LIGHTHOUSE
A lighthouse is a tower, building, or framework designed to emit light from a system of lamps and lenses or, in older times, from a fire and used as an aid to navigation and to pilots at sea or on inland waterways.
Lighthouses are used to mark dangerous coastlines, hazardous shoals and reefs, and safe entries to harbors
In a lighthouse, the source of light is called the "lamp" (whether electric or fueled by oil) and the concentration of the light is by the "lens" or "optic". Originally lit by open fires and later candles, the Argand hollow wick lamp and parabolic reflector was developed around 1781 in Europe. In the US, whale oil was used with solid wicks as the source of light, until the Argand parabolic reflector system was introduced around 1810 by Winslow Lewis. Colza oil replaced whale oil in the early 1850s, but US farmers' lack of interest in growing this caused the service to switch to lard oil in the mid 1850s. Kerosene started replacing lard oil in the 1870s and the service was finally totally converted by the late 1880s. Electricity and carbide (acetylene gas) started to replace kerosene around the turn of the 20th century. The use of the latter was promoted by the Dalén light, which automatically lit the lamp at nightfall and extinguished it at dawn.
This concentration of light is accomplished with a rotating lens assembly. In classical period lighthouses, the light source was a kerosene lamp, or earlier an animal or vegetable oil Argand lamp, and the lenses rotated by a weight driven clockwork assembly wound by lighthouse keepers, sometimes as often as every two hours. The lens assembly sometimes floated in mercury to reduce friction. In more modern lighthouses, electric lights and motor drives were used, generally powered by diesel electric generators. These also supplied electricity for the lighthouse keepers. Efficiently concentrating the light from a large omnidirectional light source requires a very large diameter lens. This would require a very thick, heavy lens if naïvely implemented. Development of the Fresnel lens in 1822 revolutionized lighthouses in the 1800s, focusing 85% of a lamp's light versus the 20% focused with the parabolic reflectors of the time. Its design enabled construction of lenses of large size and short focal length without the weight and volume of material in conventional lens designs. Although the Fresnel lens was invented in 1822, it was not used in the US until the 1850s due to the parsimonious administrator of the United States Lighthouse Establishment, Stephen Pleasonton. With the creation of the United States Lighthouse Board in 1852, all US lighthouses received Fresnel lenses by 1860.
Fresnel lenses were ranked by Order, with a first order lens being the largest, most powerful and expensive; and a sixth order lens being the smallest. The order is based on the focal length of the lens. A first order lens has the longest focal length, with the sixth being the shortest. Coastal lighthouses generally use first, second or third order lenses, while harbor lights and beacons use fourth, fifth or sixth order lenses.
Sometimes a lighthouse needs to be constructed in the water itself. Wave-washed lighthouses are masonry structures constructed to withstand water impact, such as Eddystone Lighthouse in Britain and the St. George Reef Light off California. In shallower bays, screw pile ironwork structures are screwed into the seabed and a low wooden structure is placed above the open framework, such as Thomas Point Shoal Lighthouse. As screw piles can be disrupted by ice, in northern climates steel caisson lighthouses such as Orient Point Light are used. Orient Long Beach Bar Light (Bug Light) is a blend of a screw pile light that was later converted to a caisson light because of the threat of ice damage.
Lighthouse development accelerated in the seventeenth century with national lighthouse services established in Denmark (1650), and Britain's Trinity House constructing its first in 1609. The first Eddystone Lighthouse was lit in 1698, though its third incarnation was the most enduring, designed by John Smeaton and finished in 1759. As Britain became the dominant seapower, lighthouses constructed by the Stevenson family for the Northern Lighthouse Board began to appear in Scotland.
The first lighthouse in America was Boston Light on Little Brewster Island (1716). The first keeper was George Worthylake who drowned, along with his wife and daughter, when returning to the island in 1718. The original tower was destroyed by the British during the evacuation of Boston and eventually reconstructed in 1784. The oldest existing lighthouse in America is Sandy Hook Lighthouse, NJ (1764), which is still in operation. By the end of the 19th century, the United States, with its long coastlines had the most lighthouses of any nation.
The US Bureau of Lighthouses was created in 1789 by the 9th Act of the first Congress which placed lighthouses under federal control. Over the years, lighthouses were placed under the direction of Department of Revenue (this department was disbanded in 1820), Department of Treasury (until 1903), then the Department of Commerce. The Lighthouse Board (of the U.S. Lighthouse Establishment) held sway from 1852 to July 1, 1910, when Commerce created the Lighthouse Service. The United States Coast Guard took over on July 7, 1939.
After 1852 the US was divided into Lighthouse Districts; originally eight, they eventually numbered 19. Each District was run by a Naval Officer appointed by the Lighthouse Board as the District Inspector. He ran the district in tandem with an Army Corps of Engineers' officer who was in charge of engineering projects. In 1910, civilians started replacing the military officers.
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