Compass

History

The oldest known compasses were used by the Chinese at the 11th century, at which her place is very much used in Géomancie (see also Mysticisme). Their compasses resembled plates then and switches was a kind of spoon with soup (photo) symbolizing the Grande Ourse and directed towards the south (see external bonds) . The use which was made magnetic field of the Earth constituted a Spectacle because the arrows were manufactured like the dice: they were aligned on North thanks to their magnetism, bluffant the assistance. Curiously, that took a certain time so that this phenomenon is used by the Chinese for the needs for navigation, but with the process becomes common. However, the Chinese scientist Shen Kuo (1031 - 1095) of the Dynastie Song (960 - 1279 AD) was the first to describe the magnetic compass which was used for navigation.

The Européens started to use the compass only as from the 11th century, initially in the Roman Empire of the East where she had arrived by the Silk route, then in the navigators Génois and Vénitiens, and starting from the end of the 13th century in Spain and to the Portugal, during great maritime forwardings (Compass of old Chinese navy).

Its use spreads in first half of the 13th century. In 1358, a Monk English of the name of Nicholas de Lynne, would have been navigator thanks to his competence and to its knowledge of “the magnetic compass” (see Inventio Fortunata).

Before the introduction of the compass, navigation at sea was carried out mainly by means of the célestielle navigation (navigation by even latitude : the ship " calait" on the latitude of arrival and remained there), supplemented in some places by the use of the Sondage S. the difficulties emerged if the Mer were too deep to carry out surveys, if the atmospheric conditions were continuously bad or if the air Brume ux prevented the vision of the sun.

Thus the compass was not same utility everywhere. For example, the Arabs could generally hope on a clear sky to sail in the Persian Gulf and the Indian Ocean (also thanks to the foreseeable nature of the Mousson S). This can partly explain the relatively late adoption of the compass. The sailors in the Baltic, sea relatively not very deep, made great use of the surveys.

However, in the Mediterranean basin and since Antiquity, the voyages at sea were not done between October and April, because of absence of clear sky during the Mediterranean Hiver and of the sea too much deep for the surveys.

With the improvement of the methods of navigation per estimate and with the better development Chart S, this stop seasonal is modified during second half of the 13th century. Around 1290, the season of navigation starts in January or February and finishes in December. The additional months are of considerable economic importance; they allow the Venetian convoys, for example, to make two voyages return ticket per year in the Eastern Mediterranean instead of only one.

At the same time the traffic between Mediterranean Europe and the Scandinavia increases and one of the reasons is undoubtedly that the compass returned the crossing of the the Bay of Biscay surer and easier.

Physical principle

A compass can be made up of any device using a Aiguille magnetized turning freely on a pivot, so that it can indicate the direction of the magnetic north of the Magnétosphère of our Planet.

Formerly, certain compasses were equipped with a Sundial (using the shadow of a needle or a folding triangle) making it possible to correlate the approximate hour with the indication of the orientation of the magnetized needle (see bonds), this device approaches in its function the Astrolabe.

A Gyrometer (in English: variation compass ) is a specialized instrument, of rather delicate construction; it is employed by observing the variations of the needle.

A gyroscopic compass can also be employed to find the true north.

The basic element is a magnetic stem. One can carry it out by aligning a stem of Fer or Acier on the Magnetic field of the Earth and then making it heat then to cool (to reheat) or by rubbing it. However, this method produces only a Aimant of low power; thus of other methods are preferable.

This magnetized stem (or switches magnetic) is then placed on a support of quasi-null friction to allow him pivot er freely to align itself on the ambient magnetic field. One then affixes there a mark at an end so that the user can distinguish the directions north and south. A modern convention wants that the end of north is marked in an unspecified way, often of fluorescent or red painting.

Use of the compass

Other characteristics common to the portable modern compasses with the hand are a bed plate equipped with scales making it possible to measure the distances on the charts, a revolving Lunette to measure the angle formed between the magnetic north (see magnetic Déclinaison) indicated by the Aiguille and the direction of the point concerned, and a Miroir reflecting the image of the needle on the dial when a point is signed locates. The majority of the compasses have also a system of aiming made up of a bead and a Guidon being used as Collimateur or of a wire tended in one obviously, or of a line painted or traced in the lid. Certain compasses have a magnetized needle supporting a mobile dial (like the Compass card of the compasses of navy) and the reading is done then automatically by means of a line traced on glass (see the photograph of the compass of the American army). A third type of compass, still more sophisticated, has a Prisme directed towards the edge external of the dial and a Oculaire in which one can directly read the value of angle (see photographs).

- the compass has several uses: Navigation, Artillery, Geodesy etc In navigation, it can be used for to determine the position present of the user or to indicate a procedure to follow .

