Stephen Davis asked in USMA 18353 >I'm sure this topic has been discussed before but I have heard it said a >few times that due to certain conditions, the original equation of the >measurement from France to the North pole (or was it the South pole) for >the metre was inaccurate!! > >I would be interested to know just how inaccurate!!
It may be that we don't know. In 1793 it was estimated that the distance from the north pole to the equator was 5 132 430 toises. Delambre et M�chain completed their survey from Dunkerque to Barcelona in 1797. It was very well done, but irregularities in the crust of the earth may have affected it. From their survey they deduced that the flattening of the earth from the equator to the pole was 1/150. That seemed unlikely, so the international commission in 1799 decided to combine Delambre and M�chain's results with a survey done in Peru between 1736 and 1740, That gave a flattening of the earth as 1/334 and a length of 5 130 740 toises for the quarter meridian. That meant that the provisional metre of 1793 was too long by 0.324 mm. On the basis of this result, prototype metres were made in platinum, and from then on there was no more discussion of the quarter meridian. It is interesting that now the provisional metre of 1793 is considered to be more exactly 1/10 000 000 of the quarter quadrant than the prototype metre of 1799. "Astronomy" by F.R.Moulton, Macmillan, 1931, gives the ellipticty of the earth as 1/297 and says that French geodisists in the first half of the 18th century measured an arc of 3� in Peru, 9� in middle Europe, and 1� in Lapland. "It follows from the accuracy with which individual measurements are made and from the agreement among the results of measurements on all continents that the uncertainty in the radius of the earth can not exceed 50 meters. That is, the uncertainty is only one part in 100,000." Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 TEL. 416-486-6071
