Archive for the ‘history of science’ Category
what is electricity? part 9 – the first battery
from Wikipedia, etc
Canto: So, going back to the eighteenth century, now. The exploration of electricity was becoming thoroughly fashionable. Lightning was an obviously powerful force that scientists of the day were looking to tame and harness. Most of these modern histories begin with Franklin, but what, or who, turned him on to the subject?
Jacinta: Well of course knowledge and influences developed slowly in the eighteenth century and before. I’ve already spoken of William Gilbert’s De Magnete, written some 150 years before Franklin’s work. Gilbert posited that the Earth itself was essentially a gigantic magnet, with an iron core, which was pretty clever in 1600. He studied static electricity, using amber, and called its effects an electric force, the first modern usage. He was one of the first modern experimentalists, undervalued in his own time, most unfortunately by Francis Bacon, who contributed so much to the development of new scientific methods.
Canto: The 1600s were important in Britain, of course, the period of their Scientific Enlightenment, but one of the most intriguing and brilliant experimenters upon electrostatics in that century was the German polymath Otto von Guericke. His work on vacuums and static electricity in the mid 17th century found its way to England and inspired Robert Boyle to experiment in these fields. But no great breakthroughs occurred, at least for electricity, and no real attempts were made to mathematise electrical concepts until the eighteenth and nineteenth centuries.
Jacinta: Yes, we won’t dwell for too long on these pioneers (famous last words), but J L Heilbron’s 1979 book Electricity in the 17th and 18th centuries: a study of early modern physics, much of which is available online, should guide us towards the advances made by Volta and the nineteenth century mathematisers, notably Maxwell.
Canto: Yes, Heilbron divides the physics of this period into three stages, the first, before 1700, was a relatively amateur, narrow form of neo-Aristotelian systemising (pace Gilbert), and the second involved new discoveries and experiments treated without systematic quantising, which gave way to a more modern, mathematical third stage leading to new discoveries and inventions, such as the battery, just at the end of the 18th century.
Jacinta: We’ve mentioned triboelectric effects in an earlier post. These were the first static effects, between all sorts of different materials, experimented with by scientific pioneers such as Newton and many others. The enormous variety of these effects were, and still are, difficult to quantise. Why was their attraction in some cases and repulsion in others? In fact, ACR, the attraction-contact-repulsion process, came gradually to be recognised, but with no understanding of atoms and particles, or elements in the modern sense, little sense could be made of it.
Canto: There were some attempts to characterise the phenomenon, which was considered a fluid in those early days. In 1733 the French chemist Charles DuFay, one of many electrical experimenters of the time, divided these fluids into two types, vitreous and resinous – the positive and negative forms of today, sort of. Perhaps he was trying to define an attracting and a repelling force.
Jacinta: Effluvia was in the air at that time… ‘particles of electrical matter, which effect attraction and repulsion either by direct impact or by mobilising the air’, to quote Heilbron. But I should mention here the work of Stephen Gray, one of those marvellous upwellers from the lower classes with great practical skills and an experimental spirit, who, like Newton, built his own telescope, with which he made discoveries about sunspots and other things. An obviously alert observer, he noted that electricity could be conducted over distances in various substances, while other substances, such as silk, damped down the effect, acting as insulators. These discoveries were of vital importance, but Gray is probably the most underrated and unrecognised of all the electrical pioneers.
Canto: With the ‘discovery’ of the Leyden jar in 1745 the idea of electricity as a fluid, or two fluids, was laid to rest. This instrument, the key components of which were a jar of glass with metal sheets attached to its inner and outer surfaces, and ‘a metal terminal projecting vertically through the jar lid to make contact with the inner foil’ (Wikipedia), was the first type of capacitor, though it took time for their storage capacity, and those of other devices, to be quantised. Today it’s understood that these early Leyden jars could be charged to as much as 60,000 volts.
Jacinta: Another important early device was called an electrophore, or electrophorus, first invented in 1762 and later improved by Alessandro Volta. These instruments, and the increasing realisation throughout the eighteenth century that this mysterious force, substance or capacity called electricity was a Big Thing, with enormous potential, kept interest in the phenomenon bubbling along.
Canto: An electrophore typically consists of a plastic plate, which won’t conduct electricity, connected to a metal conducting disc with an insulating handle. There are some useful demonstration videos of this, and I’m describing one. If you rub the plastic with some silk cloth, this will, as we now know, transfer electrons from the silk to the plastic, giving it a negative charge (the triboelectric effect). Placing the metal disc on the plastic will not enable too much transfer of electrons, or electron flow. It will in fact cause a polarisation in the disc, positively charging it on the side facing the plastic, and negatively charging it on its opposite side, due to like charges repelling, though this wasn’t known in Volta’s time.
Jacinta: The plastic plate, or sheet, has become a dielectric, I think, which is a pretty complicated concept, involving dielectric constants and relatively complicated mathematical formulae, but for our current purpose (and theirs in the 18th century) this electrophore was a useful demonstrator of static electricity. The metal plate was on balance neutral in charge, but in a sense magnetised, with a negative charge on its upper side, which could be grounded at a touch – causing a spark. Being replaced on the plastic, it could again have its charges separated, a cycle which could be endlessly repeated in theory, though not in practice – due ultimately to the second law of thermodynamics, perhaps.
Canto: So, the battery. It was a term coined by Franklin, giving a sense of overwhelming power, though what he created in connecting Leyden jars in an array was a capacitor.
Jacinta: In fact even one Leyden jar is a capacitor. So what he created was a battery of capacitors, though not quite a supercapacitor. I think.
Canto: Volta is famously supposed to have arrived, in a roundabout way, at the construction of an effective battery due to his dispute with a soon-to-be-former friend Louis Galvani (as described in part 4 of this series), and the dispute led him to further experiments. He came to realise that the reason Galvani’s dead frogs were ‘reanimated’ by electricity had to do with the wires being used, and the chemistry of the frogs.
Jacinta: And meanwhile this ‘reanimation’ business became popularised by Galvani’s nephew, Giovanni Aldini, among others, with popular displays and discussions which led to Mary Shelley’s Frankenstein.
Canto: And meanwhile again, Volta experimented with different wires, including zinc and silver, and with moisture, because he noticed that wetness had an electrifying effect. He soon found that these wires of silver and zinc, connected in a series of water containers, increased the electric effect. Further experimentation with silver and zinc discs, separated by cardboard saturated in salt water, enhanced the effect – the more discs, the stronger the effect. And this effect was permanent (more or less). A battery in the modern sense.
