David Bowman is concerned that we have to "cheat" in trying to repeat
Eratosthenes's measurement.
You might say, "obviously!" But I'm not sure.
We don't live in a culture that travels mostly on foot, by beast of burden,
or by floating down rivers. It must have been that E. had a good sense (to
within 5 or 10%) of the distance from Aswan to Alexandria simply because
many, many people had travelled the distance and he could account for
variations to give a reasonable value for the distance. I have travelled
from Portland to here by bicycle and my sense is that map distances are
reasonable (however derived) so we are going to use them. I think thats what
E. did!
Currently, we will be sharing data with Ray Rogoway in San Jose CA, which is
about 2 degrees off our meridian. Thats less than the difference between
Alexandria and Aswan. I don't know how much E. knew about that. Today, my
students will discuss how we can account for the difference by timing our
measurements. In the end I hope they will have a sense of how much or little
this would have mattered to E. and they will understand some good science.
I think that the pedagogical point of repeating historical measurements like
the size of the earth or the speed of sound gets lost if you mix in the
precisions possible today. Students can certainly be proud or in awe of how
far we have come on these matters but only if they can see where we came
from.
Ken Murray from British Columbia
(Where, yes, a science teacher did recently get mauled by a grizzly while
riding his bike on a wilderness road.
He survived.
We promise to be careful.)