Pierre Bouguer

Pierre Bouguer ( born February 16, 1698 Le Breton croisic; † August 15, 1758 in Paris) was a French astronomer, surveyor and physicist. He became internationally known mainly as a participant in the Peru expedition, which carried out the Paris Academy for the accurate determination of the earth's shape.

The important geophysical Bouguer gravity anomalies in the 19th century named - After Bouguereau were - because of his investigations into the earth's gravitational field. He was also Professor of Nautical Science in Le Havre.

Life and scientific work

Bouguer studied at the Jesuit college in Vannes, the capital of the department of Morbihan in Brittany, and later at the University of Paris. His astronomical research dealt with the photometry of the sun and moon; for accurate angle measurements in astrometry, he developed the Heliometer.

In geodesy and geophysics, he is primarily known for the eponymous gravity anomalies, by first-time investigations of the deflection of the vertical as well as the vertical gradient and the large degree of measurement long arc of the meridian in South America. The latter took place from 1735 to 1741 in the former Viceroyalty of New Granada on the initiative of the Paris Academy ( Académie des sciences ) instead. You had with the 1736 Pierre -Louis Moreau de Maupertuis, Alexis Claude Clairaut, Anders Celsius, and other actual expedition to Swedish Lapland, the aim of clarifying the question of whether the pole radius of the earth is greater than the equatorial radius, as some older and contemporary measurements, inter alia, revealed by Jean -Dominique Cassini, or vice versa, as would be expected from Newton's theory; these measurements should also be important for the subsequent definition of the meter. Bouguers colleagues were Louis Godin ( expedition leader ) and Charles Marie de La Condamine. However, between the three scientists has resulted in significant tensions that eventually led to the splitting of the expedition crews. The degree of measurement along a profile extending from just north of Quito to just south of Cuenca revealed for the length of a degree of longitude at the equator of the earth 56753 toises ( 110.612 km ) and an equatorial radius of the Earth of 3,281,013 toises ( 6394.694 km ). With the Arctic measurements of Maupertuis, there was the Earth flattening with 1:179 ( modern value 1:298,25 ), but was improved a few years later by measurements of Cassini in France to 1:305.

Bouguer wrote several books on his research; his most famous work is La figure de la terre: déterminée par les observations de messieurs (Paris 1749). In the last part of the book, in which he deals with gravity measurements, he turns in the processing of data from the summit of Pichincha, Quito and the coast for the first time the two reductions of, now known as the open-air and as a Bouguer reduction are. La Condamine and Bouguer led an extended period in a bitter dispute over the results of the expedition, which came to an end only with death Bouguers.

With his book Traité du navire, sa de construction et de ses mouvemens ( 1746 ) put Bouguer next to Euler the foundations for the hydrostatic Basic Law, which had been founded Archimedes, but again lost. Bouguer also dealt with the navigation and control of ships. So he wrote a 1731 textbook Manière d' observer en mer la déclinaison de la boussole that handles the navigation by compass.

Through his research on light intensity Bouguer became the founder of photometry. He wrote an account of this research in the Essai d' optique, sur la gradation de la lumière (Paris 1729 ) and in more detail in the Traité d' optique sur la gradation de la lumière, published only after his death in 1760 by Lacaille. Bouguer invented 1748 the Heliometer.

In the field of geodesy, he wrote the work Traité de navigation ( Paris 1753), which by Lacaille in the second ( 1769) and by Lalande in the third edition (1792 ) has been substantially completed. About the deviation of Plumbbob under gravity by the attraction of the mountains as well as the height of the snow line, he presented the first observations ever at near the Chimborazo.