Compasses are pretty cool things. Making use of the magnetic pull of the poles a compass can tell you, at least relatively speaking, where you are even in the empty vastness of blue water. In this age of GPS, the compass rarely comes into play but in the 18th and 19th century it was the height of navigational technology.
Small ships rarely had a compass. The sloops and boats that worked the rivers and coasts - more often full of pirates than anything else - navigated with the assistance of a pilot who knew the coastline and river roads like he knew his toes. Larger ships, brigs, barks, frigates and so on, usually had two compasses on deck and a man-of-war might have as many as four.
A compass, by definition, is a circular box containing a fly or paper card suspended by two concentric rings or gimbals. The card is divided into 32 equal parts representing the points of the horizon. Beginning with north, south, east and west and working up to the minutia of north-north west of south. As noted, each of these positions on the compass was known as a point and was equal to 11 degrees and 15 minutes. With the addition of a magnetic needle that carries the card around with it, north can always be determined. Or almost always since there are seasonal and local variations as well as some deviation caused by metal in the ship itself.
It's a little hard to wrap your head around, isn't it? Navigation by the compass aboard a sailing ship was not a thing that could be taught in a classroom and the apprenticeship of midshipman was vital to obtaining this skill as well as many others.
The compass, being a delicate instrument, was of course easily subject to the vicissitudes of sun, sea water and weather. Partially due to this, the compass or compasses on deck were kept in a wooden box, generally with brass fittings, known as a binnacle. That word is unintentionally cute - it sounds like a good name for a puppy - and evidently derives from the French word habittacle meaning "little house". Two binnacles would be fitted near the wheel in order to check readings for accuracy. In larger ships, a third binnacle would stand in the waist of the ship and would be used by the Master as a piloting tool in open water.
The binnacle had a second purpose as well. Seamen were very distrustful of compasses. Their magnetic pull seemed almost magical and magic, as you know mate, is the tool of the Devil. Better to build a little house for the compass and keep it safely stowed where it's magic can be harnessed for the good of the ship. No reason to take chances.
As Matthew Green once rhymed: Though pleased to see the dolphins play; I mind my compass and my way.
And so should we all.