Page:The American Cyclopædia (1879) Volume X.djvu/464

 458 LIGHTHOUSE use, and a signal by sound is the only one that can give warning of the presence of danger. Bells are the most common signals, and when placed on light vessels they are very efficient. When, however, they are placed near light- houses, as the shore is generally between the bell and the vessel to be warned, the roar of the surf is likely to drown the noise of the bell ; so that in such cases they are inefficient, and can only be heard when the vessel is close to the lighthouse, often too close to avoid the clanger. Whistles, horns, and sirens are also used as fog signals, and are more efficient than bells, because their sounds are heard further. They are sounded by steam or air engines, and their positions are indicated by the lengths of and intervals between the blasts. The siren is actuated by steam or compressed air, and is constructed as follows : There is a hollow flat right cylinder with circular base made of strong metal. In the centre of one of the bases is a hole to which is attached a metal tube connecting the cylinder with the boiler, or reservoir of compressed air. The other base contains eight holes symmetrically ar- ranged about its centre. A plate of* metal concentric with this base, and close to it, hav- ing in it corresponding holes, is made to re- volve with any required velocity. In front of this plate is a large horn, which is in accord with the tone or note made by the siren. Then, when steam or compressed air is ad- mitted into the flat cylinder, the revolution of the metal plate opens and closes the eight holes in the base with great rapidity, pro- ducing an intense sound of great volume, which is transmitted in the required direction by the horn. Sounds from the siren have been heard at a distance of 25 m. This in- strument has been experimented upon with great success by Prof. J. Henry and Gen. J. C. Duane of the lighthouse board, and forms the best fog signal in the world. The intervals be- tween the sounds can be so arranged as to make each instrument indicative of the station where it is placed. The objection to it is its great expense, as it involves a steam engine and the persons necessary to attend it, with fuel, fresh water, &c. This expense, however, is common to the siren and the ordinary horn with the reed attachment. Constant efforts are made in all civilized countries to increase the efficiency of these signals. Buoys are anchored in the water to mark rocks, shoals, and other dangers. They are of various kinds, such as nun, can, and spar buoys, &c. A nun buoy is in shape like two equal cones brought together at their bases; it is made like a barrel with staves and iron hoops, or, as is often the case in the United States, it is made of boiler iron. A can buoy is near- ly conical in shape, and is moored at its ver- tex. A spar buoy is a spar anchored at one end. Buoys are painted of different colors to indicate upon which side they must be passed. The colors are fixed by law of congress in the United States. Thus a red buoy must be left on the starboard hand by a vessel entering a harbor from sea, and a black buoy must be left on the port hand. A buoy with red and black horizontal stripes may be left on either hand. The side of a channel upon which a buoy is placed is sometimes indicated by the kind of buoy. Thus nun buoys may be placed on the starboard side of a channel, and can buoys on the port side. IV. HISTORY AND STATISTICS. Little is known of the early history of light- houses, but sea lights are mentioned by Homer in the Odyssey, and they are also referred to in the Greek poem of Hero and Leander. These must have been merely fires kindled upon head- lands. The most noted lighthouse in the world for size and antiquity was the Pharos of Alex- andria. This building was the frustum of a square pyramid surrounded by a large base, the precise dimensions of which are not known. It was commenced by the first Ptolemy, and was finished about 280 B. C. The style and workmanship are represented to have been su- perb, and the material was a white stone. The height was about 400 ft. ; and it is stated by Jbsephus that the light, which was always kept burning on its top at night, was visible about 41 m. It was probably destroyed by an earth- quake, but the date of its destruction is not known. Enough is known, however, to make it certain that this tower existed for 1,600 years. The island upon which it is situated was named Pharos, and the structure took its name from its site. To this day the French word for lighthouse is phare, and the Italian and Spanish faro. One of the most remark- able modern lighthouses is the tower of Cor- douan, which was commenced in 1584 and finished in 1610 by Louis de Foix, the construc- tion having occupied 26 years. It is situated on a ledge of rocks in the mouth of the Ga- ronne or Gironde, in the bay of Biscay. The ledge is about 3,000 ft. long and 1,500 ft. broad, and is bare at low water. It is surrounded by detached rocks, upon which the sea breaks with terrific violence. There is but one place of access, which is a passage 300 ft. wide where there are no rocks, and which leads to within 600 ft. of the tower. The foundation is the frustum of a circular cone whose lower base is 135 ft. in diameter, and is built solid of cut stone to a height of 16 ft., a space for a cellar and water cistern 20 ft. square and 8 ft. deep having been left in the centre. The upper base of the frustum is 125 ft. in diameter. On the E. side is a stone staircase by which access to this upper base is gained. The tow- er springs from this level. A parapet wall about 11 ft. thick at the top is built entirely around the upper base of the foundation to a height of 12 ft. Between this wall and the tower are the apartments of the keepers. The tower rises from the base to a height of 115 ft., and is 50 ft. in diameter at the base ; it di- minishes in diameter as it ascends. The apart- ments of the tower are highly ornamented, and