The Circular Reasoning of “Verifying” Ohm’s Law in School

The experimental set-up

A common experiment done in high school is to verify Ohm’s law. Ohm’s law, or rather one part of it, states that the current through a resistance is directly proportional to the difference in potential (voltage) between its two ends.

The diagram below represents the circuit that is often used for verifying this relationship. A fixed resistance R is connected to a battery in series with a variable resistance (rheostat). A voltmeter is connected in parallel to R and an ammeter in series.

The resistance of the rheostat is varied to get different sets of values of voltage and current which may then be plotted on a graph to show that they are proportional.

Do voltmeters actually measure potential difference?

The fallacy arises from how voltage is measured. The analog voltmeters commonly used are actually modified galvanometers in which a magnetic needle is deflected depending on the strength of the current. In fact, voltmeters make use of Ohm’s law to convert the needle’s deflection to a voltage reading in the first place!

Digital multimeters work in a different way, but they too depend on current that’s drawn from the circuit, and their calibration too likely involves the application of Ohm’s law at some point.

It is therefore apparent that it makes little sense to “verify” Ohm’s law using measuring instruments that are themselves designed on the basis of the same law.

Axiom for Ohm, Hypothesis to be tested for Kohlrausch

What Georg Simon Ohm did was to define a new quantity called potential difference for a circuit element. Electric potential is essentially an electrostatic quantity and Ohm used it to explain what happened in a circuit with a continuous current.

Ohm himself never intended to try to measure this potential difference. However, Rudolf Kohlrausch did exactly that, a quarter of a century later.

Kohlrausch used a special, sensitive electrometer to directly measure the electrostatic potential difference between the ends of a resistance and showed that it was indeed proportional to the current.

His work was published in 1849 as a paper titled Die elektroskopischen Eigenschaften der geschlossenen galvanischen Kette (The Electrostatic Properties of a Closed Galvanic Circuit). Unfortunately, an English translation of the paper does not seem to be available.


  1. Nahum Kipnis. A Law of Physics in the Classroom: the Case of Ohm’s Law
  2. R. Kohlrausch. Die elektroskopischen Eigenschaften der geschlossenen galvanischen Kette. Annalen der Physik vol 78

Eunice Newton Foote: the Woman who Foresaw Global Warming

A short paper titled “Circumstances affecting the Heat of Sun’s rays” appeared in the 1856 edition of the American Journal of Science and Arts. It was only a page and a half long, and had a brief and crisp description of three experiments.

Effect of density

The first one studied how the warming of air by the Sun’s rays was affected by its density. Two identical containers, one with rarefied air and the other with condensed air, were kept side by side in the sun.

The author, Eunice Newton Foote, found that the temperature of the condensed air rose significantly more (to 110 oF) than that of the rarefied air (88 oF).

Effect of humidity

In the second experiment, Foote used one container with humid air and another with dry air and saw that the former became more warm.

Warming of different gases

The final experiment described in the paper compared the warming of different gases as compared to air. Foote noted that a jar filled with carbon dioxide (or “carbonic acid gas” as it was known then) got heated much more than one with common air.

She postulated that a greater proportion of carbon dioxide in the atmosphere could cause an increase in temperature, effectively predicting global warming as we know it today.

Unknown until 2010, Celebrated in 2018

Foote’s work was not widely recognised until as recently as 2010, when Ray Sorenson, a retired geologist stumbled upon her paper. Sorenson realised that Foote’s paper preceded by three years the work of John Tyndall, who had been previously credited with recognising the greenhouse effect of carbon dioxide.

In 2018, 162 years after her landmark paper, Eunice Newton Foote’s work was commemorated in a symposium at the University of California Santa Barbara. A charming short film titled Eunice was also released in the same year to honour the forgotten scientist.


  1. Wikipedia article on Eunice Newton Foote.
  2. New York Times. Overlooked No More: Eunice Foote, Climate Scientist Lost to History.
  4. American Journal of Science and Arts 1856.

Nahum Kipnis on the 7 Benefits of a Historical-Investigative Approach to Science Teaching

In the introduction to his book Rediscovering Optics, physics educator and history of science scholar Nahum Kipnis lucidly summaries what he considers to be the main benefits of a historical-investigative approach to science teaching – an approach in which historical experiments are repeated and the findings reconstructed by the students. I paraphrase them below.

