By Frederick Von Lichtenow
The attractive and repulsive forces peculiar to static electricity enable
the person experimenting in this field to do things which would be
impossible with any other kind of electricity. However insignificant
these may appear to the uninitiated, for the true experimenter they carry
a deep meaning.
Experimenting in static electricity is playing with the electricity of
the earth in microform. This fact alone throws a vast amount of
fascination into this odd and yet so natural a branch of electrical
Static electricity shows itself In probably more ways and certainly
requires less apparatus for its production and experimental conduction
than any other form of experimental electricity. A rod of glass and a
piece of silk or a sheet of hard rubber and a piece of fur, together with
some bits of tissue paper, are sufficient apparatus for the practical
study of its elementary principles.
A small static machine, however, such as the Wimshurst influence machine,
is required for t lie successful reproduction of the following
experiments, which will aid the novice in grasping the principles
The opposing or repelling chains give a simple and yet quite impressive
way of showing the repulsive effect of like-charged bodies. Two very
light and equally long brass chains, such as are usually found around
static Instruments for connection purposes, are suspended horizontally
side by side by their respective ends as shown in Fig. 1. They must hang
well off the table and under just enough tension to form only a slight
down-ward curve. The electrodes of the machine are then set beyond
sparking distance, when with a few turns of the crank handle the chains
will he caused to press sideways, each strongly repelling the other, in
which position they will remain for some time after the machine has been
stopped, gradually and slowly falling back into normal position with the
leaking away of the static charge.
If the discharge hails are brought within sparking distance, so that
sparks may pass at certain intervals, the chains will set up a rhythmic
motion - separating upon being discharged, meeting again upon
neutralization - as long as tile plates are rotated.
Fig. 2 shows the apparatus required for the static ball pendulum, which
clearly illustrates tile principle of alternate attraction and
neutralization, helped along by the weight of the ball in got gathering
momentum, which in the end effects the pendulum motion. This latter will
continue as long as the machine is working. Both balls consist of solid
brass and should be kept in a well polished condition. The smaller,
swinging ball, one-half inch in diameter, is suspended by a piece of very
thin copper wire, 3 1/2 or 4 inches long, having a loop on its upper end
to insure the necessary free movement. The larger one, measuring one inch
in diameter, is stationary, while the whole is sup- ported upon
insulating stands. No sparks must pass across the static machine gap.
Working under the same principle as that involved in experiment No. 2,
the static vibrator, as I will call it, forms another highly interesting
piece of apparatus. The smaller ball is here replaced by a short piece of
very fine, perfectly straight copper wire, about 2 1/2 inches long, held
rigid In a clip as indicated in Fig. 3. The free end of this horizontally
placed wire must reach nearly across the entire width of the brass ball,
without however touching it, and must center upon it. Both should be
separated by a gap of from one-quarter to one-half inch, this depending
entirely on the size and condition of the static machine employed. With
the discharge rods set far apart and machine put to work, the wire will
immediately be attracted to the ball, since both are oppositely charged,
as quickly released under the neutralizing spark, attracted again under
the new charge and so on, which, assisted by the spring element existing
in it, will cause it to vibrate at an incredible speed.
The "cushioning" effect of the shark can be shown in our experiment,
which at once affords a spectacular way of lighting Geissler tubes
causing them to swing at the same time, and gives an opportunity for the
study of the "cushioning" effect of the static spark.
Two medium sized Geissler tubes of equal length (of the rarefied gas and
not the heavy liquid type) are suspended a couple of inches or so apart
from insulating stands connected to the respective poles of tile Static
machine (Fig. 4).
With the passage of the electric charge they will at once approach each
other, being attracted as a consequence of their opposite polarity, when
upon meeting by their lower bulbs the spark discharge will take place
through their entire lengths, strongly lighting them up for the moment.
Being released under the effect of the neutralizing spark, they fall back
into their former positions, only to be attracted to one mother again
with the approach of the new charge (Fig. 5). This in repetition causes a
sort of swinging motion on the part of the tubes, which in the end - one
would think at least - must lead to their striking hard together; but
they never do. Each time they meet, the resulting spark acts as if it
were a cushion placed between them; in fact they sometimes seem to cling
together for the instant, while the discharge is taking place, which on
the other hand forces them always to a fresh start, in this way limiting
the momentum gained by the tubes on each trip. They will perform in this
manner as long as the machine is in action, the terminals of which tire
to be separated beyond their spark limit.
