Timeline of electromagnetism and classical
optics lists, within the history of electromagnetism,
the associated theories, technology, and events.
== Early developments ==
28th century BC — Ancient Egyptian texts
describe electric fish. They refer to them
as the "Thunderer of the Nile", and described
them as the "protectors" of all other fish.
6th century BC — Greek philosopher Thales
of Miletus observes that rubbing fur on various
substances, such as amber, would cause an
attraction between the two, which is now known
to be caused by static electricity. He noted
that the amber buttons could attract light
objects such as hair and that if the amber
was rubbed sufficiently a spark would jump.
424 BC Aristophanes "lens" is a glass globe
filled with water.(Seneca says that it can
be used to read letters no matter how small
or dim)
4th century BC Mo Di first mentions the camera
obscura, a pin-hole camera.
3rd century BC Euclid is the first to write
about reflection and refraction and notes
that light travels in straight lines
3rd century BC — The Baghdad Battery is
dated from this period. It resembles a galvanic
cell and is believed by some to have been
used for electroplating, although there is
no common consensus on the purpose of these
devices nor whether they were, indeed, even
electrical in nature.
1st century BC — Pliny in his Natural History
records the story of a shepherd Magnes who
discovered the magnetic properties of some
iron stones, "it is said, made this discovery,
when, upon taking his herds to pasture, he
found that the nails of his shoes and the
iron ferrel of his staff adhered to the ground."
130 AD. — Claudius Ptolemy (in his work
Optics) wrote about the properties of light
including: reflection, refraction, and color
and tabulated angles of refraction for several
media
8th century AD — Electric fish are reported
by Arabic naturalists and physicians.
1021 — Ibn al-Haytham (Alhazen) writes the
Book of Optics, studying vision.
1088 — Shen Kuo first recognizes magnetic
declination.
1187 — Alexander Neckham is first in Europe
to describe the magnetic compass and its use
in navigation.
1269 — Pierre de Maricourt describes magnetic
poles and remarks on the nonexistence of isolated
magnetic poles
1305 — Dietrich von Freiberg uses crystalline
spheres and flasks filled with water to study
the reflection and refraction in raindrops
that leads to primary and secondary rainbows
14th century AD — Possibly the earliest
and nearest approach to the discovery of the
identity of lightning, and electricity from
any other source, is to be attributed to the
Arabs, who before the 15th century had the
Arabic word for lightning (raad) applied to
the electric ray.
1550 — Gerolamo Cardano writes about electricity
in De Subtilitate distinguishing, perhaps
for the first time, between electrical and
magnetic forces.
== 17th century ==
1600 — William Gilbert publishes De Magnete,
Magneticisque Corporibus, et de Magno Magnete
Tellure ("On the Magnet and Magnetic bodies,
and on that Great Magnet the Earth"), Europe's
then current standard on electricity and magnetism.
He experimented with and noted the different
character of electrical and magnetic forces.
In addition to known ancient Greeks' observations
of the electrical properties of rubbed amber,
he experimented with a needle balanced on
a pivot, and found that the needle was non-directionally
affected by many materials such as alum, arsenic,
hard resin, jet, glass, gum-mastic, mica,
rock-salt, sealing wax, slags, sulfur, and
precious stones such as amethyst, beryl, diamond,
opal, and sapphire. He noted that electrical
charge could be stored by covering the body
with a non-conducting substance such as silk.
He described the method of artificially magnetizing
iron. His terrella (little earth), a sphere
cut from a lodestone on a metal lathe, modeled
the earth as a lodestone (magnetic iron ore)
and demonstrated that every lodestone has
fixed poles, and how to find them. He considered
that gravity was a magnetic force and noted
that this mutual force increased with the
size or amount of lodestone and attracted
iron objects. He experimented with such physical
models in an attempt to explain problems in
navigation due varying properties of the magnetic
compass with respect to their location on
the earth, such as magnetic declination and
magnetic inclination. His experiments explained
the dipping of the needle by the magnetic
attraction of the earth, and were used to
predict where the vertical dip would be found.
Such magnetic inclination was described as
early as the 11th century by Shen Kuo in his
Meng Xi Bi Tan and further investigated in
1581 by retired mariner and compass maker
Robert Norman, as described in his pamphlet,
The Newe Attractive. The gilbert, a unit of
magnetomotive force or magnetic potential,
was named in his honor.
1604 — Johannes Kepler describes how the
eye focuses light
1604 — Johannes Kepler specifies the laws
of the rectilinear propagation of light
1608 — first telescopes appear in the Netherlands
1611 — Marko Dominis discusses the rainbow
in De Radiis Visus et Lucis
1611 — Johannes Kepler discovers total internal
reflection, a small-angle refraction law,
and thin lens optics,
c1620 — the first compound microscopes appear
in Europe.
1621 — Willebrord van Roijen Snell states
his Snell's law of refraction
1630 — Cabaeus finds that there are two
types of electric charges
1637 — René Descartes quantitatively derives
the angles at which primary and secondary
rainbows are seen with respect to the angle
of the Sun's elevation
1646 — Sir Thomas Browne first uses the
word electricity is in his work Pseudodoxia
Epidemica.
1657 — Pierre de Fermat introduces the principle
of least time into optics
1660 — Otto von Guericke invents an early
electrostatic generator.
1663 — Otto von Guericke (brewer and engineer
who applied the barometer to weather prediction
and invented the air pump, with which he demonstrated
the properties of atmospheric pressure associated
with a vacuum) constructs a primitive electrostatic
generating (or friction) machine via the triboelectric
effect, utilizing a continuously rotating
sulfur globe that could be rubbed by hand
or a piece of cloth. Isaac Newton suggested
the use of a glass globe instead of a sulfur
one.
1665 — Francesco Maria Grimaldi highlights
the phenomenon of diffraction
1673 — Ignace Pardies provides a wave explanation
for refraction of light
1675 — Robert Boyle discovers that electric
attraction and repulsion can act across a
vacuum and do not depend upon the air as a
medium. Adds resin to the known list of "electrics."
1675 — Isaac Newton delivers his theory
of light
1676 — Olaus Roemer measures the speed of
light by observing Jupiter's moons
1678 — Christiaan Huygens states his principle
of wavefront sources and demonstrates the
refraction and diffraction of light rays.
== 18th century ==
1704 — Isaac Newton publishes Opticks, a
corpuscular theory of light and colour
1705 — Francis Hauksbee improves von Guericke's
electrostatic generator by using a glass globe
and generates the first sparks by approaching
his finger to the rubbed globe.
1728 — James Bradley discovers the aberration
of starlight and uses it to determine that
the speed of light is about 283,000 km/s
1729 — Stephen Gray and the Reverend Granville
Wheler experiment to discover that electrical
"virtue," produced by rubbing a glass tube,
could be transmitted over an extended distance
(nearly 900 ft (about 270 m)) through thin
iron wire using silk threads as insulators,
to deflect leaves of brass. This has been
described as the beginning of electrical communication.
This was also the first distinction between
the roles of conductors and insulators (names
applied by John Desaguliers, mathematician
and Royal Society member, who stated that
Gray "has made greater variety of electrical
experiments than all the philosophers of this
and the last age.") Georges-Louis LeSage built
a static electricity telegraph in 1774, based
upon the same principles discovered by Gray.
1732 — C. F. du Fay Shows that all objects,
except metals, animals, and liquids, can be
electrified by rubbing them and that metals,
animals and liquids could be electrified by
means of an electrostatic generators
1734 — Charles François de Cisternay DuFay
(inspired by Gray's work to perform electrical
experiments) dispels the effluvia theory by
his paper in Volume 38 of the Philosophical
Transactions of the Royal Society, describing
his discovery of the distinction between two
kinds of electricity: "resinous," produced
by rubbing bodies such as amber, copal, or
gum-lac with silk or paper, and "vitreous,"
by rubbing bodies as glass, rock crystal,
or precious stones with hair or wool. He also
posited the principle of mutual attraction
for unlike forms and the repelling of like
forms and that "from this principle one may
with ease deduce the explanation of a great
number of other phenomena." The terms resinous
and vitreous were later replaced with the
terms "positive" and "negative" by William
Watson and Benjamin Franklin.
