Illuminants

An oil-gas, known by the name of its inventor, Blau, of Augs burg, has been employed to some extent, particularly in Germany and Holland, since about 1906 as a substitute for ordinary oil-gas. It is produced in retorts in much the same manner as the older variety but at a lower temperature C) and can be compressed to i oo atmospheres, at which pressure the hydro carbons are liquefied. This liquid gas is stored and transported in cylinders weighing about 13o lb. and is expanded from them at about 9 atmospheres pressure into the body of the buoy or the receivers at the beacon or lighthouse. When it is used with an incandescent mantle of large size an intrinsic brightness of about 25 candle-power per sq.cm., or about 40% more than ordinary oil gas, is obtainable.

Another variety of compressed oil-gas known as B.B.T., intro duced in France about 1924, has also been used for buoy and beacon lighting. It does not liquefy at 14o atmospheres, at which pressure it is transported in containers each weighing about 2 cwt. It is burnt only in conjunction with an incandescent mantle and the intrinsic brightness obtained is slightly higher than that realized with Blau gas.

Acetylene.

Acetylene (q.v.) was first experimented with for buoy and beacon lighting about 1896, open-flame burners being used. An incandescent-mantle burner consuming acetylene was used at the Chassiron lighthouse (France) in 1902. Oil-gas, en riched by the addition of 20% of acetylene, was for a time used in Germany and Holland for buoy and beacon lighting. It was not, however, until about 1906, when the difficulties associated with its employment had been overcome by the introduction of dissolved acetylene, that the gas came into general use for coast lighting. Acetylene in this form is stored at a pressure of 1 o to 15 atmospheres in cylinders, usually weighing about 2 cwt., filled with a porous material and charged with acetone in the presence of which the gas is dissolved. Owing to the higher intrinsic bright ness of the flame and the convenient transport of the gas it is now in common use throughout the world not only for buoy and beacon lighting but also for many coast lights of secondary importance and unattended revolving lights, mantle burners being sometimes employed.

Acetylene generated on the spot on the carbide-to-water prin ciple is nevertheless still used by some lighthouse authorities, for unattended lights. Comparatively frequent attention in renewing the charge is, however, required in these cases. The intrinsic brightness obtained in some incandescent-acetylene burners is about equal to that of autoform-mantle petroleum-vapour burners.

Electricity.

Electricity for lighthouse illumination was first experimented with in England in 1858 at South Foreland by Trinity House. This was followed by its adoption at Dungeness in 1862, and at Souter point on the coast of Durham in 1871. Both these installations were later abandoned, the former in 1874 and the latter in 1923 when a first-order biform flashing-light with incandescent oil-burner replaced it. Electricity was installed at St. Catherines in the Isle of Wight in 1888 and was also in use at the Isle of May lighthouse at the mouth of the Firth of Forth from 1886 to 1924. Arc lamps formerly provided the illuminant in all

large apparatus, but the development of high power, gas-filled, electric-filament lamps has caused their supersession for light house use. A special type of lamp with highly concentrated fila ment was evolved by the Dutch lighthouse service in 1918 and has been made in sizes up to 4 kw. (Some experimental 4 kw. lamps under trial in Holland [1928] have an intrinsic brightness of about 1,800 candles/cm'. Lamps of 20 kw. have been used experi mentally for aerodrome lighting.) Economies have been effected by the introduction of these lamps combined with automatic electric equipment, and where in addi tion a local supply of current is available the reduction of mainte nance charges at electric stations is considerable. For instance at the South Foreland, which has been a permanent electric station since 1872, an engineer and four keepers were formerly required to maintain the establishment, which included a steam electric generating plant. With the introduction of the filament lamp and automatic equipment in 1926 the establishment was reduced to one keeper. High-tension cables were brought from Dover to the lighthouse; the clock machine revolving the lens is wound electrically; and a lamp-changer automatically replaces a lamp when the filament of the one in service burns out or brings a stand-by acetylene burner into focus if the electric supply fails. A tell-tale device in the keeper's quarters warns him if any derangement takes place. The filament lamp is 8,000 c.p., 8o v. and so amp., and has a mean intrinsic brightness of i,000 A somewhat similar installation has been substi tuted for the arc lamp at the Lizard (1926), but in this case the current is generated at the lighthouse, the personnel being reduced from five to three. At other important coast lighthouses including Pendeen, Skerries and Hartland point (Plate II.), in order to obviate a watch being kept during fog both in the engine room and the lantern, electric light has been introduced in place of the petroleum-vapour lamps and the apparatus in the lantern made automatic. The electric current is generated by semi-diesel engines direct-coupled to the dynamos. Similar installations have been put into four new Trinity House light-vessels (1926-27).

Electricity was used at the old south lighthouse at La Heve (France) in 1863, and in 1910 there were 13 important electric lights on the French coast. Arc lamps were employed and gen erating plant, usually steam driven, was provided at each station. The high cost of maintaining such stations prevented any exten sion of their use on a large scale in France as in other countries; but since 192o the conversion of some of the then existing electric stations to incandescent-filament lighting has been effected. At other stations too, where current from public supplies is available, electricity has been introduced. Blau gas is commonly employed for the stand-by burners in French electric lighthouses. In Hol land several electric-arc and petroleum-vapour lights have been superseded by electric filament lamps since 1919. At Ameland, a generating set is provided and at Kijkduin, current is taken from the public supply.