Happy 200th birthday John Tyndall

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2020 marks 200 years since the birth of the scientist John Tyndall, who led the Royal Institution’s research following the death of Faraday. The scientific enquiries and new discoveries of John Tyndall cover an incredible diversity, ranging from: magnetism and the bending of light, to heat absorption in gases and global warming, all the way through to bacterial spores and the motion of glaciers. On top of this dizzying array of experimental studies, he was an exceptional communicator of science to the general public.

John Tyndall also gives his name to the Tyndall National Institute at University College Cork in Ireland, where Paul Hurley works as a research scientist. In this talk he covered some examples of Tyndall’s 19th Century scientific achievements and how they relate to our current information and communication age, and to critical environmental concerns of the 21st Century.

Paul Hurley received his PhD (1990) and B.Eng. (1985, 1st class honours) in Electronic Engineering at the University of Liverpool. Paul is a currently Senior Research Scientist and Head of the Nanoelectronic Materials and Devices Group at the Tyndall National Institute at University College Cork. 

Paul leads a research team of ten PhD students, post-doctoral researchers, visiting students and Tyndall Research staff who perform basic research on high dielectric constant (high-k) thin films for applications in nanoelectronics.

https://www.ucc.ie/en/chemistry/staff/associate/paulhurley/

https://www.linkedin.com/in/paul-hurley-33aab72a/?originalSubdomain=ie

https://twitter.com/tyndallinstitut/media

https://www.tyndall.ie/

Tyndall National Institute is a leading European research centre in integrated ICT (Information and Communications Technology) hardware and systems. Specialising in both electronics and photonics – materials, devices, circuits and systems – they are globally leading in their core research areas of:

  • Smart sensors and systems
  • Optical communication systems
  • Mixed signal and analog circuit design
  • Microelectronic and photonic integration
  • Semiconductor wafer fabrication
  • Nano materials and device processing

https://www.tyndall.ie/john-tyndall

https://www.tyndall.ie/tyndall-science-at-home

#Tyndall200 is a national celebration to mark the bicentennial of John Tyndall, one of Ireland’s most extraordinary and influential scientists. Chosen as the namesake of Tyndall National Institute, his scientific legacy continues to live on through our researchers and their work to this day.

https://twitter.com/hashtag/tyndall200?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Ehashtag

https://twitter.com/hashtag/Tyndall200?src=hashtag_click

Search for #Tyndall200 on social media for more events and experiments to try at home to celebrate the bicentenary of John Tyndall’s birth.

The following are notes from the on-line lecture. Even though I could stop the video and go back over things there are likely to be mistakes because I haven’t heard things correctly or not understood them. I hope Professor Hurley and my readers will forgive any mistakes and let me know what I got wrong.

https://en.wikipedia.org/wiki/Tyndall_National_Institute

Tyndall National Institute is a European research centre in integrated ICT (Information and Communications Technology) hardware and systems and works with industry and academia to transform research into products. Core research areas include photonics and electronics.

Tyndall was founded in the complex of buildings known as the “Lee Maltings”, Cork, Ireland. The site was first developed as a flour mill in 1787. The Lee Mill was the largest water-powered flour and corn milling installation at the time on the River Lee.

In 1797, just 10 years later, the mill became The River Lee Porter Brewery. The brewery operated until 1813, where it was taken over by Beamish & Crawford (B&C).

The Lee Maltings was bought by University College Cork in 1968 and converted to laboratories.

In 1979 a silicon wafer-fabrication laboratory was established to provide R&D and specialised training facilities for the semi-conductor manufacturing industry.

The National Microelectronics Research Centre (NMRC) was established in 1981.

The Tyndall National Institute, Cork, Ireland, named after John Tyndall, was established in 2004.

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Tyndall research facilities occupy six floors, including basement, laboratory, plant and open atrium space totalling c.5,600m2 in area.

It is concerned primarily with integrated information and communication technologies and has around 600 staff and students from 52 countries

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The oldest part of the Tyndall Institute started off as a brewery and a distillery

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From 1980 research into microelectronics etc. began

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Looking at health, communication, technology etc.

Professor Hurley’s research group is the Nanoelectronic Materials and Devices Group

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Their research is involved with smart phones, computers, and virtual reality imaging.

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https://about.fb.com/news/2020/08/introducing-the-new-facebook-reality-labs/

https://www.facebook.com/careers/life/shining-a-light-on-the-future-of-tech

Facebook has an AR/VR team in Cork

https://www.youtube.com/watch?v=82tdTAA4TtQ

Look inside all the electronic devices and you will see silicon chips.

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Each chip is about 2cm by 2cm and contains integrated circuits.

If you cut the chip in half and zoom in (about 100,000 times) on one edge you see the heart of chip.

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https://www.autodesk.com/products/eagle/blog/transistors-world-modern-electrons/

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The above image shows the symbol for an N channel Field Effect Transistor (FET)

https://en.wikipedia.org/wiki/Transistor

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

https://en.wikipedia.org/wiki/Field-effect_transistor

The field-effect transistor (FET) is a type of transistor which uses an electric field to control the flow of current. FETs are devices with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source.

N channel FETs have electrons for conduction.

The gate controls the current flowing.

Professor Hurley’s group is working on making transistors more energy efficient.

Transistors can be connected to form logic gates.

https://www.youtube.com/watch?v=SW2Bwc17_wA&vl=en

https://en.wikipedia.org/wiki/Logic_gate

https://www.electronics-tutorials.ws/logic/logic_1.html

The Digital Logic Gate is the basic building block from which all digital electronic circuits and microprocessor-based systems are constructed from. Basic digital logic gates perform logical operations of AND, OR and NOT on binary numbers.

In digital logic design only two voltage levels or states are allowed and these states are generally referred to as Logic “1” and Logic “0”, or HIGH and LOW, or TRUE and FALSE. These two states are represented in Boolean Algebra and standard truth tables by the binary digits of “1” and “0” respectively.

Most digital logic gates and digital logic systems use “Positive logic”, in which a logic level “0” or “LOW” is represented by a zero voltage, 0v or ground and a logic level “1” or “HIGH” is represented by a higher voltage such as +5 volts, with the switching from one voltage level to the other, from either a logic level “0” to a “1” or a “1” to a “0” being made as quickly as possible to prevent any faulty operation of the logic circuit.

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There are also NAND (Not And) gates and NOR (Not OR) gates (and some more complicated gates)

https://en.wikipedia.org/wiki/Binary_number

In mathematics and digital electronics, a binary number is a number expressed in the base-2 numeral system or binary numeral system, which uses only two symbols: typically, “0” (zero) and “1” (one).

In 1854, British mathematician George Boole published a landmark paper detailing an algebraic system of logic that would become known as Boolean algebra. His logical calculus was to become instrumental in the design of digital electronic circuitry

https://en.wikipedia.org/wiki/Boolean_algebra

In mathematics and mathematical logic, Boolean algebra is the branch of algebra in which the values of the variables are the truth values true and false, usually denoted 1 and 0, respectively. Instead of elementary algebra, where the values of the variables are numbers and the prime operations are addition and multiplication, the main operations of Boolean algebra are the conjunction “and”, the disjunction “or”, and the negation ”not”. It is thus a formalism for describing logical operations, in the same way that elementary algebra describes numerical operations.

Boolean algebra was introduced by George Boole in his first book “The Mathematical Analysis of Logic” (1847), and set forth more fully in his “An Investigation of the Laws of Thought” (1854).

https://en.wikipedia.org/wiki/George_Boole

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George Boole (2 November 1815 – 8 December 1864) was a largely self-taught English mathematician, philosopher and logician, most of whose short career was spent as the first professor of mathematics at Queen’s College, Cork in Ireland. He worked in the fields of differential equations and algebraic logic, and is best known as the author of The Laws of Thought (1854) which contains Boolean algebra. Boolean logic is credited with laying the foundations for the information age. Boole maintained that:

“No general method for the solution of questions in the theory of probabilities can be established which does not explicitly recognise, not only the special numerical bases of the science, but also those universal laws of thought which are the basis of all reasoning, and which, whatever they may be as to their essence, are at least mathematical as to their form.”

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Boole was born in Lincoln, Lincolnshire, England. He attended primary school but was basically self-taught. At age 16, he became the breadwinner for his parents and three younger siblings, taking up a junior teaching position at a school in Doncaster. He continued studying on his own and at age 19, successfully established his own school in Lincoln.

Boole continued making his living by running schools until he was in his thirties and throughout this time he continued working on mathematics.

His status as a mathematician was recognised by his appointment in 1849 as the first professor of mathematics at Queen’s College, Cork (now University College Cork (UCC)) in Ireland.

In the early 20th century, several electrical engineers intuitively recognized that Boolean algebra was analogous to the behaviour of certain types of electrical circuits. Claude Shannon formally proved such behaviour was logically equivalent to Boolean algebra in his 1937 master’s thesis, A Symbolic Analysis of Relay and Switching Circuits.

https://en.wikipedia.org/wiki/Boolean_algebra

https://en.wikipedia.org/wiki/Claude_Shannon

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Claude Elwood Shannon (April 30, 1916 – February 24, 2001) was an American mathematician, electrical engineer, and cryptographer known as “the father of information theory”. Shannon is noted for having founded information theory with a landmark paper, “A Mathematical Theory of Communication”, which he published in 1948.

Did John Tyndall work on semiconductors?

Probably not.

But Michael Faraday, when working on silver sulphide, made the first observation of semiconductor behaviour in 1833.

https://en.wikipedia.org/wiki/Michael_Faraday

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Michael Faraday FRS (22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, diamagnetism and electrolysis.

https://en.wikipedia.org/wiki/Silver_sulfide

Silver sulfide is an inorganic compound with the formula Ag2S. A dense black solid, it is the only sulfide of silver.

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Silver sulphide surrounded by calcite

Faraday discovered that the “conducting power” of silver sufide increases with increasing temperature whereas the conductivity of metallic conductors decreases as their temperature rises. He wrote:

“On conducting power generally”. “I have lately met with an extraordinary case … which is in direct contrast with the influence of heat upon metallic bodies … On applying a lamp … the conducting power rose rapidly with the heat … On removing the lamp and allowing the heat to fall, the effects were reversed.”

Research centre

Research. Why is it done?

Research ……. Re-search, search again?

Pre-search? To boldly search where no one has searched before

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“re” intensifies the old French word for “search” so research means “intense search)

Tyndall did very intense experimental research on a wide variety of topics.

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Tyndall’s early years

https://en.wikipedia.org/wiki/John_Tyndall

John Tyndall was born in Leighlinbridge, County Carlow, Ireland, probably in 1820 (2nd of August). The reason why there is some doubt about the year is because some Irish records were lost at the start of the 20th century

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His father was a local police constable and he attended the local school until his late teens, and he was probably an assistant teacher near the end of his time there.

The subjects he learnt at school included technical drawing and mathematics with some applications of those subjects to land surveying. He was hired as a draftsman by the Ordnance Survey of Ireland in his late teens in 1839, and moved to work for the Ordnance Survey for Great Britain in 1842.

In the decade of the 1840s, a railway-building boom was in progress, and Tyndall’s land surveying experience was valuable and in demand by the railway companies. Between 1844 and 1847, he was lucratively employed in railway construction planning.

In 1847 Tyndall opted to become a mathematics and surveying teacher at Queenwood College, a boarding school in Hampshire. Recalling this decision later, he wrote: “the desire to grow intellectually did not forsake me; and, when railway work slackened, I accepted in 1847 a post as master in Queenwood College.

https://en.wikipedia.org/wiki/Queenwood_College

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Queenwood College was a British Public School, that is an independent fee-paying school, situated near Stockbridge, Hampshire, England. The school was in operation from 1847 to 1896.

Another recently arrived young teacher at Queenwood was Edward Frankland, who had previously worked as a chemical laboratory assistant for the British Geological Survey.

https://en.wikipedia.org/wiki/Edward_Frankland

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Sir Edward Frankland, KCB, FRS, FRSE (18 January 1825 – 9 August 1899) was a British chemist. He was one of the originators of organometallic chemistry and introduced the concept of combining power or valence. An expert in water quality and analysis, he was a member of the second royal commission on the pollution of rivers, and studied London’s water quality for decades. He also studied luminous flames and the effects of atmospheric pressure on dense ignited gas, and was one of the discoverers of helium (named after the Greek word for the sun “Helios”).

Frankland and Tyndall became good friends. On the strength of Frankland’s prior knowledge, they decided to go to Germany to further their education in science. Among other things, Frankland knew that certain German universities were ahead of any in Britain in experimental chemistry and physics. (British universities were still focused on classics and mathematics and not laboratory science.) The pair moved to Germany in summer 1848 and enrolled at the University of Marburg (to carry out a PhD), attracted by the reputation of Robert Bunsen as a teacher. Tyndall studied under Bunsen for two years. His Marburg dissertation was a mathematical analysis of screw surfaces in 1850

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The above image shows Europe in 1848. Germany as we know it didn’t exist then. The red dots show centres of revolution.

https://en.wikipedia.org/wiki/Robert_Bunsen

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Robert Wilhelm Eberhard Bunsen (30 March 1811 – 16 August 1899) was a German chemist.

When Tyndall left his teaching post he quoted Ralph Waldo Emerson to his students “.. the higher you climb, the fewer examples you have above you and the more dependent you are on yourself. What are the Sun, Stars, science, chemistry, geology, mathematics but pages of a book whose author is God! I want to know the meaning of this book”.

Tyndall returned to live in England in summer 1851 and was elected a Fellow of the Royal Society in 1852.

https://en.wikipedia.org/wiki/Fellow_of_the_Royal_Society

Fellowship of the Royal Society (FRS, ForMemRS and HonFRS) is an award granted by the judges of the Royal Society of London to individuals who have made a “substantial contribution to the improvement of natural knowledge, including mathematics, engineering science, and medical science”.

