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Portland Observatory
The Portland Observatory is a historic maritime signal tower at 138 Congress Street in the Munjoy Hill section of Portland, Maine. Built in 1807, it is the only known surviving tower of its type in the United States. Using both a telescope and signal flags, two-way communication between ship and shore was possible several hours before an incoming vessel reached the docks. The tower was designated a National Historic Landmark and a National Historic Civil Engineering Landmark in 2006; it is now managed by ''Greater Portland Landmarks'', a local historic preservation nonprofit. It is open to the public as a museum. Geography Portland has a deep harbor sheltered by numerous islands. Ships entering the harbor are not directly visible from the wharfs, which created problems for merchants trying to prepare for the arrival of cargoes. This problem was solved in 1807 when Captain Lemuel Moody organized the construction of an observatory on Portland's Munjoy Hill, visible from both th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Portland, Maine
Portland is the largest city in the U.S. state of Maine and the seat of Cumberland County. Portland's population was 68,408 in April 2020. The Greater Portland metropolitan area is home to over half a million people, the 104th-largest metropolitan area in the United States. Portland's economy relies mostly on the service sector and tourism. The Old Port is known for its nightlife and 19th-century architecture. Marine industry plays an important role in the city's economy, with an active waterfront that supports fishing and commercial shipping. The Port of Portland is the second-largest tonnage seaport in New England. The city seal depicts a phoenix rising from ashes, a reference to recovery from four devastating fires. Portland was named after the English Isle of Portland, Dorset. In turn, the city of Portland, Oregon was named after Portland, Maine. The word ''Portland'' is derived from the Old English word ''Portlanda'', which means "land surrounding a harbor". The Greater ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Observatory
An observatory is a location used for observing terrestrial, marine, or celestial events. Astronomy, climatology/meteorology, geophysical, oceanography and volcanology are examples of disciplines for which observatories have been constructed. Historically, observatories were as simple as containing an astronomical sextant (for measuring the distance between stars) or Stonehenge (which has some alignments on astronomical phenomena). Astronomical observatories Astronomical observatories are mainly divided into four categories: space-based, airborne, ground-based, and underground-based. Ground-based observatories Ground-based observatories, located on the surface of Earth, are used to make observations in the radio and visible light portions of the electromagnetic spectrum. Most optical telescopes are housed within a dome or similar structure, to protect the delicate instruments from the elements. Telescope domes have a slit or other opening in the roof that can be opened during ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Works Progress Administration
The Works Progress Administration (WPA; renamed in 1939 as the Work Projects Administration) was an American New Deal agency that employed millions of jobseekers (mostly men who were not formally educated) to carry out public works projects, including the construction of public buildings and roads. It was set up on May 6, 1935, by presidential order, as a key part of the Second New Deal. The WPA's first appropriation in 1935 was $4.9 billion (about $15 per person in the U.S., around 6.7 percent of the 1935 GDP). Headed by Harry Hopkins, the WPA supplied paid jobs to the unemployed during the Great Depression in the United States, while building up the public infrastructure of the US, such as parks, schools, and roads. Most of the jobs were in construction, building more than 620,000 miles (1,000,000 km) of streets and over 10,000 bridges, in addition to many airports and much housing. The largest single project of the WPA was the Tennessee Valley Authority. At its peak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Portland Observatory 1936
Portland most commonly refers to: * Portland, Oregon, the largest city in the state of Oregon, in the Pacific Northwest region of the United States * Portland, Maine, the largest city in the state of Maine, in the New England region of the northeastern United States * Isle of Portland, England, a tied island in the English Channel Portland may also refer to: Places and establishments Australia * Cape Portland, Tasmania, a cape on the north-eastern tip of Tasmania * Portland, New South Wales, a town with the first Australian cement works *Portland, Victoria, a regional city and port *City of Portland (Victoria), a former local government area (LGA) Canada *Port Lands, Toronto, Ontario (sometimes mistakenly spelled "Portlands"), the eastern part of the Toronto waterfront * Portland Island (British Columbia), a small island off the coast of Vancouver island * Portland Inlet, an inlet between southeastern Alaska and British Columbia ** Portland Canal, an arm of Portland Inlet *Portl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
View Of The City Of Portland, Maine, From The Harbor
A view is a sight or prospect or the ability to see or be seen from a particular place. View, views or Views may also refer to: Common meanings * View (Buddhism), a charged interpretation of experience which intensely shapes and affects thought, sensation, and action * Graphical projection in a technical drawing or schematic ** Multiview orthographic projection, standardizing 2D images to represent a 3D object * Opinion, a belief about subjective matters * Page view, a visit to a World Wide Web page * Panorama, a wide-angle view * Scenic viewpoint, an elevated location where people can view scenery * World view, the fundamental cognitive orientation of an individual or society encompassing the entirety of the individual or society's knowledge and point-of-view Places * View, Kentucky, an unincorporated community in Crittenden County * View, Texas, an unincorporated community in Taylor County Arts, entertainment, and media Music * ''View'' (album), the 2003 debut album b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refracting
