2A great debate between two Italian scientists about the nature of current electricity vsLuigi Galvani(Medical doctor)Alessandro Volta(Physicist)
3What causes the legs of a dead frog to twitch? Started…with an unexpectedobservation by GalvaniObserved twitching (抽搐)of frog’s legs whendissecting themClick to see !Luigi GalvaniWhat causes the legs of a dead frog to twitch?
4They also twitched during thunderstorms! More observations by GalvaniThey twitched when I was dissecting the frog near a static electricity machine!They also twitched during thunderstorms!Luigi Galvani
5The twitching may be connected in some way to electricity…… Galvani’s experimental setup 1:Frog’s legs stimulated byelectrical stormsGalvani’s experimental setup 2:Frog’s legs stimulated by anelectrostatic machineLuigi GalvaniThe twitching may be connected in some way to electricity……
6Further observationsTwitching 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 ideasHe 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.
7Based on his observations, what was Galvani’s conclusion? Luigi GalvaniObserved the twitching of frog’s legs during dissection.Further observation: Twitching of frog’s legs also occurrednear an electrostatic machine and during thunderstorms.Hypothesis: The twitching is connected with electricity.Investigation: Confirmed that the twitching still occurredwithout an external supply of electricity.(electrostatic machines and thunderstorms)Conclusion: The electricity was inside the animal.(He called it “animal electricity”)
8“The electricity comes from the animal itself.” Galvani’s followers travelled all over Europepublicly performing the demonstrations thatmade the frogs twitch.They did the demonstration using different animals.The number of supporters for Galvani kept growing.Luigi GalvaniHowever, another Italian scientist named Alessandro Volta was skeptical (懷疑) of Galvani’s explanation……Alessandro Volta
9Volta’s different viewpoints “The electricity comes from outside,not from the frog itself.”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.Alessandro Volta
10Think 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 importantfor 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 …
12Some people may interpret the symbol as a sign pointingto the right.
13Musicians may interpret this symbol as “decrescendo”, which means “get gradually softer”
14a + b > 12 Mathematicians may interpret this symbol as “greater than”
15vs objective Observation is not always Observation may be affected by personal background or training.Volta: Physicist’s viewGalvani: Medical doctor’sviewvs
16Describe this picture. Write down what you see. Don’t tell the others. ---Describe this picture.
17< Mother and Son > Why some of you see rocks and trees, while others see a mother and a son?What effect does the title have on your observation?---Describe this picture.
18This phenomenon is described as “theory-laden observation” Observation is often affected by our background knowledge and what we expect to see.This phenomenon is described as “theory-laden observation”The term “theory-laden” is not so important as long as students understand the sometimes unavoidable subjective nature of observation
19“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?
20Round OneGalvani showed the legs could twitch even when two similar metals were used for the dissection.Luigi GalvaniClick to see!Volta argued there existed a tinydifference between the metals eventhough they appeared the same.Alessandro Volta
21Round TwoGalvani successfully demonstrated that the frog’s legs could twitch in the absence of any metals!(by just touching the nerves)Luigi GalvaniIt appeared to be a piece of evidence that no one can object to!
22In fact Galvani stimulated the sciatic nerve of the frog ( 坐骨神經 )Stimulating the sciatic nerve can make the frog’s legs twitch.
23Location 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.
24Round TwoGalvani 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 Voltagot rid of the whole frog!
25Round TwoVolta’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 was the first electric battery in history providing continuous current. It was later called a Voltaic Pile.Pictures of Voltaic PileRepeated sparks
26Do you support Galvani or Volta? Q: Now you know all the evidence providedby Volta and Galvani, choose whom tosupport.What considerations affect yourevaluation of the two theories?
27Galvani 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 evidenceaffects the acceptability of the claims.Scientific experiments should be repeatable/reproducible.
28Galvani 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.GalvanometerCRO
29Significance of Volta’s Findings … The Voltaic Pile was the first device that could produce asteady current. (The first electric battery in history)Volta demonstrating hisbattery to Napoleon in 1801An Italian banknote showing Volta’s picture and his Voltaic Pile to celebrate his contribution to science.
30Significance of Galvani’s Findings … Galvani was the first scientist to discover thatmuscles and nerve cells produce electricity.Though he could not prove it due to thelimitations of technology at that timeGalvanism (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 moderntechnology, the function of nerve cells and their structures are studied in great detail nowadays.
31Scientific knowledge is tentative (暫時性的) Through the debate between Volta and Galvani, welearn 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 afterthe invention of instruments for measuring bioelectricity.)More examples: The cause of stomach ulcer (Stress / Bacterium),Nature of light (Wave / Particle / Wave-particle duality),Earth and solar system (Geocentrism / Heliocentrism?)…….etcCan you think of moreexamples?
32Scientists’ skepticism Through the debate between Volta and Galvani, we also learn that skepticism can drive the development of scientific research.Q. Can you think of recent examples whereskepticism has driven the developmentof scientific knowledge?
33Perseverance in investigation This story also tells us ……Perseverance in investigationObservation by chance+Insight+Not enough for successScientific discoverywork carried on by othersBuilding up and further development of scientific knowledge