This is an early example of a compass and binnacle patented in 1876 by Sir William Thomson (later Lord Kelvin) to overcome one of the main navigational problems of the 19th century. The growing use of iron in the construction of ships affected the accuracy of the compass, as attraction by the iron caused compass needles to deviate from magnetic north in unpredictable ways. In response, the Scottish mathematician and physicist Sir William Thomson (1824-1907) developed a new compass housing, or binnacle, to overcome this problem. He incorporated corrector magnets and iron spheres to counteract the effects of the ship's iron, a light card with small needles ( less subject to oscillation and wear than the cards previously used), and improved gimbals to keep the compass level.
The binnacle has a wooden pedestal and a brass top. The design includes a heeling error gauge in the side of the pedestal and two soft iron spheres on brackets. The correcting magnets are carried in a rack on a centre spindle, by which they can be raised and rotated. There are two brass lamp holders on the side of the top to provide additional lighting at night.
The dry card compass is mounted on gimbals. It has eight small needles (rather than a single needle), which are hung very close to the bottom of the bowl. The card is made of paper that is attached to silk threads that run from the centre boss to an aluminium ring that forms the rim. This design was intended to be very light. The card is graduated both in degrees and compass points.