Lodestone in silver case with keeper, 1762.
© Science Museum / Science & Society Picture Library
This lodestone formed part of the mechanics apparatus made by George Adams, instrument maker to the king, for King George III. It consists of a piece of natural magnetite in a silver case, elegantly engraved with the royal coat of arms. The lodestone was balanced on one arm of a beam. Then a piece of iron or steel was brought into position beneath the lodestone. The resulting downward force was balanced by adding weights to the other arm, thus weighing the magnetic attraction.