Person: Méchain, Pierre
Pierre Méchain undertook surveys to produce maps and also worked in astronomy where he is particularly famed as a discoverer of comets.
Mathematical Profile (Excerpt):
- Pierre-François, a plasterer who specialised in plastering ceilings, was a man of modest means.
- Pierre was born in Loan, a medieval town in the Picardy region of northern France.
- It was in Loan that Pierre was educated by the Jesuits and as a young boy his aim was to become an architect, although his main hobby was astronomy.
- His tutoring position put Méchain on a firmer financial footing and he was able to save enough to buy some good quality astronomical instruments so that he could pursue his hobby.
- This romantic story may not be true for Delambre, who knew Méchain very well over a period of ten years, stated in his biography of Méchain, written many years after his death, that there was no evidence to support the story.
- Whether the story is true or not, what is undoubtedly the case is that Méchain made contact with Lalande who sent him proofs of the second edition of his Traité d'astronomie Ⓣ(Treatise on astronomy).
- Méchain's assistance with the proofs soon impressed Lalande, as did his enthusiasm and abilities, so, seeing the benefits of having him enter his profession, he arranged a position for him in the cartography department in the Depôt de la Marine in Versailles in 1772.
- The position was not well paid and, certainly at first, Méchain had to tutor mathematics to make enough money to live on.
- Méchain went to Paris in the permanent position of calculator in the Depôt de la Marine, living there from around 1774.
- For the next ten years from 1780 to 1790 Méchain undertook surveys to produce maps and also worked in astronomy where he is particularly famed as a discoverer of comets.
- The Government appointed Méchain as a commissioner, along with Legendre and Dominique Cassini, to triangulate the French side.
- Initially Méchain used older surveying equipment to check Dominique Cassini's measurements with the repeating circle, but later in the project he took over measurements with the repeating circle.
- Méchain's work on comets became of major importance in 1781 when he discovered two comets in the same year.
- Méchain's memoir on these comets was presented to the Academy for the Grand Prix of 1782 and in it he showed, unexpectedly, that they were not two appearances of the same comet but indeed different comets.
- In 1785 Méchain was asked if he would take over the editorship of the astronomical almanac Connaissance des temps.
- Delambre was given charge of the Dunkerque to Rodez sector and Méchain the Rodez to Barcelona sector much of which had not been previously surveyed.
- Méchain left Paris on 28 June 1792 and travelled to Barcelona to begin his survey.
- Méchain was fanatical about accuracy and, as we shall soon see, these measurements would cause him anguish for the rest of his life.
- When war broke out between France and Spain in March 1793, Méchain had to leave Mont-Jouy which was required for military purposes.
- By March of 1794 Méchain had discovered that the latitude measurements he had taken from the inn did not agree with those from Mont-Jouy, yet he could not return to the castle to take further measurements.
- However in April 1795 the project was restarted and Méchain was told to return to Paris.
- Although Delambre sent him all the data that he was collecting, Méchain refused to let anyone see his data.
- The agony that Méchain suffered was because he had extremely high standards and he believed that the Borda repeating circle could attain essentially any desired accuracy.
- In January 1798 the Académie des Sciences set up an international conference to take place in September of that year to give an international standing to the new value of the metre which the Delambre-Méchain survey had still to finalise.
- She returned to Paris unable to convince Méchain to complete his task.
- Delambre went to help Méchain who by this time had suffered a nervous breakdown.
- It may have been the promise that he would be made director of the Paris observatory which tempted Méchain back to Paris.
- Méchain left Paris on 26 April 1803 for Spain.
- However, when he worked on Méchain's data for his Base du système métrique he discovered that Méchain had changed his readings to make them appear more precise than they were.
- We explained above how a lack of understanding of the theory of errors in Méchain's time led him to down this path since he blamed himself for the discrepancies.
- Delambre did not want confidence in the metric system destroyed and a public announcement that Méchain had altered his data might well have had this result.
- He was too honest a scientist to pretend discrepancies were not there, so he treated Méchain's results as important scientific discoveries rather than as errors.
- The more sensitive personal letters and the evidence that Méchain had fiddled the results and lied to his colleagues were sealed in the archives of the Paris observatory.
Born 16 August 1744, Laon, France. Died 20 September 1804, Castellón de la Plana, Spain.
View full biography at MacTutor
Tags relevant for this person:
Astronomy, Geography, Physics
Thank you to the contributors under CC BY-SA 4.0! 
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- non-Github:
- @J-J-O'Connor
- @E-F-Robertson
References
Adapted from other CC BY-SA 4.0 Sources:
- O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive
