A Fresnel lens is a type of compact lens developed by French physicist Augustin-Jean Fresnel for lighthouses. The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances; the idea of creating a thinner, lighter lens in the form of a series of annular steps is attributed to Georges-Louis Leclerc, Comte de Buffon. Whereas Buffon proposed grinding such a lens from a single piece of glass, the Marquis de Condorcet proposed making it with separate sections mounted in a frame. French physicist and engineer Augustin-Jean Fresnel is most given credit for the development of the multi-part lens for use in lighthouses.
According to Smithsonian magazine, the first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary. Scottish physicist Sir David Brewster is credited with convincing the United Kingdom to adopt these lenses in their lighthouses; the Fresnel lens reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections. An ideal Fresnel lens would have an infinite number of sections. In each section, the overall thickness is decreased compared to an equivalent simple lens; this divides the continuous surface of a standard lens into a set of surfaces of the same curvature, with stepwise discontinuities between them. In some lenses, the curved surfaces are replaced with flat surfaces, with a different angle in each section; such a lens can be regarded as an array of prisms arranged in a circular fashion, with steeper prisms on the edges, a flat or convex center. In the first Fresnel lenses, each section was a separate prism.'Single-piece' Fresnel lenses were produced, being used for automobile headlamps, brake and turn signal lenses, so on.
In modern times, computer-controlled milling equipment might be used to manufacture more complex lenses. Fresnel lens design allows a substantial reduction in thickness, at the expense of reducing the imaging quality of the lens, why precise imaging applications such as photography still use larger conventional lenses. Fresnel lenses are made of glass or plastic. In many cases they are thin and flat flexible, with thicknesses in the 1 to 5 mm range. Modern Fresnel lenses consist of all refractive elements; however many of the lighthouses have both refracting and reflecting elements, as shown in the photographs and diagram. That is, the outer elements are sections of reflectors while the inner elements are sections of refractive lenses. Total internal reflection was used to avoid the light loss in reflection from a silvered mirror. Fresnel produced six sizes of lighthouse lenses, divided into four orders based on their size and focal length. In modern use, these are classified as first through sixth order.
An intermediate size between third and fourth order was added as well as sizes above first order and below sixth. A first-order lens has a focal length of a maximum diameter 2590 mm high; the complete assembly is 1.8 m wide. The smallest has a focal length of an optical diameter 433 mm high; the largest Fresnel lenses are called hyperradiant Fresnel lenses. One such lens was on hand when it was decided to outfit the Makapuu Point Light in Hawaii. Rather than order a new lens, the huge optic construction, 3.7 metres tall and with over a thousand prisms, was used there. There are two main types of Fresnel lens: non-imaging. Imaging Fresnel lenses use segments with curved cross-sections and produce sharp images, while non-imaging lenses have segments with flat cross-sections, do not produce sharp images; as the number of segments increases, the two types of lens become more similar to each other. In the abstract case of an infinite number of segments, the difference between curved and flat segments disappears.
Spherical A spherical Fresnel lens is equivalent to a simple spherical lens, using ring-shaped segments that are each a portion of a sphere, that all focus light on a single point. This type of lens produces a sharp image, although not quite as clear as the equivalent simple spherical lens due to diffraction at the edges of the ridges. Cylindrical A cylindrical Fresnel lens is equivalent to a simple cylindrical lens, using straight segments with circular cross-section, focusing light on a single line; this type produces a sharp image, although not quite as clear as the equivalent simple cylindrical lens due to diffraction at the edges of the ridges. Spot A non-imaging spot Fresnel lens uses ring-shaped segments with cross sections that are straight lines rather than circular arcs; such a lens does not produce a sharp image. These lenses have application such as focusing sunlight on a solar panel. Fresnel lenses may be used as components of Köhler illumination optics resulting in effective nonimaging optics Fresnel-Köhler solar concentrators.