1737 — C. F. du Fay and Francis Hauksbee
the younger independently discover two kinds
of frictional electricity: one generated from
rubbing glass, the other from rubbing resin
(later identified as positive and negative
electrical charges).
1740 — Jean le Rond d'Alembert, in Mémoire
sur la réfraction des corps solides, explains
the process of refraction.
1745 — Pieter van Musschenbroek of Leiden
(Leyden) independently discovers the Leyden
(Leiden) jar, a primitive capacitor or "condenser"
(term coined by Volta in 1782, derived from
the Italian condensatore), with which the
transient electrical energy generated by current
friction machines could now be stored. He
and his student Andreas Cunaeus used a glass
jar filled with water into which a brass rod
had been placed. He charged the jar by touching
a wire leading from the electrical machine
with one hand while holding the outside of
the jar with the other. The energy could be
discharged by completing an external circuit
between the brass rod and another conductor,
originally his hand, placed in contact with
the outside of the jar. He also found that
if the jar were placed on a piece of metal
on a table, a shock would be received by touching
this piece of metal with one hand and touching
the wire connected to the electrical machine
with the other.
1745 — Ewald Georg von Kleist of independently
invents the capacitor: a glass jar coated
inside and out with metal. The inner coating
was connected to a rod that passed through
the lid and ended in a metal sphere. By having
this thin layer of glass insulation (a dielectric)
between two large, closely spaced plates,
von Kleist found the energy density could
be increased dramatically compared with the
situation with no insulator. Daniel Gralath
improved the design and was also the first
to combine several jars to form a battery
strong enough to kill birds and small animals
upon discharge.
1746 — Leonhard Euler develops the wave
theory of light refraction and dispersion
1747 — William Watson, while experimenting
with a Leyden jar, observes that a discharge
of static electricity causes electric current
to flow and develops the concept of an electrical
potential (voltage).
1752 — Benjamin Franklin establishes the
link between lightning and electricity by
the flying a kite into a thunderstorm and
transferring some of the charge into a Leyden
jar and showed that its properties were the
same as charge produced by an electrical machine.
He is credited with utilizing the concepts
of positive and negative charge in the explanation
of then known electrical phenomenon. He theorized
that there was an electrical fluid (which
he proposed could be the luminiferous ether,
which was used by others before and after
him, to explain the wave theory of light)
that was part of all material and all intervening
space. The charge of any object would be neutral
if the concentration of this fluid were the
same both inside and outside of the body,
positive if the object contained an excess
of this fluid, and negative if there were
a deficit. In 1749 he had documented the similar
properties of lightning and electricity, such
as that both an electric spark and a lightning
flash produced light and sound, could kill
animals, cause fires, melt metal, destroy
or reverse the polarity of magnetism, and
flowed through conductors and could be concentrated
at sharp points. He was later able to apply
the property of concentrating at sharp points
by his invention of the lightning rod, for
which he intentionally did not profit. He
also investigated the Leyden jar, proving
that the charge was stored on the glass and
not in the water, as others had assumed.
1753 — C. M. (of Scotland, possibly Charles
Morrison, of Greenock or Charles Marshall,
of Aberdeen) proposes in the 17 February edition
of Scots Magazine, an electrostatic telegraph
system with 26 insulated wires, each corresponding
to a letter of the alphabet and each connected
to electrostatic machines. The receiving charged
end was to electrostatically attract a disc
of paper marked with the corresponding letter.
1767 — Joseph Priestley proposes an electrical
inverse-square law
1774 — Georges-Louis LeSage builds an electrostatic
telegraph system with 26 insulated wires conducting
Leyden-jar charges to pith-ball electroscopes,
each corresponding to a letter of the alphabet.
Its range was only between rooms of his home.
1784 — Henry Cavendish defines the inductive
capacity of dielectrics (insulators) and measures
the specific inductive capacity of various
substances by comparison with an air condenser.
1785 — Charles Coulomb introduces the inverse-square
law of electrostatics
1786 — Luigi Galvani discovers "animal electricity"
and postulates that animal bodies are storehouses
of electricity. His invention of the voltaic
cell leads to the invention the electric battery.
