Who first measured magnetic force?
History of geomagnetism
Magnetism has been known since prehistory, but knowledge of the Earth's field developed slowly. The horizontal direction of the Earth's field was first measured in the fourth century BC but the vertical direction was not measured until 1544 AD and the intensity was first measured in 1791. At first, compasses were thought to point towards locations in the heavens, then towards magnetic mountains. A modern experimental approach to understanding the Earth's field began with "de Magnete", a book published by William Gilbert in 1600. His experiments with a magnetic model of the Earth convinced him that the Earth itself is a large magnet.
AC motor
Because of AC's advantages in long-distance high voltage transmission, there were many inventors in the United States and Europe during the late 19th century trying to develop workable AC motors. The first person to conceive of a rotating magnetic field was Walter Baily, who gave a workable demonstration of his battery-operated polyphase motor aided by a commutator on June 28, 1879, to the Physical Society of London. Describing an apparatus nearly identical to Baily's, French electrical engineer Marcel Deprez published a paper in 1880 that identified the rotating magnetic field principle and that of a two-phase AC system of currents to produce it. Never practically demonstrated, the design was flawed, as one of the two currents was “furnished by the machine itself.” In 1886, English engineer Elihu Thomson built an AC motor by expanding upon the induction-repulsion principle and his wattmeter. In 1887, American inventor Charles Schenk Bradley was the first to patent a two-phase AC power transmission with four wires.
Hans Christian Ørsted
Hans Christian Ørsted (; ; often rendered Oersted in English; 14 August 17779 March 1851) was a Danish physicist and chemist who discovered that electric currents create magnetic fields, which was the first connection found between electricity and magnetism. Oersted's law and the oersted (Oe) are named after him.
History of the metric system
In 1832 German mathematician Carl-Friedrich Gauss made the first absolute measurements of the Earth's magnetic field using a decimal system based on the use of the millimetre, milligram, and second as the base unit of time. Gauss' second was based on astronomical observations of the rotation of the earth, and was the sexagesimal second of the ancients: a partitioning of the solar day into two cycles of 12 periods, and each period divided into 60 intervals, and each interval so divided again, so that a second was 1/86,400th of the day.
This effectively established a time dimension as a necessary constituent of any useful system of measures, and the astronomical second as the base unit.
Line of force
At first Faraday considered the physical reality of the "lines of force" as a possibility, yet several scholars agree that for Faraday their physical reality became a conviction. One scholar dates this change in the year 1838. Another scholar dates this final strengthening of his belief in 1852. Faraday experimentally studied lines of magnetic force and lines of electrostatic force, showing them not to fit action at a distance models. In 1852 Faraday wrote the paper "On the Physical Character of the Lines of Magnetic Force" which examined gravity, radiation, and electricity, and their possible relationships with the transmission medium, transmission propagation, and the receiving entity.
History of geomagnetism
Europeans started to place magnetic mountains on their maps in the sixteenth century. A notable example is Gerardus Mercator, whose famous maps included a magnetic mountain or two near the North Pole. At first, he just placed a mountain in an arbitrary location; but later he attempted to measure its location based on declinations from different locations in Europe. When subsequent measurements resulted in two contradictory estimates for the mountain, he simply placed two mountains on the map.
Gravitational constant
Based on this, Hutton's 1778 result is equivalent to ≈ .
The first direct measurement of gravitational attraction between two bodies in the laboratory was performed in 1798, seventy-one years after Newton's death, by Henry Cavendish.
He determined a value for implicitly, using a torsion balance invented by the geologist Rev. John Michell (1753). He used a horizontal torsion beam with lead balls whose inertia (in relation to the torsion constant) he could tell by timing the beam's oscillation. Their faint attraction to other balls placed alongside the beam was detectable by the deflection it caused. In spite of the experimental design being due to Michell, the experiment is now known as the Cavendish experiment for its first successful execution by Cavendish.
Coulomb's law
Finally, in 1785, the French physicist Charles-Augustin de Coulomb published his first three reports of electricity and magnetism where he stated his law. This publication was essential to the development of the theory of electromagnetism. He used a torsion balance to study the repulsion and attraction forces of charged particles, and determined that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
Condensed matter physics
Magnetism as a property of matter has been known in China since 4000 BC. However, the first modern studies of magnetism only started with the development of electrodynamics by Faraday, Maxwell and others in the nineteenth century, which included classifying materials as ferromagnetic, paramagnetic and diamagnetic based on their response to magnetization. Pierre Curie studied the dependence of magnetization on temperature and discovered the Curie point phase transition in ferromagnetic materials. In 1906, Pierre Weiss introduced the concept of magnetic domains to explain the main properties of ferromagnets. The first attempt at a microscopic description of magnetism was by Wilhelm Lenz and Ernst Ising through the Ising model that described magnetic materials as consisting of a periodic lattice of spins that collectively acquired magnetization. The Ising model was solved exactly to show that spontaneous magnetization cannot occur in one dimension but is possible in higher-dimensional lattices. Further research such as by Bloch on spin waves and Néel on antiferromagnetism led to developing new magnetic materials with applications to magnetic storage devices.
Field (physics)
Michael Faraday first realized the importance of a field as a physical quantity, during his investigations into magnetism. He realized that electric and magnetic fields are not only fields of force which dictate the motion of particles, but also have an independent physical reality because they carry energy.
Lorentz force velocimetry
The use of magnetic fields in flow measurement date back to 19th century, when in 1832 Michael Faraday attempted to determine the velocity of the River Thames. Faraday applied a method in which a flow (the river flow) is exposed to a magnetic field (earth magnetic field) and the induced voltage is measured using two electrodes across the same flow. This method is the basis of the one of the most successful commercial applications in flow metering known as the inductive flowmeter. The theory of such devices has been developed and comprehensively summarized by Prof. J. A. Shercliff in early 1950s. While inductive flowmeters are widely used for flow measurement in fluids at room temperatures such as beverages, chemicals and waste water, they are not suited for flow measurement of media such as hot, aggressive or for local measurements where surrounding obstacles limit access to the channel or pipe. Since they require electrodes to be inserted into the fluid, their use is limited to applications at temperatures far below the melting points of practically relevant metals.
Electromagnet
Danish scientist Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields. British scientist William Sturgeon invented the electromagnet in 1824. His first electromagnet was a horseshoe-shaped piece of iron that was wrapped with about 18 turns of bare copper wire (insulated wire didn't exist yet). The iron was varnished to insulate it from the windings. When a current was passed through the coil, the iron became magnetized and attracted other pieces of iron; when the current was stopped, it lost magnetization. Sturgeon displayed its power by showing that although it only weighed seven ounces (roughly 200 grams), it could lift nine pounds (roughly 4 kilos) when the current of a single-cell battery was applied. However, Sturgeon's magnets were weak because the uninsulated wire he used could only be wrapped in a single spaced out layer around the core, limiting the number of turns.
John Michell
John Michell (; 25 December 1724 – 21 April 1793) was an English natural philosopher and clergyman who provided pioneering insights in a wide range of scientific fields, including astronomy, geology, optics, and gravitation. Considered "one of the greatest unsung scientists of all time", he was the first person known to propose the existence of black holes in publication, the first to suggest that earthquakes travel in waves, the first to explain how to manufacture artificial magnets, and the first to apply statistics to the study of the cosmos, recognizing that double stars were a product of mutual gravitation. He also invented an apparatus to measure the mass of the Earth. He has been called both the father of seismology and the father of magnetometry.
Einstein–de Haas effect
The effect was used to measure the properties of various ferromagnetic
elements and alloys. The key to more accurate measurements was
better magnetic shielding, while the methods were essentially similar to those of
the first experiments. The experiments measure the value of the g-factor
formula_27 (here we use the projections
of the pseudovectors formula_28 and
formula_29
onto the magnetization axis and omit the formula_30 sign). 
The magnetization and the angular momentum consist of the contributions
from the spin and the orbital angular momentum: 
formula_31, 
formula_32. 
Using the known relations 
formula_33, and
formula_34, where
formula_35 is the g-factor for the 
anomalous magnetic moment of the electron,
one can derive the relative spin contribution to magnetization as:
formula_36.
History of electromagnetic theory
This discovery gave a clue to the subsequently proved intimate relationship between electricity and magnetism which was promptly followed up by Ampère who shortly thereafter (1821) announced his celebrated theory of electrodynamics, relating to the force that one current exerts upon another, by its electro-magnetic effects, namely
Ampere brought a multitude of phenomena into theory by his investigations of the mechanical forces between conductors supporting currents and magnets.
Gauss's law for magnetism
This idea of the nonexistence of magnetic monopoles originated in 1269 by Petrus Peregrinus de Maricourt. His work heavily influenced William Gilbert, whose 1600 work De Magnete spread the idea further. In the early 1800s Michael Faraday reintroduced this law, and it subsequently made its way into James Clerk Maxwell's electromagnetic field equations.
Omega SA
On January 17, 2013 Omega announced the creation of the world's first movement that is resistant to magnetic fields greater than 1.5 tesla (15,000 gauss), far exceeding the levels of magnetic resistance achieved by any previous movement - a similar movement was used by Daniel Craig as James Bond, though the official collectors watch was labelled as resistant to 15,007 gauss in honor of the fictional secret agent's codename. Most anti-magnetic watches utilize a soft iron - Faraday cage which distributes electromagnetism in such a way that it cancels the effect on the movement contained within. This type of anti-magnetic case required de-magnetizing procedures of the case. Omega has instead built a movement of non-ferrous materials eliminating the need for such a cage and providing a far greater resistance to magnetic fields eliminating necessity of additional maintenance.
William Gilbert (astronomer)
The magnetic laws were first generalized and explained by Dr. Gilbert, whose book on magnetism published in 1600, is one of the finest examples of inductive philosophy that has ever been presented to the world. It is the more remarkable, because it preceded the "Novum Organum" of Bacon, in which the inductive method of philosophizing was first explained.
William Whewell writes in his "History of the Inductive Sciences" (1837/1859):
Gilbert... repeatedly asserts the paramount value of experiments. He himself, no doubt, acted up to his own precepts; for his work contains all the fundamental facts of the science [of magnetism], so fully examined, indeed, that even at this day we have little to add to them.
Historian Henry Hallam wrote of Gilbert in his "Introduction to the Literature of Europe in the Fifteenth, Sixteenth, and Seventeenth Centuries" (1848):
John Madsen (physicist)
In 1931 JPVM delivered a lecture to celebrate the life & work of Michael Faraday and the applications of his discovery of electro-magnetic induction. Faraday was one of the greatest experimental scientists working both in the fields of physics & chemistry. In his original notes Faraday describes his " experiments upon the production of electricity from magnetism". These experiments showed that electrical currents were induced in electrically conducting circuits when they were moved relatively to magnetic fields. One of the immediate results of this discovery was the recognition of an effective means of utilising the principle of transformation of energy from mechanical to electrical form. The converse transformation of energy from electrical to mechanical form had been demonstrated by Oersted & Ampere in 1820 & in 1821. Faraday had performed an experiment which showed how this principle could be applied to the production of the electric motor. By accepting Faraday's principles Maxwell, Kelvin & Hertz extended & developed scientific knowledge. Also it should be mentioned that in 1839 French physicist Edmond Becquerel discovered the principle of the photovoltaic effect involving the conversion of solar energy into electrical energy. At age 19 experimenting in his father's Antoine Becquerel laboratory he created the world's first photovoltaic cell. In this experiment silver chloride was placed in an acidic solution & illuminated while connected to platinum electrodes, generating voltage & current. The pioneers of science prior to this time had largely been involved with advances in astronomy which JPVM's father, Hans Frandsen Madsen had shown an interest in when he delivered a paper to the Royal Society of NSW in 1886 on the hand polishing & silvering of 18 inch glass specula.
History of geomagnetism
In about 1603, the Frenchman Guillaume le Nautonier (William the Navigator), Sieur de Castelfranc, published a rival theory of the Earth's field in his book "Mecometrie de l'eymant (Measurement of longitude with a magnet)". Le Nautonier was a mathematician, astronomer and Royal Geographer in the court of Henry IV. He disagreed with Gilbert's assumption that the Earth had to be magnetized parallel to the rotational axis, and instead produced a model in which the magnetic moment was tilted by ° – in effect, the first tilted dipole model. The last 196 pages of his book were taken up with tables of latitudes and longitudes with declination and inclination for use by mariners. If his model had been accurate, it could have been used to determine both latitude and longitude using a combination of magnetic declination and astronomical observations.
Michael Faraday
Faraday is best known for his work regarding electricity and magnetism. His first recorded experiment was the construction of a voltaic pile with seven ha'penny coins, stacked together with seven disks of sheet zinc, and six pieces of paper moistened with salt water. With this pile he decomposed sulfate of magnesia (first letter to Abbott, 12 July 1812).
Rotating magnetic field
In 1824, the French physicist François Arago formulated the existence of rotating magnetic fields using a rotating copper disk and a needle, termed Arago's rotations. English experimenters Charles Babbage and Charles Herschel found they could induce rotation in Arago's copper disk by spinning a horseshoe magnet under it with English scientist Michael Faraday later attributing the effect to electromagnetic induction. In 1879 English physicist Walter Baily replaced the horseshoe magnets with four electromagnets and, by manually turning switches on and off, demonstrated a primitive induction motor.
Coulomb's law
Early investigators of the 18th century who suspected that the electrical force diminished with distance as the force of gravity did (i.e., as the inverse square of the distance) included Daniel Bernoulli and Alessandro Volta, both of whom measured the force between plates of a capacitor, and Franz Aepinus who supposed the inverse-square law in 1758.
List of Dutch discoveries
In 1892, Hendrik Lorentz derived the modern form of the formula for the electromagnetic force which includes the contributions to the total force from both the electric and the magnetic fields. In many textbook treatments of classical electromagnetism, the Lorentz force law is used as the "definition" of the electric and magnetic fields E and B. To be specific, the Lorentz force is understood to be the following empirical statement:
Magnetic refrigeration
The effect was first observed by a German physicist Warburg (1881) Subsequently by French physicist P. Weiss and Swiss physicist A. Piccard in 1917. The fundamental principle was suggested by P. Debye (1926) and W. Giauque (1927). The first working magnetic refrigerators were constructed by several groups beginning in 1933. Magnetic refrigeration was the first method developed for cooling below about 0.3K (a temperature attainable by  refrigeration, that is pumping on the vapors).
Electrochemistry
Hans Christian Ørsted's discovery of the magnetic effect of electric currents in 1820 was immediately recognized as an epoch-making advance, although he left further work on electromagnetism to others. André-Marie Ampère quickly repeated Ørsted's experiment, and formulated them mathematically.
