The magnetic compass is one of those interesting devices that, in essence, has not changed since its invention. Oh, it has been improved upon, made more accurate and more durable; the basic concept, however, is the same as it was hundreds of years ago. There is actually some confusion about when the compass was first invented. The Chinese culture can definitely be credited with the invention, and ancient Chinese literature contains references to magnetized needles as far back as the 2nd century. However, the first incontrovertible evidence of the compass's existence dates from the 11th century; a book called "Dream Pool Essays" gives an explicit description of how a needle can be magnetized and attached to a strand of silk in order to point north. The use of the compass for travel quickly followed, the first evidence of this use being recorded in the 12th century work "Pingzhou Table Talks."
At any rate, the compass has undeniably existed for about 1000 years. However, it is doubtful whether those ancient Chinese inventors would recognize our handy little pocket compasses as the devices of their invention. Modern compasses are usually small enough to fit easily in the palm of the hand. They use north-pointing magnetized needles or dials inside fluid-filled capsules. The advantage of fluid in the capsule is that it dampens the movement of the needle, allowing it to stabilize quickly rather than oscillate back and forth. The direction of north is often marked with phosphorescent paint, enabling the user to read the compass even in dim light.
Modern compasses often incorporate a protractor that uses a separate magnetized needle. In this design, the rotating capsule containing the magnetized needle is fitted with orienting lines and an outlined orienting arrow. It is mounted in a transparent base plate that contains a direction-of-travel indicator. Compasses with protractors can be used to take bearings directly from a map. The edge of the compass is placed on the map so that it connects the current location with the desired destination. The orienting lines in the base of the compass dial are then rotated to align with true north by aligning them with a marked line of longitude, ignoring the compass needle entirely. The resulting map bearing may then be read at the direction-of-travel line, which may be followed to the destination.
When using a compass, it is important to make compensations for any nearby object that may exert a magnetic force. If the compass is close to a car, for example, the magnetic needle will be drawn to the electromagnetic fields of the batteries, engine, etc. Compasses used while driving must be corrected for the additional electrical influences being exerted on them. Similarly, ships contain a great deal of steel and iron, which strongly affect the accuracy of a compass.
Compasses come in a wide variety of designs and levels. A basic compass intended for hiking will only be about $10 to $15, and this is as much as the typical recreational hiker needs. However, compasses can run up to several hundred dollars, depending on the construction and the abilities of the device. Also, many watches designed for hikers in corporate compasses, and these pieces are usually in the range of $150.
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The Compass: Know The Basics
