Newton and Galileo

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Later in the 1670’s, Newton became very interested in theology. He studied Hebrew scholarship and ancient and modern theologians at great length, and became convinced that Christianity had departed from the original teachings of Christ. He felt unable to accept the current beliefs of the Church of England, which was unfortunate because he was required as a Fellow of Trinity College to take holy orders.

Happily, the Church of England was more flexible than Galileo had found the Catholic Church in these matters, and King Charles II issued a royal decree excusing Newton from the necessity of taking holy orders! Actually, to prevent this being a wide precedent, the decree specified that, in perpetuity, the Lucasian professor need not take holy orders. (The current Lucasian professor is Stephen Hawking.)



Anomaly and the Emergence of Scientific Discoveries

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Clearly we need a new vocabulary and concepts for analyzing events like the discovery of oxygen. Though undoubtedly correct, the sentence, “Oxygen was discovered,” misleads by suggesting that discovering something is a single simple act assimilable to our usual (and also questionable) concept of seeing. That is why we so readily assume that discovering, like seeing or touching, should be unequivocally attributable to an individual and to a moment in time. But the latter attribution is always impossible, and the former often is as well.

What Lavoisier announced in his papers from 1777 on was not so much the discovery of oxygen as the oxygen theory of combustion. That theory was the keystone for a reformulation of chemistry so vast that it is usually called the chemical revolution.


  2. Next


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Though almost non-existent during periods of normal science, they recur regularly just before and during
scientific revolutions, the periods when paradigms are first under attack
and then subject to change. The transition from Newtonian to quantum
mechanics evoked many debates about both the nature and the
standards of physics, some of which still continue.4 There are people
alive today who can remember the similar arguments engendered by
Maxwell’s electromagnetic theory and by statistical mechanics.5 And
earlier still, the assimilation of Galileo’s and Newton’s mechanics gave
rise to a particularly famous series of debates with Aristotelians,
Cartesians, and Leibnizians about the standards legitimate to science.

Consider, for a single example, the quite large and diverse community
constituted by all physical scientists. Each member of that group today
is taught the laws of, say, quantum mechanics, and most of them employ
these laws at some point in their research or teaching. But they do not all learn the same
applications of these laws, and they are not therefore all affected in the
same ways by changes in quantum-mechanical practice. On the road to
professional specialization, a few physical scientists encounter only the
basic principles of quantum mechanics. Others study in detail the
paradigm applications of these principles to chemistry, still others to the
physics of the solid state, and so on. What quantum mechanics means to
each of them depends upon what courses he has had, what texts he has
read, and which journals he studies. It follows that, though a change in
quantum-mechanical law will be revolutionary for all of these groups, a
change that reflects only on one or another of the paradigm applications
of quantum mechanics need be revolutionary only for the members of a
particular professional subspecialty. For the rest of the profession and
for those who practice other physical sciences, that change need not be
revolutionary at all. In short, though quantum mechanics (or
Newtonian dynamics, or electromagnetic theory) is a paradigm for
many scientific groups, it is not the same paradigm for them all.
Therefore, it can simultaneously determine several traditions of normal
science that overlap without being coextensive. A revolution produced
within one of these traditions will not necessarily extend to the others as


The Structure of Scientific Revolutions by T. S. Kuhn

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Postscript-1969 ………………………………………… 174

I. Introduction: A Role for History

… the textbooks from which each new scientific generation learns to practice its trade. Inevitably, however, the aim of such books is persuasive and pedagogic; a concept of science drawn from them is no more likely to fit the enterprise that produced them than an image of a national culture drawn from a tourist brochure or a language text. This essay attempts to show that we have been misled by them in fundamental ways.

Concerned with scientific development, the historian then appears to have two main tasks. On the one hand, he must determine by what man and at what point in time each contemporary scientific fact, law, and theory was discovered or invented.

Rather than seeking the permanent contributions of an older science to our present vantage, they attempt to display the historical integrity of that science in its own time. They ask, for example, not about the relation of Galileo’s views to those of modern science, but rather about the relationship between his views and those of his group, i.e., his teachers, contemporaries, and immediate successors in the sciences.

We shall note, for example, in Section II that the early developmental stages of most sciences have been characterized by continual competition between a number of distinct views of nature, each partially derived from, and all roughly compatible with, the dictates of scientific observation and method. [P 4]

The most obvious examples of scientific revolutions are those …  major turning points in scientific development associated with the names of Copernicus, Newton, Lavoisier, and Einstein. More clearly than most other episodes in the history of at least the physical sciences, these display what all scientific revolutions are about. [P6]

Each of them necessitated the community’s rejection of one time-honored scientific theory in favor of another incompatible with it. Each produced a consequent shift in the problems available for scientific scrutiny and in the standards by which the profession determined what should count as an admissible problem or as a legitimate problem-solution. And each transformed the scientific imagination in ways that we shall ultimately need to describe as a transformation of the world within which scientific work was done. Such changes, together with the controversies that almost always accompany them, are the defining characteristics of scientific revolutions. [P6]

That is why a new theory, however special its range of application, is seldom or never just an increment to what is already known. Its assimilation requires the reconstruction of prior theory and the re-evaluation of prior fact, an intrinsically revolutionary process that is seldom completed by a single man and never overnight. [P7]

II. The Route to Normal Science [P10]
In this essay, ‘normal science’ means research firmly based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice. Today such achievements are recounted, though seldom in their original form, by science textbooks, elementary and advanced. These textbooks expound the body of accepted theory, illustrate many or all of its successful applications, and compare these applications with exemplary observations and experiments. Before such books became popular early in the nineteenth century (and until even more recently in the newly matured sciences), many of the famous classics of science fulfilled a similar function. Aristotle’s Physica, Ptolemy’s Almagest, Newton’s Principia and Opticks, Franklin’s Electricity, Lavoisier’s Chemistry, and Lyell’s Geology—these and many other works served for a time implicitly to define the legitimate problems and methods of a research field for succeeding generations of practitioners.

No period between remote antiquity and the end of the seventeenth century exhibited a single generally accepted view about the nature of light. Instead there were a number of competing schools and sub-schools, most of them espousing one variant or another of Epicurean, Aristotelian, or Platonic theory. [P12]

At various times all these schools made significant contributions to the body of concepts, phenomena, and techniques from which Newton drew the first nearly uniformly accepted paradigm for physical optics. Anyone examining a survey of physical optics before Newton may well conclude that, though the field’s practitioners were scientists, the net result of their activity was something less than science. [P13]

The history of electrical research in the first half of the eighteenth century provides a more concrete and better known example of the way a science develops before it acquires its first universally received paradigm. [P13]

The Natural History by Pliny The Elder, 70 AD [P16]


Aristotle 384 – 322BC, Stagira, Greece Motion
Archimedes 287-212 BC, Syracuse, Sicily Statics
Robert Boyle 1627-91 Ireland Chemistry
James Hutton 1726-97, Scotland Geology
Joseph Black 1728-99  Bordeaux, France Study of heat
Francis Bacon 1561-1626, England father of empiricism
Pliny The Elder 70AD The Natural History


.. in the early stages of the development of any science different men confronting the same range of phenomena, but not usually all the same particular phenomena, describe and interpret them in different ways. What is surprising, and perhaps also unique in
its degree to the fields we call science, is that such initial divergences
should ever largely disappear.  P17

The Physics

Prior to the Renaissance, the most significant works in mechanics were those written in the Fourth Century BCE by the Greek philosopher Aristotle of Stagira (384–322 BCE) — these were Mechanics, On the Heavens, and The Nature or in Greek Μηχανικά (Mekhanika), Περί Ουρανού (Peri Uranu), and Φυσική Ακρόασις (Fysike Akroasis). Although the first section of every general physics textbook is about mechanics, Aristotle’s Mechanics probably wasn’t written by him and won’t be discussed here. On the Heavens will be discussed later in this book.

The Nature is Aristotle’s work that’s most relevant to this book. That’s because it’s the origin of the word physics. The full name Φυσική Ακρόασις (Fysike Akroasis) translates literally to “Lesson on Nature” but “The Lesson on the Nature of Things” is probably more faithful. The Nature acquired great stature in the Western world and was identified almost reverently by academics as Τὰ Φυσικά (Ta Fysika) — The Physics. In this book Aristotle introduced the concepts of space, time, and motion as elements in a larger philosophy of the natural world. Consequently, a person who studied the nature of things was called a “natural philosopher” or “physicist” and the subject they studied was called “natural philosophy” or “physics”. Incidentally, this is also the origin of the words “physician” (one who studies the nature of the human body) and “physique” (the nature or state of the human body).