History of geodesy
Muslim astronomers and geographers were aware of magnetic declination by the 15th century, when the Egyptian astronomer 'Abd al-'Aziz al-Wafa'i (d. 1469/1471) measured it as 7 degrees from Cairo.
Magnetoresistance
The first magnetoresistive effect was discovered by William Thomson, better known as Lord Kelvin, in 1856, but he was unable to lower the electrical resistance of anything by more than 5%. Nowadays, systems, e.g. semimetals or concentric ring EMR structures, are known where a magnetic field can change resistance by orders of magnitude. As the resistance may depend on magnetic field through various mechanisms, it is useful to separately consider situations where it depends on magnetic field directly, e.g. geometric magnetoresistance and multiband magnetoresistance, and those where it does so indirectly through magnetisation, e.g. AMR, TMR.
Cavity magnetron
In 1910 Hans Gerdien of the Siemens corporation invented a magnetron. In 1912, Swiss physicist Heinrich Greinacher was looking for new ways to calculate the electron mass. He settled on a system consisting of a diode with a cylindrical anode surrounding a rod-shaped cathode, placed in the middle of a magnet. The attempt to measure the electron mass failed because he was unable to achieve a good vacuum in the tube. However, as part of this work, Greinacher developed mathematical models of the motion of the electrons in the crossed magnetic and electric fields.
Magnetochemistry
The primary measurement in magnetochemistry is magnetic susceptibility. This measures the strength of interaction on placing the substance in a magnetic field. The volume magnetic susceptibility, represented by the symbol formula_1 is defined by the relationship
where, formula_3 is the magnetization of the material (the magnetic dipole moment per unit volume), measured in amperes per meter ( SI units), and formula_4 is the magnetic field strength, also measured in amperes per meter. Susceptibility is a dimensionless quantity. For chemical applications the molar magnetic susceptibility (χ) is the preferred quantity. It is measured in m·mol (SI) or cm·mol (CGS) and is defined as
where ρ is the density in kg·m (SI) or g·cm (CGS) and "M" is molar mass in kg·mol (SI) or g·mol (CGS). 
A variety of methods are available for the measurement of magnetic susceptibility.When an isolated atom is placed in a magnetic field there is an interaction because each electron in the atom behaves like a magnet, that is, the electron has a magnetic moment. There are two types of interaction.
When the atom is present in a chemical compound its magnetic behaviour is modified by its chemical environment. Measurement of the magnetic moment can give useful chemical information.
Magnetomotive force
The term "magnetomotive force" was coined by Henry Augustus Rowland in 1880. Rowland intended this to indicate a direct analogy with electromotive force. The idea of a magnetic analogy to electromotive force can be found much earlier in the work of Michael Faraday (1791-1867) and it is hinted at by James Clerk Maxwell (1831-1879). However, Rowland coined the term and was the first to make explicit an Ohm's law for magnetic circuits in 1873.
On Physical Lines of Force
In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch performed an experiment with a Leyden jar and established the ratio of electric charge as measured statically to the same electric charge as measured electrodynamically. Maxwell used this ratio in Isaac Newton's equation for the speed of sound, as applied using the density and transverse elasticity of his sea of molecular vortices. He obtained a value which was very close to the speed of light, as recently measured directly by Hippolyte Fizeau. Maxwell then wrote
"we can scarcely avoid the inference that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena"
History of electromagnetic theory
The experiment which led Faraday to the discovery of electromagnetic induction was made as follows: He constructed what is now and was then termed an induction coil, the primary and secondary wires of which were wound on a wooden bobbin, side by side, and insulated from one another. In the circuit of the primary wire he placed a battery of approximately 100 cells. In the secondary wire he inserted a galvanometer. On making his first test he observed no results, the galvanometer remaining quiescent, but on increasing the length of the wires he noticed a deflection of the galvanometer in the secondary wire when the circuit of the primary wire was made and broken. This was the first observed instance of the development of electromotive force by electromagnetic induction.
History of electrochemistry
Hans Christian Ørsted's discovery of the magnetic effect of electric currents in 1820 was immediately recognised as an important advance, although he left further work on electromagnetism to others. André-Marie Ampère quickly repeated Ørsted's experiment, and formulated them mathematically (which became Ampère's law) . Ørsted also discovered that not only is a magnetic needle deflected by the electric current, but that the live electric wire is also deflected in a magnetic field, thus laying the foundation for the construction of an electric motor. Ørsted's discovery of piperine, one of the pungent components of pepper, was an important contribution to chemistry, as was his preparation of aluminium in 1825.
Henry Gellibrand
Henry Gellibrand (1597–1637) was an English mathematician. He is known for his work on the Earth's magnetic field. He discovered that magnetic declination – the angle of dip of a compass needle – is not constant but changes over time. He announced this in 1635, relying on previous observations by others, which had not yet been correctly interpreted.
History of Maxwell's equations
The discovery of this relationship started in 1855, when Wilhelm Eduard Weber and Rudolf Kohlrausch determined that there was a quantity related to electricity and magnetism, "the ratio of the absolute electromagnetic unit of charge to the absolute electrostatic unit of charge" (in modern language, the value formula_2), and determined that it should have units of velocity. They then measured this ratio by an experiment which involved charging and discharging a Leyden jar and measuring the magnetic force from the discharge current, and found a value , remarkably close to the speed of light, which had recently been measured at by Hippolyte Fizeau in 1848 and at by Léon Foucault in 1850. However, Weber and Kohlrausch did not make the connection to the speed of light. Towards the end of 1861 while working on part III of his paper "On Physical Lines of Force", Maxwell travelled from Scotland to London and looked up Weber and Kohlrausch's results. He converted them into a format which was compatible with his own writings, and in doing so he established the connection to the speed of light and concluded that light is a form of electromagnetic radiation.
Magnetism
Alexander Neckam, by 1187, was the first in Europe to describe the compass and its use for navigation. In 1269, Peter Peregrinus de Maricourt wrote the "Epistola de magnete", the first extant treatise describing the properties of magnets. In 1282, the properties of magnets and the dry compasses were discussed by Al-Ashraf, a Yemeni physicist, astronomer, and geographer.
International System of Units
In 1832, the German mathematician Carl Friedrich Gauss, assisted by Wilhelm Weber, implicitly defined the second as a base unit when he quoted the Earth's magnetic field in terms of millimetres, grams, and seconds. Prior to this, the strength of the Earth's magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a suspended magnet of known mass by the Earth's magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length and time to the magnetic field.
Magnetoelectric effect
The first example of a magnetoelectric effect was discussed in 1888 by Wilhelm Röntgen, who showed that a dielectric material moving through an electric field would become magnetized. The possibility of an intrinsic magnetoelectric effect in a (non-moving) material was conjectured by P. Curie in 1894, while the term "magnetoelectric" was coined by P. Debye in 1926.
A mathematical formulation of the linear magnetoelectric effect was included in L. D. Landau and E. Lifshitz famous book series on theoretical physics. Only in 1959, I. Dzyaloshinskii, using an elegant symmetry argument, derived the form of a linear magnetoelectric coupling in CrO.
The experimental confirmation came just few months later when the effect was observed for the first time by D. Astrov. The general excitement which followed the measurement of the linear magnetoelectric effect lead to the organization of the series of MEIPIC (Magnetoelectric Interaction Phenomena in Crystals) conferences. Between the prediction of I. Dzialoshinskii and the MEIPIC first edition (1973), more than 80 linear magnetoelectric compounds were found. Recently, technological and theoretical progress, driven in large part by the advent of multiferroic materials, triggered a renaissance of these studies and magnetoelectric effect is still heavily investigated.
