History Of The Magnetic Compass

Despite the increase in the use of electronic navigation devices, the magnetic compass is still an essential navigation instrument. It’s cheap, simple and reliable.

The earliest known references to the use of magnetism to attract a needle are from China around 2000 years ago and the earliest Chinese compass is mentioned around 1000 years ago.

The earliest known compass in Europe appeared in 1190. It’s not known if the technology developed independently or if news of the Chinese compass reached Europe. However Chinese compasses pointed South and European compasses invariably point North.

The first compasses were very simply a magnetised needle attached to a float in a bowl of water.

Development of the Mariners Compass

Around 1300 the mariners compass we still use up to this day was developed. A compass card or compass rose is attached to a magnetised rod. The card is placed on a pivot in a box and the box placed on the centre line of the ship. As the ship changes direction the heading can be read directly off the card. The first successful liquid filled version we are familiar with today was invented by Toumas Vohlonen the founder of Suunto in 1936. The liquid damps or slows down the movement of the compass card making it easier to read.

Prior to the invention of the compass, navigation was largely done using heavenly bodies which are not always readily visible and no doubt became obscured at the most inconvenient times. The adoption of the compass enabled ships to navigate with more certainty and travel further afield. This lead to an increase in sea trade around the Mediterranean and northern Europe.

How Compasses Work

Compasses work because the earth acts like a big magnet with magnetic north somewhere near but not at the northpole. This creates a magnetic field, running roughly north south with which the compass lines up.

Problems and Limitations

As with all things there are problems and limitations. Some of them are due to the earth not being perfect. The magnetic poles move around a bit and magnetic field is distorted by the make up of the earth itself. Also the north pole can flick around and become the south pole and back. This happens on average every 250,000 years but the last time was 780,000 years ago so watch out.

Magnetic Field Variation

We call the irregularities in the earths magnetic field variation. Variation is marked on our navigation charts and must be allowed for when working out a compass course on the chart.

Flux Gate Compass

The electronic age has lead to the development and use of the flux gate compass. This compass is an electromagnetic device still reliant on the earths magnetic field. It can however produce a digital signal used for directing the electronic autopilot.