The Paris inch or pouce is an archaic

unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatrical presentation Music * ''Unit'' (alb ...

length Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Interna ...

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 unique

prime symbol The prime symbol , double prime symbol , triple prime symbol , and quadruple prime symbol are used to designate units and for other purposes in mathematics, science, linguistics and music. Although the characters differ little in appearance fr ...

( ′ ), 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 en, Viennese , iso_code = AT-9 , registration_plate = W , postal_code_type = Postal code , postal_code = , timezone = CET , utc_offset = +1 , timezone_DST ...

, 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 Great refractor refers to a large telescope with a lens, usually the largest refractor at an observatory with an equatorial mount. The preeminence and success of this style in observational astronomy defines an era in modern telescopy in the 19t ...

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 also invented the spectroscope and developed diffract ...

, 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 Sears, Roebuck and Co. ( ), commonly known as Sears, is an American chain of department stores founded in 1892 by Richard Warren Sears and Alvah Curtis Roebuck and reincorporated in 1906 by Richard Sears and Julius Rosenwald, with what began a ...

catalog of having 25 ''lignes'' diameter aperture, or about 80 mm (8 cm). Description observatoire de bordeaux

References

{{reflist Optics Units of length

See also

References