# RE: Variable Capacitance and Inductance

```Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Terry,

>"Modern" equtions and methods account for the errors in that often cited
formula.  Trying to use it today is of no value other than teaching student
how to apply Maxwell's equation to a coil.  It is really a bad example, but
a good example would be too complex for the purpose.  That old formala has
nothing to do with the definition of inductance but it is just a poor
example of how to use the difinitions.

I wasn't meaning to say that inductance is defined as a coil. I was trying
to say that the inductance of a coil is defined by its physical parameters
times the permeability constant, just like the capacitance of a capacitor is
defined as its physical parameters times the permittivity constant.

It is reasonable that if the inductance of a coil is not defined as the
physical parameters times the permeability constant that it wouldn't be
taught in the classroom.

>But the modern equations work perfectly fine without the Earth's effects.

The modern Wheeler's equations already account for the earth's effects.
What I'm doing now, as a result of this discussion, is searching NASA files
for any information about air core coils in space.  If I don't find anything
this weekend, I'll write NASA and ask for information.  If I'm right about
Wheeler's formula already taking the earth effect into account, then an air
core coil in space will have a slightly higher inductance reading.  If I'm
wrong, it won't.

>So Tesla's tests could have a lot of interfeerence error :-(  Atmospheric
electrity, AC hum, sun spots...   That stuff is not the raised sphere's
problem.

Capacitance is not entirely a property of the sphere.  That's why the
formulas for capacitor capacitance and coil inductance have constants
attached to them that account for the effects of free space.  So it is the
raised sphere's problem because it's effective capacitance in the circuit
must deal with the effects of "interference" as you call it.  The
"interference" or added dielectric strength has to be dealt with by the
oscillating system.  It can't be ignored.

>It would have to be reproduced today with trusted equipment where the
details are known or could be determined.  Then the results could be
beleived and trusted.

Exactly.  That's all I'm saying too.  We need to duplicate Tesla's work
before we can conclusively say he was right or wrong.

>I see Paul just delivered a good knockout punch  =:o<

I didn't think so.  He misrepresented my position to the point that he was
attacking something I didn't say or believe.  I would call it shadow boxing
:-).

>What would be needed is a clear table for values of the 30 inch sphear's
elevation vs. capacitance with the wire there.  Like this:

I'll get to this later.  I've got to leave for a bit.

Dave

```