Sketching the History of Classical Electromagnetism
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Many things are known about optics: the rectilinearity of light rays; the law of reflection; transparency of materials; that rays passing obliquely from less dense to more dense medium are refracted toward the perpendicular of the interface; general laws for the relationship between the apparent location of an object in reflections and refractions; the existence of metal mirrors (glass mirrors being a 19^{th} century invention).

5^{th}

cent

BC

cent

BC

Empedocles (b. ca. 492 BC) speculates (based on reason) that the speed of light is finite.

ca

300

BC

300

BC

Convex lenses in existence at Carthage.

Euclid of Alexandria (ca. 325 BC – ca. 265 BC) writes, among many other works, *Optics* and *Catoptrica*, dealing with vision theory and perspective.

1^{st}

cent

BC

cent

BC

Chinese fortune tellers begin using loadstone to construct their divining boards, eventually leading to the first compasses. (Mentioned in Wang Ch'ung's *Discourses weighed in the balance* of 83 B.C.)

1^{st}

cent

cent

South-pointing divining boards become common in China.

ca

65

65

Lucius Annaeus Seneca (ca. 4 BC – 65 AD) writes *Naturales quaestiones*, collecting many natural discoveries, including a reference to the production of colors similar those of a rainbow by sunlight passing through glass prisms.

2^{nd}

cent

cent

Hero of Alexandria (ca. 10 – ca. 75 AD) writes on the topics of mirrors and light, also showing that light rays take the shortest path available.

Claudius Ptolemy (ca. 85 – ca. 165) writes *Optics*, an experimental and mathematical treatment, extending earlier work on reflection by Euclid and Hero, including both concave and convex spherical and cylindrical mirrors, and doing original research on refraction.

ca

271

271

True compasses come into use by this date in China.

6^{th}

cent

cent

(China) Discovery that loadstones could be used to magnetize small iron needles.

11^{st}

cent

cent

Abu Ali al-Hasan ibn al-Haitam (Alhazen) (965–1039) writes *Kitab al-manazir* (translated into Latin as *Opticae thesaurus Alhazeni* in 1270) on optics, dealing with reflection, refraction, lenses, parabolic and spherical mirrors, aberration and atmospheric refraction. He adapts the mathematical extramission theory (which he rejects) to the intramission framework.

(China) Iron magnetized by heating it to red hot temperatures and cooling while in south-north orientation.

1086

1150s

Earliest explicit reference to magnets per se, in *Roman d'Enéas.* (see reference)

1190s

Alexander Neckam (1157–1217)'s *De naturis rerum* contains the first western reference to compasses used for navigation, and it had by this time been in common use.

13^{rd}

cent

cent

Robert Grosseteste (ca. 1168–1253) writes *De Iride*, *De Luce*, *De Colore*, and other works on optics and light, lenses and mirrors, describing rectilinear light propagation as a wave phenomenon analogous to sound, and analyzing the optics of the rainbow in terms of refraction.

Witelo (d. ca. 1281) writes *Perspectiva* around 1270, treating geometric optics, including reflection and refraction. He also reproduces the data given by Ptolemy on optics, though was unable to generalize or extend the study.

John Pecham (ca. 1230–92)'s work on optics and light.

Roger Bacon (1214–94) writes many works on the nature of light and optics (and some on magnetism). Greatly furthering the work of Grosseteste and Alhazen, and having access to and mastery of the major literature on optics, Bacon develops a unified framework for the understanding of light and geometric optics.

Theodoric of Freiberg (ca. 1250 – ca. 1310), working with prisms and transparent crystalline spheres, formulates a sophisticated theory of refraction in raindrops which is close to the modern understanding, though it did not become very well known. (René Descartes (1596–1650) presents a nearly identical theory roughly 450 years later.)

Eyeglasses, convex lenses for the far-sighted, first invented in or near Florence (as early as the 1270s or as late as the late 1280s — concave lenses for the near-sighted appearing in the late 15^{th} century).

1269

Pierre de Maricourt, aka Petri Pergrinus (fl. 1269) writes Letter on the magnet of Peter the Pilgrim of Maricourt to Sygerus of Foucaucourt, Soldier, the first western analysis of polar magnets and compasses. He demonstrates in France the existence and fundamental role of two poles of a magnet by tracing the directions of a needle laid on to a natural magnet. (First printed in 1558.)

16^{th}

cent

cent

Girolamo Cardano (1501–76) elaborates the difference between amber and loadstone.

1508

John of St. Amand (fl. 1508) suggests the ideas of magnetic poles, the Earth as a magnet, and magnetic currents.

1558

Giambattista Della Porta (1535–1615) publishes his major work, *Magia naturalis,* analyzing, among many other things, magnetism.

1600

William Gilbert (1544–1603), after 18 years of experiments with magnetic and electrical materials, finishes his book *De Magnete.* The work included: the first major classification of electric and non-electric materials; gives the name "electric" to the substance behind electrical phenomena; a comarative study of electric and magnetic field effects; the relation of moisture and electrification; showing that electrification effects metals, liquids and smoke; noting that electrics were the attractive agents (as opposed to the air between objects); that heating dispelled the attractive power of electrics; and showing the earth to be a magnet. Gilbert is influenced by, among many others, the mariner Robert Norman (fl. 1590).

1603

Johannes Kepler (1571–1630) finishes *Astronomiae Pars Optica*, going over parallax, reflection of mirrors, the inverse square law and related phenomena in astronomy.

1606

Della Porta first describes the heating effects of light rays.

1618

April 2^{nd}, Francesco Maria Grimaldi (1618–63) discovers diffraction patterns of light and becomes convinced that light is a wave-like phenomenon. The theory is given little attention.

1621

Willebrord van Roijen Snell (1580–1626) experimentally determines the law of angles of incidence and reflection for light and for refraction between two media.

1629

Nicolo Cabeo (1586–1650) publishes his observations on electrical repulsion, noting that attracting substances may later repel one another after making contact.

1630

Vincenzo Cascariolo discovers a substance that shines in the dark after exposure to sunslight, the so-called Bologna phosphorus.

1637

René Descartes (1596–1650) publishes his *Dioptics* and *On Meteors* as appendices to his *Discourseins a Method*, detailing a theory of refraction and going over a theory of rainbows which, while containing nothing essentially new, encouraged experimental exploration of the subject.

1644

Descartes' *Principia philosophiae*, describing magnetism as the result of the mechanical motion of channel particles and their displacements, and proposing the absence of both void and action at a distance.

1646

1657

Pierre de Fermat (1601–65) formulates the principle of least time for understanding the way in which light rays move.

1660

Otto von Guericke (1602–86) builds the first electrical machine, a rotating frictional generator.

1661

Fermat is able to apply his principle of least time to understand the refractive indices of different materials.

1664

Robert Hooke (1635–1703) puts forth a wave theory of light in his Micrographia, considering light to be a very high speed rectilinear propagation of longitudinal vibrations of a medium in which individual wavelets spherically spread. He also introduces wave-front analysis, the nation of a material's optical density and a theory of color.

1665

Francesco Maria Grimaldi (1618–63)'s *Prysico-mathesis de lumine coloribus et iride* describes experiments with diffraction of light and states his wave theory of light.

1669

Erasmus Bartholin (1625–98) publishes *A Study of Iceland Spar*, about his discovery of double refraction.

1671

Isaac Newton (1642–1727) presents his observations on color and suggests color to be a property of light rays.

1672

Newton presents a corrected account of Christiaan Huyghens (1629–95)' discovery of polarization phenomena.

1675

Robert Boyle (1627–91) writes *Experiments and Notes about the Mechanical Origine or Production of Electricity.* Electrical attraction, it was written, was "a Material Effluvium issuing from and returning to, the Electrical Body."

