Lighthouse
2 of the 7 encyclopedias on this shelf carry an entry for Lighthouse. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
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.
Collier's New Encyclopedia (1921)
a lofty tower or other structure, erected at the entrance of a harbor, or at some important or dangerous part of a coast, and having a strong light at the top, to guide vessels, and warn them of danger. Originally they were lighted up with fires, but now oil, gas, and electricity are used, the power of the light being increased by the adoption of glass reflectors, lenses, and prisms. In the United States these matters are under the supervision of the Lighthouse Board. The most important lighthouse in the United States is the great tower with lights of 30,000,000 candle power. The illumination can be seen 100 miles at sea. None of the early lighthouse buildings now exist. The Pharos of Alexandria (331 B. C.) gave its name to its suc- The Romans built lighthouses cessors. at Ostia, Ravenna, Puteoli, and other ports. The Phœnician Pharos at Coruna was repaired during the reign of the Emperor Trajan, was re-established as a lighthouse about 1634, and in 1847 had a dioptric apparatus placed in it. Till the end of the 18th century the lighthouses of Great Britain and America were few in number, and of an inferior description in the great essential PETIT-MANON GRANITE TOWER LIGHT- HOUSE, MAINE of a lighthouse-viz., sending the greatest number of rays of light toward the horizon. As an example of a modern lighthouse tower we may take Skerry vore, which is 139 feet height feet in diameter at the base, containing a mass of 58,580 cubic feet of granite. (See EDDYSTONE.) To Augustin Fresnel belongs the honor of inventing and first employing, in 1822, the dioptric system for lighthouse purposes in combination with a central lamp having four concentric wicks. He devised the lighthouse lens, which is planoconvex, 3 feet 3 inches in height by 2 feet 6 inches in breadth, composed of a central disk, surrounded by annular rings gradually decreasing in breadth as they recede from the center. If these lenses be assembled on a frame with eight or more sides, having a lamp in their common focus, and be made to rocks, producing revolve, a dioptric revolving light is protravels with such duced. The electric light was first shown seen the instant which is simply sion, takes about mile, hence the followed by thunder about If a mile distant ce the slight. by thunder LIGHT distant, LIGHTNING trivance used in against passage BELL NING AB tricity through sed in teleg line wires are SERVICE ROOM brass, usually ough the This plate rests BED ROOM are attack nected with the lly serrated separated by a rests on LOW LIGHT material. ROOM the grow LIGHTNING LIVING ROOM ance designed to its inmates against ENG COND CRANE ROOM age by lighting ed to prote Benjamin Franklin against de an iron rod rises STORE ROOM of the building protect. Its height OIL ROOM its thickness at inches. Its top OIL ROOM copper. From the or a bar of iron the ground, ENTRANCE ramifications 18 surface, in many WATER eral opinion now TANK of rods with many from the building