DIPPING NEEDLE

An instrument for showing the direction of the magnetic force of the earth. It is a magnetic needle, furnished with an axis at right angles to its length, and pa ing as exactly as po ible through its centre of gravity, about which it moves in a vertical plane. When a needle thus mounted ^is placed any where not on the magnetic equator, it dips, or points downwards; and if the vertical plane in which it moves coincides with the maanetic meridian (which is always known by means of a variation compa ), the position which it a umes shows at once the direction of the magnetic force; and the intersection of two or more directions, found by making the experiment at different places, indicates the place of the magnetic pole. Though the principles on which the dipping needle acts are abundantly simple, its practical construction is found to be exceedingly difficult. It must be ao [s. 364]