1676

Ole Christensen Rømer (1644–1710) demonstrates the finite speed of light via observations of the eclipses of the satellites of Jupiter. While not calculating a speed for light, he estimates the Sun-Earth transit time for light to travel as roughly 11 minutes.

1677

Huyghens extends the wave theory of light in his work *Treatise on Light*, unpublished until 1690.

1687

Newton notes magnetism to be a non-universal force and derives an inverse cubed law for two poles of a magnet.

1690

Publication of Huyghens' work *Treatise on Light* (originally presented to the *Académie* in 1678). This work includes a wave theory of light with a finite speed, a numerical estimate of the speed of light as 180,000,000 toises per second (roughly 131,000 miles per sec), explanations of wave propagation, reflection, single and double refraction, and polarization.

1699

Nicolas Malebranche (1638–1715) proposes monochromatic light to depend on periodic vibrations and that brightness is in proportion to their amplitude.

1704

Newton's research on light culminates in the publication of his *Optics*, describing light both in terms of wave theory and his corpuscular theory.

1709

1728

James Bradley (1693–1762) discovers the phenomenon of steller aberration, confirming and providing a new method for determining the finite speed of light.

1729

Stephen Gray (ca. 1670–1736) shows static electricity to be transported via substances, especially metals.

1733

Charles-Francois de Cisternai du Fay (1698–1739) discovers that electric charges are of two types and that like charges repell while unlike charges attract.

1745

Ewald Georg von Kleist (1700–48) discovers a method to store electrical charge (known later as a Kleistian or Leyden jar).

1746

William Watson (1715–89) suggests conservation of electric charge.

1747

Benjamin Franklin (1706–90) proposes that electricity be modeled by a single fluid with two states of electrification, materials have more or less of a normal amount of electric fluid, independently proposing conservation of electric charge, and introducing the convention of describing the two types of charges as positive and negative.

Watson passes electrical charge along a two mile long wire.

1750

John Michell (1724–93) demonstrates that the action of a magnet on another can be deduced from an inverse square law of force between individual poles of the magnet, published in his work, *A Treatise on Artificial Magnets*.

1759

Franz Ulrich Theodosius Aepinus (1724–1802) publishes *An Attempt at a Theory of Electricity and Magnetism*, the first book applying mathematical techniques to the subject.

1764

Johan Carl Wilcke (1732–96) invents the electrophorus, a device which can produce relatively large amounts of electric charge easily and repeatedly.

1766

Joseph Priestley (1733–1804) deduces the inverse square law for electric charges using the results of experiments showing the absence of electrical effects inside a charged hollow conducting sphere.

1772

Henry Cavendish (1731–1810) publishes, "An Attempt to Explain some of the Principal Phenomena of Electricity, by Means of an Elastic Fluid."

1775

Alessandro Guiseppe Antonio Anastasio Volta (1745–1827) invents an electrometer, a plate condenser and the electrophorus.

1777

Charles Augustin de Coulomb (1736–1806) research sets a new direction in research into electricity and magnetism.

1780s

(early 1780s) Luigi Galvani (1737–98) uses the response of animal tissue to begin studies of electrical currents produced by chemical action rather than from static electricity. The mechanical response of animal tissue to contact with two dissimilar metals is now known as galvanism.

1785

1799

Volta shows that galvanism is not of animal origin but occurred whenever a moist substance is placed between two metals. This discovery eventually leads to the "Volta pile" a year linsert into rst electric batteries.

1800

Volta writes a paper on electricity by contact.

1801

Thomas Young (1773–1829) work on interference revives interest in the wave theory of light. He also accounts for the recently discovered phenomenon of light polarization by suggesting that light is a vibration in the aether transverse to the direction of propagation.

