The Compass (Edited from Wikipedia)

SUMMARY

A compass is an instrument used for navigation and orientation that shows direction relative to the geographic "cardinal directions", or "points". Usually, a diagram called a compass rose, shows the directions north, south, east, and west as abbreviated initials marked on the compass. When the compass is used, the rose can be aligned with the corresponding geographic directions, so, for example, the "N" mark on the rose really points to the north. Frequently, in addition to the rose or sometimes instead of it, angle markings in degrees are shown on the compass. North corresponds to zero degrees, and the angles increase clockwise, so east is 90 degrees, south is 180, and west is 270. These numbers allow the compass to show azimuths or bearings, which are commonly stated in this notation.

The magnetic compass was first invented as a device for divination as early as the Chinese Han Dynasty (since about 206 BC), and later adopted for navigation by the Song Dynasty Chinese during the 11th century. The use of a compass is recorded in Western Europe and in Persia around the early 13th century.

HISTORY

Prior to the introduction of the compass, geographical position and direction at sea were primarily determined by the sighting of landmarks, supplemented with the observation of the position of celestial bodies. On cloudy days, the Vikings may have used cordierite or some other birefringent crystal to determine the sun's direction and elevation from the polarization of daylight; their astronomical knowledge was sufficient to let them use this information to determine their proper heading. The invention of the compass enabled the determination of heading when the sky was overcast or foggy, and when landmarks were not in sight. This enabled mariners to navigate safely far from land, increasing sea trade, and contributing to the Age of Discovery.

In China

The compass was invented in China during the Han Dynasty between the 2nd century BC and 1st century AD, where it was called the "south-governor". The magnetic compass was not, at first, used for navigation, but for geomancy and fortune-telling by the Chinese. The earliest Chinese magnetic compasses were possibly used to order and

1 harmonize buildings in accordance with the geomantic principles of feng shui. These early compasses were made with lodestone, a form of the mineral magnetite that is a naturally-occurring magnet and aligns itself with the Earth’s magnetic field. People in ancient China discovered that if a lodestone was suspended so it could turn freely, it would always point toward the magnetic poles. Early compasses were used to choose areas suitable for building houses and to search for rare gems. Compasses were later adapted for navigation during the Song Dynasty in the 11th century.

At present, scholarly consensus is that the Chinese invention used in navigation pre- dates the first European mention of a compass by 150 years. However, there are questions over diffusion. The first recorded appearance of the use of the compass in Europe (1190) is earlier than in the Muslim world (1232), as a description of a magnetized needle and its use among sailors occurs in Alexander Neckam's De naturis rerum (On the Natures of Things ), written in 1190.

The earliest reference to a compass in the Middle East is attributed to the Persians, who describe an iron fish-like compass in a talebook dating from 1232. In the Arab world, the earliest reference comes in The Book of the Merchants' Treasure , written by one Baylak al-Kibjaki in Cairo about 1282. Since the author describes having witnessed the use of a compass on a ship trip some forty years earlier, some scholars are inclined to antedate its first appearance accordingly.

The common shape of the early compass as a magnetized needle floating in a bowl of water is considered as an evidence of diffusion from China to Europe. Another evidence supported diffusion theory is the temporal proximity of the Chinese beginning to use compass (after its first use in feng shui) in navigation to the first appearance of compass in Europe and Arab. The Persian compass is described as fish-like, which is a characteristic of early Chinese compasses from the 11th century, suggesting transmission from China to Persia. The view of some academics that compass was transmitted to Europe from China, through the Islamic world.

Some suggested the compass was transmitted to Europe and Arab through Indian Ocean from China. Other scholars suggested compass was brought by crusades to Europe from China. However, some scholars proposed an independent European invention of the compass: The first record of a magnetic compass in Europe (1187 by Neckam) proceeded those by Arabs, and the Arabic word for compass (al-kunbas) appears to be derived from Italian roots, which indicates an independent European invention.

2 Impact on Europe

Alexander Neckam reported the use of a magnetic compass for the region of the English Channel between 1187 and 1202, after he returned to England from France and prior to entering the Augustinian abbey at Cirencester. Robert Southey suggested that the Siete Partidas contained a reference from the 1250s to the needle being used for navigation. In 1269 Petrus Peregrinus of Maricourt described a floating compass for astronomical purposes as well as a dry compass for seafaring, in his well-known Epistola de magnete.

In the Mediterranean, the introduction of the 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. However, critics like Kreutz have suggested that it was later in 1410 that anyone really started steering by compass.

CONSTRUCTION constructing a compass. This can be created by aligning an iron or steel rod with Earth's magnetic field and then tempering or striking it. However, this method produces only a weak magnet so other methods are preferred. For example, a magnetised rod can be created by repeatedly rubbing an iron rod with a magnetic lodestone. This magnetised rod (or magnetic needle) is then placed on a low friction surface to allow it to freely pivot to align itself with the magnetic field. It is then labeled so the user can distinguish the north-pointing from the south-pointing end; in modern convention the north end is typically marked in some way.

