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# Re: Would you like to share some data?

At 17:14 -0400 6/6/01, John S. Denker wrote:

[snip]

Measuring the size of the earth is an extreme case, because the answer is
so well known. Indeed, you don't even need a highway map! To get a good
estimate of the circumference of the earth, you can just measure the length
of a meter stick (which is pretty easy :-) then multiply by 40,000. Even
in less extreme cases, known quantities manage to insinuate themselves into
measurements in all sorts of ways.

Philip and Phylis Morrison did the Eratosthenes experiment some years
back for the PBS series "The Ring of Truth." They made their
independent distance measurement using the odometer of their truck as
it drove down one of those ramrod straight north-south highways in
the midwest for several hundred miles. They measured the elevation of
a star (Antares, as I recall) as it crossed the local meridian each
night.

The fact that the distance unit they used was miles, whose modern
definition is related to the meter, which was originally related to
the circumfirence of the earth is really irrelevant. They could have
measured the distance traveled in truck lengths, or (as E. did) in
stadia (which were related to the average length of a human stride),
or any other arbitrary unit (furlongs or chains, or any other unit
whose origin is unrelated to the circ. of the earth). Then measuring
the earth's circ. in these units and comparing that to a nominal
definition of the meter as 1/40,000,000 of the earth's circ., would
give the relationship between the units, but no prior assumptions
about the size of the earth enter into this sort of procedure.

Unfortunately, when you have two static groups and cannot directly
measure the distance between them, the problem is a bit more
complicated, as John D. and John B. have eloquently pointed out.

Hugh
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