An Encyclopaedia of Indian Archaeology v1.c10.s2.1

v1.c10.s2.1

Written record of magnetic data from various parts of the world is available only from the last century. But earlier records have been preserved in baked clay objects which have remained in position after cooling down. This property is called thermoremanent magnetism and is induced in iron oxide minerals in the clay by the geomagnetic field as they cool from temperature of 700°C and above. During the process of cooling baked clay acquires a weak but permanent megnetization in the direction of and in intensity proportional to the ambient field.