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From: RS Peterson (no email)
Date: Fri May 07 2004 - 17:32:20 EDT
Brooke --
This one I can't resist, so I'll make my own WAG (Wild A_ _ Guess). An
interesting reference "Magnetic Compasses and Magnetometers" by Alfred Hine
refers to two instruments for the purpose of measuring the magnetic variation
and horizontal intensity. On a steel ships (soft iron) this would be
necessary for determining the magnetic shielding around a binnacle and part
of the compass adjusting process. The shielding is a different influence
from the "heeling error" correction which is even more important for compass
adjusting on steel vessels.
First: a Kew magnetometer -- uses a thread mounted magnet to measure the
horizontal swing and thus variation. Totally useless on a pitching ship so
this is strictly land based.
Second: (and more interesting) a "sea deflector" -- standard type flat-top
compass that has a deflecting magnet (oriented horizontally) of known
strength mounted vertically above the compass axis. The effect of the known
magnet will deflect the compass card to reflect the horizontal strength of
the surrounding magnetic field. The "sea deflector" works by changing the
strength of the known magnet; however, this same influence is possible by
varying the distance of the standard magnet. This is how I think this
Russian instrument works. The vertical "tower" holds a horizontal "magnet
cage" which can be moved up or down to force a standard deflection of the
main compass. The closer the distance to the compass magnets the greater the
swing. Of course, the "B" and "C" coefs need to be taken into account. The
horizontal intensity, H, is given by:
H =MC/sin(alpha)
M = the moment of the deflecting magnet
C = constant depending on the distance of the magnet and measured ashore
alpha = deflection angle.
If you're willing to risk the shipping and the long wait, this looks like a
steal at $200. If my wife had not sworn me to "no more additions to the
collection", I'd make a run at this. It looks very interesting. And I'd
like to hear those more expert than I on their take.
-- Bob Peterson
On Friday 07 May 2004 12:00 pm, Brooke Clarke wrote:
> Hi:
>
> How is this used?
>
> eBay item 3721631458
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=37967&item=372163145
>8
>
> Thanks,
>
> Brooke Clarke, N6GCE
> http://www.PRC68.com
-- Robert S. Peterson 31 N Alfred, Elgin IL 60123 USA 847/697-6491 Compass Adjusting for Lake Michigan navigators since 1985 Physics @ Bartlett HS e-mail: rpeterson(at)enc.k12.il.us
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