Depite what you have learned, Benjamin Franklin did not "invent" electricity. In fact, electricity did not begin when Benjamin Franklin at when he flew his kite during a thunderstorm or when light bulbs were installed in houses all around the world.
The truth is that electricity has always been around because it naturally exists in the world. Lightning, for instance, is simply a flow of electrons between the ground and the clouds. When you touch something and get a shock, that is really static electricity moving toward you.
Hence, electrical equipment like motors, light bulbs, and batteries aren't needed for electricity to exist. They are just creative inventions designed to harness and use electricity.
The first discoveries of electricity were made back in ancient Greece. Greek philosophers discovered that when amber is rubbed against cloth, lightweight objects will stick to it. This is the basis of static electricity.
Over the centuries, there have been many discoveries made about electricity. We've all heard of famous people like Benjamin Franklin and Thomas Edison, but there have been many other inventors throughout history that were each a part in the development of electricity.
Franklin was an American writer, publisher, scientist and diplomat, who helped to draw up the famous Declaration of Independence and the US Constitution. In 1752 Franklin proved that lightning and the spark from amber were one and the same thing. The story of this famous milestone is a familiar one, in which Franklin fastened an iron spike to a silken kite, which he flew during a thunderstorm, while holding the end of the kite string by an iron key. When lightening flashed, a tiny spark jumped from the key to his wrist. The experiment proved Franklin's theory, but was extremely dangerous - He could easily have been killed.
Galvani and Volta
In 1786, Luigi Galvani, an Italian professor of medicine, found that when the leg of a dead frog was touched by a metal knife, the leg twitched violently. Galvani thought that the muscles of the frog must contain electricity. By 1792 another Italian scientist, Alessandro Volta, disagreed: he realised that the main factors in Galvani's discovery were the two different metals - the steel knife and the tin plate - apon which the frog was lying. Volta showed that when moisture comes between two different metals, electricity is created. This led him to invent the first electric battery, the voltaic pile, which he made from thin sheets of copper and zinc separated by moist pasteboard.
In this way, a new kind of electricity was discovered, electricity that flowed steadily like a current of water instead of discharging itself in a single spark or shock. Volta showed that electricity could be made to travel from one place to another by wire, thereby making an important contribution to the science of electricity. The unit of electrical potential, the Volt, is named after Volta.
The credit for generating electric current on a practical scale goes to the famous English scientist, Michael Faraday. Faraday was greatly interested in the invention of the electromagnet, but his brilliant mind took earlier experiments still further. If electricity could produce magnetism, why couldn't magnetism produce electricity.
In 1831, Faraday found the solution. Electricity could be produced through magnetism by motion. He discovered that when a magnet was moved inside a coil of copper wire, a tiny electric current flows through the wire. Of course, by today's standards, Faraday's electric dynamo or electric generator was crude, and provided only a small electric current be he discovered the first method of generating electricity by means of motion in a magnetic field.
Thomas Edison and Joseph Swan
Nearly 40 years went by before a really practical DC (Direct Current) generator was built by Thomas Edison in America. Edison's many inventions included the phonograph and an improved printing telegraph. In 1878 Joseph Swan, a British scientist, invented the incandescent filament lamp and within twelve months Edison made a similar discovery in America.
Swan and Edison later set up a joint company to produce the first practical filament lamp. Prior to this, electric lighting had been my crude arc lamps.
Edison used his DC generator to provide electricity to light his laboratory and later to illuminate the first New York street to be lit by electric lamps, in September 1882. Edison's successes were not without controversy, however - although he was convinced of the merits of DC for generating electricity, other scientists in Europe and America recognised that DC brought major disadvantages.
George Westinghouse and Nikola Tesla
Westinghouse was a famous American inventor and industrialist who purchased and developed Nikola Tesla's patented motor for generating alternating current. The work of Westinghouse, Tesla and others gradually persuaded American society that the future lay with AC rather than DC (Adoption of AC generation enabled the transmission of large blocks of electrical, power using higher voltages via transformers, which would have been impossible otherwise). Today the unit of measurement for magnetic fields commemorates Tesla's name.
When Edison's generator was coupled with Watt's steam engine, large scale electricity generation became a practical proposition. James Watt, the Scottish inventor of the steam condensing engine, was born in 1736. His improvements to steam engines were patented over a period of 15 years, starting in 1769 and his name was given to the electric unit of power, the Watt.
Watt's engines used the reciprocating piston, however, today's thermal power stations use steam turbines, following the Rankine cycle, worked out by another famous Scottish engineer, William J.M Rankine, in 1859.
Andre Ampere and George Ohm
Andre Marie Ampere, a French mathematician who devoted himself to the study of electricity and magnetism, was the first to explain the electro-dynamic theory. A permanent memorial to Ampere is the use of his name for the unit of electric current.
George Simon Ohm, a German mathematician and physicist, was a college teacher in Cologne when in 1827 he published, "The galvanic Circuit Investigated Mathematically". His theories were coldly received by German scientists but his research was recognised in Britain and he was awarded the Copley Medal in 1841. His name has been given to the unit of electrical resistance.
900 BC - Magnus,
a Greek shepherd, walks across a field of
black stones which pull the iron nails out of his sandals
and the iron tip from his shepherd's staff (authenticity
This region becomes known as Magnesia.
600 BC - Thales of Miletos
rubs amber (elektron in Greek) with
cat fur and picks up bits of feathers.
1269 - Petrus Peregrinus
of Picardy, Italy, discovers that
natural spherical magnets (lodestones) align needles with lines of longitude
pointing between two pole positions on the stone.
1600 - William Gilbert,
court physician to Queen Elizabeth, discovers
that the earth is a giant magnet just like one of the stones of
how compasses work.
He also discusses static electricity and invents an electric
fluid which is liberated by rubbing.
ca. 1620 - Niccolo Cabeo
discovers that electricity can be repulsive
as well as attractive.
1630 - Vincenzo Cascariolo,
a Bolognese shoemaker, discovers
1638 - Rene Descartes
theorizes that light is a pressure wave through
the second of his three types of matter of which the universe is made.
He invents properties of this fluid that make it possible to
calculate the reflection and refraction of light.
The ``modern'' notion of the aether is born.
1638 - Galileo
attempts to measure the speed of light by
a lantern relay between distant hilltops.
He gets a very large answer.
1644 - Rene Descartes
theorizes that the magnetic poles are
on the central axis of a spinning vortex of one of his fluids.
This vortex theory remains popular for a long time, enabling
Leonhard Euler and two of the Bernoullis to share a prize of
the French Academy as late as 1743.
1657 - Pierre de Fermat
shows that the principle of least time
is capable of explaining refraction and reflection of light.
Fighting with the Cartesians begins.
(This principle for reflected light had been anticipated
anciently by Hero of Alexandria.)
1665 - Francesco Maria Grimaldi,
in a posthumous report, discovers
and gives the name of diffraction to the bending of light
around opaque bodies.
1667 - Robert Hooke
reports in his Micrographia
the discovery of the rings of light formed
by a layer of air between two glass plates.
These were actually first observed by Robert Boyle, which explains
why they are now called
In the same work he gives the matching-wave-front
derivation of reflection and refraction that is
still found in most introductory physics texts.
These waves travel through the aether.
He also develops a theory of color in which
white light is a simple disturbance and
colors are complex distortions of the basic simple
1671 - Isaac Newton
destroys Hooke's theory of color by
experimenting with prisms to show
that white light is a mixture of all the colors and that
once a pure color is obtained it can never be changed into
Newton argues against light being a vibration of the
ether, preferring that it be something else that is
capable of traveling through the aether.
He doesn't insist that this something else consist
of particles, but allows that it may be some other
kind of emanation or impulse.
In Newton's own words, ``...let every man here take his fancy.''
1675 - Olaf Roemer
repeats Galileo's experiment using the
moons of Jupiter as the distant hilltop.
He measures m/s.
1678 - Christiaan Huygens
introduces his famous construction
and principle, thinks about translating his manuscript into
Latin, then publishes it in the original French in 1690.
He uses his theory to discuss the double refraction of Iceland Spar.
His is a theory of pulses, however, not of periodic waves.
1717 - Newton
shows that the ``two-ness'' of double refraction clearly rules
out light being aether waves.
(All aether wave theories were sound-like, so Newton was right;
longitudinal waves can't be polarized.)
1728 - James Bradley
shows that the orbital motion of the earth
changes the apparent motions of the stars in a way that is consistent
with light having a finite speed of travel.
1729 - Stephen Gray
shows that electricity doesn't have to
be made in place by rubbing but can also be transferred
from place to place with
He also shows that the charge on electrified objects resides
on their surfaces.
1733 - Charles Francois du Fay
discovers that electricity comes
in two kinds which he called resinous(-) and vitreous(+).
1742 - Thomas Le Seur and Francis Jacquier,
in a note to the
edition of Newton's Principia that they publish, show
that the force law between two magnets is inverse cube.
1749 - Abbe Jean-Antoine Nollet
invents the two-fluid
1745 - Pieter van Musschenbroek
invents the Leyden jar,
or capacitor, and nearly kills his friend Cunaeus.
1747 - Benjamin Franklin
invents the theory of one-fluid
electricity in which one of Nollet's fluids exists and the
other is just the absence of the first.
He proposes the principle of
conservation of charge and calls
the fluid that exists and flows
educated guess ensures
that undergraduates will always be confused about
the direction of current flow.
He also discovers that electricity can act at a distance
in situations where fluid flow makes no sense.
1748 - Sir William Watson
uses an electrostatic machine
and a vacuum pump to make the first glow discharge.
His glass vessel is
three feet long and three inches in diameter:
the first fluorescent light bulb.
1750 - John Michell
discovers that the two poles of a magnet
are equal in strength and that the force law for
individual poles is inverse square.
1752 - Johann Sulzer
puts lead and silver together in his
mouth, performing the first recorded ``tongue test'' of a battery.
1759 - Francis Ulrich Theodore Aepinus
shows that electrical
effects are a
combination of fluid flow confined to matter and
action at a distance.
He also discovers charging by induction.
1762 - Canton
reports that a red hot poker placed close
to a small electrified body destroys its electrification.
1764 - Joseph Louis Lagrange
discovers the divergence
theorem in connection with the study of gravitation.