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed. For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence ''θ1'' and angle of refraction ''θ2'' is equal to the ratio of phase velocities (''v''1 / ''v''2) in the two media, or equivalently, to the refractive indices (''n''2 / ''n''1) of the two media. :\frac =\frac=\frac Optical prisms and lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wavelength ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromatic Aberration
In optics, chromatic aberration (CA), also called chromatic distortion and spherochromatism, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the wavelength of light. The refractive index of most transparent materials decreases with increasing wavelength. Since the focal length of a lens depends on the refractive index, this variation in refractive index affects focusing. Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image. Types There are two types of chromatic aberration: ''axial'' (''longitudinal''), and ''transverse'' (''lateral''). Axial aberration occurs when different wavelengths of light are focused at different distances from the lens (focus ''shift''). Longitudinal aberration is typical at long focal lengths. Transverse aberration occurs when different wavelengths are focused at different positions i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cupola
In architecture, a cupola () is a relatively small, most often dome-like, tall structure on top of a building. Often used to provide a lookout or to admit light and air, it usually crowns a larger roof or dome. The word derives, via Italian, from lower Latin ''cupula'' (classical Latin ''cupella''), (Latin ''cupa''), indicating a vault resembling an upside-down cup. Background The cupola evolved during the Renaissance from the older oculus. Being weatherproof, the cupola was better suited to the wetter climates of northern Europe. The chhatri, seen in Indian architecture, fits the definition of a cupola when it is used atop a larger structure. Cupolas often serve as a belfry, belvedere, or roof lantern above a main roof. In other cases they may crown a spire, tower, or turret. Barns often have cupolas for ventilation. Cupolas can also appear as small buildings in their own right. The square, dome-like segment of a North American railroad train caboose that contains the seco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Above Sea Level
Height above mean sea level is a measure of the vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as ''orthometric heights''. The combination of unit of measurement and the physical quantity (height) is called "metres above mean sea level" in the metric system, while in United States customary and imperial units it would be called "feet above mean sea level". Mean sea levels are affected by climate change and other factors and change over time. For this and other reasons, recorded measurements of elevation above sea level at a reference time in history might differ from the actual elevation of a given location over sea level at a given moment. Uses Metres above sea level is the standard measurement of the elevation or altitude of: * Geographic locations such as towns, mountains and other landmarks. * The top of buildings and other structures. * Flying objects such ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fieldstone
Fieldstone is a naturally occurring type of stone, which lies at or near the surface of the Earth. Fieldstone is a nuisance for farmers seeking to expand their land under cultivation, but at some point it began to be used as a construction material. Strictly speaking, it is stone collected from the surface of fields where it occurs naturally. Collections of fieldstones which have been removed from arable land or pasture to allow for more effective agriculture are called clearance cairns. In practice, fieldstone is any architectural stone used in its natural shape and can be applied to stones recovered from the topsoil or subsoil. Although fieldstone is generally used to describe such material when used for exterior walls, it has come to include its use in other ways including garden features and interiors. It is sometimes cut or split for use in architecture. Glacial deposition Fieldstone is common in soils throughout temperate latitudes due to glacial deposition. The type of f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lighthouse
A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lenses and to serve as a beacon for navigational aid, for maritime pilots at sea or on inland waterways. Lighthouses mark dangerous coastlines, hazardous shoals, reefs, rocks, and safe entries to harbors; they also assist in aerial navigation. Once widely used, the number of operational lighthouses has declined due to the expense of maintenance and has become uneconomical since the advent of much cheaper, more sophisticated and effective electronic navigational systems. History Ancient lighthouses Before the development of clearly defined ports, mariners were guided by fires built on hilltops. Since elevating the fire would improve the visibility, placing the fire on a platform became a practice that led to the development of the lighthouse. In antiquity, the lighthouse functioned more as an entrance marker to ports than as a warning signal for reefs a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Octagon
In geometry, an octagon (from the Greek ὀκτάγωνον ''oktágōnon'', "eight angles") is an eight-sided polygon or 8-gon. A '' regular octagon'' has Schläfli symbol and can also be constructed as a quasiregular truncated square, t, which alternates two types of edges. A truncated octagon, t is a hexadecagon, . A 3D analog of the octagon can be the rhombicuboctahedron with the triangular faces on it like the replaced edges, if one considers the octagon to be a truncated square. Properties of the general octagon The sum of all the internal angles of any octagon is 1080°. As with all polygons, the external angles total 360°. If squares are constructed all internally or all externally on the sides of an octagon, then the midpoints of the segments connecting the centers of opposite squares form a quadrilateral that is both equidiagonal and orthodiagonal (that is, whose diagonals are equal in length and at right angles to each other).Dao Thanh Oai (2015), "Equilatera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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