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Speculum Metal
Speculum metal is a mixture of around two-thirds copper and one-third tin, making a white brittle alloy that can be polished to make a highly reflective surface. It was used historically to make different kinds of mirrors from personal grooming aids to optical devices until it was replaced by more modern materials such as metal-coated glass mirrors. Speculum metal mixtures usually contain two parts copper to one part tin along with a small amount of arsenic, although there are other mixtures containing silver, lead, or zinc. This is about twice the proportion of tin to copper typically used in bronze alloys. Archaeologists and others prefer to call it "high-tin bronze", although this broad term is also used for other alloys such as bell metal, which is typically around 20% tin. Large speculum metal mirrors are hard to manufacture, and the alloy is prone to tarnish, requiring frequent re-polishing. However, it was the only practical choice for large mirrors in high-precision opti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
40-foot Telescope Mirror
4 (four) is a number, numeral (linguistics), numeral and numerical digit, digit. It is the natural number following 3 and preceding 5. It is a square number, the smallest semiprime and composite number, and is tetraphobia, considered unlucky in many East Asian cultures. Evolution of the Hindu-Arabic digit Brahmic numerals represented 1, 2, and 3 with as many lines. 4 was simplified by joining its four lines into a cross that looks like the modern plus sign. The Shunga Empire, Shunga would add a horizontal line on top of the digit, and the Northern Satraps, Kshatrapa and Pallava dynasty, Pallava evolved the digit to a point where the speed of writing was a secondary concern. The Arabs' 4 still had the early concept of the cross, but for the sake of efficiency, was made in one stroke by connecting the "western" end to the "northern" end; the "eastern" end was finished off with a curve. The Europeans dropped the finishing curve and gradually made the digit less cursive, endi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bronze Mirror
Bronze mirrors preceded the glass mirrors of today. This type of mirror, sometimes termed a copper mirror, has been found by archaeologists among elite assemblages from various cultures, from Etruscan Italy to Japan. Typically they are round and rather small, in the West with a handle, in East Asia with a knob to hold at the back, often with a loop for a cord, or silk tassel. Some were fitted with small stands, and others had a hinged protective cover. In surviving ancient examples the surface is too corroded to be reflective, but some bronze mirrors are still made. They are first-surface mirrors, where the immediate bronze surface is flat, plain and highly polished to be reflective, rather than second-surface mirrors, like modern glass mirrors, where the reflection comes from a backing applied to the glass. They are significantly inferior to modern mirrors in terms of the quality of the reflection, but in older societies were sufficiently impressive to have religious ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Newtonian Reflector
The Newtonian telescope, also called the Newtonian reflector or just a Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton, using a concave primary mirror and a flat diagonal secondary mirror. Newton's first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope. The Newtonian telescope's simple design has made it very popular with amateur telescope makers. Description 
A Newtonian telescope is composed of a
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Isaac Newton
Sir Isaac Newton () was an English polymath active as a mathematician, physicist, astronomer, alchemist, theologian, and author. Newton was a key figure in the Scientific Revolution and the Age of Enlightenment, Enlightenment that followed. His book (''Mathematical Principles of Natural Philosophy''), first published in 1687, achieved the Unification of theories in physics#Unification of gravity and astronomy, first great unification in physics and established classical mechanics. Newton also made seminal contributions to optics, and Leibniz–Newton calculus controversy, shares credit with German mathematician Gottfried Wilhelm Leibniz for formulating calculus, infinitesimal calculus, though he developed calculus years before Leibniz. Newton contributed to and refined the scientific method, and his work is considered the most influential in bringing forth modern science. In the , Newton formulated the Newton's laws of motion, laws of motion and Newton's law of universal g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gregorian Telescope
The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke. James Gregory was a contemporary of Isaac Newton, and both often worked simultaneously on similar projects. Gregory's design was published in 1663 and pre-dates the first practical reflecting telescope, the Newtonian telescope, built by Sir Isaac Newton in 1668."Isaac Newton: adventurer in thought", by Alfred Rupert Hallpage 67 However, Gregory's design was only a theoretical description, and he never actually constructed the telescope. It was not successfully built until five years after Newton's first reflecting telescope. History The Gregorian telescope is named after the James Gregory design, which appeared in his 1663 publication (The Advance of Optics). Similar theoretical designs have been found in the writings of Bonaventura Cavalieri ( (On Burning Mirrors), 1632) and Marin Mersenne (, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James Gregory (astronomer And Mathematician)
