1.Introduction It is now generally recognized that measurements of the directions of magnetisation of samples from a magnetically stable rock formation allow the direction of the Earth’s magnetic field at the time wh...1.Introduction It is now generally recognized that measurements of the directions of magnetisation of samples from a magnetically stable rock formation allow the direction of the Earth’s magnetic field at the time when the rock was formed to be determined.The direction of the Earth’s magnetic field has been recorded at observatories in many places over the past few hundred years,and from an analysis of these records it is possible to recognise two components in the geomagnetic field:the first being approximately that of a dipole at the centre of the Earth with its axis along the axis of rotation,and the second a much smaller non-dipole component which undergoes variations with periods of the order of hundreds of years.展开更多
文摘1.Introduction It is now generally recognized that measurements of the directions of magnetisation of samples from a magnetically stable rock formation allow the direction of the Earth’s magnetic field at the time when the rock was formed to be determined.The direction of the Earth’s magnetic field has been recorded at observatories in many places over the past few hundred years,and from an analysis of these records it is possible to recognise two components in the geomagnetic field:the first being approximately that of a dipole at the centre of the Earth with its axis along the axis of rotation,and the second a much smaller non-dipole component which undergoes variations with periods of the order of hundreds of years.
