Mexico and the early history of magnetism*

Abstract

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 Fe$_3$O$_4$) 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 many objects 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 thousand years before the first Chinese compasses were made.