Who was Benjamin Franklin?
Benjamin Franklin was one of the leaders of the American Revolution
and Founding Fathers of the United States, helped draft the Declaration
of Independence and was one of its signers.
Franklin was a man of many talents and among others he was a printer,
journalist, publisher, author, philanthropist, abolitionist, public
servant, scientist, librarian, diplomat, and inventor.
What Did Benjamin Franklin Invent?
Benjamin Franklin made important contributions in many fields. His
scientific achievements in science and invention include the Franklin
stove, bifocals, medical catheter, swim fins, library chair, the
odometer, glass armonica and more (a few of this devices he only
improved or came up with his own version).
In electricity he invented the lightning rod, discovered the
principle of conservation of charge and identified positive and negative
electrical charges. But he’s best remembered for the Franklin’s kite
experiment (see below), and no wonder that sometimes he’s referred to as
“Master of Electricity”.
In literature and journalism he’s best known for writing, printing and publishing the famous
Poor Richard's Almanac and
The Pennsylvania Gazette.
Franklin was also a diplomat and represented the United States in
France during the American Revolution, and secured the French support
that helped to make independence of the United States possible.
He was also a civil servant and in 1775 Franklin became the first U.S. Postmaster General.
Franklin's Kite Experiment
Ben Franklin himself never wrote the story of the most dramatic of
his experiments. All that is known about what he did on that famous day,
of no known for sure date, comes from two resources:
Joseph Priestley's account, published fifteen years afterwards in
1767 appears to be based on Franklin’s account himself through close and
intense correspondence between them. (
The History and Present State of Electricity, with original experiments, by Joseph Priestley, 1775 Vol. I pp 216-217)
A letter in which Franklin described his kite experiment that was
written in Philadelphia on October 1752 and was addressed to Peter
Collinson, who had earlier provided Franklin with some simple apparatus
for performing electrical experiments. A copy of the original letter is
at present in the archives of the Royal Society in London.
http://www.aip.org/history/gap/Franklin/Franklin.html (Letter XI)
According to these sources, Franklin, on June 1752, built a kite with
a sharp pointed wire attached to the kite to attract easier electrical
charges (working like a lightning rod). He attached a key to the end of
the kite string, near his holding hand, but held the kite with a silk
ribbon also tied to the key for insulation security reasons. A thin
metal wire, connected also to the key, was inserted into a Leyden jar, a
container for storing electrical charges. Then, on a thunderstorm he
let the kite fly. The kite was struck by lightning and cloud sparks
(electrical charges / static electricity) flew through the wet kite and
string to the key and inside the Leyden jar. After he noticed that loose
fibers of the string were bristling outward because the string was
charged with static electricity, he intentionally reached out his
knuckle to touch the key and he felt an electrical shock.
This experiment - the electrical shock to Franklin’s hand, the
charged Leyden jar and the string's bristling fibers - proves beyond any
doubt that lightning is an electric phenomenon.
Many cast doubt at the possibility that Franklin really performed
this experiment. For example, Tommy Tucker, a science writer, offers two
reasons in particular for rejecting the kite story. One is that in
describing the experiment in his newspaper,
The Pennsylvania Gazette,
Franklin does not say that he did it. The other is that the experiment
as Franklin described it would be unlikely to succeed because of the
design of the kite and the difficulty of flying it under the conditions
outlined by Franklin.
(
Tucker, Tom. Bolt of fate; Benjamin Franklin and his electric kite hoax. Public Affairs, 2003.)
On The other hand, others believe that Franklin indeed performed this
experiment. Bernard Cohen, states that Franklin was in close contact
with Priestley and therefore it is safe to assume that Priestley’s
detailed report is based on Franklin himself.
(
Benjamin Franklin's Science I. Bernard Cohen, Harvard University Press, Cambridge, Massachusetts, and London, England, 1990)
http://books.google.com/books?id=franklin+kite+experiment+priestly+Collinson
Schiffer, professor of anthropology at the University of Arizona,
accepts the tradition of the kite experiment, although he says it is "a
long and inconclusive story."
