Magnet

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https://en.wikipedia.org/wiki/Magnet 

A "horseshoe magnet" made of alnico, an iron alloy. The magnet, made in the shape of a horseshoe, has the two magnetic poles close together. This shape creates a strong magnetic field between the poles, allowing the magnet to pick up a heavy piece of iron.

 

Magnetic field lines of a solenoid electromagnet, which are similar to a bar magnet as illustrated below with the iron filings

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets.

A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt and their alloys, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.

Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization.

An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of "soft" ferromagnetic material such as mild steel, which greatly enhances the magnetic field produced by the coil.

Discovery and development

Main article: History of electromagnetism

See also: Magnetism history

Ancient people learned about magnetism from lodestones (or magnetite) which are naturally magnetized pieces of iron ore. The word magnet was adopted in Middle English from Latin magnetum "lodestone", ultimately from Greek μαγνῆτις [λίθος] (magnētis [lithos]) meaning "[stone] from Magnesia", a place in Anatolia where lodestones were found (today Manisa in modern-day Turkey). Lodestones, suspended so they could turn, were the first magnetic compasses. The earliest known surviving descriptions of magnets and their properties are from Anatolia, 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.

By the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere.

Physics

Magnetic field

Iron filings that have oriented in the magnetic field produced by a bar magnet

The magnetic flux density (also called magnetic B field or just magnetic field, usually denoted B) is a vector field. The magnetic B field vector at a given point in space is specified by two properties:

1. Its direction, which is along the orientation of a compass needle.
2. Its magnitude (also called strength), which is proportional to how strongly the compass needle orients along that direction.

In SI units, the strength of the magnetic B field is given in teslas.

Magnetic moment

Main article: Magnetic moment

A magnet's magnetic moment (also called magnetic dipole moment and usually denoted μ) is a vector that characterizes the magnet's overall magnetic properties. For a bar magnet, the direction of the magnetic moment points from the magnet's south pole to its north pole, and the magnitude relates to how strong and how far apart these poles are. In SI units, the magnetic moment is specified in terms of A·m² (amperes times meters squared).

A magnet both produces its own magnetic field and responds to magnetic fields. The strength of the magnetic field it produces is at any given point proportional to the magnitude of its magnetic moment. In addition, when the magnet is put into an external magnetic field, produced by a different source, it is subject to a torque tending to orient the magnetic moment parallel to the field. The amount of this torque is proportional both to the magnetic moment and the external field. A magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the magnet and source. If the field is uniform in space, the magnet is subject to no net force, although it is subject to a torque.

A wire in the shape of a circle with area A and carrying current I has a magnetic moment of magnitude equal to IA.

Magnetization

Main article: Magnetization

The magnetization of a magnetized material is the local value of its magnetic moment per unit volume, usually denoted M, with units A/m. It is a vector field, rather than just a vector (like the magnetic moment), because different areas in a magnet can be magnetized with different directions and strengths (for example, because of domains, see below). A good bar magnet may have a magnetic moment of magnitude 0.1 A·m² and a volume of 1 cm³, or 1×10⁻⁶ m³, and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million amperes per meter. Such a large value explains why iron magnets are so effective at producing magnetic fields.

Modelling magnets

Field of a cylindrical bar magnet computed accurately

 

See also: Two definitions of moment

Two different models exist for magnets: magnetic poles and atomic currents.

Although for many purposes it is convenient to think of a magnet as having distinct north and south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The magnet does not have distinct north or south particles on opposing sides. If a bar magnet is broken into two pieces, in an attempt to separate the north and south poles, the result will be two bar magnets, each of which has both a north and south pole. However, a version of the magnetic-pole approach is used by professional magneticians to design permanent magnets.

In this approach, the divergence of the magnetization ∇·M inside a magnet is treated as a distribution of magnetic monopoles. This is a mathematical convenience and does not imply that there are actually monopoles in the magnet. If the magnetic-pole distribution is known, then the pole model gives the magnetic field H. Outside the magnet, the field B is proportional to H, while inside the magnetization must be added to H. An extension of this method that allows for internal magnetic charges is used in theories of ferromagnetism.

Another model is the Ampère model, where all magnetization is due to the effect of microscopic, or atomic, circular bound currents, also called Ampèrian currents, throughout the material. For a uniformly magnetized cylindrical bar magnet, the net effect of the microscopic bound currents is to make the magnet behave as if there is a macroscopic sheet of electric current flowing around the surface, with local flow direction normal to the cylinder axis. Microscopic currents in atoms inside the material are generally canceled by currents in neighboring atoms, so only the surface makes a net contribution; shaving off the outer layer of a magnet will not destroy its magnetic field, but will leave a new surface of uncancelled currents from the circular currents throughout the material. The right-hand rule tells which direction positively-charged current flows. However, current due to negatively-charged electricity is far more prevalent in practice.

Polarity

The north pole of a magnet is defined as the pole that, when the magnet is freely suspended, points towards the Earth's North Magnetic Pole in the Arctic (the magnetic and geographic poles do not coincide, see magnetic declination). Since opposite poles (north and south) attract, the North Magnetic Pole is actually the south pole of the Earth's magnetic field. As a practical matter, to tell which pole of a magnet is north and which is south, it is not necessary to use the Earth's magnetic field at all. For example, one method would be to compare it to an electromagnet, whose poles can be identified by the right-hand rule. The magnetic field lines of a magnet are considered by convention to emerge from the magnet's north pole and reenter at the south pole.

Magnetic materials

Main article: Magnetism

The term magnet is typically reserved for objects that produce their own persistent magnetic field even in the absence of an applied magnetic field. Only certain classes of materials can do this. Most materials, however, produce a magnetic field in response to an applied magnetic field – a phenomenon known as magnetism. There are several types of magnetism, and all materials exhibit at least one of them.

The overall magnetic behavior of a material can vary widely, depending on the structure of the material, particularly on its electron configuration. Several forms of magnetic behavior have been observed in different materials, including:

• Ferromagnetic and ferrimagnetic materials are the ones normally thought of as magnetic; they are attracted to a magnet strongly enough that the attraction can be felt. These materials are the only ones that can retain magnetization and become magnets; a common example is a traditional refrigerator magnet. Ferrimagnetic materials, which include ferrites and the oldest magnetic materials magnetite and lodestone, are similar to but weaker than ferromagnetics. The difference between ferro- and ferrimagnetic materials is related to their microscopic structure, as explained in Magnetism.
• Paramagnetic substances, such as platinum, aluminum, and oxygen, are weakly attracted to either pole of a magnet. This attraction is hundreds of thousands of times weaker than that of ferromagnetic materials, so it can only be detected by using sensitive instruments or using extremely strong magnets. Magnetic ferrofluids, although they are made of tiny ferromagnetic particles suspended in liquid, are sometimes considered paramagnetic since they cannot be magnetized.
• Diamagnetic means repelled by both poles. Compared to paramagnetic and ferromagnetic substances, diamagnetic substances, such as carbon, copper, water, and plastic, are even more weakly repelled by a magnet. The permeability of diamagnetic materials is less than the permeability of a vacuum. All substances not possessing one of the other types of magnetism are diamagnetic; this includes most substances. Although force on a diamagnetic object from an ordinary magnet is far too weak to be felt, using extremely strong superconducting magnets, diamagnetic objects such as pieces of lead and even mice can be levitated, so they float in mid-air. Superconductors repel magnetic fields from their interior and are strongly diamagnetic.