Magnetic refrigeration
The effect was discovered first observed by a German physicist Warburg (1881) Subsequently by French physicist P. Weiss and Swiss physicist A. Piccard in 1917.
Magnetic anomaly detector
Geoexploration by measuring and studying variations in the Earth's magnetic field has been conducted by scientists since 1843. The first uses of magnetometers were for the location of ore deposits. Thalen's "The Examination of Iron Ore Deposits by Magnetic Measurements", published in 1879, was the first scientific treatise describing this practical use.
Spheromak
In 1951 efforts to produce controlled fusion for power production began. These experiments generally used some sort of pulsed power to deliver the large magnetic forces required in the experiments. The current magnitudes and the resulting forces were unprecedented. In 1957 Harold Furth, Levine and Waniek reported on the dynamics of large magnets, demonstrating that the limiting factor in magnet performance was physical; stresses in the magnet would overcome its own mechanical limits. They proposed winding these magnets in such a way that the forces within the magnet windings cancelled out, the "force-free condition". Although it was not known at the time, this is the same magnetic field as in a spheromak.
History of electromagnetic theory
About 1876 the American physicist Henry Augustus Rowland of Baltimore demonstrated the important fact that a static charge carried around produces the same magnetic effects as an electric current. The Importance of this discovery consists in that it may afford a plausible theory of magnetism, namely, that magnetism may be the result of directed motion of rows of molecules carrying static charges.
François Arago
Arago's earliest physical researches were on the pressure of steam at different temperatures, and the velocity of sound, 1818 to 1822. His magnetic observations mostly took place from 1823 to 1826. He discovered rotatory magnetism, what has been called Arago's rotations, and the fact that most bodies could be magnetized; these discoveries were completed and explained by Michael Faraday.
19th century in science
In 1831, Faraday (and independently Joseph Henry) discovered the reverse effect, the production of an electric potential or current through magnetism – known as electromagnetic induction; these two discoveries are the basis of the electric motor and the electric generator, respectively. In 1834, Carl Jacobi discovered his uniformly rotating self-gravitating ellipsoids (the Jacobi ellipsoid). In 1834, John Russell observed a nondecaying solitary water wave (soliton) in the Union Canal near Edinburgh and used a water tank to study the dependence of solitary water wave velocities on wave amplitude and water depth. In 1835, William Hamilton stated Hamilton's canonical equations of motion. In the same year, Gaspard Coriolis examined theoretically the mechanical efficiency of waterwheels, and deduced the Coriolis effect. In 1841, Julius Robert von Mayer, an amateur scientist, wrote a paper on the conservation of energy but his lack of academic training led to its rejection. In 1842, Christian Doppler proposed the Doppler effect. In 1847, Hermann von Helmholtz formally stated the law of conservation of energy. In 1851, Léon Foucault showed the Earth's rotation with a huge pendulum (Foucault pendulum).
Oersted's law
This was discovered on 21 April 1820 by Danish physicist Hans Christian Ørsted (1777–1851), when he noticed that the needle of a compass next to a wire carrying current turned so that the needle was perpendicular to the wire. 
Ørsted investigated and found the physical law describing the magnetic field, now known as Ørsted's law. 
Ørsted's discovery was the first connection found between electricity and magnetism, and the first of two laws that link the two; the other is Faraday's law of induction. 
These two laws became part of the equations that govern electromagnetism, Maxwell's equations.
Electromechanics
The first electric motor was invented in 1821 by Michael Faraday. The motor was developed only a year after Hans Christian Ørsted discovered that the flow of electric current creates a proportional magnetic field. This early motor was simply a wire partially submerged into a glass of mercury with a magnet at the bottom. When the wire was connected to a battery a magnetic field was created and this interaction with the magnetic field given off by the magnet caused the wire to spin.
Magnetic reluctance
The term "reluctance" was coined in May 1888 by Oliver Heaviside. The notion of "magnetic resistance" was first mentioned by James Joule in 1840. The idea for a magnetic flux law, similar to Ohm's law for closed electric circuits, is attributed to Henry Augustus Rowland in an 1873 paper. Rowland is also responsible for coining the term "magnetomotive force" in 1880, also coined, apparently independently, a bit later in 1883 by Bosanquet.
Oliver Heaviside
In 1889, Heaviside first published a correct derivation of the magnetic force on a moving charged particle, which is now called the Lorentz force.
Einstein's thought experiments
In the very first paragraph of Einstein's seminal 1905 work introducing special relativity, he writes: 
This opening paragraph recounts well-known experimental results obtained by Michael Faraday in 1831. The experiments describe what appeared to be two different phenomena: the "motional EMF" generated when a wire moves through a magnetic field (see Lorentz force), and the "transformer EMF" generated by a changing magnetic field (due to the Maxwell–Faraday equation). James Clerk Maxwell himself drew attention to this fact in his 1861 paper "On Physical Lines of Force". In the latter half of Part II of that paper, Maxwell gave a separate physical explanation for each of the two phenomena.
Fundamental interaction
Electrical and magnetic phenomena have been observed since ancient times, but it was only in the 19th century James Clerk Maxwell discovered that electricity and magnetism are two aspects of the same fundamental interaction. By 1864, Maxwell's equations had rigorously quantified this unified interaction. Maxwell's theory, restated using vector calculus, is the classical theory of electromagnetism, suitable for most technological purposes.
Geophysics
Although geophysics was only recognized as a separate discipline in the 19th century, its origins date back to ancient times. The first magnetic compasses were made from lodestones, while more modern magnetic compasses played an important role in the history of navigation. The first seismic instrument was built in 132 AD. Isaac Newton applied his theory of mechanics to the tides and the precession of the equinox; and instruments were developed to measure the Earth's shape, density and gravity field, as well as the components of the water cycle. In the 20th century, geophysical methods were developed for remote exploration of the solid Earth and the ocean, and geophysics played an essential role in the development of the theory of plate tectonics.
Galvanometer
The deflection of a magnetic compass needle by current in a wire was first described by Hans Oersted in 1820. The phenomenon was studied both for its own sake and as a means of measuring electric current.
Earth's magnetic field
The Earth's magnetic field strength was measured by Carl Friedrich Gauss in 1832 and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years. The Magsat satellite and later satellites have used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The later Ørsted satellite allowed a comparison indicating a dynamic geodynamo in action that appears to be giving rise to an alternate pole under the Atlantic Ocean west of South Africa.
Magnetic detector
Ernest Rutherford had first used the hysteresis of iron to detect Hertzian waves in 1896 by the demagnetization of an iron needle when a radio signal passed through a coil around the needle, however the needle had to be remagnetized so this was not suitable for a continuous detector. Many other wireless researchers such as E. Wilson, C. Tissot, Reginald Fessenden, John Ambrose Fleming, Lee De Forest, J.C. Balsillie, and L. Tieri had subsequently devised detectors based on hysteresis, but none had become widely used due to various drawbacks. Many earlier versions had a rotating magnet above a stationary iron band with coils on it. This type was only periodically sensitive, when the magnetic field was changing, which occurred as the magnetic poles passed the iron.
Lorentz force velocimetry
The Lorentz force velocimetry was invented by the A. Shercliff. However, it did not find practical application in these early years up until recent technical advances; in manufacturing of rare earth and non rare-earth strong permanent magnets, accurate force measurement techniques, multiphysical process simulation software for magnetohydrodynamic (MHD) problems that this principle could be turned into a feasible working flow measurement technique. LFV is currently being developed for applications in metallurgy as well as in other areas.
