terre . There he met Joan Blaeu , who had come to almost the same conclusion as Picard in his work on the circumference of the earth.

When his ship had to anchor on the way because of a storm, he observed sunspots , which by chance were also seen by Cassini in Paris .

In Copenhagen, Erasmus Bartholin supported him in his project. He also introduced him to the young Ole Rømer , who assisted him with his measurements on the island of Ven and then accompanied him to Paris at his request, where he worked at the Paris Observatory for ten years . On Ven there were hardly any remains of the wall of Tycho Brahe's Uraniborg, but Picard set up his own, provisional observatory with which he not only determined the polar height, but also the geographic longitude in relation to Paris by observing the orbit of Jupiter's moons . In the almost three months of his activity on Ven at the end of 1671, Picard also surveyed a number of surrounding places and made various astronomical observations.

Surveying work in France

Corrected map of France from 1682

In the years 1672 to 1680 Picard initially carried out various astronomical observations a. a. in Montpellier and Sète as well as in Lyon. In between he had to carry out surveying work for the water supply of the palace gardens of Versailles , which in the eyes of the king was urgent. This included clarifying in 1674 that the proposal by the Riquet , who was involved in the construction of the Canal du Midi , to divert part of the Loire into the castle park was not feasible.

In preparation for the mapping of France ordered by Colbert, Picard and Philippe de La Hire carried out geodetic work in Brest and Nantes , Bayonne , Bordeaux and Royan and on the French north coast between 1679 and 1681 . La Hire ended it with surveys of the Provence coast.

This work, supplemented by measurements of other geodesics, made it possible for La Hire to add a new coastline to a map of France based on previous views. This Carte de France corrigée par Ordre du Roy sur les observations de Messieurs de l'Académie des Sciences ( map of France, corrected according to the order of the king according to the observations of the gentlemen of the Académie des Sciences ) was presented to the Académie and the King in 1682 then jokingly stated that "ces Messieurs de l'Académie lui avaient enlevé une partie de ses États" ( these gentlemen of the academy have taken away part of his state from him ).

In 1681 Picard suggested extending his own degree measurement to Dunkirk and Perpignan as a basis for mapping the entire country and combining it with a triangulation along the borders and coasts. That was the starting point for the creation of the Carte de Cassini , which spanned decades and is still accessible online as a historical map series in the French Géoportail .

Others

When Picard examined the air pressure at different altitudes with a mercury barometer in 1675 , he observed glow discharges on the barometer (see Geissler tube ). However, static electricity as a phenomenon was already known in ancient times.

Picard was the founder of the first astronomical yearbook , the Connaissance des temps , in 1679 , which he published until his death.

The lunar crater Picard is named after him.

Fonts

  • Mesure de la Terre . Imprimerie royale, Paris 1671 (30 pages, digitized on Gallica ). (With complete picture panels)
  • Mesure de la Terre . Imprimerie royale, Paris (392 pages, full text in the Google book search). An anthology published posthumously by Philippe de La Hire around 1685 with the following content:
    • Mesure de la Terre , pp. 1-59
    • Voyage d'Uranibourg ou Observations Astronomiques faites en Dannemarck par Monsieur Picard , pp. 61–99
    • Observations astronomiques faites en divers endroits du Royaume de France par Monsieur Picard , pp. 101–120
    • Observations astronomiques faites à Brest et à Nantes pendant l'année 1679 par Messieurs Picard et de la Hire , pp. 121-134
    • Observations faites à Bayonne, Bordeaux et Royan pendant l'année 1680 par Mess. Picard & de la Hire , pp. 135-144
    • Observations faites aux costes septentrionales de France pendant l'année 1681 par Mess. Picard & de la Hire , 145-160
    • Observations faites en Provence et à Lyon sur la fin de l'année 1682 par Monsieur de la Hire , pp. 161–180
    • De la pratique des grands cadrans par le calcul. Par M. Picard , pp. 182-224
    • Traité du Nivellement, by M. Picard; Préface par M. de la Hire , pp. 225-283
    • Relation de plusieurs nivellements fait par ordre de sa Majesté par M. Picard , pp. 284–297
    • Abbregé de la Mesure de la Terre faite par M. Picard , pp. 298-309
    • De mensuris (comparison of different units of measurement, Latin), pp. 311–317
    • Mesures prises sur les originaux & comparées avec le pied du Chastelet de Paris par M. Auzout , pp. 317-320
    • De Mensura Liquidorum et Aridorum , pp. 321-331
    • Fragmens de Dioptrique par Monsieur Picard ; Pp. 333-392
  • De la Hire (ed.): Traité du Nivellement, avec une relation de quelques Nivellements faits par ordre du Roy . Estienne Michallet, Paris 1684 ( full text in the Google book search).
  • De la Hire (ed.): Traité du Nivellement, avec une relation de quelques Nivellements faits par ordre du Roy . Montalant, Paris 1728 ( full text in the Google book search).

