|By Larry LeMasters
As most of us know, a compass is an instrument used for navigation or orientation. All compasses show direction relative to geographical cardinal directions, such as north, south, east, and west.
Depending on which list you read, the compass is consistently listed as the fourth or fifth greatest invention of all time. This makes sense when one considers all of the great explorations of earth were made possible by a compass.
Compasses originated in China, circa 206 BC, in the Han Dynasty where they were used as divination devices. Nearly 1,300 years later, circa 11th century, the Song Dynasty of China adopted a compass for navigational use on the oceans. The first usage of a compass for navigation on the high seas occurred in Europe around 1190. These early compasses were made of lodestone, a naturally magnetized iron ore.
There are several different types of compass, but the magnetic compass, which points to “magnetic north,” is the type of compass most of us are familiar with. When used properly, a magnetic compass will point toward Earth’s north magnetic pole, allowing sailors to steer using this bearing.
When using a compass, one should be aware that there is a difference, magnetic declination, between the North Pole and “true north.” Compasses, unless able to compensate for the magnetic declination, point to magnetic north, not true north, which can throw a person or ship off by hundreds of miles.
The earliest, nearly accurate compasses, called needle-and-bowl compasses, were made of iron needles, magnetized by striking them with a lodestone and placing them in a cork in water. Around 1300 in Medieval Europe, dry compasses first appeared. It was not until the early 20th century that liquid-filled magnetic compasses appeared.
Dry compasses use a magnetized needle or dial inside a capsule that is completely filled with a liquid (lamp oil, mineral oil, white spirits, purified kerosene and ethyl alcohol are common liquids that are used). The liquid inside a dry compass served to limit the oscillation movement and increase stability. Some liquid-filled compasses are “non-compressible under pressure,” meaning they can work accurately underwater to several depths.
Orienteering compasses have a transparent base plate and are used for taking directional bearings directly from a map.
Many collectors search for a US M-1950 military compass, which does not use a liquid-filled capsule. The M-1950 uses electromagnetic induction to control oscillation of its magnetized card. Caution should be used when purchasing a M-1950 or other military compass since many of the compasses contain the radioactive mineral tritium. For instance, the M-1950, equipped with self-luminous lighting, contains 120 mCi (millicuries) of tritium.
Collectors erroneously believe some M-1950 compasses are broken because they no long provide illumination. This is not true. Tritium has a half-life of about 12 years, which means a M-1950 compass that contained 120 mCi when new, only contains 60 mCi when it is 12 years old, and only 30 mCi when it is 24 years old. Since an original M-1950 (the model number indicates it was produced in 1950) is now 69 years old, it should contain less than 3.75 mCi, which may not be enough to provide any illumination, making the compass face appear faded.
Mariners’ compasses are eagerly sought by some collectors; although, they are bulky and somewhat difficult to describe to non-collectors. Mariners’ compasses typically have two or more magnets permanently attached to the compass card. A lubber line, which is usually a marking on the compass bowl, indicates the ship’s heading on the compass card. Collectors of mariner compasses must learn several new words that are only associated with such compasses, such as rhumbs, gimbal, and binnacle.
There are many different, specialized compasses that are remarkable and found in good compass collections. Some of these compasses include a thumb compass (often used for orienteering), a Qibla compass (used by Muslims to show the direction to Mecca for prayers), optical or prismatic compasses (often used by surveyors), and trough compasses (centuries-old surveying compasses).
Along with physical compasses, collectors also seek words of wisdom reflected in a compass image or use. Henry David Thoreau said, “Go confidently in the direction of your dreams. Live the life you’ve imagined.”
Finally, in collecting, as in life, it is best to let your compass be your guide!