  1. Aristotelian Physics
  2. Almagest   by Claudius Ptolemy

  3. Newton’s Principia for the Common Reader by Subrahmanijan Chandrasekhar

  4. OPTICKS by Sir Issac Newton
  5. Electrical
    1. Electricity by Ben Franklin
    2. Corpuscularianism

    3.  Electrical conduction.  By Stephen Gray
  6. The Natural History by Pliny the Elder, 70AD
  7. Baconian Method and  A System of Logic by John Stuart Mill

The Scientific Revolution 1700 – 1800

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Advances in science have been termed “revolutions” since the 18th century. In 1747, Clairaut wrote that “Newton was said in his own lifetime to have created a revolution.” A new view of nature emerged, replacing the Greek view that had dominated science for almost 2,000 years.

Greek view was based on faith. It was not based on “Reason” – the new lifeblood of science. Faith replacing “Reason?” What is that?

Take a look at the following in keeping with the Ptolemaic system:

There is talk of a new astrologer who wants to prove that the earth moves and goes around instead of the sky, the sun, the moon, just as if somebody were moving in a carriage or ship might hold that he was sitting still and at rest while the earth and the trees walked and moved. But that is how things are nowadays: when a man wishes to be clever he must . . . invent something special, and the way he does it must needs be the best! The fool wants to turn the whole art of astronomy upside-down. However, as Holy Scripture tells us, so did Joshua bid the sun to stand still and not the earth.”  – Martin Luther, 1539 

The “new astrologer” Martin Luther is referring to is Copernicus.   Martin Luther made negative comments about Copernicus because the idea of the heliocentric universe seemed to contradict the Bible. The new science moved forward with “Reason” plus “Scientific observation.”

The transition from ancient superstition and dogma of the 15th century to Newton’s laws marked the start of the scientific age.

  1. The Renaissance
    1. Humanists placed low value on science
      1. More interested in classical antiquity and the authority of the ancients
    2. Arabic translations of Greek classics
    3. Rediscovery of Ptolemy and Archimedes
    4. The universe as machine
    5. Developing collaboration between artisans and intellectuals
    6. Building machines for practical use
    7. The laws of perspective and optics
    8. Alchemy and astrology
    9. Voyages of discovery
      1. Travelers’ accounts of foreign lands
      2. Attacking the authority of the ancients


Ptolemaic system with the Earth as the center of the universe.

Religious Opposition

Ptolemy’s model was accepted as Church doctrine.
Heliocentrism was nothing less than heresy:
-Giordano Bruno was burned at the stake in 1600 for his heliocentric views.
-Galileo was forced to recant and placed under house arrest.
-Many others picked their words carefully to avoid a similar fate
-It was only around the time of Newton that it became safe (even respectable) to express    such heretical views.

When we talk about science there are four words we use more often than any others — facts, theories, hypotheses, evidence. But none of these words exist in their modern sense before the Scientific Revolution. This new vocabulary means that something we can recognize as modern science doesn’t exist until the age of Newton. Scientific results must be subjected to scrutiny and be open to refutation. Science does not just require certain ways of gathering and processing information; it requires a critical community which subjects results to scrutiny and a collaborative community which seeks to carry forward the work of others.

  1. The Copernican Revolution

    1. Medieval science
      1. Authority of the ancients: Aristotle and Ptolemy
        1. Heavenly bodies orbit in a hierarchy of spheres
        2. Heavens and earth composed of different matter
        3. The “quintessence” (the ether)
        4. Earth, air, fire, and water
        5. The “prime mover”
    2. Late Middle Ages developments
      1. Ptolemaic system did not conform to observations
      2. Retrograde motion
      3. Roman calendar out of alignment with movement of heavenly bodies
        1. The “problem” of Easter and other holy days
    3. Nicolaus Copernicus (1473-1543)
      1. Renaissance Man
      2. Ptolemaic system had become too messy
      3. Copernican system
        1. The earth moved and was not the center of the planetary system
        2. The earth rotated on its axis and orbited the sun
      4. Believed he had restored a pure understanding of God’s plan but was troubled by its implications
      5. New problems and inconsistencies
      6. On the Revolutions of the Heavenly Spheres (1543)