1. Doing something “real”

Most laboratory work in school can be described as “cookbook experiments”. There are pre-determined procedures to be followed with expected pre-determined outcomes. The students are assessed on how well they can follow the procedure and analyse the data obtained. It has very little in common with a real scientific investigation.

Recreating a historical experiment, on the other hand, places the activity in a context. The students can be introduced to the question that was being investigated by scientists in the past, and can carry out the experiment as if they were trying to find the answer themselves. Reliving an important event in the history of science may also be exciting to many students.

2. As smart as Galileo and Newton!

Students tend to ask questions and harbour preconceptions that are often remarkably similar to the ones early scientists did. In repeating historical experiments, the students can also independently arrive at conclusions similar to those put forward by these scientists. This could enable students to see themselves as scientists, and boost their self-confidence and interest in learning science.

3. Doing, not watching

This is not specific to the historical-investigative approach, but generally students engage better if they themselves carry out an experiment rather than simply watch it demonstrated by the teacher. In this approach, however, it becomes imperative since the students are trying to find an answer to a question on their own.

4. The scientific method in practice

By carrying out a series of experiments and deducing scientific concepts independently, the students are enacting a microcosm of the discoveries made in the past. This would give them a taste of how new knowledge is constructed by the interaction of theory and experiment.

5. “Obsolete” theories can help in understanding

Many old theories are based on simple models. This makes them more easily accessible than modern theories to students who are introduced to a new topic for the first time. The students can analyse and critique them while they make sense of the phenomena under study.

For example, while teaching electrostatics to class 6 students, I have found it helpful to completely sidestep the modern knowledge of subatomic particles and use the 18th century conception of two electrical fluids – resinous and vitreous.

Teachers need not feel that they are teaching something “wrong” by tapping into the potential of the old theories. History of science tells us that no theory is final.

6. Qualitative, not quantitative

Until the mid-1800s, most scientific experiments were qualitative. Many of the quantities and units that we obsess over in high school science were yet to be precisely defined. Several important physical laws were derived from rather crude measurements.

In a historical approach, this opens the door for setting up a much wider variety of experiments than the standard ones, using commonly available materials. Aspects of experimental work like precise measurements and estimation of error which are given a lot of attention in the modern labs are of much less consequence for early experiments.

7. Treasure trove of stories

History of science is full of fascinating stories that are sure to captivate students, whether they are interested in science or not. They also reveal the messy human side of science, which is totally ignored in a conventional approach that focuses on the mastery of modern scientific knowledge.

Ampere’s Alternate Interpretation of Electromagnetism

A. K. T. Assis is a Brazilian scholar who has written some intriguing books on physics and the history of physics. He has very generously made all these books available for free access on his website –

I have been flipping through the book Ampere’s Electrodynamics by Prof. Assis. It requires a much closer study, but I wanted to write about one thing that stood out for me.

All this while, I had thought of the development of electromagnetism as a linear timeline. I had thought that starting with Oersted’s experiment, other scientists had added bit by bit to the understanding of electromagnetic phenomena, until Maxwell synthesised all the knowledge into one single theory. This book showed me that the actual history was very different.

It seems that there were many differences of opinion between Ampere and the other prominent scientists of the time regarding how to interpret the phenomena. The following snapshot from the book’s Contents pages promises an enticing discussion of these scientific controversies.

The most remarkable aspect of Ampere’s theory was that he imagined all magnetic phenomena as arising from electric currents. In this, almost all his contemporaries disagreed with him vehemently.

For Ampere, there was no ‘magnetic field’ – it was simply a manifestation of an interaction between currents. He hypothesised that there were circular electric currents inside magnets and inside the Earth, which we know today to be true.

The following muse (edited for readability) from Ampere’s writings is a striking example of the role of imagination and creativity in science:

“Suppose we had known that a magnetic needle is influenced by an electric current into a position perpendicular to the wire before knowing that a magnetic needle points to the geographical north. Then, would not the simplest idea and the one that would occur immediately to anyone who wanted to explain it be that there is an electric current inside the Earth?

Andre Marie Ampere

Assis’ book also includes a complete English translation of Ampere’s classic work written in 1826, Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience.

I hope to write more on this when I do manage to study this book in detail.