There are various other types of magnetism, such as spin glass, superparamagnetism, superdiamagnetism, and metamagnetism.

Common uses

Hard disk drives record data on a thin magnetic coating

 

Magnetic hand separator for heavy minerals

• Magnetic recording media: VHS tapes contain a reel of magnetic tape. The information that makes up the video and sound is encoded on the magnetic coating on the tape. Common audio cassettes also rely on magnetic tape. Similarly, in computers, floppy disks and hard disks record data on a thin magnetic coating.
• Credit, debit, and automatic teller machine cards: All of these cards have a magnetic strip on one side. This strip encodes the information to contact an individual's financial institution and connect with their account(s).
• Older types of televisions (non flat screen) and older large computer monitors: TV and computer screens containing a cathode ray tube employ an electromagnet to guide electrons to the screen.
• Speakers and microphones: Most speakers employ a permanent magnet and a current-carrying coil to convert electric energy (the signal) into mechanical energy (movement that creates the sound). The coil is wrapped around a bobbin attached to the speaker cone and carries the signal as changing current that interacts with the field of the permanent magnet. The voice coil feels a magnetic force and in response, moves the cone and pressurizes the neighboring air, thus generating sound. Dynamic microphones employ the same concept, but in reverse. A microphone has a diaphragm or membrane attached to a coil of wire. The coil rests inside a specially shaped magnet. When sound vibrates the membrane, the coil is vibrated as well. As the coil moves through the magnetic field, a voltage is induced across the coil. This voltage drives a current in the wire that is characteristic of the original sound.
• Electric guitars use magnetic pickups to transduce the vibration of guitar strings into electric current that can then be amplified. This is different from the principle behind the speaker and dynamic microphone because the vibrations are sensed directly by the magnet, and a diaphragm is not employed. The Hammond organ used a similar principle, with rotating tonewheels instead of strings.
• Electric motors and generators: Some electric motors rely upon a combination of an electromagnet and a permanent magnet, and, much like loudspeakers, they convert electric energy into mechanical energy. A generator is the reverse: it converts mechanical energy into electric energy by moving a conductor through a magnetic field.
• Medicine: Hospitals use magnetic resonance imaging to spot problems in a patient's organs without invasive surgery.
• Chemistry: Chemists use nuclear magnetic resonance to characterize synthesized compounds.
• Chucks are used in the metalworking field to hold objects. Magnets are also used in other types of fastening devices, such as the magnetic base, the magnetic clamp and the refrigerator magnet.
• Compasses: A compass (or mariner's compass) is a magnetized pointer free to align itself with a magnetic field, most commonly Earth's magnetic field.
• Art: Vinyl magnet sheets may be attached to paintings, photographs, and other ornamental articles, allowing them to be attached to refrigerators and other metal surfaces. Objects and paint can be applied directly to the magnet surface to create collage pieces of art. Metal magnetic boards, strips, doors, microwave ovens, dishwashers, cars, metal I beams, and any metal surface can be used magnetic vinyl art.
• Science projects: Many topic questions are based on magnets, including the repulsion of current-carrying wires, the effect of temperature, and motors involving magnets.

Magnets have many uses in toys. M-tic uses magnetic rods connected to metal spheres for construction.

• Toys: Given their ability to counteract the force of gravity at close range, magnets are often employed in children's toys, such as the Magnet Space Wheel and Levitron, to amusing effect.
• Refrigerator magnets are used to adorn kitchens, as a souvenir, or simply to hold a note or photo to the refrigerator door.
• Magnets can be used to make jewelry. Necklaces and bracelets can have a magnetic clasp, or may be constructed entirely from a linked series of magnets and ferrous beads.
• Magnets can pick up magnetic items (iron nails, staples, tacks, paper clips) that are either too small, too hard to reach, or too thin for fingers to hold. Some screwdrivers are magnetized for this purpose.
• Magnets can be used in scrap and salvage operations to separate magnetic metals (iron, cobalt, and nickel) from non-magnetic metals (aluminum, non-ferrous alloys, etc.). The same idea can be used in the so-called "magnet test", in which a car chassis is inspected with a magnet to detect areas repaired using fiberglass or plastic putty.
• Magnets are found in process industries, food manufacturing especially, in order to remove metal foreign bodies from materials entering the process (raw materials) or to detect a possible contamination at the end of the process and prior to packaging. They constitute an important layer of protection for the process equipment and for the final consumer.
• Magnetic levitation transport, or maglev, is a form of transportation that suspends, guides and propels vehicles (especially trains) through electromagnetic force. Eliminating rolling resistance increases efficiency. The maximum recorded speed of a maglev train is 581 kilometers per hour (361 mph).
• Magnets may be used to serve as a fail-safe device for some cable connections. For example, the power cords of some laptops are magnetic to prevent accidental damage to the port when tripped over. The MagSafe power connection to the Apple MacBook is one such example.

Medical issues and safety

Because human tissues have a very low level of susceptibility to static magnetic fields, there is little mainstream scientific evidence showing a health effect associated with exposure to static fields. Dynamic magnetic fields may be a different issue, however; correlations between electromagnetic radiation and cancer rates have been postulated due to demographic correlations (see Electromagnetic radiation and health).

If a ferromagnetic foreign body is present in human tissue, an external magnetic field interacting with it can pose a serious safety risk.

A different type of indirect magnetic health risk exists involving pacemakers. If a pacemaker has been embedded in a patient's chest (usually for the purpose of monitoring and regulating the heart for steady electrically induced beats), care should be taken to keep it away from magnetic fields. It is for this reason that a patient with the device installed cannot be tested with the use of a magnetic resonance imaging device.

Children sometimes swallow small magnets from toys, and this can be hazardous if two or more magnets are swallowed, as the magnets can pinch or puncture internal tissues.

Magnetic imaging devices (e.g. MRIs) generate enormous magnetic fields, and therefore rooms intended to hold them exclude ferrous metals. Bringing objects made of ferrous metals (such as oxygen canisters) into such a room creates a severe safety risk, as those objects may be powerfully thrown about by the intense magnetic fields.

Magnetizing ferromagnets

See also: Remanence

Ferromagnetic materials can be magnetized in the following ways:

• Heating the object higher than its Curie temperature, allowing it to cool in a magnetic field and hammering it as it cools. This is the most effective method and is similar to the industrial processes used to create permanent magnets.
• Placing the item in an external magnetic field will result in the item retaining some of the magnetism on removal. Vibration has been shown to increase the effect. Ferrous materials aligned with the Earth's magnetic field that are subject to vibration (e.g., frame of a conveyor) have been shown to acquire significant residual magnetism. Likewise, striking a steel nail held by fingers in a N-S direction with a hammer will temporarily magnetize the nail.
• Stroking: An existing magnet is moved from one end of the item to the other repeatedly in the same direction (single touch method) or two magnets are moved outwards from the center of a third (double touch method).
• Electric Current: The magnetic field produced by passing an electric current through a coil can get domains to line up. Once all of the domains are lined up, increasing the current will not increase the magnetization.

