Articulo de magnetismo

˜ ENSENANZA

REVISTA MEXICANA DE F´ ISICA E 50 (1) 51–53

JUNIO 2004

Mexico and the early history of magnetism∗
A.P. Guimar˜ es a Centro Brasileiro de Pesquisas F´sicas ı Rua Xavier Sigaud 150, Rio de Janeiro - 22290-180, Brazil
Recibido el 30 de mayo de 2003; aceptado el 17 de septiembre de 2003 The phenomenon of magnetism has been known by mankind for more than three thousand years.This fact is documented in references to the naturally occurring magnetic mineral magnetite (the iron oxide Fe3 O4 ) in clay tablets in ancient Mesopotamia, as early as the second millennium BC. Less known, however, is the possible evidence for the knowledge of the magnetic properties of rocks by the peoples of pre-Columbian America. In fact, archaeologists have found in Olmec sites in Mexico manyobjects made of iron ore that may reveal an early acquaintance with magnetism. The Olmecs constituted the first complex culture that appeared in the Americas, before 1000 BC, in the east coast of Mexico. Among these objects, there has been found a polished bar that is magnetic, dating from 1400-1000 BC, which has led to speculations that it may have been part of a magnetic compass, one thousandyears before the first Chinese compasses were made. Keywords: Magnetism; Olmecs; Mexico. El fen´ meno del magnetismo ha sido conocido por la humanidad hace m´ s de tres mil a˜ os. Esto est´ documentado por referencias a la o a n a ´ magnetita (el oxido de hierro Fe3 O4 ), mineral magn´ tico encontrado en la naturaleza, en tablas de arcilla de la Mesopotamia antigua, que e son del segundo milenio AC.Menos difundida es la posible evidencia del conocimiento, de los pueblos de Am´ rica pre-Colombina, sobre e las propiedades magn´ ticas de las rocas. Arque´ logos han encontrado, en sitios Olmecas en M´ xico, varios objetos hechos en minerales que e o e contienen hierro y que podr´an revelar familiaridad de esta civilizaci´ n con el magnetismo. Los Olmecas fueran la primera cultura elaborada ı o queapareci´ en Am´ rica - antes de 1000 AC - en la costa oriental de M´ xico. Entre los objetos se encontr´ una barra pulida magn´ tica, o e e o e datada de 1400-1000 AC, y que dio lugar a la especulaci´ n de que ser´a parte de un comp´ s magn´ tico, mil a˜ os antes de la construcci´ n de o ı a e n o las primeras br´ julas chinas. u Descriptores: Magnetismo; Olmecas; M´ xico. e PACS: 91.60.Pn;01.65.+g; 91.25.Ng

1. The Olmecs
The first complex culture that appeared in the Americas was that of the Olmecs, in about 1400 BC, centered in the coastal areas of east Mexico, in the present states of Veracruz and Tabasco [1,2]. The name Olmec means ’inhabitants of the region of the rubber plant (hule)’. The main sites are along the Gulf of Mexico: San Lorenzo, La Venta, Laguna de los Cerros andTres Zapotes. They show in their sculptures a distinct art style, with a special way of treating volumes, and with a predominance of human figures. Some of these figures have characteristic baby faces, frequently with mixed jaguar traits (“were-jaguars”). The relation of kinship with the jaguars was apparently part of the myths of creation of the Olmecs. The archaeological remains of the Olmec cultureshow that this society was able to mobilize manpower in large scale for building and earth-moving work. Some of the most remarkable finds left by the Olmecs are their characteristic colossal stone heads, weighing up to 50 tons; some sixteen of those have been found. The stone for these monumental sculptures in one site was quarried some 80 km away, in the Tuxla Mountains, floated down a river anddragged overland, an amazing feat in itself. The Olmecs influenced the later civilizations that developed in Mesoamerica, especially the Mayas. For this reason they were traditionally described as a ”mother” culture, although the present trend is to value the importance of the mutual influences between the different Mesoamerican cultures [1].

Many authors attribute to the Olmecs the creation of...