Paris inch

1 paris inch =
SI units
27.069×10^−3 m 27.0690 mm
US customary units (Imperial units)
88.809×10^−3 ft 1.06571 in

"The Paris inch is commonly employed as the unit by which to express the focal length of lenses, and it cannot, therefore, be dispensed with"

—The Ophthalmoscope (1864) [1]

The Paris inch or pouce is an archaic unit of length that, among other uses, was common for giving the measurement of lenses. [1] The Paris inch could be subdivided into 12 Paris lines (ligne), and 12 Paris inches made a Paris foot.[1] The Paris foot, Paris inch and Paris line could be abbreviated with the prime symbol ( ′ ), double prime symbol ( ″ ), and triple prime symbol ( ‴ ) respectively, like some other inch and foot units.[1] The Paris inch is longer than the English inch and the Vienna inch, although the Vienna inch was subdivided with a decimal, not 12 lines.[1][2][3]

A famous measurement made using the Paris inch is the lens measurement of the first great refractor telescope, the Dorpat Great Refractor, also known as the Fraunhofer 9-inch. The 9-Paris inch diameter lens was made by Joseph von Fraunhofer, which works out to about 24 centimetres (9.4 in) (English inches) aperture achromatic lens (the largest of its day).[4][5]

References

  1. 1 2 3 4 5 Zander, Adolf (1864). Google Books The Ophthalmoscope Check |url= value (help).
  2. ↑ warre.biobees.com/christ.pdf, Notes by David Heaf on Anweisung zur nützlichen and angenehmen Bienenzucht für alle Gegenden by Pfarrer Johann Ludwig Christ (1739-1813) Rodheim, Hessen, Germany
  3. ↑ http://web.archive.org/web/20070621175054/http://www.btinternet.com/~matthewbrown/h-m.htm[]
  4. ↑ adsabs link Fraunhofer and the Great Dorpat Refractor, Waaland, J. Robert, American Journal of Physics, Volume 35, Issue 4, pp. 344-350 (1967)
  5. ↑ http://www.obs.ee/obs/instrumendid/fr.htm

See also

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