Demagnetizing ferromagnets

Magnetized ferromagnetic materials can be demagnetized (or degaussed) in the following ways:

• Heating a magnet past its Curie temperature; the molecular motion destroys the alignment of the magnetic domains. This always removes all magnetization.
• Placing the magnet in an alternating magnetic field with intensity above the material's coercivity and then either slowly drawing the magnet out or slowly decreasing the magnetic field to zero. This is the principle used in commercial demagnetizers to demagnetize tools, erase credit cards, hard disks, and degaussing coils used to demagnetize CRTs.
• Some demagnetization or reverse magnetization will occur if any part of the magnet is subjected to a reverse field above the magnetic material's coercivity.
• Demagnetization progressively occurs if the magnet is subjected to cyclic fields sufficient to move the magnet away from the linear part on the second quadrant of the B–H curve of the magnetic material (the demagnetization curve).
• Hammering or jarring: mechanical disturbance tends to randomize the magnetic domains and reduce magnetization of an object, but may cause unacceptable damage.

Types of permanent magnets

A stack of ferrite magnets

Magnetic metallic elements

Many materials have unpaired electron spins, and the majority of these materials are paramagnetic. When the spins interact with each other in such a way that the spins align spontaneously, the materials are called ferromagnetic (what is often loosely termed as magnetic). Because of the way their regular crystalline atomic structure causes their spins to interact, some metals are ferromagnetic when found in their natural states, as ores. These include iron ore (magnetite or lodestone), cobalt and nickel, as well as the rare earth metals gadolinium and dysprosium (when at a very low temperature). Such naturally occurring ferromagnets were used in the first experiments with magnetism. Technology has since expanded the availability of magnetic materials to include various man-made products, all based, however, on naturally magnetic elements.

Composites

Ceramic, or ferrite, magnets are made of a sintered composite of powdered iron oxide and barium/strontium carbonate ceramic. Given the low cost of the materials and manufacturing methods, inexpensive magnets (or non-magnetized ferromagnetic cores, for use in electronic components such as portable AM radio antennas) of various shapes can be easily mass-produced. The resulting magnets are non-corroding but brittle and must be treated like other ceramics.

Alnico magnets are made by casting or sintering a combination of aluminium, nickel and cobalt with iron and small amounts of other elements added to enhance the properties of the magnet. Sintering offers superior mechanical characteristics, whereas casting delivers higher magnetic fields and allows for the design of intricate shapes. Alnico magnets resist corrosion and have physical properties more forgiving than ferrite, but not quite as desirable as a metal. Trade names for alloys in this family include: Alni, Alcomax, Hycomax, Columax, and Ticonal.

Injection-molded magnets are a composite of various types of resin and magnetic powders, allowing parts of complex shapes to be manufactured by injection molding. The physical and magnetic properties of the product depend on the raw materials, but are generally lower in magnetic strength and resemble plastics in their physical properties.

Flexible magnet

Flexible magnets are composed of a high-coercivity ferromagnetic compound (usually ferric oxide) mixed with a resinous polymer binder. This is extruded as a sheet and passed over a line of powerful cylindrical permanent magnets. These magnets are arranged in a stack with alternating magnetic poles facing up (N, S, N, S...) on a rotating shaft. This impresses the plastic sheet with the magnetic poles in an alternating line format. No electromagnetism is used to generate the magnets. The pole-to-pole distance is on the order of 5 mm, but varies with manufacturer. These magnets are lower in magnetic strength but can be very flexible, depending on the binder used.

For magnetic compounds (e.g. Nd₂Fe₁₄B) that are vulnerable to a grain boundary corrosion problem it gives additional protection.

Rare-earth magnets

Ovoid-shaped magnets (possibly Hematine), one hanging from another

 

Main article: Rare-earth magnet

Rare earth (lanthanoid) elements have a partially occupied f electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare-earth magnets are samarium–cobalt and neodymium–iron–boron (NIB) magnets.

Single-molecule magnets (SMMs) and single-chain magnets (SCMs)

Main article: Single-molecule magnet

In the 1990s, it was discovered that certain molecules containing paramagnetic metal ions are capable of storing a magnetic moment at very low temperatures. These are very different from conventional magnets that store information at a magnetic domain level and theoretically could provide a far denser storage medium than conventional magnets. In this direction, research on monolayers of SMMs is currently under way. Very briefly, the two main attributes of an SMM are:

1. a large ground state spin value (S), which is provided by ferromagnetic or ferrimagnetic coupling between the paramagnetic metal centres
2. a negative value of the anisotropy of the zero field splitting (D)

Most SMMs contain manganese but can also be found with vanadium, iron, nickel and cobalt clusters. More recently, it has been found that some chain systems can also display a magnetization that persists for long times at higher temperatures. These systems have been called single-chain magnets.

Nano-structured magnets

Some nano-structured materials exhibit energy waves, called magnons, that coalesce into a common ground state in the manner of a Bose–Einstein condensate.

Rare-earth-free permanent magnets

The United States Department of Energy has identified a need to find substitutes for rare-earth metals in permanent-magnet technology, and has begun funding such research. The Advanced Research Projects Agency-Energy (ARPA-E) has sponsored a Rare Earth Alternatives in Critical Technologies (REACT) program to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund Rare-Earth Substitute projects.

Costs

The current cheapest permanent magnets, allowing for field strengths, are flexible and ceramic magnets, but these are also among the weakest types. The ferrite magnets are mainly low-cost magnets since they are made from cheap raw materials: iron oxide and Ba- or Sr-carbonate. However, a new low cost magnet, Mn–Al alloy, has been developed and is now dominating the low-cost magnets field. It has a higher saturation magnetization than the ferrite magnets. It also has more favorable temperature coefficients, although it can be thermally unstable. Neodymium–iron–boron (NIB) magnets are among the strongest. These cost more per kilogram than most other magnetic materials but, owing to their intense field, are smaller and cheaper in many applications.

Temperature

Temperature sensitivity varies, but when a magnet is heated to a temperature known as the Curie point, it loses all of its magnetism, even after cooling below that temperature. The magnets can often be remagnetized, however.

Additionally, some magnets are brittle and can fracture at high temperatures.

The maximum usable temperature is highest for alnico magnets at over 540 °C (1,000 °F), around 300 °C (570 °F) for ferrite and SmCo, about 140 °C (280 °F) for NIB and lower for flexible ceramics, but the exact numbers depend on the grade of material.

Electromagnets

Main article: Electromagnet

An electromagnet, in its simplest form, is a wire that has been coiled into one or more loops, known as a solenoid. When electric current flows through the wire, a magnetic field is generated. It is concentrated near (and especially inside) the coil, and its field lines are very similar to those of a magnet. The orientation of this effective magnet is determined by the right hand rule. The magnetic moment and the magnetic field of the electromagnet are proportional to the number of loops of wire, to the cross-section of each loop, and to the current passing through the wire.

If the coil of wire is wrapped around a material with no special magnetic properties (e.g., cardboard), it will tend to generate a very weak field. However, if it is wrapped around a soft ferromagnetic material, such as an iron nail, then the net field produced can result in a several hundred- to thousandfold increase of field strength.

Uses for electromagnets include particle accelerators, electric motors, junkyard cranes, and magnetic resonance imaging machines. Some applications involve configurations more than a simple magnetic dipole; for example, quadrupole and sextupole magnets are used to focus particle beams.