Linear A non-imagin
New Point Loma Lighthouse
The New Point Loma Lighthouse is a lighthouse at the southern tip of the Point Loma peninsula in San Diego, California. It was first lighted on March 23, 1891, replacing the Old Point Loma Lighthouse, atop the 400 feet cliffs of Point Loma; the new light is only 88 feet above the water. The first lighthouse keeper was Robert Decatur Israel, keeper at the old lighthouse for 18 years; the original light was 600,000 candlepower and could be seen at a distance of 15 nautical miles. There was a two-tone diaphone fog horn and living quarters for several families; the structure is the only one of its kind remaining on the West Coast. It is similar to Coney Island Light, Plum Island Range Rear Light, La Pointe Light, Duluth South Breakwater Inner Light, all of which were built at about the same time; the latter three of these are all on the National Register of Historic Places. The light was automated in 1973. In February 2013, the light, in use since 1999 was replaced with a VLB-44; the LED apparatus reduces the maintenance cost of the lighthouse and is brighter than the previous light.
List of lighthouses in the United States United States Coast Guard
World War II
World War II known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries; the major participants threw their entire economic and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China, it included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, the only use of nuclear weapons in war. Japan, which aimed to dominate Asia and the Pacific, was at war with China by 1937, though neither side had declared war on the other. World War II is said to have begun on 1 September 1939, with the invasion of Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom.
From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Finland and the Baltic states. Following the onset of campaigns in North Africa and East Africa, the fall of France in mid 1940, the war continued between the European Axis powers and the British Empire. War in the Balkans, the aerial Battle of Britain, the Blitz, the long Battle of the Atlantic followed. On 22 June 1941, the European Axis powers launched an invasion of the Soviet Union, opening the largest land theatre of war in history; this Eastern Front trapped most crucially the German Wehrmacht, into a war of attrition. In December 1941, Japan launched a surprise attack on the United States as well as European colonies in the Pacific. Following an immediate U. S. declaration of war against Japan, supported by one from Great Britain, the European Axis powers declared war on the U.
S. in solidarity with their Japanese ally. Rapid Japanese conquests over much of the Western Pacific ensued, perceived by many in Asia as liberation from Western dominance and resulting in the support of several armies from defeated territories; the Axis advance in the Pacific halted in 1942. Key setbacks in 1943, which included a series of German defeats on the Eastern Front, the Allied invasions of Sicily and Italy, Allied victories in the Pacific, cost the Axis its initiative and forced it into strategic retreat on all fronts. In 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained its territorial losses and turned toward Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in Central China, South China and Burma, while the Allies crippled the Japanese Navy and captured key Western Pacific islands; the war in Europe concluded with an invasion of Germany by the Western Allies and the Soviet Union, culminating in the capture of Berlin by Soviet troops, the suicide of Adolf Hitler and the German unconditional surrender on 8 May 1945.
Following the Potsdam Declaration by the Allies on 26 July 1945 and the refusal of Japan to surrender under its terms, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August respectively. With an invasion of the Japanese archipelago imminent, the possibility of additional atomic bombings, the Soviet entry into the war against Japan and its invasion of Manchuria, Japan announced its intention to surrender on 15 August 1945, cementing total victory in Asia for the Allies. Tribunals were set up by fiat by the Allies and war crimes trials were conducted in the wake of the war both against the Germans and the Japanese. World War II changed the political social structure of the globe; the United Nations was established to foster international co-operation and prevent future conflicts. The Soviet Union and United States emerged as rival superpowers, setting the stage for the nearly half-century long Cold War. In the wake of European devastation, the influence of its great powers waned, triggering the decolonisation of Africa and Asia.
Most countries whose industries had been damaged moved towards economic expansion. Political integration in Europe, emerged as an effort to end pre-war enmities and create a common identity; the start of the war in Europe is held to be 1 September 1939, beginning with the German invasion of Poland. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred and the two wars merged in 1941; this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935; the British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the fo
Alcatraz Island is located in San Francisco Bay, 1.25 miles offshore from San Francisco, United States. The small island was developed with facilities for a lighthouse, a military fortification, a military prison, a federal prison from 1934 until 1963. Beginning in November 1969, the island was occupied for more than 19 months by a group of Native Americans from San Francisco, who were part of a wave of Native activism across the nation, with public protests through the 1970s. In 1972, Alcatraz became part of a national recreation area and received designation as a National Historic Landmark in 1986. Today, the island's facilities are managed by the National Park Service as part of the Golden Gate National Recreation Area. Visitors can reach the island in a little under 15 minutes by ferry ride from Pier 33, located between the San Francisco Ferry Building and Fisherman's Wharf, San Francisco. Hornblower Cruises and Events, operating under the name Alcatraz Cruises, is the official ferry provider to and from the island.