In 1853, Tyndall attained the prestigious appointment of Professor of Natural Philosophy (Physics) at the Royal Institution in London, due in no small part to the esteem his work had garnered from Michael Faraday, the leader of magnetic investigations at the Royal Institution.

https://en.wikipedia.org/wiki/Royal_Institution

The Royal Institution of Great Britain (often abbreviated as the Royal Institution or Ri) is an organisation devoted to scientific education and research, based in the City of Westminster. It was founded in 1799 by the leading British scientists of the age. Its foundational principles were diffusing the knowledge of, and facilitating the general introduction of, useful mechanical inventions and improvements, as well as enhancing the application of science to the common purposes of life (including through teaching, courses of philosophical lectures, and experiments).

Much of the Institution’s initial funding and the initial proposal for its founding were given by the Society for Bettering the Conditions and Improving the Comforts of the Poor. Since its founding it has been based at 21 Albemarle Street in Mayfair. Its Royal Charter was granted in 1800.

Tyndall was appointed the successor to the positions held by Michael Faraday at the Royal Institution on Faraday’s retirement in about 1863 and he became the director when Faraday died in 1867.

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Magnetism and diamagnetism

1) Before Tyndall

(a) Democritus

https://en.wikipedia.org/wiki/Democritus

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Painting by Charles-Antoine Coypel

Democritus (c. 460 – c. 370 BC) was an Ancient Greek pre-Socratic philosopher primarily remembered today for his formulation of an atomic theory of the universe.

Democritus held that everything is composed of “atoms,” which are physically, but not geometrically, indivisible; that between atoms, there lies empty space; that atoms are indestructible, and have always been and always will be in motion; that there is an infinite number of atoms and of kinds of atoms, which differ in shape and size. Of the mass of atoms, Democritus said, “The more any indivisible exceeds, the heavier it is.

Universe of infinite, uncreated and eternal “atoms” (“atomos” – ancient Greek meaning “indivisible”)

Democritus, along with others, proposed the earliest views on the shapes and connectivity of atoms. They reasoned that the solidness of the material corresponded to the shape of the atoms involved. Thus, iron atoms are solid and strong with hooks that lock them into a solid; water atoms are smooth and slippery; salt atoms, because of their taste, are sharp and pointed; and air atoms are light and whirling, pervading all other materials. Using analogies from humans’ sense experiences, he gave a picture or an image of an atom that distinguished them from each other by their shape, their size, and the arrangement of their parts. Moreover, connections were explained by material links in which single atoms were supplied with attachments: some with hooks and eyes, others with balls and sockets. The Democritean atom is an inert solid (merely excluding other bodies from its volume) that interacts with other atoms mechanically. In contrast, modern, quantum-mechanical atoms interact via electric and magnetic force fields and are far from inert.

The qualities of an object result from the kind of atoms that compose it.

(b) John Dalton

https://en.wikipedia.org/wiki/John_Dalton

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Dalton by Charles Turner after James Lonsdale (1834, mezzotint)

John Dalton FRS (6 September 1766 – 27 July 1844) was an English chemist, physicist, and meteorologist. He is best known for introducing the atomic theory into chemistry,

The most important of all Dalton’s investigations are concerned with the atomic theory in chemistry. While his name is inseparably associated with this theory, the origin of Dalton’s atomic theory is not fully understood. The theory may have been suggested to him either by researches on ethylene (olefiant gas) and methane (carburetted hydrogen) or by analysis of nitrous oxide (protoxide of azote) and nitrogen dioxide (deutoxide of azote).

The main points of Dalton’s atomic theory, as it eventually developed, are:

Elements are made of extremely small particles called atoms.

Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties.

Atoms cannot be subdivided, created or destroyed.

Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

In chemical reactions, atoms are combined, separated or rearranged.

“All matter is composed of atoms, indivisible and indestructible building blocks”

“While all atoms of an element were identical, different elements had atoms of differing size and mass”

(c) About magnets

https://en.wikipedia.org/wiki/Magnet

Magnets have been known about for a very long time. The name “Magnet” was adopted in Middle English from Latin magnetum “lodestone”, ultimately from Greek (magnētis [lithos]) meaning “[stone] from Magnesia”, a part of ancient Greece where lodestones were found.

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Magnesia within Greece

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.

A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. It produces a force that is greater than the force due to gravity. And it can work against gravity

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Iron filings that have oriented in the magnetic field produced by a bar magnet.

Magnets exert forces on each other due to microscopic currents of electrically charged electrons orbiting nuclei and the intrinsic magnetism of fundamental particles (such as electrons) that make up the material. Both of these are modelled quite well as tiny loops of current called magnetic dipoles that produce their own magnetic field and are affected by external magnetic fields. The most elementary force between magnets, therefore, is the magnetic dipole–dipole interaction. If all of the magnetic dipoles that make up two magnets are known then the net force on both magnets can be determined by summing up all these interactions between the dipoles of the first magnet and that of the second.

It is often more convenient to model the force between two magnets as being due to forces between magnetic poles having magnetic charges ‘smeared’ over them. Positive and negative magnetic charge is always connected by a string of magnetized material, and isolated magnetic charge does not exist. This model works quite well in predicting the forces between simple magnets where good models of how the ‘magnetic charge’ is distributed are available.

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There is an attractive force between unlike poles. There is a repulsive force between two like poles.

https://en.wikipedia.org/wiki/Ferromagnetism

Ferromagnetism is the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism (along with the similar effect ferrimagnetism) is the strongest type and is responsible for the common phenomenon of magnetism in magnets encountered in everyday life. Substances respond weakly to magnetic fields with three other types of magnetism—paramagnetism, diamagnetism, and antiferromagnetism—but the forces are usually so weak that they can be detected only by sensitive instruments in a laboratory. An everyday example of ferromagnetism is a refrigerator magnet used to hold notes on a refrigerator door. The attraction between a magnet and ferromagnetic material is “the quality of magnetism first apparent to the ancient world, and to us today”

Permanent magnets (materials that can be magnetised by an external magnetic field and remain magnetised after the external field is removed) are either ferromagnetic or ferrimagnetic, as are the materials that are noticeably attracted to them. Only a few substances are ferromagnetic. The common ones are iron, cobalt, nickel and most of their alloys, and some compounds of rare earth metals. Ferromagnetism is very important in industry and modern technology, and is the basis for many electrical and electromechanical devices such as electromagnets, electric motors, generators, transformers, and magnetic storage such as tape recorders, and hard disks, and nondestructive testing of ferrous materials.

Ferromagnetic materials can be divided into magnetically “soft” materials like annealed iron, which can be magnetized but do not tend to stay magnetised, and magnetically “hard” materials, which do. Permanent magnets are made from “hard” ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture to align their internal microcrystalline structure, making them very hard to demagnetise. To demagnetise a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. “Hard” materials have high coercivity, whereas “soft” materials have low coercivity. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization.

https://en.wikipedia.org/wiki/Paramagnetism

Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behaviour, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field. Paramagnetic materials include most chemical elements and some compounds; they have a relative magnetic permeability slightly greater than 1 (i.e., a small positive magnetic susceptibility) and hence are attracted to magnetic fields. The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect and modern measurements on paramagnetic materials are often conducted with a SQUID magnetometer.

Paramagnetism is due to the presence of unpaired electrons in the material, so most atoms with incompletely filled atomic orbitals are paramagnetic, although exceptions such as copper exist. Due to their spin, unpaired electrons have a magnetic dipole moment and act like tiny magnets. An external magnetic field causes the electrons’ spins to align parallel to the field, causing a net attraction. Paramagnetic materials include aluminium, oxygen, titanium, and iron oxide (FeO). Therefore, a simple rule of thumb is used in chemistry to determine whether a particle (atom, ion, or molecule) is paramagnetic or diamagnetic: If all electrons in the particle are paired, then the substance made of this particle is diamagnetic; If it has unpaired electrons, then the substance is paramagnetic.

Unlike ferromagnets, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field because thermal motion randomizes the spin orientations (Some paramagnetic materials retain spin disorder even at absolute zero, meaning they are paramagnetic in the ground state, i.e. in the absence of thermal motion.). Thus, the total magnetization drops to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnetic materials is non-linear and much stronger, so that it is easily observed, for instance, in the attraction between a refrigerator magnet and the iron of the refrigerator itself.

https://en.wikipedia.org/wiki/Antiferromagnetism

In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighbouring spins (on different sublattices) pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism.

Generally, antiferromagnetic order may exist at sufficiently low temperatures, but vanishes at and above the Néel temperature. Above the Néel temperature, the material is typically paramagnetic.

https://en.wikipedia.org/wiki/Diamagnetism

Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted by a magnetic field. Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism, the material is called diamagnetic. In paramagnetic and ferromagnetic substances, the weak diamagnetic force is overcome by the attractive force of magnetic dipoles in the material. The magnetic permeability of diamagnetic materials is less than the permeability of vacuum, μ0. In most materials, diamagnetism is a weak effect which can only be detected by sensitive laboratory instruments, but a superconductor acts as a strong diamagnet because it repels a magnetic field entirely from its interior.

(d) Diamagnetism was first discovered when Anton Brugmans observed in 1778 that bismuth was repelled by magnetic fields.

https://en.wikipedia.org/wiki/Anton_Brugmans

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Anton Brugmans (1732–1789) was Dutch physicist who proposed a two-fluid theory of magnetism. He did magnetism experiments by putting objects on water or mercury, using surface tension to make them float and magnets to move them. He discovered the diamagnetism of bismuth.

https://en.wikipedia.org/wiki/Bismuth

Bismuth is a chemical element with the symbol Bi and atomic number 83.

https://www.youtube.com/watch?v=hUoUSz-hD8A

http://revue.elth.pub.ro/viewpdf.php?id=55

In his experiments Brugmans chose water or mercury depending on form and consistence of the substance. Pulverised material was supported by a little sheet of paper. Supported by surface tension the specimen could align almost frictionless in the field of a bar magnet which was brought near to the specimen. He investigated many different substances such as soils, stones, gemstones, ores, salts of the sulfuric acid, asbestos, different metals and many more. He mainly focused on providing evidence that the investigated substances contained iron or not, respectively whether they were attracted by a magnet or not. But in 1778, as Brugmans investigated bismuth, he made a new observation

“…Only the dark and almost violet-coloured bismuth displayed a particular phenomenon in the study; for when I laid a piece of it upon a round sheet of paper floating atop water, it was repelled by both poles of the magnet.”

In this moment Brugmans had found a new form of magnetism which later was named “diamagnetism”. But due to the weak diamagnetic forces and the lack of stronger magnets he did not have the possibilities to further investigate the observed phenomenon. He had to leave this to the following generations of scientists.

(e) Julius Plücker

https://en.wikipedia.org/wiki/Julius_Pl%C3%BCcker

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Julius Plücker (16 June 1801 – 22 May 1868) was a German mathematician and physicist. He made fundamental contributions to the field of analytical geometry and was a pioneer in the investigations of cathode rays that led eventually to the discovery of the electron.

In 1836, Plücker was made professor of physics at University of Bonn. In 1848, after a year of working with vacuum tubes he published his first classical researches on the action of the magnet on the electric discharge in rarefied gases. He found that the discharge caused a fluorescent glow to form on the glass walls of the vacuum tube, and that the glow could be made to shift by applying an electromagnet to the tube, thus creating a magnetic field. It was later shown that the glow was produced by cathode rays.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4524391/

His experiments, initially with vegetable materials, led him to suppose that the alignment of fibres might influence the magnetic behaviour of matter and that the structure of crystals might produce a similar effect. In his work on crystals, published in Poggendorff’s Annalen, he found that the optic axes of crystals are repelled by the poles of a magnet, that the force is independent of the magnetic or diamagnetic condition of the crystal, and that it diminishes less, as the distance from the poles increases, than the magnetic or diamagnetic forces. In other words, he suggested that there is a new repulsive force at work. The question of polarity remained elusive, Plücker commenting ‘I have made many but unsuccessful experiments to discover a diamagnetic polarity’…‘The simplest hypothesis…that in which diamagnetism is regarded as a general repulsive force of nature’.

He then described, in the next article in the same issue of Poggendorff’s Annalen, the apparently anomalous results for cherry bark, which set equatorially if placed close between the poles but axially if the poles are wider apart or if placed above or below the line between the poles, noting that De la Rive had made similar observations with charcoal. He explained this in terms of the magnetic force diminishing less than the diamagnetic in proportion to the increase of distance from the poles. Plücker wrote to Faraday on 3 November sending copies of both papers and summarising his findings. Faraday replied on 11 November regretting his inability to read German and sending him a piece of heavy glass for experiments. Plücker wrote again on 6 February claiming to have shown air to be diamagnetic, although there is no recorded reply.

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Plücker felt his results showed:

Diamagnetic force decreases faster than the magnetic as the distance increases

Optical axes of crystals are repelled by the poles of a magnet.

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https://en.wikipedia.org/wiki/Iceland_spar

Iceland spar, formerly known as Iceland crystal (lit. silver-rock), is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light.

It has been speculated that the sunstone (Old Norse: sólarsteinn, a different mineral from the gem-quality sunstone) mentioned in medieval Icelandic texts was Iceland spar, and that Vikings used its light-polarizing property to tell the direction of the sun on cloudy days for navigational purposes.

The recovery of an Iceland spar sunstone from the Elizabethan ship Alderney, which sank in 1592, suggests that this navigational technology may have persisted after the invention of the magnetic compass.

Magneto-crystallic force (inherent in the crystals)

Magneto-crystallic force (induced by the magnetic field)

Plücker’s optic axis force (inherent in the crystals)

https://en.wikipedia.org/wiki/Magnetocrystalline_anisotropy

In physics, a ferromagnetic material is said to have magnetocrystalline anisotropy if it takes more energy to magnetize it in certain directions than in others. These directions are usually related to the principal axes of its crystal lattice. It is a special case of magnetic anisotropy.

https://en.wikipedia.org/wiki/Magnetic_anisotropy

In condensed matter physics, magnetic anisotropy describes how an object’s magnetic properties can be different depending on direction. In the simplest case, there is no preferential direction for an object’s magnetic moment. It will respond to an applied magnetic field in the same way, regardless of which direction the field is applied. This is known as magnetic isotropy. In contrast, magnetically anisotropic materials will be easier or harder to magnetize depending on which way the object is rotated.

For most magnetically anisotropic materials, there are two easiest directions to magnetize the material, which are a 180° rotation apart. The line parallel to these directions is called the easy axis. In other words, the easy axis is an energetically favourable direction of spontaneous magnetization. Because the two opposite directions along an easy axis are usually equivalently easy to magnetize along, and the actual direction of magnetization can just as easily settle into either direction.

(f) Faraday’s experiments in diamagnetism (1845)

In 1845, Michael Faraday demonstrated that it was a property of matter and concluded that every material responded (in either a diamagnetic or paramagnetic way) to an applied magnetic field. Faraday first referred to the phenomenon as diamagnetic (the prefix dia- meaning through or across), then later changed it to diamagnetism.

A simple rule of thumb is used in chemistry to determine whether a particle (atom, ion, or molecule) is paramagnetic or diamagnetic: If all electrons in the particle are paired, then the substance made of this particle is diamagnetic; If it has unpaired electrons, then the substance is paramagnetic.

Faraday discovered the magneto-optical effect while experimenting in his laboratory at the Royal Institution in London. There Faraday had found that the rotation of the plane of polarization of a light beam passing through a piece of heavy glass (silico borate of lead) could be influenced by a magnetic field.

While examining other materials he found further transparent materials which also showed this effect. Faraday quickly named these materials “dimagnetics” in analogy with dielectrics.

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Faraday’s great electromagnet.

Faraday experimented again with a piece of heavy glass which this time he had hung between the poles of a powerful electromagnet (image above).

Faraday could observe that the heavy glass aligned itself exactly between the electromagnet poles when it was switched on. Not knowing about Brugman’s work Faraday had rediscovered what he later called diamagnetism. He systematically investigated this phenomenon and exposed different substances to the action of his electromagnet: A piece of apple, caffeine, dried blood, sulphates, minerals, acids, different metals among uranium, phosphorus, arsenic, different gases and so one.

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Faraday classified the investigated substances in order of their reaction to the magnetic field. Substances which were attracted towards the electromagnet’s poles he called “magnetic” and substances which were moved from stronger points of the field to weaker points “diamagnetic”. Furthermore, he arranged the substances according to the strength of the attracting and repelling force. Faraday’s experimental results and theoretical treatments considering diamagnetism were published in the “Philosophical Transactions” of the Royal society and thus were available for a broad scientific community.

Diamagnetism is a property of all materials, and always makes a weak contribution to the material’s response to a magnetic field. However, other forms of magnetism (such as ferromagnetism or paramagnetism) are so much stronger that, when multiple different forms of magnetism are present in a material, the diamagnetic contribution is usually negligible. Substances where the diamagnetic behaviour is the strongest effect are termed diamagnetic materials, or diamagnets. Diamagnetic materials are those that some people generally think of as non-magnetic, and include water, wood, most organic compounds such as petroleum and some plastics, and many metals including copper, particularly the heavy ones with many core electrons, such as mercury, gold and bismuth.

Faraday gave the Bakerian Lecture on 7 December 1848. He showed that the crystallisation of bismuth affects the position it takes up in a magnetic field, and using poles which give a uniform magnetic field he demonstrated that crystals align themselves axially in the lines of force in a ‘magnecrystallic’ manner, which appeared to present a new form of force in the molecules of the matter, the ‘magnecrystallic force’. The crystal can set either way axially, so the words ‘axial’ and ‘axiality’ were preferable to Faraday than ‘polar’ and ‘polarity’. The line of magnecrystallic force is perpendicular to one particular line of cleavage, and ‘the line or axis of magnecrystallic force tends to place itself parallel, or as at a tangent, to the magnetic curve or line of magnetic force, passing through the place where the crystal is situated’. In all this work, Faraday continued to explain diamagnetics as moving from the stronger to the weaker part of the field, and the magnecrystallic force as tending to line up with the magnetic field (or resultant of magnetic force), rather than attraction or repulsion. He demonstrated the same with antimony and with arsenic. He did try to see if a magnetic field affected the crystallisation of bismuth, as might have been expected, but could not show it

(g) William Thomson (Lord Kelvin)

https://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvin

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William Thomson, 1st Baron Kelvin, OM, GCVO, PC, PRS, FRSE (26 June 1824 – 17 December 1907) was a British mathematical physicist and engineer born in Belfast.

William Thomson gave mathematical rigour to the diamagnetism discovery, showing in May 1847 that the equations governing the behaviour of (para)magnetic and diamagnetic substances under the influence of a magnet are the same but of opposite sign, illustrating Faraday’s conclusion that a diamagnetic substance tends to move from stronger to weaker places or points of force. Both Faraday, conceptually, and Thomson, more mathematically, demonstrated clearly the effect in three dimensions of the strength of the magnetic force at any particular place, when the force (or field) is not uniform in space. Incidentally, in this paper Thomson also predicted the possibility of stable magnetic levitation of diamagnetic substances.

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Thomson doubted magnetic levitation would happen because he didn’t think the force was strong enough and he didn’t think there was any material light enough to be lifted up.

In June 1849 Thomson wrote to Michael Faraday suggesting that the concept of a uniform magnetic field could be used to predict the motions of small magnetic and diamagnetic bodies.

https://discovery.ucl.ac.uk/id/eprint/1468599/1/00033790.2014.929743.pdf

2) Tyndall’s studies of diamagnetism

Before Tyndall there were a number of conflicting magnetism results such as the diamagnetic force decreases with distance differently to a normal magnet and the optical poles of a crystal (Icelandic spar) can be repelled by a magnet (Plücker’s findings). Icelandic spar does undergo birefringence, but was it caused by magnets?

https://www.youtube.com/watch?v=y4pknNBvEeE

https://en.wikipedia.org/wiki/Birefringence

Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light.

https://www.physicsclassroom.com/class/light/Lesson-1/Polarization

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In the simplest situation polarisation removes all the vibration directions except one.

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Tyndall’s early original work in physics was his experiments on magnetism and diamagnetic polarity, on which he worked from 1850 to 1856. His two most influential reports were the first two. One of them was entitled “The magneto-optic properties of crystals, and the relation of magnetism and diamagnetism to molecular arrangement”, dated May 1850. The two described an inspired experiment, with an inspired interpretation. These and other magnetic investigations very soon made Tyndall known among the leading scientists of the day.

Tyndall started his experiments in 1849, whilst still in Marburg, just before he finished his PhD. He carried on sustained periods of work from 1849-1852 and 1854-1856, producing a meticulously constructed body of experimental evidence and theoretical interpretation. He challenged Faraday’s theory with a model of diamagnetic polarity and magnetic forces acting in couples, based on a firm vision of the importance of the underlying structure of materials in defining their properties. In doing so he took on the might of Faraday, Thomson and the German mathematician turned physicist Julius Plücker, often in public at British Association meetings, or at the Royal Institution and Royal Society.

He carried out experiments with bismuth and took great care with its preparation. He designed and built his own equipment and carefully obtained the necessary materials.

Bismuth was used because it is the most naturally occurring diamagnetic material.

“I neglected no precaution to secure the perfect purity of the substance examined”. This was to ensure impurities were minimised.

(i) Dissolve bismuth in nitric acid (ii) Precipitate the compound in distilled water (iii) Filter and wash the compound over six days (iv) Reduce the compound using black flux (a reducing flux composed of powdered carbon and alkali-metal carbonate) (v) Melt the product in a hessian crucible

https://en.wikipedia.org/wiki/Hessian_crucible

A Hessian crucible is a type of ceramic crucible that was manufactured in the Hesse region of Germany from the late Middle Ages through the Renaissance period.

(vi) Add saltpetre to the product and stir briskly

https://en.wikipedia.org/wiki/Potassium_nitrate

Potassium nitrate is a chemical compound with the chemical formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−, and is therefore an alkali metal nitrate. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpeter or saltpetre.

(vii) Add foreign ingredients (Tyndall doesn’t say what they are): oxidise and skim (viii) Purify the metal and cast in a bullet mould

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(ix) Remove the outer surface and scour the bismuth bullet with sand (x) Finally boil the bismuth in hydrochloric acid.

Tyndall explored a wide range of elements and compounds in terms of magnetic or diamagnetic response such as sulphur and calcium carbonate

His source for sulphur was “Flowers of Sulphur” – which had a minimum iron contamination

https://en.wikipedia.org/wiki/Flowers_of_sulfur

This is a very fine, bright yellow sulfur powder that is produced by sublimation and deposition

His source of ” Calcareous Spar – CaCO3” also had a minimum iron contamination

These precautions were necessary as Tyndall wanted to make sure there was no iron in any of the materials he used, as iron would dominate the weaker diamagnetic force, he was looking for.

The critical point here is that any Iron contamination in a sample (ferromagnetic) – will swamp the diamagnetic response.

Tyndall checked all samples by dissolving them and then adding Potassium Ferricyanide. It there was any iron – it would react to form a blue compound – called Prussian Blue. In this way Tyndall could check for Iron contamination

The lowest Iron content for Sulfur and Calcareos Spar – were from Sicily and the Harz Mountains

Tyndall used a torsion balance to measure these repulsive forces.

A torsion balance is an instrument used to measure small forces. It is based on the principle that a wire or thread resists twisting with a force that is proportional to the stress. In Tyndall’s experiment the force was produced by the electromagnetic helical coils.

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The diamagnetism of bismuth is proved because it is repelled by a magnet irrespective of which pole is used.

https://www.jstor.org/stable/pdf/108509.pdf

https://www.gutenberg.org/files/24527/24527-h/24527-h.htm

John Tyndall’s finding was that the magnetic force of repulsion/attraction and the diamagnetic force of repulsion followed exactly the same law.

This is the inverse square law. If you double the distance the magnetic force falls by a factor of four.

3) Following Tyndall

(a) We now know that the magnetic effect is caused by spinning electrons. The electrons rotate or spin around their own axis.The spinning of an electron produces a magnetic dipole. This is one of fundamental properties of an electron that it has a magnetic dipole moment, i.e., it behaves like a tiny magnet

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If the majority of electrons in the atom spins in the same direction, a strong magnetic field is produced. The direction of the electrons spin determines the direction of magnetic field. If the same number of electrons in the atom spins in opposite directions, the electron spins will cancels out. Thus, the magnetism will also be cancelled.

The questions is, where are these electrons?

https://www.edinformatics.com/math_science/nature-of-magnets.html

https://en.wikipedia.org/wiki/Electron

Te idea of charge is very old. The ancient Greeks new about attraction and repulsion.

In the early 1700s, French chemist Charles François du Fay concluded that electricity consists of two electrical fluids.

https://en.wikipedia.org/wiki/Charles_Fran%C3%A7ois_de_Cisternay_du_Fay

Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess (+) or deficit (−). He gave them the modern charge nomenclature of positive and negative respectively.

https://en.wikipedia.org/wiki/Benjamin_Franklin

In 1859 Julius Plücker observed that the phosphorescent light, which was caused by radiation emitted from the cathode, appeared at the tube wall near the cathode, and the region of the phosphorescent light could be moved by application of a magnetic field.

During the 1870s, the English chemist and physicist Sir William Crookes developed the first cathode ray tube to have a high vacuum inside. He then showed in 1874 that the cathode rays can turn a small paddle wheel when placed in their path. Therefore, he concluded that the rays carried momentum. Furthermore, by applying a magnetic field, he was able to deflect the rays, thereby demonstrating that the beam behaved as though it were negatively charged. In 1879, he proposed that these properties could be explained by regarding cathode rays as composed of negatively charged gaseous molecules in fourth state of matter in which the mean free path of the particles is so long that collisions may be ignored.

https://en.wikipedia.org/wiki/William_Crookes

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Sir William Crookes OM PRS (17 June 1832 – 4 April 1919) was a British chemist and physicist who attended the Royal College of Chemistry in London, and worked on spectroscopy. He was a pioneer of vacuum tubes, inventing the Crookes tube which was made in 1875. This was a foundational discovery that eventually changed the whole of chemistry and physics.

In 1897, the British physicist J. J. Thomson performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier. Thomson made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called “corpuscles”, had perhaps one thousandth of the mass of the least massive ion known: hydrogen. He showed that their charge-to-mass ratio, e/m, was independent of cathode material. He further showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal. These negatively charged particles were given the name “electron”.

https://en.wikipedia.org/wiki/J._J._Thomson

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Sir Joseph John Thomson OM PRS (18 December 1856 – 30 August 1940) was a British physicist and Nobel Laureate in Physics, credited with the discovery of the electron, the first subatomic particle to be discovered.

https://www.khanacademy.org/science/ap-chemistry/electronic-structure-of-atoms-ap/history-of-atomic-structure-ap/a/discovery-of-the-electron-and-nucleus

Below is a diagram of J.J. Thomson’s cathode ray tube. The ray originates at the cathode and passes through a slit in the anode. The cathode ray is deflected away from the negatively-charged electric plate, and towards the positively-charged electric plate. The amount by which the ray was deflected by a magnetic field helped Thomson determine the mass-to-charge ratio of the particles. Image from Openstax, CC BY 4.0.

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As part of his experiments with cathode ray tubes, Thomson tried changing the cathode material, which was the source of the particles. Since the same particles were emitted even when the cathode materials were changed to different metals, Thomson concluded that the particle was a fundamental part of all atoms.

https://history.aip.org/history/exhibits/electron/

https://en.wikipedia.org/wiki/Plum_pudding_model

J. J. Thomson realised that these electrons came from the atom. The atom was no longer indivisable.

He proposed this model before the atomic nucleus had been discovered. The model tried to explain two properties of atoms then known: that electrons are negatively-charged particles and that atoms have no net electric charge. The plum pudding model has electrons surrounded by a volume of positive charge, like negatively-charged “plums” embedded in a positively-charged “pudding”. The word “plums” in 19th-century English “plum pudding” is an archaic use of the word; it referred at that time to raisins, not plums.

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https://en.wikipedia.org/wiki/Rutherford_model

https://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment

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Left: Had Thomson’s model been correct, all the alpha particles should have passed through the foil with minimal scattering.

Right: What Geiger and Marsden observed was that a small fraction of the alpha particles experienced strong deflection.

Ernest Rutherford wasn’t happy with Thomson’s model of the atom before he asked Geiger and Marsden to do the gold foil experiment which involved firing alpha particles at a sheet of gold foil.

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https://en.wikipedia.org/wiki/Ernest_Rutherford

Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, FRS, HonFRSE[2] (30 August 1871 – 19 October 1937) was a New Zealand–born British physicist who came to be known as the father of nuclear physics.

https://en.wikipedia.org/wiki/Hans_Geiger

Johannes Wilhelm “Hans” Geiger (30 September 1882 – 24 September 1945) was a German physicist.

https://en.wikipedia.org/wiki/Ernest_Marsden

Sir Ernest Marsden CMG CBE MC FRS (19 February 1889 – 15 December 1970) was an English-New Zealand physicist.

http://www.thestargarden.co.uk/Rutherfords-atom.html

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So Rutherford’s atom consisted of a positive nucleus with the electrons moving around the outside. He wasn’t completely happy though as the mass of the nucleus was greater than one would expect for the number of protons to equal the number of electrons.

Further work done by his team identified the neutron in 1932, which made up the nucleus with the protons.

https://www.britannica.com/science/Rutherford-model

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Since 1932 a lot of work has been done and below shows the most up-to-date image of the atom.

https://www.particleadventure.org/modern_atom.html

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This is the modern atom model.

Electrons are in constant motion around the nucleus, protons and neutrons jiggle within the nucleus, and quarks jiggle within the protons and neutrons.

This picture is quite distorted. If we drew the atom to scale and made protons and neutrons a centimetre in diameter, then the electrons and quarks would be less than the diameter of a hair and the entire atom’s diameter would be greater than the length of thirty football fields! 99.999999999999% of an atom’s volume is just empty space!

So the origin of the different forms of magnetism is due to the spinning of electrons that are found somewhere ouside the nucelus.

With electrons you either know where they are or what their momenta are. You can’t know both.

(b) In 1939 Werner Braunbek did the first demonstration of bismuth and graphite being levitated using an electromagnet.

https://en.wikipedia.org/wiki/Werner_Braunbeck

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Werner Braunbeck (Werner Braunbek; 8 January 1901 – 9 February 1977) was a German physicist.

(c) In 1997 Andre Geim levitated a live frog (as a vegan I do not aprove) using a 16T magnetic field. He won the 2000 Ig Nobel Prize.

https://en.wikipedia.org/wiki/Andre_Geim

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Sir Andre Konstantinovich Geim FRS, HonFRSC, HonFInstP (born 21 October 1958) is a Russian-born Dutch-British physicist working in England in the School of Physics and Astronomy at the University of Manchester.

Geim shared the 2000 Ig Nobel Prize in physics with Michael Berry for the frog experiment. He received it for using the magnetic properties of water scaling to levitate a small frog with magnets.

https://en.wikipedia.org/wiki/Ig_Nobel_Prize

The Ig Nobel Prize is a satiric prize awarded annually since 1991 to celebrate ten unusual or trivial achievements in scientific research, its stated aim being to “honour achievements that first make people laugh, and then make them think.” The name of the award is a pun on the Nobel Prize, which it parodies, and the word ignoble.

Organized by the scientific humour magazine Annals of Improbable Research (AIR), the Ig Nobel Prizes are presented by Nobel laureates in a ceremony at the Sanders Theatre, Harvard University, and are followed by the winners’ public lectures at the Massachusetts Institute of Technology.

(d) Diamagnetism experiments

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Pyrolytic graphite floating above magnets. A current of air can make the floating air to move around

https://en.wikipedia.org/wiki/Pyrolytic_carbon

Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets as a result of imperfections in its production.

Few materials can be made to magnetically levitate stably above the magnetic field from a permanent magnet. Although magnetic repulsion is obviously and easily achieved between any two magnets, the shape of the field causes the upper magnet to push off sideways, rather than remaining supported, rendering stable levitation impossible for magnetic objects. Strongly diamagnetic materials, however, can levitate above powerful magnets.

With the easy availability of rare-earth permanent magnets in recent years, the strong diamagnetism of pyrolytic carbon makes it a convenient demonstration material for this effect.

In 2012, a research group in Japan demonstrated that pyrolytic carbon can respond to laser light or sufficiently powerful natural sunlight by spinning or moving in the direction of the field gradient. The carbon’s magnetic susceptibility weakens upon sufficient illumination, leading to an unbalanced magnetization of the material and movement when using a specific geometry.

Diamagnetism: Geometric alignment

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A member of the audience suggested that the field lines are easier to see if you place the green sheet vertically over the magnets. N-S, N-N and S-S show better

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Where will the graphite sit when it is placed on the squares of the diamagnetic material? Is it A B or C?

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The graphite levitates at the cross

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The answer to the quiz is B

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Videos showing simple diamagnetism experiments

https://www.youtube.com/watch?v=KRr2MBuzuG4

https://www.youtube.com/watch?v=bHLCy-3iOww

Absorption of radiant heat by gases

1) Global warming

https://en.wikipedia.org/wiki/Joseph_Fourier

Jean-Baptiste Joseph Fourier (21 March 1768 – 16 May 1830) was a French mathematician and physicist born in Auxerre and best known for initiating the investigation of Fourier series, which eventually developed into Fourier analysis and harmonic analysis, and their applications to problems of heat transfer and vibrations. The Fourier transform and Fourier’s law of conduction are also named in his honour. Fourier is also generally credited with the discovery of the greenhouse effect.

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In 1822 Fourier published his work on heat flow in Théorie analytique de la chaleur (The Analytical Theory of Heat), in which he based his reasoning on Newton’s law of cooling, namely, that the flow of heat between two adjacent molecules is proportional to the extremely small difference of their temperatures. This book was translated, with editorial ‘corrections’, into English 56 years later.

What is the temperature of the Earth’s surface?

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Every day the Sun’s rays strike the Earth’s surface and Warm it up, so why doesn’t the planet keep heating up until it is as hot as the Sun itself?

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When Fourier calculated the effect mathematically, he found the Earth’s temperature to average -18oC rather than the average measured temperature of +15oC, The Earth should be an iceball

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Something was stopping the emission of heat – like a “box with a glass lid”.

Fourier examined various possible sources of the additional observed heat in articles published in 1824 and 1827. While he ultimately suggested that interstellar radiation might be responsible for a large portion of the additional warmth, Fourier’s consideration of the possibility that the Earth’s atmosphere might act as an insulator of some kind is widely recognized as the first proposal of what is now known as the greenhouse effect, although Fourier never called it that.

In his articles, Fourier referred to an experiment by de Saussure, who lined a vase with blackened cork. Into the cork, he inserted several panes of transparent glass, separated by intervals of air. Midday sunlight was allowed to enter at the top of the vase through the glass panes. The temperature became more elevated in the more interior compartments of this device. Fourier concluded that gases in the atmosphere could form a stable barrier like the glass panes. This conclusion may have contributed to the later use of the metaphor of the “greenhouse effect” to refer to the processes that determine atmospheric temperatures. Fourier noted that the actual mechanisms that determine the temperatures of the atmosphere included convection, which was not present in de Saussure’s experimental device.

https://en.wikipedia.org/wiki/Horace_B%C3%A9n%C3%A9dict_de_Saussure

Horace Bénédict de Saussure (17 February 1740 – 22 January 1799) was a Genevan geologist, meteorologist, physicist, mountaineer and Alpine explorer, often called the founder of alpinism and modern meteorology, and considered to be the first person to build a successful solar oven.

2) Tyndall and IR absorption by gases

Work on glaciers alerted Tyndall to the research of de Saussure into the heating effect of sunlight, and the concept of Fourier, that heat from the sun penetrates the atmosphere more easily than “obscure heat” (infrared) “terrestrial radiation” from the warmed Earth, causing what we now call the greenhouse effect. In the spring of 1859 Tyndall began research into how thermal radiation, both visible and obscure, affects different gases and aerosols. He developed differential absorption spectroscopy using the electro-magnetic thermopile devised by Melloni.

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Above left: Bismuth-copper cells in series as the voltage produces by one was very small. Above centre shows a Leslie cube and a thermal detector. This equipment could detect a person 30 feet from the IR detector (or a cow from 100 feet). Above right: Macedonio Melloni

https://en.wikipedia.org/wiki/Macedonio_Melloni

Macedonio Melloni (11 April 1798 – 11 August 1854) was an Italian physicist, notable for demonstrating that radiant heat has similar physical properties to those of light.

https://en.wikipedia.org/wiki/Thermopile

A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel. Such a device works on the principle of the thermoelectric effect, i.e., generating a voltage when its dissimilar metals (thermocouples) are exposed to a temperature difference.

Thermocouples operate by measuring the temperature differential from their junction point to the point in which the thermocouple output voltage is measured. Once a closed circuit is made up of more than one metal and there is a difference in temperature between junctions and points of transition from one metal to another, a current is produced as if generated by a difference of potential between the hot and cold junction.

https://www.youtube.com/watch?v=Fo8aSxLj6QM

https://www.newport.com/n/thermopile-physics

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Thermopile sensors are based on thermocouples. A thermocouple consists of two dissimilar metals connected in series. To detect radiation, one metal junction is typically blackened to absorb the radiation. The temperature rise of this junction with respect to another non-irradiated junction generates a voltage. This effect is the basis of all thermocouple temperature sensors. The thermocouple materials used in thermopiles are usually bismuth and antimony, which have a relatively high thermoelectric coefficient (a measure of the magnitude of the induced voltage in response to the temperature difference). An individual thermocouple typically produces a low output voltage, which results in a low detectivity and limits its use as a sensing device. So, one way to increase the output voltage is to connect many thermocouple junctions (typically 20 to 120) in series. All the “hot” junctions are placed close together to collect the radiation. This constitutes a thermopile.

Tyndall began intensive experiments on 9 May 1859, with the idea that a heated surface must emit non-luminous heat (invisible infrared radiation), which carries the heat energy away into space. As absorption of heat by gases and vapours was a perfectly unexplored field of enquiry.

On 10 June he demonstrated the research in a Royal Society lecture, noting that coal gas and ether strongly absorbed (infrared) radiant heat, and his experimental confirmation of the (greenhouse effect) concept; that solar heat crosses an atmosphere, but “when the heat is absorbed by the planet, it is so changed in quality that the rays emanating from the planet cannot get with the same freedom back into space. Thus, the atmosphere admits of the entrance of solar heat; but checks its exit, and the result is a tendency to accumulate heat at the surface of the planet.

Tyndall explained the heat in the Earth’s atmosphere in terms of the capacities of the various gases in the air to absorb radiant heat, in the form of infrared radiation. His measuring device, which used thermopile technology, is an early landmark in the history of absorption spectroscopy of gases. He was the first to correctly measure the relative infrared absorptive powers of the gases nitrogen, oxygen, water vapour, carbon dioxide, ozone, methane, and other trace gases and vapours. He concluded that water vapour is the strongest absorber of radiant heat in the atmosphere and is the principal gas controlling air temperature. Absorption by the other gases is not negligible but relatively small. Prior to Tyndall it was widely surmised that the Earth’s atmosphere warms the surface in what was later called a greenhouse effect, but he was the first to prove it. The proof was that water vapour strongly absorbed infrared radiation. Relatedly, Tyndall in 1860 was first to demonstrate and quantify that visually transparent gases are infrared emitters.

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Tyndall’s sensitive ratio spectrophotometer (drawing published in 1861) measured the extent to which infrared radiation was absorbed and emitted by various gases filling its central tube. He had to think up and build his own equipment.

https://en.wikipedia.org/wiki/Leslie_cube

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Leslie’s cube is a device used in the measurement or demonstration of the variations in thermal radiation emitted from different surfaces at the same temperature.

The upper photographs of Leslie’s cube (in colour) are taken using an infrared camera; the black and white photographs underneath are taken with an ordinary camera. The face of the cube that has been painted black emits thermal radiation strongly. The polished face of the aluminium cube emits much more weakly, and the reflected image of the warm hand is clear.

The Leslie cube is the source of the IR radiation

https://en.wikipedia.org/wiki/John_Leslie_(physicist)

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Sir John Leslie, FRSE KH (10 April 1766 – 3 November 1832) was a Scottish mathematician and physicist best remembered for his research into heat.

In 1804, he experimented with radiant heat using a cubical vessel filled with boiling water. One side of the cube is composed of highly polished metal, two of dull metal (copper) and one side painted black. He showed that radiation was greatest from the black side and negligible from the polished side. The apparatus is known as a Leslie cube.

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Rock salt formed the IR transparent window

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Illustration of John Tyndall’s setup for measuring the radiant heat absorption of gases. This illustration dates from 1861 and it is taken from one of John Tyndall’s presentations where he describes his setup for measuring the relative radiant-heat absorption of gases and vapours. The galvanometer quantifies the difference in temperature between the left and right sides of the thermopile. The reading on the galvanometer is settable to zero by moving the Heat Screen a bit closer or farther from the left-hand heat source. That is the only role for the heat source on the left. The heat source on the righthand side directs radiant heat into the long brass tube. The long brass tube is highly polished on the inside, which makes it a good reflector (and non-absorber) of the radiant heat inside the tube. Rock-salt (NaCl) is practically transparent to radiant heat, and so plugging the ends of the long brass tube with rock-salt plates allows radiant heat to move freely in and out at the tube endpoints, yet completely blocks the gas within from moving out. To begin the measurements, both heat sources are turned on, the long brass tube is evacuated as much as possible with an air suction pump, the galvanometer is set to zero, and then the gas under study is released into the long brass tube. The galvanometer is looked at again. The extent to which the galvanometer has changed from zero indicates the extent to which the gas has absorbed the radiant heat from the righthand heat source and blocked this heat from radiating to the thermopile through the tube. If a highly polished metal disc is placed in the space between the thermopile and the brass tube it will completely block the radiant heat coming out of the tube from reaching the thermopile, thereby deflecting the galvanometer by the maximum extent possible with respect to blockage in the tube. Thus, the system has minimum and maximum readings available, and can express other readings in percentage terms. (The galvanometer’s responsiveness was physically nonlinear, but well understood, and mathematically linearizable.)

In one of his public lectures to non-professional audiences Tyndall gave the following indication of instrument sensitivity: “My assistant stands several feet off. I turn the thermopile towards him. The heat from his face, even at this distance, produces a deflection of 90 degrees [on the galvanometer dial]. I turn the instrument towards a distant wall, judged to be a little below the average temperature of the room. The needle descends and passes to the other side of zero, declaring by this negative deflection that the pile feels the chill of the wall.”. To reduce interference from human bodies, the galvanometer was read through a telescope from across the room. The thermopile & galvanometer system was invented by Leopoldo Nobili and Macedonio Melloni. Melloni measured radiant heat absorption in solids and liquids but didn’t have the sensitivity for gases. Tyndall greatly improved the sensitivity of the overall setup (including putting an offsetting heat source on the other side of the thermopile, and putting the gas in a brass tube), and as a result of his superior apparatus he was able to confidently reach conclusions that were quite different from Melloni’s concerning radiant heat in gases. Air from which water vapor and carbon dioxide had been removed deflected the galvanometer dial by less than 1 degree, in other words a detectable but very small amount. Many other gases and vapours deflected the galvanometer by a large amount — thousands of times greater than air.

As a check on his system’s reliability, Tyndall painted the inside walls of the brass tube with a strong absorber of radiant heat (namely lampblack). This greatly reduced the radiant heat that reached the thermopile when the tube was empty. Nevertheless, the percentage absorptions by the different gases and vapours relative to the empty tube were largely and essentially unchanged by this change to the absorption property of the tube’s walls. That’s excluding a few gases and vapours such as chlorine that must be excluded because they tarnish brass, changing its heat reflectivity. As another test of the reliability of the system, the long brass tube was cut to about a quarter of its original length, and the exact same quantity of gas was released into the shorter tube. Thus the shorter tube will have about four times higher gas density. It was found that the percentage of radiant heat absorbed by or transmitted through the gas relative to the empty-tube state was entirely unchanged by this (even though the two tubes don’t have equal empty-tube states). Varying the absolute quantity of the gas in the tube causes corresponding changes in the absorption percentages, but varying the density doesn’t matter, nor does the absolute value of the empty-tube reference point.

The emission spectrum of the particular source of heat makes a difference — sometimes a big difference — in the amount of radiant heat a gas will absorb, and different gases can respond differently to a change in the source. Tyndall said in 1864, “a long series of experiments enables me to state that probably no two substances at a temperature of 100°C emit heat of the same quality [i.e. of the same spectral profile]. The heat emitted by isinglass, for example, is different from that emitted by lampblack, and the heat emitted by cloth, or paper, differs from both.” Looking at an electrically-heated platinum wire, it is obvious to the human eye that the heat’s spectral profile depends on whether the wire is heated to dull red, bright orange, or white hot. Some gases were relatively stronger absorbers of the dull-red platinum heat while other gases were relatively stronger absorbers of the white-hot platinum heat, he found. For his original and primary benchmark in 1859, he used the heat from 100°C lampblack (akin to a theoretical “blackbody radiator”). Later he got some of his more interesting findings from using other heat sources. E.g., when the source of radiant heat was any one kind of gas, then this heat was strongly absorbed by another body of the same kind of gas, regardless of whether the gas was a weak absorber of broad-spectrum sources. In the illustration above, the radiant heat that is going into the brass tube comes from a pot of simmering water; the heat radiates from the exterior surface of the pot, not from the water, and not from the gas flame that keeps the water at a simmer. An alternative illustration with a modified setup taken was from the same book. The main difference is that the heat source is separated from the brass tube by open air, which eliminates the need for circulating cold water cooling at the interface between heat source and brass tube.

Date 1861 and 1872

Source: The illustration appears in John Tyndall’s 1872 book “Contributions to Molecular Physics in the Domain of Radiant Heat” (downloadable at Archive.org). It has been subsequently annotated in coloured typeface. The book is a compilation of research reports published by Tyndall in the 1860s. The particular illustration is part of a report dated January 10, 1861.

Tyndall brought all the different components for the experiment.

Absorption of radiant heat by gases and vapours (1861)

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Effect of water vapour is 16,000 times larger than pure air!!

Contributions to molecular physics in the domain of radiant heat – John Tyndall 1861

http://web.gps.caltech.edu/~vijay/Papers/Spectroscopy/tyndall-1861.pdf

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Carbonic acid is carbon dioxide.

John Herschel was very impressed with Tyndall’s work, as it was an area he was interested in.

https://en.wikipedia.org/wiki/John_Herschel

Sir John Frederick William Herschel, 1st Baronet KH FRS (7 March 1792 – 11 May 1871) was an English polymath, mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint, and did botanical work.

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Herschel’s father, William Herschel, discovered infrared radiation in sunlight by passing it through a prism and holding a thermometer just beyond the red end of the visible spectrum. This thermometer was meant to be a control to measure the ambient air temperature in the room. He was shocked when it showed a higher temperature than the visible spectrum. Further experimentation led to Herschel’s conclusion that there must be an invisible form of light beyond the visible spectrum.

https://en.wikipedia.org/wiki/William_Herschel

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Frederick William Herschel KH, FRS (German: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer of music.

John Herschel invented the actinometer in 1825 to measure the direct heating power of the sun’s rays.

John Tyndall wrote” Remove for a single summer-night the aqueous vapour from the air whish overspreads this country, and you would assuredly destroy every plant capable of being destroyed by a freezing temperature. The warmth of our fields and gardens would pour itself unrequited into space, and the Sun would rise upon an island held fast in the iron grip of frost.”

John Herschel wrote to John Tyndall on the topic of thermal radiation. “You have made a grand step in meteorology in showing that the dry air is perfectly transcalescent and that the invisible moisture is what stops the sun’s heat.”

Tyndall used his infrared equipment for many things and found that London was a “heat island”

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London in the 1860s

Tyndall commenting on global warming “As a dam built across a river causes a deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the Earth’s surface.”

Thus in 1862 John Tyndall described the key to climate change.

Water vapour and carbon dioxide are opaque to radiant heat rays.

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The above image shows that the temperature has increased by about 4oC in the last 50 years because of the increasing amount of greenhouse gases in the atmosphere.

Tyndall would make hundreds of measurements and check they were reproducible before he published anything.

In recognition for Tyndall’s work The Tyndall Centre for climate change research was set up.

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3) On the other side of the Atlantic

https://en.wikipedia.org/wiki/Eunice_Newton_Foote

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There are no known photos of Eugene Newton Foote, so here is a photo of her daughter, Mary Foote Henderson, instead.

Eunice Newton Foote (July 17, 1819 – September 30, 1888) was an American scientist, inventor, and women’s rights campaigner from Seneca Falls, New York.

She was the first scientist known to have experimented on the warming effect of sunlight on different gases, and went on to theorise that changing the proportion of carbon dioxide in the atmosphere would change its temperature, in her paper Circumstances affecting the heat of the sun’s rays at the American Association for the Advancement of Science conference in 1856. Although it appears that women were allowed to present papers to AAAS at that time, Professor Joseph Henry of the Smithsonian Institution delivered the paper that identified the research as her work.

https://www.nytimes.com/2020/04/21/obituaries/eunice-foote-overlooked.html

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Eunice Foote’s experiment for her studies on greenhouse gases, as recreated in the 2018 short film “Eunice. ”Credit…Paul Bancilhon and Matteo Marcolini

https://www.climate.gov/news-features/features/happy-200th-birthday-eunice-foote-hidden-climate-science-pioneer

Foote conducted a series of experiments that demonstrated the interactions of the sun’s rays on different gases. She used an air pump, four mercury thermometers, and two glass cylinders. First, she placed two thermometers in each cylinder, then by using the air pump, she evacuated the air from one cylinder and compressed it in the other. Allowing both cylinders to reach the same temperature, she placed the cylinders in the sunlight to measure temperature variance once heated and under different moisture conditions. She performed this experiment on CO2, common air, and hydrogen. Of the gases she tested, Foote concluded that carbonic acid (CO2) trapped the most heat, reaching a temperature of 52oC. From this experiment, she stated ““The receiver containing this gas became itself much heated—very sensibly more so than the other—and on being removed [from the Sun], it was many times as long in cooling.” Looking to the history of the Earth, Foote theorised that “An atmosphere of that gas would give to our earth a high temperature; and if, as some suppose, at one period of its history, the air had mixed with it a larger proportion than at present, an increased temperature from its own action, as well as from increased weight, must have necessarily resulted.

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John Tyndall was unaware of Foote’s work, or did not think it was relevant

Tyndall Scattering

When Tyndall was working on his heat absorption experiments, he thought about what visible light would do.

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The tube was gradually filled with smoke

Tyndall began to experiment with light, shining beams through various gases and liquids and recording the results. He used this simple glass tube to simulate the sky, with a white light at one end to represent the sun. He discovered that when he gradually filled the tube with smoke the beam of light appeared to be blue from the side but red from the far end. Tyndall realised that the colour of the sky is a result of light from the sun scattering around particles in the upper atmosphere, in what is now known as the ‘Tyndall effect’. He thought that the light scattered off particles of dust or water vapour in the atmosphere, like the smoke particles in the tube, but it’s now known that the light scatters off the molecules of the air itself.

Tyndall knew that white light was made up of a whole rainbow of coloured light and thought that the blue light appeared because it was more likely to scatter off the particles. We now know that this is because it has a much shorter wavelength than red light and is much more easily scattered, so to our eyes the sky looks blue.

This experiment also explains why the sky often appears to be red in colour as the sun sets. As the sun gets lower in the sky the angle means that the light we see passes through more atmosphere. By the time it reaches us the blue light has already scattered off, leaving the longer frequency red light to be seen.

Tyndall’s blue-sky tube is a very simple but effective way of demonstrating this scattering effect. You can easily create your own version using a glass beaker of water: shine a white light through the water and slowly stir in a few drops of milk at a time and see what happens.

https://www.rigb.org/our-history/iconic-objects/iconic-objects-list/tyndall-blue-sky

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IV. On the blue colour of the sky, the polarization of skylight, and on the polarization of light by cloudy matter generally

John Tyndall

Published: 01 January 1869

https://royalsocietypublishing.org/doi/10.1098/rspl.1868.0033

https://www.jstor.org/stable/pdf/112380.pdf

https://www.sciencedirect.com/science/article/abs/pii/S0016003269902282

https://www.sciencedirect.com/sdfe/pdf/download/eid/1-s2.0-S0016003269902282/first-page-pdf

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https://en.wikipedia.org/wiki/Tyndall_effect

The Tyndall effect is light scattering by particles in a colloid or in a very fine suspension. Also known as Tyndall scattering, it is similar to Rayleigh scattering, in that the intensity of the scattered light is inversely proportional to the fourth power of the wavelength, so higher energy blue light is scattered much more strongly than lower energy red light. An example in everyday life is the blue colour sometimes seen in the smoke emitted by motorcycles, in particular two-stroke machines where the burnt engine oil provides these particles.

Under the Tyndall effect, the longer wavelengths are more transmitted while the shorter wavelengths are more diffusely reflected via scattering. The Tyndall effect is seen when light-scattering particulate matter is dispersed in an otherwise light-transmitting medium, when the diameter of an individual particle is the range of roughly between 40 and 900 nm, i.e. somewhat below or near the wavelengths of visible light (400–750 nm).

It is particularly applicable to colloidal mixtures and fine suspensions; for example, the Tyndall effect is used in nephelometers to determine the size and density of particles in aerosols and other colloidal matter.

Examples of Tyndall scattering

Blue Sky – Red Sunset

https://www.thoughtco.com/why-the-sky-is-blue-experiment-606169

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What makes sunrise and sunset different from the daytime sky? It’s the amount of atmosphere the sunlight has to cross before it reaches your eyes. If you think of the atmosphere as a coating covering the Earth, sunlight at noon passes through the thinnest part of the coating (which has the least number of particles). Sunlight at sunrise and sunset has to take a sideways path to the same point, through a lot more “coating”, which means there are a lot more particles that can scatter light.

While multiple types of scattering occur in the Earth’s atmosphere, Rayleigh scattering is primarily responsible for the blue of the daytime sky and reddish hue of the rising and setting sun. The Tyndall effect also comes into play, but it is not the cause of blue-sky colour because molecules in air are smaller than the wavelengths of visible light.

https://en.wikipedia.org/wiki/Rayleigh_scattering

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c2

Rayleigh scattering refers to the scattering of light off the molecules of the air, and can be extended to scattering from particles up to about a tenth of the wavelength of the light. It is Rayleigh scattering off the molecules of the air which gives us the blue sky.

Rayleigh scattering can be considered to be elastic scattering since the photon energies of the scattered photons is not changed.

https://www.britannica.com/science/Rayleigh-scattering

The angle through which sunlight in the atmosphere is scattered by molecules of the constituent gases varies inversely as the fourth power of the wavelength; hence, blue light, which is at the short wavelength end of the visible spectrum, will be scattered much more strongly than will the long wavelength red light. This results in the blue colour of the sunlit sky, since, in directions other than toward the Sun, the observer sees only scattered light. The Rayleigh laws also predict the variation of the intensity of scattered light with direction, one of the results being that there is complete symmetry in the patterns of forward scattering and backward scattering from single particles.

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Above left: Flour suspended in water appears to be blue because only scattered light reaches the viewer and blue light is scattered by the flour particles more than red light. Above right: The Tyndall effect in opalescent glass. It appears blue from the side, but orange light shines through

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A blue iris in an eye is due to Tyndall scattering in a translucent layer in the iris. Brown and black irises have the same layer except with more melanin in it. The melanin absorbs light. In the absence of melanin, the layer is translucent (i.e. the light passing through is randomly and diffusely scattered) and a noticeable portion of the light that enters this translucent layer re-emerges via a scattered path. That is, there is backscatter, the redirection of the lightwaves back out to the open air. Scattering takes place to a greater extent at the shorter wavelengths. The longer wavelengths tend to pass straight through the translucent layer with unaltered paths, and then encounter the next layer further back in the iris, which is a light absorber. Thus, the longer wavelengths are not reflected (by scattering) back to the open air as much as the shorter wavelengths are. Because the shorter wavelengths are the blue wavelengths, this gives rise to a blue hue in the light that comes out of the eye. The blue iris is an example of a structural colour, in contradistinction to a pigment colour.

Bending light in a falling jet of water

1) How do we see?

In the fifth century BC, Empedocles postulated that light shone out from the eye making sight possible. If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun.

https://en.wikipedia.org/wiki/Empedocles

Empedocles (c. 494 – c. 434 BC, fl. 444–443 BC) was a Greek pre-Socratic philosopher and a native citizen of Akragas, a Greek city in Sicily. Empedocles’ philosophy is best known for originating the cosmogonic theory of the four classical elements.

In about 300 BC, Euclid wrote Optica, in which he studied the properties of light. Euclid postulated that light travelled in straight lines and he described the laws of reflection and studied them mathematically. He questioned that sight is the result of a beam from the eye, for he asks how one sees the stars immediately, if one closes one’s eyes, then opens them at night. If the beam from the eye travels infinitely fast this is not a problem.

https://en.wikipedia.org/wiki/Euclid

Euclid (300 BC), sometimes called Euclid of Alexandria to distinguish him from Euclid of Megara, was a Greek mathematician, often referred to as the “founder of geometry” or the “father of geometry”.

We now know that we see objects because light reflects off them and enters our eyes. This light stimulates the retina which sends electrical signals to the brain. Our brain interprets these signals and we “see” the object.

https://wiki.ucl.ac.uk/pages/viewpage.action?pageId=21430670&navigatingVersions=true

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As well as reflection, we also need refraction to be able to see. It is through refraction at the cornea and lens that allows light to be focused onto the retina.

http://ffden-2.phys.uaf.edu/211_fall2013.web.dir/jessica_garvin/refraction_eye.htm

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2) Reflection and refraction

(a) Reflection of light

https://en.wikipedia.org/wiki/Reflection_(physics)

https://www.youtube.com/watch?v=-_Is2o74aRQ

https://www.physicsclassroom.com/class/refln/Lesson-1/The-Law-of-Reflection

Light is known to behave in a very predictable manner. If a ray of light could be observed approaching and reflecting off of a flat mirror, then the behaviour of the light as it reflects would follow a predictable law known as the law of reflection. The diagram below illustrates the law of reflection.

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In the diagram, the ray of light approaching the mirror is known as the incident ray (labelled I in the diagram). The ray of light that leaves the mirror is known as the reflected ray (labelled R in the diagram). At the point of incidence where the ray strikes the mirror, a line can be drawn perpendicular to the surface of the mirror. This line is known as a normal line (labelled N in the diagram). The normal line divides the angle between the incident ray and the reflected ray into two equal angles. The angle between the incident ray and the normal is known as the angle of incidence. The angle between the reflected ray and the normal is known as the angle of reflection. (These two angles are labelled with the Greek letter “theta” accompanied by a subscript; read as “theta-i” for angle of incidence and “theta-r” for angle of reflection.) The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.

https://www.physicsclassroom.com/class/refln/Lesson-1/Specular-vs-Diffuse-Reflection

The Law of Reflection is Always Observed (regardless of the orientation of the surface) but most surfaces are not like mirrors.

Reflection off of smooth surfaces such as mirrors or a calm body of water leads to a type of reflection known as specular reflection. Reflection off of rough surfaces such as clothing, paper, and the black material used on roads leads to a type of reflection known as diffuse reflection. Whether the surface is microscopically rough or smooth has a tremendous impact upon the subsequent reflection of a beam of light. The diagram below depicts two beams of light incident upon a rough and a smooth surface.

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(b) Refraction of light

https://www.physicsclassroom.com/class/refrn/Lesson-1/Boundary-Behavior

https://en.wikipedia.org/wiki/Refraction

In physics, refraction of light is the change in direction of a wave passing from one transparent medium to another or from a gradual change in the medium.

Refraction of light is caused by the fact that it travels at different speeds in different mediums. Its greatest speed occurs in a vacuum (or air, which does not change the speed by much) and this speed decreases if it enters any other transparent medium such as air, water, or glass. When light leaves the medium and returns to a vacuum, and ignoring any effects of gravity, its speed returns to the usual speed of light in a vacuum, c (3 x 108 m/s).

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If a light wave passes from a medium in which it travels slow (relatively speaking) into a medium in which it travels fast, then the light wave would refract away from the normal. In such a case, the refracted ray will be farther from the normal line than the incident ray.

If a light wave passes from a medium in which it travels fast (relatively speaking) into a medium in which it travels slow, then the light wave will refract towards the normal. In such a case, the refracted ray will be closer to the normal line than the incident ray.

The diagram above shows a light ray undergoing refraction as it passes from air (less dense) into water (more dense).

The incident ray is a ray (drawn perpendicular to the wavefronts) that shows the direction that light travels as it approaches the boundary.

the refracted ray is a ray (drawn perpendicular to the wavefronts) that shows the direction that light travels after it has crossed over the boundary. In the diagram, a normal line is drawn to the surface at the point of incidence. This line is always drawn perpendicular to the boundary. The angle that the incident ray makes with the normal line is referred to as the angle of incidence. Similarly, the angle that the refracted ray makes with the normal line is referred to as the angle of refraction.

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the speed is related to the optical density of a material that is related to the index of refraction of a material.

https://www.physicsclassroom.com/Class/refrn/u14l1d.cfm#index

Like any wave, the speed of a light wave is dependent upon the properties of the medium. In the case of an electromagnetic wave, the speed of the wave depends upon the optical density of that material which relates to the sluggish tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave in the form of vibrating electrons before reemitting it as a new electromagnetic disturbance. The more optically dense that a material is, the slower that a wave will move through the material.

One indicator of the optical density of a material is the index of refraction value of the material. Index of refraction values (represented by the symbol n) are numerical index values that are expressed relative to the speed of light in a vacuum. The index of refraction value of a material is a number that indicates the number of times slower that a light wave would be in that material than it is in a vacuum. A vacuum is given an n value of 1.0000. The n values of other materials are found from the following equation:

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Light travelling through air, then glass and then air again

The law of refraction or Snell’s law and can be written as

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In optics, therefore, the law of refraction is typically written as

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3) Optics

https://en.wikipedia.org/wiki/History_of_optics

Optics began with the development of lenses by the ancient Egyptians and Mesopotamians, followed by theories on light and vision developed by ancient Greek philosophers, and the development of geometrical optics in the Greco-Roman world. The word optics is derived from a Greek term meaning “appearance, look”. Optics was significantly reformed by the developments in the medieval Islamic world, such as the beginnings of physical and physiological optics, and then significantly advanced in early modern Europe, where diffractive optics began. These earlier studies on optics are now known as “classical optics”. The term “modern optics” refers to areas of optical research that largely developed in the 20th century, such as wave optics and quantum optics.

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Alhazen (Ibn al-Haytham), “the father of Optics

https://en.wikipedia.org/wiki/Ibn_al-Haytham

Hasan Ibn al-Haytham (Latinized as Alhazen and full name Abū ʿAlī al-Hasan ibn al-Ḥasan ibn al-Haytham c. 965 – c. 1040) was an Arab mathematician, astronomer, and physicist of the Islamic Golden Age. Referred to as “the father of modern optics”, he made significant contributions to the principles of optics and visual perception in particular. His most influential work is titled Kitāb al-Manāẓir (“Book of Optics”), written during 1011–1021, which survived in a Latin edition. A polymath, he also wrote on philosophy, theology and medicine.

He was the first to explain that vision occurs when light reflects from an object and then passes to one’s eyes. He was also the first to demonstrate that vision occurs in the brain, rather than in the eyes. Building upon a naturalistic, empirical method pioneered by Aristotle in ancient Greece, Ibn al-Haytham was an early proponent of the concept that a hypothesis must be supported by experiments based on confirmable procedures or mathematical evidence—an early pioneer in the scientific method five centuries before Renaissance scientists.

The English Franciscan, Roger Bacon (c. 1214–1294) produced writings on optics. In these (the Perspectiva, the De multiplicatione specierum, and the De speculis comburentibus) he cited a wide range of recently translated optical and philosophical works, including those of Alhazen, Aristotle, Avicenna, Averroes, Euclid, al-Kindi, Ptolemy, Tideus, and Constantine the African. Although he was not a slavish imitator, he drew his mathematical analysis of light and vision from the writings of the Arabic writer, Alhazen.

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Optical diagram showing light being refracted by a spherical glass container full of water. (from Roger Bacon, De multiplicatione specierum)

https://en.wikipedia.org/wiki/Roger_Bacon

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Roger Bacon OFM (c. 1219/20 – c. 1292), also known by the scholastic accolade Doctor Mirabilis, was a medieval English philosopher and Franciscan friar who placed considerable emphasis on the study of nature through empiricism.

Johannes Kepler (1571–1630) picked up the investigation of the laws of optics from his lunar essay of 1600.

His manuscript, presented on January 1, 1604, was published as Astronomiae Pars Optica (The Optical Part of Astronomy). In it, Kepler described the inverse-square law governing the intensity of light, reflection by flat and curved mirrors, and principles of pinhole cameras, as well as the astronomical implications of optics such as parallax and the apparent sizes of heavenly bodies. Astronomiae Pars Optica is generally recognized as the foundation of modern optics (though the law of refraction is conspicuously absent).

https://en.wikipedia.org/wiki/Johannes_Kepler

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Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, and astrologer.

Willebrord Snellius (1580–1626) found the mathematical law of refraction, now known as Snell’s law, in 1621.

https://en.wikipedia.org/wiki/Willebrord_Snellius

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Willebrord Snellius (born Willebrord Snel van Royen) (13 June 1580 – 30 October 1626) was a Dutch astronomer and mathematician, known in the English-speaking world as Snell. In the west, especially the English speaking countries, his name is attached to the law of refraction of light (Snell’s law).

Isaac Newton (1643–1727) investigated the refraction of light and was responsible for improving telescopes including the invention of the reflecting telescope.

https://en.wikipedia.org/wiki/Isaac_Newton

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Sir Isaac Newton PRS (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, theologian, and author (described in his own day as a “natural philosopher”) who is widely recognised as one of the most influential scientists of all time and as a key figure in the scientific revolution.

The effects of diffraction of light were carefully observed and characterized by Francesco Maria Grimaldi, who also coined the term diffraction, from the Latin diffringere, ‘to break into pieces’, referring to light breaking up into different directions. The results of Grimaldi’s observations were published posthumously in 1665.

https://en.wikipedia.org/wiki/Francesco_Maria_Grimaldi

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Francesco Maria Grimaldi (2 April 1618 – 28 December 1663) was an Italian Jesuit priest, mathematician and physicist who taught at the Jesuit college in Bologna.

In 1803 Thomas Young did his famous experiment observing interference from two closely spaced slits in his double slit interferometer. Explaining his results by interference of the waves emanating from the two different slits, he deduced that light must propagate as waves.

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Thomas Young’s sketch of two-slit diffraction, which he presented to the Royal Society in 1803.

https://en.wikipedia.org/wiki/Thomas_Young_(scientist)

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Thomas Young FRS (13 June 1773 – 10 May 1829) was a British polymath who made notable contributions to the fields of vision, light, solid mechanics, energy, physiology, language, musical harmony, and Egyptology. He “made a number of original and insightful innovations”.

There are of, course, many people who have been involved in the study of optics over the years, and it has continued.

4) Total internal reflection

https://www.cyberphysics.co.uk/topics/light/TIR.htm

When a wave hits a boundary with a medium that it can travel faster in (e.g. light going from glass into air) it will be refracted through a larger angle than its angle of incidence.

The bigger the angle of incidence gets the bigger the angle of refraction will get. This has a limit though! The angle of refraction cannot get bigger than 90o.

A special name is given to the angle of incidence that produces an angle of refraction of 90o. It is called the critical angle.

If the angle of incidence gets any bigger refraction is not possible and all the light is then reflected.Total Internal Reflection causes 100% reflection. In no other situation in nature does this occur, so it is unique and very useful as it is 100% efficient at transferring the light energy.

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https://en.wikipedia.org/wiki/Jean-Daniel_Colladon

Jean-Daniel Colladon (15 December 1802, Geneva – 30 June 1893) was a Swiss physicist. He was to give a lecture on his measurement of the speed of sound and the breaking up of water jets but he had a problem as the audience couldn’t see the water jet. So, he used a tube to collect and pipe sunlight to the lecture table. The light was trapped by the total internal reflection of the tube until the water jet, upon which edge the light incidented at a glancing angle, broke up and carried the light in a curved flow. Colladon reported this experiment to a wider audience in the Comptes rendus, the French Academy of Sciences’ journal, in 1842.

His experiments formed one of the core principles of modern-day optical fibres

http://www.ecoc2011.org/Conference-Program/Sunday-Public-Talks/PDF_01_Jeff-Hecht.aspx

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Colladon’s “light pipe”, as illustrated in an 1884 article. Light source is a horizontal arc lamp but sunlight was initially used. Total internal reflection occurred at the water-air interface and the light was guided along the parabola. Scattering occurred in the turbulent water droplets. Dark regions occurred at the smooth areas.

https://i-fiberoptics.com/pdf/12_0120-if_514.pdf

In 1854, John Tyndall, using a jet of water that flowed from one container to another and a beam of light, demonstrated that light used internal reflection to follow a specific path. As water poured out through the spout of the first container, Tyndall directed a beam of sunlight at the path of the water. The light, as seen by the audience, followed a zigzag path inside the curved path of the water. This simple experiment, illustrated in below, marked the first research into the guided transmission of light (although, as noted above, he wasn’t the first person to do the experiment).

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Why didn’t Tyndall credit Colladon?

In his handwritten notes he apologised for not showing “something entirely new.” The presentation he had planned was “unripe” and Faraday suggested the water jet. Tyndall had not seen it before and wrote that it was difficult.

Faraday was usually careful in crediting others. His possible source of information was from Colladon’s 1841 demonstration of the water jet in London

Faraday was a close friend of de la Rive

https://en.wikipedia.org/wiki/Auguste_Arthur_de_la_Rive

Faraday spent the summer of 1841 in Switzerland, trying to recover from memory problems

Conclusions:

Faraday hadn’t mentioned de la Rive or Colladon probably because he forgot owing to having memory problems

Tyndall didn’t want to say Faraday was forgetful as he wasn’t claiming scientific credit

So how did Tyndall get credit?

Narinder Kapany found a reference in 1955 when writing up his PhD on fibre bundles for H. H. Hopkins. He later wrote the first book on fibre optics

https://en.wikipedia.org/wiki/Narinder_Singh_Kapany

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Narinder Singh Kapany (born 31 October 1926) is an Indian-born American physicist known for his work in fibre optics

Tyndall was a credible source because his books had been popular for decades and he did not say where the idea had come from.

There was no readily available conflicting evidence so Colladon’s work was forgotten.

Professor Hurley demonstrating light travelling in a water stream

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There was a very large time gap between John Tyndall’s work on total internal reflection and the optical fibres as we know it. However, there were some prototype uses, which weren’t fully developed.

https://en.wikipedia.org/wiki/Photophone

https://www.thoughtco.com/alexander-graham-bells-photophone-1992318

On June 3, 1880, Alexander Graham Bell transmitted the first wireless telephone message on his newly invented “photophone,” a device that allowed for the transmission of sound on a beam of light. Bell held four patents for the photophone and built it with the help of an assistant, Charles Sumner Tainter. The first wireless voice transmission took place over a distance of 700 feet.

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Although the photophone was an extremely important invention, the significance of Bell’s work was not fully recognized in its time. This was largely due to practical limitations in the technology of the time: Bell’s original photophone failed to protect transmissions from outside interferences, such as clouds, that easily disrupted transport.

That changed nearly a century later when the invention of fibre optics in the 1970s allowed for the secure transport of light. Indeed, Bell’s photophone is recognized as the progenitor of the modern fibre optic telecommunications system that is widely used to transmit telephone, cable, and internet signals across large distances.

https://en.wikipedia.org/wiki/Alexander_Graham_Bell

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Alexander Graham Bell (March 3, 1847 – August 2, 1922) was a Scottish-born inventor, scientist, and engineer who is credited with inventing and patenting the first practical telephone.

https://journals.sagepub.com/doi/pdf/10.1177/014107680009300815

John Logie Baird is best known for his work on television but he also made a contribution to fibreoptics. In 1926 he applied for a patent for “An improved method and means of producing optical images”. The method was a honeycomb-like assembly of hollow rods which allowed the transmission of an image without “the use of lens, concave mirror or like device”. He stated that the structure could be made of very thin glass rods, which would transmit the image by internal reflection and could be flexible

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Baird’s patent was granted in 1928. However, there were no more publications on fibreoptics until 1954 and Baird never worked on his invention

Tyndall: The science communicator

Tyndall was a very effective communicator – a lecturer. He carried out hundreds of lectures

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Above left: John Tyndall lecturing to children at the Royal Institution in 1876 (from a pen-and-ink sketch by S.P. Thompson). Above right lecturing to an older audience

And an author

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He also did lecture tours

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He made a $13,000 profit and gave it all to the benefit of science in America (although why he didn’t give it to British Universities is a mystery to me). In this he supported graduate fellowships for Harvard, Columbia and Pennsylvania Universities

“Knowledge once gained casts a light beyond its own immediate boundaries” John Tyndall

Other interests of Tyndall

1) Alpine mountaineering

Tyndall visited the Alps mountains in 1856 for scientific reasons and ended up becoming a pioneering mountain climber. He visited the Alps almost every summer from 1856 onward, was a member of the very first mountain-climbing team to reach the top of the Weisshorn (1861), and lead of one of the early teams to reach the top of the Matterhorn (1868). He is one the names associated with the “Golden age of alpinism” — the mid-Victorian years when the more difficult of the Alpine peaks were summited for the first time.

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https://en.wikipedia.org/wiki/Weisshorn

The Weisshorn is a major peak of Switzerland and the Alps, culminating at 4,506 metres above sea level. It is part of the Pennine Alps and is located between the valleys of Anniviers and Zermatt in the canton of Valais. In the latter valley, the Weisshorn is one of the many 4000ers surrounding Zermatt, with Monte Rosa and the Matterhorn.

“Sometimes it was a fair pull upwards, sometimes an oblique twist round the corner of a rock tower; sometimes it was the grip of the finger ends in a fissure and lateral shifting of the whole body in a line parallel to the crack. Many times, I found myself with my feet highest and my head the lowest.”

2) Glaciers

In the Alps, Tyndall studied glaciers, their ascent, origin and especially glacier motion.

His explanation of glacial flow brought him into dispute with others. Much of the early scientific work on glacier motion had been done by Forbes, but Forbes at that time didn’t know of the phenomenon of regelation which was discovered a little later by Michael Faraday. Regelation played a key role in Tyndall’s explanation. Forbes didn’t see regelation in the same way at all. Complicating their debate, a disagreement arose publicly over who deserved to get investigator credit for what. Articulate friends of Forbes, as well as Forbes himself, thought that Forbes should get the credit for most of the good science, whereas Tyndall thought the credit should be distributed more widely. When Forbes and Tyndall were in the grave, their disagreement was continued by their respective official biographers. Everyone tried to be reasonable, but agreement wasn’t attained. More disappointingly, aspects of glacier motion remained not understood or not proved.

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https://en.wikipedia.org/wiki/James_David_Forbes

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James David Forbes FRS FRSE FGS (1809–1868) was a Scottish physicist and glaciologist who worked extensively on the conduction of heat and seismology. He described the motion of glaciers as that of a viscous fluid.

Tyndall proposed an alternative theory that combined fracture and regelation.

https://en.wikipedia.org/wiki/Regelation

Regelation is the phenomenon of melting under pressure and refreezing when the pressure is reduced. It can be demonstrated by looping a fine wire around a block of ice, with a heavy weight attached to it. The pressure exerted on the ice slowly melts it locally, permitting the wire to pass through the entire block. The wire’s track will refill as soon as pressure is relieved, so the ice block will remain solid even after wire passes completely through. This experiment is possible for ice at −10 °C or cooler, and while essentially valid, the details of the process by which the wire passes through the ice are complex. The phenomenon works best with high thermal conductivity materials such as copper, since latent heat of fusion from the top side needs to be transferred to the lower side to supply latent heat of melting. In short, the phenomenon in which ice converts to liquid due to applied pressure and then re-converts to ice once the pressure is removed is called regelation.

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Regelation was discovered by Michael Faraday. It occurs only for substances such as ice, that have the property of expanding upon freezing, for the melting points of those substances decrease with the increasing external pressure. The melting point of ice falls by 0.0072 °C for each additional atmosphere of pressure applied. For example, a pressure of 500 atmospheres is needed for ice to melt at −4 °C.

3) Foghorns

In the late 1860s and early 1870s Tyndall wrote an introductory book about sound propagation in air, and was a participant in a large-scale British project to develop a better foghorn. In laboratory demonstrations motivated by foghorn issues, Tyndall established that sound is partially reflected (i.e. partially bounced back like an echo) at the location where an air mass of one temperature meets another air mass of a different temperature; and more generally when a body of air contains two or more air masses of different densities or temperatures, the sound travels poorly because of reflections occurring at the interfaces between the air masses, and very poorly when many such interfaces are present. (He then argued, though inconclusively, that this is the usual main reason why the same distant sound, e.g. foghorn, can be heard stronger or fainter on different days or at different times of day.

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One of John Tyndall’s setups for demonstrating reflection of sound in air. The tall black object on the left labelled f in the illustration is a flame from flammable gas, which is coming out of a small nozzle under high pressure. The sound-collecting cone directs the sound to the base of this tall flame, just above the nozzle. At the tall flame’s base, tiny compressions and decompressions to the air from sound waves cause tiny changes in the flow of the gas, which cause non-tiny, visible wobbles and flutters higher up the flame column. When there is no sound, the tall flame is perfectly erect and tranquil. This is Tyndall’s sound detector (largely developed by himself, after he got the original basic idea from John Le Conte). The sound generator emits a high pitch, and it’s emitted in a directed way via a small cone. In the centre of the illustration is a set of ordinary or low-pressure gas burners. When some of these burners are lit, the volume of sound that reaches the sound detector is reduced; and when all of them are lit, no sound at all reaches the detector. (A large set of weak burners is more effective at blocking the sound than a smaller set of stronger burners). Now, Tyndall relocated the sound collecting & detecting unit to the place marked f’ on the righthand side of the illustration, behind the sound emitter. When the grill is off the detector doesn’t detect the sound at this new location. But when the grill is on, the sound is detected there. Thus, the lit grill has reflected the sound (bounced it like an echo). The direction the sound is reflected to can be shaped by shaping the array of gas burners. The difference between the lit and unlit grill is essentially heat and the low-density air associated with heat. Although the air density disparities are very high in this experiment, the experiment is taken to demonstrate that sound is reflected at the interfaces between air masses of different densities, more generally.

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Sound is partially reflected (like an echo) at the location where an air mass of one temperature meets another air mass of a different temperature. This is why we seem to hear distant sounds, such as train whistles and ringing church bells, better as a storm aproaches.

https://en.wikipedia.org/wiki/Foghorn

A foghorn or fog signal is a device that uses sound to warn vehicles of navigational hazards like rocky coastlines, or boats of the presence of other vessels, in foggy conditions. The term is most often used in relation to marine transport. When visual navigation aids such as lighthouses are obscured, foghorns provide an audible warning of rock outcrops, shoals, headlands, or other dangers to shipping.

4) Optically pure air and germ theory

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In the lab Tyndall came up with the following simple way to obtain “optically pure” air, i.e. air that has no visible signs of particulate matter. He built a square wooden box with a couple of glass windows on it. Before closing the box, he coated the inside walls and floor of the box with glycerin, which is a sticky syrup-like material. He found that after a few days’ wait the air inside the box was entirely particulate-free when examined with strong light beams through the glass windows. The various floating-matter particulates had all ended up getting stuck to the walls or settling on the sticky floor. Now, in the optically pure air there were no signs of any “germs”, i.e. no signs of floating micro-organisms. Tyndall sterilised some meat-broths by simply boiling them, and then compared what happened when he let these meat-broths sit in the optically pure air, and in ordinary air. The broths sitting in the optically pure air remained “sweet” (as he said) to smell and taste after many months of sitting, while the ones in ordinary air started to become putrid after a few days. However, the next year (1876) Tyndall failed to consistently reproduce the result. Some of his supposedly heat-sterilized broths rotted in the optically pure air. From this Tyndall was led to find viable bacterial spores (endospores) in supposedly heat-sterilized broths. He discovered the broths had been contaminated with dry bacterial spores from hay in the lab. All bacteria are killed by simple boiling, except that bacteria have a spore form that can survive boiling, he correctly contended. Tyndall found a way to eradicate the bacterial spores that came to be known as “Tyndallization”. Tyndallization historically was the earliest known effective way to destroy bacterial spores. At the time, it affirmed the “germ theory” against a number of critics whose experimental results had been defective from the same cause.

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The above illustration originally appeared in year 1876 in “The optical deportment of the atmosphere in relation to the phenomena of putrefaction and infection” by John Tyndall in Philosophical Transactions of the Royal Society of London, Vol. 166, page 30. It depicts John Tyndall’s mid-1870s scientific setup for the long-term preservation of fresh food broths inside a semi-sealed wooden box. Intentionally, outside air is allowed to enter the box, but there is blockage of micro-organisms from entering the box. The two wavy objects labelled a and b at the top of the box are glass pipes. They are filled with densely packed cottonwool. These pipes connect the outside air to the air inside the box. Floating micro-organisms and other air particulates in the outside air are blocked by the cottonwool from entering inside. Tyndall said in 1871: “The inability of air which had been filtered through cotton-wool to generate microscopic life had been demonstrated by [Heinrich] Schroeder [in the 1850s] and Pasteur.” (Dust and Disease, 1871). For the box to be able to preserve fresh broths or other foods, the box cannot have micro-organisms inside it to begin with. For that objective, Tyndall came up with the idea of coating the inside walls and floor of the box with glycerin, which is a sticky syrup. After closing the box and waiting for a few days, he found the air inside the box becomes entirely particulate-free because the various floating-matter particulates all end up getting stuck to the walls or settling on the sticky floor. The glass vials at the bottom of the box are not coated with the glycerin. To sterilize the glass vials, Tyndall immersed them in boiling water from underneath the box, for half an hour, after the air had cleared. The two windows on the sides of the box are there to enable verification that the air inside the box does not contain floating micro-organisms or other particulates. Finally, newly boiled meat and vegetable broth is dropped into the glass vials via the long pipette at the top centre of the box. At the spot where the pipette enters the box, the box material is rubber, and the rubber is pierced with just a pinhole to let the pipette enter. This system worked for Tyndall in 1875. But it failed in 1876. Tyndall traced the failure to bacterial endospores which are not killed by boiling. He then originated a way to destroy the endospores, called Tyndallization, which historically was the earliest known effective way to destroy endospores.