Units and calculations

Main article: Magnetostatics

For most engineering applications, MKS (rationalized) or SI (Système International) units are commonly used. Two other sets of units, Gaussian and CGS-EMU, are the same for magnetic properties and are commonly used in physics.

In all units, it is convenient to employ two types of magnetic field, B and H, as well as the magnetization M, defined as the magnetic moment per unit volume.

1. The magnetic induction field B is given in SI units of teslas (T). B is the magnetic field whose time variation produces, by Faraday's Law, circulating electric fields (which the power companies sell). B also produces a deflection force on moving charged particles (as in TV tubes). The tesla is equivalent to the magnetic flux (in webers) per unit area (in meters squared), thus giving B the unit of a flux density. In CGS, the unit of B is the gauss (G). One tesla equals 10⁴ G.
2. The magnetic field H is given in SI units of ampere-turns per meter (A-turn/m). The turns appear because when H is produced by a current-carrying wire, its value is proportional to the number of turns of that wire. In CGS, the unit of H is the oersted (Oe). One A-turn/m equals 4π×10⁻³ Oe.
3. The magnetization M is given in SI units of amperes per meter (A/m). In CGS, the unit of M is the oersted (Oe). One A/m equals 10⁻³ emu/cm³. A good permanent magnet can have a magnetization as large as a million amperes per meter.
4. In SI units, the relation B = μ₀(H + M) holds, where μ₀ is the permeability of space, which equals 4π×10⁻⁷ T•m/A. In CGS, it is written as B = H + 4πM. (The pole approach gives μ₀H in SI units. A μ₀M term in SI must then supplement this μ₀H to give the correct field within B, the magnet. It will agree with the field B calculated using Ampèrian currents).

Materials that are not permanent magnets usually satisfy the relation M = χH in SI, where χ is the (dimensionless) magnetic susceptibility. Most non-magnetic materials have a relatively small χ (on the order of a millionth), but soft magnets can have χ on the order of hundreds or thousands. For materials satisfying M = χH, we can also write B = μ₀(1 + χ)H = μ₀μ_rH = μH, where μ_r = 1 + χ is the (dimensionless) relative permeability and μ =μ₀μ_r is the magnetic permeability. Both hard and soft magnets have a more complex, history-dependent, behavior described by what are called hysteresis loops, which give either B vs. H or M vs. H. In CGS, M = χH, but χ_SI = 4πχ_CGS, and μ = μ_r.

Caution: in part because there are not enough Roman and Greek symbols, there is no commonly agreed-upon symbol for magnetic pole strength and magnetic moment. The symbol m has been used for both pole strength (unit A•m, where here the upright m is for meter) and for magnetic moment (unit A•m²). The symbol μ has been used in some texts for magnetic permeability and in other texts for magnetic moment. We will use μ for magnetic permeability and m for magnetic moment. For pole strength, we will employ q_m. For a bar magnet of cross-section A with uniform magnetization M along its axis, the pole strength is given by q_m = MA, so that M can be thought of as a pole strength per unit area.

Fields of a magnet

Field lines of cylindrical magnets with various aspect ratios

Far away from a magnet, the magnetic field created by that magnet is almost always described (to a good approximation) by a dipole field characterized by its total magnetic moment. This is true regardless of the shape of the magnet, so long as the magnetic moment is non-zero. One characteristic of a dipole field is that the strength of the field falls off inversely with the cube of the distance from the magnet's center.

Closer to the magnet, the magnetic field becomes more complicated and more dependent on the detailed shape and magnetization of the magnet. Formally, the field can be expressed as a multipole expansion: A dipole field, plus a quadrupole field, plus an octupole field, etc.

At close range, many different fields are possible. For example, for a long, skinny bar magnet with its north pole at one end and south pole at the other, the magnetic field near either end falls off inversely with the square of the distance from that pole.

Calculating the magnetic force

Main article: force between magnets

Pull force of a single magnet

The strength of a given magnet is sometimes given in terms of its pull force — its ability to pull ferromagnetic objects. The pull force exerted by either an electromagnet or a permanent magnet with no air gap (i.e., the ferromagnetic object is in direct contact with the pole of the magnet) is given by the Maxwell equation:

${\displaystyle F={{B^{2}A} \over {2\mu _{0}}}}$,

where

F is force (SI unit: newton)

A is the cross section of the area of the pole in square meters

B is the magnetic induction exerted by the magnet

This result can be easily derived using Gilbert model, which assumes that the pole of magnet is charged with magnetic monopoles that induces the same in the ferromagnetic object.

If a magnet is acting vertically, it can lift a mass m in kilograms given by the simple equation:

${\displaystyle m={{B^{2}A} \over {2\mu _{0}g}},}$

where g is the gravitational acceleration.

Force between two magnetic poles

Further information: Magnetic moment § Forces between two magnetic dipoles

Classically, the force between two magnetic poles is given by:

${\displaystyle F={{\mu q_{m1}q_{m2}} \over {4\pi r^{2}}}}$

where

F is force (SI unit: newton)

q_m1 and q_m2 are the magnitudes of magnetic poles (SI unit: ampere-meter)

μ is the permeability of the intervening medium (SI unit: tesla meter per ampere, henry per meter or newton per ampere squared)

r is the separation (SI unit: meter).

The pole description is useful to the engineers designing real-world magnets, but real magnets have a pole distribution more complex than a single north and south. Therefore, implementation of the pole idea is not simple. In some cases, one of the more complex formulae given below will be more useful.

Force between two nearby magnetized surfaces of area A

The mechanical force between two nearby magnetized surfaces can be calculated with the following equation. The equation is valid only for cases in which the effect of fringing is negligible and the volume of the air gap is much smaller than that of the magnetized material:

${\displaystyle F={\frac {\mu _{0}H^{2}A}{2}}={\frac {B^{2}A}{2\mu _{0}}}}$

where:

A is the area of each surface, in m²

H is their magnetizing field, in A/m

μ₀ is the permeability of space, which equals 4π×10⁻⁷ T•m/A

B is the flux density, in T.

Force between two bar magnets

The force between two identical cylindrical bar magnets placed end to end at large distance ${\displaystyle z\gg R}$ is approximately:

${\displaystyle F\simeq \left[{\frac {B_{0}^{2}A^{2}\left(L^{2}+R^{2}\right)}{\pi \mu _{0}L^{2}}}\right]\left[{\frac {1}{z^{2}}}+{\frac {1}{(z+2L)^{2}}}-{\frac {2}{(z+L)^{2}}}\right]}$

where:

B₀ is the magnetic flux density very close to each pole, in T,

A is the area of each pole, in m²,

L is the length of each magnet, in m,

R is the radius of each magnet, in m, and

z is the separation between the two magnets, in m.

${\displaystyle B_{0}\,=\,{\frac {\mu _{0}}{2}}M}$ relates the flux density at the pole to the magnetization of the magnet.

Note that all these formulations are based on Gilbert's model, which is usable in relatively great distances. In other models (e.g., Ampère's model), a more complicated formulation is used that sometimes cannot be solved analytically. In these cases, numerical methods must be used.