Alcatraz Island is home to the abandoned prison, the site of the oldest operating lighthouse on the West Coast of the United States, early military fortifications, natural features such as rock pools and a seabird colony. According to a 1971 documentary on the history of Alcatraz, the island measures 1,675 feet by 590 feet and is 135 feet at highest point during mean tide; the total area of the island is reported to be 22 acres. Landmarks on the island include the Main Cellhouse, Dining Hall, Lighthouse, the ruins of the Warden's House and Officers' Club, Parade Grounds, Building 64, Water Tower, New Industries Building, Model Industries Building, the Recreation Yard; the first Spaniard to document the island was Juan Manuel de Ayala, who charted San Francisco Bay in 1775 and named one of the three islands he identified as "La Isla de los Alcatraces," which translates as "The Island of the Gannets" but is believed to translate as "The Island of the Pelicans," from the archaic Spanish alcatraz.
Over the years, the Spanish version "Alcatraz" became popular and is now used. In August 1827, French Captain Auguste Bernard Duhaut-Cilly wrote "... running past Alcatraze's Island... covered with a countless number of these birds. A gun fired over the feathered legions caused them to fly up in a great cloud and with a noise like a hurricane." The California brown pelican is not known to nest on the island today. The Spanish built several small buildings on other minor structures; the earliest recorded owner of the island of Alcatraz is Julian Workman, to whom it was given by Mexican governor Pio Pico in June 1846, with the understanding that Workman would build a lighthouse on it. Julian Workman is the baptismal name of William Workman, co-owner of Rancho La Puente and personal friend of Pio Pico. In 1846, acting in his capacity as Military Governor of California, John C. Frémont, champion of Manifest Destiny and leader of the Bear Flag Republic, bought the island for $5,000 in the name of the United States government from Francis Temple.
In 1850, President Millard Fillmore ordered that Alcatraz Island be set aside as a United States military reservation, for military purposes based upon the U. S. acquisition of California from Mexico following the Mexican–American War. Frémont had expected a large compensation for his initiative in purchasing and securing Alcatraz Island for the U. S. government, but the U. S. government invalidated the sale and paid Frémont nothing. Frémont and his heirs sued for compensation during protracted but unsuccessful legal battles that extended into the 1890s. Following the acquisition of California by the United States as a result of the Treaty of Guadalupe Hidalgo which ended the Mexican–American War, the onset of the California Gold Rush the following year, the U. S. Army began studying the suitability of Alcatraz Island for the positioning of coastal batteries to protect the approaches to San Francisco Bay. In 1853, under the direction of Zealous B. Tower, the United States Army Corps of Engineers began fortifying the island, work which continued until 1858, when the initial version of Fort Alcatraz was complete.
The island's first garrison, numbering about 200 soldiers, arrived at the end of that year. When the American Civil War broke out in 1861, the island mounted 85 cannons in casemates around its perimeter, though the small size of the garrison meant only a fraction of the guns could be used at one time. At this time it served as the San Francisco Arsenal for storage of firearms to prevent them falling into the hands of Confederate sympathizers. Alcatraz, built as a "heavily fortified military site on the West Coast", was to form a "triangle of defense" with Fort Point and Lime Point, but the contemplated work on Lime Point was never built; the first operational lighthouse on the West Coast of the United States was built on Alcatraz. During the war, Fort Alcatraz was used to imprison Confederate sympathizers and privateers on the west coast, but never fired its guns at an enemy. Studies in 2018 by archeologists using ground-penetrating radar and laser scans found the remains of structures, ammunition magazines, tunnels below the penitentiary, built later.
