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Re: Variable Capacitance and Inductance

Original poster: "rob by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rob-at-pythonemproject-dot-com>

Tesla list wrote:
> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> Hi Dave,
>          The quote from Tesla contains excellent examples of limited
> knowledge and/or misinterpretation of results. For example:
> On 21 May 2002, at 8:03, Tesla list wrote:
> > Original poster: "David Thomson by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
> >
> > We have discussed on this list individual observations of variations in
> > inductance measurements of coils.  It has brought about sometimes heated
> debate
> > as to whether this was a malfunction of machinery or a change of
> > conditions.  At least one person on this list has proposed to run a
test over
> > time to see if there were indeed a variation in inductance in a coil.
> <snip to relevant passage>
> > Continuing the investigation of this astonishing phenomenon I observed
> that the
> > ca­pacity varied with the elevation of the conducting surface above the
> ground,
> > and I soon ascertained the law of this variation. The capacity increased
> as the
> > conduct­ing surface was elevated, in open space, from one-half to
> > three-quarters of 1 per cent per foot of elevation. In buildings,
however, or
> > near large structures, this increase often amounted to 50 per cent per
> foot of
> > elevation, and this alone will show to what extent many of the scientific
> > experiments recorded in technical liter­ature are erroneous. In
> determining the
> > length of the coils or conductors such as I employ in my system of wireless
> > telegraphy, for instance, the rule which I have given is, in view of the
> above,
> > important to observe.
> The assertion that the capacitance of the terminal increases with
> height simply doesn't stand to reason (unless it was just a few
> inches from the coil to begin with - mutual shading). In elevating it
> (outdoors), he is moving it further away from ground (closer to the
> ionosphere for sure, but an absolutely trifling amount by comparison).
>      What he observed was a drop in the resonant frequency of his
> coil. What he appears not to have taken into account in explaining
> this was the extra length of conductor leading to the terminal. If
> the length of a monopole antenna is increased, its resonant frequency
> drops due to the extra inductance and capacitance of the wire.
>      Some of the actual measurements he took appear to be grossly in
> error also. Richard Hull noted at least one pertaining to terminal
> capacitance in his "Guide to the Colorado Springs Notes".
> > ?Far more interesting, however, for men of science is the fact I observed
> > later, that the capacity undergoes an annual variation with a maximum in
> > summer, and a minimum in winter. In Colorado, where I continued with
> > methods of inves­tigations begun in New York, and where I found the rate of
> > increase slightly great­er, I furthermore observed that there was a diurnal
> > variation with a maximum during the night. Further, I found that sunlight
> > causes a slight increase in capa­city. The moon also produces an effect,
> but I
> > do not attribute it to its light.
> The sun undoubtably has some effects - most notably on LF/MF
> propagation due to its influence on the ionosphere (day/night and
> probably summer/winter as well when its angle to one or other of the
> poles is more oblique). I'm not sure how much of this was known or
> quantified in Tesla's time.
> >
> >
> > ?The importance of these observations will be better appreciated when it is
> > sta­ted that owing to these changes of a quantity supposed to be
constant an
> > electrical circuit does not vibrate at a uniform rate, but its rate is
> modified
> > in accordance with the modifications of the capacity. Thus a circuit
> vibrates a
> > little slower at an elevation than when at a lower level. An oscillating
> > system, as used in teleg­raphy without wires, vibrates a little quicker
> > the ship gets into the harbor than when on open sea. Such a circuit
> oscillates
> > quicker in the winter than in the summer, though it be at the same
> temperature,
> > and a trifle quicker at night than in daytime, particularly if the sun is
> > shining.
> So water vapour in excess (clouds) appears to have had some influence
> on his measurements.
>      All this to show that one must be careful in drawing conclusions.
> Malcolm

I think elevation above see level would effect capacitance, since we are
not in a vacuum :)
I wonder if higher barometric pressure leads to higher capacitance? 

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