When Young Faraday’s First Discovery Led to Charges of Plagiarism

Two Faradays and two electromagnetic discoveries

Michael Faraday is one of the most well known names in science, probably even for people outside science. He made two landmark discoveries which led to the invention of the electric motor and the electric generator — two devices which we benefit from, every single day of our lives. But equally legendary is Faraday’s fairytale journey from being a bookbinder’s apprentice to the assistant of Britain’s biggest scientist of the time, Humphry Davy.

The relationship of Faraday and Davy — master and servant, professor and student, and eventually and inevitably rivals — is a fascinating story in itself. A story that reveals a lot about not just the two individuals but also the quirks of English society at the time.

The two discoveries in electromagnetism referred to above were not made together. In fact, they were separated by a decade. And they were made by two different Faradays. The first by a 30-year old lab assistant with his head brimming with ideas and craving for an intellectual outlet; the second by a 40-year old established scientist, elected to the Royal Society and successor to the illustrious position previously occupied by his mentor.

It is the first discovery that is the subject of this article.

Electromagnetic Rotations

In the summer of 1820, Danish scientist H. C. Oersted had discovered that a magnetic compass needle is deflected when kept near a current-carrying wire. News of this momentous discovery soon reached all parts of Europe, and it reached Humphry Davy too. Faraday got the opportunity to learn about the phenomenon assisting Davy in his recreation of Oersted’s experiment, and it captivated him.

By now, Faraday had been in the service of Davy and the Royal Institution for over eight years. From the very first days, Davy had recognised the brilliance of Faraday’s intellect. As Faraday assisted Davy in the laboratory, the two would engage in conversations that played a big part in Faraday growing into a scientist in his own right.

The deflection of the magnetic needle was a hot topic of discussion that year. Faraday had probably been a spectator if not a participant in the conversations Davy had with his friend William Hyde Wollaston on the subject. Wollaston thought that it must be possible to somehow produce continuous motion using magnets and electric currents, but had failed in his attempts.

After his work hours, Faraday played with wires and batteries and magnets. One day, he put together a strange apparatus. He fixed a long magnet in the middle of a cup and filled the rest of the cup with mercury. Above the magnet and the cup was a support from which a piece of wire was hanging freely, with one end dipped in the mercury.

Faraday connected one terminal of a battery to the hanging wire through its support, and the other terminal to the mercury in the cup. The moment the circuit was completed, the hanging wire began going around the magnet, in circumambulation. Faraday had got what he was looking for — continuous electromagnetic rotations!

Announcement and indignation

This should have been the moment when Faraday became a celebrated scientist, but it wasn’t.

Faraday excitedly called on Wollaston to tell him about the electromagnetic rotations, but Wollaston was out of town. Faraday knew that he had discovered something extremely important, and couldn’t wait to communicate it to the world. He wrote a 16-page article titled “On Some New Electro-Magnetical Motions” and naively sent it to the Quarterly Journal of Science for publication.

Within days, all hell broke loose. Members of the scientific community accused Faraday of stealing Wollaston’s ideas while the latter was still working on them. Faraday was also condemned for not acknowledging the knowledge he gained by assisting Davy in his experiments.

Davy did not overtly criticise Faraday. However, his silence when he could have doused the raging controversy suggests that he felt the criticism was deserved. Wollaston himself was graceful, and invited Faraday to come and discuss his new experiments. Wollaston must have realised that his own ideas were somewhat different from Faraday’s electromagnetic rotations.

Into an exile from electromagnetism

Faraday received the support of scientists in continental Europe, and he quickly grew in stature. However, in London, he was still Davy’s servant.

Over the next few months and years, Davy kept Faraday busy with many non-scientific tasks. Even in science, Davy assigned work in other areas of research that made sure there wasn’t much time for Faraday to build on his work in electromagnetism. Faraday’s diary entries of the 1820s reveal that he hardly did any electromagnetic experiments for the rest of the decade.

Still, Davy couldn’t stop the emergence of Faraday as a scientist. In 1823, Faraday’s name came up for election as a Fellow of the Royal Society. Davy staunchly opposed the nomination, and for the first time publicly condemned Faraday for his indiscretion of a couple of years earlier. Faraday, however, had the support of a majority of the members including Wollaston, who clearly did not hold any grudge against him.

Nevertheless, it was only after the death of Davy in 1829 that Faraday could truly get back to the work that he was destined to do. This time, in 1831, Faraday would go on to discover how electric currents could be produced by the motion of a magnet and a wire. Even today, most of our electrical energy is produced using this principle uncovered by him.