In the first case, the user must raise the layer of benchmarks (bridge, bell-tower of church, top of mountain etc) visible from the place where it is and compare its observations with a chart. For this purpose, it will direct the sighting device of its compass towards the point marking chosen and will turn then the glasses to put the reference mark indicating the magnetic north compared to the direction indicated by the needle, visible in the mirror. The observer will place then the compass on the chart (posed flat and directed towards the magnetic north) and will locate the position of the point marking beforehand concerned. To determine its position compared to this object, it will trace a straight line on the basis of the outstanding point passing by the center of the dial (not of rotation of the needle) and function of the measured angle. One second line on the basis of an other visible point marking and cutting the first will make it possible to determine the position present with more precision.

to determine a procedure to follow (a course ), the simplest manner is first of all to consider that the needle always indicates the same direction, i.e. north. If one carefully notes the distances covered (time and rate of travel) and the angles measured with each change of management, one can trace the evolution of his own route and return to his starting point only using one compass alone (without chart). Except the areas presenting a strong magnetic deviation (e.g. presence of ferruginous metals in the ground) of 20 degrees or more, one simple compass (of bracket) will be enough on short distance to avoid working in an entirely false direction insofar as the ground is about flat and no obstacle comes to obstruct the visibility.

Foot-note: If one uses the compass in connection with a chart, one must then apply an entirely different method. It is necessary to take account of the magnetic Déclinaison. This one variable according to the position in space and of time, it will be necessary possibly to calculate it (or to ask it the local club of excursion) to determine how much degrees measures the angle between the magnetic north (indicated by the needle) and the true north (high of the chart). This angle will have to be taken into account at the time of the aiming of the benchmark.

To measure a true angle, i.e. compared to the true north and not at the Magnetic north ), for example using a compass having a side in the form of scale, one will place item zero of the rule on the position present located on the chart (beforehand directed with the top towards the true north) and one will direct the rule in the direction of the desired destination (certain sources recommend to the beginners for more safety to trace a line on the chart). One will turn then the glasses (supporting the transparent dial of the compass) to direct the zero of the angular graduation towards the true north by aligning the parallel lines on the North-South lines (longitude) or on the side edge of the chart. The course to be followed is then indicated on the line of sight of the compass. Horizontally to hold then the compass with the level them eyes and to direct it so that the needle remains compared to the value of angle corresponding to the magnetic north. The longitudinal axis of the compass (generally materialized by an arrow) will indicate the course to be followed.

simplified Method: (without directing the chart top towards north) one can determine on the chart its position present according to a visible benchmark in the landscape by directing towards this last the arrow of aiming of the compass and while turning the glasses so as to align the parallel lines and the needle. One will then place on the chart a corner of the compass on the benchmark concerned and one will make it turn until the parallel lines are aligned on the lines of longitude (North-South) of the chart. The position presents is on the scale of the compass or in its prolongation. One second line traced starting from an other benchmark and cutting the first will make it possible to determine the position with more precision.

Conversely, this method is also applicable to determine the course to follow. To initially place the compass on the chart, the edge of the rule being on an imaginary line connecting the position present and item zero on the objective to be reached, without taking account of the needle. To turn the glasses then (supporting the transparent dial of the compass) to align the parallel lines on the North-South lines of the chart (or on the side edge of the chart) by preserving the northern reference mark (zero) “northern” side. The angle thus defined by these lines and the side of the case of the compass correspond within the meaning of the procedure to follow compared to the north, materialized by the arrow of the compass. By holding the compass with the level of the eyes (with end of arm), to place itself in manner such that the needle is aligned on the parallel lines and is pointed towards north.

The photo watch a top aimed starting from the indications of the chart.

Compasses of marine and compass of navigation

For more technical informations to consult:

Compasses of wrist

There exist various types of compasses carried to the wrist like a watch. They are especially used in deep-sea diving. There were also other models for infantrymen such as for example that of the Red Army (see photograph gallery). The American soldiers also had for example during the Guerre of Korea of the rudimentary compasses of wrist (see photographs on ebay) .

Aeronautics

to see Compass (navigation)

electronic Compasses

Certain watches and other measuring instruments have a compass containing electronics components. They are generally two or three Capteur S of magnetic field providing the source data to a Microprocesseur. Trigonometrical calculation makes it possible to post the course.

Often, the device is component discrete providing a signal (numerical or analogical) proportional to its orientation. This signal is then interpreted by a Contrôleur or a microprocessor and treaty in-house or transmitted to a display device (see an example of realization, with the basic components and the corresponding wiring diagram).

Points of the compass/Graduation

Traditionally, the dial or Compass card is divided into thirty-two equidistant points (called like quarters , the quarter is worth 11° 15 ') although the modern compasses are graduated in degrees rather than cardinal points (see low graduation ). The four principal directions - is, western, Northern and southern - are the cardinal points and the names of the others are derived from the latter (example: south = 180°; south-south-east = 157° 30 ').

There exist several systems of graduation for the compasses:

most known is division in 360 degrees.
Of other systems uses division in 400 rank S (Gon S) or in 6400 Thousandth S.
the armies of the Eastern European countries (old Soviet Bloc) use compasses similar to the face of a watch, graduated in 60 minutes, a right angle measuring 15 " unités" (photo watch of the NVA). They are sometimes also graduated in the anti-clockwise direction (see photo watch of Russian wrist).
Some are equipped with a Inclinomètre to measure the vertical angles and with a spirit level.

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