Linda’s Monday Morning Moaning’s,
Let’s start with, “What is a lighthouse”? Very simply a tower, building or other type of structure designed to emit a light system of lamps and lenses and to serve as a beacon for navigational aid on the seas or inland waterways. Lighthouses helped mark the way around dangerous coastlines, shoals, reefs, and give safe passage into harbors. It was used to provide a mariner at sea with a find point of reference to aid in the ability to navigate in the dark when the shore or an offshore hazard can’t be seen directly.
Lighthouses have always had two principle functions, to warn of danger from a spot that sailors could see from a safe distance both night and day. They are used to guide ships into harbors and anchorages. Theses structures were often constructed under precarious circumstances by skilled builders and were maintained , often at great personal risk by very dedicated keepers.
The distance at which such a light can be seen depends on the height and intensity of the light. The brighter the light and the greater its height above the sea, the farther it can be seen. In 1822, the Frenchman Augustin-Jean Fresnel invented a lens that captured and focused a much larger fraction of the light emitted by the lamps than did the reflectors, previous used. These Fresnel lens were are quickly adopted in England, France and other European seafaring nations.
Fresnel lighthouse lenses are ranked by ‘order’, a measure of refracting power, with a first order lens being the largest, most powerful and expensive, with the sixth order lens being the smallest. The order is based on the focal length of the lens. the first order lens has the longest focal length, with the sixth being the shortest. Coastal lighthouses generally use first, second or third order lens, while harbor lights and beacons use fourth, fifth or sixth order lens.
On that ‘wee note’ till next week.
Smithsonian National Museum of American History.
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Linda Osborne Cynowa 