An Explorer’s Best Friend

15 November 2007

The lodestone: objects with which I expect few people are familiar, and yet which have undoubtedly shaped our past.

These lumps of magnetised magnetite (iron oxide) signify the foundations of our understanding of magnetism. They are the only source of natural magnetic material on earth, and were first used by the Ancient Greeks – in fact, the name ‘magnet’ refers to the area of Magnesia in central Greece where lodestones were found. They were used at this time, among other things, to cure headaches! However, the legend goes back much further. The Egyptian Queen Cleopatra was reputed to have worn a lodestone while sleeping to minimise the signs of aging. Superstitions surrounding this fascinating material continued until the time of William Gilbert. He was able to dispel these myths in his work De Magnet where he noted The application of loadstones to all sorts of headaches no more cures them (as some make out) than would an iron helmet or a steel cap.”

These stones are not just any old iron oxide, however. The correct crystalline structure must be present, and it is now also thought that the properties are only revealed once the stone has been struck by lightning, something that Gilbert hinted at when describing iron “magnetised like a lodestone after being struck on a church spire.”

Chinese scientists at around the year 1000 revealed that lodestones could magnetise iron, and pointed south if floated in a bowl of water, and by the 12th century they were being used for navigational purposes. It was this experimentation with lodestones, which eventually led to the development of the magnetic compass by the Chinese.

Hence why lodestones were fundamental in shaping our past – if the Greeks and then Chinese had not discovered these natural magnets, it is very unlikely that compasses would have been invented in time for the likes of Christopher Columbus, resulting in a rewriting of the history books. Three cheers for the humble lodestone!