Magnetogram
In the context of the magnetic field of the Sun, the term magnetogram refers to a pictorial representation of the "spatial" variations in strength of the solar magnetic field. Magnetograms are often produced by exploiting the Zeeman effect (or, in some cases, the Hanle effect), which George Ellery Hale employed in the first demonstration that sunspots were magnetic in origin, in 1908. Solar magnetograms are produced by suitably instrumented telescopes referred to as magnetographs. Some magnetographs can only measure the component of the magnetic field along the line of sight from the observer to the source (the field's "longitudinal" component). One example of such a "line-of-sight" or "longitudinal" magnetograph is the Michelson Doppler Imager (MDI), a scientific instrument that takes magnetograms of the Sun in order to measure velocity and magnetic fields in the Sun's photosphere to learn about the convection zone and about the magnetic fields which control the structure of the solar corona. A vector magnetograph also measures the component of the magnetic field perpendicular to the line of sight (the field's "transverse" component), from which all three components of the magnetic field vector can be deduced. Two examples include the National Solar Observatory's SOLIS instrument and the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics Observatory satellite.
Neutron magnetic moment
The value for the neutron's magnetic moment was first directly measured by Luis Alvarez and Felix Bloch at Berkeley, California in 1940. Using an extension of the magnetic resonance methods developed by Rabi, Alvarez and Bloch determined the magnetic moment of the neutron to be . By directly measuring the magnetic moment of free neutrons, or individual neutrons free of the nucleus, Alvarez and Bloch resolved all doubts and ambiguities about this anomalous property of neutrons.
David Cohen (physicist)
Working in this area, and using large magnets, he became interested in the other extreme; this was the measurement of very weak magnetic fields, which for example might be produced by the weak natural currents in the human body. In 1963, he proposed a method using a magnetically shielded room to keep out external magnetic disturbances, as in radiation shielding in nuclear experiments. At that time others reported the first biomagnetic measurement, where the MCG ("magnetocardiogram", the magnetic field due to heart currents) was measured; this was done without shielding, hence showed much external interference. Cohen then built a modest shielded room, and with somewhat clearer signals verified the heart’s magnetic field. He also made the first measurement of the MEG ("magnetoencephalogram", the magnetic field of the brain). However, all these early biomagnetic measurements were generally too noisy, both because of the use of insensitive detectors, and incomplete magnetic shielding.
Hall effect
The Hall effect was discovered in 1879 by Edwin Hall while he was working on his doctoral degree at Johns Hopkins University in Baltimore, Maryland. Eighteen years before the electron was discovered, his measurements of the tiny effect produced in the apparatus he used were an experimental tour de force, published under the name "On a New Action of the Magnet on Electric Currents".
History of geomagnetism
At a given location, a full representation of the Earth's magnetic field requires a vector with three coordinates (see figure). These can be Cartesian (North, East and Down) or spherical (declination, inclination and intensity). In the latter system, the declination (the deviation from true north, a horizontal angle) must be measured first to establish the direction of magnetic North; then the dip (a vertical angle) can be measured relative to magnetic North. In China, the horizontal direction was measured as early as the fourth century BC, and the existence of declination first recognized in 1088. In Europe, this was not widely accepted until the middle of the fifteenth century AD. Inclination (also known as "magnetic dip") was first measured in 1544 AD. The intensity was not measured until 1791, after advances in the understanding of electromagnetism.
Electromagnetism
At the time of discovery, Ørsted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework. However, three months later he began more intensive investigations. Soon thereafter he published his findings, proving that an electric current produces a magnetic field as it flows through a wire. The CGS unit of magnetic induction (oersted) is named in honor of his contributions to the field of electromagnetism.
His findings resulted in intensive research throughout the scientific community in electrodynamics. They influenced French physicist André-Marie Ampère's developments of a single mathematical form to represent the magnetic forces between current-carrying conductors. Ørsted's discovery also represented a major step toward a unified concept of energy.
John Tyndall
Tyndall's early original work in physics was his experiments on magnetism and diamagnetic polarity, on which he worked from 1850 to 1856. His two most influential reports were the first two, co-authored with Knoblauch. One of them was entitled "The magneto-optic properties of crystals, and the relation of magnetism and diamagnetism to molecular arrangement", dated May 1850. The two described an inspired experiment, with an inspired interpretation. These and other magnetic investigations very soon made Tyndall known among the leading scientists of the day. He was elected a Fellow of the Royal Society in 1852. In his search for a suitable research appointment, he was able to ask the longtime editor of the leading German physics journal (Poggendorff) and other prominent men to write testimonials on his behalf. In 1853, he attained the prestigious appointment of Professor of Natural Philosophy (Physics) at the Royal Institution in London, due in no small part to the esteem his work had garnered from Michael Faraday, the leader of magnetic investigations at the Royal Institution. About a decade later Tyndall was appointed the successor to the positions held by Michael Faraday at the Royal Institution on Faraday's retirement.
Tachometer
The first mechanical tachometers were based on measuring the centrifugal force, similar to the operation of a centrifugal governor. The inventor is assumed to be the German engineer Dietrich Uhlhorn; he used it for measuring the speed of machines in 1817. Since 1840, it has been used to measure the speed of locomotives.
Magnetometer
In 1833, Carl Friedrich Gauss, head of the Geomagnetic Observatory in Göttingen, published a paper on measurement of the Earth's magnetic field. It described a new instrument that consisted of a permanent bar magnet suspended horizontally from a gold fibre. The difference in the oscillations when the bar was magnetised and when it was demagnetised allowed Gauss to calculate an absolute value for the strength of the Earth's magnetic field.
Faraday's law of induction
Electromagnetic induction was discovered independently by Michael Faraday in 1831 and Joseph Henry in 1832. Faraday was the first to publish the results of his experiments. In Faraday's first experimental demonstration of electromagnetic induction (August 29, 1831), he wrapped two wires around opposite sides of an iron ring (torus) (an arrangement similar to a modern toroidal transformer). Based on his assessment of recently discovered properties of electromagnets, he expected that when current started to flow in one wire, a sort of wave would travel through the ring and cause some electrical effect on the opposite side. He plugged one wire into a galvanometer, and watched it as he connected the other wire to a battery. Indeed, he saw a transient current (which he called a "wave of electricity") when he connected the wire to the battery, and another when he disconnected it. This induction was due to the change in magnetic flux that occurred when the battery was connected and disconnected. Within two months, Faraday had found several other manifestations of electromagnetic induction. For example, he saw transient currents when he quickly slid a bar magnet in and out of a coil of wires, and he generated a steady (DC) current by rotating a copper disk near the bar magnet with a sliding electrical lead ("Faraday's disk").
Magnetic field
Magnetic fields are widely used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass.
Although magnets and magnetism were studied much earlier, the research of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field on the surface of a spherical magnet using iron needles. Noting that the resulting field lines crossed at two points he named those points 'poles' in analogy to Earth's poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them.
Biomagnetism
The origin of the word biomagnetism is unclear, but seems to have appeared several hundred years ago, linked to the expression "animal magnetism". The present scientific definition took form in the 1970s, when an increasing number of researchers began to measure the magnetic fields produced by the human body. The first valid measurement was actually made in 1963, but the field of research began to expand only after a low-noise technique was developed in 1970. Today the community of biomagnetic researchers does not have a formal organization, but international conferences are held every two years, with about 600 attendees. Most conference activity centers on the MEG (magnetoencephalogram), the measurement of the magnetic field of the brain.
