Which means nautical mile?
Nautical mile is a unit approximately equal to two miles, or rather, 1852 meters. In the "Big Soviet encyclopedia it is mentioned that this value was approved in 1929 at the International hydrographic conference. It is true in the CIS and a number of other States, although not included in the list of international system of units.
Where did such a value? It is known that the distance of 1853 meters is the approximate length of one minute of latitude, that is, 1/60 of an arc of Meridian. It should be noted that the length of the Meridian corresponds only to the middle latitudes of the globe. We would add that the nautical mile has a capacity of 10 cables.
A little different the value of nm in the UK, where until 1929, it was assumed that mi is equal to 1853 meters. This was due to the convenience translation in the usual mile in the sea. In this case it was enough to add to the land mile, the number of 800, to obtain the nautical mile in feet.
What does a nautical knot?
Knot displays a certain speed of the vessel. The ship, which took place one nautical mile per hour – made one knot. The number of miles that held the ship in one hour equals the number of nodes. Not to speak of the speed of the vessel, as the number of nodes per hour. If you specify that a ship making twelve knots, it is understood that the same number of miles he will travel in sixty minutes.
Why knot got its name? It turns out the concept connected with the sea instrument, which previously measured the speed of the ship – lag. Lag was a cargo on a long rope, which was thrown overboard. Rope pre-tied knots in increments of 50 feet. Then the captain or his assistant counted the number of knots in the rope, which will be submerged for some time. Their number and match the speed of the vessel.
Now the speed of the vessel measured in knots rarely, only in Britain it is accepted to speak about nautical miles per hour. In most countries, the speed of sea transport is measured in kilometers per hour.