James Gregory (November 1638 – October 1675) was a Scottish mathematician and astronomer. His surname is sometimes spelt as Gregorie, the original Scottish spelling. He described an early practical design for the reflecting telescope – the Gregorian telescope – and made advances in trigonometry, discovering infinite series representations for several trigonometric functions. In his book ''Geometriae Pars Universalis'' (1668) Gregory gave both the first published statement and proof of the fundamental theorem of the calculus (stated from a geometric point of view, and only for a special class of the curves considered by later versions of the theorem), for which he was acknowledged by Isaac Barrow. Biography Gregory was born in 1638. His mother Janet was the daughter of Jean and David Anderson and his father was John Gregory, an Episcopalian Church of Scotland minister, James was youngest of their three children and he was born in the manse at Drumoak, Aberdeenshire, and wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parabolic Reflector
A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a Mirror, reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis. The parabolic reflector transforms an incoming plane wave travelling along the axis into a spherical wave converging toward the focus. Conversely, a spherical wave generated by a point source placed in the focus (optics), focus is reflected into a plane wave propagating as a collimated beam along the axis. Parabolic reflectors are used to collect energy from a distant source (for example sound waves or incoming star light). Since the principles of Specular reflection, reflection are reversible, parabolic reflectors can also be used to collimate radiation from an isotropic source into a parallel beam (optics), beam. In optics, parabolic mirrors are used to gather light in reflecting telescop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
First Surface Mirror
A first-surface mirror or front-surface mirror (also commonly abbreviated FS mirror or FSM) is a mirror with the reflective surface being above a backing, as opposed to the conventional, second-surface mirror with the reflective surface behind a transparent substrate such as glass or acrylic. Historically, the bronze mirror, an FSM type, was standard from ancient times until relatively recent centuries. These were simply highly polished pieces of bronze or other metals, usually small and round, and designed for a person to see their face. First-surface mirrors are now made for applications requiring a strict reflection without a ''ghosting'' effect as seen with a second-surface mirror, where a faint secondary reflection could be observed, coming from the front surface of the glass. This includes most optics applications where light is being manipulated in a specific manner. Reflecting telescopes, rear-projection televisions, periscopes, non-reversing mirrors, high-quality ka ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Early Modern Europe
Early modern Europe, also referred to as the post-medieval period, is the period of European history between the end of the Middle Ages and the beginning of the Industrial Revolution, roughly the mid 15th century to the late 18th century. Historians variously mark the beginning of the early modern period with the invention of moveable type printing in the 1450s, the Fall of Constantinople and end of the Hundred Years' War in 1453, the end of the Wars of the Roses in 1485, the beginning of the High Renaissance in Italy in the 1490s, the end of the Reconquista and subsequent voyages of Christopher Columbus to the Americas in 1492, or the start of the Protestant Reformation in 1517. The precise dates of its end point also vary and are usually linked with either the start of the French Revolution in 1789 or with the more vaguely defined beginning of the Industrial Revolution in late 18th century England. Some of the more notable trends and events of the early modern period included th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gregorian Telescope Circa 1735 In Putnam Gallery, 2009-11-24
Gregorian may refer to: *The thought or ideology of Pope Gregory I or Pope Gregory VII (also called ''Gregorianism'') *Things named for Pope Gregory I: **Gregorian chant, the central tradition of Western plainchant, a form of monophonic, unaccompanied sacred song of the western Roman Catholic Church ** Gregorian mass ** Brotherhood of Saint Gregory, a community of friars within the Anglican Communion. The community's members, known as "Gregorians", include clergy and laymen. Since 1987 there has also been a parallel order of sisters, the Sisters of Saint Gregory ** Gregorian Antiphonary, an early Christian antiphonary, i.e. book of choral music to be sung antiphonally in services; it is associated traditionally with Pope Gregory I ** Gregorian Sacramentary, a 10th-century illuminated Latin manuscript containing a sacramentary. Since the 16th century it has been in the Vatican Library as ''Lat. 3806'' *Things named for Pope Gregory VII: **The Gregorian Reform, a series of reforms in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
60" Mirror For William Parsons, Earl Of Rosse (9237613525)
6 (six) is the natural number following 5 and preceding 7. It is a composite number and the smallest perfect number. In mathematics A six-sided polygon is a hexagon, one of the three regular polygons capable of tiling the plane. A hexagon also has 6 edges as well as 6 internal and external angles. 6 is the second smallest composite number. It is also the first number that is the sum of its proper divisors, making it the smallest perfect number. It is also the only perfect number that doesn't have a digital root of 1. 6 is the first unitary perfect number, since it is the sum of its positive proper unitary divisors, without including itself. Only five such numbers are known to exist. 6 is the largest of the four all-Harshad numbers. 6 is the 2nd superior highly composite number, the 2nd colossally abundant number, the 3rd triangular number, the 4th highly composite number, a pronic number, a congruent number, a harmonic divisor number, and a semiprime. 6 is also the firs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
