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 1745
PIETER VAN MUSSCHENBROEK, of Leyden, Holland. Invented the Leyden Jar (an early
form of capacitor) after accidentally discovering it had interesting
characteristics. It
must be remembered that the scientists of this period were still playing around
with frictional apparatus, since no other means of generating electricity had
been discovered. It occurred to Musschenbroek that electricity might be able to
be bottled or, rather, confined within a glass bottle so that it could be used
at some other time. Whether the idea was originally his is hard to determine,
since histories vary. In any case, the idea was that if water were placed within
a bottle and then charged by means of a frictional electric generator, the
charge would remain in the corked bottle because glass is a good insulator. Fate
took a hand the day Musschenbroek was conducting
the experiment. He was turning the crank of his static electric generator,
whilst his assistant, Cunaeus, was holding the jar with one hand and was, with
the other trying to draw off sparks from a gun barrel. The circuit consisted of
the gun barrel connected to one side of the friction electric generator with the
other to a brass wire, which entered the jar, partly filled with water. Had
Cunaeus placed the jar on the table, nothing would have happened, and the
capacitor might not have been heard of today. As it was, his hand formed one
plate, the liquid in the jar the other plate and, while Musschenbroek cranked
the machine the improvised capacitor eventually
charged up – then Cunaeus must have thought his world had come to an
end!
The tremendous spark that resulted caused the whole charge to pass through his
body – the records have it that Cunaeus was incapacitated for two full days.
Nollet, another scientist of that period, heard of the experiment and, unwilling
to be the subject himself, got together approximately 200 soldiers, had them all
join hands in a large circle, and then, in much the same manner as Musschenbroek
and Cunaeus had done, sent a severe  charge
through them. The fact that they all instantly jumped
with vigour pleased him no end, and gave him much to marvel at. Naturally
both Musschenbroek and Nollet tried to figure out what caused the effect, and it
wasn’t for some time that a definite conclusion was arrived at. They found
that when they placed the jar of water on the table, it would refuse to be
electrified (since the hand or other plate of the capacitor was missing) and
that, only when the hand was placed around the jar could
the
phenomenon be repeated. But volunteers for the experiment were probably lacking;
so eventually it was discovered that placing the jar over a metal plate seemed
to do just as well. Later on, an outside tinfoil covering was substituted, with
improved results, and for many years this was the construction of Leyden jars
– the grandfather of all of today’s capacitors (it is interesting to note
that even up until the 1930’s the unit of capacity was commonly referred to as
a “jar”).
 1751
BENJAMIN FRANKLIN, American statesman, philosopher and scientist. While
others had previously noted the similarity between laboratory sparks and
lightning, Franklin was the first to design an experiment, which conclusively
proved the electrical nature of lightning. The experiment used a kite attached
by a damp string and flown into a thunderstorm, the bottom end of the string
having a metal key attached from which sparks jumped to an earth point. Franklin
also involved himself in a number of other scientific endeavours that are
probably less well known than his work with lightning. Some of his deductions
resulting from these have played an important role in the development of
electricity since he employed the same calm logic and methodical precision which
made him famous as a statesman and philosopher. Franklin established the law of
conservation of electric charge; that there is a positive and negative type of
electricity; that lightning and thunder are related to the crashing and sparks
obtained when electrically charged bodies become discharged. He invented the
lightning rod, to prevent the great damage done to property by lightning. His
theories led to his follower’s discovery that air may be substituted as a
dielectric in place of glass in the construction of a Leyden jar, as well as the
law: “like charges repel, unlike charges attract”.
1780
ALOYSIUS GALVANI, Italian professor of anatomy. Up to his time only two
means of obtaining electricity were known; one by means of the friction machine,
the other from the clouds,  as discovered by Franklin. Galvani, by accident,
noticed that an electrical charge applied to a dead frog’s nerve would make it
kick and struggle as if it were still alive. Continuing his experiments along
this line, he found that a number of frogs he had prepared and suspended along
his balcony would respond to lightning flashes in similar manner and that, even
before the storm, if a frog’s legs happened to touch the balcony, the
twitching muscular movement would occur. Later on he determined that any two
metals joined together, so that one touched a leg muscle and the other a nerve,
would cause the muscular twitching. Galvani then reasoned that the muscle was
akin to a Leyden jar, and the electricity is the fluid, which made a circuit
from the muscle to the nerve, then through the metallic conductors back to the
muscle again. He called the “fluid” animal “electricity”; but true galvanic
electricity, as caused by two dissimilar metals in contact, was not
recognised by Galvani who theorised that the electricity originated in the
frog’s leg.
1790
ALESSANDRO VOLTA, Italian professor. Shortly after Galavni’s exp eriments,
Volta devised what became known as the “voltaic pile”, Consisting of a pile
of alternate zinc
and copper discs (each pair being separated by a moistened pasteboard [thick
paper] disc termed a “couple”); so that by using quite a large pile of
discs, a distinct shock was obtained when the finger tips were placed on each
end of the pile. The disadvantages of this arrangement were that, when the
pasteboard discs dried out the voltage diminished. Consequently Volta devised
copper and zinc strips, joined at the ends and placed in separate jars
containing a weak acid solution. Now we have the first real battery
– a unit destined to be of great help to future scientists and inventors
in their explorations into the realm of electricity. In honour
of this discovery, Volta’s name was immortalised when, later on, the volt was the name given to the unit of electrical force.
1800
NICHOLSON AND CARLISLE, English experimenters. Set up a voltaic pile and
showed that water could be decomposed into its elements, hydrogen and oxygen, by
passing an electric current through it. Known now as electrolysis of water.
1820
HANS CHRISTIAN OERSTED,
 Dane and Professor at Copenhagen. For thirteen
years
Professor Oersted had experimented with electricity and its effects on a
compass needle,
having read in Benjimin
Franklin’s report that there was some effect and relation between the two.
While lecturing to
a class, Oersted had his attention called to the wavering of a compass needle,
whenever a switch was
thrown which connected a voltaic pile. After the students had departed, he
investigated the phenomenon – finally ascertaining that, when the compass
needle was placed along the wire, there
was a deflection with the needle
coming to a stationary position across
the wire. When the
compass was placed above the wire the
needle turned one way and when placed under it turned the other way. This was
the basis for determining magnetic lines of force, and without a doubt
the foundation for measuring and indicating electrical instruments, which use
analogue meters, for the next 150 years. In the same year, history tells us that
one week after Oersted made his discovery, Andre Marie Ampere (shown
below), French
scientist, made the important discovery that two parallel wires carrying an
electric current, but free to move, attracted each other if the currents
traveled in the same direction and
repelled each other if the currents were opposite. Also he determined not only
that a wire
carrying an electric current would attract a magnetized needle,  but the needle
would also attract the wire. Today we find the unit of current, the ampere,
named in his honor. Likewise Oersted has had the unit of magnetizing force name
in his honor.
1826
GEORGE
SIMON OHM, Bavaria. His outstanding accomplishment is the law, which now bears
his name: “A current flowing in any closed circuit is proportional to the
force or voltage and inversely proportional to the resistance in the circuit”.
Today we express Ohm’s Law simply by
mathematical means, viz., I=E/R.
1831
JOSEPH HENRY, American physicist, improved the electromagnet (developed
by Argo in 1820) by using silk covered wire, which allowed the use of many
layers of turns. This technique allowed him to make coil-magnets large enough to
lift several pounds. The unit of inductance, the
henry, is named after him.
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