Disc overy of Current Electric ity. A great debate between two Italian scientists about the nature of current electricity. vs. Luigi Galvani 1737-1798 (Medical doctor). Alessandro Volta 1745 - 1827 (Physicist). Luigi Galvani. Started…with an unexpected observation by Galvani.
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1745 - 1827
Started…with an unexpected
observation by Galvani
Observed twitching (抽搐)
of frog’s legs when
Click to see !
What causes the legs of a dead frog to twitch?
More observations by Galvani
They twitched when I was dissecting the frog near a static electricity machine!
They also twitched during thunderstorms!
Galvani’s experimental setup 1:
Frog’s legs stimulated by
Galvani’s experimental setup 2:
Frog’s legs stimulated by an
The twitching may be connected in some way to electricity……
Twitching still occurred in good weather conditions away from the static electricity generator when he hung the dead frogs from an iron fence by brass hooks through their spinal cord.
Galvani began a series of investigations to test his ideas
He transferred the garden setting to his laboratory (with no thunderstorm or electrostatic machine). Twitching still occurred when he laid the frog on an iron plate and pressed the brass hook, which passed through the spinal cord, against the plate.
Observed the twitching of frog’s legs during dissection.
Further observation: Twitching of frog’s legs also occurred
near an electrostatic machine and during thunderstorms.
Hypothesis: The twitching is connected with electricity.
Investigation: Confirmed that the twitching still occurred
without an external supply of electricity.
(electrostatic machines and thunderstorms)
Conclusion: The electricity was inside the animal.
(He called it “animal electricity”)
“The electricity comes from the animal itself.”
However, another Italian scientist named Alessandro Volta was skeptical (懷疑) of Galvani’s explanation……
“The electricity comes from outside,
not from the frog itself.”
Skepticism (懷疑)is important
for advances in scientific knowledge.
symbol as a sign pointing
to the right.
which means “get gradually softer”
Mathematicians may interpret
this symbol as “greater than”
Galvani: Medical doctor’s
Observation is not always
Observation may be affected by personal background or training.
Describe this picture.
Observation is often affected by our background knowledge and what we expect to see.
Science is evidence-based.It is always evidence that matters. Evidence can help to establish or refute
Q: Imagine you are Galvani, what evidence would you give to support your “animal electricity” theory ?
Q: Now imagine you are Volta, what evidence would you give to support your theory, that it is the two different metals that cause the twitching of the frog’s body?
Galvani showedthe legs could twitch even when two similar metals were used for the dissection.
Click to see!
Volta arguedthere existed a tiny
difference between the metals even
though they appeared the same.
Galvani successfully demonstrated thatthe frog’s legs could twitch in the absence of any metals!
(by just touching the nerves)
It appeared to be a piece of evidence that no one can object to!
the sciatic nerve of the frog
( 坐骨神經 )
Stimulating the sciatic nerve can make the frog’s legs twitch.
The sciatic nerve is a large nerve that runs down the lower limb. It is the longest single nerve in the body.
Galvani successfully demonstrated that the frog’s legs could twitch in the absence of any metals!
Had Galvani defeated Volta?
Galvani got rid of the metal but Volta
got rid of the whole frog!
Pictures of Voltaic Pile
Q: Now you know all the evidence provided
by Volta and Galvani, choose whom to
What considerations affect your
evaluation of the two theories?
Reason 1: Other scientists can reproduce Volta’s experimental work easily.
(Just putting two metals into sodium chloride solution)
Galvani’s experimental work is relatively more difficult to repeat. (Good surgical skills are required to dissect and stimulate the nerve ends of frog’s legs)
The difficulty of reproducing evidence
affects the acceptability of the claims.
Scientific experiments should be repeatable/reproducible.
The electric current produced by Volta’s work could be easily demonstrated by showing repeated sparks.
However, “bioelectricity” (生物電流) in living cells is too small and Galvani did not have the technology (e.g. CRO) to measure the current.
Actually both Galvani and Volta were right!
Limitation of technology can hinder the development of science.
The Voltaic Pile was the first device that could produce a
steady current. (The first electric battery in history)
An Italian banknote showing Volta’s picture and his Voltaic Pile to celebrate his contribution to science.
Volta demonstrating his
battery to Napoleon in 1801
Galvani was the first scientist to discover that
muscles and nerve cells produce electricity.
Though he could not prove it due to the
limitations of technology at that time
Galvanism(電療法) describes the contraction of a muscle stimulated by an electric current. (This effect was named by Volta to honour Galvani.)
With the help of modern
technology, the function of nerve cells and their structures are studied in great detail nowadays.
Through the debate between Volta and Galvani, we
Scientific knowledge changes because of
- New evidence
(Volta’s evidence refuted Galvani’s “animal electricity” theory.)
- Advances in technology
(Galvani’s “animal electricity” was recognized only after
the invention of instruments for measuring bioelectricity.)
Can you think of more
Through the debate between Volta and Galvani, we also learn thatskepticism can drive the development of scientific research.
Q. Can you think of recent examples where
skepticism has driven the development
of scientific knowledge?
work carried on by others
Building up and further development of scientific knowledge
Perseverance in investigation
Observation by chance
Not enough for success