Jacinta: In effect. So voltage is electric potential, as we keep saying. So it’s there even when the battery isn’t connected to anything, a storage device which provides electrical flow when connected. And that potential is measurable, as in a 1.5v battery. Current is the actual flow, which is often quite small, especially in Volta’s original pile, though he was able to build a potential, or voltage of up to 20v. The key to an effective battery, I think, is to get as much current per volt as possible. That’s current flowing steadily, reliably and safely over time. A typical lithium ion phone battery of 3.7 volts delivers between 100 and 400 milliamps of current, whereas Volta’s pile will get you not much more than 1/2 of a milliamp of steady flow. And by the way, why did salt enhance the electrical effect?
Canto: That has to do with with the ionisation of the salt, which when dissolved in water splits into positively charged sodium ions and negatively charged chlorine ions. Sending a current through the water will drive the chlorine ions to the positive terminal and the sodium ions to the negative terminal. This creates a bridge of ions, somehow.
Jacinta: Yeah, great explanation. And apparently one of the most interesting features of Volta’s weak battery, or voltaic pile, at the time was its use in separating H2O into hydrogen and oxygen. This new chemical power – electrolysis – particularly interested Humphrey Davy in England. He proceeded to create the largest battery of the age at the Royal Institution, using it to isolate a large number of elements for the first time, including sodium, calcium, potassium, magnesium, boron and strontium. That was in the first decade of the 19th century – and electricity was really coming of age.
References (just some)
How Volta Invented the First Battery Because He Was Jealous of Galvani’s Frog (video – Kathy loves physics)
https://sciencing.com/salt-water-can-conduct-electricity-5245694.html
https://en.wikipedia.org/wiki/Humphry_Davy
22 – sex, reproduction, science, bonobos
the act, depicted by Leonardo, along with his intriguing mirror writing
Thinking on dolphins again, I remember reading claims about sophisticated dolphin language, at a vocal range beyond human hearing, and I’ve also read scientific dismissals of such claims. I’m thinking again about these questions (the communications of some birds also comes to mind) because the communicative complexity of language would have enabled human apes to, among other things, be species-aware of the connection between sex and reproduction – though unfortunately failures in that communication still result in unwanted teenage pregnancies.
But I don’t seriously imagine that any other species – on this planet at least – knows that the joys of rump-pumpy lead to the much-later popping out of wee human replicants. For one thing, Matthew Cobb’s book The egg & sperm race provides an account of how confused we humans were, even at the time of Leonardo, about ‘the exact relationship between male, female and offspring’. They were particularly confused with regard to non-human generation. Ideas about barnacle geese being hatched from barnacles, mice being generated from wheat and vipers from dust were entertained at the highest level, even at the Royal Society in the 17th century. The spontaneous generation of the tiniest creatures was essentially a given for millennia. But human generation was also much of a mystery until relatively recently. Here’s a little summary from Cobb:
Although the real situation now appears obvious, discovering exactly what goes on was a long, complicated process. Even what might seem to be the most obvious step in generation – the link between sexual intercourse and pregnancy in humans – is really quite difficult to demonstrate. Part of the problem is that the clear signs of pregnancy do not immediately follow the sexual act. Even menstruation does not necessarily appear to be directly linked to pregnancy: although women stop menstruating when they are pregnant, some women always have irregular periods, while teenage girls can get pregnant without ever having menstruated. The link between sex and generation is so unobvious that in the 20th-century the Trobriand Islanders in the Pacific Ocean were said to be very surprised to learn that there is a connection between the two. All around the world, folktales of conception taking place in the most astonishing ways, such as by eating fruit (mango, lemon, apple, orange, peach ..), accidentally swallowing crane dung, or, more politically, being touched by the rays of a dragon.
The late 17th century, however, was the period in Europe when most of this confusion was cleared up, at least in the so-called developed world, thanks mainly to the work of four gifteded individuals, Francesco Redi (1626-97), Jan Swammerdam (1637-80), Nicolas Steno (1638-86) and Reinier de Graaf (1641-1673). Much of this work took place in the Netherlands, a major progressive and scientific nation in this period, backed by massive profits from the spice and slave trades. Of course another power of the period was England, and one of the most important figures in researching ‘generation’, as the problem of sorting out the reproductive process was then called, was William Harvey, famous mostly for working out the role of the heart in circulating the blood. Harvey was a pioneering experimentalist, and his approach to the issues was essentially correct, and quite revolutionary, but he lacked the necessary to work out the detail of generation. In particular, he lacked a microscope. His late work, de generatione animalium (1651), though mostly a restatement of Aristotelian doctrine, was inspirational in that he emphasised, through experiment, the importance of the egg in generation, regardless of species. Without a microscope, however, this claim couldn’t be fully verified. Microscopes, or magnifiers of various kinds, had been used since antiquity, but their full development came only after the invention of the telescope. Galileo built his own compound microscope in the 1620s but they remained largely a novelty until later in the 17th century, with the founding of scientific societies and academies, and the sharing of scientific experiments and tools.
The four above-mentioned intellectuals (the word scientist didn’t gain currency until the nineteenth century) – one Italian and three Dutch – were friends, colleagues, and sometimes frenemies at a time when being first with scientific breakthroughs was even more important than during the covid19 era. There were no professional researchers of course, so you had to publish to get recognition and encourage patronage (and you often needed patronage to get published).
Francesco Redi, who combined a more rigorous experimentalism than was common at the time with the wit and urbanity that made him a mainstay at the court of Grand Duke Ferdinando II of Tuscany, to whom he acted as physician among other things, carried out careful research on insects which proved that they weren’t generated spontaneously in rotting foodstuff or anything else. His interest in the subject was inspired by Steno who had come to Tuscany from his studies in Leiden, via Paris, with a reputation as an expert in dissection and cutting-edge experimentation. Steno was in turn influenced by the greater mathematical rigour of the intellectuals at Ferdinando’s court. The two worked together on fossils and geology as well as animal anatomy. Steno was interested in the difference between viviparous and oviparous reproduction – that’s to say, between creatures who produce live young and those who lay eggs – and stumbled on a new, decisive insight, that female ‘testicles’, at the time believed to be internalised versions of male testicles, were in fact ovaries, a housing for the female’s eggs. This was an insight from observation, rather than experiment, but it was of course correct, and revolutionary.
