Barometer

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1899 chart showing pressure (hauteur barométrique) decreasing with altitude

An instrument to measure pressure and thus altitude.

Classically, a tube containing mercury and sealed at one end and submerged in a basin. The weight of the mercury presses against the weight of the atmosphere; thus, if pressure decreases, the mercury falls lower.[1]

While mercury barometers were considered more exact, aneroid barometers, using a metal compartment containing air, were in common use by aeronauts.[2]

The relationship between pressure and altitude, in constant temperature was explained Edme Mariotte and formalized Edmond Halley in the 17th century.[3] Laplace also developed equations along these lines. (Different how? Maybe to do with barometer readings.)[4]

The equations were verified by experiments on mountains and then on balloons. Jacques Charles took a barometer with him on his ascent of 1 December 1783 (the first voyage in a gas balloon). Bénédict de Saussure, recognizing the scientific importance of ballooning, traveled to Lyons, where he met Joseph Montgolfier and Pilâtre de Rozier and traveled in a balloon.[5]

A photographic recording instrument designed by Louis Paul Cailletet generated especially copious data.[4]

Links

References

  1. "Barometer", London Encyclopedia Vol. 3 (1829), p. 563.
  2. Boutineaux, 1899, p. 43.
  3. Banet-Rivet, 1898, L'Aéronautique, p. 18. "Mariotte a, le premier, démontre que si l'on suppose la température constante suivant une verticale, les pressions décroissent, suivant cette verticale, en progression géometrique, lorsque les hauterus auxquelles elles correspondent croissent en progression arithmétique. Halley, traduisant algébriquement cette loi, connue sous le nom de loi du nivellement, a donné une formule approchée permettant de calculer l'altitude en fonction de la pression atmosphérique et, réciproquement, la pression atmosphérique en fonction de l'altitude."
  4. 4.0 4.1 Boutineaux, 1899, p. 46.
  5. Hildebrandt, 1908, Airships Past and Present, pp. 238–239. See also w:fr:Horace-Bénédict de Saussure.
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Short Brothers barometer with feature for recording maximum height.