Johan Maurits Mohr

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Johan Maurits Mohr (* around August 18, 1716 in Eppingen ; † October 25, 1775 in Jakarta ) was a German-Dutch clergyman and astronomer in Batavia .

The Portuguese Buitenkerk in Batavia

Life

Mohr studied theology (free of charge) at the University of Groningen from August 1733 , which he concluded with a public disputation on the role of visions in the Bible in 1736. In 1737 he went to Batavia, which was then Dutch, where he worked from October 1737 initially as a vicar and from 1739 as a preacher for the Portuguese community on behalf of the Dutch East India Company. In 1743 he became rector of the theological seminary in Batavia. His passion was astronomical and scientific (meteorology, volcanology, geomagnetic field) observations, which he published in the Philosophical Transactions of the Royal Society and the negotiations of the Hollandsche Maatschappij der Wetenschappen .

As a theologian, he published a translation of the Bible into Portuguese and Malay.

Passage of Venus in 1761 and 1769

Mohr's Observatory in Batavia, J. Clement 1768

In 1761 he observed the transit of Venus in Batavia, albeit with insufficient instruments. In 1765 he built his own observatory at his own (very high) expense (the funds came from his wife's inheritance), with which he was one of the worldwide observers of the transit of Venus on June 3, 1769 (and also of the passage of Mercury on November 10 ). The worldwide observation of this phenomenon was one of the high points of astronomical life in the 18th century and was used to measure the solar system. James Cook , who had observed the passage in Tahiti, stopped at Batavia on the way back to England. Through his intermediation, Mohr's observations were also published (in Latin) in the Philosophical Transactions of the Royal Society in 1771. Mohr also published it (in Dutch) in the negotiations of the Hollandsche Maatschappij der Wetenschappen in 1770 in Haarlem. Cook lost many of his crew, including his astronomer Charles Green, to malaria during his stay in Batavia - Batavia was notorious for this epidemic among seafarers at the time, there was a lot of stagnant water in canals. In addition to Cook, Louis Antoine de Bougainville also visited him in 1768 on his world tour and reported on the Mohr observatory.

Comparison of the simultaneously observed Venus positions during the transit of 1769, for a southern observer in Tahiti and a northern observer in Vardø (Norway).

Mohr's observation of the passage of Venus in 1769 almost failed because the passage of Venus began four hours before sunrise and the sun was covered by clouds for the first two hours of the day (observations were only possible from 8 a.m.). Mohr had prepared himself carefully and had precisely determined the geographic coordinates of Batavia over the past few years. He had much better instruments than in 1761: a Gregorian reflecting telescope with a focal length of 3.5 inches (made by John Dollond ) as well as a heliometer for observing the sun, an astronomical pendulum clock by John Shelton (with anchor gear according to George Graham ) and a quadrant of 2.5  feet (Manufacturer John Bird, London) for correcting the astronomical clock.

While Mohr's observations of 1761 (which he also published in Dutch) were useless, those of 1769 were correct, but apparently they were not considered accurate enough, so that they were not taken into account in Johann Franz Encke's report on the passage of Venus, for example . In particular, his determination of the length of Batavia was not thought to be accurate enough, although Cook praised it.

The time after

Mohr continued his astronomical observations after 1769 and recorded daily observations of the weather and geomagnetic field, which he did not publish. His last publication from 1773 deals with the eruption of the 3000 m high Gunung Papadajan volcano (165 km southeast of Batavia) in August 1772.

After his death there was no successor for his observations in Batavia and his observatory fell apart. In 1780 it was badly damaged by an earthquake. Mohr's widow Anna Elizabeth van t'Hoff died in 1782 and the building was used to accommodate employees of the East India Company and from 1809 as a barracks. It was subsequently torn down (in 1844 only the foundations were visible).

The future Admiral Francis Beaufort visited the observatory at the age of 15 in August 1789, which made a very strange impression on him. There was only one observation room at the top of the building at 100 feet. If you stamped your foot in the rest of the house, it shook the instruments in the observatory.

A boom in scientific life in Batavia only followed after Mohr's death in 1778 when the Royal Batavian Society of Arts and Sciences was founded . The founding was initiated by Mohr, but initially did not materialize due to a lack of support from official bodies. The members initially wanted to continue Mohr's observations and one of the most active members of the society, the clergyman Johannes Hooijman, bought the instruments from Mohr's widow in 1776. But it turned out that they had suffered badly from the tropical climate - the efforts to make astronomical observations soon came to nothing in Batavia. Since there were no instrument makers in Batavia, the instruments were sent to Amsterdam for repair. There they were forgotten for a while, but some of them were used again and the tracks of some instruments could later be followed in various Dutch museums.

Others

The minor planet 5084 Johanmohr is named after him.

literature

  • HJ Zuidervaart, RH van Gent: A Bare Outpost of Learned European Culture on the Edge of the Jungles of Java: Johan Maurits Mohr (1716–1775) and the Emergence of Instrumental and Institutional Science in Dutch Colonial Indonesia . In: Isis , Vol. 95, 2004, pp. 1-33, PMID 15301065
  • Robert H. van Gent: Observations of the 1761 and 1769 transits of Venus from Batavia (Dutch East Indies) . In: DW Kurtz: Transits of Venus , Proc. International Astronomical Union (IAU Colloquium 196), Cambridge University Press, 2005, p. 67
  • J. van der Bilt: Venus tegen de Zonneschijf 1761, 1769; een bladzijde uit de geschiedenis the nederlandsche starology . Wolters, Groningen 1940
  • HJ Zuidervaart: Van "Konstgenoten" en Hemelse Fenomenen: Nederlandse sterrenkunde in de Achttiende eeuw . Erasmus Publishing, Rotterdam 1999

Web links

Individual evidence

  1. ↑ First he was to become pastor in the Portuguese parish in the Dutch branch in Galle on Ceylon; But that was postponed because he wanted to learn Portuguese first - after his marriage to Johanna Cornelia van der Sluys he stayed entirely in Batavia.
  2. ↑ K. van Berkel: In het voetspoor van Stevin. Geschiedenis van de natuurwetenschap in Nederland 1580-1940 . Boom, Amsterdam 1985, p. 211 ff.
  3. ^ Mohr: Transitus Veneris et Mercurii in eorum exitu e disco solis, 4to mensis juniii et 10to novembris 1769 observatus . In: Phil. Trans. Roy. Soc. , Volume 61, 1771, gallica.bnf.fr
  4. ↑ So did the astronomer Van der Bilt in his book 1940
  5. ^ Robert H. van Gent in Kurtz: Transits of Venus , discussion, p. 73
personal data
SURNAME Mohr, Johan Maurits
BRIEF DESCRIPTION German-Dutch astronomer
DATE OF BIRTH August 18, 1716
PLACE OF BIRTH Eppingen
DATE OF DEATH October 25, 1775
Place of death Jakarta