The Earth’s Magnetic Field
The earth behaves like a giant magnet with its south pole in the northern hemisphere and North Pole in the southern hemisphere. It produces a magnetic field which is a weak field but is strong enough to cause a compass needle to set in the north south direction.
Magnetic Element of a Place
These are angle of declination, angle of dip and the horizontal component of the earth magnetic field.
A freely suspended magnet will come to rest with its axis pointing in the north south direction, since it is under the influence of earth magnetic field.
The vertical plane through the magnetic axis of a magnet is called magnetic meridian.
The geographic meridian is the vertical plane passing through the geographic north and south poles of the earth.
The angle of declination is the angle between the magnetic and the geographic meridian, it varies from place to place. Place on earth surface with the same angle of declination are joined by a line called isogonal line
Magnetic and geographic meridian coincides at place where angle of declination is zero (0).
The isogonal of places with zero declination is called agonic line
Angle of Dip or Inclination:
This is the angle between the direction of the earth’s resultant magnetic field and the horizontal.
Horizontal and Vertical Components of the Earth Magnetic Field
The earth magnetic field can be resolved into two since it is a vector quantity.
Horizontal component (H) of the earth field is the magnetic force acting in a horizontal direction.
The vertical component (V) of the earth field at a point is the magnetic force acting in a vertical direction.