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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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a great debate between two italian scientists about the nature of current electricity
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)

slide3

Luigi Galvani

Started…with an unexpected

observation by Galvani

Observed twitching (抽搐)

of frog’s legs when

dissecting them

Click to see !

What causes the legs of a dead frog to twitch?

slide4

Luigi Galvani

More observations by Galvani

They twitched when I was dissecting the frog near a static electricity machine!

They also twitched during thunderstorms!

slide5

Luigi Galvani

Galvani’s experimental setup 1:

Frog’s legs stimulated by

electrical storms

Galvani’s experimental setup 2:

Frog’s legs stimulated by an

electrostatic machine

The twitching may be connected in some way to electricity……

further observations
Further observations

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.

based on his observations what was galvani s conclusion

Luigi Galvani

Based on his observations, what was Galvani’s conclusion?

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”)

slide8

Luigi Galvani

“The electricity comes from the animal itself.”

However, another Italian scientist named Alessandro Volta was skeptical (懷疑) of Galvani’s explanation……

  • Galvani’s followers travelled all over Europe
  • publicly performing the demonstrations that
  • made the frogs twitch.
  • They did the demonstration using different animals.
  • The number of supporters for Galvani kept growing.

Alessandro Volta

volta s different viewpoints
Volta’s different viewpoints
  • He drew attention to the different metals used in Galvani’s experiments.
  • He suggested that the twitching could only be produced when two different metals were used in dissection or in the setup.

“The electricity comes from outside,

not from the frog itself.”

Alessandro Volta

think about these questions
Think about these questions …
  • What would have happened if no one had been skeptical of the “animal electricity” theory proposed by Galvani?
  • Since Galvani was facing the challenge by Volta, he had to further investigate to find more solid evidence for his claim. Volta also had to seek for more evidence to challenge Galvani’s view.

Skepticism (懷疑)is important

for advances in scientific knowledge.

  • Suggest why Volta and Galvani had different theories about the same observation(twitching of frog’s legs)?
  • Let’s play a game …
slide12

Some people may interpret the

symbol as a sign pointing

to the right.

slide13

Musicians may interpret this symbol as

“decrescendo”,

which means “get gradually softer”

slide14

a + b > 12

Mathematicians may interpret

this symbol as “greater than”

slide15

Volta: Physicist’s view

Galvani: Medical doctor’s

view

Observation is not always

objective

Observation may be affected by personal background or training.

vs

slide17

< Mother and Son>

Describe this picture.

slide18

Observation is often affected by our background knowledge and what we expect to see.

  • This phenomenon is described as “theory-laden observation”
animal electricity vs metal electricity
“Animal electricity” vs“Metal electricity”

Science is evidence-based.It is always evidence that matters. Evidence can help to establish or refute

(駁倒)scientific knowledge.

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?

round one
Round One

Galvani showedthe legs could twitch even when two similar metals were used for the dissection.

Luigi Galvani

Click to see!

Volta arguedthere existed a tiny

difference between the metals even

though they appeared the same.

Alessandro Volta

round two
Round Two

Galvani successfully demonstrated thatthe frog’s legs could twitch in the absence of any metals!

(by just touching the nerves)

Luigi Galvani

It appeared to be a piece of evidence that no one can object to!

slide22

In fact Galvani stimulated

the sciatic nerve of the frog

Sciatic nerve

( 坐骨神經 )

Stimulating the sciatic nerve can make the frog’s legs twitch.

location of the sciatic nerve inside the frog
Location of the sciatic nerve inside the frog

The sciatic nerve is a large nerve that runs down the lower limb. It is the longest single nerve in the body.

round two24
Round Two

Galvani successfully demonstrated that the frog’s legs could twitch in the absence of any metals!

Had Galvani defeated Volta?

Not yet…

Galvani got rid of the metal but Volta

got rid of the whole frog!

round two25
Round Two
  • Volta’s Experiment:Put pieces of zinc metal and pieces of copper metal alternately with cotton pads soaked in a solution of sodium chloride (electrolyte) between each pair. Electricity was generated as shown by repeated sparks.This wasthe first electric battery in history providing continuous current. It was later called a Voltaic Pile.

Pictures of Voltaic Pile

Repeated sparks

do you support galvani or volta
Do you support Galvani or Volta?

Q: Now you know all the evidence provided

by Volta and Galvani, choose whom to

support.

What considerations affect your

evaluation of the two theories?

slide27

Galvani was defeated! (for a while…)

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.

slide28

Galvani was defeated! (for a while…)

Reason 2:

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.

Galvanometer

CRO

slide29

Significance of Volta’s Findings …

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

slide30

Significance of Galvani’s Findings …

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.

slide31

Scientific knowledge is tentative (暫時性的)

Through the debate between Volta and Galvani, we

learn that:

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

examples?

scientists skepticism
Scientists’skepticism

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?

slide33

This story also tells us ……

Scientific discovery

work carried on by others

Building up and further development of scientific knowledge

Perseverance in investigation

Observation by chance

Insight

+

+

Not enough for success