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    Re: Test your magnetic compass.
    From: Alexandre Eremenko
    Date: 2012 Nov 16, 22:10 -0500

    > Power lines almost always carry alternating current
    > and so could be expected to have a magnetic field alternating
    > at 50 or 60 Hz and I would not expect an effect on a magnetic compass.
    That power lines in MY appartment have an effect is an experimental fact,
    of which I have no explanation:-) In the immediate vicinity.
    > Like Byron, I believed that magnetic force between two
    > magnets varies inversely as the square of the distance between them, but
    > the Admiralty Manual of Navigation 1970 (B.R.45 (1) states  that "...the
    > field strength due to a short magnet varies inversely as the cube of the
    > distance from the magnet..."
    Admiralty manual is right:-) See for example, "Magnetic dipole" on
    Wikipedia. This explains, by the way, the fact which puzzled me a lot in
    my childhood: how can steel ships use magnetic compass ?

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