Johann Georg von Soldner (1776–1833) makes a calculation for the deflection of light by the sun assuming a finite speed of light corpuscles and a non-zero mass. (The result, 0.85 arc-sec, was rederived independently by Cavendish and Albert Einstein (1879–1955) (1911), but went unnoticed until 1921. )

1807

Humphry Davy (1778–1829)'s lecture, "On Some Chemical Agents of Electricity," drawing close the possible relationships of chemical and electrical forces.

1812

Simeon-Denis Poisson (1781–1840) formulates the concept of macroscopic charge neutrality as a natural state of matter and describes electrification as the separation of the two kinds of electricity. He also points out the usefulness of a potential function for electrical systems.

Hans Christian Oersted (1777–1851) suggests that experiments on galvanism could show the relationship between electricity and magnetism.

1813

Measurements of specific heat of air as a function of pressure by Delarache and Joseph Frédéric Bérard (1789–1828).

1814

Augustin-Jean Fresnel (1788–1827) independently discovers the interference phenomena of light and explains its existence in terms of wave theory.

1817

Fresnel predicts a dragging effect on light in the aether.

1818

Fresnel's essay on optics and the aether.

1820

(Spring) Oersted notes the deflection of a magnetic compass needle caused by an electric current after giving a lecture demonstration. He then demonstrates that the effect is reciprocal. This initiates the unification program of electricity and magnetism.

July 27, André Marie Ampère (1775–1836) confirms Oersted's results and presents extensive experimental results to the French Academy of Science. He models magnets in terms of molecular electric currents. His formulation inaugurates the study of electrodynamics independent of electrostatics.

Fall, Jean-Baptiste Biot (1774–1862) and Felix Savart (1792–1841) deduce the formula for the strength of the magnitec effect produced by a short segment of current carrying wire.

1825

Ampère's memoirs are published on his research into electrodynamics.

1827

Georg Simon Ohm (1789–1854) formulates the relationship between current to electromotive force and electrical resistance.

Ampère publishes *Memoir on the Mathematical Theory of Electrodynamics, Uniquely Deduced from Experiment*.

1828

George Green (1793–1841) introduces the notion of potential and formulates what is now called Green's Theorem relating the surface and volume distributions of charge. (The work goes unnoticed until 1846.)

1831

Michael Faraday (1791–1867) begins his investigations into electromagnetism.

1832

Johann Carl Friedrich Gauss (1777–1855) independently states Green's Theorem without proof. He also reformulates Coulomb's law in a more general form, and establishes experimental methods for measuring magnetic intensities.

1835

Gauss formulates separate electrostatic and electrodynamical laws, including "Gauss's law." All of it remains unpublished until 1867.

1838

Faraday explains electromagnetic ininduction, electrochemistry and formulates his notion of lines of force, also criticizing action-at-a-distance theories.

Wilhelm Eduard Weber (1804–91) and Gauss apply potential theory to the magnetism of the earth.

1839

1842

William Thomson (Lord Kelvin) (1824–1907) writes a paper, "On the uniform motion of heat and its connection with the mathematical theory of electricity," based on the ideas of Joseph Fourier (1768–1830). The analogy allows him to formulate a continuity equation of electricity, implying a conservation of electric flux.

1845

to

1850

to

1850

G T Fechner (1801–87) proposes a connection between Ampère's law and Faraday's law in order to explain Lenz's law.

Faraday introduces the idea of "contiguous magnetic action" as a local interaction, instead of the idea of instantaneous action at a distance, using concepts now known as fields. He also estabishes a connection between light and electrodynamics by showing that the transverse polarization direction of a light beam was rotated about the axis of propagation by a strong magnetic field (today known as "Faraday rotation").

1846

Weber proposes a synthesis of electrostatics, electrodynamics and induction using the idea that electric currents are moing charged particles. The interactions are instantaneous forces. Weber's theory contains a limiting velocity of electromagnetic origin with the value *sqrt(2) c*.

The partial-drag theory of George Gabriel Stokes (1819–1903) is revived for the explanation of stellar aberration.