3 If a needle is rubbed on a lodestone or other magnet, the needle becomes magnetized. When it is inserted in a cork or piece of wood, and placed in a bowl of water it becomes a compass. Such devices were universally used as compass until the invention of the box-like compass with a 'dry' pivoting needle sometime around 1300.

MODERN COMPASSES

Modern compasses usually use a magnetized needle or dial inside a capsule completely filled with a liquid (lamp oil, mineral oil, white spirits, purified kerosene, or ethyl alcohol is common). While older designs commonly incorporated a flexible rubber diaphragm or airspace inside the capsule to allow for volume changes caused by temperature or altitude, some modern liquid compasses utilize smaller housings and/or flexible capsule materials to accomplish the same result. The liquid inside the capsule serves to damp the movement of the needle, reducing oscillation time and increasing stability.

Key points on the compass, including the north end of the needle are often marked with phosphorescent, photoluminescent, or self-luminous materials to enable the compass to be read at night or in poor light. As the compass fill liquid is noncompressible under pressure, many ordinary liquid-filled compasses will operate accurately underwater to considerable depths.

Many modern compasses incorporate a baseplate and protractor tool, and are referred to variously as "orienteering", "baseplate", "map compass" or "protractor" designs. This type of compass uses a separate magnetized needle inside a rotating capsule, an orienting "box" or gate for aligning the needle with magnetic north, a transparent base containing map orienting lines, and a bezel (outer dial) marked in degrees or other units of angular measurement. The capsule is 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 modern orienteering compasses are map and romer scales for measuring distances and plotting positions on maps, luminous markings on the face or bezels, 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. The sport of orienteering has also resulted in the development of models with extremely fast-settling and stable needles for optimal use with a topographic map, a land navigation technique known as terrain association.

The military forces of a few nations, notably the United States Army, continue to issue field compasses with magnetized compass dials or cards instead of needles. A magnetic

4 card compass is usually equipped with an optical, lensatic, or prismatic sight, which allows the user to read the bearing or azimuth off the compass card while simultaneously aligning the compass with the objective (see photo). Magnetic card compass designs normally require a separate protractor tool in order to take bearings directly from a map.

The U.S. M-1950 military lensatic compass does not use a liquid-filled capsule as a damping mechanism, but rather electromagnetic induction to control oscillation of it magnetized card. A "deep-well" design is used to allow the compass to be used globally with a card tilt of up to 8 degrees without impairing accuracy. As induction forces provide less damping than fluid-filled designs, a needle lock is fitted to the compass to reduce wear, operated by the folding action of the rear sight/lens holder. The use of air-filled induction compasses has declined over the years, as they may become inoperative or inaccurate in freezing temperatures or extremely humid environments due to condensation or water ingress.

Some military compasses contain the radioactive material tritium (1H3) and a combination of phosphors. The U.S. M-1950 equipped with self-luminous lighting contains 120 mCi (millicuries) of tritium. The purpose of the tritium and phosphors is to provide illumination for the compass, via radioluminescent tritium illumination, which does not require the compass to be "recharged" by sunlight or artificial light. However, tritium has a half-life of only about 12 years, so a compass that contains 120 mCi of tritium when new will contain only 60 when it is 12 years old, 30 when it is 24 years old, and so on. Consequently, the illumination of the display will fade.

Mariner's compasses can have two or more magnets permanently attached to a compass card, which moves freely on a pivot. A lubber line, which can be a marking on the compass bowl or a small fixed needle, indicates the ship's heading on the compass card. Traditionally the card is divided into thirty-two points (known as rhumbs), although modern compasses are marked in degrees rather than cardinal points. The glass-covered box (or bowl) contains a suspended gimbal within a binnacle. This preserves the horizontal position.

FENG SHUI

Feng Shui is a Chinese philosophical system of harmonizing everyone with the surrounding environment. It is closely linked to Daoism. The term feng shui literally translates as "wind-water" in English. This is a cultural shorthand taken from the passage of the now-lost Classic of Burial recorded in Guo Pu's commentary: Feng shui is one of the Five Arts of Chinese Metaphysics, classified as physiognomy (observation of appearances through formulas and calculations). The feng shui practice discusses

5 architecture in metaphoric terms of "invisible forces" that bind the universe, earth, and humanity together, known as qi.

Historically, feng shui was widely used to orient buildings—often spiritually significant structures such as tombs, but also dwellings and other structures—in an auspicious manner. Depending on the particular style of feng shui being used, an auspicious site could be determined by reference to local features such as bodies of water, stars, or a compass.

