Lodestone

Origin

The process by which lodestone is created has long been an open question in geology. Only a small amount of the magnetite on the Earth is found magnetized as lodestone. Ordinary magnetite is attracted to a magnetic field as iron and steel are, but does not tend to become magnetized itself; it has too low a magnetic coercivity, or resistance to magnetization or demagnetization.{{cite book

The other question is how lodestones get magnetized. The Earth's magnetic field at 0.5 gauss is too weak to magnetize a lodestone by itself. The leading theory is that lodestones are magnetized by the strong magnetic fields surrounding lightning bolts. Magnetite is a ferrimagnetic material, so a lightning strike can align its magnetic domains and create a lodestone.{{cite book | editor-last1 = Kirschvink | editor-first1= J. L. | editor-last2 = Jones | editor-first2= D. S. | editor-last3 = MacFadden | editor-first3= B. J. This is supported by the observation that they are mostly found near the surface of the Earth, rather than buried at great depth.

History

One of the earliest known references to lodestone's magnetic properties was made by 6th century BC Greek philosopher Thales of Miletus, whom the ancient Greeks credited with discovering lodestone's attraction to iron and other lodestones. The name magnet may come from lodestones found in Magnesia, Anatolia. The ancient Indian medical text Sushruta Samhita describes using magnetic properties of the lodestone to remove arrows embedded in a person's body.

The earliest Chinese literary reference to magnetism occurs in the 4th-century BC Book of the Devil Valley Master (Guiguzi). In the chronicle Lüshi Chunqiu, from the 2nd century BC, it is explicitly stated that "the lodestone makes iron come or it attracts it." The earliest mention of a needle's attraction appears in a work composed between 20 and 100 AD, the Lunheng (Balanced Inquiries): "A lodestone attracts a needle." In the 2nd century BC, Chinese geomancers were experimenting with the magnetic properties of lodestone to make a "south-pointing spoon" for divination. When it is placed on a smooth bronze plate, the spoon would invariably rotate to a north–south axis. While this has been shown to work, archaeologists have yet to discover an actual spoon made of magnetite in a Han tomb.

Based on his discovery of an Olmec artifact (a shaped and grooved magnetic bar) in North America, astronomer John Carlson suggests that lodestone may have been used by the Olmec more than a thousand years prior to the Chinese discovery. Carlson speculates that the Olmecs, for astrological or geomantic purposes, used similar artifacts as a directional device, or to orient their temples, the dwellings of the living, or the interments of the dead. Detailed analysis of the Olmec artifact revealed that the "bar" was composed of hematite with titanium lamellae of Fe2–xTixO3 that accounted for the anomalous remanent magnetism of the artifact.

"A century of research has pushed back the first mention of the magnetic compass in Europe to Alexander Neckam about +1190, followed soon afterwards by Guyot de Provins in +1205 and Jacques de Vitry in +1269. All other European claims have been excluded by detailed study..."

Lodestones have frequently been displayed as valuable or prestigious objects. The Ashmolean Museum in Oxford contains a lodestone adorned with a gilt coronet that was donated by Mary Cavendish in 1756, possibly to secure her husband's appointment as Chancellor of Oxford University. Isaac Newton's signet ring reportedly contained a lodestone which was capable of lifting more than 200 times its own weight. And in 17th century London, the Royal Society displayed a 6 in spherical lodestone (a terrella or 'little Earth'), which was used to illustrate the Earth's magnetic fields and the function of mariners' compasses. One contemporary writer, the satirist Ned Ward, noted how the terrella "made a paper of Steel Filings prick up themselves one upon the back of another, that they stood pointing like the Bristles of a Hedge-Hog; and gave such Life and Merriment to a Parcel of Needles, that they danc'd [...] as if the devil were in them."

References

References

1. Du Trémolet de Lacheisserie, Étienne. (2005). "Magnetism: Fundamentals". Springer.
2. Dill, J. Gregory. (Jan–Feb 2003). "Lodestone and Needle: The rise of the magnetic compass". Navigator Publishing.
3. Merrill, Ronald T.. (1998). "The Magnetic Field of the Earth". Academic Press.
4. Needham, Joseph. (1986). "The Shorter Science and Civilization in China". Cambridge Univ. Press.
5. (2009). "Lodestone". Merriam-Webster, Inc..
6. {{OED. lodestone: 'Literally 'way-stone', from the use of the magnet in guiding mariners.'
7. Brand, Mike. (1995). "Lodestone". US National High Magnetic Field Laboratory.
8. Keithley, Joseph F.. (1999). "The Story of Electrical and Magnetic Measurements: From 500 B.C. to the 1940s". John Wiley and Sons.
9. (28 May 2005). "Magnet". Language Hat blog.
10. The section "Fanying 2" ([[:s:鬼谷子. 反應第二]]) of ''The [[Guiguzi]]'': "{{lang. zh. 其察言也，不失若磁石之取鍼，舌之取燔骨".
11. Dillon, Michael. (2017). "Encyclopedia of Chinese History". Routledge.
12. Li, Shu-hua. (1954). "Origine de la Boussole II. Aimant et Boussole". Isis.
13. In the section "[https://archive.org/stream/lunheng02wang#page/350/mode/1up A Last Word on Dragons]" ({{lang. zh. 亂龍篇 ''Luanlong'') of the ''[[Lunheng]]'': "[[Amber]] takes up straws, and a load-stone attracts needles" ({{lang. zh. 頓牟掇芥，磁石引針).
14. Tom, K. S.. (1989). "Echoes from Old China: Life, Legends, and Lore of the Middle Kingdom". University of Hawaii Press.
15. Qian, Gonglin. (2000). "Chinese Fans: Artistry and Aesthetics". Long River Press.
16. Curtis Wright, David. (2001). "The History of China: (The Greenwood Histories of the Modern Nations)". Greenwood Publishing Group.
17. Joseph Needham, ''Clerks and Craftsmen in China and the West: Lectures and Addresses on the History of Science and Technology''. Cambridge: University Press, 1970, p. 241.
18. (1975). "Lodestone Compass: Chinese or Olmec Primacy?: Multidisciplinary analysis of an Olmec hematite artifact from San Lorenzo, Veracruz, Mexico". Science.
19. [http://deepblue.lib.umich.edu/bitstream/handle/2027.42/23074/0000648.pdf?sequence=1 Evans, B. J., ''Magnetism and Archaeology: Magnetic Oxides in the First American Civilization,'' p. 1097, Elsevier, Physica B+C 86-88 (1977), S. 1091-1099]
20. Needham, ''Clerks and Craftsmen'', p. 240.
21. Kell, Patricia. (1996). "Inv. 47759 - Sphaera article".
22. Thompson, Sylvanus. (1891). "The Electromagnet, and Electromagnetic Mechanism". E. & F. N. Spon.
23. "A terella".
24. Fara, Patricia. (1996). "Sympathetic Attractions: Magnetic Practices, Beliefs, and Symbolism in Eighteenth-Century England". Princeton University.