Compass: Difference between revisions

In 1936 [[Tuomas Vohlonen]] invented the first successful portable liquid-filled compass designed for individual use.<ref>http://www.prh.fi/en/tietoaprhsta/innogalleria/vohlonen_takes_a_bearing.html</ref>

A magnetic rod is required when 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. 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, often by being painted red.

[[Flavio Gioja]] (fl. [[1302]]), an Italian [[pilot (harbour)|marine pilot]], is sometimes credited with perfecting the sailor's compass by suspending its needle over a [[fleur-de-lis]] design, which pointed [[north]]. He also enclosed the needle in a little box with a glass cover.

[[image:liquid filled compass.jpg|thumb|Liquid filled lensatic compass]]

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.

Some modern military compases, like the [SandY-183 http://www.orau.org/PTP/collection/radioluminescent/armycompass.htm](the one pictured) contains the radioactive material [[Tritium]] (<small>3</small>H) and a combination of Phosphorous. The SandY-183 contained 120mCi (millicuries) of tritium. The name SandY-183 is derived from the name of the company, Stocker and Yale (SandY).

Small compasses found in clocks, [[cell phone]]s (e.g. the [[Nokia 5140i]]) and other electronic gear are [[Solid-state electronics]] 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.

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 [[digital electronics|digitized]].

A '''bearing compass''' is a magnetic compass mounted in such a way that it allows the taking of bearings of objects by aligning them with the lubber line of the bearing compass.

* [http://www.westmarinebooks.com/webapp/wcs/stores/servlet/WestAdvisorDisplayView?storeId=30003&langId=-1&catalogId=10001&advisor=bearing.htm West Marine: How to use a hand bearing compass]

[[Image:MuseeMarine-compas-p1000468.jpg|thumb|150px|A [[binnacle]] containing a ship's steering compass, with the two iron balls which correct the effects of [[ferromagnetism|ferromagnetic]] materials]]

{{main|Magnetic deviation}}

* Literature [http://www.travel-island.com/travel.outdoor.gears/how.works.compass.maps.html]

Because the Earth's magnetic field varies 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.

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{{main|Boxing the compass}}

Most military defense forces have adopted the 'mil' system, in which the compass dial is spaced into 6400 units (some nations use 6000) or 'mils' for additional precision when measuring angles, laying artillery, etc.

* [[Azimuth]]

* [[Beam compass]]

* [[Wrist compass]]

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Image:Compass_Fitted_To_A_Yacht.jpg|A simple compass typical to a small [[yacht]]

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<div class="references-small"><references/></div>

* Admiralty manual of navigation, Chapter XXV The Magnetic Compass (continued) the analysis and correction of the deviation, His Majesty's Stationary Office, London, 1914.

* Alan Gurney, ''Compass: A Story of Exploration and Innovation'', W.W. Norton & Company, 2004, ISBN 0-393-32713-2.

* Li Shu-hua, “Origine de la Boussole 11. Aimant et Boussole,” ''Isis'', Vol. 45, No. 2. (Jul., 1954), pp. 175-196.

{{Commons|Compass}}

* [http://geomag.usgs.gov USGS Geomagnetism Program]

{{Flight instruments}}

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