In ancient times, lightning was
seen as a tool of the gods. In Viking
legend, it was Thor’s hammer striking an anvil in the sky that was responsible
for lightning. For the Greeks, it was
Zeus who threw lightning down to the earth.
North American Indian tribes thought that lightning was produced by a
mystical bird with flashing feathers whose flapping caused thunder.
Even now,
hundreds of years after the first scientific work with lightning, people remain
in awe of its power. In the 18th
century, the first systematic scientific study of lightning was carried out by
Benjamin Franklin. Before Franklin’s
experiments, electrical science had grown to the point of separating positive
and negative charges, and had developed primitive capacitors. The sparks produced in laboratories were
noted as similar to lightning, but it was Franklin who designed an experiment
to prove that lightning was electrical.
Benjamin
Franklin believed that clouds must be electrically charged, which would mean
that lightning must also be electrical.
For his first experiment, he stood on an electrical stand with an iron
rod in one hand to achieve an electrical discharge between the other hand and
the ground. If Franklin’s belief that
the clouds were electrically charged was correct, then sparks should leap
between the iron rod and a grounded wire held by and insulating wax candle. This test method was published in London and
performed in both England and France.
Thomas Francois D’Alibard of France was the first to successfully
perform this experiment in May of 1752, when sparks were seen jumping from the
iron rod during a thunderstorm.
Image taken
from: http://www.thebakken.org/electricity/Franklin-kite-experiment.html
Before Benjamin
Franklin achieved results from his first experiment, he devised a better way of
testing his hypothesis. This new
experiment was his infamous kite experiment.
The kite replaced the iron rod, as it could reach a higher
elevation. In 1752 Franklin found
success during a Pennsylvania thunderstorm.
When a storm cloud passed over his kite, sparks flew from a key tied to
the bottom of the damp kite string. He
was also able to collect a charge on a Leyden Jar, which was a simple
capacitor, that was connected to the key via a thin metal wire. Using this he was able to determine that the
charge was negative. Franklin was not
affected by the charges thanks to an insulating dry silk ribbon that connected
the kite string to Franklin’s hand.
Upon reaching out to touch the key, the negative charges were attracted
so strongly to the positive charges in his body that a spark jumped to
Franklin’s hand. Many who have
attempted to duplicate Franklin’s experiment have died trying.