In working out these static "stunts" I had in mind not only the beginner,
but the less capitalized experimenter who, unable to buy the more
expensive auxiliary apparatus, may not be satisfied with the average run
of experiments belonging in the tissue paper - tinfoil - pithball class.
The next experiments are described by Percival G. Bull. The "bronze" or
"metal" paper needed in the experiment seems, as I faintly remember, to
be an uncertain article on the local market. There is something entirely
wrong with it. Either the demand for it is so brisk that stocks are early
exhausted, or there is no call for it at all, and, consequently, nobody
bothers with it. I was for a time inclined to think the latter was the
case, until finally, after a prolonged and fruitless search among the
various stationery stores, I was shown at some small place what looked to
be the remnant at of a once glorious pile. Whether I purchased the real,
honest-to-goodness "metal" paper or not has been an open question with me
to this day, since it was not sold to me under that somewhat mysterious
sounding name. At any rate, It works.
The following illustrations and short descriptions give the results of my
tests with three kinds of the metal-coated paper (Fig. 6).
One characteristic of this paper is that the sparks always show a strong
tendency toward branching out over its surface, whether the distance
between the jars be a few inches or a foot, or even more. Their color is
a beautiful bluish-white. With the jars separated a few Inches, up to six
inches or so, the discharge manifests itself in thousands of bright
little stars hanging together by shiny threads.
These very striking effects are due to the relatively high conducting
quality of the metal particles covering this paper.
The paper illustrated in Fig. 7, offering a somewhat higher resistance to
the condenser discharge titan the former, limits the distance between the
jars to nine inches. At or near that distance the sparks are very
pronounced and appear concentrated in the form of miniature lightning
bolts of a clear white color. They hit around in curves and are
accompanied by a loud report. If the jars are approached to within four
inches or less, as indicated, the sparks will dart in spray fashion
across the intervening space, lighting up in a vivid emerald green. This
paper is the worst conductor of the three, and, consequently, permits
only a separation of a few inches between the Leyden jars. Set at that
distance, the spark effect is very similar to the one last noticed on the
"copper-bronze" paper, however, it is not quite so distinct. The color
shade of the sparks runs more into a dull yellowish green, not unlike
that of oxidized brass.
The above spark-and-color effects are those as observed in an
artificially (moderately) lighted room. The papers may be placed in
triple or quadruple layers. thus insuring a better insulation for the
Leyden jars, in addition to which an oil-cloth covering on the table may
be advisable. Care must be taken that the discharge balls of the machine
are first to be separated beyond sparking distance while charging the
jars and not set "a few inches apart" as prescribed by the text book,
which may be misunderstood, since the small Wimshurst machine I used in
these tests delivers a three-inch spark when in a healthy condition, not
to speak of the many larger static machines with their correspondingly
much greater spark lengths. After thus charging the jars for a short
while the electrodes are gradually and slowly brought toward each other,
when upon reaching the stress limit the resulting spark wil1 be
accompanied by the condenser discharge across the paper. Following the
above tests I was led to another experiment, terminating in the following
discovery - if I may call it such - which I will give here for what it is
In order to ascertain the conducting value of these metal papers as a
circuit link, I had introduced a separate gap (spark gap) into the former
set-up. With the conductors of the machine placed wide apart I was
testing the spark across this new gap under various adjustments, when,
happening to glance around while turning the crank, I noticed my gold
leaf electroscope standing some distance away near the further end of the
table, under the influence of a strong discharge. I discharged it and
tried again with the same result, then looked at the gap, where only a
silent discharge was taking place, caused by being set at the spark
Without disturbing anything, I studied their respective positions and
found the knob of the electroscope to be at exactly the same elevation as
the busy end of the gap, with the latter squarely facing the former.
Therein rested the secret, evidently. The oscillatory waves set up by the
spark were in this way forced upon and recorded by the very sensitive
instrument, which latter fact proves that a strong, unipolar factor
predominated in the charge (Fig. 10).
The discharge rods of the spark gap, being in a vertical position, are
curved in order to be capable of a wide range of adjustments. The rods
consist of heavy, polished brass wire and carry at their terminals
one-inch solid brass balls well polished, as all the terminals on static
instruments should be. All in all, the spark gap is a "concoction" of my
own, brought about by the dire need for just such a gap (Fig. 9). No
sparks will occur between the Leyden jars in this connection.
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