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Introduction

Ancient China gave the world several of the mathematical and scientific concepts we take for granted today, such as the compass. The magnetic compass was invented in China for use by Feng Shui practitioners, to “align” the forces of the earth to help them maintain balance in their lives for later to become an important navigational tool. It was adapted from the “south pointing spoon,” or Si Nan. Because of variations over time in the earth’s magnetic fields, three compass systems were superimposed over each other during the span of half a millennium to establish the compass that Feng Shui practitioners use today.

Compass is an instrument that indicates direction, used by mariners, aviators, campers, hunters, and other travellers to enable them to get from one place to another. It consists of a magnetized pointer free to align itself accurately with Earth's magnetic field, which is of great assistance in navigation. The face of the compass generally highlights the cardinal points of north, south, east and west. A compass can be used in conjunction with a marine chronometer to calculate longitude and a sextant to calculate latitude, providing a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient.

An early form of the compass was invented in China in the 11th century. The familiar mariner's compass was invented in Europe around 1300, from whence later originated the liquid magnetic compass. Often compasses are built as a stand-alone sealed instrument with a magnetized bar or needle turning freely upon a pivot, or floating in a fluid, thus able to point in a northerly and southerly direction.

In the magnetic compass, directions are obtained by means of one or more magnetic needles pointing in the general direction of the magnetic North Pole under the influence of the magnetic field of the earth.

Many enhancements have been developed. A compass dial is a small pocket compass with a sundial.

A variation compass is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. An Orienteering compass consists of a rugged zed needle compass permanently attached to a transparent base plate containing tools to assist the user in working with maps in a field setting.

A recent development is the electronic compass, which detects the magnetic directions without requiring moving parts. This device frequently appears as an optional subsystem built into Global Positioning Satellite Receivers (GPSRs).

There are other, more accurate, devices for determining north (known in such cases as true north, as opposed to magnetic north), which do not depend on the earth's magnetic field for operation. A gyrocompass (ships), developed at the beginning of the 20th century or astrocompass (aircraft) can be used to find true north, while being unaffected by stray magnetic fields, nearby electrical power circuits or nearby large masses of ferrous metals.

The gyrocompass, which is unaffected by the magnetism of the earth, consists of a gyroscope, with the spinning wheel on an axis confined to the horizontal plane so that its axle aligns itself with the north-south line parallel to the axis of the rotation of the earth, thereby indicating true north.

The history

The magnetic compass is an old Chinese invention, probably first made in China during the Qin dynasty (221-206 B.C.). Chinese fortune tellers used lodestones (a mineral composed of an iron oxide which aligns itself in a north-south direction) to construct their fortune telling boards.

Eventually someone noticed that the lodestones were better at pointing out real directions, leading to the first compasses. They designed the compass on a square slab which had markings for the cardinal points and the constellations.

The pointing needle was a lodestone spoon-shaped device and the plate is of bronze., with a handle that would always point south. Rather than navigation, these simple direction pointers were likely used for geomancy, the technique of aligning buildings according to forces of nature.

The original magnetic compass used for navigation was constructed in the seventh or eighth century with the needle floating in water.

The true north-south meridian was first set down by Chiu Yun Han (c. 713 - 741 A. D.) and known as the Cheng Chen. This was used until roughly 880, when readings were so far off the mark that immediate correction was required. In the eight or ninth century it was further refined with the discovery of magnetic declination. Yang Yun Sang added specialized compass points to compensate for the variation. The Feng Chen or “seam needle” fixed the Cheng Chen’s variations. The compass was again adjusted in the 1100s when Lai Wen-Chun came up with the Chung Chen (the central needle).

It has also been thought that the compass was invented by the Arabs (a theory supported by the fact that at that time they enjoyed unchallenged superiority in the scientific field and were highly skilled in the art of navigation), even though other scholars observe that the Arabs, Turks and Persians called the instrument "bossola", a word derived from Italian. This means that the object must have had foreign origins, as did the word used to describe it. Whatever its origins, what is certain is that the first documents concerning the use of compasses for navigation came from China in around 1100 a.D., from the Arab world in the thirteenth century, from Scandinavia in about 1250 and from Europe in around 1187.

Dry compass

The familiar dry compass was invented in Europe around 1300. The true mariner's compass consists of three elements: A freely pivoting needle on a pin enclosed in a little box with a glass cover and a wind rose, whereby "the wind rose or compass card is attached to a magnetized needle in such a manner that when placed on a pivot in a box fastened in line with the keel of the ship the card would turn as the ship changed direction, indicating always what course the ship was on". While pivoting needles in glass boxes had already been described by the French scholar Peter Peregrinus in 1269, there is an inclination to honour tradition and credit Flavio Gioja (fl. 1302), an Italian marine pilot from Amalfi, with perfecting the sailor's compass by suspending its needle over a compass card, giving thus the compass its familiar appearance. Such a compass with the needle attached to a rotating card is also described in a commentary on Dante's Divine Comedy from 1380, while an earlier source refers to a portable compass in a box (1318), supporting the notion that the dry compass was known in Europe by then.

Impact in the Mediterranean

In the Mediterranean, the introduction of the mariner's compass, at first only known as a magnetized pointer floating in a bowl of water, went hand in hand with improvements in dead reckoning methods, and the development of Portolan charts, leading to more navigation during winter months in the second half of the 13th century. While the practice from ancient times had been to curtail sea travel between October and April, due in part to the lack of dependable clear skies during the Mediterranean winter, the prolongation of the sailing season resulted in a gradual, but sustained increase in shipping movement: By around 1290 the sailing season could start in late January or February, and end in December. The additional few months were of considerable economic importance. For instance, it enabled Venetian convoys to make two round trips a year to the Levant, instead of one.

