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Alidade
An alidade () (archaic forms include alhidade, alhidad, alidad) or a turning board is a device that allows one to sight a distant object and use the line of sight to perform a task. This task can be, for example, to triangulate a scale map on site using a plane table drawing of intersecting lines in the direction of the object from two or more points or to measure the angle and horizontal distance to the object from some reference point's polar measurement. Angles measured can be horizontal, vertical or in any chosen plane. The alidade sighting ruler was originally a part of many types of scientific and astronomical instrument. At one time, some alidades, particularly using circular graduations as on astrolabes, were also called ''diopters''. With modern technology, the name is applied to complete instruments such as the ' plane table alidade'. Origins The word in Arabic ( , "the ruler"), signifies the same device. In Greek and Latin, it is respectively called , "''dioptra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mariner's Astrolabe
The mariner's astrolabe, also called sea astrolabe, was an inclinometer used to determine the latitude of a ship at sea by measuring the sun's noon altitude (declination) or the meridian altitude Meridian altitude is a method of celestial navigation to calculate an observer's latitude. It notes the altitude angle of an astronomical object above the horizon at culmination. Principle Meridian altitude is the simplest calculation of celestia ... of a star of known declination. Not an astrolabe proper, the mariner's astrolabe was rather a graduated circle with an alidade used to measure vertical angles. They were designed to allow for their use on boats in rough water and/or in heavy winds, which astrolabes are ill-equipped to handle. It was invented by the Portuguese people, a nation known for its maritime prowess and dominated the sea for multiple centuries. In the sixteenth century, the instrument was also called a ring. History Many dates can be found for the appearance of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plane Table
A plane table (plain table prior to 1830) is a device used in surveying site mapping, exploration mapping, coastal navigation mapping, and related disciplines to provide a solid and level surface on which to make field drawings, charts and maps. The early use of the name ''plain table'' reflected its simplicity and plainness rather than its flatness. History The earliest mention of a plane table dates to 1551 in Abel Foullon's ''"Usage et description de l'holomètre"'', published in Paris.Turner, Anthony, ''Early Scientific Instruments, Europe 1400-1800'', Sotheby's Publishing, 1987, . page 81 However, since Foullon's description was of a complete, fully developed instrument, it must have been invented earlier. A brief description was also added to the 1591 edition of Digge's ''Pantometria''. The first mention of the device in English was by Cyprian Lucar in 1590.Turner, Gerard L'E., ''Scientific Instruments 1500-1900, An Introduction'', University of California Press, 1998 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrolabe
An astrolabe ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستارهیاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate inclinometer and an analog calculation device capable of working out several kinds of problems in astronomy. In its simplest form it is a metal disc with a pattern of wires, cutouts, and perforations that allows a user to calculate astronomical positions precisely. Historically used by astronomers, it is able to measure the altitude above the horizon of a celestial body, day or night; it can be used to identify stars or planets, to determine local latitude given local time (and vice versa), to survey, or to triangulate. It was used in classical antiquity, the Islamic Golden Age, the European Middle Ages and the Age of Discovery for all these purposes. The astrolabe's importance comes not only from the early developments into the study of ast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graphometer
The graphometer, semicircle or semicircumferentor is a surveying instrument used for angle measurements. It consists of a semicircular limb divided into 180 degrees and sometimes subdivided into minutes. The limb is subtended by the diameter with two sights at its ends. In the middle of the diameter a "box and needle" (compass) is fixed. On the same middle the alidade with two other sights is fitted. The device is mounted on a staff via a ball and socket joint. In effect the device is a half- circumferentor. For convenience, sometimes another half-circle from 180 to 360 degrees may be graduated in another line on the limb. Pages: vol. 1 p. 179 for "Graphometer", vol. 2 p. 50 for "Semi-Circle" The form was introduced in Philippe Danfrie Philippe Danfrie the elder (about 1532 in Cornouaille in Brittany - 1606 in Paris), was a designer and maker of mathematical instruments in metal and paper, as well as a type-cutter, engraver, minter of coins and medals, publisher and author. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Octant (instrument)
