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Re: Polar Confusion (was Earth's Magnetic Field)

This kind of gibberish that Larry (see the copy at the bottom) has found
in the instructions for "The Model 28000 Magnetizer" is exactly why I'm
afraid to let students read instructions that come with equipment before I
have a chance to do the same. You should see the nonsense that comes with
some of our demonstration compasses. From the inappropriate tense and
ordering of the explanations, I usually assume that the text was
originally written in some other language (commonly Chinese) and then
"transliterated" into something approximating English. But this would
hardly explain the errors in science of which they are mostly composed.

I goes like this: (BTW: If you want a really complete explanation see
Benjamin Franklin's "On the Magnetics of Compasses".)

The north end of a compass needle was chosen as north because that's the
geographic direction to which the point of a proper compass needle will
orient itself. And that simple statement DEFINES the magnetic poles of a
compass. We are the ones that have selected the the direction of the
magnetic field lines --- we could have as easily chosen the reverse.
[Notice that I will slip to the singular word definition (as opposed to
definitions), as does Franklin, because defining one end of a compass
needle (pole) as north necessarily defines the other end (pole) as south.]
Once this definition has been made, it necessarily follows that the "north
geographic pole" is in actuality a "south magnetic pole" and the "south
geographic pole" is in actuality a "north magnetic pole".

Also, let me assure you that sailors are rarely "confused when directed to
steer a course". This despite the US Army's statement to Congress that
they can only train approximately 18% of the GI's (General Inductees) to
properly use a compass. It was this statement that lead to the
developmental funding for "miniaturizing" the GPS Location Device. This
is why these boxes are now available at such a low cost (I just talked to
a friend that received one free from Shell Oil in some promotion).

And I cannot pass up the opportunity to point out that we train every Boy
Scout you'll meet to use a compass very effectively or they don't even
make Tenderfoot.

+=================================++=================================+
ERTEL SENDS.
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===========================
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+==================================================+
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| Physics Department, 9C Office : 410-293-6657 |
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On Mon, 10 May 1999, Larry Smith wrote:

Seems like this topic has come up before, but I just received a shipment of
new equipment for our lab and read the following in the instructions for
the Electro-Technic Magnetizer:

-------begin quote------
The convention for marking polarity for compass needles is to mark the pole
seeking the Earth's north magnetic pole with a "N". That way sailors are
not confused when directed to steer a course. The convention for marking
bar magnets is such that a compass needle will point in the direction of
the lines of flux as though they were traveling from the "N" pole to the
"S" pole. This places the "N" at the end of the bar that if suspended as a
compass needle will point north. Relative to the Earth's magnet field, a
Nort seeking pole has to be the south pole of the bar. Opposite poles
attract. Even so, the convention is to makr it "N".

The Model 28000 Magnetizer is marked with a "N" on the right side and a "S"
on the left. When operated, the magnet produced causes a compass needle's
north seeking pole to point to the end placed into the "N" cavity. A
magnet produced by the magnetizer if suspended by a string woudl point the
end marked "N" to the south which is exactly opposite to the convention.

The logic for doing it this way is that most customers are unaware of the
convention, and in the beginning one of our distributors complained when a
magnet thus produced caused a compass needle's "N" pole to be attracted to
the "S" pole of the magnet. We did some testing and discovered that most
inexpensive magnets are made with the polarity reversed. So
Electro-Technic bowed to the popular perception even thought it is counter
to the convention. IN all the years and thousands of magnetizers sold, the
number of complaints about polarity have been very few.

For some, this may pose a problem. If you have inadvertently magnetized
your magnet backwards, and have been inconvenienced by this problem, we
apologize. If you want to reverse it, simply magnetize it correctly by
placing the magnet pole marked "N" into the "S" cavity of the magnetizer
and the magnet produced will be configured in accordance with the
convention.
---------end quote-------

If I'm even understanding this clearly, it seems to be backward to the way
H&R and Serway have it. True, a convention is just a convention, and we
could have done it the other way; so I don't care which way we decide to do
it, as long as we can all agree together. What is the vote on this list
for the convention?

Thanks,
Larry Smith