It later becomes known as Gauss's law. (See 1813).
1766 - Joseph Priestly,
acting on a suggestion in
a letter from Benjamin Franklin, shows that hollow
charged vessels contain no charge on the inside and
based on his knowledge that hollow shells of mass
have no gravity inside correctly deduces that
the electric force law is inverse square.
ca 1775 - Henry Cavendish
invents the idea of
capacitance and resistance (the latter without
any way of measuring current other than the level of
But being indifferent to fame he is content to wait for his
work to be published by Lord Kelvin in 1879.
1777 - Joseph Louis Lagrange
invents the concept of the scalar
potential for gravitational fields.
1780 - Luigi Galvani
causes dead frog legs to twitch with
static electricity, then also discovers that the same twitching
can be caused by contact with dissimilar metals.
His followers invent another invisible
fluid, that of ``animal electricity'',
to describe this effect.
1782 - Pierre Simon Laplace
shows that Lagrange's potential
1785 - Charles Augustin Coulomb
uses a torsion balance to
verify that the electric force law is inverse square.
He also proposes a combined fluid/action-at-a-distance theory
like that of Aepinus but with
two conducting fluids instead of one.
Fighting breaks out between
single and double fluid partisans.
He also discovers that the electric force near a conductor is
proportional to its surface charge density and
makes contributions to the two-fluid theory of magnetism.
1793 - Alessandro Volta
makes the first batteries
and argues that animal electricity is just ordinary electricity
flowing through the frog legs under the impetus of the
force produced by the contact of dissimilar metals.
He discovers the importance of ``completing the circuit.''
In 1800 he discovers the Voltaic pile (dissimilar metals
separated by wet cardboard)
which greatly increases
the magnitude of the effect.
1800 - William Nicholson and Anthony Carlisle
water may be separated into hydrogen and oxygen by the
action of Volta's pile.
1801 - Thomas Young
gives a theory of Newton's rings based
on constructive and destructive interference of waves.
He explains the dark spot in the middle by proposing that
there is a phase shift on reflection between a less dense
and more dense medium, then uses essence of sassafras
(whose index of refraction is intermediate between
those of crown and flint glass) to get a light
spot at the center.
1803 - Thomas Young
explains the fringes at the edges
by means of the wave theory of light.
The wave theory begins its ascendance, but has one
important difficulty: light is thought of as a
longitudinal wave, which makes it difficult to
explain double refraction effects in certain crystals.
1807 - Humphrey Davy
shows that the essential element of
Volta's pile is chemical action since pure water gives
He argues that chemical effects are electrical in nature.
1808 - Laplace
gives an explanation of double refraction
using the particle theory, which Young attacks as
1808 - Etienne Louis Malus,
a military engineer,
enters a prize competition sponsored by
the French Academy
``To furnish a mathematical theory of double refraction,
and to confirm it by experiment.''
He discovers that light reflected at certain
angles from transparent substances as well as the separate
rays from a double-refracting crystal have the same
property of polarization.
In 1810 he receives the prize and emboldens the proponents
of the particle theory of light because no one sees how
a wave theory can make waves of different polarizations.
1811 - Arago
shows that some crystals alter the polarization
of light passing through them.
1812 - Biot
shows that Arago's crystals rotate the plane
of polarization about the propagation direction.
1812 - Simeon Denis Poisson
further develops the two-fluid theory
of electricity, showing that the charge on conductors must
reside on their surfaces and be so distributed that the electric force
within the conductor vanishes.
This surface charge density calculation is carried out in detail for
He also shows that the potential within a distribution of electricity
satisfies the equation.
1812 - Michael Faraday,
a bookbinders apprentice,
writes to Sir Humphrey Davy asking
for a job as a scientific assistant.
Davy interviews Faraday and finds that he has educated himself
by reading the books he was supposed to be binding.
He gets the job.
ca. 1813 - Laplace
shows that at the surface of a conductor
the electric force is perpendicular to the surface.
1813 - Karl Friedrich Gauss
rediscovers the divergence theorem
It will later become known as Gauss's law.
1815 - David Brewster
establishes his law of complete
polarization upon reflection at a special angle
now known as Brewster's angle.
He also discovers that in addition of uniaxial cystals
there are also biaxial ones.
For uniaxial crystals there is the faint possibility of a
wave theory of longitudinal-type, but this appears
to be impossible for biaxial ones.
1816 - David Brewster
invents the kaleidoscope.
1816 - Francois Arago,
an associate of Augustin Fresnel,
visits Thomas Young and describes to him a series of
experiments performed by Fresnel and himself which shows
that light of differing polarizations cannot interfere.
Reflecting later on this curious effect Young sees that
it can be explained if light is transverse instead of
This idea is communicated to Fresnel in 1818 and he
immediately sees how it clears up many of the remaining
difficulties of the wave theory.
Six years later the particle theory is dead.
1817 - Augustin Fresnel
annoys the French Academy.
The Academy, hoping to destroy the wave
theory once and for all, proposes diffraction
as the prize subject for 1818.