The octant, also called a reflecting quadrant, is a reflecting instrument used in navigation. Etymology The name ''octant'' derives from the Latin ''octans'' meaning ''eighth part of a circle'', because the instrument's arc is one eighth of a circle. ''Reflecting quadrant'' derives from the instrument using mirrors to reflect the path of light to the observer and, in doing so, doubles the angle measured. This allows the instrument to use a one-eighth of a turn to measure a quarter-turn or quadrant. Origin of the octant Newton's reflecting quadrant Isaac Newton's reflecting quadrant was invented around 1699. A detailed description of the instrument was given to Edmond Halley, but the description was not published until after Halley's death in 1742. It is not known why Halley did not publish the information during his life, as this prevented Newton from getting the credit for the invention that is generally given to John Hadley and Thomas Godfrey. One copy of this ins ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Johannes Hevelius
Johannes Hevelius Some sources refer to Hevelius as Polish: * * * * * * * Some sources refer to Hevelius as German: * * * * *of the Royal Society * (in German also known as ''Hevel''; pl, Jan Heweliusz; – 28 January 1687) was a councillor and mayor of Gdańsk (Danzig), in the Polish–Lithuanian Commonwealth. As an astronomer, he gained a reputation as "the founder of lunar topography", and described ten new constellations, seven of which are still used by astronomers. Etymology According to the Polish Academy of Sciences (1975) the origin of the name goes back to the surname Hawke, a historical alternative spelling for the English word hawk, which changed into ''Hawelke'' or ''Hawelecke''. In Poland he is known as ''Jan Heweliusz''. Other versions of the name include Hewel, Hevel, Hevelke or Hoefel, Höwelcke, Höfelcke. According to Feliks Bentkowski (1814), during his early years he also signed as Hoefelius. Along with the Latinized version of his name, Ludwig G ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sextant
A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation. The estimation of this angle, the altitude, is known as ''sighting'' or ''shooting'' the object, or ''taking a sight''. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart—for example, sighting the Sun at noon or Polaris at night (in the Northern Hemisphere) to estimate latitude (with sight reduction). Sighting the height of a landmark can give a measure of ''distance off'' and, held horizontally, a sextant can measure angles between objects for a position on a chart. A sextant can also be used to measure the lunar distance between the moon and another celestial object (such as a star or planet) in order to determine Greenwich Mean Time and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theodolite
A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and infrastructure construction, and some specialized applications such as meteorology and rocket launching. It consists of a moveable telescope mounted so it can rotate around horizontal and vertical axes and provide angular readouts. These indicate the orientation of the telescope, and are used to relate the first point sighted through the telescope to subsequent sightings of other points from the same theodolite position. These angles can be measured with accuracies down to microradians or seconds of arc. From these readings a plan can be drawn, or objects can be positioned in accordance with an existing plan. The modern theodolite has evolved into what is known as a total station where angles and distances are measured electronically, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Osborne Fire Finder
The Osborne Fire Finder is a type of alidade used by fire lookouts to find a directional bearing (azimuth) to smoke in order to alert fire crews to a wildland fire. History and development The forerunner to the device was invented around 1840 by Sir Francis Ronalds to help combat fire in London – he also named his innovation the “Fire Finder”. Ronalds' fire finder comprised a theodolite atop a watchtower. Bearings and vertical angles from the horizon to surrounding features were recorded either on a surrounding cylinder in the form of a panorama or on a circular table at the base of the instrument. The location of any fire could thus be pinpointed even in the dark. The modern version was created by William "W.B." Osborne, a United States Forest Service employee from Portland, Oregon, and has been in service since 1915. Mr. Osborne also designed the photo-recording transit for making panoramic records of forest conditions, as well as a collapsible water-bag knapsack for fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gunsight
A sight is an aiming device used to assist in visually aligning ranged weapons, surveying instruments or optical illumination equipments with the intended target. Sights can be a simple set or system of physical markers that have to be aligned together with the target (such as iron sights on firearms), or optical devices that allow the user to see an optically enhanced — often magnified — target image aligned in the same focus with an aiming point (e.g. telescopic sights, reflector sights and holographic sights). There are also sights that actively project an illuminated point of aim (a.k.a. "hot spot") onto the target itself so it can be observed by, such as laser sights and infrared illuminators on some night vision devices. Simple sights At its simplest, a sight typically has two components, front and rear aiming pieces that have to be lined up. Sights such as this can be found on many types of devices including weapons, surveying and measuring instruments, and na ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