1791 — Luigi Galvani discovers galvanic
electricity and bioelectricity through experiments
following an observation that touching exposed
muscles in frogs' legs with a scalpel which
had been close to a static electrical machine
caused them to jump. He called this "animal
electricity". Years of experimentation in
the 1780s eventually led him to the construction
of an arc of two different metals (copper
and zinc for example) by connecting the two
metal pieces and then connecting their open
ends across the nerve of a frog leg, producing
the same muscular contractions (by completing
a circuit) as originally accidentally observed.
The use of different metals to produce an
electrical spark is the basis that led Alessandro
Volta in 1799 to his invention of his voltaic
pile, which eventually became the galvanic
battery.
1799 — Alessandro Volta, following Galvani's
discovery of galvanic electricity, creates
a voltaic cell producing an electric current
by the chemical action of several pairs of
alternating copper (or silver) and zinc discs
"piled" and separated by cloth or cardboard
which had been soaked brine (salt water) or
acid to increase conductivity. In 1800 he
demonstrates the production of light from
a glowing wire conducting electricity. This
was followed in 1801 by his construction of
the first electric battery, by utilizing multiple
voltaic cells. Prior to his major discoveries,
in a letter of praise to the Royal Society
1793, Volta reported Luigi Galvani's experiments
of the 1780s as the "most beautiful and important
discoveries," regarding them as the foundation
of future discoveries. Volta's inventions
led to revolutionary changes with this method
of the production of inexpensive, controlled
electric current vs. existing frictional machines
and Leyden jars. The electric battery became
standard equipment in every experimental laboratory
and heralded an age of practical applications
of electricity. The unit volt is named for
his contributions.
1800 — William Herschel discovers infrared
radiation from the Sun.
1800 — William Nicholson, Anthony Carlisle
and Johann Ritter use electricity to decompose
water into hydrogen and oxygen, thereby discovering
the process of electrolysis, which led to
the discovery of many other elements.
1800 — Alessandro Volta invents the voltaic
pile, or "battery", specifically to disprove
Galvani's animal electricity theory.
== 19th century ==
=== 1801-1850 ===
1801 — Johann Ritter discovers ultraviolet
radiation from the Sun
1801 — Thomas Young demonstrates the wave
nature of light and the principle of interference
1802 — Gian Domenico Romagnosi, Italian
legal scholar, discovers that electricity
and magnetism are related by noting that a
nearby voltaic pile deflects a magnetic needle.
He published his account in an Italian newspaper,
but this was overlooked by the scientific
community.
1803 — Thomas Young develops the Double-slit
experiment and demonstrates the effect of
interference.
1806 — Alessandro Volta employs a voltaic
pile to decompose potash and soda, showing
that they are the oxides of the previously
unknown metals potassium and sodium. These
experiments were the beginning of electrochemistry.
1808 — Étienne-Louis Malus discovers polarization
by reflection
1809 — Étienne-Louis Malus publishes the
law of Malus which predicts the light intensity
transmitted by two polarizing sheets
1809 — Humphry Davy first publicly demonstrates
the electric arc light.
1811 — François Jean Dominique Arago discovers
that some quartz crystals continuously rotate
the electric vector of light
1816 — David Brewster discovers stress birefringence
1818 — Siméon Poisson predicts the Poisson-Arago
bright spot at the center of the shadow of
a circular opaque obstacle
1818 — François Jean Dominique Arago verifies
the existence of the Poisson-Arago bright
spot
1820 — Hans Christian Ørsted, Danish physicist
and chemist, unites the separate sciences
of electricity and magnetism. He develops
an experiment in which he notices a compass
needle is deflected from magnetic north when
an electric current from the battery he was
using was switched on and off, convincing
him that magnetic fields radiate from all
sides of a live wire just as light and heat
do, confirming a direct relationship between
electricity and magnetism. He also observes
that the movement of the compass-needle to
one side or the other depends upon the direction
of the current. Following intensive investigations,
he published his findings, proving that a
changing electric current produces a magnetic
field as it flows through a wire. The oersted
unit of magnetic induction is named for his
contributions.
