A liquid compass is a compass which is filled with fluid. The fluid acts as a buffer, absorbing shock and vibrations to avoid damage to the elements in the liquid compass, and it also helps to stabilize the compass needle to make the device easier to read. Many compasses are liquid filled, and they come in a variety of styles ranging from ball compasses to small models which are designed to clip onto a keychain so that they are available for easy reference.
The concept of the liquid compass was introduced as early as the 1600s, but did not catch on until the 1900s, when they were adopted as standard navigational instruments by several navies. The compass includes a needle which is sensitized so that it will always point towards Earth's magnetic north, with a backing which is marked with degrees so that users can determine which direction they are facing on the basis of the marking the needle lands on. Using a liquid compass, people can determine which direction they are heading in, and use this information in navigation.
The viscosity of the fluid can depend on the design; alcohol, oil, and kerosene are three common choices for fluid, and it may be dyed to increase visibility. The compass is designed to allow the liquid to expand and contract slightly without breakage. One advantage to using a liquid compass is that the needle stabilizes very quickly and prevents wobbling, allowing people to take accurate measurements more easily. Another is that the device tends to be more tolerant of shaking, dropping, and other forms of abuse.
Numerous companies make liquid compasses of all shapes and sizes. The liquid damped compass continues to be a handy basic navigation tool, although it has been largely supplanted by things like GPS devices. A compass will still work when GPS is broken or unavailable, however, and many people learn the basics of compass navigation as part of their training for hiking, boating, and other outdoor activities, during which being able to navigate can be very important.
One important thing to be aware of when someone uses a compass is that the device points towards magnetic north, not true north. Magnetic north actually wobbles around the geographic north, making it necessary to adjust for declination, the variance between magnetic and true north. Many compasses allow users to adjust for this, and declination information is usually published on maps and charts.