Force between two cylindrical magnets

For two cylindrical magnets with radius ${\displaystyle R}$ and length ${\displaystyle L}$, with their magnetic dipole aligned, the force can be asymptotically approximated at large distance ${\displaystyle z\gg R}$ by,

${\displaystyle F(z)\simeq {\frac {\pi \mu _{0}}{4}}M^{2}R^{4}\left[{\frac {1}{z^{2}}}+{\frac {1}{(z+2L)^{2}}}-{\frac {2}{(z+L)^{2}}}\right]}$

where ${\displaystyle M}$ is the magnetization of the magnets and ${\displaystyle z}$ is the gap between the magnets. A measurement of the magnetic flux density very close to the magnet ${\displaystyle B_{0}}$ is related to ${\displaystyle M}$ approximately by the formula

${\displaystyle B_{0}={\frac {\mu _{0}}{2}}M}$

The effective magnetic dipole can be written as

${\displaystyle m=MV}$

Where ${\displaystyle V}$ is the volume of the magnet. For a cylinder, this is ${\displaystyle V=\pi R^{2}L}$.

When ${\displaystyle z\gg L}$, the point dipole approximation is obtained,

${\displaystyle F(x)={\frac {3\pi \mu _{0}}{2}}M^{2}R^{4}L^{2}{\frac {1}{z^{4}}}={\frac {3\mu _{0}}{2\pi }}M^{2}V^{2}{\frac {1}{z^{4}}}={\frac {3\mu _{0}}{2\pi }}m_{1}m_{2}{\frac {1}{z^{4}}}}$

which matches the expression of the force between two magnetic dipoles.

Republicanism

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Republicanism 

Republicanism is a political ideology centered on citizenship in a state organized as a republic. Historically, it ranges from the rule of a representative minority or oligarchy to popular sovereignty. It has had different definitions and interpretations which vary significantly based on historical context and methodological approach.

Republicanism may also refer to the non-ideological scientific approach to politics and governance. As the republican thinker and second president of the United States John Adams stated in the introduction to his famous A Defense of the Constitutions of Government of the United States of America, the "science of politics is the science of social happiness" and a republic is the form of government arrived at when the science of politics is appropriately applied to the creation of a rationally designed government. Rather than being ideological, this approach focuses on applying a scientific methodology to the problems of governance through the rigorous study and application of past experience and experimentation in governance. This is the approach that may best be described to apply to republican thinkers such as Niccolò Machiavelli (as evident in his Discourses on Livy), John Adams, and James Madison.

The word "republic" derives from the Latin noun-phrase res publica (public thing), which referred to the system of government that emerged in the 6th century BCE following the expulsion of the kings from Rome by Lucius Junius Brutus and Collatinus.

This form of government in the Roman state collapsed in the latter part of the 1st century BCE, giving way to what was a monarchy in form, if not in name. Republics recurred subsequently, with, for example, Renaissance Florence or early modern Britain. The concept of a republic became a powerful force in Britain's North American colonies, where it contributed to the American Revolution. In Europe, it gained enormous influence through the French Revolution and through the First French Republic of 1792–1804.

Historical development of republicanism

Main article: Classical republicanism

Classical antecedents

Ancient Greece

Sculpture of Aristotle

In Ancient Greece, several philosophers and historians analysed and described elements we now recognize as classical republicanism. Traditionally, the Greek concept of "politeia" was rendered into Latin as res publica. Consequently, political theory until relatively recently often used republic in the general sense of "regime". There is no single written expression or definition from this era that exactly corresponds with a modern understanding of the term "republic" but most of the essential features of the modern definition are present in the works of Plato, Aristotle, and Polybius. These include theories of mixed government and of civic virtue. For example, in The Republic, Plato places great emphasis on the importance of civic virtue (aiming for the good) together with personal virtue ('just man') on the part of the ideal rulers. Indeed, in Book V, Plato asserts that until rulers have the nature of philosophers (Socrates) or philosophers become the rulers, there can be no civic peace or happiness.

A number of Ancient Greek city-states such as Athens and Sparta have been classified as "classical republics", because they featured extensive participation by the citizens in legislation and political decision-making. Aristotle considered Carthage to have been a republic as it had a political system similar to that of some of the Greek cities, notably Sparta, but avoided some of the defects that affected them.

Ancient Rome

Both Livy, a Roman historian, and Plutarch, who is noted for his biographies and moral essays, described how Rome had developed its legislation, notably the transition from a kingdom to a republic, by following the example of the Greeks. Some of this history, composed more than 500 years after the events, with scant written sources to rely on, may be fictitious reconstruction.

The Greek historian Polybius, writing in the mid-2nd century BCE, emphasized (in Book 6) the role played by the Roman Republic as an institutional form in the dramatic rise of Rome's hegemony over the Mediterranean. In his writing on the constitution of the Roman Republic, Polybius described the system as being a "mixed" form of government. Specifically, Polybius described the Roman system as a mixture of monarchy, aristocracy, and democracy with the Roman Republic constituted in such a manner that it applied the strengths of each system to offset the weaknesses of the others. In his view, the mixed system of the Roman Republic provided the Romans with a much greater level of domestic tranquility than would have been experienced under another form of government. Furthermore, Polybius argued, the comparative level of domestic tranquility the Romans enjoyed allowed them to conquer the Mediterranean. Polybius exerted a great influence on Cicero as he wrote his politico-philosophical works in the 1st century BCE. In one of these works, De re publica, Cicero linked the Roman concept of res publica to the Greek politeia.

The modern term "republic", despite its derivation, is not synonymous with the Roman res publica. Among the several meanings of the term res publica, it is most often translated "republic" where the Latin expression refers to the Roman state, and its form of government, between the era of the Kings and the era of the Emperors. This Roman Republic would, by a modern understanding of the word, still be defined as a true republic, even if not coinciding entirely. Thus, Enlightenment philosophers saw the Roman Republic as an ideal system because it included features like a systematic separation of powers.

Romans still called their state "Res Publica" in the era of the early emperors because, on the surface, the organization of the state had been preserved by the first emperors without significant alteration. Several offices from the Republican era, held by individuals, were combined under the control of a single person. These changes became permanent, and gradually conferred sovereignty on the Emperor.

Cicero's description of the ideal state, in De re Publica, does not equate to a modern-day "republic"; it is more like enlightened absolutism. His philosophical works were influential when Enlightenment philosophers such as Voltaire developed their political concepts.

In its classical meaning, a republic was any stable well-governed political community. Both Plato and Aristotle identified three forms of government: democracy, aristocracy, and monarchy. First Plato and Aristotle, and then Polybius and Cicero, held that the ideal republic is a mixture of these three forms of government. The writers of the Renaissance embraced this notion.

Cicero expressed reservations concerning the republican form of government. While in his theoretical works he defended monarchy, or at least a mixed monarchy/oligarchy, in his own political life, he generally opposed men, like Julius Caesar, Mark Antony, and Octavian, who were trying to realise such ideals. Eventually, that opposition led to his death and Cicero can be seen as a victim of his own Republican ideals.

Tacitus, a contemporary of Plutarch, was not concerned with whether a form of government could be analyzed as a "republic" or a "monarchy". He analyzed how the powers accumulated by the early Julio-Claudian dynasty were all given by a State that was still notionally a republic. Nor was the Roman Republic "forced" to give away these powers: it did so freely and reasonably, certainly in Augustus' case, because of his many services to the state, freeing it from civil wars and disorder.

Tacitus was one of the first to ask whether such powers were given to the head of state because the citizens wanted to give them, or whether they were given for other reasons (for example, because one had a deified ancestor). The latter case led more easily to abuses of power. In Tacitus' opinion, the trend away from a true republic was irreversible only when Tiberius established power, shortly after Augustus' death in 14 CE (much later than most historians place the start of the Imperial form of government in Rome). By this time, too many principles defining some powers as "untouchable" had been implemented.

Renaissance republicanism

The Allegory of Good Government is part of a series of frescoes by Ambrogio Lorenzetti.

In Europe, republicanism was revived in the late Middle Ages when a number of states, which arose from medieval communes, embraced a republican system of government. These were generally small but wealthy trading states in which the merchant class had risen to prominence. Haakonssen notes that by the Renaissance, Europe was divided, such that those states controlled by a landed elite were monarchies, and those controlled by a commercial elite were republics. The latter included the Italian city-states of Florence, Genoa, and Venice and members of the Hanseatic League. One notable exception was Dithmarschen, a group of largely autonomous villages, which confederated in a peasants' republic. Building upon concepts of medieval feudalism, Renaissance scholars used the ideas of the ancient world to advance their view of an ideal government. Thus the republicanism developed during the Renaissance is known as 'classical republicanism' because it relied on classical models. This terminology was developed by Zera Fink in the 1940s, but some modern scholars, such as Brugger, consider it confuses the "classical republic" with the system of government used in the ancient world. 'Early modern republicanism' has been proposed as an alternative term. It is also sometimes called civic humanism. Beyond simply a non-monarchy, early modern thinkers conceived of an ideal republic, in which mixed government was an important element, and the notion that virtue and the common good were central to good government. Republicanism also developed its own distinct view of liberty. Renaissance authors who spoke highly of republics were rarely critical of monarchies. While Niccolò Machiavelli's Discourses on Livy is the period's key work on republics, he also wrote the treatise The Prince, which is better remembered and more widely read, on how best to run a monarchy. The early modern writers did not see the republican model as universally applicable; most thought that it could be successful only in very small and highly urbanized city-states. Jean Bodin in Six Books of the Commonwealth (1576) identified monarchy with republic.

Classical writers like Tacitus, and Renaissance writers like Machiavelli tried to avoid an outspoken preference for one government system or another. Enlightenment philosophers, on the other hand, expressed a clear opinion. Thomas More, writing before the Age of Enlightenment, was too outspoken for the reigning king's taste, even though he coded his political preferences in a utopian allegory.

In England a type of republicanism evolved that was not wholly opposed to monarchy; thinkers such as Thomas More and Sir Thomas Smith saw a monarchy, firmly constrained by law, as compatible with republicanism.

Dutch Republic

Anti-monarchism became more strident in the Dutch Republic during and after the Eighty Years' War, which began in 1568. This anti-monarchism was more propaganda than a political philosophy; most of the anti-monarchist works appeared in the form of widely distributed pamphlets. This evolved into a systematic critique of monarchy, written by men such as the brothers Johan and Peter de la Court. They saw all monarchies as illegitimate tyrannies that were inherently corrupt. These authors were more concerned with preventing the position of Stadholder from evolving into a monarchy, than with attacking their former rulers. Dutch republicanism also influenced French Huguenots during the Wars of Religion. In the other states of early modern Europe republicanism was more moderate.

Polish–Lithuanian Commonwealth

In the Polish–Lithuanian Commonwealth, republicanism was the influential ideology. After the establishment of the Commonwealth of Two Nations, republicans supported the status quo, of having a very weak monarch, and opposed those who thought a stronger monarchy was needed. These mostly Polish republicans, such as Łukasz Górnicki, Andrzej Wolan, and Stanisław Konarski, were well read in classical and Renaissance texts and firmly believed that their state was a republic on the Roman model, and started to call their state the Rzeczpospolita. Atypically, Polish–Lithuanian republicanism was not the ideology of the commercial class, but rather of the landed nobility, which would lose power if the monarchy were expanded. This resulted in an oligarchy of the great landed magnates.

Enlightenment republicanism

Caribbean

Victor Hugues, Jean-Baptiste Raymond de Lacrosse and Nicolas Xavier de Ricard were prominent supporters of republicanism for various Caribbean islands. Edwin Sandys, William Sayle and George Tucker all supported the islands becoming republics, particularly Bermuda. Julien Fédon and Joachim Philip led the republican Fédon's rebellion between 2 March 1795 and 19 June 1796, an uprising against British rule in Grenada.

Corsica

The first of the Enlightenment republics established in Europe during the eighteenth century occurred in the small Mediterranean island of Corsica. Although perhaps an unlikely place to act as a laboratory for such political experiments, Corsica combined a number of factors that made it unique: a tradition of village democracy; varied cultural influences from the Italian city-states, Spanish empire and Kingdom of France which left it open to the ideas of the Italian Renaissance, Spanish humanism and French Enlightenment; and a geo-political position between these three competing powers which led to frequent power vacuums in which new regimes could be set up, testing out the fashionable new ideas of the age.

From the 1720s the island had been experiencing a series of short-lived but ongoing rebellions against its current sovereign, the Italian city-state of Genoa. During the initial period (1729–36) these merely sought to restore the control of the Spanish Empire; when this proved impossible, an independent Kingdom of Corsica (1736–40) was proclaimed, following the Enlightenment ideal of a written constitutional monarchy. But the perception grew that the monarchy had colluded with the invading power, a more radical group of reformers led by the Pasquale Paoli pushed for political overhaul, in the form of a constitutional and parliamentary republic inspired by the popular ideas of the Enlightenment.

Its governing philosophy was both inspired by the prominent thinkers of the day, notably the French philosophers Montesquieu and Voltaire and the Swiss theorist Jean-Jacques Rousseau. Not only did it include a permanent national parliament with fixed-term legislatures and regular elections, but, more radically for the time, it introduced universal male suffrage, and it is thought to be the first constitution in the world to grant women the right to vote female suffrage may also have existed. It also extended Enlightened principles to other spheres, including administrative reform, the foundation of a national university at Corte, and the establishment of a popular standing army.

The Corsican Republic lasted for fifteen years, from 1755 to 1769, eventually falling to a combination of Genoese and French forces and was incorporated as a province of the Kingdom of France. But the episode resonated across Europe as an early example of Enlightened constitutional republicanism, with many of the most prominent political commentators of the day recognising it to be an experiment in a new type of popular and democratic government. Its influence was particularly notable among the French Enlightenment philosophers: Rousseau's famous work On the Social Contract (1762: chapter 10, book II) declared, in its discussion on the conditions necessary for a functional popular sovereignty, that "There is still one European country capable of making its own laws: the island of Corsica. valour and persistency with which that brave people has regained and defended its liberty well deserves that some wise man should teach it how to preserve what it has won. I have a feeling that some day that little island will astonish Europe."; indeed Rousseau volunteered to do precisely that, offering a draft constitution for Paoli'se use. Similarly, Voltaire affirmed in his Précis du siècle de Louis XV (1769: chapter LX) that "Bravery may be found in many places, but such bravery only among free peoples". But the influence of the Corsican Republic as an example of a sovereign people fighting for liberty and enshrining this constitutionally in the form of an Enlightened republic was even greater among the Radicals of Great Britain and North America, where it was popularised via An Account of Corsica, by the Scottish essayist James Boswell. The Corsican Republic went on to influence the American revolutionaries ten years later: the Sons of Liberty, initiators of the American Revolution, would declare Pascal Paoli to be a direct inspiration for their own struggle against the British; the son of Ebenezer Mackintosh was named Pascal Paoli Mackintosh in his honour, and no fewer than five American counties are named Paoli for the same reason.

England

Oliver Cromwell set up a Christian republic called the Commonwealth of England (1649–1660) which he ruled after the overthrow of King Charles I. James Harrington was then a leading philosopher of republicanism. John Milton was another important Republican thinker at this time, expressing his views in political tracts as well as through poetry and prose. In his epic poem Paradise Lost, for instance, Milton uses Satan's fall to suggest that unfit monarchs should be brought to justice, and that such issues extend beyond the constraints of one nation. As Christopher N. Warren argues, Milton offers “a language to critique imperialism, to question the legitimacy of dictators, to defend free international discourse, to fight unjust property relations, and to forge new political bonds across national lines.” This form of international Miltonic republicanism has been influential on later thinkers including 19th-century radicals Karl Marx and Friedrich Engels, according to Warren and other historians.

The collapse of the Commonwealth of England in 1660 and the restoration of the monarchy under Charles II discredited republicanism among England's ruling circles. Nevertheless, they welcomed the liberalism, and emphasis on rights, of John Locke, which played a major role in the Glorious Revolution of 1688. Even so, republicanism flourished in the "country" party of the early 18th century (commonwealthmen), which denounced the corruption of the "court" party, producing a political theory that heavily influenced the American colonists. In general, the English ruling classes of the 18th century vehemently opposed republicanism, typified by the attacks on John Wilkes, and especially on the American Revolution and the French Revolution.

French and Swiss thought

Portrait of Montesquieu

French and Swiss Enlightenment thinkers, such as Voltaire, Baron Charles de Montesquieu and later Jean-Jacques Rousseau, expanded upon and altered the ideas of what an ideal republic should be: some of their new ideas were scarcely traceable to antiquity or the Renaissance thinkers. Concepts they contributed, or heavily elaborated, were social contract, positive law, and mixed government. They also borrowed from, and distinguished republicanism from, the ideas of liberalism that were developing at the same time.

Liberalism and republicanism were frequently conflated during this period, because they both opposed absolute monarchy. Modern scholars see them as two distinct streams that both contributed to the democratic ideals of the modern world. An important distinction is that, while republicanism stressed the importance of civic virtue and the common good, liberalism was based on economics and individualism. It is clearest in the matter of private property, which, according to some, can be maintained only under the protection of established positive law.

Jules Ferry, Prime Minister of France from 1880 to 1885, followed both these schools of thought. He eventually enacted the Ferry Laws, which he intended to overturn the Falloux Laws by embracing the anti-clerical thinking of the Philosophes. These laws ended the Catholic Church's involvement in many government institutions in late 19th-century France, including schools.

The Thirteen British Colonies in North America

Main article: Republicanism in the United States

In recent years a debate has developed over the role of republicanism in the American Revolution and in the British radicalism of the 18th century. For many decades the consensus was that liberalism, especially that of John Locke, was paramount and that republicanism had a distinctly secondary role.

The new interpretations were pioneered by J.G.A. Pocock, who argued in The Machiavellian Moment (1975) that, at least in the early 18th century, republican ideas were just as important as liberal ones. Pocock's view is now widely accepted. Bernard Bailyn and Gordon Wood pioneered the argument that the American founding fathers were more influenced by republicanism than they were by liberalism. Cornell University professor Isaac Kramnick, on the other hand, argues that Americans have always been highly individualistic and therefore Lockean. Joyce Appleby has argued similarly for the Lockean influence on America.

In the decades before the American Revolution (1776), the intellectual and political leaders of the colonies studied history intently, looking for models of good government. They especially followed the development of republican ideas in England. Pocock explained the intellectual sources in America:

The Whig canon and the neo-Harringtonians, John Milton, James Harrington and Sidney, Trenchard, Gordon and Bolingbroke, together with the Greek, Roman, and Renaissance masters of the tradition as far as Montesquieu, formed the authoritative literature of this culture; and its values and concepts were those with which we have grown familiar: a civic and patriot ideal in which the personality was founded in property, perfected in citizenship but perpetually threatened by corruption; government figuring paradoxically as the principal source of corruption and operating through such means as patronage, faction, standing armies (opposed to the ideal of the militia), established churches (opposed to the Puritan and deist modes of American religion) and the promotion of a monied interest – though the formulation of this last concept was somewhat hindered by the keen desire for readily available paper credit common in colonies of settlement. A neoclassical politics provided both the ethos of the elites and the rhetoric of the upwardly mobile, and accounts for the singular cultural and intellectual homogeneity of the Founding Fathers and their generation.

The commitment of most Americans to these republican values made the American Revolution inevitable. Britain was increasingly seen as corrupt and hostile to republicanism, and as a threat to the established liberties the Americans enjoyed.

Leopold von Ranke in 1848 claimed that American republicanism played a crucial role in the development of European liberalism:

By abandoning English constitutionalism and creating a new republic based on the rights of the individual, the North Americans introduced a new force in the world. Ideas spread most rapidly when they have found adequate concrete expression. Thus republicanism entered our Romanic/Germanic world.... Up to this point, the conviction had prevailed in Europe that monarchy best served the interests of the nation. Now the idea spread that the nation should govern itself. But only after a state had actually been formed on the basis of the theory of representation did the full significance of this idea become clear. All later revolutionary movements have this same goal... This was the complete reversal of a principle. Until then, a king who ruled by the grace of God had been the center around which everything turned. Now the idea emerged that power should come from below.... These two principles are like two opposite poles, and it is the conflict between them that determines the course of the modern world. In Europe the conflict between them had not yet taken on concrete form; with the French Revolution it did.

Républicanisme

Portrait of Jean-Jacques Rousseau

Republicanism, especially that of Rousseau, played a central role in the French Revolution and foreshadowed modern republicanism. The revolutionaries, after overthrowing the French monarchy in the 1790s, began by setting up a republic; Napoleon converted it into an Empire with a new aristocracy. In the 1830s Belgium adopted some of the innovations of the progressive political philosophers of the Enlightenment.

Républicanisme is a French version of modern republicanism. It is a form of social contract, deduced from Jean-Jacques Rousseau's idea of a general will. Ideally, each citizen is engaged in a direct relationship with the state, removing the need for identity politics based on local, religious, or racial identification.

Républicanisme, in theory, makes anti-discrimination laws unnecessary, but some critics argue that colour-blind laws serve to perpetuate discrimination.

Ireland

Main article: Irish republicanism

Inspired by the American and French Revolutions, the Society of United Irishmen was founded in 1791 in Belfast and Dublin. The inaugural meeting of the United Irishmen in Belfast on 18 October 1791 approved a declaration of the society's objectives. It identified the central grievance that Ireland had no national government: "...we are ruled by Englishmen, and the servants of Englishmen, whose object is the interest of another country, whose instrument is corruption, and whose strength is the weakness of Ireland..." They adopted three central positions: (i) to seek out a cordial union among all the people of Ireland, to maintain that balance essential to preserve liberties and extend commerce; (ii) that the sole constitutional mode by which English influence can be opposed, is by a complete and radical reform of the representation of the people in Parliament; (iii) that no reform is practicable or efficacious, or just which shall not include Irishmen of every religious persuasion. The declaration, then, urged constitutional reform, union among Irish people and the removal of all religious disqualifications.

