Buoys for particular places are further differ entiated by color and top marks. See BUOY.
Fog-signals.-- During the prevalence of fog and snowstorms the most powerful lights are obscured, and it becomes necessary to guide the mariner by sound signals. Hence a fog-signal has become a adjunct of a fully equipped lighthouse station. Various instru ments, such as bells, gongs, guns, steam whistles, explosive charges of tonne, reed trumpets and sirens sounded by steam, elec tricity or compressed air, are used. The most efficient and powerful fog-signal is the siren sounded by compressed air. In spite of the recent improvements in fog-signals they are undoubtedly the weak point in coast protec tion, as the exact direction from which a sound is coming is not easy to locate, and owing to the capricious and uncertain range at which sound can be heard. Submarine signals have been developed in recent years and have a more effective and constant range than signals sounded in the air. The usual type consists of a bell of special design, submerged to a distance free from wave disturbance and with a striking mechanism attached. At light sta tions the bell is often supported on a tripod on the sea bottom and the striking mechanism is operated electrically by means of a cable; a characteristic number of blows at intervals may be given in this manner to identify the station.
To obtain the best results with submarine sig nals, a receiving apparatus is attached to ships; it is similar to a telephone and by it the bear ing of the signal can be determined approxi mately. The sound is heard on ships without the apparatus when the observer is below the water line, and particularly in iron or steel ships, but in this case the bearing of the signal is not easily determined.
Administration.—The United States Light house Board was formed in 1789, and recon structed in 1852; a reorganization of the Light house Service under Act of Congress took effect 1 July 1910. In Great Britain, the Trin ity House of London, the Irish Lighthouse Board and the Northern Lighthouse Board are the lighthouse authorities. The two last named were not constituted till 1786, but the Trinity House may be said to have originated in 1514. The French Commission des Phares was con stituted in 1792 and remodeled in 1811. In Sweden, Norway, Holland, Denmark, Russia and Austria the lighthouse administration is under the Admiralty or Minister of Marine.. In Spain, the system of administration is similar to that of France. For American administra tion see the article LIGHTHOUSE SERVICE OF THE