Steven Davis asked in USMA 18440: >It's just that, from time to time, Bill (or Barbara) I hear the lame >excuse from imperial types that the whole metric system is based on a >measurement 'proved' to be inaccurate!! > >I know myself that this is obviously reactionary rubbish, but I like to be >armed with as many facts as possible to counter these ludicrous claims; >and what better way to do that than to ask those in the know from time to >time??
So what? Since 1799 the metre has not been defined as 1/10 000 000 of the distance from the north pole to the equator although that was what the metre was intended to be. A degree of latitude is longer at the poles than at the equator. The equator is longer than 40 000 km. And locally the length of a degree depends on the bearing as well as the latitude. All this was perfectly understood by the definers of the metric system in 1799, and that is why the terrestrial quadrant was abandoned as the standard.. However for practical purposes a kilometre is near enough to 0,009� on the surface of the earth. This history is not mentioned in the present definitve document, "The International System of Units". There were no serious mistakes in the original survey. M�chain, one of the surveyors of the arc from Dunkerque to Barcelona, worried himself to death because of an error of three seconds of angle. The distance measured by modern methods in 1980 was 10 metres longer than that determined by M�chain and Delambre, which was more than 1000 km. Interestingly, the estimate made in 1795 was closer to the present value than the result of M�chain and Delambre. Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 TEL. 416-486-6071
