The Paris inch or pouce is an archaic unit of

length Length is a measure of distance. In the International System of Quantities, length is a quantity with Dimension (physical quantity), dimension distance. In most systems of measurement a Base unit (measurement), base unit for length is chosen, ...

that, among other uses, was common for giving the measurement of lenses. The Paris inch could be subdivided into 12 Paris lines (''ligne''), and 12 Paris inches made a Paris foot. The abbreviations are the same as for other inch and foot units, i.e.: for Paris foot a single prime symbol ( ′ ), for Paris inch a double prime symbol ( ″ ) and for Paris line a triple prime symbol ( ‴ ), 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. 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 Joseph Ritter von Fraunhofer (; ; 6 March 1787 – 7 June 1826) was a German physicist and optical lens manufacturer. He made optical glass, an achromatic telescope, and objective lenses. He developed diffraction grating and also invented the ...

, 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. The term for telescopes persisted even in the 20th century, with a telescope listed in the 1909 Sears Roebuck catalog of having 25 ''lignes'' diameter aperture, or about 56 mm (5.6 cm). The measurement SPI (Stitches per inch) for leather

pricking iron In leathercraft, a pricking iron is a handheld tool resembling a fork that is used to create dimples in leather a fixed distance apart that can then be pierced with an awl and stitched. A pricking iron is different from a leather chisel in that ...

s and stitch marking wheels also commonly uses the Paris inch instead of the Imperial inch. Description observatoire de bordeaux

References

{{reflist Optics Units of length

See also

References