At the same time, traffic between the Mediterranean and northern Europe also increased, with first evidence of direct commercial voyages from the Mediterranean into the English Channel coming in the closing decades of the 13th century, and one factor may be that the compass made traversal of the Bay of Biscay safer and easier.

Although critics like Kreutz feels that it was later in 1410 that anyone really started steering by compass.

Mining

Modern compasses

Modern hand-held navigational compasses use a magnetized needle or dial inside a fluid-filled (oil, kerosene, or alcohol is common) capsule; the fluid causes the needle to stop quickly rather than oscillate back and forth around magnetic north. Most modern recreational and military compasses integrate a protractor with the compass, using a separate magnetized needle. In this design the rotating capsule containing the magnetized needle is fitted with orienting lines and an outlined orienting arrow, then mounted in a transparent baseplate containing a direction-of-travel (DOT) indicator for use in taking bearings directly from a map. Other features found on some modern handheld compasses are map and romer scales for measuring distances and plotting positions on maps, luminous markings or bezels for use at night or poor light, various sighting mechanisms (mirror, prism, etc.) for taking bearings of distant objects with greater precision, 'global' needles for use in differing hemispheres, adjustable declination for obtaining instant true bearings without resort to arithmetic, and devices such as inclinometers for measuring gradients.

Solid state compasses

Small compasses found in clocks, cell phones (e.g. the Nokia 5140i) and other electronic gear are solid-state devices usually built out of two or three magnetic field sensors that provide data for a microprocessor. Using trigonometry the correct heading relative to the compass is calculated.

Often, the device is a discrete component which outputs either a digital or analog signal proportional to its orientation. This signal is interpreted by a controller or microprocessor and used either internally, or sent to a display unit. An example implementation, including parts list and circuit schematics, shows one design of such electronics. The sensor uses precision magnetics and highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field. The electrical signal is then processed or digitized.

Compass balancing

Because the Earth's magnetic field's inclination and intensity vary at different latitudes, compasses are often balanced during manufacture. Most manufacturers balance their compass needles for one of five zones, ranging from zone 1, covering most of the Northern Hemisphere, to zone 5 covering Australia and the southern oceans. This balancing prevents excessive dipping of one end of the needle which can cause the compass card to stick and give false readings. Suunto has recently introduced two-zone compasses that can be used in one entire hemisphere, and to a limited extent in another without significant loss of accuracy. 

NOTES: 

1) The Earth's North Magnetic Pole is the wandering point on the Earth's surface at which the Earth's magnetic field points vertically downwards (i.e. the "dip" is 90°). The North Magnetic Pole should not be confused with the lesser known North Geomagnetic Pole.

As of 2005 the North Magnetic Pole lay near Ellesmere Island in northern Canada at 82.7° N 114.4° W. Its southern hemisphere counterpart is the South Magnetic Pole. Because the Earth's magnetic field is not exactly symmetrical, the North and South Magnetic Poles are not antipodal: a line drawn from one to the other does not pass through the centre of the Earth (it actually misses by about 530 km or 329.3 mi).

2) A sundial is a device that measures time by the position of the Sun. The most commonly seen designs, such as the horizontal or garden sundial, cast a shadow on a flat surface marked with the hours of the day. As the position of the sun changes, the time indicated by the shadow changes. However, sundials can be designed for any surface where a fixed object casts a predictable shadow.

Most sundial designs indicate apparent solar time. Minor design variations can measure standard and daylight saving time, as well.

3) True north is a navigational term referring to the direction of the North Pole relative to the navigator's position. In other words, it is the direction of the geographical North Pole from a given point. This is different from the magnetic north pole. Its concept was first discovered and noted by the Chinese polymath Shen Kuo in the 11th century.

True north is compared to magnetic north (the direction of the magnetic north pole) and grid north (the direction northwards along the grid lines of a map projection).

The direction of true north is marked in the skies by the north celestial pole. For most practical purposes, this is the position of Polaris. However, due to the precession of the Earth's axis, true north rotates in an arc that takes approximately 25,000 years to complete. In 2002, Polaris was at its closest approach to the celestial north pole. 2,000 years ago, the closest star to the celestial north pole was Thuban.

On maps issued by the United States Geological Survey, and the U.S. military, true north is marked with a line terminating in a five-pointed star. Maps issued by the Ordnance Survey contain a diagram showing the difference between true north, grid north and magnetic north at a point on the sheet.

4) In the liquid compass, which is the most stable type of mariner’s compass, the bowl is filled with a liquid, usually a mixture of alcohol and water. The liquid helps to support the graduated card, which, in this type of compass, pivots about its center and floats in the liquid, thereby reducing pivot friction and lessening the vibrations of the card caused by the motion of the vessel. Because of these advantages the liquid compass is used more often than the dry compass. In both types a black vertical line, known as the lubber’s line, is drawn on the inner surface of the bowl. The course of the ship may be obtained by reading the number of degrees on the card opposite the lubber’s line. The magnetic compass points toward the magnetic north only if the ship is free of magnetism and if no iron or steel objects are nearby. If the ship is magnetic and iron and steel objects deflect the magnetic needle, the error known as deviation occurs. To correct deviation, the compass is installed in a stand called a compensating binnacle, which is equipped with a system of magnets arranged to compensate for the disturbing influences.