The earth quadrant is known to be wrong by about 2 km in 10000. I never heard of the seconds pendulum, or the brass meter. As brass standards have a relatively poor experience in both US and UK standards history, I would need to see proof before I accepted anything prior to the 1799 meter. Also, in the late 1700's, timekeeping was not up to modern atomic standards, and the length of the day is know to change slowly (that's why we have leap seconds); I would not count on their "seconds" being that good. I don't know that we have the knowledge to reproduce "their" second vs a modern second.
The 1799 platinum-iridium bar was sanctioned in 1889 following intercomparison with the various national meters to within 0.01 mm (which is pretty good measurement for 1889). See summary of 1st CGPM in The SI Brochure. Anything else is just hearsay. Note that the disagreement among standard copies of the meter (1889) is 1 in 100 000, only 20X better than the earth quadrant in 1790. The next 100 years made considerably more precision progress. ________________________________ From: Pat Naughtin <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Mon, October 18, 2010 3:16:24 PM Subject: [USMA:48673] The metre we use Dear All, From time to time I read the line (in various sources) that goes something like: The metre has never changed in length, only the definition has been rewritten to provide better accuracy and precision. This poses the question, "Which is the metre we use?" A brief chronology goes like this: 1790 May 8 The French National Assembly decides that the length of the metre will be equal to the length of a pendulum with a half-period of one second. 1791 March 30 Recognising that a universal standard of measurement was needed, the French National Assembly accepted the proposal by the French Academy of Sciences that the new definition for the metre be equal to one ten-millionth of the length of the Earth's meridian along a quadrant of the Earth, that is the distance from the equator to the north pole. To determine this length about one tenth of the Earth's circumference, from Dunkirk, in France, to Barcelona, in Spain, was meticulously measured. Due to lack of knowledge of the true shape of the Earth, this definition was never implemented. 1795 A provisional metre bar was constructed of brass. 1799 December 10 The French National Assembly specifies a platinum metre bar deposited in the National Archives, as the final standard of length for the whole world.A platinum rod was produced in Paris that was exactly one metre from end to end. This became the master standard for the whole world's measuring system. Known as the 'Mètre des Archives'it became the "universal measure" that is the basis for the metric system we now all use. From this it looks like the pendulum was never officially recognised and neither was the metre derived from this measurement of the Earth. Does this mean that the length of the 1795 brass bar is still the world standard for the length of a metre assuming that it is true all subsequent definitions of the metre have kept this same length (as the 1795 brass bar) while only the words of the definitions changed to achieve greater accuracy and precision. Am I misreading this history? Is the 1799 platinum bar the one that takes precedence? Cheers, Pat Naughtin Author of the ebook, Metrication Leaders Guide, see http://metricationmatters.com/MetricationLeadersGuideInfo.html Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com/ or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