literature

  • Rudolf Wolf: History of Astronomy . In: History of the Sciences in Germany. Modern times . At the instigation and with the support of His Majesty the King of Bavaria, Maximilian II. Ed. by the Historical Commission at the Königl. Academy of Sciences. tape 16 . Oldenbourg, Munich 1877, p. 447 ( Digitale-sammlungen.de ).
  • Jean Baptiste Joseph Delambre: Histoire de l'astronomie moderne . tape 2 . V e Courcier, Paris 1821, p. 597 ( full text in Google Book Search).

Web links

Commons : Jean Picard  - collection of images, videos and audio files

Individual evidence

  1. ^ A b Jean Baptiste Joseph Delambre: Histoire de l'astronomie moderne . tape 2 . V e Courcier, Paris 1821, p. 597 ( full text in Google Book Search).
  2. ↑ Delambre mentions that, according to other sources, Picard did not die until the beginning of 1683. There seems to be no basis for the date given in the Encyclopedia Britannica.
  3. ^ A b William Fox: Jean Picard. In: Catholic Encyclopedia , Appleton, New York 1907–1912 (in the English Wikisource)
  4. ^ Rudolf Wolf: History of Astronomy. Pp. 460-462
  5. ^ A b John J. O'Connor, Edmund F. Robertson: Jean Picard. In: MacTutor History of Mathematics archive
  6. ^ Louis Moreri: Supplement au grand dictionaire historique genealogique, geographique, & c .; pour servir à la dernière edition de l'an 1732 & aux précédents . tape 2 . Jacques Vincent, Jean-Baptiste Coignard, Pierre-Gilles Lemercier, Jean-Thomas Herissant, Paris 1735, p. 292 ( full text in Google Book Search).
  7. ^ Report on June 21, 1667. Procès-verbaux. T3 (11 avril 1668-27 mars 1669, Registre de mathématique) / Académie royale des sciences; on Gallica
  8. ↑ Carte particulière des environs de Paris ... Map of the area around Paris from 1690, with the meridian of Paris at 22 ° 30 ′ of the Ferro meridian
  9. ^ Rudolf Wolf: History of Astronomy . P. 363
  10. ↑ Picard described the leveling device in detail Mesure de la Terre.
  11. ^ Meeting of May 23, 1668 Procès-Verbaux. T3 (1667–1668, Registre de mathématique) / Académie royale des sciences, p. 23 r ff, p. 25 v
  12. ↑ Meeting of May 30, 1668 Procès-Verbaux. T3 (1667–1668, Registre de mathématique) / Académie royale des sciences, p. 30 r
  13. ^ Rudolf Wolf: History of Astronomy. P. 613
  14. ↑ Picard described it in detail in Mesure de la Terre.
  15. ↑ According to Picard, Snellius used in his triangulation of 1615 between Alkmaar and Bergen-op-Zoom a baseline of only 1245 m, a large number of small triangles and instruments with simple sights, with which an exact result could not be achieved.
  16. ↑ Toise du Châtelet, introduced in 1688
  17. ^ Rudolf Wolf: History of Astronomy. P. 601
  18. ↑ The information in this section is taken from Picard's Voyage d'Uraniborg ...
  19. ↑ Jean Picard described the surveying work carried out in: Relation de plusieurs nivellements fait par ordre de sa Majesté par M. Picard . In: De laHire (ed.): Mesure de la Terre . Imprimerie royale, Paris, p. 284 ( full text in Google Book Search).
  20. ↑ Meeting of February 8, 1681 Procès-Verbaux. T9 (November 18, 1679-29 June 1683, Registre de mathématique) / Académie royale des sciences, p. 96 r ; on Gallica
  21. ↑ Carte de Cassini on Géoportail
  22. ^ Encyclopedia Britannica: Jean Picard
  23. ^ Encyclopedia Britannica: Barometric light
personal data
SURNAME Picard, Jean
ALTERNATIVE NAMES Abbé Picard
BRIEF DESCRIPTION French astronomer and geodesist
DATE OF BIRTH July 21, 1620
PLACE OF BIRTH La Flèche
DATE OF DEATH October 12, 1682
Place of death Paris