Dip Needle
Dip (or Dipping)Needle, an instrument used to measure the earth's magnetism and to detect underground magnetic materials. It works like a magnetic compass placed on its side. A magnetized needle is placed in a framework so that it pivots up and down, from a horizontal to a vertical position.
The amount of dipping increases as a dip needle is taken closer to the earth's magnetic poles. At the north magnetic pole, the needle points straight down; at the south magnetic pole, it points straight up; at the aclinic line (magnetic equator), it remains horizontal. A dip needle dips more than usual at a given location if magnetic materials, such as steel cables or cast-iron pipes, are just below the earth's surface.