Lighthouse
a structure in which a light is maintained at night for the guidance or warning of sailors. The earlier lighthouses were built usually on dangerous shoals, points, or rocks to warn off vessels. Now they are maintained as well to show the way into harbors. About 331 B. C. a beacon tower for the guidance of mariners was built on the Isle of Pharos at the entrance to the port of Alexandria, Egypt. It was called the Pharos, a name applied to light-houses ever since. The Phoenicians, and after them the Romans, erected lighthouses at various points frequented by their ships about the Mediterranean and along the Atlantic coast. A Phoenician lighthouse at Corunna, Spain, has been repaired from time to time and is still in use. The remains of a Roman Pharos are still to be seen at Dover, England. The most celebrated lighthouses of Great Britain are those of the Eddystone, Bell Rock, and the Skerryvore. One of the most noted in the United States is that on Minot's Ledge, off the coast of Massachusetts.
The heaviest waves are said to strike with a force equivalent to three and one-half tons per square foot. It is necessary, therefore, that a lighthouse in an exposed situation should be heavy and possess great strength. Granite, concrete, and iron are the principal materials used. The construction, particularly the laying to the foundation, is often attended with great difficulty. The restless waves permitted General Alexander, the builder of the lighthouse on Minot's Ledge, only thirty hours' work in the first year. A typical granite lighthouse is 140 feet in height and has a base from 40 to 50 feet in diameter. It is drawn in more rapidly at first, then it tapers with a uniform slant to the top, which is about 16 feet in diameter. To give the waves the least possible hold on the building, it is made circular in out line. Such an edifice contains from 50,000 to 60,000 cubic feet of masonry and weighs over 4,000 tons. A lighthouse on Spectacle Reef in Lake Huron cost $300,000. A very ordinary station costs $50,000.
At the beginning of the nineteenth century there were hardly to exceed a score of lighthouses in England. Nearly 900 now guard the waters of Great Britain and Ireland. In the United States there are about 3,000 lighthouses, light buoys, or light ships and fog signals. There are over 500 on the Great Lakes. Four keepers are usually assigned to an American lighthouse. Three tend the lights, while one is ashore. They take turns in relieving each other, so that each keeper has two weeks ashore and six in the lighthouse.
The earlier lighthouses were mere beacons on the tops of which fires of wood or oil were kept burning; in fact, coal fires, some of them burning 300 or 400 tons annually, were depended upon in Great Britain as late as the first quarter of the nineteenth century. They were not discontinued in continental Europe until the middle of the century. One hundred years ago the Eddystone lighthouse had a chandelier of tallow candles burning within a reflector of glass mirrors.
Oil and electricity are now employed. The Barnegat station at the eastern point of New Jersey, guarding the entrance to New York Harbor, has an electric light plant operated by steam capable of generating 30,000,000 candle power. The light used is a 6,000 candle power arc light. It passes through a bull's-eye eighteen inches in diameter and may be seen twenty miles away. Were it not for the curvature of the earth's surface, it might be seen at a distance of one hundred miles. Various devices have been adopted for distinguishing the different lights. Flashes at different intervals, as well as colored lights, enable the mariner going from Charleston, South Carolina, to Boston, for instance, to distinguish every lighthouse on the coast. Even though he should be driven out of his course into absolute darkness and beat up toward land again, he recognizes the lights at once, and is as certain of his course as the woodsman who catches sight of a familiar tree, hill, or body of water. The signals shown at ever rock or harbor are recorded. The lights of Sandy Hook, for instance, may be identified by the intelligent shipmaster from any part of the world.