Steno, Swammerdam and de Graaf had all met in Leiden where they engaged in their first adult studies (Leiden University in the mid 17th century had more student enrolments than Cambridge and was one of the most progressive learning institutes in Europe), and Steno and Swammerdam, being in the same year, became firm friends and collaborators there. After their Leiden studies, all three went to to France, a common destination for young Dutch intellectuals. Swammerdam and Steno were attracted there by an extraordinary French polymath, Melchisédech Thévenot, who had visited Leiden during their studies there, and who was head of a private academy in Paris, which eventually morphed into the Académie Royale des Sciences.
But I’m getting bogged down in fascinating detail. Read Cobb’s The egg & sperm race for the story of how these individuals, and others, sorted out the story of ovaries, testes, semen and the equal contribution of males and females to offspring production. It’s a story of collaboration, rivalry and the struggle for both knowledge and recognition that captures much of scientific activity, then and now.
The point of all this is to recognise how difficult it was for even the most complex species on the planet to work out the relationship between the pleasures of sex and the rather more mixed experience of childbirth – deadly for many, including my own grandmother.
And yet, bonobos do it for pleasure and relief, openly, and manage to avoid having endless pregnancies, unlike Anne Stuart, queen of Great Britain (18 pregnancies, none surviving to adulthood) and Maria Theresia, empress of Austria, and many other regions (16 pregnancies, only 3 of whom died in infancy), not to mention a horde of less ’eminent’ catholic martyrs to the world’s peopling. Bonobos have between five and seven infants, on average, in a lifetime, which is certainly more than enough. I’m not sure of the survival rate of offspring, but it would probably be higher if not for human depradations.
References
Matthew Cobb, The egg & sperm race
reading matters 13: the glass universe
Canto: So The glass universe, published in 2016, has a cute title, referring as it does to the ‘glass ceiling’, another clever term for that invisible barrier up there that appears to prevent women from rising in politics, business and science, but also to the glass photographic plates upon which were recorded the spectrographic signatures of a vast arrays of stars, clusters and the like, in the decades of the late nineteenth century and early twentieth century, by a somewhat less vast array of human computers – the name given to the largely underpaid female stargazers and recorders of Harvard College observatory and elsewhere.
Jacinta: Yes, Dava Sobel, author of the fascinating little book Longitude, as well as Galileo’s Daughter, which is in a stack of books here waiting to be read, has brought to life a group of dedicated women and their male supporters over a period when the higher education of women was just starting to be addressed.
Canto: Yes, it all started with the Drapers, a wealthy and well-connected couple in the 1870s. Henry was a leading astronomer of the day, and ‘Mrs Henry’, aka Anna, a socialite and heiress. Their social evenings were mostly science-focused, with guests including the inventor Thomas Edison, the zoologist Alexander Agassiz, and Prof. Edward Pickering, of Harvard. Henry Draper was working on the chemical make-up of stars, using ‘a prism that split starlight into its spectrum of component colours’, for which he’d won great acclaim, when he died suddenly of a flu-like illness in his mid-forties. His devoted and rich widow, keen to continue his legacy, helped finance, along with Pickering, a continuation of his ground-breaking research.
Jacinta: And so the computers of Harvard College Observatory were born. We need to explain – or try to – the science of spectrographic analysis, but I’d like to first briefly describe some of the women who did this work. They include Williamina (Mina) Fleming, a canny Scotswoman frae Dundee (our birthplace), whose first American job was as the Pickering’s maid but who soon proved her worth as a star spotter and tracker, classifier, and organiser, leading the team of computers in the early decades. In 1899 she was given the title of ‘curator of astronomical photographs’, becoming the first titled female in the university’s history. As such she presided over 12 women ‘engaged in the care of the photographs; identification, examination and measurement of them; reduction of these measurements, and preparation of results for the printer’.
Canto: Far from just bureaucratic work – this would’ve involved a lot of learning and conjecture, noting patterns and anomalies and trying to account for them.
Jacinta: Absolutely. Antonia Maury, Annie Jump Cannon, Cecilia Payne-Gaposchkin, Henrietta Leavitt and the tragically short-lived Adelaide Ames were among the most noteworthy of these computers, and I should stop using the term, because they weren’t machines and they all made lasting contributions to the field…
Canto: And they all have their own Wikipedia pages. What more evidence do we need?
Jacinta: They contributed to academic papers, often without attribution, especially in the early years, and had their findings read out in academic institutions to which they were barred. Over time they became established teachers and lecturers, in the women’s colleges which started to become a thing in the twenties. But let’s get onto the daunting stuff of science. How were these glass plates created and what did they reveal?
Canto: So spectroscopy became a thing in the 1860s. Spectroscopes were attached to telescopes, and they separated starlight into ‘a pale strip of coloured light ranging from reddish at one end through orange, yellow, green, and blue to violet at the other’. I quote from the book. But what these changing colours meant exactly, as well as the ‘many black vertical lines interspersed at intervals along the coloured strip’, this was all something of a mystery, a code that needed to be cracked. Henry Draper had captured these spectral lines and intervals on photographic plates, which were bequeathed to Harvard by his widow. They formed the beginning of the collection.
Jacinta: The term spectrum was first used by Isaac Newton two centuries earlier, and he correctly claimed that this coloration wasn’t due to flaws in glass and crystals but was a property of light itself. The dark lines within the stellar spectra on Draper’s plates are called Fraunhofer lines, after a Bavarian lens-maker, Joseph von Fraunhofer, who built the first spectroscope. He at first thought the dark lines between the rainbow of colours his instrument produced were somehow artificial, but continued work convinced him that they were a natural effect. He gave them alphabetical labels according to their thickness, including the letter D for a double line in the pale orange region. He mapped hundreds of them, though today we’ve detected many thousands of them in sunlight. He didn’t understand what they were, though he realised they were something significant. Later in the 19th century Robert Bunsen and Gustav Kirchov conducted experiments with various chemical elements and found that they burned in colours around those black lines, which we now know as absorption lines.
Canto: Yes, it was Kirchov who connected the colours created by burning elements to the spectral lines that the sun’s light could be separated into, concluding that this great fireball of gases producing white light in the sky was actually a mixture of burning elements, or elements being transformed into other elements. As to the absorption lines, Sobel puts it this way:
As light radiated through the sun’s outer layers, the bright emission lines from the solar conflagration were absorbed in the cooler surrounding atmosphere, leaving dark telltale gaps in the solar spectrum.
These absorption lines, which together with emission lines, are spectral lines in the visible spectrum which ‘can be used to identify the atoms, elements or molecules present in a star, galaxy or cloud of interstellar gas’, to quote from this Swinburne University site.
Jacinta: So we’ll try to keep within the confines of the book, and the scientific developments of the period which these women, in particular, contributed to. So, rather, surprisingly to us modern wiseacres, these revelations about the sun as a super-hot fireball and a producer of elements was a bit hard for 19th century folk to take in, but scientists were excited. Henry Draper described spectral analysis as having ‘made the chemist’s arms millions of miles long’, and in 1872 he began photographing the spectra of other stars. It was long known that they had different colours and brightnesses – called ‘apparent luminosities’ – but spectral analysis provided more detailed data for categorisation, and sets of photographs revealed changes in luminosity and colour over time. Williamina Fleming, Harvard’s principal computer, took charge of Draper’s thousands of plates, which provided the most detailed spectral data of stars up to that time, and was able to analyse them into classes, via their absorption lines, in new and complex ways. It was cutting edge science.
Canto: There was also an interest in throwing more light, so to speak, on variable stars. They were so numerous and complex in their variability that Pickering needed more computers to track them. Lacking funds, he advertised for volunteers, emphasising the role of women in particular, whose effectiveness he’d seen plenty of evidence for.
Jacinta: Not to mention their willingness to work for less, or effectively nothing. These were often siblings or partners of astronomers or other scientists, with unfulfilled scientific ambitions. Later, though, came from the newly created ‘Ladies’ Colleges, such as Radcliffe and Wellesley.
Canto: The Orion Nebula was a particularly rich source of these variable stars, and Pickering found an ideal computer, Henrietta Leavitt, a Radcliffe graduate, to explore them. Within six months, she’d confirmed previous identifications of variables in the nebula and added more than 50 others, afterwards confirmed by Fleming. Then, using a combination of negative and positive glass plates, she found hundreds more, in the Orion Nebula and the Small Magellanic Cloud. As Pickering pointed out, due to the lack of resolution in the plates, this number was likely the tip of the iceberg. In writing up a report of her findings, Leavitt described a pattern she’d found: ‘It is worthy of notice… that the brighter variables [aka cepheid variables] have the longer periods’. This brightness (or luminosity) and its relationship to periodicity (the time taken to go through a full cycle of change) is now known as the Leavitt Law, though of course it took decades for Henrietta Leavitt to receive full recognition for discovering it.
Jacinta: Yes, it’s worth noting that these women worked painstakingly on data analysis, developing new and more rigorous classification systems, studying and theorising about anomalies, and communicating their findings to leading astronomers and researchers around the world. And it’s also worth noting that they were supported and highly appreciated at Harvard by Edward Pickering and his successor as Director of the Harvard College Observatory, Harlow Shapley – though of course there were plenty of naysayers.
Canto: Okay so we’ve spoken of two or three of the computer stars’, and there were many more, but let’s finish with the work of Antonia Maury.
Jacinta: Well we must also mention Annie Jump Cannon (great name), star classifier and photographer extraordinaire, suffragist and generally formidable persona, in spite of being almost completely deaf. She classified around 350,000 stars and contributed greatly to the Harvard Classification Scheme, the first international star classification system. Antonia Coetana de Paiva Pereira Maury (I’m not kidding), a graduate of Vassar College, was a niece of Henry Draper.
Canto: Not what you know but who you know?
Jacinta: It is partly that – and that cliché is worth a whole book to itself – but Maury was no slouch, she was a keen and observant star observer and systemiser. One important discovery she shared with Pickering was one of the first known binary star systems, in the handle of the Big Dipper. This required months of careful observation from 1887 through 1889, as they noted one spectral line separating into two then the lines merging again, then separating, with one line shifting slightly to the red end of the spectrum and the other to the blue. Once they recognised that they were dealing with binary star systems, others were soon found. And once these systems were confirmed, Maury carefully calculated their orbital periods and speeds.
Canto: There were many other important breakthroughs. Spectral colours, as we’ve pointed out, were connected to particular chemical elements, and Cecilia Payne, whose major focus was the measurement of stellar temperatures, found a superabundance in the elements hydrogen and helium, which confounded other experts and soon made her doubt her own calculations. Payne wrote up her findings in the Proceedings of the National Academy of Sciences in 1925, ‘admitting’ that the percentages of hydrogen and helium were ‘improbably high’ and ‘almost certainly not real’.
Jacinta: Yes, it’s well worth noting that the knowledge we have of stars today, which seems almost eternal to us, is in fact very recent. The book also covers the dispute between Harlow Shapley and Edwin Hubble – with many on either side of course – as to whether other galaxies existed. That dispute was only resolved in the thirties, and now we count other galaxies in the trillions. So the period covered in Sobel’s book was a truly transformative period in our understanding of the universe, as well as transformative in terms of women’s education and women’s participation in the most heavenly of all the sciences.
Canto: Whateva.
References
The glass universe, by Dava Sobel, 2016
https://science.nasa.gov/astrophysics/focus-areas/what-are-galaxies
https://en.wikipedia.org/wiki/Annie_Jump_Cannon
https://en.wikipedia.org/wiki/Antonia_Maury
https://en.wikipedia.org/wiki/Williamina_Fleming
a brief history of radical mastectomy
Siddhartha Mukherjee is an oncologist, an academic and an astonishingly gifted writer and story-teller, in the Indian tradition of seemingly effortless, self-effacing wordsmiths. I read, and learned heaps from, his 2016 book The Gene a while back, and now I’m being educated by his first book The Emperor of all Maladies, a history of cancer.
The book twists together different threads of cancer treatment in the modern era, most notably various forms of chemotherapy, and surgery. I’m focusing solely on surgery here, as it pertains to breast cancer, because it highlights the relation between experts (very predominantly male) and sufferers (exclusively female).
The term mastectomy is a bit of a mystery, at least to me. The suffix –ectomy is clear enough, meaning ‘cutting out’, or surgical removal, and ‘lumpectomy’ is a slightly dismissive term for the surgical removal of lumps (from the days when full-blown excision was king) . Maybe mastectomy refers to the removal of a mass of tissue, though why it wouldn’t be called massectomy or masectomy, and why it refers only to the breast, I don’t know. It has nothing to do with mast cells.
The radical mastectomy – the concept refers to ‘root’ as in rooting out, rather than quasi-political radicalism – is most associated with an American physician, William Halsted, though radical surgery in the treatment of cancer was far from unknown when Halsted began practising in the 1870s. Cancer at the time was recognised as the growth and spread of malignant tissue, at mysteriously varying rates, and the surgical removal of that tissue seemed the obvious response. Nineteenth century developments in anaesthesia helped to make the procedure more bearable for all, but operations in the US were often ad hoc and unsanitary. In the late 1870s Halsted made a trip to Europe, which radically changed his outlook and practice. He encountered and absorbed the ideas of various pioneers in surgery and anatomy, including Joseph Lister, Theodor Billroth, Richard von Volkmann and Hans Chiari, then returned to the US, and in the 1880s he quickly established a reputation for boldness and skill as a surgeon. Having become familiar with cocaine, which he recommended as an anaesthetic, he soon became addicted to the drug, which gave him seemingly boundless energy. He tried using morphine to kick the habit, and then found himself in a struggle with both drugs, but this barely damped his work-rate.
Hasted had become particularly interested in Volkmann’s surgical work on breast cancer, and noted that, though the surgeries became more extensive, the cancers returned. An English surgeon, Charles Moore, was experiencing the same problem. Moore’s painstaking analysis of the operations and the following relapses showed that malignant cells had begun to proliferate around the edges of previous surgeries. It seemed clear to him that the surgeries just weren’t extensive enough, and by limiting the surgery to the clearly evident cancerous tissue, and not widening the margins to ensure that the malignant region was properly cleaned out, surgeons were exercising ‘mistaken kindness’. Of course, the problem with this argument was that more radical surgery could itself be life-threatening as well as permanently disfiguring and debilitating. What was also not known at the time was the detailed mechanism of cancer’s metastatic spread throughout the body via the blood and lymph systems. However, this was a time when medical expertise tended to go unquestioned. Halsted and his surgical followers were considered heroes, and the delayed return of the cancers tended not to be dwelt on. The surgeons certainly did buy time for their patients, but often at great cost. Volkmann, for example, had taken breast surgery further by removing not just the breast but the muscle beneath it, the pectoralis minor, to try to ensure the complete removal of the cancer. Impressed, Halsted took things to the next level, cutting through the more vital pectoralis major, essentially killing off movement of the shoulder and arm. Radical mastectomy had now truly arrived, and was to become even more radical, with the collarbone and the group of lymph nodes beneath it becoming the next target, and it didn’t stop there, as cancer kept recurring. As Mukherjee describes it:
A macabre marathon was in progress. Halsted and his disciples would rather evacuate the entire contents of the body than be faced with cancer recurrences. In Europe, one surgeon evacuated three ribs and other parts of the rib cage and amputated a shoulder and a collarbone from a woman with breast cancer.
Siddhartha Mukherjee, The Emperor of all Maladies, p65
There were, of course, no female surgeons at this time, and precious few female doctors, and the male-female power imbalance was coupled with that of the expert and his suffering if not panicking victim to create a kind of juggernaut of largely unnecessary suffering. It took years to reverse this radicalising trend. Nowadays, radical mastectomies are very rarely performed, but with so many giants in the field – who often controlled the nature of clinical trials related to cancer – having earned their reputations through their surgical expertise, change was slow in coming, in spite of a gradual increase in often heroic dissenting voices. For example, Rachel Carson, the author of Silent Spring, refused to undergo a radical mastectomy, which would in any case have offered only brief respite as the cancer had already spread to her bones. Changing attitudes to experts and their secret and superior knowledge was of course a feature of the sixties and seventies, when the turning point really occurred. Developments in the field of course played their part. The knock-out blow for the procedure is largely associated, according to Mukherjee, with another surgeon, not unlike Halsted in energy and drive.
Bernard Fisher had been analysing the data of Halsted’s critics, notably Geoffrey Keynes in England and George Crile in the US, and became increasingly convinced, for a number of reasons, that radical mastectomy was a wrong-headed approach. In 1967, Fisher became the chair of a national consortium in the US, the National Surgical Adjuvant Breast and Bowel Project (NSABP), and began an uphill battle to run large-scale trials to test the efficacy of different treatments of breast cancer. Patients were reluctant to engage, and most surgeons were hostile. The process took years, but results were finally made public in 1981. Here’s Mukherjee’s summary.
The rates of breast cancer recurrence, relapse, death and distant caner metastasis were statistically identical among all three groups [i.e treated with radical mastectomy, with simple mastectomy, or with surgery followed by radiation]. The group treated with the radical mastectomy had paid heavily in morbidity, but accrued no benefits in survival, recurrence or mortality.
Siddhartha Mukherjee, The Emperor of all Maladies, p201
So. Richard Feynman once famously/notoriously said ‘science is the belief in the ignorance of experts. When someone says science teaches us such and such, s/he’s using the word incorrectly – science doesn’t teach us, experience teaches us.’ I agree. Science isn’t a person, let alone an expert person. Science is, to me, an open-ended set of methods based on experience. Experience creates new methods out of which new experiences are created, and we move on, trying to right the wrongs and to minimise the damage, while always maintaining our skepticism.
Reference
The Emperor of all Maladies: a biography of cancer, by Siddhartha Mukherjee, 2011
towards James Clerk Maxwell 6: Newton’s universal law of gravitation and G
Newton’s law of gravity goes like this:
where F is the force of gravitational attraction, G is the constant of proportionality or gravitational constant, m is an entity, particle or object with a particular mass, and r is the distance between the centres of mass of the two entities, particles or objects.
What’s the relation between all this and Maxwell’s electromagnetic work? Good question – to me, it’s about putting physics on a mathematical footing. Newton set us on this path more than anyone. The task I’ve set myself is to understand all this from the beginning, with little or no mathematical expertise.
The law of gravity, in its un-mathematical form, says that every object of mass attracts every other massive object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
It seems often to be put about that Newton was revolutionary because he was the first to wonder why objects fell to the ground. This is unlikely, and Newton wasn’t the first to infer an inverse square law in relation to such falling. Two Italian experimenters, Francesco Grimaldi and Giovanni Riccioli, investigated the free fall (where no force acts besides gravity) of objects between 1640 and 1650, and noted that the distance of the fall was proportional to the time taken. Galileo had previously conducted free fall experiments and found that objects fell with uniform acceleration – an acceleration that is proportional to the square of the elapsed time. Nor was he the first to find a time-squared relationship. The point of all this is that science doesn’t proceed via revolutions proceeding from one brilliant person (which shouldn’t diminish Galileo or Newton’s genius). The more you find out about it, the more incremental and fascinatingly collaborative and confirmative over time it is.
Galileo used the geometry of his time to present his time squared law, but algebraic notation, invented principally by Descartes, superseded this approach in the seventeenth century.
What about the gravitational constant? This appears to be a long and complicated mathematical story. I think it tries to answer the question – why do objects fall to Earth at such and such a rate of acceleration? But I’m not sure. The rate of acceleration would have been easy enough to measure – it’s approximately 9.8 m/sec2. This rate would appear to be caused by the mass of the Earth. The Moon has a fraction of Earth’s mass, and I believe the gravitational force it exerts is approximately one sixth that of Earth. It has been measured as 1.62 m/sec² (for Mars it’s 3.71).
It’s frustratingly difficult to get an explanation online of what the gravitational constant (G) is or really means – without very quickly getting into complex (for me) mathematics. Tantalisingly, Wikipedia tells us that the aforementioned Grimaldi and Riccioli ‘made [an attempted] calculation of the gravitational constant by recording the oscillations of a pendulum’, which means nothing to me. Clearly though, there must be some relationship between G and the mass of the Earth, though how this can be ascertained via pendulums is beyond me. Anyway, on with the struggle.
We do have a number for G, or ‘Big G’, as it’s called (explanation to come), and it’s a very very small number, indicating that, considering that the multiplied masses divided by the square of the distance between them then get multiplied by G, gravitation is mostly a very small force, and only comes into play when we’re talking about Big Stuff, like stars and planets, and presumably whole galaxies. Anyway here’s the actual number:
G = 0.0000000000667408, or 6.67408 × 10-11
I got the number from this useful video, though of course it’s easily available on the net. Now, my guess is that this ‘Big G’ is specific to the mass of the Earth, whereas small g is variable depending on which mass you’re referring to. In other words, G is one of the set of numbers in g. We’ll see if that’s true.
Now, looking again at the original equation, F stands for force, measured in newtons, m for mass, measured in kilograms, and and r for distance in metres (these are the SI units for mass and distance). The above-mentioned video ‘explains’ that the newtons on one side of the equation are not equivalent to the metres and kilograms squared on the other side, and G is introduced to somehow get newtons onto both sides of the equation. This has thrown me into confusion again. The video goes on to explain how G was used by Einstein in relativity and by Max Planck to calculate the Planck length (the smallest possible measure of length). Eek, I’m hoping I’m just experiencing the storm before the calm of comprehension.
So, to persist. This G value above isn’t, and apparently cannot be, precise. That number is ‘the average of the upper and lower limit’, so it has an uncertainty of plus or minus 0.00031 x 10-11, which is apparently a seriously high level of uncertainty for physicists. The reason for this uncertainty, apparently, is that gravitational attraction is everywhere, existing between every particle of mass, so there’s a signal/noise problem in trying to isolate any two particles from all the others. It also can’t be calculated precisely through indirect relation to the other forces (electromagnetism, the strong nuclear force and the weak nuclear force), because no relationship, or compatibility, has been found between gravity and those other three forces.
The video ends frustratingly, but providing me with a touch of enlightenment. G is described as a ‘fundamental value’, which means we don’t know why it has the value it does. It is just a value ‘found experimentally’. This at least tells me it has nothing to do with the mass of the Earth, and I was quite wrong about Big G and small g – it’s the other way round, which makes sense, Big G being the universal gravitational constant, small g pertaining to the Earth’s gravitational force-field.
Newton himself didn’t try to measure G, but this quote from Wikipedia is sort of informative:
In the Principia, Newton considered the possibility of measuring gravity’s strength by measuring the deflection of a pendulum in the vicinity of a large hill, but thought that the effect would be too small to be measurable. Nevertheless, he estimated the order of magnitude of the constant when he surmised that “the mean density of the earth might be five or six times as great as the density of water”
Pendulums again. I don’t quite get it, but the reference to the density of the Earth, which of course relates to its mass, means that the mass of the Earth comes back into question when considering this constant. The struggle continues.
I’ll finish by considering a famous experiment conducted in 1798 by arguably the most eccentric scientist in history, the brilliant Henry Cavendish (hugely admired, by the way, by Maxwell). I’m hoping it will further enlighten me. For Cavendish’s eccentricities, go to any online biography, but I’ll just focus here on the experiment. First, here’s a simplification of Newton’s law: F = GMm/R2, in which M is the larger mass (e.g. the Earth), and m the smaller mass, e.g a person. What Cavendish was trying to ascertain was nothing less than the mass and density of the Earth. In doing so, he came very close – within 1% – of the value for G. Essentially, all that has followed are minor adjustments to that value.
The essential item in Cavendish’s experiment was a torsion balance, a wooden bar suspended horizontally at its centre by a wire or length of fibre. The experimental design was that of a colleague, John Michell, who died before carrying out the experiment. Two small lead balls were suspended, one from each end of the bar. Two larger lead balls were suspended separately at a specific distance – about 23cms – from the smaller balls. The idea was to measure the faint gravitational attraction between the smaller balls and the larger ones.
Wikipedia does a far better job than I could in explaining the process:
The two large balls were positioned on alternate sides of the horizontal wooden arm of the balance. Their mutual attraction to the small balls caused the arm to rotate, twisting the wire supporting the arm. The arm stopped rotating when it reached an angle where the twisting force of the wire balanced the combined gravitational force of attraction between the large and small lead spheres. By measuring the angle of the rod and knowing the twisting force (torque) of the wire for a given angle, Cavendish was able to determine the force between the pairs of masses. Since the gravitational force of the Earth on the small ball could be measured directly by weighing it, the ratio of the two forces allowed the density of the Earth to be calculated, using Newton’s law of gravitation.
To fully understand this, I’d have to understand more about torque, and how it’s measured. Clearly this weak interaction is too small to be measured directly – the key is in the torque. Unfortunately I’m still a way from fully comprehending this experiment, and so much else, but I will persist.
References
https://en.wikipedia.org/wiki/Newton’s_law_of_universal_gravitation
https://en.wikipedia.org/wiki/Gravitational_constant
https://energyeducation.ca/encyclopedia/Gravitational_constant
https://en.wikipedia.org/wiki/Cavendish_experiment
https://www.school-for-champions.com/science/gravitation_cavendish_experiment.htm#.XSrCrS3L1QI
Go to youtube for a number of useful videos on the gravitational constant
towards James Clerk Maxwell 5: a bit about light
Canto: Our last piece in this Maxwell series dealt with the apparently irrelevant matter of Newton’s laws of motion…
Jacinta: But not irrelevant in that Newton was so seminal to the foundation of, and mathematisation of, modern physics, and he set the course…
Canto: Yes and we’ll have to go back to his work on gravity to really get a feel for the maths side of things I think.
Jacinta: No doubt, but in keeping with our disorganised approach to out topic I’m going to fast forward to give a partial account of Maxwell himself, before he did his major work. Maxwell was clearly indefatigably curious about the physical world even in childhood. He was conducting various chemical, electrical and magnetic experiments at home and later at the University of Edinburgh, from his early teens, and writing papers – the first at the age of fourteen – which were accepted by the Royal Society of Edinburgh, though he was considered too young to present them himself.
Canto: But we’re going to focus here on his focus on light, since we’ve been going on mostly about electricity and magnetism thus far. Light, and its wave properties, is something we’re going to have to get our heads around as we approach Maxwell’s work from various angles, and it’s horribly mathematical.
Jacinta: Yes, the properties of polarised light were among Maxwell’s earliest and most abiding areas of interest and research, so we need to understand what that’s all about.
Canto: Okay, here’s a simple definition of the term ‘polarisation’. It’s ‘a property applying to transverse waves that specifies the geometrical orientation of the oscillations’. That’s from Wikipedia.
Jacinta: That’s not simple. Do you understand that?
Canto: No, not yet. So waves are generally of two types, transverse and longitudinal. A moving wave oscillates. That’s the up-and-down movement you might see on a graph. In a transverse wave, the oscillations are at right angles to the movement of the wave. Light waves are transverse waves apparently, as opposed to sound waves, which are longitudinal – in which the wave oscillates, or vibrates, in the direction of propagation. That doesn’t make immediate sense to me, but for now we’ll focus on transverse light waves and polarisation. A light wave, we now know, is an electromagnetic wave, but don’t worry about that for now. Let me try to explain unpolarised light. The light from the sun is unpolarised, as is your bedroom light or that from a struck match. The light waves from these sources are vibrating in a multitude of directions – every direction, you might say. Polarised light is light that we can get to vibrate on a single plane, or in some other specific way..- .
Jacinta: So how do we polarise light is presumably the question. And why do we call it polarised?
Canto: I don’t know why it’s called polarised, but it’s light that’s controlled in a specific way, for example by filtration. The filter might be a horizontal grid or a vertical grid. Let me quote two sentences from one of many explaining sites, and we’ll drill down into them:
Natural sunlight and almost every other form of artificial illumination transmits light waves whose electric field vectors vibrate in all perpendicular planes with respect to the direction of propagation. When the electric field vectors are restricted to a single plane by filtration, then the light is said to be polarized with respect to the direction of propagation and all waves vibrate in the same plane.
So electric field vectors (and we know that vectors have something to do with directionality, I think) are directions of a field, maybe. And a ‘field’ here is an area of electric charge – the area in which that charge has an influence, say on other charges. It was Michael Faraday who apparently came up with this idea of an electric field, which weakens in proportion to distance, in the same manner as gravity. A field is not actually a force, but more a region of potential force.
Jacinta: It seems we might have to start at the beginning with light, which is a huge fundamental force or energy, which has been speculated on and researched for millennia. I’ve just been exploring the tip of that particular iceberg, and it makes me think about how particular forces or phenomena, which are kind of universal with regard to humans on our modern earth, are taken for granted until they aren’t. Think for example of gravity, which wasn’t even a thing before Newton came along, it was just ‘natural’ that things fell down to earth. And think of air, which many people still think of as ’empty’. Light is another of those phenomena, but it’s been explored for longer than the others because it’s much more variable and multi-faceted, at least at first glance haha.. Darkness, half-light, firelight, shadow effects, the behaviour of light in water, rainbows and other tricks of light would’ve challenged the curious from the beginning, so it’s not surprising that theories of light and optics go back such a long way.
Canto: Yes and the horror of it – for some – is that mathematics is key to understanding so much of it – especially trigonometry. But returning to those electric field vectors – and maybe we’ll go back to the beginning with light in the future, – in a light wave, the oscillations are the electric and magnetic fields, pointing in all directions perpendicular to the wave’s propagation.
Jacinta: Yes, I get that, and polarised light limits all those perpendicular directions, or perpendicular planes, to one, by filtration, or maybe some other means.
Canto: Right, but notice I spoke of electric and magnetic fields, which is why light is described as an electromagnetic wave. It should also be pointed out that we tend to call them light waves only in the part of the spectrum visible to humans, but physics deals with all electromagnetic waves. Our eyes, and it’s different for many other species, detect light from a very small part of the entire wave, or electromagnetic, spectrum. Wavelengths of less than about 380 nanometres (even less when we’re young) at the ‘ultraviolet’ end, and of more than about 750 nm at the long ‘infrared’ end, form the visible spectrum for humans. Beyond UV light we have x-rays and then gamma rays, and beyond the infrared we have microwaves and then radio waves.
Jacinta: I wonder if Maxwell knew about all this in his day.
Canto: We’ll no doubt find out…
References
https://en.wikipedia.org/wiki/Transverse_wave
https://www.physicsclassroom.com/class/light/Lesson-1/Polarization
Towards James Clerk Maxwell 2 – Francis Hauksbee’s experiments
Canto: So we’ve witnessed electricity since we’ve had the wit to witness, in lightning. And through our attempts to understand and harness those scary bursts of energy we’ve transformed our world.
Jacinta: We’ve written about lightning before, but the info we presented there was accumulated over centuries. Now we’re going to travel back to the early years of the Royal Society in England, the early 1700s, a mere 300 years ago, to reflect on the first experiments with electricity – remembering that there was no electric power and light in those days, that gods were in the air and much was mysterious.
Canto: Electricity from the start was much sexier, and scarier, than magnetism – lightning very very frightning was the most obvious physical manifestation, and its power was easily recognised. It could kill at a stroke, while magnetism seemed all about metals getting stuck together, and needles pointing north. Interesting, but hardly earth-shattering.
Jacinta: Lightning was all about gigantic sparks shattering the sky, and the ancients, who spent so much of their time in darkness, must have seen other, less impressive and dangerous sparks, the sparks of static electricity, and wondered.
Canto: In the recent BBC documentary The story of electricity, narrator Jim Al-Khalili begins by describing Francis Hauksbee‘s experiments with static electricity and electroluminescence in the early 1700s, which dazzled visitors to the Royal Society. These were the first properly documented experiments with the mysterious force, and a collection of his papers describing these experiments was widely read by the 18th century cognoscenti – including Joe Priestley and Ben Franklin. He employed the newly-invented air pump (simply a pump for pushing out air, as in a common bike pump), popularised in England by Robert Hooke some decades before. Hauksbee made his own improvements, enabling the pump to create a vacuum.