James Hamilton. A life of discovery : Michael Faraday, giant of the scientific revolution

Electrostatics in Middle-School – Part 3: Early Electrical Knowledge in the Classroom

Read the previous parts if you haven’t: Part 1 Part 2

In the previous article, I briefly introduced the major developments in the knowledge of electricity up to the first half of the 17th century. So, what lessons and activities for the classroom can be designed based on this?

I intend to describe one possible approach here. I leave it to the creativity and imagination of readers who may be teachers to think of better ways. I hope you’ll come back and share your ideas in the comments if you get inspired by this and come up with other ideas to try out!

From plastic ruler to amber

Every student would invariably have rubbed a plastic ruler on hair and observed tiny paper bits flying towards it. I would tell my students that people in ancient Greece had done the same thing with amber, as a starting point for the narrative. Although amber itself is a rare and expensive material and difficult to come by, some students would have read about it and would be eager to share with the class what they knew about it.

Is it magnetism?

It might seem like a trivial thing, but asking students whether they think that this attraction happens due to magnetism is a good way to get them warmed up for scientific inquiry. The students will be forced to articulate why the attracting power of the rubbed plastic ruler cannot be magnetism. And if you’re lucky, you may even have one student in class who asserts that it is magnetism and states her reasons — then it won’t be a trivial discussion any more!

Depending on how the debate unfolds, there may be opportunities to get the students to design simple experiments to check if a rubbed plastic ruler has any properties of a magnet.

  • Does a rubbed plastic ruler have poles? Are the paper bits attracted more strongly to the ends as in the case of iron pieces to a magnet?
  • Does the rubbed plastic ruler have any directionality? Does it align in the north-south direction if suspended by a thread?

Which other materials become attracting when rubbed?

The students can then repeat William Gilbert’s experiments to find out which materials around them get this attracting power when rubbed. I would get the students to make their own simple versorium by hanging a pencil from their desks with a thread. They would then pick up every substance they could find around them and check whether they can make the versorium rotate when rubbed. Some students might start exploring the question of whether the material used for rubbing matters.

Gilbert’s versorium
(Image: Public domain)

This activity is great fun, but it also quickly reveals the difficulties and limitations of scientific inquiry in the classroom. What the students will learn from the activity depends a lot on what materials they have with them to test with the versorium.

Ideally there would be several materials that are electrics and several that are non-electrics. However, this is not so easy in practice. Apart from most plastics like polythene, PVC, etc. there aren’t too many common materials that easily become charged on rubbing. In very dry weather, you can succeed in charging candle wax, a rubber eraser and sometimes paper — enough to detect with a versorium.

One question I was faced with was whether I should choose the set of materials I wanted the students to experiment with. I could make sure that there were different kinds of electrics and non-electrics in the set. But wasn’t that cheating? Wasn’t that in a way pre-determining what the students would “discover”? Could I even say that the students were “discovering” anything?

This is a complex question and I’ll share my thoughts on it in a later post. Here, it would suffice to say that in such situations, I’ve almost always tilted towards a pre-determined outcome — mostly due to my own personal discomfort with not knowing how a class will unfold!

Attraction and repulsion

One last experiment that can be done by the students based on this part of the story is on electrical repulsion. This can be demonstrated the first time, in case the students do not stumble upon this phenomenon on their own in the limited time they have.

It is actually the same experiment with the plastic ruler, but using small bits of aluminium foil instead of paper. With bits of aluminium foil, repulsion happens in a far more noticeable way when the pieces hit the ruler. Sometimes you can even get a foil piece to dance up and down between the ruler and the table!

Students can be asked to form their own hypotheses about why the aluminium foil pieces sometimes rebounded.

Electrostatics in Middle School – Part 2: Early Knowledge of Electricity

Read Part 1 if you haven’t.

Amber and Lodestone

Since antiquity, people have been fascinated and mystified by rare materials with special properties. Two such materials were amber — a fossilised resin from extinct pine-like trees — and lodestone — an iron-containing mineral that we now recognise as permanently magnetic.

The ancient Greek (4th century BCE) knew about the property of amber to attract light objects like feathers when rubbed. They also knew that lodestone could attract small bits of iron. Amber and lodestone were often mentioned in the same breath, because their powers to attract objects were strikingly similar.

