Compass

The History of the Compass:

The earliest compasses are believed to have been invented by the Chinese in around 1050 BCE. They were created first for the purposes of spiritual life or developing a feng shui environment and then later used for navigation. It is disputed whether other cultures, such as some Mesoamerican societies, may have developed the idea for the magnetized compass first, also in accordance for spiritual aligning rather than navigation.

Compasses were originally developed when lodestones, a mineral that has naturally magnetized iron ore, were suspended above a board with the ability to pivot and turn. It was discovered that the stones would always point in the same direction, and align themselves with the north/south axis of the earth.

Is a Compass Useful?

No matter where you stand on Earth, you can hold a compass in your hand and it will point toward the North Pole. What an unbelievably neat and amazing thing! Imagine that you somehow end up in the middle of the ocean, and you are looking all around you in every direction and all you can see is water, and since it is overcast, you cannot see the sun... How in the world would you know which way to go unless you had a compass to tell you which way is "up"? Long before Global Positioning System (GPS) satellites and other high-tech navigational aids, the compass gave humans an easy and inexpensive way to orient themselves.

Reading a Compass:

Like mentioned above, no matter the compass, one end of the needle always points North. Usually it's the RED end, but its a good idea to test your compass before starting to use it. If you are north of the equator, stand facing the sun around lunchtime. Whichever end of the needle points towards the sun is South and the end that points at you is North. If you're 'down under' the North end points towards the sun and the South end points at you.

To read your compass:

1.Hold your compass steadily in your hand so the baseplate is level and the direction-of-travel arrow is pointing straight away from you.

2.Hold it about halfway between your face and waist in a comfortable arm position with your elbow bent and compass held close to your stomach.

3.Look down at the compass and see where the needle points.

How does a Compass work? 

A compass is an extremely simple device. A magnetic compass (as opposed to a gyroscopic compass) consists of a small, lightweight magnet balanced on a nearly friction-less pivot point. The magnet is generally called a needle. One end of the needle is often marked "N," for north, or colored in some way to indicate that it points toward north. On the surface, that's all there is to a compass.

The reason why a compass works is more interesting. It turns out that you can think of the Earth as having a gigantic bar magnet buried inside. In order for the north end of the compass to point toward the North Pole, you have to assume that the buried bar magnet has its south end at the North Pole, as shown in the diagram at the right. If you think of the world this way, then you can see that the normal "opposites attract" rule of magnets would cause the north end of the compass needle to point toward the south end of the buried bar magnet. So the compass points toward the North Pole.

To be completely accurate, the bar magnet does not run exactly along the Earth's rotational axis. It is skewed slightly off center. This skew is called the declination, and most good maps indicate what the declination is in different areas (since it changes a little depending on where you are on the planet).

The magnetic field of the Earth is fairly weak on the surface. After all, the planet Earth is almost 8,000 miles in diameter, so the magnetic field has to travel a long way to affect your compass. That is why a compass needs to have a lightweight magnet and a friction-less bearing. Otherwise, there just isn't enough strength in the Earth's magnetic field to turn the needle.

The "big bar magnet buried in the core" analogy works to explain why the Earth has a magnetic field, but obviously that is not what is really happening. So what is really happening?

No one knows for sure, but there is a working theory currently making the rounds. As seen on the above, the Earth's core is thought to consist largely of molten iron (red). But at the very core, the pressure is so great that this super-hot iron crystallizes into a solid. Convection caused by heat radiating from the core, along with the rotation of the Earth, causes the liquid iron to move in a rotational pattern. It is believed that these rotational forces in the liquid iron layer lead to weak magnetic forces around the axis of spin.

It turns out that because the Earth's magnetic field is so weak, a compass is nothing but a detector for very slight magnetic fields created by anything. That is why we can use a compass to detect the small magnetic field produced by a wire carrying a current (see How Electromagnets Work).

Below are some of the compasses that are currently offered: