The Spinning Magnet: The Electromagnetic Force That Created the Modern World--and Could Destroy It

by Alanna Mitchell

James Clark Ross first pinpointed the Earth’s magnetic north pole in 1831.

Knowing where you were depended on being able to adjust for the difference between magnetic north, where the compass pointed, and geographical north.

I need to know physical explaination

That required understanding the strange force that pulled the compass.

Part of the answer why the diff btn mag north and geo north

British explorer Sir John Franklin vanished in the 1840s along with his 128 men and their two ships.