Charlie Pridham wrote:
In article ,
says...
If I remember correctly, the metre was defined as "one ten-millionth
of the length of the earth's meridian along a quadrant (one-fourth
the polar circumference of the earth)." That seems quite sensible to
me. The fact that "imperial" measurements are still used for air and
sea travel is due to history, international convention, and the
danger involved in changing. But it will happen someday (probably
when computers rule all transportation, and measurements become
irrelevant).
In the meantime, I am happy to weigh a kilo of water when I can't
find my measuring jug, and know I have a litre (or vice-versa).
Care to do the same with imperial meaures?
--
Jeff
(cut "thetape" to reply)
You miss the point, yes the meter was supposed to be 1 millionth of
the earths circumference (but they got it wrong so it is in fact a
totally arbitrary amount) and I use only metres at home. but a
nautical mile is a rotational measurement and is defined as the
distance at the equator of 1' of longitude, and since there are 60
min in a degree and 60 sec in a min you can see the advantage a of a
distance that comes out at roughly 6000 feet! (the earth not being
perfectly round it actually varies depending on where you are)
further more a fathom at 6 feet also neatly divided but the
hydrographic office quite sensibly changed depths on charts over to
meters back in the 1970's to avoid grounding accidents as a lot of
other countries use uk charts but they did not change the distance
scales and never will as latitude and longitude is the best way of
defining your position in an empty ocean
Yes, they got the metre wrong, but that was a measurement fault, not a
design fault. It's not particularly different for the nautical mile, as you
noted (this from Wikipedia):
"The historical definition differs from the length-based standard in that a
minute of arc, and hence a nautical mile, is not a constant length at the
surface of the Earth but gradually lengthens with increasing distance from
the equator, as a corollary of the Earth's oblateness, whence the need for
"mean" in the preceding sentence. This length equals about 1,861 metres at
the poles and 1,843 metres at the Equator, a variation of one percent."
One percent; quite a variation. The original metre was out by about 0.5
mm - that's only 0.05%.
No argument about defining position in an open ocean, but it's not very
practical for trying to ascertain the distance between two points (you
wouldn't want to think about a rescue mission in terms of degrees of arc to
travel for a lifeboat or helicopter. 15.5 nautical miles (or the equivalent
in km) is more sensible).
And that is the whole point about the metric system; it is far easier to
use.
Mind you, it isn't that difficult to put the decimal point in the wrong
place ;-(
--
Jeff
(cut "thetape" to reply)