Magnetoresistance
William Thomson (Lord Kelvin) first discovered ordinary magnetoresistance in 1856. He experimented with pieces of iron and discovered that the resistance increases when the current is in the same direction as the magnetic force and decreases when the current is at 90° to the magnetic force. He then did the same experiment with nickel and found that it was affected in the same way but the magnitude of the effect was greater. This effect is referred to as anisotropic magnetoresistance (AMR).
Ammeter
The relation between electric current, magnetic fields and physical forces was first noted by Hans Christian Ørsted who, in 1820, observed a compass needle was deflected from pointing North when a current flowed in an adjacent wire. The tangent galvanometer was used to measure currents using this effect, where the restoring force returning the pointer to the zero position was provided by the Earth's magnetic field. This made these instruments usable only when aligned with the Earth's field. Sensitivity of the instrument was increased by using additional turns of wire to multiply the effect – the instruments were called "multipliers".
Carl Friedrich Gauss
In 1831, Gauss developed a fruitful collaboration with the physics professor Wilhelm Weber, leading to new knowledge in magnetism (including finding a representation for the unit of magnetism in terms of mass, charge, and time) and the discovery of Kirchhoff's circuit laws in electricity. It was during this time that he formulated his namesake law. They constructed the first electromechanical telegraph in 1833, which connected the observatory with the institute for physics in Göttingen. Gauss ordered a magnetic observatory to be built in the garden of the observatory, and with Weber founded the "Magnetischer Verein" ("magnetic association"), which supported measurements of Earth's magnetic field in many regions of the world. He developed a method of measuring the horizontal intensity of the magnetic field which was in use well into the second half of the 20th century, and worked out the mathematical theory for separating the inner and outer (magnetospheric) sources of Earth's magnetic field.
Introduction to electromagnetism
Coulomb's law states that the force on a charged particle due to the field from another particle is dependent on the magnitudes of the two charges as well as the distance between them. The further away the particle is, the weaker the force on it is. Positive charges exert attractive forces on negative charges (and vice versa) while positive charges exert repulsive forces on other positive charges (and similarly for the force between negative charges). The SI units of force are newtons (N).
Michael Faraday and James Clerk Maxwell, first introduced the concept of a field in his 1831 paper on electromagnetic induction, (called "lines of magnetic and electric force" in this publication): "...by "line of magnetic force", or "magnetic line of force", or "magnetic curve", I mean that exercise of magnetic force which is exerted in the lines usually called magnetic curves, and which equally exist as passing from or to magnetic poles, or forming concentric circles round an electric current. By "line of electric force", I mean the force exerted in the lines joining two bodies, acting on each other according to the principles of static electric induction."Certain conventions are followed when drawing and interpreting electric field lines:The SI unit of the electric field is volt per meter (V/m), or equivalently, newton per coulomb (N/C). In mathematical expressions it is often represented as a vector-valued function formula_5. The electric field can be calculated in many ways, including Gauss' law, Coulomb's law, or Maxwell's equations. The electric field can also be interpreted as the electric force per unit charge.
Frans Michel Penning
Penning investigated the effect of magnetic fields on low pressure gas discharges. He determined that the energy current through a discharge tube in a magnetic field could be used to reliably measure the pressure. In his first attempt to measure the energy current, Penning used a triode ion gauge system with a linear electron flight path. This method worked, but was fragile and ineffective at very low pressures. In his second attempt, he equipped his vacuum tube with a ring shaped cathode and two anode plates above and below in a magnetic field. Electrons now traveled a longer flight path out of the ring, between electrodes in a spiral orbit. Increasing the electron flight path allowed for more collisions with meta-stable atoms. This amplified the electron signal, which was sufficient to measure gas pressure. The Penning manometer (vacuum gauge) emerged as a practical application.
John Michell
Michell studied magnetism and discovered the "inverse-square law", the fact that the magnetic force exerted by each pole of a magnet decreases in proportion to the square of the distance between them. His 1750 paper Treatise of Artificial Magnets, which was written for seamen and instrument makers and intended as a practical manual on how to make magnets, included a list of the "Properties of Magnetical Bodies" that represented a major contribution to the understanding of magnetism.
John Wikswo
In 1977 he became an Assistant Professor in the Department of Physics and Astronomy at Vanderbilt University, where he set up a laboratory to study Living State Physics. In 1980, he made the first measurement of the magnetic field of an isolated nerve, by threading the a frog sciatic nerve through a wire-wound, ferrite-core toroid and detecting the induced current using a SQUID magnetometer.
At the same time, Wikswo and Ken Swinney calculated the magnetic field of a nerve axon.
Magnetometer
Faraday force magnetometry uses the fact that a spatial magnetic field gradient produces force that acts on a magnetized object, F=(M⋅∇)B. In Faraday Force Magnetometry the force on the sample can be measured by a scale (hanging the sample from a sensitive balance), or by detecting the displacement against a spring. Commonly a capacitive load cell or cantilever is used because of its sensitivity, size, and lack of mechanical parts. Faraday Force Magnetometry is approximately one order of magnitude less sensitive than a SQUID. The biggest drawback to Faraday Force Magnetometry is that it requires some means of not only producing a magnetic field, but also producing a magnetic field gradient. While this can be accomplished by using a set of special pole faces, a much better result can be achieved by using set of gradient coils. A major advantage to Faraday Force Magnetometry is that it is small and reasonably tolerant to noise, and thus can be implemented in a wide range of environments, including a dilution refrigerator. Faraday Force Magnetometry can also be complicated by the presence of torque (see previous technique). This can be circumvented by varying the gradient field independently of the applied DC field so the torque and the Faraday Force contribution can be separated, and/or by designing a Faraday Force Magnetometer that prevents the sample from being rotated.
South Magnetic Pole
The first calculation of the magnetic inclination to locate the magnetic South Pole was made on January 23, 1838 by the hydrographer , a member of the Dumont d'Urville expedition in Antarctica and Oceania on the corvettes "L'Astrolabe" and "Zélée" in 1837-1840, which discovered Adelie Land.
History of electrochemistry
Charles-Augustin de Coulomb developed the law of electrostatic attraction in 1781 as an outgrowth of his attempt to investigate the law of electrical repulsions as stated by Joseph Priestley in England. To this end, he invented a sensitive apparatus to measure the electrical forces involved in Priestley's law. He also established the inverse square law of attraction and repulsion magnetic poles, which became the basis for the mathematical theory of magnetic forces developed by Siméon Denis Poisson. Coulomb wrote seven important works on electricity and magnetism which he submitted to the Académie des Sciences between 1785 and 1791, in which he reported having developed a theory of attraction and repulsion between charged bodies, and went on to search for perfect conductors and dielectrics. He suggested that there was no perfect dielectric, proposing that every substance has a limit, above which it will conduct electricity. The SI unit of charge is called a coulomb in his honour.
History of electromagnetic theory
In 1822 Johann Schweigger devised the first galvanometer. This instrument was subsequently much improved by Wilhelm Weber (1833). In 1825 William Sturgeon of Woolwich, England, invented the horseshoe and straight bar electromagnet, receiving therefor the silver medal of the Society of Arts. In 1837 Carl Friedrich Gauss and Weber (both noted workers of this period) jointly invented a reflecting galvanometer for telegraph purposes. This was the forerunner of the Thomson reflecting and other exceedingly sensitive galvanometers once used in submarine signaling and still widely employed in electrical measurements. Arago in 1824 made the important discovery that when a copper disc is rotated in its own plane, and if a magnetic needle be freely suspended on a pivot over the disc, the needle will rotate with the disc. If on the other hand the needle is fixed it will tend to retard the motion of the disc. This effect was termed Arago's rotations.
Futile attempts were made by Charles Babbage, Peter Barlow, John Herschel and others to explain this phenomenon. The true explanation was reserved for Faraday, namely, that electric currents are induced in the copper disc by the cutting of the magnetic lines of force of the needle, which currents in turn react on the needle. Georg Simon Ohm did his work on resistance in the years 1825 and 1826, and published his results in 1827 as the book "Die galvanische Kette, mathematisch bearbeitet".
He drew considerable inspiration from Fourier's work on heat conduction in the theoretical explanation of his work. For experiments, he initially used voltaic piles, but later used a thermocouple as this provided a more stable voltage source in terms of internal resistance and constant potential difference. He used a galvanometer to measure current, and knew that the voltage between the thermocouple terminals was proportional to the junction temperature. He then added test wires of varying length, diameter, and material to complete the circuit. He found that his data could be modeled through a simple equation with variable composed of the reading from a galvanometer, the length of the test conductor, thermocouple junction temperature, and a constant of the entire setup. From this, Ohm determined his law of proportionality and published his results. In 1827, he announced the now famous law that bears his name, that is:
Electromotive force = Current × Resistance
Ohm brought into order a host of puzzling facts connecting electromotive force and electric current in conductors, which all previous electricians had only succeeded in loosely binding together qualitatively under some rather vague statements. Ohm found that the results could be summed up in such a simple law and by Ohm's discovery a large part of the domain of electricity became annexed to theory.
Francesco Zantedeschi
In a tract of 16 pages, published in 1859, Zantedeschi defended the claims of Gian Domenico Romagnosi to the discovery in 1802 of the magnetic effect of the electric current, a discovery which is usually accredited to Hans Christian Ørsted in 1820. Zantedeschi's experiments and papers on the repulsion of flames by a strong magnetic field (discovered by Padre Bancalari of the Pious Schools in 1847) attracted general attention at the time.
Invention of radio
Various scientists proposed that electricity and magnetism were linked. Around 1800 Alessandro Volta developed the first means of producing an electric current. In 1802 Gian Domenico Romagnosi may have suggested a relationship between electricity and magnetism but his reports went unnoticed. In 1820 Hans Christian Ørsted performed a simple and today widely known experiment on electric current and magnetism. He demonstrated that a wire carrying a current could deflect a magnetized compass needle. Ørsted's work influenced André-Marie Ampère to produce a theory of electromagnetism. Several scientists speculated that light might be connected with electricity or magnetism.
De Haas–van Alphen effect
Experimentally it was discovered in 1930 by W.J. de Haas and P.M. van Alphen under careful study of the magnetization of a single crystal of bismuth. The magnetization oscillated as a function of the field. The inspiration for the experiment was the recently discovered Shubnikov–de Haas effect by Lev Shubnikov and de Haas, which showed oscillations of the electrical resistivity as function of a strong magnetic field. De Haas thought that the magnetoresistance should behave in an analogous way.
Magnetometer
Francis Ronalds and Charles Brooke independently invented magnetographs in 1846 that continuously recorded the magnet's movements using photography, thus easing the load on observers. They were quickly utilised by Edward Sabine and others in a global magnetic survey and updated machines were in use well into the 20th century.
Rotating magnetic field
Practical application of a rotating magnetic field in an AC motor is generally attributed to two inventors, the Italian physicist and electrical engineer Galileo Ferraris, and the Serbian-American inventor and electrical engineer Nikola Tesla.
Tesla claimed in his autobiography that the idea came to him in 1882 when he was walking in a park, drawing it in the sand to illustrate how it worked to a friend. Ferraris wrote about researching the concept and built a working model in 1885, although there is no independent verification for either claim. In 1888 Tesla obtained a United States patent () for his design and Ferraris published his research in a paper to the "Royal Academy of Sciences" in Turin.
Giovanni Francesco Sagredo
Sagredo shared an interest in both astronomy and magnetism with Galileo and Paolo Sarpi. By 1600 Sagredo’s name was known to Tycho Brahe, who in a letter to Gian Vincenzo Pinelli referred to him as a good contact for the two copies of the star charts that Tycho had offered to the Doge and Senate. Another letter, to William Gilbert describes Sagredo as a "great Magneticall man". One of the hopes that resulted from Gilbert's work was that an all-encompassing mapping of global magnetic declination could be used to solve the problem of calculating longitude. Galilei devised an instrument to measure the magnetic inclination, which Sagredo took with him on his later trip to Syria. Sagredo had a particular contribution to make the advancing the understanding of magnetism - he ran the family mines near Borca di Cadore, from which magnetic iron ore was extracted. Galileo learned how to arm these magnets and the most powerful - known as Rodomonte - was offered for sale to Ferdinando I de' Medici, Grand Duke of Tuscany and to Emperor Rudolf II.
André-Marie Ampère
In September 1820, Ampère's friend and eventual eulogist François Arago showed the members of the French Academy of Sciences the surprising discovery of Danish physicist Hans Christian Ørsted that a magnetic needle is deflected by an adjacent electric current. Ampère began developing a mathematical and physical theory to understand the relationship between electricity and magnetism. Furthering Ørsted's experimental work, Ampère showed that two parallel wires carrying electric currents attract or repel each other, depending on whether the currents flow in the same or opposite directions, respectively - this laid the foundation of electrodynamics. He also applied mathematics in generalizing physical laws from these experimental results. The most important of these was the principle that came to be called Ampère's law, which states that the mutual action of two lengths of current-carrying wire is proportional to their lengths and to the intensities of their currents. Ampère also applied this same principle to magnetism, showing the harmony between his law and French physicist Charles Augustin de Coulomb's law of magnetic action. Ampère's devotion to, and skill with, experimental techniques anchored his science within the emerging fields of experimental physics.
19th century in science
In 1800, Alessandro Volta invented the electric battery (known of the voltaic pile) and thus improved the way electric currents could also be studied. A year later, Thomas Young demonstrated the wave nature of light—which received strong experimental support from the work of Augustin-Jean Fresnel—and the principle of interference. In 1813, Peter Ewart supported the idea of the conservation of energy in his paper "On the measure of moving force". In 1820, Hans Christian Ørsted found that a current-carrying conductor gives rise to a magnetic force surrounding it, and within a week after Ørsted's discovery reached France, André-Marie Ampère discovered that two parallel electric currents will exert forces on each other. In 1821, William Hamilton began his analysis of Hamilton's characteristic function. In 1821, Michael Faraday built an electricity-powered motor, while Georg Ohm stated his law of electrical resistance in 1826, expressing the relationship between voltage, current, and resistance in an electric circuit. A year later, botanist Robert Brown discovered Brownian motion: pollen grains in water undergoing movement resulting from their bombardment by the fast-moving atoms or molecules in the liquid. In 1829, Gaspard Coriolis introduced the terms of work (force times distance) and kinetic energy with the meanings they have today.
