Magnetism, from the Dawn of Civilization to Today
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The historical approach of this chapter introduces qualitative ideas which will be reconsidered and analysed in later chapters. The great adventure of magnetism has progressed, slowly at first, following the pioneers who lived long ago at Sumer, in China or in Greece, while the last two centuries have witnessed an explosion in knowledge, investigative techniques, and industrial applications in this model domain of Science. In 1779, the Encycloptedia of Diderot and d'Alembert [ 1] still said about magnetite: "It is in this metal married with salt and oil rather than in stony substances that resides true magnetism" We have come a long wa~ in the years that followed... !
1.
THE DISCOVERY OF LODESTONE AND THE OBSERVATION OF MAGNETIC PHENOMENA THROUGH THE AGES
The oldest manuscript that mentions the existence of lodestone is the work of a Chinese writer, Guanzhong (died 645 BC), but objects made from magnetic materials have been found in archaeological sites dating from much further back.
1.1. OBJECTS MADE FROM IRON AND LODESTONE IN ANCIENT TIMES Small tubular beads made from iron of meteoritic origin (containing at least 7.5% nickel) were discovered in many Sumerian and pre-dynastic Egyptian tombs (fourth millenium BC). These appear to be the oldest traces of ferromagnetic objects wrought by human hands. The question remains, however, as to whether their "attractive properties" had been discovered in these distant times. The ancient Egyptians, who
MAGNETISM- FUNDAMENTALS
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called iron bia-n-pet (=metal from the sky), did not study the metallurgy of iron until relatively late, and certainly after the Hittites, who did so about 1500 BC; the tomb of Tutankhamon (1340 BC) already contained a dagger and various other objects made of iron and iron ores [2]. Much later, in the temple of Edfu, an inscription mentions "living metal": this was the expression of the ancient Egyptians for lodestone [3]. In Crete, at the palace of Knossos (2000 BC - 1300 BC), the throne room of Minos is paved in the centre with a rectangular flagstone made of iron oxide, consisting mainly of magnetite. Perhaps this was not a random choice, it is possible that the ancient Cretans understood its magnetic properties, which could justify its presence in such a central part of the palace.
1.2. THE FIRST TEXTS DEALING WITH LODESTONE. ORIGIN OF THE NAME "MAGNETISM" Ali our information on the origins of magnetism in China were taken from the Chinese work The History of Electromagnetism [4] as well as from a recent work by M. Soutif on the origins of Science and Technology in the East [5]. We know from Guanzhong that, in ancient Chinese civilization, lodestones were called "soft stones". This is the general name of ali strongly magnetic oxides existing in nature and having a permanent magnetic character. They are the magnetic minerals based on iron: y-Fe203, FeO-Ti02-Fe203, sometimes also FeSt+x• and especially magnetite Fe304. The name "soft stones" is due to their attraction for ferrous metals, in analogy with the tenderness that a mother shows h
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