92 ALESSANDRO VOLTA
F
or centuries, philosophers
had wondered at the
terrifying power of
lightning, and also at the way in
which sparks can be drawn from
solids such as amber when rubbed
with a silk cloth. The Greek word
for amber was “electron,” and the
sparking phenomenon became
known as static electricity.
In an experiment of 1754,
Benjamin Franklin flew a kite
into a thunderstorm and showed
that these two phenomena were
closely related. When he saw
sparks flying from a brass key tied
to the kite’s line, he proved that
the clouds were electrified, and
that lightning is also a form of
electricity. Franklin’s work inspired
Joseph Priestley to publish a
comprehensive work on The History
and Present State of Electricity in
176 7. But it was the Italian Luigi
Galvani, a lecturer in anatomy at
the University of Bologna, who, in
1780, took the first major steps
toward understanding electricity
when he noticed a frog’s leg twitch.
Galvani was investigating a
theory that animals are driven by
“animal electricity,” whatever that
was, and was dissecting frogs to
look for evidence of this. He noticed
that if there was a machine nearby
generating static electricity, a frog’s
leg lying on the bench suddenly
twitched, even though the frog
was long dead. The same thing
happened when a frog’s leg was
hung on a brass hook that came
into contact with an iron fence.
Galvani believed this evidence
supported his belief that electricity
was coming from the frog itself.Luigi Galvani is shown here
conducting his famous frog’s legs
experiment. He believed that animals
were driven by an electrical force,
which he called “animal electricity.”IN CONTEXT
BRANCH
PhysicsBEFORE
1754 Benjamin Franklin
proves that lightning is natural
electricity with his famous
kite experiment.1767 Joseph Priestley
publishes a comprehensive
account of static electricity.1780 Luigi Galvani conducts
his frog’s legs experiments
with “animal electricity.”AFTER
1800 English chemists William
Nicholson and Anthony Carlisle
use a Voltaic pile to split water
into its two elements, oxygen
and hydrogen.1807 Humphry Davy isolates
the elements potassium and
sodium using electricity.1820 Hans Christian Ørsted
reveals the link between
magnetism and electricity.Volta’s breakthrough
Galvani’s younger colleague
Alessandro Volta, a professor of
natural philosophy, was intrigued
by Galvani’s observations and was
initially convinced by his theory.
Volta himself had a notable
background in electricity
experiments. In 1775, he had
invented the “electrophorus,”
a device that provided an
instant source of electricity for an
experiment (the modern equivalent
is a capacitor). It consisted of aA dead frog’s legs twitch
when connected to two
different pieces of metal.When the two metals
are touched to the tongue,
it produces a curious
sensation...The force can be
multiplied by connecting
a series of these metals
in a column.This electrical force
must come from the two
different metals attached
to the frog’s leg.