What unit of measurement was originally defined as “one ten-millionth of the distance from the Equator to the North Pole along Paris Meridian” but is now the “distance travelled by light in free space in 1299,792,458 of a second”?
Paris meridian extrapolated from this measurement the distance from the North Pole to the Equator which was 5 130 740 toises. As the metre had to be equal to one ten-million of this distance, it was defined as 0,513074 toises or 443,2936 lignes of the Toise of Peru (see below). In the early 19th century, the Paris meridian's arc was recalculated with greater precision between Shetland and the Balearic Islands by the astronomer François Arago, whose name now appears on the plaques or medallions tracing the route of the meridian through Paris (see below). Biot and Arago published their work as a
History of the metre favored the "seconds pendulum" (a pendulum with a half-period of one second), but this was rejected when it was discovered that it varied from place to place with local gravity. A new unit of length, the "metre" was introduced - defined as one ten-millionth of the distance from the North Pole to the equator. For practical purposes however, the standard metre was made available in the form of a platinum bar held in Paris. This in turn was replaced in 1889 by thirty platinum-iridium bars kept across the globe. However, using such physical objects as the standard had been something