On Thu, 13 Nov 2003 17:48:04 GMT, "BruceS" wrote:


"Gene Nygaard" wrote in message
news
On Thu, 13 Nov 2003 16:05:24 GMT, "BruceS" wrote:


"Phred" wrote in message
...
In article , "John Gilmer"
wrote:



Might the "hand", being almost exactly 0.1 meters, end
up one day as a handy nickname for the decimeter?

Maybe.

After what those dirty rats did to the nautical mile (no longer 6280')
anything is possible!

Must say I always thought the nautical mile was 6080 feet. But, yes,
even so, that "approved" definition of 1852 m is only about 6076 feet
http://physics.nist.gov/cuu/Units/outside.html
so I could now miss my favourite coral trout bombie by 40 feet! :-(

AIUI, the nautical mile is one of the few "old" measures with a rational
basis. It is the distance along the Earth's circumference at the equator
that equals one minute of arc.

No, it is not.

There were some geographical miles based on the equatorial
circumference; the ones I have seen used were 4 minutes of arc, or
about 7.421 km. But nautical miles are not and never have been based
on the equator.

A minute of arc at sea level on the equator is about 1855.325 m, or
6087.023 ft. That's 1.0018 international nautical miles, or 1.0012
U.K. Admiralty miles, or 1.0011 of the old pre-1954 U.S. nautical
miles.

However, if you go north and south across the equator, a minute of arc
(for the normal geodetic latitudes) is less than 0.9950 international
nautical mile.

Show me anybody's nautical mile that was equal to a minute of arc on
the equator.

Try these:
http://dnr.cbi.tamucc.edu/Waves/Naut...on?action=diff
http://people.howstuffworks.com/question79.htm
http://www.tpub.com/content/engineer.../14071_198.htm
http://www.subsowespac.org/wwwboard/messages/269.html

You've got to learn to do a better job evaluating the credibility of
your sources.

Go look up the radius of the Earth at sea level at the Equator, or
the circumference there. You can find it in most printed
encyclopedias or almanacs, or at thousands of sites online, with
slightly varying numbers based on various reference ellipsoids that
have been used over the years. No, it isn't anywhere near the 40,003
km that one of your sources above stole from the other. It is about
40,075.0 km to 40,075.2 km on all the 20th or 21st century ellipsoids.
For example, an equatorial radius of 6378.137 km in WGS-84, or a
radius of 6378.160 km in Geodetic Reference System 1967.

Then do the math yourself. How long is one minute of arc at the
equator, in terms of meters or feet?

Gene Nygaard

"It's not the things you don't know
what gets you into trouble.

"It's the things you do know
that just ain't so."
Will Rogers


If there is a need to make the relation of
meter to nautical mile use fewer digits, it is the meter that should be
adjusted. I'm outraged, simply outraged, that the noble nautical mile
should
be compromised for the benefit of the lowly meter.

We don't have a perfectly round earth. That's the problem.

Do you have a proposal to correct this problem?

The meter, exactly like the nautical mile, and unlike feet and statute
miles, *is* based on the Earth.

A centigrade is to a kilometer as a nautical mile is to a minute of
arc.

So if they were based on the same midrange value, or if we really had
a perfect sphere for the Earth, we would have 1 km = 0.54 nmi exactly.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/