An ant preserved in amber
Image: Anders L. Damgaard. CC-BY-SA

Jerome Cardan, a 16th century Italian mathematician and physician, was one of the first to make a clear distinction between the action of amber and lodestone. He noted that rubbed amber attracted any light object while lodestone attracted only objects made of iron. He also observed that the lodestone’s attraction was the strongest at its ends (poles) while amber seemed to have no such polarity.

Such distinctions between amber and lodestone remained scattered until the end of the 16th century. It was William Gilbert — Queen Elizabeth’s physician — who first studied electrical phenomena independently. His book De Magnete (“On the Magnet”) was published in 1600. The book was mostly about magnetism, but included Gilbert’s experiments on electricity. It is ironic that electricity was discussed only as a part of one chapter on magnetic attraction, yet it established the study of electricity as a separate branch of science.

William Gilbert demonstrating electrical experiments to Queen Elizabeth.
Image: Public Domain

Not just amber

Perhaps Gilbert’s greatest contribution to the study of electricity was his discovery that not just amber, but a large number of other substances too showed similar attractive powers when rubbed. His list included precious stones such as diamond, sapphire, carbuncle, opal and amethyst, artificial materials like glass, minerals like fluorspar from the mines, fossils like belemnites, sulfur and hard sealing wax.

Gilbert coined a new term for such materials which displayed the amber effect — he called them “electrics“.

The first electrical instrument

Gilbert also invented a handy little device to identify whether a substance was an electric or not. It consisted of a thin metal needle suspended such that it could rotate freely. If a rubbed electric was brought near one end, the needle promptly turned towards the electric. He called it the ‘versorium’ – Latin for ‘turn-about’.

Gilbert’s Versorium
Image: Public Domain

The versorium enabled Gilbert to detect even electrics with very weak attracting power, because the needle needed very little force to rotate on its support. Before the versorium was invented, an electric could be identified only if it directly attracted small objects, which needed a stronger force.

Do electrics repel too?

Thus far, all the studies on electricity only mentioned the power of attraction. In 1629, an Italian scholar named Niccolo Cabeo first reported that when a light object was attracted to an electric, often it rebounded to a distance of several inches after touching the electric. This seems to have been the first observation of electrical repulsion. Cabeo found this strange behaviour hard to explain, and the rebounding remained a mystery.

No significant progress in electrical research took place for almost another 100 years. Electricity continued to arouse the curiosity of scientists during this time, and several intriguing experiments were carried out. However, given that my primary purpose is to lay out a convenient narrative for teaching, I choose to skip them here.


In the next article, I will examine the lessons and classroom activities that can be designed based on the early discoveries discussed so far.


Duane Roller and Duane H. D. Roller. The Development of the Concept of Electric Charge: Electricity from the Greeks to Coulomb. Harvard Case Histories in Experimental Science – Volume 2

Sparks and Giggles: Electrostatics in Middle-School — Part 1 (Prelude)

Electrostatics and the school science curriculum

Electrostatics is a topic that sits awkwardly in the school science curriculum. In fact, it is hardly a topic in itself before it is introduced in all its mathematical glory in grade 11. Until then, students normally only encounter a handful of scattered electrostatic facts and phenomena without getting the opportunity to make meaningful connections.

As a student, I had carried out the ubiquitous experiment of rubbing a plastic ruler on my hair and seen little paper bits get attracted to it. I was told that this happened because the plastic ruler had become electrically charged. I was told that there were two kinds of charges, one was called positive and the other, negative. I was also told that the same kind of charges repelled each other and the opposite kinds attracted each other.

There seemed nothing unusual about all this, and I was happy to accept it as the truth. Many years later, I realised that perhaps it was the analogy with the easily observable magnetic poles that made it so easy to unquestioningly accept the existence of two kinds of electrical charges and their behaviour. (There is a fascinating historical connection here, which I will examine in an upcoming sequel.)

As an extension, the metal-leaf electroscope was touched upon, and so too the fact that lightning was a strong discharge of static electricity. That was all the electrostatics I learnt until grade 10, and I’m sure most others did, and continue to do today as well.

The neglect of electrostatics is not surprising at all when you look at the electrical devices around. Whether it is a lamp, a motor, a heater or a computer, almost all the devices we use work on electrical currents. There is a closed circuit involved, and there is electricity in motion. There are hardly any electrical devices in daily use where electrostatic charges build up and attract tiny bits of paper (old CRT-televisions being a notable exception, of course).