To the chagrin of the particle-theory partisans
in the Academy the winning memoir in 1818 is that of
Augustin Fresnel who explains diffraction as the mutual
interference of the secondary waves emitted by the
unblocked portions of the incident wave, in the style
One of the judges from the particle camp of
the Academy is Poisson, who points out
that if Fresnel's theory were to be indeed correct, then there should be
a bright spot at the center of the shadow of a circular
This, he suggests to Fresnel, must be
The experiment doesn't go as Poisson hopes, however,
and the spot becomes known as ``Poisson's spot.''
1820 - Hans Christian Oersted
discovers that electric current
in a wire causes a compass needle to orient itself perpendicular
to the wire.
1820 - Andre Marie Ampere,
one week after hearing of Oersted's
discovery, shows that parallel currents attract each other and
that opposite currents attract.
1820 - Jean-Baptiste Biot and Felix Savart
show that the
magnetic force exerted on a magnetic pole by a wire falls off like 1/r
and is oriented perpendicular to the wire.
Whittaker then says that ``This result was soon further analyzed,''
1820 - John Herschel
shows that quartz
samples that rotate the plane of polarization of light in opposite
directions have different crystalline forms.
This difference is helical in nature.
1821 - Faraday
begins electrical work by repeating Oersted's
1821 - Humphrey Davy
shows that direct current is carried throughout
the volume of a conductor and establishes that
for long wires.
He also discovers that resistance is increased as the
1822 - Thomas Johann Seebeck
discovers the thermoelectric effect
by showing that a current will flow in a circuit made of dissimilar
metals if there is a temperature difference between the metals.
1824 - Poisson
invents the concept of the magnetic scalar potential
and of surface and volume pole densities
described by the formulas.
He also finds the magnetic field inside a spherical
cavity within magnetized material.
1825 - Ampere
publishes his collected results on magnetism.
His expression for the magnetic field produced by a small
segment of current is different from that which follows naturally
from the Biot-Savart law by an additive term which integrates
to zero around closed circuit.
It is unfortunate that electrodynamics and relativity decide in favor
of Biot and Savart rather than for the much more sophisticated Ampere,
memoir contains both mathematical analysis and experimentation,
artfully blended together.
In this memoir are given some special instances of
the result we now call Stokes theorem
or as we usually write it.
Maxwell describes this work as ``one of the most brilliant
achievements in science. The whole, theory and experiment,
seems as if it had leaped, full-grown and full-armed, from the
brain of the `Newton of electricity'.
It is perfect in form and unassailable in accuracy; and it is summed
up in a formula from which all the phenomena may be deduced, and
which must always remain the cardinal formula of electrodynamics.''
1825 - Fresnel
shows that combinations of waves of opposite
circular polarization traveling at different speeds can
account for the rotation of the plane of polarization.
1826 - Georg Simon Ohm
establishes the result now known
as Ohm's law.
V=IR seems a pretty simple law to name after someone,
but the importance of Ohm's work does not lie in this
What Ohm did was develop the idea of voltage as the
driver of electric current.
He reasoned by making an analogy between Fourier's
theory of heat flow and electricity.
In his scheme
and voltage correspond as do
heat flow and electrical current.
It was not until some years later that Ohm's
electroscopic force (V in his law)
and Poisson's electrostatic potential were shown
to be identical.
1827 - Augustin Fresnel
publishes a decade of research in
the wave theory of light.
Included in these collected papers are explanations
of diffraction effects, polarization effects,
double refraction, and Fresnel's sine and tangent laws
for reflection at the interface between two transparent
1827 - Claude Louis Marie Henri Navier
publishes the correct
equations for vibratory motions in one type of
elastic solid. This begins the quest for a detailed
mathematical theory of the aether based on the equations
of continuum mechanics.
1827 - F. Savery,
after noticing that the current from
a Leyden jar magnetizes needles in alternating layers,
conjectures that the electric motion during the discharge
consists of a series of oscillations.
1828 - George Green
generalizes and extends the work of
Lagrange, Laplace, and Poisson and attaches the name
potential to their scalar function.
Green's theorems are given, as well as the divergence
theorem (Gauss's law), but Green doesn't know of the
work of Lagrange and Gauss and only references
Priestly's deduction of the inverse square law from
Franklin's experimental work on the charging of
1828 - Augustine Louis Cauchy
presents a theory
similar to Navier's, but based on a direct study
of elastic properties rather than using a molecular
hypothesis. These equations are more general
In Cauchy's theory, and in much of what follows,
the aether is supposed to have the same inertia
in each medium, but different elastic properties.
1828 - Poisson
shows that the equations of Navier
and Cauchy have wave solutions of two types: transverse
and longitudinal. Mathematical physicists spend the
next 50 years trying to invent an elastic aether for
which the longitudinal waves are absent.
1831 - Faraday
shows that changing currents in one
circuit induce currents in a neighboring circuit.
Over the next several years he performs hundreds of
experments and shows that they can all be explained
by the idea of changing magnetic flux.
No mathematics is involved, just picture thinking
using his field-lines.
1831 - Ostrogradsky
rediscovers the divergence
theorem of Lagrange, Gauss, and Green.
1832 - Joseph Henry
1833 - Faraday
begins work on the relation of
electricity to chemistry.
In one of his notebooks he concludes after a series
of experiments, ``...there is a certain absolute
quantity of the electric power associated with each
atom of matter.''
