Paris inch
Paris inch | |
---|---|
Unit system | French |
Unit of | length |
Conversions | |
1 paris inch in ... | ... is equal to ... |
US units | 0.08881 ft 1.0657 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
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]
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 24.4 centimetres (9.59 English inches). This lens had the largest aperture of its day for an achromatic lens.[3][4]
The term for telescopes persisted even in the 20th century, with a telescope listed in the 1909
See also
- international inch
- Vienna inch
- Traditional French units of measurement
References
- ^ a b c d e Zander, Adolf (1864). The Ophthalmoscope.
- ^ 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
- ^ adsabs link Fraunhofer and the Great Dorpat Refractor, Waaland, J. Robert, American Journal of Physics, Volume 35, Issue 4, pp. 344-350 (1967)
- ^ "Fraunhoferi refraktor".
- ^ "What does "lignes" mean for aperture of antique telescope?". Sky & Telescope. 2006-07-24. Retrieved 2019-10-16.