Nicolai Copernicito Torinensis De Revolutionibus Orbium Coelestium, Libri VI (title page of 2nd edition, Basel, 1566)

Although the medieval model of the universe persisted throughout the Renaissance, a new theory about the shape of the universe arose around 1512, when Polish astronomer Nicholaus Copernicus (1473–1543) wrote De Revolutionibus Orbium Coelestium (Revolution of the Heavenly Spheres), explaining his heliocentric theory. This theory held that the Earth, along with the other planets, rotated around the sun. Copernicus had arrived at this theory using mathematics and observation of the stars and planets. Though he was convinced of his findings, he was reluctant to publicize his ideas, since they contradicted the teachings of the church. According to church leaders the Earth was the center of the universe because the humans who lived there were the constant focus of God’s divine rule. Copernicus waited more than thirty years to have his work published, but many European astronomers knew of his theories and some continued his work.It is traditionally assumed to start with the Copernican Revolution (initiated in 1543) and to be complete in the “grand synthesis” of Isaac Newton’s 1687 Principia. The first scientific society to be established was the Royal Society of England. The major features of Copernican theory are:

  1. The center of the universe is near the Sun.
  2. Around the Sun, in order, are Mercury, Venus, Earth and Moon, Mars, Jupiter, Saturn, and the fixed stars.
  3. The Earth has three motions: daily rotation, annual revolution, and annual tilting of its axis.

Pump problem (three views)

 Center: Italian physicist Galileo Galilei’s circa 1630-1646 experiment for testing the “force of the vacuum”. Right: The 1641 siphon experiment, done by Gasparo Berti, created by means of an 11 meter high column of water. Demo in Rome, for an invited audience which included Raffaelo Magiotti, Athanasius Kircher, and Nicolo Zucchi.


Galileo’s Dialogue concerning the Two Chief World Systems (1632), which argues for the superiority of the heliocentric Copernican over the geocentric Ptolemaic system, is a classic straw man argument. By 1632, astronomers had all but abandoned the Ptolemaic system, which had become untenable in the light of the evidence from telescopes for more than 20 years, which showed, for example, that Mercury and Venus orbited the sun. Refracting telescopes first appeared in the Netherlands in 1608. Galileo was one of the first scientists to use this new tool for his astronomical observations in 1609.

The Catholic church sanctioned the First Edition of Galileo’s complete works in the 18th century (Roman Inquisition above), considering “the affair” closed. However, Pope John Paul II issued an official church investigation into Galileo’s claims in 1979 and published an official papal pardon for Galileo in 1992. As shown in the figure above, the chapter on Heliocentrism ended in 1992.

Galileo never realised that he had seen the rings of Saturn, but he certainly did see what we now call the rings of Saturn.

Pre-Newton Era


(4) Issac Newton: Law of Gravity

Copernicus never uses the word “system” — or rather its equivalent in Latin. After Galileo’s book on the two chief world systems it becomes commonplace to refer to the Ptolemaic, Tychonic, and Copernican systems — the word system here, as in Galileo, just means “model” or “theory” or even “diagram”. The real world is not a system because systems are always things you find in books, and to refer to one of these systems you use the name of the author of the book in which it first appears — just as we say “Einstein’s theory” they write “the Copernican system”.

All this changes with Newton’s theory of gravity. For the first time people start writing about “the solar system”. In other words the real world has now acquired the characteristics of a system. What are the characteristics of a system? It is something where the different parts are connected together. What connects together the different parts of the solar system is gravity, and a change in any of the parameters of one body — its mass, its speed, its direction — has an effect on all the others. No previous intellectual system had been interactive in this way, and no one had previously claimed that the real world consisted of feedback systems of this sort.

Kepler it is true had imagined that the sun might emit some sort of force driving the planets, but he had not claimed that the planets reciprocally affected the sun or each other — his was a physical astronomy, not merely a mathematical astronomy, but his was not a system in this new sense. The term the solar system thus encapsulates an intellectual revolution, and one that isn’t just important in physics — it provides the crucial model for the development of economics as a theory of interactions in what we now call the economy — Quesnay, the first to produce such an account insisted that he took his inspiration from Newton.

In 1727 (84 ME),  Isaac Newton, at the time of his death (reaction end), had amassed all the world’s knowledge into a large collected works set, estimates of which, still not yet finalized (Ѻ), indicate 40-volumes±, including: 25-volume set of correspondence, 8-volume plus set of mathematical papers, 3-volume plus set of optics, one volume plus on Philosophical Questions, and untold volumes on alchemical pursuits and religious ventures; the apex of which being his Principia (1686) and Optics (1718), the latter of which, via Query 31, launched the chemical revolution.


(5) William Harvey: Circulation of Blood

Further groundbreaking work was carried out by William Harvey, who published De Motu Cordis in 1628. Harvey made a detailed analysis of the overall structure of the heart, going on to an analysis of the arteries, showing how their pulsation depends upon the contraction of the left ventricle, while the contraction of the right ventricle propels its charge of blood into the pulmonary artery. He noticed that the two ventricles move together almost simultaneously and not independently like had been thought previously by his predecessors.


A line that connects a planet to the sun sweeps out equal areas in equal times.

This is one of Kepler’s laws.This empirical law discovered by Kepler arises from conservation of angular momentum. When the planet is closer to the sun, it moves faster, sweeping through a longer path in a given time.

Renaissance Medicine
Since the days of Aristotle science had been based on the belief that all of the Earth’s matter was made up of four elements: earth, water, air, and fire. Human beings were thought to be microcosms, or little worlds, that were smaller versions of the macrocosm, or the world at large. Thus the four elements of the world were thought to correspond to four humors, or body fluids, in humans. These fluids, which were associated with human characteristics, were believed to exist in a state of balance within the body. The four humors had the following corresponding elements and traits:

Blood corresponded to the element of fire and was associated with a cheerful character. Phlegm (mucus) corresponded to earth and was associated with a slow, unexcitable nature. Black bile (digestive juices) corresponded with water and was associated with sadness and depression.

Yellow bile corresponded to air and was associated with anger and bad temper. Renaissance philosophy held that imbalance in the body’s humors resulted in disease. Thus treatments for disease were usually attempts to restore balance by draining off an excess of one of the humors. Elizabethan doctors frequently practiced bloodletting—cutting open a vein to let the blood flow—to cure fevers, infections, and diseases. Sometimes they placed leeches (blood-sucking worms) on prescribed parts of the body to suck out blood. In other cases they induced vomiting. According to modern medicine most of these remedies were harmful, or at least not helpful, to the patient.

In the early Renaissance, some scholars began to study the human body through dissection, cutting the body open in order to examine the organs, and systematic observation. The pioneers of the new science of anatomy were Leonardo da Vinci, whose fascination in the workings of the human body led to masterful sketches of its internal structures, and Belgian anatomist and physician Andreas Vesalius (1514–1564). In 1543 Vesalius wrote a seven-volume text on the structure of the human body illustrated with engravings based on his own drawings. Vesalius rejected the medical theories that had been passed down from the ancient Greeks and Romans. He believed that the only reliable source of information on human anatomy was the close observation of a dissected human corpse. He showed the human body to be composed of internal organs that function together, and his descriptions and drawings were the most accurate study of anatomy ever undertaken up to that time.

Albert Einstein


Einstein had a new idea about gravity. He thought that gravity is what happens when space itself is curved or warped around a mass, such as a star or a planet. Thus, a star or planet would cause kind of a dip in space so that any other object that came too near would tend to fall into the dip.

This 2-D animation gives an idea of how gravity works in 3-D.

For example, if gravity is a force that causes all matter to be attracted to all other matter, why are atoms mostly empty space inside? (There is really hardly any actual matter in an atom as seen above!) How are the forces that hold atoms together different from gravity? Is it possible that all the forces we see at work in nature are really different sides of the same basic force or structure?

Discovery Of Vacuum

Torricelli mercury column (1644)

A 1644 rendition of experiments of Torricelli on making a vacuum by means of a mercury column, Florence.