A blanket on fire and electrified children on chairs!

I grew up in the humid coastal state of Kerala. It was at the age of 22 that I moved to Pune for work. There, I first experienced a dry winter — when the relative humidity could fall as low as 20%. And one night I discovered that this had other ramifications apart from having to apply petroleum jelly to avoid cracked lips.

That winter, I was using a coarse woollen blanket provided by the school to cover myself while sleeping. One night, I woke up feeling cold. The blanket had slipped off my body. As I pulled the blanket back over me, I was dazzled by an intricate web of dim yellow sparkles emanating from the blanket. There was also a faint crackling sound.

Initially I thought I was dreaming and I pinched myself to check if I was. And no, the sparkling and crackling were real!

The next day, I spoke to a friend and colleague — also a science teacher — about what I saw. He explained to me that the extremely low humidity made it possible for electrostatic charges to accumulate to very high potentials, making such brilliant discharges possible.

I came to know from him that some children in the school had found innovative ways to have fun during dry weather. They would make one person sit on a plastic chair with her legs folded up. Another person would hit the back of the chair many times with a woollen sweater. Then, when you touch the person sitting on the chair, you get a strong shock that makes you jump!

It all started with electrostatics

All this piqued my curiosity immensely and I was lucky to find two indispensable sources to learn more about electrostatic phenomena. One was the BBC Four documentary series – Shock and Awe: The Story of Electricity hosted by Jim Al-Khalili, and the other was the Harvard Case History on the development of the concept of electric charge.

And what I learned from these sources completely turned the tables on what I thought I knew about electricity. For the first 200 years or so of its development (roughly 1600-1800), ‘electricity’ meant electrostatic phenomena. There were no batteries, no motors, no devices that you would recognise today as ‘electrical’. And an awful lot was discovered about electricity during this time.

This made me wonder if it was possible to approach the teaching of electricity in school from an entirely different angle. One that paralleled the historical development of ideas, and drew on those stories of discovery.

This was 2011, I was teaching chemistry to grades 9 and 10, and I wasn’t able to actually try this out. In 2013, I left teaching to explore other areas of work. However, I did return to teaching in 2016 and this time I had grade 6 science to teach. Exactly the age group I wanted to explore electrostatics with.

In the coming posts, I intend to document my attempt at teaching electrostatics using a historical approach to eager 11-year olds.

A Medical Doctor’s Sabbatical to Do Science Experiments

A forgotten name in science

Key contributions to scientific knowledge are almost always intertwined with the names of the scientist(s) who made those contributions. A glaring exception exists in the case of one of the most fundamental discoveries of all in the life sciences – photosynthesis.

Jan Ingen-Housz (1730-1799) was a Dutch physician who, at some points in his career served as the family doctor to the royal houses of England and Austria. He was interested in science and kept himself informed of the most recent advances in science, but did not have the time or equipment to do experimental work himself.

Jan Ingen-Housz
(Public Domain)

Through his reading, Ingen-Housz came to know about the work of Joseph Priestley on different kinds of gases (yes, Priestley again!). One experiment of Priestley’s particularly caught his imagination.

Priestley stumbles upon the action of plants on air

It was well known at the time that a candle covered by a glass jar got extinguished in a few seconds. Remember, this was before the modern understanding of oxygen and combustion, so Priestley and his contemporaries thought of it as burning “reducing the quality of air”. They knew that air in which a candle had burned out could not support life either.

This made Priestley wonder why it was that the air in nature did not permanently “go bad”. So many animals and human beings breathed in it and numerous forest fires burned year after year. What was nature’s secret way of purifying the air and making it breathable again?

In August 1771, Priestley carried out several experiments in his attempt to answer this riddle, some of which might seem laughable to us today. In one such experiment, Priestley kept a mint plant in a jar in which a candle had burned out. After 10 days, he took the mint plant out, taking care to ensure that the air in the jar did not mix with the air outside. When he introduced a lighted candle into this jar, it continued to burn just as if the air in the jar had been fresh air from outside.

Priestley’s confusion and Ingen-Housz’s clarity

Priestley should have discovered photosynthesis at this stage, but he didn’t. He did write a report on his experiment, but when other scientists tried to replicate his experiment, they failed to get the same result. They wrote back to him saying they weren’t convinced, and when Priestley tried repeating his own experiment, his own results this time were mixed. His confidence was shaken, though he continued to believe that plants had the power to purify air.