1849

Armand Hippolyte Louis Fizeau (1819–96) begins experiments to determine the speed of light.

1852

Stokes names and explains the phenomena of fluorescence.

1854

Bernhard Riemann (1826–66) makes unpublished conjectures about an "investigation of the connection between electricity, galvanism, light and gravity."

1855

Weber and R Kohlrausch (1809–58) determine a limiting velocity which turns up in Weber's electrodynamic theory, and that it's value is about 439,450 km/s.

1855

to

1868

to

1868

James Clerk Maxwell (1831–79) completes his formulation of the field equations of electromagnetism. He established, among many things, the connection between the speed of propagation of an electromagnetic wave and the speed of light, and establishing the theoretical understanding of light.

1858

Riemann generalizes Weber's unification program and derives his results via a solution to a wave function of a electrodynamical potential (finding the speed of propagation, correctly, to be *c*). He claimed to have found the connection between electricity and optics. (Results published postumously in 1867.)

1861

Riemann uses Joseph Louis Lagrange (1736–1813)'s theorem to deal with velocity-dependent electrical accelerations.

Gustav Robert Kirchhoff (1824–87) formulates the model of the black body.

1863

1864

Maxwell publishes *A Dynamical Theory of the Electromagnetic Field*, his first publication to make use of his mathematical theory of fields.

1865

Maxwell's *A Dynamical Theory of the Electromagnetic Field*, formulating an electrodynamical formulation of wave propagation using Lagrangian and Hamiltonian techniques, obtaining the theoretical possibility of generating electromagnetic radiation. (The derivation is independent of the microscopic structures which may underlie such phenomena.)

1870

Hermann Ludwig Ferdinand von Helmholtz (1821–94) developes a theory of electricity and shows Weber's theories to be inconsistent with the conservation of energy.

1873

The first edition of Maxwell's *Treatise on Electricity and Magnetism* is published.

1874

George Johnstone Stoney (1826–1911) estimates the charge of an electron to be about 10^{-20} Coulombs and introduces the term "electron."

1875

Hendrik Antoon Lorentz (1853–1928), in his doctoral thesis, derives the phenomena of reflection and refraction in terms of Maxwell's theory.

W Crookes (1832–1919) performs experiments on cathode rays.

1879

Maxwell suggests that an earth-based experiment to detect possible aether drifts could be performed, but that it would not be sensitive enough.

1881

Albert Abraham Michelson (1852–1931) begins his interferometry experiments to detect a luminiferous aether.

Joseph John Thomson (1856–1940) paper, "On the electric and magnetic effects produced by the motion of electrified bodies" explores inertial effects due to displacement currents.

1884

Heinrich Rudolf Hertz (1857–94) develops a reformulation of electrodynamics and shows his and Helmholtz's theories both amount to Maxwell's theory.

John Henry Poynting (1852–1914) establishes a principle of electromagnetic radiation energy which can be localized and flow (the first such energy localization principle established); not confined to existing only in conductors, but throughout space, independent of matter.

1885

to

1887

to

1887

Oliver Heaviside (1850–1925) writes *Electromagnetic induction and its propagation* over the course of two years, re-expressing Maxwell's results in 3 (complex) vector form, giving it much of its modern form and collecting together the basic set of equations from which electromagnetic theory may be derived (often called "Maxwell's equations"). In the process, He invents the modern vector calculus notation, including the gradient, divergence and curl of a vector.

1887

Hertz experimentally produces electromagnetic radiation with radio waves in the GHz range, also discovering the photoelectric effect and predicting that gravitation would also have a finite speed of propagation.

W Voight, working through an analysis of Doppler effects using an elastic model of the luminiferous aether to describe optical properties, produces a set of relations between space and time intervals which are later rediscovered independently by Lorentz and now knows as the "Lorentz equations" (first so-called by Jules Henri Poincaré (1854–1912) in 1904).