Schiffer, Draw the Lightning Down, (2003, University of California Press)
Others think that basically Franklin performed this experiment but
with some required changes and not the way it is often described,
namely, he did tie a key to the kite string, fly it in a thunderstorm,
and wait for it to be struck by lightning - had he done so, most chances
are that he wouldn’t survive it without to be killed. Evidence, from
his writings, shows that he was aware of the dangers of electricity and
to other possible safe alternatives to perform this dangerous experiment
- among them, to draw sparks directly into the Leyden jar, from the
key, without the need to touch it and as shown by his invention of the
lightning rod using of the concept of electrical ground.
http://www.mos.org/sln/toe/kite.html
It doesn’t really matter if Benjamin Franklin indeed performed the
kite experiment in reality. What really matters is the question if this
experiment (or maybe only a theoretical proposal) is founded on sound
scientific principles and as a matter of fact it is a possible
experiment that enables the conclusion that lightning is an electric
phenomenon. Since we think that the answers to these questions are “yes”
than we also think that Franklin should be fully credited with this
experiment.
There is some evidence that also Jacques de Romas, a Frenchmen,
invented the famous kite experiment independently. Romas produced very
long sparks in front of enthusiastic crowds in 1753. But regretfully
only the name of Franklin is remembered.
(
The noteworthy involvement of Jacques de Romas in the experiments on the electric nature of lightning, Berger Gérard ; Ait Amar Sonia, Journal of electrostatics, 2009, vol. 67, no2-3, pp. 531-535.)
The Invention of the Lightning Rod
In 1750, Benjamin Franklin published a proposal for an experiment to
determine if lightning was electricity. He proposed extending a
conductor into a cloud that appeared to have the potential to become a
thunderstorm. If electricity existed in the cloud, the conductor could
be used to extract it. Basically this experiment is the same as the one
with the kite except the fact that the pointed conductor in the case of
the kite is much higher and closer to the charged clouds.
On May 10, 1752, Thomas-François Dalibard of France conducted
Franklin's experiment using a 40-foot (12 m)-tall iron rod instead of a
kite, and he extracted electrical sparks from a cloud.
There is evidence that in the early 1750s Franklin himself tried the iron rod method for experimentation.
It is clear that Franklin's electrical experiments led to his invention
of the lightning rod. He noted that conductors with a sharp rather than a
smooth point were capable of discharging silently (like the case with
the kite), and at a far greater distance. He surmised that this
knowledge could be of use in protecting buildings from lightning, by
attaching upright rods of iron, made sharp and gilt to prevent rusting,
and from the foot of those rods a wire down to the outside of the
Building into the Ground. Following a series of experiments on
Franklin's own house, lightning rods were installed on the Academy of
Philadelphia (later the University of Pennsylvania) and the Pennsylvania
State House (later Independence Hall) in 1752.
http://www.benjaminfranklinhouse.org/site/sections/about_franklin/PhysicsTodayVol59no1p42_48.pdf
In the early 1750s, Franklin erected a lightning rod on top of his
house for the purposes of experimentation, protection and, perhaps, to
get electricity for experimentation without having to go through the
laborious process of creating it himself via a primitive battery.
Franklin's "iron rod" drew lightning down into his house. The rod was
connected to a bell and a second bell was connected to a grounded wire.
Every time there was an electrical storm, the bells would ring and
sparks would illuminate his house (see below).
http://www.ushistory.org/franklin/info/kite.htm
Basically, the kite experiment and the lightning rod are based on the
same scientific principle that electric charges try to find their way
in the shortest and easiest way to the ground. In the case of the kite
experiment it was the wet kite and string, the key and Franklins body
that grounded the clouds static electricity, and in the case of the
lightning rod it is the sharp metallic rod.
