Re: Selecting a Coordinate System

Subject: RE: Coordinate systems
Author: John Conway <conway@math.Princeton.EDU>
Date: Sun, 8 Feb 1998 12:06:58 -0500 (EST)
On Sun, 8 Feb 1998, Jesse Yoder wrote:
> RESPONSE: I find your comments on fluid dynamics very interesting, since
> I claim that Circular Geometry has implications for the measurement of
> fluid flow in pipes. So what you are saying, then, is that engineers
> measuring circular pipes use coordinate systems that are appropriate for
> the particular circular shapes they are measuring. I find this very
> encouraging to hear.
 Thanks for your thanks. I think it's not really in "measuring
circular pipes" so much as in considering (say) fluid flow around
such pipes, that a special coordinate-system would be used.
> I also find it interesting to hear you say this, since you have
> indicated that you don't find the idea of selecting a Point size to suit
> a particular measurement to be a worthwhile concept -- yet you claim
> that other people already do something even more extreme -- select a
> different coordinate system to suit a particular measurement. So
> according to you, it's just fine to shift coordinate systems to make a
> particular measurement, which is implied by what I have been saying all
> along.
> Jesse Yoder
 I think that what you call "selecting a Point size to suit a
particular measurement" is obviously very sensible, but that it's
silly to use "Point" and "point" with different meanings. Have you
any strong reason for doing this rather than using the same language 
as everyone else - for instance saying something like "working to
within a tolerance of 1/100 of an inch"? I thought you had, namely
that you felt Euclid's "points" didn't exist, but perhaps some
absolute "Points" did. 
 I'm surprised that you regard changing a coordinate-system as
"extreme": to me it seems a rather trivial and practical matter.
 I have a suggestion to make. If it's really the case that
your distinguishing between "points" and "Points" is practical
rather than theoretical, why not just drop it and use a more
traditional language in the interests of better communication 
even if (like many other people) you'd really prefer it if language 
hadn't developed in the way it has? I say this because talking
about the use of words is much less valuable than talking about
the things they represent, and your present terminology has made
it very difficult (at least for me) to understand what you're
really trying to say.
 John Conway





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