They believe. Because of its isolation from the outside by the cold, tremendous currents of the waters of San Francisco Bay, Alcatraz was used to house soldiers who were guilty of crimes as early as 1859. By 1861, the fort was the military priso
The Viceroyalty of New Spain was an integral territorial entity of the Spanish Empire, established by Habsburg Spain during the Spanish colonization of the Americas. It covered a huge area that included territories in North America, South America and Oceania, it originated in 1521 after the fall of Mexico-Tenochtitlan, the main event of the Spanish conquest, which did not properly end until much as its territory continued to grow to the north. It was created on 8 March 1535 as a viceroyalty, the first of four viceroyalties Spain created in the Americas, its first viceroy was Antonio de Mendoza y Pacheco, the capital of the viceroyalty was Mexico City, established on the ancient Mexico-Tenochtitlan. It included what is now Mexico plus the current U. S. states of California, Colorado, New Mexico, Texas, Washington and parts of Idaho, Wyoming, Kansas and Louisiana. The political organization divided the viceroyalty into captaincies general; the kingdoms were those of New Spain. There were four captaincies: Captaincy General of the Philippines, Captaincy General of Cuba, Captaincy General of Puerto Rico and Captaincy General of Santo Domingo.
These territorial subdivisions had a captain general. In Guatemala, Santo Domingo and Nueva Galicia, these officials were called presiding governors, since they were leading royal audiences. For this reason, these hearings were considered "praetorial." There were two great estates. The most important was the Marquisate of the Valley of Oaxaca, property of Hernán Cortés and his descendants that included a set of vast territories where marquises had civil and criminal jurisdiction, the right to grant land and forests and within which were their main possessions; the other estate was the Duchy of Atlixco, granted in 1708, by King Philip V to José Sarmiento de Valladares, former viceroy of New Spain and married to the Countess of Moctezuma, with civil and criminal jurisdiction over Atlixco, Guachinango and Tula de Allende. King Charles III introduced reforms in the organization of the viceroyalty in 1786, known as Bourbon reforms, which created the intendencias, which allowed to limit, in some way, the viceroy's attributions.
New Spain developed regional divisions, reflecting the impact of climate, indigenous populations, mineral resources. The areas of central and southern Mexico had dense indigenous populations with complex social and economic organization; the northern area of Mexico, a region of nomadic and semi-nomadic indigenous populations, was not conducive to dense settlements, but the discovery of silver in Zacatecas in the 1540s drew settlement there to exploit the mines. Silver mining not only became the engine of the economy of New Spain, but vastly enriched Spain and transformed the global economy. New Spain was the New World terminus of the Philippine trade, making the viceroyalty a vital link between Spain's New World empire and its Asian empire. From the beginning of the 19th century, the viceroyalty fell into crisis, aggravated by the Peninsular War, its direct consequence in the viceroyalty, the political crisis in Mexico in 1808, which ended with the government of viceroy José de Iturrigaray and gave rise to the Conspiracy of Valladolid and the Conspiracy of Querétaro.
This last one was the direct antecedent of the Mexican War of Independence, when concluding in 1821, disintegrated the viceroyalty and gave way to the Mexican Empire, in which Agustín de Iturbide would be crowned. The Kingdom of New Spain was established following the Spanish conquest of the Aztec Empire in 1521 as a New World kingdom dependent on the Crown of Castile, since the initial funds for exploration came from Queen Isabella. Although New Spain was a dependency of Spain, it was a kingdom not a colony, subject to the presiding monarch on the Iberian Peninsula; the monarch had sweeping power in the overseas territories,The king possessed not only the sovereign right but the property rights. Every privilege and position, economic political, or religious came from him, it was on this basis that the conquest and government of the New World was achieved. The Viceroyalty of New Spain was established in 1535 in the Kingdom of New Spain, it was the first New World viceroyalty and one of only two in the Spanish empire until the 18th century Bourbon Reforms.