1834 - Faraday
discovers self inductance.
1834 - Jean Charles Peltier
discovers the flip side
of Seebeck's thermoelectric effect.
He finds that current driven in a circuit made of
dissimilar metals causes the different metals to be
at different temperatures.
1834 - Emil Lenz
formulates his rule for determining
the direction of Faraday's induced currents.
In its original form it was a force law rather
than an induced emf law: ``Induced currents flow
in such a direction as to produce magnetic forces
that try to keep the magnetic flux the same.''
So Lenz would predict that if you try to push
a conductor into a strong magnetic field,
it will be repelled.
He would also predict that if you try to pull a
conductor out of a strong magnetic field that
the magnetic forces on the induced currents will
oppose the pull.
1835 - James MacCullagh and Franz Neumann
Cauchy's theory to crystalline media
1837 - Faraday
discovers the idea of the
1837 - George Green
attacks the elastic aether problem
from a new angle. Instead of deriving boundary conditions
between different media by finding which ones give
agreement with the experimental laws of optics, he derives
the correct boundary conditions from general dynamical
principles. This advance makes the elastic theories not
quite fit with light.
1838 - Faraday
shows that the effects of induced
electricity in insulators are analogous to
induced magnetism in magnetic materials.
Those more mathematically inclined immediately
appropriate Poisson's theory of induced
1838 - Faraday
discovers Faraday's dark space, a dark
region in a glow discharge near the negative electrode.
1839 - James MacCullagh
invents an elastic aether
in which there are no longitudinal waves. In this
aether the potential energy of deformation depends
only on the rotation of the volume elements and
not on their compression or general distortion.
This theory gives the same wave equation as that
satisfied by in Maxwell's
1839 - William Thomson (Lord Kelvin)
removes some of the
objections to MacCullagh's rotation theory by inventing a
mechanical model which satisfies MacCullagh's energy of
rotation hypothesis. It has spheres, rigid bars, sliding
contacts, and flywheels.
1839 - Cauchy and Green
present more refined elastic
aether theories, Cauchy's removing the longitudinal
waves by postulating a negative compressibility, and
Green's using an involved description of crystalline
1841 - Michael Faraday
is completely exhausted by his
efforts of the previous 2 decades, so he rests for 4 years.
1841 - James Prescott Joule
shows that energy is conserved
in electrical circuits involving current flow, thermal
heating, and chemical transformations.
1842 - F. Neumann and Matthew O'Brien
optical properties in materials arise from differences
in the amount of force that the particles of matter exert
on the aether as it flows around and between them.
1842 - Julius Robert Mayer
asserts that heat and work
His paper is rejected by Annalen der Physik.
1842 - Joseph Henry
rediscovers the result of F. Savery
about the oscillation of the electric current in a
capacitive discharge and states, ``The phenomena require us
to admit the existence of a principal discharge in one direction,
and then several reflex actions backward and forward, each
more feeble than the preceding, until equilibrium is
1842 - Christian Doppler
gives the theory of the Doppler effect.
1845 - Faraday
quits resting and
discovers that the plane of polarization
of light is rotated when it travels in glass along the
direction of the magnetic lines of force produced by
an electromagnet (Faraday rotation).
1845 - Franz Neumann
uses (i) Lenz's law, (ii) the assumption
that the induced emf is proportional to the magnetic force
on a current element, and (iii) Ampere's analysis
to deduce Faraday's law.
In the process he finds a potential function from which
the induced electric field can be obtained, namely the vector potential
(in the Coulomb gauge), thus discovering the
result which Maxwell wrote.
1846 - George Airy
modifies MacCullagh's elastic aether theory to
account for Faraday rotation.
1846 - Faraday, inspired by his discovery of the magnetic
rotation of light,
writes a short paper speculating that
light might electro-magnetic in nature.
He thinks it might be transverse vibrations of
his beloved field lines.
1846 - Faraday
He sees the effect in heavy glass, bismuth, and
1846 - Wilhelm Weber
combines Ampere's analysis,
Faraday's experiments, and the assumption of
Fechner that currents consist of equal amounts
of positive and negative electricity moving opposite
to each other at the same speed to derive an electromagnetic
theory based on forces between moving charged particles.
This theory has a velocity-dependent potential energy
and is wrong, but it stimulates much work on
electromagnetic theory which eventually leads to the
work of Maxwell and Lorenz.
It also inspires a new look at gravitation by
to see if
a velocity-dependent correction to the gravitational
energy could account for the precession of Mercury's
1846 - William Thomson
shows that Neumann's electromagnetic
potential is in fact the vector potential
from which may be obtained.
1847 - Weber
proposes that diamagnetism is just Faraday's
law acting on molecular circuits.
In answering the objection that this would mean that
everything should be diamagnetic he correctly guesses that
diamagnetism is masked in paramagnetic and ferromagnetic
materials because they have relatively strong permanent
This work rids the world of magnetic fluids.
1847 - Hermann von Helmholtz
writes a memoir ``On the
Conservation of Force'' which emphatically states the
principle of conservation of energy: ``Conservation of energy
is a universal principle of nature. Kinetic and potential
energy of dynamical systems may be converted into heat
according to definite quantitative laws as taught by
Rumford, Mayer, and Joule.