John Tyndall – one of the greatest experimentalist scientists of the 19th Century

Scientific theories: To find the general from the particular and the timeless from the transitory

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John Tyndall’s illustration of his setup for looking at aerosols (1868), subsequently annotated in coloured typeface. The above apparatus is meant to be looked at in a dark room, i.e., a room with no light except for the illuminated glass tube at the centre of the picture. Its basic idea is to bring a chemical vapour into the illuminated glass tube by a suction pump (the suction pump is under the table). The illustration dates from 1868. With this apparatus John Tyndall found that a variety of vapours, initially clear and transparent to light, became cloudy with more exposure to the light due to chemical decomposition of the vapor molecules. He verified that it was the light itself that caused this decomposition. The chemical reaction in response to the light was in some cases rapid (e.g. when the vapor was amyl nitrite) and in other cases very gradual (e.g. when the vapor was isopropyl iodide). Some vapours formed white clouds, others formed blue or purple clouds. The clouds took on distinctive shapes and swirled in “paroxysms of motion”, in some cases. Tyndall demonstrated that the particular wavelengths that produced a photochemical decomposition depended on the particular type of vapor molecule that was decomposed, although in all cases the light was predominantly or exclusively in the blue and near UV area. Tyndall uses these photochemical reactions as context for talking about the question of the mechanism by which molecules absorb radiant energy. The illustration is in Tyndall’s report “New Chemical Reactions Produced by Light” (1868) and again in Tyndall’s “On the Action of Rays of High Refrangibility upon Gaseous Matter” (1870). It is also included in the later editions of his book Heat as a Mode of Motion even though it is not a heat phenomenon.

With this setup Tyndall observed new chemical reactions produced by high frequency light waves acting on certain vapours. The main scientific interest here from his point of view was the additional hard data it lent to the grand question of the mechanism by which molecules absorb radiant energy.

“The brightest flashes in the world of thought are incomplete until they have been proven to have their counterparts in the world of fact”

“You must have accurate experiments for scientific discoveries”

John Tyndall and Louisa Hamilton

Tyndall did not marry until age 55. His bride, Louisa Hamilton, was the 30-year-old daughter of a member of parliament (Lord Claud Hamilton, M.P.). The following year, 1877, they built a summer chalet at Belalp in the Swiss Alps. Before getting married Tyndall had been living for many years in an upstairs apartment at the Royal Institution and continued living there after marriage until 1885 when a move was made to a house near Haslemere 45 miles southwest of London. The marriage was a happy one and without children. He retired from the Royal Institution at age 66 having complaints of ill health.

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In his last years Tyndall often took chloral hydrate to treat his insomnia. When bedridden and ailing, he died from an accidental overdose of this drug in 1893 at the age of 73, and was buried at Haslemere. The overdose was administered by his wife Louisa. “My darling,” said Tyndall when he realized what had happened, “you have killed your John.”

https://www.youtube.com/watch?v=53tFu9unKhQ

https://www.youtube.com/watch?v=3A-3gRA8vnk

John Tyndall’s work applied in the 21st century

1) Global warming

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https://www.brinknews.com/why-values-matter-in-combating-climate-change/

https://www.vox.com/2014/10/22/18093094/how-do-we-know-global-warming-is-real

https://www.climatecentral.org/gallery/graphics/global-temperatures-and-co2-concentrations-2020

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2) Optical communications

https://en.wikipedia.org/wiki/Optical_communication

Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices.

https://en.wikipedia.org/wiki/Fiber-optic_communication

Fibre-optic communication is a method of transmitting information from one place to another by sending pulses of infrared light through an optical fibre. The light is a form of carrier wave that is modulated to carry information. Fibre is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference is required. This type of communication can transmit voice, video, and telemetry through local area networks or across long distances.

Optical fibre is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers at Bell Labs have reached internet speeds of over 100 petabit × kilometre per second using fibre-optic communication.

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https://www.osa-opn.org/home/articles/volume_26/march_2015/features/scaling_optical_fiber_networks_challenges_and_solu/

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https://www.polytechnichub.com/fiber-optic-communication/

https://www.photonicssociety.org/awards/john-tyndall-award

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3) Science outreach communication

https://www.rigb.org/christmas-lectures

Most universities now have outreach activities

The Institute of Physics puts on lectures for the general public (I suspect that the RSC does too, but they won’t be as good).

Television is also a good source of science information, as are video providers such as YouTube

4) Tyndall remembered

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Portrait of John Tyndall by John McLure, oil on canvas, 1893, National Portrait Gallery

John Tyndall was a draftsman, surveyor, geologist, atmospheric scientist, physics professor, science communicator, microbiologist, mountaineer and poet

Professor Hurley (and me) thanks

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https://www.rolandjackson.co.uk/

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Questions and answers

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1) Tyndall’s wife gave him a sleeping draught by mistake instead of milk of magnesia. He realised quite quickly the mistake and tried to make himself sick. Unfortunately, it didn’t work.

His wife was determined to write a book about her husband, but her failure to do so is why so little was known about him.

2) Can diamagnetic levitation be used for monorail trains for people transportation?

No because the force is so weak and couldn’t lift something as heavy as a train. There is no stable point of levitation.

Diamagnetic levitation could, perhaps, be used to move things on a micro-scale, as most things are diamagnetic.

3) He anticipated the “hard problem” of consciousness in 1868 referring to an “impassable intellectual chasm between the physics of the brain and the states of consciousness even if the details were known”.

Tyndall was a materialist. He believed the mind was a physical thing.

4) Is diamagnetism actually a repulsive force? The Meissner effect in superconductors is not just repulsive: it is do to the expulsion of a magnetic field.

https://en.wikipedia.org/wiki/Meissner_effect

The Meissner effect (or Meissner–Ochsenfeld effect) is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state when it is cooled below the critical temperature.

The phenomenon was discovered in 1933 by measuring the magnetic field distribution outside superconducting tin and lead samples. The samples, in the presence of an applied magnetic field, were cooled below their superconducting transition temperature, whereupon the samples cancelled nearly all interior magnetic fields. The effect was only indirectly detected because the magnetic flux is conserved by a superconductor: when the interior field decreases, the exterior field increases. The experiment demonstrated for the first time that superconductors were more than just perfect conductors and provided a uniquely defining property of the superconductor state. The ability for the expulsion effect is determined by the nature of equilibrium formed by the neutralization within the unit cell of a superconductor.

Superconductors in the Meissner state exhibit perfect diamagnetism, or superdiamagnetism, meaning that the total magnetic field is very close to zero deep inside them (many penetration depths from the surface). This means that their magnetic susceptibility = −1. Diamagnetics are defined by the generation of a spontaneous magnetisation of a material which directly opposes the direction of an applied field. However, the fundamental origins of diamagnetism in superconductors and normal materials are very different. In normal materials diamagnetism arises as a direct result of the orbital spin of electrons about the nuclei of an atom induced electromagnetically by the application of an applied field. In superconductors the illusion of perfect diamagnetism arises from persistent screening currents which flow to oppose the applied field (the Meissner effect); not solely the orbital spin.

Diamagnetism is only a repulsive force. Electrons orbiting the atom experience a force in a magnetic field, but this field is opposed by the force.

If all the electrons are paired up there is no net magnetic moment in the material, and the material is diamagnetic.

According to the Pauli Exclusion Principle which states that no two electrons may occupy the same quantum state at the same time, the electron spins are oriented in opposite directions. This causes the magnetic fields of the electrons to cancel out; thus, there is no net magnetic moment, and the atom cannot be attracted into a magnetic field. In fact, diamagnetic substances are weakly repelled by a magnetic field.

Ferromagnetic and paramagnetic materials also have diamagnetism, but this is overwhelmed by the normal magnetic effect. Diamagnetism should be present in all materials,

5) http://www.tyndallscientific.com/authors-2/norman-mcmillan/

http://www.rjtechne.org/tyndall/philosop.htm

6) Are there any discoveries that are languishing in the historical records waiting for someone to pick up and explore further?

Nothing significant at the moment. There may be more diamagnetism information out there.

Tyndall’s work on sound hasn’t really be followed up – sound is partially reflected by different densities of air.

Tyndall examined lots of materials – optical axes of crystals and 33 types of wood. Perhaps he missed something.

William Bragg wrote a paper on Tyndall’s work – this is an area that could be re-visited.

7) In Professor Hurley’s demonstration of light travelling in a water stream, why did the water only come out when the bottle lid was opened?

https://www.metrofamilymagazine.com/simple-science-experiment-drip-drop-bottle/#:~:text=When%20you%20cover%20up%20the,it%20keeps%20the%20water%20in!

https://www.scientificamerican.com/article/holes-that-do-not-leak/

When the lid is on the bottle, the water is pulling down but the air up in the top of the bottle is becoming a vacuum. That means “low pressure.” The air pressure outside the bottle is higher, so it actually tries to push into the bottle through the bottom hole. In doing so, it keeps the water in!

8) The poetry of John Tyndall

https://www.uclpress.co.uk/products/168206

https://www.amazon.co.uk/Ascent-John-Tyndall-Mountaineer-Intellectual-ebook/dp/B077TSN5NH/ref=sr_1_1?crid=11AT3ASVZ8YA8&dchild=1&keywords=john+tyndall&qid=1604309088&sprefix=john+tyndall%2Caps%2C151&sr=8-1

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Rising from a humble background in rural southern Ireland, John Tyndall became one of the foremost physicists, communicators of science, and polemicists in mid-Victorian Britain. In science, he is known for his important work in meteorology, climate science, magnetism, acoustics, and bacteriology. His discoveries include the physical basis of the warming of the Earth’s atmosphere (the basis of the greenhouse effect), and establishing why the sky is blue. But he was also a leading communicator of science, drawing great crowds to his lectures at the Royal Institution, while also playing an active role in the Royal Society. Tyndall moved in the highest social and intellectual circles. A friend of Tennyson and Carlyle, as well as Michael Faraday and Thomas Huxley, Tyndall was one of the most visible advocates of a scientific world view as tensions grew between developing scientific knowledge and theology. He was an active and often controversial commentator, through letters, essays, speeches, and debates, on the scientific, political, and social issues of the day, with strongly stated views on Ireland, religion, race, and the role of women. Widely read in America, his lecture tour there in 1872-73 was a great success. Roland Jackson paints a picture of an individual at the heart of Victorian science and society. He also describes Tyndall’s importance as a pioneering mountaineer in what has become known as the Golden Age of Alpinism. Among other feats, Tyndall was the first to traverse the Matterhorn. He presents Tyndall as a complex personality, full of contrasts, with his intense sense of duty, his deep love of poetry, his generosity to friends and his combativeness, his persistent ill-health alongside great physical stamina driving him to his mountaineering feats. Drawing on Tyndall’s letters and journals for this first major biography of Tyndall since 1945, Jackson explores the legacy of a man who aroused strong opinions, strong loyalties, and strong enmities throughout his life.

Biography

Roland Jackson is a historian of science, with interests also in contemporary science and innovation policy, and in bioethics. His recent posts include: Head of the Science Museum, London; Chief Executive of the British Science Association; and Executive Chair of Sciencewise. He is a General Editor of The Correspondence of John Tyndall, being published in 19 volumes by the University of Pittsburgh Press.

His new book – The Ascent of John Tyndall – is the first substantive biography of this remarkable Victorian scientist, mountaineer, and public intellectual since 1945.

Review

Mr. Jackson amasses a wealth of detail to give a fuller picture of this extraordinary man… [He] has done a great service in his detailed and careful presentation of John Tyndall’s life at a time when science is under attack, neglected and misunderstood, especially by those in government. (Peter Pesic, Wall Street Journal)
It was not until 1945, more than half a century after his death, that a semi-authorised biography of Tyndall was published. Now Jackson has authoritatively redressed this injustice. (Jules Stewart, Geographical)
This story reveals much about Tyndall … [this biography] is immensely long and devotedly successful at unearthing the facts of Tyndall’s life… (Jonathan Parry, London Review of Books)
Roland Jackson has done a thorough job… it is certainly the best biography of Tyndall. (John Gribbin, Literary Review)
Splendid monument of a biography. (Barbara Kiser, Nature)
The book is well written, at times witty, at other times entirely engrossing. But its major strength is the close, first-hand knowledge of all of Tyndall’s writings. Jackson knows Tyndall’s primary sources better than anyone and that is why this biography is so satisfying. Jackson is close to his subject, fully grasps the science, has followed Tyndall’s paths across the Alps, and has managed to write about it in a smooth, engaging style. (Michael Reidy, Metascience)
In Jackson’s hands, Tyndall becomes the perfect lens through which to analyse the questions and controversies we are still dealing with today: the role of the humanities and sciences both in broader culture and in our education systems; the role of gases in global warming; and the increasingly close ties between science, industry, and government. (Michael Reidy, Metascience)
One of the most important mountaineering biographies to have been published in recent years… Roland Jackson’s biography of John Tyndall is not only a tour de force of scholarship, its also an eminently readable book… It’s a magnificent piece of work and a must-read for every scholar of Alpine history. (Alex Roddie, The Great Outdoors)
Excellent biography… The Ascent of John Tyndall is a long-overdue, magnificent tribute to an important, but largely under-appreciated scientist. Highly recommended. (Richard Carter, Friends of Darwin)
Roland Jackson paints a picture of an individual at the heart of Victorian science and society. (Playing Pasts)

About the Author

Roland Jackson is a historian of science, with interests also in contemporary science and innovation policy, and in bioethics. His recent posts include: Head of the Science Museum, London; Chief Executive of the British Science Association; and Executive Chair of Sciencewise. He is a General Editor of The Correspondence of John Tyndall, being published in 19 volumes by the University of Pittsburgh Press.

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