The shape of Earth’s magnetic field is approximately similar to the magnetized ball’s field. Earth’s magnetic poles drift slowly. Presently they are close to geographic poles. According to Canada’s geologic survey, has Earth’s magnetic South Pole drifted with a mean speed of about 11 km/year in the past century? It should be noted that since 1970, the speed has increased up to 40 km/year. One hundred years ago, the magnetic South Pole was located about 1900 km from the geographical North Pole. In 2005 the distance was decreased to 800 km. The value of the induction of Earth’s magnetic field changes slowly in time, as well. It has decreased by about ≈10 % in the past one hundred and fifty years.
On the magnetic equator, magnetic induction of Earth’s magnetic field is directed horizontally and vertically on magnetic poles. In other places of our planet, the vector of magnetic induction is tilted concerning the vertical direction, i.e., it has both horizontal and vertical components. The direction of the horizontal component of the induction of Earth’s magnetic field is also called the direction of a magnetic meridian. The angle of inclination (angle β in figure 1) is the angle between the direction of the horizontal component of Earth’s magnetic induction and horizontal plane. The angle between geographic and magnetic meridians in the same place is called the angle of declination. The magnetic needle that can rotate around its vertical axis only turns in the horizontal plane due to the horizontal component BH of Earth’s magnetic field. This property of the magnetic needle (compass needle) is exploited in a tangent galvanometer for measuring the horizontal component of Earth’s magnetic field. Note that in the whole work, the horizontal component of the induction of Earth’s magnetic field is referred to as the horizontal component of Earth’s magnetic field.