Any of these forms of energy may be converted into
chemical, electrostatic, voltaic, and magnetic forms.''
He reads it before the Physical Society of Berlin whose
older members regard it as too speculative and reject it
for publication in Annalen der Physik.
1848-9 - Gustav Kirchoff
extends Ohm's work to
conduction in three dimensions, gives his laws for
circuit networks, and finally shows that Ohm's
``electroscopic force'' which drives current through
resistors and the old electrostatic potential of Lagrange,
Laplace, and Poisson are the same.
He also shows that in steady state electrical currents
distribute themselves so as to minimize the amount of
1849 - A. Fizeau
repeats Galileo's hilltop experiment
(9 km separation distance) with a rapidly rotating toothed
wheel and measures m/s.
1849 - George Gabriel Stokes
studies diffraction around
opaque bodies both theoretically and experimentally and
shows that the vibration of aether particles are executed
at right angles to the plane of polarization.
Three years later he comes to the same conclusion by applying
aether theory to light scattered from the sky.
This result is, however, inconsistent with optics in crystals.
ca. 1850 - Stokes
overcomes some of the difficulties
with crystals by turning Cauchy's hypothesis around and
letting the elastic properties of the aether be the
same in all materials, but allowing the inertia to
differ. This gives rise to the conceptual difficulty of having
the inertia be different in different directions
(in anisotropic crystals).
ca. 1850 - Jean Foucault improves on Fizeau's measurement
and uses his apparatus to show that the speed of light is
less in water than in air.
1850 - Stokes
law is stated
without proof by Lord Kelvin (William Thomson).
Later Stokes assigns the proof of this theorem as
part of the examination for the Smith's Prize.
Presumably, he knows how to do the problem.
Maxwell, who was a candidate for this prize, later
remembers this problem, traces it back to Stokes and
calls it Stokes theorem.
1850 - William Thomson (Lord Kelvin)
invents the idea of
magnetic permeability and susceptibility, along with
the separate concepts.
1851 - Thomson
gives a general theory of thermoelectric
phenomena, describing the effects seen by Seebeck and Peltier.
1853 - Thomson
uses Poisson's magnetic theory to derive
the correct formula for magnetic energy:
He also gives the formula and gives the world
the powerful, but confusing, analysis where the forces on
circuits are obtained by taking either the positive or
negative gradient of the magnetic energy.
Knowing which sign to use is, of course, the confusing
1853 - Thomson
gives the theory of the RLC circuit providing
a mathematical description for the observations of Henry and
1854 - Faraday
clears up the problem of disagreements
in the measured speeds of signals along transmission lines
by showing that it is crucial to include the effect of
1854 - Thomson,
in a letter to Stokes, gives the
equation of telegraphy ignoring the inductance:
where R is the cable resistance and where C is the
capacitance per unit length.
Since this is the diffusion equation, the signal does not travel
at a definite speed.
1855 - Faraday
retires, living quietly in a house provided
by the Queen until his death in 1867.
1855 - James Clerk Maxwell
writes a memoir in which he attempts
to marry Faraday's intuitive field line ideas with Thomson's
In this memoir the physical importance of the divergence and
curl operators for electromagnetism first become evident.
1857 - Gustav Kirchoff
derives the equation of telegraphy
for an aerial coaxial cable where the inductance is
important and derives the full telegraphy equation:
where L and C are the inductance per unit
length and the capacitance
per unit length.
He recognizes that when the resistance is small, this
is the wave equation with propagation speed,
which for a coaxial cable turns out to be very close to the
speed of light.
Kirchoff notices the coincidence, and is thus the first to
discover that electromagnetic signals can travel at the speed of
1861 - Bernhard Riemann
develops a variant of Weber's
electromagnetic theory which is also wrong.
1861 - Maxwell
publishes a mechanical model of the
Magnetic fields correspond to rotating vortices with
idle wheels between them and electric fields correspond
to elastic displacements, hence displacement currents.
This addition completes Maxwell's equations and it is now
easy for him to derive the wave equation exactly as done
in our textbooks on electromagnetism and to note that
the speed of wave propagation was close to the measured
speed of light.
Maxwell writes, ``We can scarcely avoid the inference
that light in the transverse undulations of the same
medium which is the cause of electric and magnetic
Thomson, on the other hand, says of the displacement
current, ``(it is a) curious and ingenious, but not
wholly tenable hypothesis.''
1864 - Maxwell
reads a memoir before the Royal Society
in which the mechanical model is stripped away and
just the equations remain. He also discusses the
vector and scalar potentials, using the Coulomb gauge.
He attributes physical significance to both of these
He wants to present the predictions of his theory on
the subjects of reflection and refraction, but
the requirements of his mechanical model keep him
from finding the correct boundary conditions, so
he never does this calculation.
1867 - Stokes
performs experiments that kill his own
anisotropic inertia theory.
1867 - Joseph Boussinesq
instead of aether being different in different media,
perhaps the aether is the same everywhere, but it
interacts differently with different materials, similar to
the modern electromagnetic wave theory.
1867 - Riemann
proposes a simple electric theory
of light in which Poisson's equation is replaced.
1867 - Ludwig Lorenz
develops an electromagnetic theory
of light in which the scalar and vector potentials,
in retarded form, are the starting point.
