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Re: Metric Time (was Re: Why not 13 months? (Was La Systeme Metrique))
Andrew Reid (are494@lulu.acns.nwu.edu)
10 Oct 1995 04:44:07 GMT
In article <45bm0n$jje@fg70.rz.uni-karlsruhe.de>,
Thomas Koenig <Thomas.Koenig@ciw.uni-karlsruhe.de> wrote:
>In alt.folklore.computers, john@polo.demon.co.uk (John Winters) wrote:
>
>>Your problem here was converting from a volumetric
>>measurement to a weight measurement, which would have been just as hard
>>in a metric system. Do *you* know how many litres of strawberries there
>>are to the kilo?
>
>Well, water has the convenient density of 1 kg/litre, which is fairly
>easy to remember.
>
Well, much as I am a fan of metric, having had the opportunity to
torment my parents with my superior knowledge of it whilst Canada
(where I lived at the time) was undergoing conversion, it does seem
to have a systematic flaw -- to be properly "metric", every unit in
the system has to be either derived from some human- or earth-centred
measurable quantity, or be a composite of such units.
But you can get into trouble when these criteria give different
answers -- my personal favourite example is pressure. The SI unit of
pressure, the Pascal, is one Newton per square metre, that is to say,
one kilogram per second-squared per metre. It's a derived unit,
obviously, but the problem is that for the obvious day-to-day pressure
measurement, it seems to me that the obvious earth-centred unit is
the International Standard Atmosphere. It has all the alleged advantages
of a metric unit, being more-or-less unit-sized in the conventional
range. In spite of my rigorous metric education, I have no idea how
many Pascals the atmospheric pressure is, I think it's a few hundred
thousand, but for actual applications, I use different units -- even
when in Canada, many years after metrication, I still inflated
my car tires to about twenty-five or thirty pounds per square inch,
(around two atmospheres, btw...) and I know if the barometric pressure
is very much over thirty inches of mercury, it's likely to be sunny out.
And I don't know any serious scientists who use Pascals -- most of them
use units called "Torr", or else millimetres of mercury, to measure
pressure, respectively for high and low pressure applications.
The Celsius temperature scale has a similar, though less serious,
flaw, in that it is thoroughly arbitrary. It does have the advantage
that most scientists use it or the closely-related Kelvin scale,
but the water-oriented zero and hundred marks are not notably more
intuitive than the Farenheit(sp?) scale, which has the intuitive
advantage (as I learned in our recent Chicago heat wave...) that
100 F is getting to be uncomfortably warm, and 0 F is getting to be
dangerously cold. So it actually *does* make a certain kind of
sense.
In spite of pitching my own two cents around rather vigorously,
I get annoyed at overly-vigorous defenses of either system. They
both work fine, the decision is ultimately political.
Incidentally, there's an interesting point made about this in
a book about the construction of the Concorde (ObCite: Brian Calvert,
"Flying Concorde", Fontana, 1981) in which he mentions that the
difference between measurement systems between the French and British
engineers was a total non-problem -- high-precision hardware fit
perfectly every time.
Andrew "So there." Reid
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