Torricelli used a glass tube about 1 m in length, and filled it with mercury. He sealed the open end of the tube with a fingertip and then flipped the sealed end of the tube facing downwards. He then submerged the tube in a mercury reservoir and removed his finger, allowing the mercury inside the tube to be in contact with the reservoir. The column of mercury in the tube sank to 76 cm, measured from the liquid surface of the reservoir. The space left in the glass tube above the mercury was in fact a vacuum.

The experiment demonstrated that the space left above the mercury after turning the tube upside down was in fact a vacuum: the mercury level was independent of the volume above, and it could be filled completely with water admitted from below. This experiment was the first successful attempt to produce vacuum and subsequently convinced the scientific community.

Foundations Of Atomic Theory


John Dalton 1803: He discovered Electron and won a Nobel prize for this.
J J Thomson In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles, which he calculated must have bodies much smaller than atoms and a very large value for their charge-to-mass ratio. J.J. Thomson, a British scientist, discovers the electron, leading to his “plum-pudding” model.
1904 Hantaro Nagaoka, a Japanese physicist, suggests that an atom has a central nucleus. Electrons move in orbits like the rings around Saturn.
1911 New Zealander Ernest Rutherford states that an atom has a dense, positively charged nucleus. He called them Protons. Electrons move randomly in the space around the nucleus.
Niels Bohr 1913 In Niels Bohr’s model, the electrons move in spherical orbits at fixed distances from the nucleus.
Louis de Broglie 1924 Frenchman Louis de Broglie proposes that moving particles like electrons have some properties of waves. Within a few years evidence is collected to support his idea.
Erwin Schrödinger

1926 Erwin Schrödinger develops mathematical equations to describe the motion of electrons in atoms. His work leads to the electron cloud model (Shown above).

James Chadwick

1932 James Chadwick, a British physicist and Student of Rutherford, discovered neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.

1900 Max Planck suggests that radiation is quantized (it comes in discrete amounts.)
1905 Albert Einstein, one of the few scientists to take Planck’s ideas seriously, proposes a quantum of light (the photon) which behaves like a particle. Einstein’s other theories explained the equivalence of mass and energy, the particle-wave duality of photons, the equivalence principle, and special relativity.
1909 Hans Geiger and Ernest Marsden, under the supervision of Ernest Rutherford, scatter alpha particles off a gold foil and observe large angles of scattering, suggesting that atoms have a small, dense, positively charged nucleus.
1911 Ernest Rutherford infers the nucleus as the result of the alpha-scattering experiment performed by Hans Geiger and Ernest Marsden.
1912 Albert Einstein explains the curvature of space-time.
1913 Niels Bohr succeeds in constructing a theory of atomic structure based on quantum ideas.
1919 Ernest Rutherford finds the first evidence for a proton.
1921 James Chadwick and E.S. Bieler conclude that some strong force holds the nucleus together.
1923 Arthur Compton discovers the quantum (particle) nature of x rays, thus confirming photons as particles.
1924 Louis de Broglie proposes that matter has wave properties.
1925 (Jan) Wolfgang Pauli formulates the exclusion principle for electrons in an atom.
1925 (April) Walther Bothe and Hans Geiger demonstrate that energy and mass are conserved in atomic processes.
1926 Erwin Schroedinger develops wave mechanics, which describes the behavior of quantum systems for bosons. Max Born gives a probability interpretation of quantum mechanics. G.N. Lewis proposes the name “photon” for a light quantum.
1927 Certain materials had been observed to emit electrons (beta decay). Since both the atom and the nucleus have discrete energy levels, it is hard to see how electrons produced in transition could have a continuous spectrum (see 1930 for an answer.)
1927 Werner Heisenberg formulates the uncertainty principle: the more you know about a particle’s energy, the less you know about the time of the energy (and vice versa.) The same uncertainty applies to momenta and coordinates.
1928 Paul Dirac combines quantum mechanics and special relativity to describe the electron.
1930 Quantum mechanics and special relativity are well established. There are just three fundamental particles: protons, electrons, and photons. Max Born, after learning of the Dirac equation, said, “Physics as we know it will be over in six months.”
1930 Wolfgang Pauli suggests the neutrino to explain the continuous electron spectrum for beta decay.
1931 Paul Dirac realizes that the positively-charged particles required by his equation are new objects (he calls them “positrons”). They are exactly like electrons, but positively charged. This is the first example of antiparticles.
1931 James Chadwick discovers the neutron. The mechanisms of nuclear binding and decay become primary problems.
1933-34 Enrico Fermi puts forth a theory of beta decay that introduces the weak interaction. This is the first theory to explicitly use neutrinos and particle flavor changes.


