II—The Use of Compasses in High Latitudes

The Earth's magnetic field can evidently be divided into its horizontal and vertical components, the horizontal component being of more immediate interest to the navigator since it directs the compass needle in the horizontal plane. Whereas on the magnetic equator the full field is horizontal (about 0·400 c.g.s. units), in high latitudes, with the angle of dip between 60° and 70°, H, the horizontal force, maybe about 0·180 c.g.s. units. At the magnetic pole H is negligible and, given the opportunity, the compass needle would point vertically downwards, the instrument then having no directional properties in the horizontal plane.