He shows that these retarded potentials each satisfy the
wave equation and that Maxwell's equations for the field
His vector potential does not obey the Coulomb gauge,
however, but another relation now known as the Lorenz gauge.
Although he is able to derive Maxwell's equations from his
retarded potentials, he does not subscribe to Maxwell's view
that light involves electromagnetic waves in the aether.
He feels, rather, that the fundamental basis of all luminous
vibrations is electric currents, arguing that space has
enough matter in it to support the necessary currents.
1868 - Maxwell
decides that giving physical significance
to the scalar and vector potentials is a bad idea and bases
his further work on light.
1869 - Maxwell
presents the first calculation in which a
dispersive medium is made up of atoms with natural frequencies.
This makes possible detailed modeling of dispersion with
refractive indices having resonant denominators.
1869 - Hittorf
finds that cathode rays can cast a shadow.
1870 - Helmholtz
derives the correct laws of reflection
and refraction from Maxwell's equations by using the following
boundary condition. Once these boundary conditions are taken Maxwell's theory
is just a repeat of MacCullagh's theory.
The details were not given by Helmholtz himself, but appear
rather in the inaugural dissertation of H. A. Lorentz.
1870-1900 - The hunt is on for physical models of the
aether which are natural and from which Maxwell's equations
can be derived.
The physicists who work on this problem include Maxwell,
Thomson, Kirchoff, Bjerknes, Leahy, Fitz Gerald, Helmholtz,
1872 - E. Mascart
looks for the motion of the earth
through the aether by measuring the rotation of the
plane of polarization of light propagated along the
axis of a quartz crystal.
1873 - Maxwell
publishes his Treatise on Electricity
and Magnetism, which discusses everything known at the time
about electromagnetism from the viewpoint of Faraday.
His own theory is not very thoroughly discussed, but he does
introduce his electromagnetic stress tensor in this work,
including the accompanying idea of electromagnetic momentum.
1875 - John Kerr
shows that ordinary dielectrics subjected
to strong electric fields become double refracting, showing
directly that electric fields and light are closely related.
1876 - Henry Rowland
performs an experiment inspired by
Helmholtz which shows for the first time that moving electric
charge is the same thing as an electric current.
1876 - A. Bartoli
infers the necessity of light pressure
from thermal arguments, thus beginnning the exploration
of the connection between electromagnetism and thermodynamics.
1879 - J. Stefan
discovers the Stefan-Boltzmann law, i.e.,
that radiant emission is proportional.
1879 - Edwin Hall
performs an experiment that had been
suggested by Henry Rowland and discovers the Hall effect,
including its theoretical description
by means of the Hall term in Ohm's law.
1879 - Sir William Crookes
invents the radiometer and studies
the interaction of beams of cathode ray particles in vacuum
1879 - Ludwig Boltzmann
uses Hall's result to estimate
the speed of charge carriers (assuming that
charge carriers are only of one sign.)
1880 - Rowland
shows that Faraday rotation can be obtained
by combining Maxwell's equations and the Hall term in
Ohm's law, assuming that displacement currents are affected
in the same way as conduction currents.
1881 - J. J. Thomson
attempts to verify the existence
of the displacement current by looking for magnetic effects
produced by the changing electric field made by a moving
1881 - George Fitz Gerald
points out that J. J. Thomson's
analysis is incorrect because he left out the effects of the
conduction current of the moving sphere.
Including both currents makes the separate effect of the
displacement current disappear.
1881 - Helmholtz,
in a lecture in London, points out that
the idea of charged particles in atoms can be consistent with
Maxwell's and Faraday's ideas, helping to pave the way for
our modern picture of particles and fields interacting instead
of thinking about everything as a disturbance of the aether,
as was popular after Maxwell.
1881 - Albert Michelson and Edwin Morley
attempt to measure
of the earth through the aether by using interferometry.
They find no relative velocity.
Michelson interprets this result as supporting Stokes
hypothesis in which the aether in the neighborhood of
the earth moves at the earth's velocity.
1883 - Fitz Gerald
proposes testing Maxwell's theory
by using oscillating currents in what we would now call
a magnetic dipole antenna (loop of wire).
He performs the analysis and discovers that very
high frequencies are required to make the test.
Later that year he proposes obtaining the required
high frequencies by discharging a capacitor into
1883-5 - Horace Lamb and Oliver Heaviside
interaction of oscillating electromagnetic fields with
conductors and discover the effect of skin depth.
1884 - John Poynting
shows that Maxwell's equations predict
that energy flows through empty space with the energy
He also investigates energy flow in Faraday fashion
by assigning energy to moving tubes of electric and magnetic
1884 - Heinrich Hertz
asserts that made by
charges and made by a changing magnetic field
Working from dynamical ideas based on this assumption
and some of Maxwell's equations, Hertz is able to derive
the rest of them.
1887 - Svante Arrhenius
deduces that in dilute solutions
electrolytes are completely dissociated into positive and
1887 - Hertz
finds that ultraviolet light falling on the
negative electrode in a spark gap facilitates conduction by the
gas in the gap.
1888 - R. T. Glazebrook
revives one of Cauchy's wave theories
and combines it with Stokes anisotropic aether inertia theory to get
agreement with the experiments of Stokes in 1867.
1888 - Hertz
discovers that oscillating sparks can be produced
in an open secondary circuit if the frequency of the primary
is resonant with the secondary.
He uses this radiator to show that electrical signals are
propagated along wires and through the air at about the
same speed, both about the speed of light.
He also shows that his electric radiations, when passed
through a slit in a screen, exhibit diffraction effects.
Polarization effects using a grating of parallel metal
wires are also observed.
1888 - Roentgen
shows that when an uncharged dielectric
is moved at right angles to a magnetic
field is produced.
1889 - Hertz
gives the theory of radiation from his
oscillating spark gap.
1889 - Oliver Heaviside
finds the correct form for the
electric and magnetic fields of a moving charged
particle, valid for all speeds v < c.
1889 - J. J. Thomson
shows that Canton's effect (1762)
in which a red hot poker can neutralize the electrification
of a small charged body is due to electron emission causing
the air between the poker and the body to become conducting.
1890 - Fitz Gerald
uses the retarded potentials of
L. Lorenz to calculate electric dipole radiation
from Hertz's radiator.
1892 - Oliver Lodge
performs experiments on the propagation of light
near rapidly moving steel disks to test Stokes hypothesis
that moving matter drags the aether with it.
No such effect is observed.
1892 - Hendrik Anton Lorentz
presents his electron theory of
electrified matter and the aether.
This theory combines Maxwell's equations, with the
source terms and with the Lorentz
force law for the acceleration of charged particles:
Lorentz's aether is simply space endowed with certain
Lorentz gives the modern theory of dielectrics
involving and also includes the
effect of magnetized matter.
He also gives what we now call the Drude-Lorentz harmonic
oscillator model of the index of refraction.
But Lorentz's theory has a ``stationary aether'', which
conflicts with the negative Michelson-Morley result.
1892 - George Fitz Gerald
proposes length contraction as
a way to reconcile Lorentz's theory and the null results
on the motion of the earth through the aether.
At the end of this year Lorentz endorses this idea.
1894 - J. J. Thomson
measures the speed of cathode rays
and shows that they travel much more slowly than the speed of
light. The aether model of cathode rays begins to die.
1894 - Philip Lenard
studies the penetration of cathode rays
1895 - Pierre Curie
discovers Curie's law for paramagnetism
and also shows that there is no temperature effect for
1895 - Lorentz,
in his ``Search for a theory of electrical
and optical effects in moving bodies'' gives the Lorentz
transformation to first order in v/c.
The transformed time variable he calls ``local time''.
1895 - Wilhelm Roentgen
discovers X-rays produced by
bremsstrahlung in cathode ray tubes.
1896 - Arthur Shuster, Emil Wiechert, and George Stokes
that X-rays are aether waves of exceedingly small wavelength.
1896 - J. J. Thomson
discovers that materials through which
X-rays pass are rendered conducting.
1896 - Henri Becquerel
discovers that some sort of natural radiation
from uranium salts can expose a photographic plate wrapped in
thick black paper.
1896 - P. Zeeman
discovers the splitting of atomic line
spectra by a magnetic field.
1896 - Lorentz
gives an electron theory of the Zeeman effect.
1897 - J. J. Thomson
argues that cathode rays must be
charged particles smaller in size than atoms (Emil Wiechert
made the same suggestion independently in this same year).
In response Fitz Gerald suggests that ``we are dealing with
free electrons in these cathode rays.''
1897 - W. Wien
discovers that positively-charged
moving particles can also be made (the so-called
canal rays of E. Goldstein) and that they have
a much smaller q/m ratio than cathode rays.
1897 - J. J. Thomson
deflects cathode rays by crossed electric
and magnetic fields and measures e/m.
1898 - Marie and Pierre Curie
separate from pitchblende
two highly radioactive elements which they name polonium
1899 - Ernest Rutherford
discovers that the rays from uranium
come in two types, which he calls alpha and beta radiation.
1900 - Marie and Pierre Curie
show that beta rays and
cathode rays are identical.
1900 - Emil Wiechert
shows that simply replacing
charge from Lorentz's theory
with the charge of a moving point
particle gives incorrect results.
Instead the Lienard-Wiechert retarded potentials must be used.
1900 - Joseph Larmor
obtains the second order corrections
to the Lorentz Transformation.
1901 - R. Blondlot
performs experiments that show that Lorentz's
theory in which there is no moving aether gives the
correct result in cases where the hypothesis of a moving
aether gives the wrong result.
1902 - Lord Rayleigh
performs experiments to test whether
the Fitz Gerald contraction is capable of causing double
refraction in moving transparent substances.
No such effect is found.
1903 - The Hagen-Rubens
connections between the conductivity
of metals and their optical properties are experimentally
1903 - Lorentz
gives the famous square root formulas
for the Lorentz transformation giving the effect to
all orders in v/c.
1904 - Lorentz
gives his electron-collision
theory of electrical conduction
1905 - H. A. Wilson
performs experiments similar to those of
Blondlot; again, Lorentz's theory is found to give
the correct result.
1905 - Albert Einstein
completes Lorentz's work on
space-time transformations and relativity is born.