:: As a conclusion ::
The adventure of the metre...

One can wonder what is the actual worth of the works that led to the determination of our units of length and mass.

Here is the opinion of the contemporary people of that time, according to Tarbé (1813):

"They took the value of each angle, without caring about neither the other angles nor the sum of the three angles of a triangle […] Observations were taken as they were, without correcting them, without putting right anything afterwards. Yet, out of the 115 triangles which join the meridian ends together, there are 36 for which the error made when calculating the three angles altogether is nearly one second. There are triangles in which the error - for which it is the most important - is nearly 5 seconds, that is to say one 720th of degree for the three angles.

"Two bases were measured, one between Melun and Lieusaint, the other between Vernet and Salces, near Perpignan. […] Measuring them led to […] the two following measures, at sea level and at the temperature of 16 degrees and one quarter on the centigrade thermometre: base of Melun, 6,075.90 toises; base of Perpignan, 6,006.25. One indisputable evidence of the operations accuracy is that the base of Perpignan, deduced from the base of Melun thanks to the chain of triangles that link the first to the latter, differs from its actual measure from only 10 to 11 inches, although these bases are 700,000 metre apart."

And here are the results from modern verifications:

From 1870 to 1896, step by step, the Armed Force Geography Service realized a new French meridian measurement, with methods and instruments that had made great progress in comparison to the methods and instruments that Delambre and Méchain had. The results of these modern operations coincided outstandingly with the 1799 results: the Mètre des Archives is nearly 0.2 mm shorter than the ten-millionth part of the earth quadrant to which its definition depended.

On the other hand, in its original definitions, the kilogramme had the weight of one cubic decimetre of water at 4 degrees centigrade. Several checkings made between 1895 and 1905 by the IBWM have shown that the International Kilogramme exceeds the mass that results from this definition by 28 milligrammes.

These differences are so slight - 2 ten-thousandth and 28 millionth - that they show the 1792-1799 operations were led with the utmost accuracy.

Moreover, whether it is about the 1889 standards or the meter's definitions of 1960 and the following years, every new definition was chosen within the limits of uncertainty of the previous definition.

Therefore, the present metre and kilogramme are really close to their "natural" definition of 1793.

History to be continued !

October 28, 2010. Kilogram to be overhauled? (on Gizmag)