(Any guesses what Priestley was missing?!)

Ingen-Housz had come to know of Priestley’s experiment in 1773, but it was only in 1779 that Ingen-Housz finally managed to take the vacation he had been longing for. For six long years he had turned around in his mind the question of plants’ action on air. And that had prepared him to grab the opportunity to do his own experiments in spectacular fashion.

In the summer of 1779, Ingen-Housz went to stay in the English countryside and in a short three-month period, completed over 500 experiments that would form the body of his book, Experiments Upon Vegetables.

Ingen-Housz made several key discoveries that collectively form the bulk of our modern understanding of photosynthesis. However, two specific insights stand out, since they dispelled the mists of confusion that clouded Priestley’s ambiguous experiments.

Ingen-Housz realised that plants ‘improve the quality of air’ only in the presence of sunlight. In the dark, they reduce the quality of air, just like animals do. Furthermore, he recognised that only the leaves of plants had the ability to improve the air, while other parts like roots, flowers and fruits breathed like animals did.

He also showed that most of the dry weight of the plants came from the components of air that were ‘fixed’ during this process. In other words, plants were mostly “solidified air”!

Fading away into oblivion

It’s interesting to wonder why we don’t remember Jan Ingen-Housz the way we do numerous other scientists who made momentous discoveries. That’s the subject of an entire paper that was presented at a conference of the European Philosophy of Science Association in 2007.

It seems that Ingen-Housz was a humble person, keen to avoid fame and preserve his anonymity. Also, though he formulated most of the concepts of what we understand as photosynthesis today, the term itself was coined much later, in 1893. Probably we don’t remember Ingen-Housz, because what he discovered did not have a name!


  1. Leonard K. Nash. Plants and the Atmosphere. Harvard Case Histories in Experimental Science.
  2. Geerdt Magiels. Dr. Jan Ingen-Housz, or why we don’t know who discovered photosynthesis. 1st Conference of the European Philosophy of Science Association.

Time for Science Education

In a previous post, I looked at resources from the mid-20th century, when history and philosophy of science had been at the centre of debates on science education. Later, probably as a consequence of the Space Race starting in the late 1950’s, a more technocratic view of science education took over and history of science was relegated to the status of an esoteric discipline.

In recent decades, Michael Matthews, professor at University of New South Wales, Sydney, has been at the forefront of reviving interest in the history and philosophy of science as an area of core relevance to science education. It is one of his books, Time for Science Education, that I wish to look at in this blog post.

If I ever get to meet Prof. Matthews, I would like to ask him if he intended a pun in the book title! But on the surface, the ‘time’ in the title refers to timekeeping and time measurement. The theme of the book is how the history of clocks and timekeeping can be used to teach science through a historical-investigative approach.

I realised for the first time on reading this book that the simple pendulum — ubiquitous and dealt with in an abstract way in the school curriculum — had a rich and complex history that was closely tied to the development of clocks. Beginning with Galileo’s simple ‘pulsilogium’ (a weight suspended by a thread of adjustable length) that he used as a medical student to count the pulse rate of patients, to the precision of John Harrison’s famed clocks that kept accurate time on rough seas, there is a lot to delve into about the deceptively simple pendulum than just the formula of its time period.

It was also a revelation for me that until around as late as the 15th century, there was no real unit of time. The period of daylight was often divided into 12 equal hours, which meant that a summer hour was longer than a winter hour. This was good enough for people to go about their daily lives effectively.

What changed the game was the beginning of the Age of Exploration, and the need to determine longitude accurately at sea. Latitude could be determined easily by noting the position of certain stars or the Sun, but longitude was a very tricky affair and often the difference between life and death for mariners. It was this new need that drove an intense and competitive search for an accurate timekeeping mechanism. The mechanical clocks that were invented as a result, are some of the most fascinating devices ever made by humans.

One of the questions that the book opened up for me in science teaching was about the value of bringing in historical-social-cultural connections to the topics that are taught. Apart from making the topic appealing to students having a wider range of personalities and interests, situating the scientific idea in its broader context seemed to me to serve an important purpose of broadening the students’ worlds and imagination. And that might be more important than mastering certain scientific concepts, especially for the vast majority who never learn science after school.

Time for Science Education is a fairly expensive academic publication, but a limited preview is available on Google Books, to take a peek at some of the chapters: