Английский язык от И. Ерохина / тысячи / compass

Compass, in navigation, an instrument used to indicate directions. It ranks as one of the most important inventions ever made. The usual compass shows the cardinal points—north, east, south, and west—and a number of intermediate points. Most compasses are also graduated in the degrees of a circle, north being 0°; east, 90°; south, 180°; and west, 270°. Surveyors, however, reverse this arrangement and measure clockwise from the south, so that a bearing of 90° in a survey is west. The Magnetic CompassThe magnetic compass is the simplest form of compass. The ordinary pocket compass has a magnetized needle mounted on a pivot so that it swings freely above a dial. The needle comes to rest in line with the earth's magnetic field at the place where the compass is used. The lines of force of the earth's magnetic field run between the earth's magnetic poles, in a roughly north-south direction. However, a magnetic compass at a given location will not necessarily point to a magnetic pole because the lines of force follow an irregular path. In a large area surrounding each magnetic pole, the lines of force are perpendicular to the earth's surface and a magnetic compass is useless.A magnetic compass by itself is useful in determining the direction of one landmark relative to another. In general, true north (or south) can be computed from a compass reading only when the exact direction of the lines of force is known for the location at which the compass is being used. The angle between magnetic north (or south) and true north (or south) is called declination, or variation. The declinations over a given region are determined by magnetic surveys and are published on charts. These charts are regularly updated because the orientation of the lines of force of the earth's magnetic field at any given place slowly changes with time.An error in a compass reading caused by local magnetic fields, such as those produced by an airplane's electrical equipment or the magnetization of a ship's hull, is called deviation. Deviation can be corrected by installing magnetic devices to counteract the magnetic attraction of nearby objects.The Mariner's Compassconsists of a round card, called a compass card, with several parallel steel magnets attached to the underside, and a steel pivot at the center. The compass is mounted on a series of rings in such a way that the dial (compass card) remains horizontal, no matter how the ship may pitch and toss. The rings, called gimbals, and compass are placed in a box called a binnacle. On the binnacle, a vertical line called the lubber line marks the direction in which the ship's bow is pointed. The person who steers the ship keeps on course by aligning the lubber line with the compass card point that marks the heading the ship is to follow.The Induction Compassalso is called the earth inductor and magnetic-induction compass. It indicates magnetic north accurately when as close as 300 miles (480 km) to either of the earth's magnetic poles. The ordinary magnetic compass is useless within 1,200 miles (1,900 km) of either pole. The induction compass is operated by small electric currents set up in a coil of wire when it is moved through the earth's magnetic field. Currents from two coils of this kind are amplified and used to move the direction-pointing element of the compass. Nonmagnetic CompassesThe GyrocompassThis type of compass has been used on all ships since World War I and is used also on airplanes, torpedoes, and some guided missiles. On ships and aircraft the magnetic compass supplements the gyrocompass, one being used to check the other.The heart of a gyrocompass is a heavy gyroscope driven by an electric motor. It is not affected by magnetism or by the pitching of a ship. When properly mounted, adjusted, and corrected, it will always point to true north, rather than to magnetic north. Electric circuits relay information from the gyroscope to instruments called repeaters in various parts of the ship. These instruments can indicate direction or keep a constant record of the ship's movements. A gyropilot is a repeater and other equipment coupled with the steering mechanism that keeps the ship on course. Gyropilots are also used to steer torpedoes and some guided missiles. The gyrocompass must be constantly corrected as the vessel changes course, speed, and latitude. Instruments have been developed that make these corrections automatically.Other TypesThere are other means of finding true north, and some instruments for determining direction by astronomical and navigational methods are called compasses. Among these are the solar compass, which tells direction from the light of the sun, and the radio compass, or direction finder, which relies on radio signals. HistoryBefore the compass was invented, a captain's only guide to his position was his knowledge of winds, tides, landmarks, and the sun and stars. In open, unfamiliar waters he could only guess which way he was going. The Chinese are thought to have invented the compass as far back as the first century A.D. The original device consisted of a floating piece of magnetized iron in a bowl of water. The Arabs used the compass as early as the eighth century. It reached Europe in the 12th century.The ordinary magnetic compass was satisfactory for most kinds of navigation until magnetic deviation became a problem with the development of steel ships in the 19th century. This problem was finally overcome with the invention of the gyrocompass in 1906. Aerial navigation requires several different types of compasses that must be constantly checked one against the other. Special compasses have been developed for work near the North and South poles.