Earth's magnetic field
The most common way of analyzing the global variations in the Earth's magnetic field is to fit the measurements to a set of spherical harmonics. This was first done by Carl Friedrich Gauss. Spherical harmonics are functions that oscillate over the surface of a sphere. They are the product of two functions, one that depends on latitude and one on longitude. The function of longitude is zero along zero or more great circles passing through the North and South Poles; the number of such "nodal lines" is the absolute value of the "order" . The function of latitude is zero along zero or more latitude circles; this plus the order is equal to the "degree" ℓ. Each harmonic is equivalent to a particular arrangement of magnetic charges at the center of the Earth. A "monopole" is an isolated magnetic charge, which has never been observed. A "dipole" is equivalent to two opposing charges brought close together and a "quadrupole" to two dipoles brought together. A quadrupole field is shown in the lower figure on the right.
History of geomagnetism
In 1269, Pierre de Maricourt (commonly referred to as "Petrus Peregrinus") wrote a letter to a friend in which he described two kinds of compass, one in which an oval lodestone floated in a bowl of water, and the first dry compass with the needle mounted on a pivot. He also was the first to write about experiments with magnetism and describe the laws of attraction. An example is the experiment where a magnet is broken into two pieces and the two pieces can attract and repel each other (in modern terms, they both have north and south poles). This letter, generally referred to as "Epistola de Magnete", was a landmark in the history of science.
Line of force
Early on in his research (circa 1831), Faraday calls the patterns of apparently continuous curves traced out in metallic filings near a magnet "magnetic curves". Later on he refers to them as just an instance of magnetic lines of force or simply lines of force. Eventually Faraday would also begin to use the phrase "magnetic field".
Diamagnetism
Diamagnetism was first discovered when Sebald Justinus Brugmans observed in 1778 that bismuth and antimony were repelled by magnetic fields. In 1845, Michael Faraday demonstrated that it was a property of matter and concluded that every material responded (in either a diamagnetic or paramagnetic way) to an applied magnetic field. On a suggestion by William Whewell, Faraday first referred to the phenomenon as "diamagnetic" (the prefix "dia-" meaning "through" or "across"), then later changed it to "diamagnetism".
History of the compass
In 1300, an Arabic treatise written by the Egyptian astronomer and muezzin Ibn Simʿūn describes a dry compass used for determining qibla. Like Peregrinus' compass, however, Ibn Simʿūn's compass did not feature a compass card. In the 14th century, the Syrian astronomer and timekeeper Ibn al-Shatir (1304–1375) invented a timekeeping device incorporating both a universal sundial and a magnetic compass. He invented it for the purpose of finding the times of prayers. Arab navigators also introduced the 32-point compass rose during this time. In 1399, an Egyptian reports two different kinds of magnetic compass. One instrument is a “fish” made of willow wood or pumpkin, into which a magnetic needle is inserted and sealed with tar or wax to prevent the penetration of water. The other instrument is a dry compass.
In the 15th century, the description given by Ibn Majid while aligning the compass with the pole star indicates that he was aware of magnetic declination. An explicit value for the declination is given by ʿIzz al-Dīn al-Wafāʾī (fl. 1450s in Cairo).
History of gravitational theory
To make this into an equal-sided formula or equation, there needed to be a multiplying factor or constant that would give the correct force of gravity no matter the value of the masses or distance between them. This gravitational constant was first measured in 1797 by Henry Cavendish.
Blinded experiment
The French Academy of Sciences originated the first recorded blind experiments in 1784: the Academy set up a commission to investigate the claims of animal magnetism proposed by Franz Mesmer. Headed by Benjamin Franklin and Antoine Lavoisier, the commission carried out experiments asking mesmerists to identify objects that had previously been filled with "vital fluid", including trees and flasks of water. The subjects were unable to do so. The commission went on to examine claims involving the curing of "mesmerized" patients. These patients showed signs of improved health, but the commission attributed this to the fact that these patients believed they would get better—the first scientific suggestion of the now well-known placebo effect.
Magnet
Ancient people learned about magnetism from lodestones (or magnetite) are naturally magnetized pieces of iron ore. The word "magnet" was adopted in Middle English from Latin "magnetum" "lodestone", ultimately from Greek ("magnētis [lithos]") meaning "[stone] from Magnesia", a part of ancient Greece where lodestones were found. Lodestones, suspended so they could turn, were the first magnetic compasses. The earliest known surviving descriptions of magnets and their properties are from Greece, India, and China around 2500 years ago. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia "Naturalis Historia".
Gian Domenico Romagnosi
Although Romagnosi was not a scientist, he made some experiments with a voltaic pile and its influence on a compass. He published two accounts of his findings in 1802, in Italian newspapers. It is sometimes assumed that he found a relationship between electricity and magnetism, about two decades before Hans Christian Ørsted's 1820 discovery of electromagnetism. However, his experiments did not deal with electric currents, and only showed that an electrostatic charge from a voltaic pile could deflect a magnetic needle. 
However, as Joseph Hamel has pointed out, Romagnosi's discovery was documented in the book by Joseph Izarn, "Manuel du Galvanisme" (1805), where a galvanic current ("courant galvanique") is explicitly mentioned. 
It was also mentioned on page 340 of the book by Giovanni Aldini, "Essai théorique et expérimental sur le Galvanisme" (1804): "Cette nouvelle propriété du galvanisme a été constatée par d'autres observateurs, et dernièrement par M. Romanesi, physicien. de Trente, qui a reconnu que le galvanisme faisait décliner l'aiguille aimantée." Aldini was also communicating with Ørsted at the time, Hamel notes.
History of electromagnetic theory
George Green wrote "An Essay on the Application of Mathematical Analysis to the Theories of Electricity and Magnetism" in 1828. The essay introduced several important concepts, among them a theorem similar to the modern Green's theorem, the idea of potential functions as currently used in physics, and the concept of what are now called Green's functions. George Green was the first person to create a mathematical theory of electricity and magnetism and his theory formed the foundation for the work of other scientists such as James Clerk Maxwell, William Thomson, and others.
Magnetic quantum number
where formula_24 is the reduced Planck constant. Note this formula_25 for formula_26 and approximates formula_27 for high formula_2. It is not possible to measure the angular momentum of the electron in all three axes simultaneously. These properties were first demonstrated in the Stern-Gerlach experiment, by Otto Stern and Walther Gerlach.
Etheric force
Thomas Edison announced the discovery, which he called "etheric force", to the press and reports began to appear in Newark newspapers from November 29, 1875. While etheric force initially met with an enthusiastic reception, sceptics began to question whether it truly was a new phenomenon or merely a consequence of some already known phenomenon such as electromagnetic induction. Leaders among the doubters were James Ashley, editor of the "Telegrapher", the inventor Elihu Thomson and Edwin Houston, a high school teacher with whom Thomson had studied. Thomson and Houston conducted a series of careful experiments where they discovered that the sparks actually carried a charge, and they announced their results, not in the popular press as Edison had done, but in a scientific journal, the "Journal of the Franklin Institute". This prompted a reply from Edison, more experiments and more scientific papers.
Force
Meanwhile, the Lorentz force of magnetism was discovered to exist between two electric currents. It has the same mathematical character as Coulomb's Law with the proviso that like currents attract and unlike currents repel. Similar to the electric field, the magnetic field can be used to determine the magnetic force on an electric current at any point in space. In this case, the magnitude of the magnetic field was determined to be
History of electromagnetic theory
The magnetic monopole in the "quantum" theory of magnetic charge started with a paper by the physicist Paul A.M. Dirac in 1931. The detection of magnetic monopoles is an open problem in experimental physics. In some theoretical models, magnetic monopoles are unlikely to be observed, because they are too massive to be created in particle accelerators, and also too rare in the Universe to enter a particle detector with much probability.