Re: Variable Capacitance and Inductance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi David,

Thanks for sharing. That was quite interesting, especially seeing that
Tesla must have performed
some ongoing experiments over quite a long duration in order to come to
such conclusions (all of
which are conceivable and even a slight change is a change).

Take care,
Bart

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 atmospheric
> 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.
>
> Today I was going through Tesla's writings and came across this article
written
> in 1901.  Apparently Tesla also noticed the variation of capacitance and
> inductance.  If you have been part of this debate, you will find this article
> quite interesting.
>
> New York Sun
>
> Jan. 30, 1901
>
> TESLA’S NEW DISCOVERY
>
> Capacity of Electrical Conductors is Variable
>
>  <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
>
> Not Constant, and Formulas Will Have to Be Rewritten - Capacity Varies With
> Abso­lute Height Above Sea Level, Relative Height From Earth and Distance
From
> the Sun.
>
>
>
> Nikola Tesla announced yesterday another new discovery in electricity. This
> time it is a new law and by reason of it, Mr. Tesla asserts, a large part of
> technical literature will have to be rewritten. Ever since anything has been
> known about electricity, scientific men have taken for granted that the
> capacity of an electrical conductor is constant. When Tesla was experimenting
> in Colorado he found out that this capacity is not constant - but variable.
> Then he determined to find out the law governing this phenomenon. He did so,
> and all this he explained to The Sun yesterday. Here is what he said:
>
>
>
> “Since many years scientific men engaged in the study of physics and
electrical
> research have taken it for granted that certain quantities, entering
> continuously in their estimates and calculations, are fixed and unalterable.
> The exact determination of these quantities being of particular importance in
> electrical vibra­tions, which are engrossing more and more the attention of
> experimenters all over the world, it seems to be important to acquaint others
> with some of my observations, which have finally led me to the results now
> attracting universal attention. These observations, with which I have
long been
> familiar, show that some of the quantities referred to are variable and that,
> owing to this, a large portion of the technical literature is defective. I
> shall endeavor to convey the knowledge of the facts I have discovered in
plain
> language, devoid as much as possible of technicalities.
>
>
>
> “It is well known that an electric circuit compacts itself like a spring
with a
> weight attached to it. Such a spring vibrates at a definite rate, which is
> deter­mined by two quantities, the pliability of the spring and the mass
of the
> weight. Similarly an electric circuit vibrates, and its vibration, too, is
> dependent on two quantities, designated as electrostatic capacity and
> inductance. The capacity of the electric circuit corresponds to the
pliability
> of the spring and the induct­ance to the mass of the weight.
>
>
>
> “Exactly as mechanics and engineers have taken it for granted that the
> pliability of the spring remains the same, no matter how it be placed or
used,
> so electricians and physicists have assumed that the electrostatic
capacity of
> a conducting body, say of a metallic sphere, which is frequently used in
> experiments, remains a fixed and unalterable quantity, and many scientific
> results of the greatest importance are dependent on this assumption. Now, I
> have discovered that this capacity is not fixed and unalterable at all.
On the
> contrary, it is susceptible to great changes, so that under certain
conditions
> it may amount to many times its theoretical value, or may eventually be
> smaller. Inasmuch as every electrical conductor, besides pos­sessing an
> inductance, has also a certain amount of capacity, owing to the
varia­tions of
> the latter, the inductance, too, is seemingly modified by the same causes
that
> tend to modify the capacity. These facts I discovered some time before I
gave a
> technical description of my system of energy transmission and telegraphy
> without wires, which, I believe, became first known through my Belgian and
> British patents.
>
>
>
> “In this system, I then explained, that, in estimating the wave-length of the
> electrical vibration in the transmitting and receiving circuits, due regard
> must be had to the velocity with which the vibration is propagated
through each
> of the circuits, this velocity being given by the product of the wave-length
> and the number of vibrations per second. The rate of vibration being,
however,
> as before stated, dependent on the capacity and inductance in each case, I
> obtained discordant values.
>
>
>
> 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.
>
>
>
> “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 improved
> 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 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 when
> 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.
>
>
>
> “Taking together the results of my investigations I find that this
variation of
> the capacity and consequently of the vibration period is evidently dependent,
> first on the absolute height above sea level, though in a smaller degree;
> second, on the relative height of the conducting surface or capacity with
> respect to the bodies surrounding it; third, on the distance of the earth
from
> the sun, and fourth, on the relative change of the circuit with respect
to the
> sun, caused by the diurnal rotation of the earth. These facts may be of
> particular interest to meteorologists and astronomers, inasmuch as practical
> methods of inquiry may result from these ob­servations, which may be
useful in
> their respective fields. It is probable that we shall perfect instruments for
> indicating the altitude of a place by means of a cir­cuit, properly
constructed
> and arranged, and I have thought of a number of other uses to which this
> principle may be put.
>
>
>
> “It was in the course of investigations of this kind in Colorado that I first
> noted certain variations in electrical systems arranged in peculiar ways.
These
> variations I first discovered by calculating over the results I had
previously
> no­ted, and it was only subsequently that I actually perceived them. It will
> thus be clear that some who have ventured to attribute the phenomena I have
> observed to or­dinary atmospheric disturbances have made a hasty conclusion.”