Isogonic Lines of Earth

“The magnetic poles of the earth do notc oincide with its geographical poles and, condequently, in some places, the magnetic needle does not point ot the geographical north. The angle that the axis of a compass-bneedle makes with the geographical meridian at any place is called the declination or variation of the needle at that place...Lines drawn through places on the earth where the declination is the sam are called isogonic lines, as shown.” -Avery 1895

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