The movement was influenced, at least in part, by the French Revolution. Public interest, already strongly aroused, was brought to a pitch by the publication in 1790 of Edmund Burke's Reflections on the Revolution in France, and Thomas Paine's response, Rights of Man, in February 1791. Theobald Wolfe Tone wrote later that, "This controversy, and the gigantic event which gave rise to it, changed in an instant the politics of Ireland." Paine himself was aware of this commenting on sales of Part I of Rights of Man in November 1791, only eight months after publication of the first edition, he informed a friend that in England "almost sixteen thousand has gone off – and in Ireland above forty thousand". Paine may have been inclined to talk up sales of his works but what is striking in this context is that Paine believed that Irish sales were so far ahead of English ones before Part II had appeared. On 5 June 1792, Thomas Paine, author of the Rights of Man was proposed for honorary membership of the Dublin Society of the United Irishmen.

The fall of the Bastille was to be celebrated in Belfast on 14 July 1791 by a Volunteer meeting. At the request of Thomas Russell, Tone drafted suitable resolutions for the occasion, including one favouring the inclusion of Catholics in any reforms. In a covering letter to Russell, Tone wrote, "I have not said one word that looks like a wish for separation, though I give it to you and your friends as my most decided opinion that such an event would be a regeneration of their country". By 1795, Tone's republicanism and that of the society had openly crystallized when he tells us: "I remember particularly two days thae we passed on Cave Hill. On the first Russell, Neilson, Simms, McCracken and one or two more of us, on the summit of McArt's fort, took a solemn obligation...never to desist in our efforts until we had subverted the authority of England over our country and asserted her independence."

The culmination was an uprising against British rule in Ireland lasting from May to September 1798 – the Irish Rebellion of 1798 – with military support from revolutionary France in August and again October 1798. After the failure of the rising of 1798 the United Irishman, John Daly Burk, an émigré in the United States in his The History of the Late War in Ireland written in 1799, was most emphatic in its identification of the Irish, French and American causes.

Modern republicanism

Main article: Modern republicanism

 

As a liberal nationalist, Finnish president K. J. Ståhlberg (1865–1952) was a strong supporter of republicanism.

During the Enlightenment, anti-monarchism extended beyond the civic humanism of the Renaissance. Classical republicanism, still supported by philosophers such as Rousseau and Montesquieu, was only one of several theories seeking to limit the power of monarchies rather than directly opposing them.

Liberalism and socialism departed from classical republicanism and fueled the development of the more modern republicanism.

Theory

Neo-republicanism

Neorepublicanism is the effort by current scholars to draw on a classical republican tradition in the development of an attractive public philosophy intended for contemporary purposes. Neorepublicanism emerges as an alternative postsocialist critique of market society from the left.

Prominent theorists in this movement are Philip Pettit and Cass Sunstein, who have each written several works defining republicanism and how it differs from liberalism. Michael Sandel, a late convert to republicanism from communitarianism, advocates replacing or supplementing liberalism with republicanism, as outlined in his Democracy's Discontent: America in Search of a Public Philosophy.

Contemporary work from a neorepublican include jurist K. Sabeel Rahman's book Democracy Against Domination, which seeks to create a neorepublican framework for economic regulation grounded in the thought of Louis Brandeis and John Dewey and popular control, in contrast to both New Deal-style managerialism and neoliberal deregulation. Philosopher Elizabeth Anderson's Private Government traces the history of republican critiques of private power, arguing that the classical free market policies of the 18th and 19th centuries intended to help workers only lead to their domination by employers. In From Slavery to the Cooperative Commonwealth, political scientist Alex Gourevitch examines a strain of late 19th century American republicanism known as labour republicanism that was the producerist labour union The Knights of Labor, and how republican concepts were used in service of workers rights, but also with a strong critique of the role of that union in supporting the Chinese Exclusion Act.

Democracy

Portrait of Thomas Paine

 

A revolutionary republican hand-written bill from the Stockholm riots during the Revolutions of 1848, reading: "Dethrone Oscar he is not fit to be a king – rather the Republic! Reform! Down with the Royal house – long live Aftonbladet! Death to the king – Republic! Republic! – the people! Brunkeberg this evening." The writer's identity is unknown.

In the late 18th century there was convergence of democracy and republicanism. Republicanism is a system that replaces or accompanies inherited rule. There is an emphasis on liberty, and a rejection of corruption. It strongly influenced the American Revolution and the French Revolution in the 1770s and 1790s, respectively. Republicans, in these two examples, tended to reject inherited elites and aristocracies, but left open two questions: whether a republic, to restrain unchecked majority rule, should have an unelected upper chamber—perhaps with members appointed as meritorious experts—and whether it should have a constitutional monarch.

Though conceptually separate from democracy, republicanism included the key principles of rule by consent of the governed and sovereignty of the people. In effect, republicanism held that kings and aristocracies were not the real rulers, but rather the whole people were. Exactly how the people were to rule was an issue of democracy: republicanism itself did not specify a means. In the United States, the solution was the creation of political parties that reflected the votes of the people and controlled the government (see Republicanism in the United States). In Federalist No. 10, James Madison rejected democracy in favor of republicanism. There were similar debates in many other democratizing nations.

In contemporary usage, the term democracy refers to a government chosen by the people, whether it is direct or representative. Today the term republic usually refers to representative democracy with an elected head of state, such as a president, who serves for a limited term; in contrast to states with a hereditary monarch as a head of state, even if these states also are representative democracies, with an elected or appointed head of government such as a prime minister.

The Founding Fathers of the United States rarely praised and often criticized democracy, which they equated with mob rule; James Madison argued that what distinguished a democracy from a republic was that the former became weaker as it got larger and suffered more violently from the effects of faction, whereas a republic could get stronger as it got larger and combatted faction by its very structure. What was critical to American values, John Adams insisted, was that the government should be "bound by fixed laws, which the people have a voice in making, and a right to defend." Thomas Jefferson warned that "an elective despotism is not the government we fought for." Professors Richard Ellis of Willamette University and Michael Nelson of Rhodes College argue that much constitutional thought, from Madison to Lincoln and beyond, has focused on "the problem of majority tyranny." They conclude, "The principles of republican government embedded in the Constitution represent an effort by the framers to ensure that the inalienable rights of life, liberty, and the pursuit of happiness would not be trampled by majorities."

Constitutional monarchs and upper chambers

Some countries (such as the United Kingdom, the Netherlands, Belgium, Luxembourg, the Scandinavian countries, and Japan) turned powerful monarchs into constitutional ones with limited, or eventually merely symbolic, powers. Often the monarchy was abolished along with the aristocratic system, whether or not they were replaced with democratic institutions (such as in France, China, Iran, Russia, Germany, Austria, Hungary, Italy, Greece, Turkey and Egypt). In Australia, New Zealand, Canada, Papua New Guinea, and some other countries the monarch, or its representative, is given supreme executive power, but by convention acts only on the advice of his or her ministers. Many nations had elite upper houses of legislatures, the members of which often had lifetime tenure, but eventually these houses lost much power (as the UK House of Lords), or else became elective and remained powerful.