SUMMARY / RELATED TOPICS

Battle of Burgos

The Battle of Burgos known as Battle of Gamonal, was fought on November 10, 1808, during the Peninsular War in the village of Gamonal, near Burgos, Spain. A powerful French army under Marshal Bessières overwhelmed and destroyed the outnumbered Spanish troops under General Belveder, opening central Spain to invasion. Spanish history remembers this battle for the vain gallantry of the Guard and Walloon regiments under Vicente Genaro de Quesada. Forming a rearguard for the shattered Spanish lines, these troops repelled repeated charges by General Lasalle's; the cost was high with only 74 of the 307 men in the rearguard surviving. It is said that Bessières returned Quesada's sword and had his wounds treated in the French field hospital; these acts of chivalry became rare as the Peninsular War dragged on. The Battle of Gamonal

Epiactis lisbethae

Epiactis lisbethae known as Lisbeth's brooding anemone, is a species of sea anemone in the family Actiniidae. It is similar in appearance to the common brooding anemone, like it is native to shallow waters on the western coast of North America. E. lisbethae is similar to the more common brooding anemone but is larger, with a column diameter greater than 50 mm. When contracted, it is dome-shaped, sand particles do not adhere to the column. Bold striping on the pedal base, which flares out over the rock surface, extends as striations up the column. At some seasons of the year, the young are brooded in a band of several hundred on the outside of the column, these juveniles are all much the same size; this anemone is dull red, brown or orange in colour, the oral disc having fine white radial lines extending from the tentacles to the mouth. First described in 1986 from the San Juan Islands of Washington State, the species was named in honour of Lisbeth Francis, a marine biologist at Western Washington University.

Its range extends from Bamfield on Vancouver Island, southwards to Coos Bay in southern Oregon and to northern California, United States. It is uncommon in California; the sexes are separate in this breeding is seasonal. After internal fertilisation, the eggs are retained in the gastrovascular cavity, they are expelled from the mouth and move down the column, where they adhere in a broad belt halfway down. When sufficiently developed, the juveniles slither or crawl down the column and move to a new location. Red and brown anemones tend to have pinkish young while orange individuals have orange young

Magnetic field

A magnetic field is a vector field that describes the magnetic influence of electric charges in relative motion and magnetized materials. The effects of magnetic fields are seen in permanent magnets, which pull on magnetic materials and attract or repel other magnets. Magnetic fields surround and are created by magnetized material and by moving electric charges such as those used in electromagnets, they exert forces on nearby moving electrical torques on nearby magnets. In addition, a magnetic field that varies with location exerts a force on magnetic materials. Both the strength and direction of a magnetic field vary with location; as such, it is described mathematically as a vector field. In electromagnetics, the term "magnetic field" is used for two distinct but related fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter. B, magnetic flux density, is measured in tesla, equivalent to newton per meter per ampere.

H and B differ in. In a vacuum, B and H are the same aside from units. Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated, are both components of the electromagnetic force, one of the four fundamental forces of nature. Magnetic fields are used throughout modern technology in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric 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 clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them. Three centuries William Gilbert of Colchester replicated Petrus Peregrinus's work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilbert's work, De Magnete, helped to establish magnetism as a science. In 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated. Building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by "magnetic poles" and magnetism is due to small pairs of north/south magnetic poles.

Three discoveries in 1820 challenged this foundation of magnetism, though. Hans Christian Ørsted demonstrated that a current-carrying wire is surrounded by a circular magnetic field. André-Marie Ampère showed that parallel wires with currents attract one another if the currents are in the same direction and repel if they are in opposite directions. Jean-Baptiste Biot and Félix Savart announced empirical results about the forces that a current-carrying long, straight wire exerted on a small magnet, determining that the forces were inversely proportional to the perpendicular distance from the wire to the magnet. Laplace deduced, but did not publish, a law of force based on the differential action of a differential section of the wire, which became known as the Biot–Savart law. Extending these experiments, Ampère published his own successful model of magnetism in 1825. In it, he showed the equivalence of electrical currents to magnets and proposed that magnetism is due to perpetually flowing loops of current instead of the dipoles of magnetic charge in Poisson's model.

This has the additional benefit of explaining. Further, Ampère derived both Ampère's force law describing the force between two currents and Ampère's law, like the Biot–Savart law described the magnetic field generated by a steady current. In this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism. In 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field, he described this phenomenon in. Franz Ernst Neumann proved that, for a moving conductor in a magnetic field, induction is a consequence of Ampère's force law. In the process, he introduced the magnetic vector potential, shown to be equivalent to the underlying mechanism proposed by Faraday. In 1850, Lord Kelvin known as William Thomson, distinguished between two magnetic fields now denoted H and B; the former applied to the latter to Ampère's model and induction. Further, he derived how B relate to each other.

The reason magnetic fields H and B are used for the two magnetic fields has been a sour