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nœud [French]

A unit of speed used by ships and aircraft, = 1 mille marin per hour. The mille marin being 1852 meters, a noeud is a speed of 0.5144 meters per second. Symbol, nd, or kn (from the English “knot”).

Formerly a ship's speed was measured by counting equally-spaced knots on a rope pulled out from the stern of the ship. For how knots were actually measured on shipboard in 1795, see this description.

source

Chacun des nœuds du loch parcouru dans les 30 secondes du sablier ou dans la 1/120 partie d'une heure correspond à une marche d'un mille marin par heure. Ainsi 9 nœuds filés en 30 secondes indiquent une marche de 9 milles ou de 3 lieues marines par heure.

Each knot of the log-line run out in the 30 seconds of the sand-glass, or in 120th part of an hour, corresponds to the speed of one mille marin per hour. Thus, 9 knots run out in 30 seconds indicate a speed of 9 milles marines or 3 lieues marines per hour.

Édouard Hospitalier.
Formulaire Pratique de l'Electricien.
Paris: G. Masson, 1883.
Page 32.