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Backstaff
The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis, who described it in his book ''Seaman's Secrets'' in 1594. Types of backstaffs Backstaff is the name given to any instrument that measures the altitude of the sun by the projection of a shadow. It appears that the idea for measuring the sun's altitude using back observations originated with Thomas Harriot. Many types of instruments evolved from the cross-staff that can be classified as backstaves. Only the Davis quadrant remains dominant in the history of navigation instruments. Indeed, the Davis quadrant is essentially synonymous with backstaff. However, Davis was neither the first nor the last to design such an instrument and others are considered here ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cross-staff
The term Jacob's staff is used to refer to several things, also known as cross-staff, a ballastella, a fore-staff, a ballestilla, or a balestilha. In its most basic form, a Jacob's staff is a stick or pole with length markings; most staffs are much more complicated than that, and usually contain a number of measurement and stabilization features. The two most frequent uses are: * in astronomy and navigation for a simple device to measure angles, later replaced by the more precise sextants; * in surveying (and scientific fields that use surveying techniques, such as geology and ecology) for a vertical rod that penetrates or sits on the ground and supports a compass or other instrument. The simplest use of a Jacob's staff is to make qualitative judgements of the height and angle of an object relative to the user of the staff. In astronomy and navigation In navigation the instrument is also called a cross-staff and was used to determine angles, for instance the angle between the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elton's Quadrant
An Elton's quadrant is a derivative of the Davis quadrant. It adds an index arm and artificial horizon to the instrument. It was invented by John Elton a sea captain who patented his design in 1728Bennett, Jim, "Catadioptrics and commerce in eighteenth-century London", in History of Science, vol xliv, 2006, pages 247-277. and published details of the instrument in the Philosophical Transactions of the Royal Society in 1732.Elton, John, ''The Description of a New Quadrant for Taking Altitudes Without an Horizon, Either at Sea or Land'', Philosophical Transactions of the Royal Society, Vol 37, No. 423, 1731-1732. Construction This instrument clearly reflects the shape and features of the Davis quadrant. The significant differences are the change in the upper arc to a simple triangular frame and the addition of an index arm. The triangular frame at the top spans 60° as did the arc on the backstaff. The main graduated arc subtends 30° as in the backstaff. The 30° arc is gradu ... [...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] |
Quadrant (instrument)
A quadrant is an instrument used to measure angles up to 90°. Different versions of this instrument could be used to calculate various readings, such as longitude, latitude, and time of day. Its earliest recorded usage was in ancient India in Rigvedic times by Rishi Atri to observe a solar eclipse. It was then proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers. Mural quadrants were important astronomical instruments in 18th-century European observatories, establishing a use for positional astronomy. Etymology The term ''quadrant'', meaning one fourth, refers to the fact that early versions of the instrument were derived from astrolabes. The quadrant condensed the workings of the astrolabe into an area one fourth the size of the astrolabe face; it was essentially a quarter of an astrolabe. History During Rigvedic times in ancient India, quadrants called 'Tureeyam's were use ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Almucantar
An almucantar (also spelled almucantarat or almacantara) is a circle on the celestial sphere parallel to the horizon. Two stars that lie on the same almucantar have the same altitude. The term was introduced into European astronomy by monastic astronomer Hermann Contractus of Reichenau, Latinized from the Arabic word ' ("the almucantar, sundial", plural: '), derived from ' ("arch, bridge") Almucantar staff An almucantar staff is an instrument chiefly used to determine the time of sunrise and sunset, in order to find the amplitude and consequently the variations of the compass. Usually made of pear tree or boxwood, with an arch of 15° to 30°,May, William Edward, ''A History of Marine Navigation'', G. T. Foulis & Co. Ltd., Henley-on-Thames, Oxfordshire, 1973, it is an example of a backstaff. The sun casts that shadow of a vane (B in the adjacent image) on a ''horizon vane'' (A). The horizon vane has a slit or hole to allow the observer to see the horizon in the dist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Davis (English Explorer)
John Davis ( – 29 December 1605) was one of the chief navigators of Queen Elizabeth I of England. He led several voyages to discover the Northwest Passage and served as pilot and captain on both Dutch and English voyages to the East Indies. He discovered the Falkland Islands in August 1592. Life and career Davis was born in the parish of Stoke Gabriel in Devon circa 1550, and spent his childhood in Sandridge Barton nearby. It has been suggested that he learned much of his seamanship as a child while playing boats along the river Dart, and went to sea at an early age. His childhood neighbours included Adrian Gilbert and Humphrey Gilbert and their half-brother Walter Raleigh. From early on, he also became friends with John Dee. He began pitching a voyage in search of the Northwest Passage to the queen's secretary Francis Walsingham in 1583. Two years later, in 1585, the secretary relented and funded the expedition, which traced Frobisher's route to Greenland's east coast, ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Plough Instrument
''The'' () is a grammatical article in English, denoting persons or things that are already or about to be mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the most frequently used word in the English language; studies and analyses of texts have found it to account for seven percent of all printed English-language words. It is derived from gendered articles in Old English which combined in Middle English and now has a single form used with nouns of any gender. The word can be used with both singular and plural nouns, and with a noun that starts with any letter. This is different from many other languages, which have different forms of the definite article for different genders or numbers. Pronunciation In most dialects, "the" is pronounced as (with the voiced dental fricative followed by a schwa) when followed by a consonant sound, and as (homophone of the archaic pro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thomas Hood (mathematician)
Thomas Hood (1556–1620) was an English mathematician and physician, the first lecturer in mathematics appointed in England, a few years before the founding of Gresham College. He publicized the Copernican theory, and discussed the nova SN 1572. (Tycho's Nova). He also innovated in the design of mathematical and astronomical instruments. Life He entered Trinity College, Cambridge in 1573, and graduated B.A. in 1578; he was elected to a fellowship in the same year, and graduated M.A. in 1581. His Cambridge licence to practice as a physician was from 1585. He was approached to lecture in mathematics in 1582, by the merchant Thomas Smythe. The lectures in fact began in 1588. W. W. Rouse Ball, ''A History of the Study of Mathematics at Cambridge'' (1889), pp. 23-4. He lectured from 1588 to 1592. The applications in view were military (intended for Captains of train bands, in other words for militia commanders at the time of the Spanish Armada), and subsequently aimed at naval ne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Navigation
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space (or on the surface of the Earth) without having to rely solely on estimated positional calculations, commonly known as " dead reckoning", made in the absence of satellite navigation or other similar modern electronic or digital positioning means. Celestial navigation uses "sights", or timed angular measurements, taken typically between a celestial body (e.g. the Sun, the Moon, a planet, or a star) and the visible horizon. Celestial navigation can also take advantage of measurements between celestial bodies without reference to the Earth horizon, such as when the Moon and other selected bodies are used in the practice called "lunars" or lunar distance method, used for determining precise time when time is unknown. Celestial navigation by taking sights ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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