1820 — André-Marie Ampère, professor of
mathematics at the Ecole Polytechnique, a
short time after learning of Ørsted's discovery
that a magnetic needle is acted on by a voltaic
current, conducts experiments and publishes
a paper in Annales de Chimie et de Physique
attempting to give a combined theory of electricity
and magnetism. He shows that a coil of wire
carrying a current behaves like an ordinary
magnet and suggests that electromagnetism
might be used in telegraphy. He mathematically
develops Ampère's law describing the magnetic
force between two electric currents. His mathematical
theory explains known electromagnetic phenomena
and predicts new ones. His laws of electrodynamics
include the facts that parallel conductors
currying current in the same direction attract
and those carrying currents in the opposite
directions repel one another. One of the first
to develop electrical measuring techniques,
he built an instrument utilizing a free-moving
needle to measure the flow of electricity,
contributing to the development of the galvanometer.
In 1821, he proposed a telegraphy system utilizing
one wire per "galvanometer" to indicate each
letter, and reported experimenting successfully
with such a system. However, in 1824, Peter
Barlow reported its maximum distance was only
200 feet, and so was impractical. In 1826
he publishes the Memoir on the Mathematical
Theory of Electrodynamic Phenomena, Uniquely
Deduced from Experience containing a mathematical
derivation of the electrodynamic force law.
Following Faraday's discovery of electromagnetic
induction in 1831, Ampère agreed that Faraday
deserved full credit for the discovery.
1820 — Johann Salomo Christoph Schweigger,
German chemist, physicist, and professor,
builds the first sensitive galvanometer, wrapping
a coil of wire around a graduated compass,
an acceptable instrument for actual measurement
as well as detection of small amounts of electric
current, naming it after Luigi Galvani.
1821 — André-Marie Ampère announces his
theory of electrodynamics, predicting the
force that one current exerts upon another.
1821 — Thomas Johann Seebeck discovers the
thermoelectric effect.
1821 — Augustin-Jean Fresnel derives a mathematical
demonstration that polarization can be explained
only if light is entirely transverse, with
no longitudinal vibration whatsoever.
1825 — Augustin Fresnel phenomenologically
explains optical activity by introducing circular
birefringence
1825 — William Sturgeon, founder of the
first English Electric Journal, Annals of
Electricity, found that an iron core inside
a helical coil of wire connected to a battery
greatly increased the resulting magnetic field,
thus making possible the more powerful electromagnets
utilizing a ferromagnetic core. Sturgeon also
bent the iron core into a U-shape to bring
the poles closer together, thus concentrating
the magnetic field lines. These discoveries
followed Ampère's discovery that electricity
passing through a coiled wire produced a magnetic
force and that of Dominique François Jean
Arago finding that an iron bar is magnetized
by putting it inside the coil of current-carrying
wire, but Arago had not observed the increased
strength of the resulting field while the
bar was being magnetized.
1826 — Georg Simon Ohm states his Ohm's
law of electrical resistance in the journals
of Schweigger and Poggendorff, and also published
in his landmark pamphlet Die galvanische Kette
mathematisch bearbeitet in 1827. The unit
ohm (Ω) of electrical resistance has been
named in his honor.
1829 & 1830 — Francesco Zantedeschi publishes
papers on the production of electric currents
in closed circuits by the approach and withdrawal
of a magnet, thereby anticipating Michael
Faraday's classical experiments of 1831.
1831 — Michael Faraday began experiments
leading to his discovery of the law of electromagnetic
induction, though the discovery may have been
anticipated by the work of Francesco Zantedeschi.
His breakthrough came when he wrapped two
insulated coils of wire around a massive iron
ring, bolted to a chair, and found that upon
passing a current through one coil, a momentary
electric current was induced in the other
coil. He then found that if he moved a magnet
through a loop of wire, or vice versa, an
electric current also flowed in the wire.
He then used this principle to construct the
electric dynamo, the first electric power
generator. He proposed that electromagnetic
forces extended into the empty space around
the conductor, but did not complete that work.
Faraday's concept of lines of flux emanating
from charged bodies and magnets provided a
way to visualize electric and magnetic fields.
That mental model was crucial to the successful
development of electromechanical devices which
were to dominate the 19th century. His demonstrations
that a changing magnetic field produces an
electric field, mathematically modeled by
Faraday's law of induction, would subsequently
become one of Maxwell's equations. These consequently
evolved into the generalization of field theory.
1831 — Macedonio Melloni uses a thermopile
to detect infrared radiation
1832 — Baron Pavel L'vovitch Schilling (Paul
Schilling) creates the first electromagnetic
telegraph, consisting of a single-needle system
in which a code was used to indicate the characters.
Only months later, Göttingen professors Carl
Friedrich Gauss and Wilhelm Weber constructed
a telegraph that was working two years before
Schilling could put his into practice. Schilling
demonstrated the long-distance transmission
of signals between two different rooms of
his apartment and was the first to put into
practice a binary system of signal transmission.
1833 — Heinrich Lenz states Lenz's law:
if an increasing (or decreasing) magnetic
flux induces an electromotive force (EMF),
the resulting current will oppose a further
increase (or decrease) in magnetic flux, i.e.,
that an induced current in a closed conducting
loop will appear in such a direction that
it opposes the change that produced it. Lenz's
law is one consequence of the principle of
conservation of energy. If a magnet moves
towards a closed loop, then the induced current
in the loop creates a field that exerts a
force opposing the motion of the magnet. Lenz's
law can be derived from Faraday's law of induction
by noting the negative sign on the right side
of the equation. He also independently discovered
Joule's law in 1842; to honor his efforts,
Russian physicists refer to it as the "Joule-Lenz
law."
1833 — Michael Faraday announces his law
of electrochemical equivalents
1834 — Heinrich Lenz determines the direction
of the induced electromotive force (emf) and
current resulting from electromagnetic induction.
Lenz's law provides a physical interpretation
of the choice of sign in Faraday's law of
induction (1831), indicating that the induced
emf and the change in flux have opposite signs.
1834 — Jean-Charles Peltier discovers the
Peltier effect: heating by an electric current
at the junction of two different metals.
1835 — Joseph Henry invents the electric
relay, which is an electrical switch by which
the change of a weak current through the windings
of an electromagnet will attract an armature
to open or close the switch. Because this
can control (by opening or closing) another,
much higher-power, circuit, it is in a broad
sense a form of electrical amplifier. This
made a practical electric telegraph possible.
He was the first to coil insulated wire tightly
around an iron core in order to make an extremely
powerful electromagnet, improving on William
Sturgeon’s design, which used loosely coiled,
uninsulated wire. He also discovered the property
of self inductance independently of Michael
Faraday.
1836 — Dr. David Alter invents and demonstrates
to witnesses the first American electric telegraph
in Elderton, Pennsylvania. In a later interview
in the book, Biographical and Historical Cyclopedia
of Indiana and Armstrong Counties he states:
"I may say that there is no connection at
all between the telegraph of Morse and others
and that of myself...Professor Morse most
probably never heard of me or my Elderton
telegraph." In 1840 he invents an electric
buggy, forerunner of the automobile. His inventions
also include an electric clock and a short-range
type of telephone, forerunner to Alexander
Graham Bell's telephone. He is also credited
with the origins of Spectrum Analysis by his
idea that every element has its own emission
spectrum, and an expansion of spectrum analysis
to include the optical properties of gases.
1837 — Samuel Morse develops an alternative
electrical telegraph design capable of transmitting
long distances over poor quality wire. He
and his assistant Alfred Vail develop the
Morse code signaling alphabet. In 1838 Morse
successfully tested the device at the Speedwell
Ironworks near Morristown, New Jersey, and
publicly demonstrated it to a scientific committee
at the Franklin Institute in Philadelphia,
Pennsylvania. The first electric telegram
using this device was sent by Morse on 24
May, 1844 from Baltimore to Washington, D.C.,
bearing the message "What hath God wrought?"
1838 — Michael Faraday uses Volta's battery
to discover cathode rays.
1839 — Alexandre Edmond Becquerel observes
the photoelectric effect with an electrode
in a conductive solution exposed to light.
1840 — James Prescott Joule formulates Joule's
Law (sometimes called the Joule-Lenz law)
quantifying the amount of heat produced in
a circuit as proportional to the product of
the time duration, the resistance, and the
square of the current passing through it.
1845 — Michael Faraday discovers that light
propagation in a material can be influenced
by external magnetic fields (Faraday effect)
1849 — Hippolyte Fizeau and Jean-Bernard
Foucault measure the speed of light to be
about 298,000 km/s
=== 1851-1900 ===
1852 — George Gabriel Stokes defines the
Stokes parameters of polarization
1852 — Edward Frankland develops the theory
of chemical valence
1854 — Gustav Robert Kirchhoff, physicist
and one of the founders of spectroscopy, publishes
Kirchhoff's Laws on the conservation of electric
charge and energy, which are used to determine
currents in each branch of a circuit.
1855 — James Clerk Maxwell submits On Faraday's
Lines of Force for publication containing
a mathematical statement of Ampère's circuital
law relating the curl of a magnetic field
to the electrical current at a point.
1861 — the first transcontinental telegraph
system spans North America by connecting an
existing network in the eastern United States
to a small network in California by a link
between Omaha and Carson City via Salt Lake
City. The slower Pony Express system ceased
operation a month later.
1864 — James Clerk Maxwell publishes his
papers on a dynamical theory of the electromagnetic
field
1865 — James Clerk Maxwell publishes his
landmark paper A Dynamical Theory of the Electromagnetic
Field, in which Maxwell's equations demonstrated
that electric and magnetic forces are two
complementary aspects of electromagnetism.
He shows that the associated complementary
electric and magnetic fields of electromagnetism
travel through space, in the form of waves,
at a constant velocity of 3.0 × 108 m/s.
He also proposes that light is a form of electromagnetic
radiation and that waves of oscillating electric
and magnetic fields travel through empty space
at a speed that could be predicted from simple
electrical experiments. Using available data,
he obtains a velocity of 310,740,000 m/s and
states "This velocity is so nearly that of
light, that it seems we have strong reason
to conclude that light itself (including radiant
heat, and other radiations if any) is an electromagnetic
disturbance in the form of waves propagated
through the electromagnetic field according
to electromagnetic laws."
1866 — the first successful transatlantic
telegraph system was completed. Earlier submarine
cable transatlantic cables installed in 1857
and 1858 failed after operating for a few
days or weeks.
1869 — William Crookes invents the Crookes
tube.
1873 — Willoughby Smith discovers the photoelectric
effect in metals not in solution (i.e., selenium).
1871 — Lord Rayleigh discusses the blue
sky law and sunsets (Rayleigh scattering)
1873 — J. C. Maxwell publishes A Treatise
on Electricity and Magnetism which states
that light is an electromagnetic phenomenon.
1874 — German scientist Karl Ferdinand Braun
discovers the "unilateral conduction" of crystals.
Braun patents the first solid state diode,
a crystal rectifier, in 1899.
1875 — John Kerr discovers the electrically
induced birefringence of some liquids
1878 — Thomas Edison, following work on
a "multiplex telegraph" system and the phonograph,
invents an improved incandescent light bulb.
This was not the first electric light bulb
but the first commercially practical incandescent
light. In 1879 he produces a high-resistance
lamp in a very high vacuum; the lamp lasts
hundreds of hours. While the earlier inventors
had produced electric lighting in lab conditions,
Edison concentrated on commercial application
and was able to sell the concept to homes
and businesses by mass-producing relatively
long-lasting light bulbs and creating a complete
system for the generation and distribution
of electricity.
1879 — Jožef Stefan discovers the Stefan-Boltzmann
radiation law of a black body and uses it
to calculate the first sensible value of the
temperature of the Sun's surface to be 5700
K
1880 — Edison discovers thermionic emission
or the Edison effect.
1882 — Edison switches on the world's first
electrical power distribution system, providing
110 volts direct current (DC) to 59 customers.
1884 — Oliver Heaviside reformulates Maxwell's
original mathematical treatment of electromagnetic
theory from twenty equations in twenty unknowns
into four simple equations in four unknowns
(the modern vector form of Maxwell's equations).
1886 — Oliver Heaviside coins the term inductance.
1887 — Heinrich Hertz invents a device for
the production and reception of electromagnetic
(EM) radio waves. His receiver consists of
a coil with a spark gap.
1888 — Introduction of the induction motor,
an electric motor that harnesses a rotating
magnetic field produced by alternating current,
independently invented by Galileo Ferraris
and Nikola Tesla.
1888 — Heinrich Hertz demonstrates the existence
of electromagnetic waves by building an apparatus
that produced and detected UHF radio waves
(or microwaves in the UHF region). He also
found that radio waves could be transmitted
through different types of materials and were
reflected by others, the key to radar. His
experiments explain reflection, refraction,
polarization, interference, and velocity of
electromagnetic waves.
1893 — Victor Schumann discovers the vacuum
ultraviolet spectrum.
1895 — Wilhelm Conrad Röntgen discovers
X-rays
1895 — Jagadis Chandra Bose gives his first
public demonstration of electromagnetic waves
1896 — Arnold Sommerfeld solves the half-plane
diffraction problem
1897 — J. J. Thomson discovers the electron.
1899 — Pyotr Lebedev measures the pressure
of light on a solid body.
1900 — The Liénard–Wiechert potentials
are introduced as time-dependent (retarded)
electrodynamic potentials
1900 — Max Planck resolves the ultraviolet
catastrophe by suggesting that black body
radiation consists of discrete packets, or
quanta, of energy. The amount of energy in
each packet is proportional to the frequency
of the electromagnetic waves. The constant
of proportionality is now called Planck's
constant in his honor.
== 20th century ==
1904 — John Ambrose Fleming invents the
thermionic diode, the first electronic vacuum
tube, which had practical use in early radio
receivers.
1905 — Albert Einstein proposes the Theory
of Special Relativity, in which he rejects
the existence of the aether as unnecessary
for explaining the propagation of electromagnetic
waves. Instead, Einstein asserts as a postulate
that the speed of light is constant in all
inertial frames of reference, and goes on
to demonstrate a number of revolutionary (and
highly counter-intuitive) consequences, including
time dilation, length contraction, the relativity
of simultaneity, the dependence of mass on
velocity, and the equivalence of mass and
energy.
1905 — Einstein explains the photoelectric
effect by extending Planck's idea of light
quanta, or photons, to the absorption and
emission of photoelectrons. Einstein would
later receive the Nobel Prize in Physics for
this discovery, which launched the quantum
revolution in physics.
1911 — Superconductivity is discovered by
Heike Kamerlingh Onnes, who was studying the
resistivity of solid mercury at cryogenic
temperatures using the recently discovered
liquid helium as a refrigerant. At the temperature
of 4.2 K, he observed that the resistivity
abruptly disappeared. For this discovery,
he was awarded the Nobel Prize in Physics
in 1913.
1919 — Albert A. Michelson makes the first
interferometric measurements of stellar diameters
at Mount Wilson Observatory (see history of
astronomical interferometry)
1924 — Louis de Broglie postulates the wave
nature of electrons and suggests that all
matter has wave properties.
1946 — Martin Ryle and Vonberg build the
first two-element astronomical radio interferometer
(see history of astronomical interferometry)
1953 — Charles H. Townes, James P. Gordon,
and Herbert J. Zeiger produce the first maser
1956 — R. Hanbury-Brown and R.Q. Twiss complete
the correlation interferometer
1960 — Theodore Maiman produces the first
working laser
1966 — Jefimenko introduces time-dependent
(retarded) generalizations of Coulomb's law
and the Biot-Savart law
1999 — M. Henny and others demonstrate the
Fermionic Hanbury Brown and Twiss Experiment
== 
See also ==
History of electromagnetic theory
History of special relativity
History of superconductivity
Timeline of luminiferous aether
== Notes and References ==
== 
Further reading and external links ==
Media related to Electromagnetism at Wikimedia
Commons
The Natural History Pliny the Elder, The Natural
History from Perseus Digital Library
The Discovery of the Electron from the American
Institute of Physics
Enterprise and electrolysis... from the Royal
Society of Chemistry (chemsoc)
Pure Science-History, Worldwide School
== 
External links ==
The Work of Jagadis Chandra Bose: 100 Years
of MM-Wave Research
Jagadis Chandra Bose and His Pioneering Research
on Microwaves