1889

George Francis FitzGerald (1851–1901) suggests that bodies contract in the direction of motion against the luminiferous aether by an amount which would account for the null results coming from the Michelson-Morley experiments on aether motion. (A more detailed calculation is performed independently by Lorentz in 1895.) FitzGerald also suggests that the speed of light is an upper bound on any possible speed. (This suggestion reappears in 1900 by Lorentz, in 1904 by Poincaré, and again in 1905 by Einstein.)

John William Strutt (Lord Rayleigh) (1842–1919) presents a model for radiation in terms of wave propagation.

Heaviside's "On the electromagnetic effects due to the motion of electrification through a dielectric," proposes part of inertial mass to be electromagnetic in origin and includes dependencies on higher-order terms in *(v/c)*.

1890

Hertz publishes his memoirs on electrodynamics, simplifying the form of the electromagnetic equations, replacing all potentials by field strengths, and deduces Ohm's, Kirchoff's and Coulomb's laws.

1892

to

1904

to

1904

Lorentz completes the description of electrodynamics by clearly separating electricity and electrodynamic fields and formulating the equations for charged particles in motion.

1893

Wilhelm Carl Werner Otto Fritz Franz Wien (1864–1928) gives his displacement law of blackbody radiation.

1896

Wien theoretically derives the radiation distribution law.

Discovery of X-rays and Becquerel radiation.

Discovery of the Zeeman effect.

1897

JJ Thomson experimentally determines the charge-to-mass ratio, *e/m*, of electrons.

1898

Poincaré suggests that a complete measurement theory must formulate a notion of distant synchronization and discusses its relevance to the apparent constancy of the speed of light.

1899

Lorentz refines the transformation laws, formulating the notion of local time and local coordinate systems in electrodynamics.

Philipp Eduard Anton von Lénárd (1862–1947) begin experimental investigations of photoelectric radiation.

1900

Wien's "On the possibility of an electromagnetic foundation of mechanics."

Poincaré's paper "The theory of Lorentz and the principle of reaction," showing electromagnetic radiation to have a momentum proportional to a field's Poynting vector, and that the momentum of a recoiling body to be *vE/c*^{2} .

Max Karl Ernst Ludwig Planck (1858–1947), studying blackbody radiation derives the correct radiation spectrum for blackbodies. Planck proposes the constant, *h* (Planck's constant), as a quantum of action in phase space.

1902

Max Abraham (1875–1922) "The dynamics of electrons," also introducing the concept of electromagnetic momentum.

Walter Kaufmann (1871–1947) performs experiments on the deflection of electrons by electric and magnetic fields and a determination of the ration *e/m*; In a second paper, he concludes that the mass of an electron is purely electromagnetic in origin.

1903

Abraham's "Principles of the dynamics of electrons," attempts to show, among other things, the electromagnetic foundation of mechanics.

1904

1905

Albert Einstein (1879–1955) analyzes the phenomena of the photoelectric effect and theorizes that light may be taken to be made up of vast amounts of packets of electromagnetic radiation in discrete units.

Einstein publishes several papers drawing out the symmetries of Maxwell, Hertz and Lorentz's electromagnetic theory, the underlying connection in measurement theory and the status of the electromagnetic aether.

1907

Hermann Minkowski (1864–1909), through considerations of the group properties of the equations of electrodynamics, reinterprets Einstein's relativity theory as a kind of geometry of spacetime, considered as a single medium.

Planck gives a corrected derivation of the mass-energy relation using Poincaré's radiation momentum.

1908

Gilbert N Lewis (1875–1946) publishes "A revision of the fundamental laws of matter and energy," deriving *dE = c*^{2} dm from considerations of radiation pressure.

1933

Experiments by Patrick Blackett (1897–1974) and Giuseppe Occhialini (1907–93) on pair production demonstrate the complete aninhilation of matter into electromagnetic energy.

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