J J Thompson (1897)

advisors John Strutt (Rayleigh)
Edward John Routh

Notable students
Charles Glover Barkla
Charles T. R. Wilson –>
Ernest Rutherford –>
Francis William Aston –>
John Townsend
J. Robert Oppenheimer
Owen Richardson –>
William Henry Bragg –>
H. Stanley Allen
John Zeleny
Daniel Frost Comstock
Max Born –>
T. H. Laby
Paul Langevin
Balthasar van der Pol
Geoffrey Ingram Taylor
Niels Bohr —>
George Paget Thomson  –>

Ernest Rutherford



  1. Rutherford at McGill University in 1905
  2. Schematic of Rutherford’s apparatus

James Chadwick

Chadwick’s neutron detector; replica Science Museum 1932


In 1920, Ernest Rutherford postulated that there were neutral, massive particles in the nucleus of atoms. This conclusion arose from the disparity between an element’s atomic number (protons = electrons) and its atomic mass (usually in excess of the mass of the known protons present). James Chadwick was assigned the task of tracking down evidence of Rutherford’s tightly bound “proton-electron pair” or neutron.

This is Chadwick’s equation:

Chadwick’s Atomic Model


  1. Scientific Revolution By Boyd
    “Reason” plus “Scientific observation”
    Formulation of “Scientific Method”
    Expansion of Scientific Knowledge
    Five theories by
    (1) Nicolous Copernicus: Heliocentric Theory
    (2) Johannes Kepler: Planetory Motion is elliptical around the sun
    (3) Galileo: Invents telescope to look into the planetary system
    (4) Issac Newton: Law of Gravity
    (5) William Harvey: Circulation of Blood
  4. Book: Philosophers Of Science 
  5. Pictures of Experimental Set-Ups 



  1. Galileo
  2. Walkling in Galileo’s Childhood Neighborhood


  1. A visit to Newton’s birthplace – Woolsthorpe Manor  By Greycoat’s Teapot


  1. Einstein’s Gravity By NASA

Foundations Of Atomic Theory

  1. Atomic Structure: Discovery of the Neutron By Tyler DeWitt
  2. Youtube: 6.1 How protons, electrons and neutrons were discovered. Ian Stuart
  3. Discovery of the Neutron (James Chadwick – 1932) Moof University

Electro-Magnetic Induction

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Michael Faraday discovered was a way of producing an electrical current in a circuit by not using batteries.

electromagnetic induction

He placed a magnet ( a bar) inside a hollow core with wire wound around it as shown above. He then attached a galvanometer with the two ends of the wire. Then by moving the magnet quickly out and in of the core, he saw deflection in the Galvanometer. When the magnet moved into the core, the current flowed in one direction.

When the magnet stops moving and is held stationary with regards to the coil the needle of the galvanometer returned back to zero as there was no physical movement of the magnetic field.

When the magnet moved out, the current moved in another direction. This is how AC current was produced without the use of a battery.

The faster the movement of the magnetic field, the greater will be the induced emf or voltage in the coil, so for Faraday’s law to hold true there must be “relative motion” or movement between the coil and the magnetic field and either the magnetic field, the coil or both can move.

Faraday’s Law of Induction
From the above description we can say that a relationship exists between an electrical voltage and a changing magnetic field to which Michael Faraday’s famous law of electromagnetic induction states: “that a voltage is induced in a circuit whenever relative motion exists between a conductor and a magnetic field and that the magnitude of this voltage is proportional to the rate of change of the flux”.

In other words, Electromagnetic Induction is the process of using magnetic fields to produce voltage, and in a closed circuit, a current.

air cored electromagnetic coil

Inductance (Lenzes Law)
Currents bound inside the atoms of strong magnets can create counter-rotating currents in a copper or aluminum pipe. This is shown by dropping the magnet through the pipe. The descent of the magnet inside the pipe is observably slower than when dropped outside the pipe [7].

