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BID : 2057_KF5JRV
Read: GUEST
Subj: MŠtre des Archives
Path: IW8PGT<CX2SA<N0KFQ<KF5JRV
Sent: 160916/1215Z 2057@KF5JRV.#NWAR.AR.USA.NA BPQ1.4.65
MŠtre des Archives
While M‚chain and Delambre were completing their survey, the commission
had ordered a series of platinum bars to be made based on the provisional
metre. When the final result was known, the bar whose length was closest
to the meridional definition of the metre was selected and placed
in the National Archives on 22 June 1799 (4 messidor An VII in the
Republican calendar) as a permanent record of the result. This standard
metre bar became known as the mŠtre des Archives.
The metric system, that is the system of units based on the metre, was
officially adopted in France on 10 December 1799 (19 frimaire An VIII)
and became the sole legal system of weights and measures from 1801.
After the restoration of the Empire, in 1812, the old names for units
of length were revived but the units redefined in terms of the metre:
this system was known as mesures usuelles, and lasted until 1840, when
the decimal metric system was again made the sole legal measure. In the
meantime, the Netherlands had adopted the metric system from 1816, the
first of several countries to follow the French lead.
It soon became apparent that M‚chain and Delambre's result (443.296 lignes)
was slightly too short for the meridional definition of the metre. Arago
and Biot extended the survey to the island of Formentera in the western
Mediterranean Sea in 1806-1809, and found that one ten-millionth of the
Earth's quadrant should be 443.31 lignes: later work increased the value
to 443.39 lignes. The modern value, for the WGS 84 reference spheroid,
is 1.000?196?57 m or 443.383?08 lignes.
Nevertheless, the mŠtre des Archives remained the legal and practical
standard for the metre in France, even once it was known that it did
not exactly correspond to the meridional definition. When it was decided
(in 1867) to create a new international standard metre, the length
was taken to be that of the mŠtre des Archives "in the state in which
it shall be found".
The only significant international use of the meridional definition of
the metre, apart from M‚chain and Delambre's original survey, was the
initial work conducted by the British Association for the Advancement
of Science (B.A.) on electrical units which was to lead to the
International System of Electrical and Magnetic Units. It was often
claimed that the international electrical units formed a coherent set
of absolute units in the quadrant-eleventh-gram-second system
(aka "QES system" or "Q.E.S. system"), where the unit length was
the quadrant of the Earth's polar circumference, the unit mass was
the "eleventh-gram" or 10?11 grams and the unit time was the second.
Nevertheless, the precision of absolute electrical measurements in
the late nineteenth century was not such that the 0.02% difference
in the definitions of the metre had any practical significance.
73, Scott kf5jrv
KF5JRV @ KF5JRV.#NWAR.AR.USA.NA
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