Re: Magnetic Polarity Re: Magnetic quenching.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 08:57 AM 4/29/2004 -0600, you wrote:
>Original poster: "teri mckenney" <mck-at-ezy-dot-net>
>Hello All,
>This is getting off topic but what I find interesting is that scientist have
>discovered by studying old lava flows that the polarity of the earth flip
>flops every so often.Something going on in the core of the earth? This would
>support an earlier post that said north and south were arbitrary.There are
>two polarity's which trade places every so often thus keeping each other
>even.
Lava flows and firing pottery:  it's the cooling while hot.

Even more OT (so Terry, kill it if you wish).. There is a reasonable 
expectation that the field will flip in the near future (possibly within 
list member's lifetime). After meandering around Hudson's Bay for 
centuries, in the last few years the N magnetic pole has started heading 
south, fast (many km/year).  The field has probably NOT changed polarity 
since the common use of the magnetic compass (say, the last few thousand 
years).

For what it's worth, the earth's magnetic field is actually not very well 
represented by a simple dipole field, although that makes for a nice photo 
in the science book.  People who depend on the earth's magnetic field (e.g. 
satellites using magnetic torquing) use better models.

Moral of the story...

Keep a battery around (electrons aren't likely to change the sign of their 
charge any time soon), a hunk of wire, and you've got a dandy "compass 
direction calibration" system.