In article ,
says...

'Charlie Pridham[_2_ Wrote:
;773663']Doesn't work at sea though! chains, cables, fathams and
nautical miles
all work exactly with the size of the earth, meters don't work at all
and
french ships have a much harder job of trying to navigate in metres
which
all has to be corrected and adjusted to fit :~)
Well nautical miles are metric and have nothing to do with fathoms. And
metres should have been good, but got buggered by the perverse use of an
old Babylonian measurement of angle, the degree, with 90 to the right
angle. (360 was a significant number in the Babylonian base 60/base 6
system).

A metre was originally defined in Napoleonic times as 1 ten-millionth
of the distance from the equator to the pole (ie 10,000 km from pole to
equator). In fact they were ever so slightly out, it's actually about
10,002 km, (or 40,007km around a circumference through the poles). And
because the earth isn't perfectly spherical, it's 40,047km around the
equator.

It is the bizarre fact of measuring 90 degrees to the right angle that
makes the metre a bit annoying, 111.11km to the degree, for navigation
purposes. Of course the French tried to make this all work by doing
angular measure not in Babylonian degrees but metric grads, also called
grades, gradians or gons, which have 100 to the right angle. But sadly
they didn't catch on for most purposes. They also put the zero meridian
through Paris, but that didn't catch on either.

Nothing imperial about nautical miles. A nautical mile is traditionally
1 minute of latitude. To the nearest metre 1 minute of latitude is
1852m. The nautical mile is today DEFINED as 1852 metres. That's
1012.6859 fathoms. The nautical mile was never 1000 fathoms. The old
British Admiralty definition of a nautical mile was 6080 feet, which
had the convenience of being precisely 800 feet more than a statute
mile, but is clearly not an exact number of yards or fathoms, so it
doesn't fit well in the imperial system either. The precise length of a
foot varied over time until it was standardised in 1959 (via 1 inch =
25.4mm precisely), and this made the admiralty nautical mile about 1m
longer than a modern metric nautical mile.

NASA lost a spacecraft around Mars because someone did some
calculations in imperial measurements and got them wrong. I'll stick to
metric, thank you.

5m is only about 0.5% different from a rod. So 25m2 is a pretty good
equivalent for a square rod, and makes the sums a lot easier.

A hectare is a piece of land 100m by 100m, very easy to visualise.

I agree that imperial measures are a pain, and that a nautical mile has
more to do with an angle measurement than a distance, (and I am afraid
that we always used the scale of the chart ie degrees and mins for
distance and this was sub divided into cables and chains not meters) I
can not accept that because someone has said how many metres long a
nautical mile is it becomes metric! I was only trying to point out that
many apparently arcane old measures did have (and sometimes still do)
have a point.
Sometimes however even at sea we bowed to tradition and after working all
my cargo figures out carefully in Tonnes and meters cubed I would then
have to produce legal documents like Bills of lading showing such wonders
as US Barrels, and ships also have port dues etc levied on them based on
Gross tons and Nett tons neither of which have anything to do with
anything!!
Back to gardening, yesterday was a bit dissapointing down here all grey
gloom but at least dry, more of the same to day, hoping to get down as
far as bench level in my greenhouse today, amazing how many plants get
stuffed in there over winter.
--
Charlie Pridham, Gardening in Cornwall
www.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea