Agonic line

The locus of points on the earth's surface where the magnetic needle points to the true north; an imaginary line determined by connecting points on the earth's surface where the needle lies in the true geographical meridian. Such a line at present, starting from the north pole goes through the west of Hudson's Bay, leaves the east coast of America near Philadelphia, passes along the eastern West Indies, cuts off the eastern projection of Brazil and goes through the South Atlantic to the south pole. Thence it passes through the west of Australia, the Indian Ocean, Arabia, the Caspian sea, Russia and the White sea to the North Pole. It crosses the equator at 70° W. and 55° E.approximately. (See Magnetic Elements)

Synonym: Agone.

[Transcriber's note: The file Earth_Declination_1590_1990.gif provided by the U.S. Geological Survey ( is an animation of the declination of the entire earth.]