Perhaps because there are few things as fascinating as observing the behavior of a pair of magnets, magnetism has always been shrouded in mystery. For the ancients it was the palpable proof of the existence of invisible forces around us. Is there anything more amazing to observe than a piece of iron mysteriously attracted to a magnet? Or feel an invisible opposition when we try to bring the north poles of two of them closer together?
Like all mysteries, the history of magnetism begins with a legend . In ancient Greece there lived a boy named Magnus . One day while tending his flock he put the tip of his metal cane on a large rock. The crook stuck to her with such force that the poor shepherd boy could not retrieve it. A small payment for going down in history as the discoverer of a rock with magical properties, named magnetite in his honor. Obviously, it’s all a fable. The word magnetism most likely comes from the Greek Magnesia region, where these stones were first found.
Magnetism in China
The Chinese also knew about this phenomenon. In the second century a. C. discovered that an elongated piece of magnetite floating in a bucket of water was aligned in a North-South direction . This finding was apparently a by-product of the superstitious practice known as geomantic divination, which involved throwing objects such as stones or engraved bits of metal onto a table in order to predict future events based on their position. In 376 BC, General Haung Ti used this curious property to lead his army , but surprisingly, the Chinese did not use it for maritime navigation until 900 years later. Shortly after, it was imported by the Arabs and, with them, it passed to Europe.
In the 13th century, while European ships were being equipped with the new instrument, the Frenchman Peter Peregrinus de Maricourt was investigating the nature of magnetism. It is not known when he was born or anything about his personal life; in fact we only know about him from what Roger Bacon wrote in his Opus Maius . We only know his treatise Epistola de Magnete , which we can date to 1269 because in one of the few surviving copies it appears at the end: “ Actum in castris in obsidione Luceriæ anno domini 1269 º 8 º filière August i” (Done in the camp during the siege of Lucera, August 8, 1269). This ‘letter’ reveals an impressive experimental finesse : it describes the detailed studies he carried out with the compass and reveals how he discovered the existence of the two magnetic polarities, which he designated north and south poles. In his opinion, the mysterious forces that compelled the iron to move towards the magnet were similar to those that compelled the planets and the Sun to revolve around the Earth.
The credit belongs to the Olmecs
Now, were the Chinese really the inventors of the compass? The most possible is that no. In 1968 archaeologists P. Krotser and MD Coe of Yale University found a curious object during the course of an excavation in an Olmec settlement in San Lorenzo, Veracruz (Mexico). It was made of hematite, a material that had been used extensively in the construction of some of the city’s buildings, such as the so-called Red Palace. Dated between 1,400 and 1,000 BC, it seemed to Coe to be a compass. Willing to check it, he placed it on a cork and floated it in a bowl of water: it immediately turned north . In 1975 astronomer John Carlson hypothesized that the Olmec might have used it as a geomantic tool, just like the Chinese.
Be that as it may, this object shows that the discovery of the compass must be delayed almost a thousand years and placed on another continent.
References
Bernal, JD (1976) Social history of science (volume I), Peninsula Editions
Boorstin, DJ (1986) The Discoverers, Review
Carlson, JB (1975) Lodestone Compass: Chinese or Olmec Primacy? Science, 89:4205, 753-760 DOI: 10.1126/science.189.4205.753