Feng shui was suppressed in mainland China during the state-imposed Cultural Revolution of the 1960s but has since then regained popularity.

Until the invention of the magnetic compass, feng shui apparently relied on astronomy to find correlations between humans and the universe. The late Yangshao site at Dadiwan includes a palace-like building at the center. The building faces south and borders a large plaza. It stands on a north-south axis with another building that apparently housed communal activities. Regional communities may have used the complex.

Beginning with palatial structures at Erlitou, all capital cities of China followed rules of feng shui for their design and layout. During the Zhou era, the Kaogong ji codified these rules. The carpenter's manual Lu ban jing codified rules for builders. Graves and tombs also followed rules of feng shui, from Puyang to Mawangdui and beyond. From the earliest records, the structures of the graves and dwellings seem to have followed the same rules.

Instruments

The astronomical history of feng shui is evident in the development of instruments and techniques. According to the Zhouli, the original feng shui instrument may have been a gnomon. Chinese used circumpolar stars to determine the north-south axis of settlements. This technique explains why Shang palaces at Xiaotun lie 10° east of due north. In some cases, as Paul Wheatley observed, they bisected the angle between the directions of the rising and setting sun to find north. This technique provided the more precise alignments of the Shang walls at Yanshi and Zhengzhou. Rituals for using a feng shui instrument required a diviner to examine current sky phenomena to set the device and adjust their position in relation to the device.

The oldest examples of instruments used for feng shui are liuren astrolabes, also known as shi. These consist of a lacquered, two-sided board with astronomical sightlines. The earliest examples of liuren astrolabes have been unearthed from tombs that date

6 between 278 BC and 209 BC. Along with divination for Da Liu Ren the boards were commonly used to chart the motion of Taiyi through the nine palaces. The markings on a liuren/shi and the first magnetic compasses are virtually identical.

The magnetic compass was invented for feng shui and has been in use since its invention. Traditional feng shui instrumentation consists of the Luopan or the earlier south-pointing spoon—though a conventional compass could suffice if one understood the differences. A feng shui ruler (a later invention) may also be employed.

Qi

Qi (pronounced "chee" in English) is a movable positive or negative life force which plays an essential role in feng shui. In feng shui as in Chinese martial arts, it refers to 'energy', in the sense of 'life force' or élan vital. A traditional explanation of qi as it relates to feng shui would include the orientation of a structure, its age, and its interaction with the surrounding environment, including the local microclimates, the slope of the land, vegetation, and soil quality.

The Book of Burial says that burial takes advantage of "vital qi". Wu Yuanyin (Qing dynasty) said that vital qi was "congealed qi", which is the state of qi that engenders life. The goal of feng shui is to take advantage of vital qi by appropriate siting of graves and structures. Some people destroyed graveyards of their enemies to weaken their qi.

One use for a loupan is to detect the flow of qi. Magnetic compasses reflect local geomagnetism which includes geomagnetically induced currents caused by space weather.

PORTOLAN CHARTS

Portolan or portulan charts are navigational maps based on compass directions and estimated distances observed by the pilots at sea. They were first made in the 13th century in Italy, and later in Spain and Portugal, with later 15th and 16th century charts noted for their cartographic accuracy. With the advent of widespread competition among seagoing nations during the Age of Discovery, Portugal and Spain considered such maps to be state secrets. The English and Dutch relative newcomers found the description of Atlantic and Indian coastlines extremely valuable for their raiding, and later trading, ships. The word portolan comes from the Italian adjective portolano, meaning "related to ports or harbors", or "a collection of sailing directions".

These charts, actually rough maps, were based on accounts by medieval Europeans who sailed the Mediterranean and Black Sea coasts. Such charts were later drafted for coastal

7 resources in the Atlantic and Indian oceans. At the beginning of the Age of Discovery, charts had been made for the coast of Africa, Brazil, India, and past the Strait of Malacca into Japan, knowledge vital for the slow rise to prominence of the English Armada and of Dutch merchants, following in the wake of the Iberian powers. Frequently drawn on sheepskin vellum, portolan charts show coastal features and ports. During that period, smaller ships could use more of the coastline as harbors than in the present era. They might need to seek refuge more often, and crews intentionally beached some ships for maintenance and repairs. Thus, mariners sought to learn of protected bays or flat beaches, not only for safe harbor but also for coastal navigation.

The straight lines shown criss-crossing many portolan charts represent the thirty-two directions (or headings) of the mariner's compass from a given point, with its principal lines oriented to the magnetic north pole. Thus the grid lines varied slightly for charts produced in different eras, due to the natural changes of the Earth's magnetic declination. These lines are similar to the compass rose displayed on later maps and charts. "All portolan charts have wind roses, though not necessarily complete with the full thirty-two points; the compass rose ... seems to have been a Catalan innovation."

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