A Flinders bar is a vertical soft iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 bar placed in a tube on the fore side of a compass

Compass

A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

 binnacle

Binnacle

A binnacle is a waist-high case or stand on the deck of a ship, generally mounted in front of the helmsman, in which navigational instruments are placed for easy and quick reference as well as to protect the delicate instruments. Its traditional purpose was to hold the ship's magnetic compass,...

. The Flinders bar is used to counteract the vertical magnetism

Magnetism

Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...

 inherent within a ship and is usually calibrated as part of the process known as swinging the compass, where deviations caused by this inherent magnetism are negated by the use of horizontal (or quadrantal) correctors.

Where the deviation from a compass point

Boxing the compass

Boxing the compass is the action of naming all thirty-two points of the compass in clockwise order. Such names are formed by the initials of the cardinal directions and their intermediate ordinal directions, and are very handy to refer to a heading in a general or colloquial fashion, without...

 cannot be counteracted through the use of Flinders bar, Kelvin

William Thomson, 1st Baron Kelvin

William Thomson, 1st Baron Kelvin OM, GCVO, PC, PRS, PRSE, was a mathematical physicist and engineer. At the University of Glasgow he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging...

's balls, Heeling error magnets and Horizontal magnets, a deviation card, or graph, is produced. This card, or graph, lists the deviation for various compass courses and is referred to by the navigator when compass courses need to be corrected.

It is named after Matthew Flinders

Matthew Flinders

Captain Matthew Flinders RN was one of the most successful navigators and cartographers of his age. In a career that spanned just over twenty years, he sailed with Captain William Bligh, circumnavigated Australia and encouraged the use of that name for the continent, which had previously been...

 (1774-1814) who wrote a paper on ships' magnetism for the British Navy.. He discovered the addition of a bar of iron would compensate for errors caused by his cargo during his travels to Australia.

External links

• Flinders education unit from Royal Geographical Society of Queensland