The Spanish Empire comprised the territories in the north overseas'Septentrion', from North America and the Caribbean, to the Philippine and Caroline Islands. At its greatest extent, the Spanish crown claimed on the mainland of
California Historical Landmark
California Historical Landmarks are buildings, sites, or places in the U. S. state of California that have been determined to have statewide historical landmark significance. Historical significance is determined by meeting at least one of the criteria listed below: The first, only, or most significant of its type in the state or within a large geographic region. California Historical Landmarks of number 770 and above are automatically listed in the California Register of Historical Resources. By contrast, a site, feature, or event, of local significance may be designated as a California Point of Historical Interest. List of California Historical Landmarks by county National Historic Sites National Register of Historic Places listings in California Los Angeles Historic-Cultural Monument List of San Francisco Designated Landmarks Johnson, Marael. Why Stop? A Guide to California Roadside Historical Markers. Houston, TX: Gulf Publishing Company. P. 213. ISBN 9780884159230. OCLC 32168093. Official OHP—California Office of Historic Preservation website OHP: California Historical Sites searchpage — links to lists by county
Point Pinos Lighthouse
Point Pinos Lighthouse was lit on February 1, 1855, to guide ships on the Pacific coast of California. It is the oldest continuously operating lighthouse on the West Coast of the United States and the lens is original. Alcatraz Island Lighthouse preceded Point Pinos by 8 months, but was replaced in 1909 by the expanding military prison; the Point Pinos Lighthouse is still an active Coast Guard aid to navigation. On-site museum exhibits and other lighthouse related functions are operated by the city of Pacific Grove, Monterey County, California; the lighthouse is surrounded by the Pacific Grove Municipal Golf Links. The present light source, located 89 feet above sea level, is a 1 kilowatt bulb, which produces a 50,000 candela beam visible under favorable conditions up to 15 nautical miles; the light had a rigid schedule of being lit one hour prior to sunset, extinguished one hour after sunrise. With automation completed in 1975, a small battery-operated back-up strobe light was installed outside the tower, the main light was turned on permanently.
The present signal has a simple 4-second cycle signature of on/3-seconds, off/1-second. As a further navigational aid, a Class D radio beacon operated continuously which had a range of up to 20 miles. A foghorn was located below the lighthouse closer to shore which could be turned on manually by the Coast Guard personnel when lack of visibility warranted its use. With the advent of global positioning satellite navigation in 1993, the radio beacon and foghorn were deactivated; the light is a third-order Fresnel lens with lenses and mechanism manufactured in France in 1853. A larger, second-order light had been planned, but delay in shipment caused the present light destined for the Fort Point Lighthouse in San Francisco, to be installed instead; the first light source was a whale oil lantern set inside the lens, whose tank the keeper had to climb the tower to fill several times a night. Whale oil was expensive and was soon replaced by liquified lard oil which gave way to kerosene in 1880. At the turn of the century, an incandescent vapor lamp was used, followed by electric lights in 1919.
From 1912 to 1940 a falling weight mechanism rotated a metal shutter around the light causing the beam to be cut off to seaward for 10 out of every 30 seconds. Thereafter a timed flasher provided the "on/off" characteristic. In 1874 Lighthouse Avenue in Pacific Grove, named for the Point Pinos Lighthouse, was laid out to ferry supplies and construction materials from the port at Monterey to the lighthouse; the point was a part of the 2,667-acre Rancho Punta de Pinos Mexican land grant made to José María Armenta in 1833, regranted to José Abrego in 1844. In 1850, after the Mexican–American War and the American acquisition of Alta California, Congress appropriated funds for the construction of lighthouses on the West Coast. In 1852, the Secretary of the Treasury ordered the building of seven beacons along the California coast, one of, to be located at Point Pinos, the dangerous southern entrance to the Monterey Bay; the government purchased 25 acres of the Rancho Punta de los Pinos for this purpose, with an additional 67 acres being purchased on.
Construction began in 1853, but difficulties with the delivery of the lenses and prisms from France delayed the opening of the lighthouse until 1855. The first lightkeeper was Charles Layton, appointed to the post at $1,000 per year, he was killed in 1855 while serving as a member of the sheriff's posse chasing the notorious outlaw, Anastacio Garcia. He was succeeded by his widow, who remained head lightkeeper until 1860, when she married her assistant lightkeeper, George Harris. Robert Louis Stevenson wrote of visiting lightkeeper Allen Luce in 1879 after a long walk through the woods from Monterey, praising Luce's hospitality, piano playing, ship models and oil paintings, he wrote about the light in his book From Scotland to Silverado. The most famous lightkeeper was Mrs. Emily Fish, who served from 1893 to 1914, she was called the "Socialite Keeper" due to her love of entertaining guests at the lighthouse. Point Pinos Lighthouse is on the National Register of Historic Places, it is 1-4pm. List of lighthouses in California Point Pinos Lighthouse