The discovery of capacitance.
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Capacitors with perforated plates
Historical notes in electronics series.
Are you interested in how Capacitors were discovered, or
possibly invented? Read on....
The Leyden Jar - Condensers.
Section 1. Cuneus and Muschenbrock's Experiments: The discovery
of the Leyden Jar.
Reference: Electricity and Magnetism, by A Guillemin, published
in 1891 by Macmillan, London and New York. Chapter 5 page 231.
"Cuneus, a pupil of Muschenbroeck, a celebrated physicist of the last
was one day trying to electrify some water in a wide-necked
bottle. For this purpose he held the bottle in one hand after having placed
in the bottle a metal rod connected to the machine. When he thought
the water was sufficiently electrified, he tried to remove the
iron rod with one hand, without loosing his hold of the bottle
with the other hand. He received a shock that surprised him.
Muschenbroeck repeated Cuneus's experiment, but the shock he received
in his arms, shoulders, and chest was so great that he lost
consciousness, and was so frightened that, in writing to Reaumur about this,
then new, discovery, he wrote that for nothing in the world, not even
for the crown of France, would he go through it again. But some other
physicists were less fearful. Allaman, Lemonnier, Winckler, and the Abbe Nollet
varied the experiment in all sorts of ways, and so a new piece of apparatus
was added to electrical science: this apparatus, called the Leyden Jar, is
named after the place where the experiment was first performed in
The modern view.
The dielectric constant of water is about 80. This is
exceptionally large for a liquid; and results in all kinds of
consequences for radio wave and microwave propagation through
rain and on to wet surfaces.
In Cuneus's experiment, the iron rod is connected to a source of
voltage that is not, in itself, large enough to give a shock to
the experimenter. The experimenter disconnects the iron rod
and jar from the supply, and then attempts to pull the rod from
the jar. The stray capacitance from the rod to the outside of the
jar, when removed, is less than 1/100 of the capacitance when it
is in the water. Since the charge Q is constant, and Q = CV,
it is clear that the voltage rises to 100 times that of the original
voltage source. This is sufficient to drive the charge through the
arms of the person doing the experiment; hence the shock.
We see here another reason why electricity is dangerous when in
conjunction with water and wet objects. Distilled water is a
reasonable insulator; it only becomes conducting when there
are dissolved salts. But it can hold a large polarisation
so capacitors with a water dielectric are efficient storers
10 March 1997