Follow in the Steps of Ben Franklin
Don’t try to repeat the kite experiment or to erect lightning rods
on building tops or elsewhere since those experiments are lethally
dangerous.
Warning: experiments with electricity
should be performed under the supervision of teachers or adults
familiar with electricity safety procedures. Especially, take in account
that experiments with capacitors (Leyden jars) can produce lethal high
voltage shocks dangerous to your health.
Build a Leyden Jar
Franklin used Leyden jars in many of his experiments as seen above.
Among others, he built, from a few Leyden jars connected in parallel, a
primitive kind of battery.
A Leyden jar is a primitive, first invented, capacitor where the
dielectric is a glass jar or a plastic container and the metal plates
are aluminum or metal foils coating the inside and outside of the jar or
container; the container is closed by a foil coated cap. A wire or
chain is connected to the inside coating and its free end is passed
through the cap. The two electrodes of the Leyden jar are the outer foil
coating and the wire or chain connected or touching the inside foil.
Take in account that in order to get good results the Leyden jar must
be grounded – put on any quite big metal surface. Wrinkles in the foil
can be a major leakage source and is recommended to apply melted
paraffin to the top of the both coatings for this end.
You can charge your Leyden jar with an electrostatic generator, such
as a Wimshurst machine or a Van de Graaf generator by connecting the
machine’s two connectors to the Leyden jar’s electrodes. If you do not
have an electrostatic machine you can also do it with an electrophorus
or simply by rubbing fur.
After your Leyden jar is charged you can discharge it and get sparks.
The following links will help you in this effort:
http://www.alaska.net/~natnkell/leyden.htm
https://nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/museum/leyden-jars
https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/leyden-jar
http://www.instructables.com/id/Make-A-Water-Leyden-Jar/
Build Your Benjamin Franklin Lightning Bells
As mentioned above, Franklin erected a lightning rod on top of his
house. The rod was connected to a bell and a second bell was connected
to a grounded wire and a clapper or ball was suspended between them from
an insulated stand. Every time there was an electrical storm
approaching, the bells would ring. This electrostatic device was
invented in 1742 by Andrew Gordon, Professor of Natural Philosophy at
the University at Erfurt, Germany. Franklin used Gordon’s idea in order
to build his storm alarm.
We are not going to connect our bells to any lightning roads since
this is extremely dangerous. Instead we are going to use either a
Wimshurst Static Electric Machine or a Van de Graaff generator or a TV
set as our static electricity resource.
How does this interesting device works? The lightning rod will charge
the bell which is connected to it. Then this bell will attract the
clapper because of rearrangement of electrical charges inside the
clapper through charge induction. When the clapper hits the charged bell
it will become charged to the same charge potential and therefore it
will be repelled. Since the opposite bell is charged oppositely this
will also attract the clapper towards it. When the ball touches the
second bell its charge is transferred to the clapper and as a result the
clapper is charged the same and is repelled again, and the process
repeats.
For more information:
http://scitoys.com/scitoys/scitoys/electro/electro4.html
http://www.rmcybernetics.com/projects/experiments/experiments_franklin_bells_lightning_detector.htm
http://www.history.org/History/teaching/enewsletter/volume7/jan09/teachstrategy.cfm
http://www.arcsandsparks.com/franklin.html
Further Reading
Links
Franklin's Kite
Franklin's Kite - Museum of Science, Boston (MOS)
Franklin and His Electric Kite - The Electric Franklin
Benjamin Franklin's Kite Experiment - codecheck.com
Was Ben Franklin's Kite a Hoax? - hoaxes.org
General Resources
The Electric Franklin
Benjamin Franklin: Glimpses of the Man - The Franklin Institute
Benjamin Franklin: A Documentary History - J.A. Leo Lemay
Benjamin Franklin - PBS
The Autobiography of Benjamin Franklin - Archiving Early America
Benjamin Franklin Biography - biography.com
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