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Kieran,I just finished the book "Latitude" and was struck by the fact that
variation of latitude was very difficult to quantify.Taking the theories of
Euler and progressing through the years of all the work of many talented
astronomers with new ideas and methods and the progression of new and more
precise instruments finally brought an understanding of the phenomenon.It
took many brilliant theorists,mathematicians and one person who was not
versed in classical astronomical theory to finally,in 1898,prove and
understand variation of latitude.I think it is just a steady progression.As
understanding,math and instuments are fine tuned the measurements
improve.All things,no matter how finely calculated or measured will always
be an approximation because numbers are infinite.This is only my opinion and
I dont know if any of the above will help you.I also will go to the book
store to get Mr. Adler's book as it appears to be interesting.

-----Original Message-----
From: Kieran Kelly [mailto:kkelly@BIGPOND.NET.AU]
Sent: Tuesday, September 30, 2003 01:08
To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Subject: Re: Measure of All Things


I recently read Ken Alder's excellent work The Measure of All Things and was
struck by Delambre's struggle to improve the accuracy of celestial sights
and transit observations for the French metric survey. In the book there is
a discussion of the difference between Precision i.e. random errors and
Accuracy i.e. constant errors when making a celestial observation either
with a theodolite, sextant or transit circle.

I am still a bit confused. Is a random error-precision-a human error either
in the sighting technique or in the calculation such as an arithmetic error?
These errors would presumably be expressed as a bell shaped curve. If so
then the accuracy must relate to the instrument and would always be
constant. Thus errors of accuracy would be expressed as a straight line when
plotted. Those who use sextants are familiar with errors such as index
error, collimation error or the errors along the arc. But I thought these
errors could be eliminated. Apparently not completely eliminated. Is this
interpretation correct?

Does it mean that because of random errors no observation is ever completely
precise as minute human variables come into play? Similarly if there was to
be no errors of accuracy then the measuring instrument - sextant, theodolite
etc would need to be perfect. On the basis that no man made machine is
perfect it would appear that all navigational fixes and surveying
triangulations are ultimately only approximations.

This was certainly the case with the French metric survey which was found to
be inaccurate with the advent of satellite navigation. What I don't
understand is how do scientists know it is inaccurate when there appears to
be no absolute standard if Delamere is to be believed. Is it possible that
in future a further technological development will prove the satellite
survey to be inaccurate?

Any assistance would be appreciated.

Kieran Kelly

   

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