In the 19th century, the rising use of iron in ship construction began to influence the accuracy of the magnetic compasses, since the creation of magnetic fields in ships made the needles to deviate from the direction of the north in an unpredictable way. In order to solve this new problem, Scotch physicomathematician Sir William Thomson (1824-1907) designed the binnacle; internally it included corrective magnets and externally 2 spheres of soft iron (green on the right and red on the left) in order to counterbalance the influence of the ship’s metals. The compass was no longer a simple needle but a light circular calibrated-per-degree disk inside a container with liquid, supported on a 3-axis suspension system so that the disk would always remain in horizontal position without being influenced by the movements of the ship.

In addition, the binnacles have on their top a rotating bronze sunshade (non-magnetic material) so that their indicator is better visible. Their basis is wooden so that magnetism is not created.

Despite the absolute prevalence now of the more accurate gyroscopic compasses, the magnetic compasses remain necessary emergency equipment for contemporary ships.