In his own words in his Personal Narrative of Travels…. Humboldt carried "Two barometers by Ramsden." (Alexander von Humboldt. Personal narrative of travels to the equinoctial regions of the New continent, during the years 1799-1804, by A. von Humboldt and A. Bonpland. translated from the French by Helen Maria Williams, 1814, p 35.) Mercurial barometers are delicate instruments and easily broken as jostling the instrument can cause the mercury to slam the closed end of the glass tube and shatter it (recall there is no air above the mercury to cushion or impede its movement). Thus, when moving a barometer one first carefully tilts it until the mercury moves to the top of the tube, then carefully inverts it completely. The mercury reservoir is then adjusted to remove all air and the barometer is carried upside down until used again, when it is carefully rotated to an upright position the mercury reservoir slowly adjusted back to its normal operating volume (the PRINCO manual linked below give a detailed proceedure for the modern instrument on display). Note that Humboldt’s barometer data appear in the “pression” column (column #10 from the left) of the Chimborazo diagram.
Selected on-line examples of early 18th and 19th-century barometers that may be similar to Humboldt's include:
Two later examples of mountain barometers are also listed to show some of the features that would have been included, such as broarder scales, in Humboldt's barometer. The enclosing tripod was a later feature.
Barometers are traditionally used to determine barometric pressure for weather prediction and, in the case of the instrument on display, to correct gas experiments to local barometric pressure. Barometers can also be used to determine altitude since atmospheric pressure drops with increasing altitude in a known way. Humboldt used his barometer constantly to determine location and local conditions. It was one of his iconic instruments, included in two of the important paintings documenting his expedition as seen in this display. The catalog scan is from: Fisher Scientific Company, Modern Laboratory Appliances, Catalog 59, New York (1958).
The barometer is described in detail in the catalog description from Fisher Scientific. The hardwood mounting board on our example is made from mahogany. A pdf copy of the PRINCO manual for this instrument is available.
© R. Paselk
Last modified 23 September 2013