Dip circles (also dip needles) are used to measure the angle between the horizon and the Earth's magnetic field (the dip angle).
Our device consists of an accurately balanced magnetic needle with a strong magnetic field, made of cobalt steel, with hardened steel pivots working in agate cup bearings.
The magnetic needle is pivoted at the centre of a circular scale, divided in four quadrants and graduated, 0-90-0-90° × 1°; for reading the inclination of the needle.
The needle can be easily removed and accurately replaced for reversal, without the risk of damage to the pivot or bearing.
The needle and the scale are housed in a non-magnetic aluminum casing with a glass window, both of which are capable of rotating about a vertical axis on a cast metal base.
The vertical rotation can be read directly from a circular scale fitted on the base.
The horizontal scale is graduated clockwise, 0-360 × 10, with a circular spirit level screwed to the face.
The base is a heavy brass tripod with three adjustable leveling screws.
When the instrument is placed with the plane of the circle in the magnetic meridian of the Earth, the needle points in the direction of the Earth’s magnetic field.