Hello to all, and thank you very much Enrico, a very nice and comprehensive document.
There is a book on the market (2005) "The Measure of all Things" by Ken Alder, Free Press New York, translated version in german (2006) "Das Mass der Welt". It tells on about 500 pages quite precise and very detailed (based on a lot of original french and other documents) the long history and big work principally of J.- B.-J. Delambre, P.- F.-A. Méchain and J.-J. Lalande fighting for the definition and introduction of the meter in the 18. century. Worth to be read I believe. I like all the discussions on this Time-Nuts platform. Concerning the relation between inch and meter I thought that the definition is fixed long time ago. When the meter was defined to be multiples of the wavelength of light in vacuum, in 1959, the relationship between inches and centimeters was redefined to be that one inch is equal to 2.540 centimeters, exactly. The new foot, derived from 1 inch = 2.54 cm (exactly), is referred to as the "international foot". There are a lot of informations about to find in the internet, but to be on the safe side I had a look on the NIST homepage: http://emtoolbox.nist.gov/Faq/Faq.asp#FAQ-Miscellaneous-6 (") Quote: What is the definition of the meter and the inch? The inch has always been tied to the meter in the U.S. After the Civil War, the Surveyor General of the U.S. set the inch as 39.37 inches to the meter. The British had a yard bar, the Canadians had 25.4 mm per inch, and the other English speaking nations had chosen one of these or some variation. They were all close, but not exactly the same. The yard bar was in fact shrinking. In 1959, a conference attended by the directors of the National Measurement Institutes from all of the English speaking countries, those who still used inches, met to standardize the inch. The 25.4 mm per inch (exactly) was chosen, and since then this is the inch used by NIST (formerly NBS). Except . . . Yes, there is always an exception. Surveyors still use the old inch because all of the mountains of measurements in place defining the positions of everything in the US are in these inches, and the job of changing them was considered too large a task. So surveyors still use the surveyor inch, 39.37 inches per meter. (") End of quote. and : http://physics.nist.gov/cuu/Units/meter.html (") Quote: ...in 1983 the CGPM replaced this latter definition by the following definition: The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. Note that the effect of this definition is to fix the speed of light in vacuum at exactly 299 792 458 m·s-1. The original international prototype of the meter, which was sanctioned by the 1st CGPM in 1889, is still kept at the BIPM under the conditions specified in 1889. (") End of quote. As well: Eric Weisstein's World of Physics http://scienceworld.wolfram.com/physics/Inch.html An nonmetric unit of length, originally defined as the lengths of three "average size" barleycorns laid end-to-end, but now more rationally defined as 2.54 cm. An older definition no longer used was 1 meter = 39.37 inches, giving 2.54000508 cm/inch. Surprisingly, these two conversions are both exact. For details on the current definition of the inch, see A Tale of Two Feet OR The Case of The Double Standard - T. J. Keefe http://physics.ccri.cc.ri.us/keefe/twofeet.htm Finally, the conversion is finally in a concrete form, as long the speed of light in vacuum does not turn out to be not constant ;-) keep watching the time and units, regards Arnold, DK2WT On Tue, 3 Apr 2007 11:37:16 +0200, Enrico Rubiola wrote: >Dear all, >I have read some weird discussion about measurement units. >There is a wonderful book I come across, by Francois Caldarelli >You may take a look >http://rubiola.org/shared/caldarelli.pdf >then it's up to you.... >Best >Enrico Rubiola >professor of electronics >web: http://rubiola.org >e-mail: [EMAIL PROTECTED] >FEMTO-ST Institute >32 av. de l'Observatoire >25044 Besancon, FRANCE >voice: +33(0)381.853940 (E.Rubiola) >voice: +33(0)381.853999 (switchboard) >fax: +33(0)381.853998 >_______________________________________________ >time-nuts mailing list >time-nuts@febo.com >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