Inductors are widely used in alternating current (AC) electronic equipment, particularly in radio equipment. They are used to block AC while allowing DC to pass; inductors designed for this purpose are called chokes. They are also used in electronic filters to separate signals of different frequencies, and in combination with capacitors to make tuned circuits, used to tune radio and TV receivers.

1. Magnetism

magnetic molecules

lines of magnetic force
Magnets can be found in a natural state in the form of a magnetic ore, with the two main types being Magnetite also called “iron oxide”, ( FE3O4 ) and Lodestone, also called “leading stone”. If these two natural magnets are suspended from a piece of string, they will take up a position in-line with the Earth’s magnetic field always pointing north.


magnetic field around conductor


Carl_Friedrich_Gauss 1777-1855
Wilhelm Weber
Gustav Kirchhoff 1824-1887
Georg Ohm
James Clerk Maxwell 1831-1879
Nikola Tesla

7. Lenzes Law Demo By MIT
12. Wilhelm Weber’s Theory on Magnetism

Alessandro Volta

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Volta demonstrates his battery to Napoleon Bonoparte
Volta demonstrates his battery to Napoleon Bonoparte in 1801.


Napoleon was very impressed by Volta’s work, giving him the aristocratic title of Count.

In 1804, Volta wanted to retire. But his sincere admirer, Napoleon, simply refused to permit Italy’s greatest scientist to retire. The French leader insisted that Volta maintain a connection with the University even if it consisted of only one lecture per year.

In 1819, at the age of 74, Volta decided it was time to hang up his capacitors, his voltaic piles, his electrophorus, and his administrative work at the university. He retired to a country house close to his home town of Como, where he could spend more time with his wife, Maria Teresa. They had three sons, Zanino, Faminio and Luigi.

At this time the only source of electric current was the galvanic or voltaic cell that Volta had invented in 1798. In Europe, Volta’s simple arrangement of two metal squares, one copper and the other zinc, in a jar of weak acid called electrolytes, had been greatly improved early in the century. Scientists abroad were using batteries consisting of dozens of plates set into the gutta-percha-lines containers, and these supplied more current at a high voltage. But Joseph Henry working alone in Albany in 1828. All through August Joseph Henry kept working on his electromagnets. From his labors was born a spool or bobbin electromagnet, later to be employed in the bell, telegraph, telephone and other electrical devices. 

As a famous scientist and director of the Smithsonian Institution, Henry received visits from other scientists and inventors who sought his advice. Henry was patient, kindly, self-controlled, and gently humorous.[13] One such visitor was Alexander Graham Bell, who on 1 March 1875 carried a letter of introduction to Henry. Henry showed an interest in seeing Bell’s experimental apparatus, and Bell returned the following day. After the demonstration, Bell mentioned his untested theory on how to transmit human speech electrically by means of a “harp apparatus” which would have several steel reeds tuned to different frequencies to cover the voice spectrum. Henry said Bell had “the germ of a great invention”. Henry advised Bell not to publish his ideas until he had perfected the invention. When Bell objected that he lacked the necessary knowledge, Henry firmly advised: “Get it!”

On 25 June 1876, Bell’s experimental telephone (using a different design) was demonstrated at the Centennial Exhibition in Philadelphia where Henry was one of the judges for electrical exhibits. On 13 January 1877, Bell demonstrated his instruments to Henry at the Smithsonian Institution and Henry invited Bell to demonstrate them again that night at the Washington Philosophical Society. Henry praised “the value and astonishing character of Mr. Bell’s discovery and invention.”

Alessandro Volta 1745- 1827 Italy
Michael Faraday Born: September 22, 1791 Died: August 25, 1867, United Kingdom
James Clerk Maxwell (1831–1879)
Humphry Davy 1778-  1829
Heinrich Hertz 1857 – 1894
Joseph Henry 1797 – 1878
Samuel Morse 1791 – 1872
André-Marie Ampère 1775 – 1836
Heinrich Lenz 1804 – 1865
Georg Ohm 1789 – 1854
Charles Darwin 1809 – 1882
AC Generator (Alternators) By Tesla
DC Generator Edison


  1. History Of Electrical Engineering