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    Re: Northern Limits of Magnetic Compass Usefulness
    From: Brad Morris
    Date: 2019 Feb 2, 15:04 -0500
    Hello Bob

    While I have no practical experience with a magnetic compass, 600 miles from the pole, I still think you will have some functionality.

    The compass may show some "dip", that is, the compass needle may no longer be parallel to the horizon.  To compensate for this, in high latitudes, the compass needle can be weighted with non-magnetic material, such as copper.  This will bring the compass needle back to horizontal.

    During the heroic age of exploration, they used a dip meter and compass to find the magnetic poles.  The Nimrod expedition, 1908, sent three men (David, Mawson and Mackay) to find it and claim it for Britain.  Which they did.   They got to within 13 nm, and then the next day, confirmed the dip to be 90°.

    Brad

    On Sat, Feb 2, 2019, 2:32 PM Bob Goethe <NoReply_Goethe@fer3.com wrote:

    I am working with Carly Butler on a thought-experiment:  a virtual journey from Vancouver, Canada, to London, England.  If one travels along the great circle route from Vanc. to London, the approximate half-way point would be in the Inuit community of Clyde River, on Baffin Island, at N 70° 28'    W 68° 34'.  From this location, it looks like one would be around 600 nm from the North Geomagnetic Pole.

    If I were to travel by land/sea to the community of Clyde River, what might I expect in terms of the behavior of my hand-compass?  When I arrive, would it be functional, impaired to some extent, or non-functional?

    If my compass is not fully functional in Clyde River, when might I imagine that my hand-compass was last useful?  Might I be able to come up with a rule of thumb, e.g. my magnetic compass will still be useful for navigation as long as I am more than "X" nautical miles from the North Geomagnetic Pole?  Alternatively, maybe the North Geomagnetic Pole is not the key location for me to keep my eye on, but the North Magnetic Pole?

    Or would my rule of thumb be better framed in terms of latitude, e.g. my magnetic compass will still be useful for navigation as long as I am below "Y" degrees of latitude?

    Thank you,

    Bob Goethe

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