Re: I need help.

[Brian Whatcott <inet@INTELLISYS.NET>]

At 05:20 AM 2/24/02, David Bowman wrote:
> Regarding Bernard C.'s recollection:
>
> > ...
> >One of my references pointed out that the resistance between two embedded
> >electrode spheres in the earth (rather more closely infinite embedding
> >medium) was ~ independent of their separation > a certain minimum
> >separation.  --IF I REMEMBER CORRECTLY.
>
> You do remember correctly.  As long as the two electrode spheres are
> placed *much* farther apart from each other than each of their
> individual radii, then the asymptotic finite resistance between them
> is given by:  R = ([rho]/(4*[pi]))*(1/a + 1/b)  where [rho] is the
> resistivity of the background medium and a & b are the respective
> radii of each of the conducting electrodes spheres.
>
> David Bowman
> David_Bowman@georgetowncollege.edu


I am surprised that this conclusion never presented itself before to me.
I well recall the demonstration of hammer  sounding on the lawn of some
 campus - was it Reading U? wherein a meter square steel plate launched
a seismic wave to reveal several proximal strata beneath using a
microphone and pen recorder setup.
This georheological (??)  demonstration would be just as interesting.

I wonder how sensitive the determination of earth rho is to using uncovered
copper plated steel rods of the kind often sold for grounding purposes?


Brian Whatcott
  Altus OK                      Eureka!