Compass | Research & Encyclopedia Articles

Compass

The compass is a tool used by land and sea explorers to help them navigate their journeys. Before compasses were developed, people used the sun, wind, and stars as their guides, but the compass allowed them to calculate their location and direction with greater accuracy.

During the first century B.C., the Chinese observed that pieces of lodestone, an iron mineral, always pointed north when they were placed on a surface; this discovery led to the development of the compass. The first Chinese compass was a spoon made of lodestone that rested on a smooth surface with markings indicating the four directions. The next step in the advancement of compasses was to enclose the lodestone in a decorative casing with a projecting needle to indicate which direction was north. One problem compass makers encountered was that the iron they used for the pointer lost its magnetism easily. After experimenting with different metals, the Chinese combined carbon and iron to make steel. The steel was stronger than iron and held its magnetic charge for a long time.

Meanwhile, other navigators around the world were also discovering the compass. Evidence suggests that Arab sailors were using compasses as early as A.D.600. As the Arab influence spread into North Africa, Spain and France, it brought an extensive knowledge of the most advanced navigation techniques known at the time. Thus, the compass was introduced to Europe. The European to write about the use of the compass was Alexander Neckham (1157-1217) in A.D. 1187. He described two compasses, one floating and one dry. By the fourteenth century, European ships carried maps on which compass readings to reach different destinations were charted. These charts used a wind rose to indicate directions of north, south, east, and west with each quarter of the rose divided into ninety degrees.

An innovation in compass design followed the development of the windrose. Compass makers glued a magnetic needle to the bottom of the wind rose with the north point of the rose and the north end of the needle aligned. When it was attached to a pivot the whole card rotated to point north rather than just the needle which made the compass much easier to read than previous styles.

During the fifteenth century, Prince Henry of Portugal (1394-1460) had a great influence on the development of sailing and navigation. He established a school for navigators in Portugal, and encouraged sailors and map makers to coordinate their information to make more accurate maps of the seas. Because of his interest in sea travel and exploration, Prince Henry fostered many improvements to the compass. One was the development of the binnacle--a glass case to protect compasses on board ship decks. The binnacle also had a place for a lamp to allow ship's pilots to read the compass at night. A stand for the compass was also developed at this time. Two brass rings were attached one inside the other so that they could move up and down. The compass was set inside the rings and attached to a stand which enabled the compass to remain level even though the ship swayed in rough waters.

Another of the innovations that came in the fifteenth century was the discovery of magnetic declination. When Christopher Columbus (1451-1506) sailed from Spain to the New World, he noticed that his compass did not align directly with the North Star. The difference between magnetic north and true north was called declination. Although sailors had known that the needle of the compass pointed slightly to the east of true north, they had assumed that the readings were consistent around the world. Columbus discovered that the degree to which the compass readings varied changed as he sailed across the ocean. In 1581, an English navigator named Robert Norman began investigating what made the compass readings vary at different points. Norman noticed that the angle of the compass needle varied according to its location as well. He conducted experiments to find out what was causing this "dip." In the course of his investigations, Norman discovered what he called the "attractive power on the earth." He deduced that it was this "attractive power" that pulled the magnetic compass toward the earth's surface.

This was consistent because the angle at which compasses dipped corresponded exactly to the angle of the earth's surface. Through further work in the area, Norman hypothesized that the earth had magnetic fields that run parallel to its surface. He made diagrams of these fields and explained the difference between the geographical axis of the earth and its magnetic axis. Charts similar to his still appear on modern maps. Norman's diagrams made it possible for navigators to determine the magnetic declination for any given position on the map, thus their calculations were much more accurate than ever before. Further improvements were made to maps and compasses when it was discovered that declination was affected not only by location but by time. Over a period of years, the earth's magnetic field shifts, changing the declination for any given place.

In the late 1500s, another Englishman, William Gilbert (1544-1603), experimented with magnets to find out why they behaved as they did. After carving a chunk of lodestone into a ball and then holding a needle near the lodestone. From this, he was able to determine north and south poles on this ball and deduced that the Earth itself must attract magnets through its magnetic poles in a similar way.

As maps and ships improved, new compasses and new problems developed. In 1789 a British doctor, Gowin Knight, rubbed a bundle of magnets on an iron bar to create super magnets, which in turn magnetized compass needles for longer periods of time. A great success, Knight's super magnets were used by the British navy for over eighty years. However, by 1850 all ships in the British Navy were iron, leading to magnetic deviation in which compasses were attracted to the small amounts of magnetism in the ships and thus gave false readings. Lord Kelvin corrected this by using small corrector magnets that surrounded the compass and prevented deviation.

Navigators next turned to the liquid compass rather than the old, dry card compasses. Scientists mixed water with alcohol to prevent the liquid from freezing, they sealed the compass bowl with rubber to prevent leaks, and they invented strong paints so that the markings would not flake away in alcohol. By the early twentieth century, liquid compasses were commonplace. In World War I, the vertical card compass was created to replace flat compasses which were too difficult to read during battle maneuvers. It was shaped like a tube and spun around on a pivot. Similar ones can sometimes be found on the dashboard of cars.

An American, Elmer Sperry, built the first gyrocompass, a device that worked day or night, anywhere on Earth even at the poles where lines of force are too close together for magnetic uses to function properly. When the gyrocompass is pointed north, it holds that position because it uses a gyroscope, a spinning wheel set in gimbals. The wheel spins due to an electric motor, and this wheel will turn in the same direction unless the position of the gimbals is changed. By 1935, many pilots used gyrocompasses because they were steady in all types of weather and they never spun wildly, even in the sharpest turns. The U.S. Nautilus used a gyrocompass when it crossed under the North Pole because it was not affected by the powerful magnetic forces there. Rockets are dependent on gyrocompasses because in space magnetic poles cannot pull needles in their directions.

The future of compasses lies in the electronic and satellite-based arenas. Electronic compasses are not inclined to the same errors magnetic compasses are like extraneous magnetic fields and vibration. Electronic compasses are more accurate and easier to calibrate. Global Positioning Systems (GPS) are not compasses in the traditional sense, but provide precise information about an object's immediate location from 24 satellites orbiting Earth. A GPS receiver process radio signals put out by the satellites to determine their position. This information can be used to steer ships or planes around other vessels or other potential path-blockers. When combined with other technologies, such as computerized maps, GPS can help guide motorists through roadways. Indeed, one company, Silva, manufactured a GPS Compass, which combines an electronic compass with a GPS receiver.