Jacinta: Yes Hauksbee was a more interesting figure than The story of electricity presents. He didn’t ‘lose interest’ but worked on his experiments and reflected on them until his final illness in 1713 – and I’m thinking that illness, since he was only in his late forties – may have been due to mercury poisoning. Hauksbee was ‘lower class’ so few details of his life are documented. However, in these experiments he wasn’t thinking so much of electricity as of ‘attractive forces’. Also as an experimenter who must always have seen himself as an underling (in his book he mentions his ‘want of a learned education’), he doubtless felt obliged to follow the guidance of his Royal Society ‘master’, Newton, which took him into different fields of research….
Canto: The term ‘electricity’ was possibly not in common use then? You’re right, though, about Hauksbee, who rose from obscurity to become a member of the Royal Society, probably under the auspices of Newton. In late 1705, as a result of some spectacular effects displayed to the Society he became intrigued by ‘mercurial phosphorus’. The fact that mercury, in a vacuum, glowed when shaken, had already been noted by Jean Picard, a 17th century French astronomer, and the Swiss mathematician Johann Bernoulli.
Jacinta: And this has to do with electricity?
Canto: We shall see. Hauksbee wanted to work out the conditions under which this mercurial light was produced. He found that the more air in the container, the weaker the light. Also the light’s intensity depended on the movement of the mercury. He concluded that the friction of the mercury against the glass was the major cause. But was it only mercury that had this property, and was it only glass that brought it out? He experimented with other materials, finding a means of rubbing them together in a section of his air pump, Amber rubbed with wool produced a light, brightened in the absence of air. By contrast metal on flint only produced sparks when air was present. Remember, oxygen wasn’t known about at the time. In late 1705 Hauksbee presented one of his most spectacular experiments for the Society. Ingenious instrument-maker that he was, he created a glass globe, from which air could be pumped in and out, on a rotating spindle. The spinning globe came into contact with woollen cloth, and the contact created a weird purple light inside the evacuated globe, which reduced as air was let in. It was a fantastic mystery.
Jacinta: I’m hoping you can solve it.
Canto: Great expectations indeed. He experimented further, and found that when he pressed his own hands against a spinning evacuated globe, the same bright purple glow was produced, which again faded when air was let in to the globe.
Jacinta: Okay, what Hauksbee was exploring in these experiments are what we now call triboelectric effects. I remember playing around with this in schooldays by rubbing a plastic pen along the sleeve of my jersey and watching the fibres stand on end as the pen passed, and hearing the prickling sound of static electricity. The pen was then capable of lifting scraps of paper from the desk, for a time. But I didn’t see any purple lights and I’m not sure how the presence or absence of air relates to it all.
Canto: Yes, triboelectricity is about the exchange of electric charge between different materials – the build-up and discharge of electrical energy. It seems that some materials have a more or less positive charge and some have a more or less negative or opposite charge (because positive and negative are really arbitrary terms, the key point is their relation to each other), and we know that like charges repel and opposite charges attract.
Jacinta: You’ve brought up the word ‘charge’ here, and I’m wondering if that’s just an arbitrary word too – like degree of positive charge just means degree of being repulsed by its opposite, negative charge. In other words, different materials are attracted to or repulsed by each other to varying degrees under various conditions, and that degree or ‘amount’ of attraction or repulsion is referred to as ‘charge’. So ‘charge’ is a relational term…
Canto: Ummm. Maybe. In any case, if you take these different materials down to the atomic level, and I’m not sure how you take plastic and wool down to that level – I mean I know plastic is a petrochemical product, but wool, which I’ve just looked up, has a very complex chemistry – but the fact that the plastic pen, after some rubbing, pulls the fibres of your woollen sleeve towards it is because there’s an attractive force operating between opposite charges. In fact there’s a movement of electrons between the materials, from the wool to the plastic. This electron transfer leaves those woollen fibres with a net positive charge, which is attracted to the now negatively charged plastic due to the electron flow. I think.
Jacinta: Mmm. None of this was understood in the early eighteenth century, obviously. But before we go back there, we’ll stay with this concept of charge, which is nowadays calculated as a fundamental or base unit, based on the electron or its opposite, charge-wise, the proton. These elementary particles have the same but opposite charge, though they’re very different in mass (something which seems suspect to me). Anyway, taking things on trust, a unit of charge is ‘defined’ in standard macro terms as a coulomb, named for the 18th century French physicist Charles-Augustin de Coulomb. One coulomb equals approximately 6.24 x 1018 protons (or electrons). We’ll come back to this later, no doubt. Returning to Hauksbee’s experiments, he soon realised that it was the glass, not the mercury inside it, that was the agent of electrical effects. His experiments with glass globes were written down in great detail, a boon to later researchers.
Canto: Interestingly, I’ve discovered that, more or less exactly at the same time, one Pierre Polinière was conducting and presenting experiments on electroluminescence in Paris:
A closer examination of these experiments reveals not only that Polinière had personally presented them before the French Academy of Sciences, but that Polinière and Hauksbee, starting from a common interest in the ‘mercurial phosphor’, had conducted similar investigations and had in fact simultaneously announced their independent discoveries of the luminescence of evacuated glass containers.
Pierre Polinière, Francis Hauksbee and electroluminescence: a case of simultaneous discovery.
David Corson, 1968.
Jacinta: So we might finish by trying to explain our current understanding of electroluminescence (EL) and its applications. It’s a sort of combo of electricity and light, as you can imagine, or electrons and photons on the level of particles. For example, semiconductors emit light when subjected to a strong electric field or current….
Canto: Is that the basis of LED lighting?
Jacinta: Absolutely. Electrons in the semiconductor material recombine with electron holes, emitting energy in the form of photons. So it has taken us three centuries to really effectively harness the electroluminescent effects demonstrated by Hauksbee in the early days of the Royal Society.
Canto: What are electron holes? I’m thinking not ‘holes in electrons’ but holes left by electrons as they’re displaced in an electric current?
Jacinta: Yes, or almost. It’s like the lack of an electron where you might expect an electron to be. These holes where you might expect an electrically charged particle (an electron) to be, act like positively charged particles – a positron, say – and move through a lattice like an electron does. We could get into very complicated electronics here, if we had the wherewithal, but these holes are examples of quasiparticles, which mostly exist within solids. Fluid movement within solids (not apparently a contradiction in terms) is extremely complicated. Who would’ve thunk it? This movement of electrons and protons within solids is ‘regulated’ by Coulomb’s Law. Remember him? We’ll be getting to that law very soon, as it’s essential to the field of electromagnetism. And that’s our topic don’t forget.