See also:

• FOCAL

See also:

• BISHOP (A.S. bisceop, from Lat. episcopus, Gr. irio-Korros, " overlooker " or " overseer ")
• BISHOP, ISABELLA (1832-1904)
• BISHOP, SIR HENRY ROWLEY (1786-1855)

The See also:

• TOTAL

. 63,56o 0 0 47,819 I 6 7 See also:

• MINOT, LAURENCE (fl. 1333—1352)

The focal plane of the light is elevated 12o ft. above high water. Besides being built of See also:

• STONE
• STONE (0. Eng. shin; the word is common to Teutonic languages, cf. Ger. Stein, Du. steen, Dan. and Swed. sten; the root is also seen in Gr. aria, pebble)
• STONE, CHARLES POMEROY (1824-1887)
• STONE, EDWARD JAMES (1831-1897)
• STONE, FRANK (1800-1859)
• STONE, GEORGE (1708—1764)
• STONE, LUCY [BLACKWELL] (1818-1893)
• STONE, MARCUS (184o— )
• STONE, NICHOLAS (1586-1647)

Catoptric apparatus, by which dual condensation is produced, are moreover sometimes used for fixed lights, the light pencils overlapping each other in azimuth. Apparatus of the third class are employed for sector lights or those throwing a See also:

• BEAM
• BEAM (from the O. Eng. beam, cf. Ger. Baum, a tree, to which sense may be referred the use of " beam " as meaning the rood or crucifix, and the survival in certain names of trees, as horn-beam)

29). Spherical metallic reflectors were introduced in France in 1781, followed by parabolic reflectors on silvered See also:

• COPPER (symbol Cu, atomic weight 63.1, H=1, or 63.6, O = 16)

Subsequently lenses by the same maker were used at See also:

• HOWTH

33). The lens belt condensed and parallelized the light rays in the vertical plane only, while the annular lens does so in every plane. The first revolving light constructed from Fresnel's designs was erected at the Cordouan lighthouse in 1823. It consisted of 8 panels of annular lenses placed round the See also:

• LAMP (from Gr. Xag ras, a torch, Xaµaav, to shine)

It was erected at the Chassiron lighthouse in 1827 (fig. 35). This combination is geometrically perfect, but not so practically on See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

The lens segments in Fresnel's See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

Bell Rock Flom. Eddystone, 12th Course, Smeaton's Tower. Eddystone, 48th Course, Douglass Tower. .e /1m w sl T _Fogel Pang - F Dooptric See also:

• MIRROR (through O. Fr. mirour, mod. miroir, from a sup-posed Late Lat. miratorium, from mirari, to admire)

In order to increase the intensity of lights in certain azimuths T. Stevenson devised his azimuthal condensing prisms which, in various forms and methods of application, have been largely used for the purpose of strengthening the light rays in required directions as, for instance, where coloured sectors are provided. Applications of this system will be referred to subsequently. Optical Glass for Lighthouses.—In the early days of lens lights the only glass used for the prisms was made in France at the St Gobain and Premontre See also:

• WORKS

Some of the glass used by See also:

• GERMAN
• GERMAN, DUTCH AND SCANDINAVIAN

Another form of occulting mechanism employed consists of a series of vertical screens mounted on a carriage and revolving round the burner. The carriage is rotated on rollers or See also:

• BALL (in Mid. Eng. bal; the word is probably cognate with " bale," Teutonic in origin, cf. also Lat. falls, and Gr. 7raXXa)
• BALL, JOHN (1585-1640)
• BALL, JOHN (1818-1889)
• BALL, JOHN (d. 1381)
• BALL, SIR ALEXANDER JOHN, BART
• BALL, THOMAS (1819- )

The lens throw,s a red beam of about 42° See also:

• AMPLITUDE (from Lat. amplus, large)

A modification of the system consists in grouping two or more lenses \\ \ 11 r\~ r,~l. ;~j'},yh fie l /;1`•' / 1\\1g1~C` ,~i~ii" /•/1(`.11 ~I 11111 //I / \\\Pe af°, pt, •/ \~•' i rl,.~:ll ;/,/1/' 1 , ' ' 1 1 // /r // , ' i // 4Q Iii { \ 1T r 1 , Ire' ; y, rl and bright rays by the See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

A sectional plan of the quadruple-flashing first order apparatus together separated by equal angles, and filling the remaining angle in azimuth by a reinforcing mirror or screen. A group-flashing distinction was proposed for gas lights by J. R. Wigham of See also:

• DUBLIN

Flashing Lights indicating See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

It is doubtful, how-ever, whether the use of refracting elements for a greater angle than 8o° vertically is attended by any material corresponding advantage. Group Flashing Lights,—One of the most useful distinctions consists in the grouping of two or more flashes separated by short intervals of darkness, the group being succeeded by a longer See also:

• ECLIPSE (Gr. €uheo,tis, falling out of place, failing)

40) in Scotland, Bull Rock and Tory Island in Ireland, Cape d'Antifer in France, Pei Yu-shan in See also:

• CHINA

The spherical form loses in efficiency if carried beyond an angle subtending 200 at the focus, and to obviate this loss Mr Stephenson designed his equiangular prisms, which have an inclination out-wards. It is claimed by the designer that the use of equiangular prisms results in less loss of light and less divergence than is the case when either the spherical or Fresnel form is adopted. An example of this design is seen (fig. 40) in the Sule Skerry apparatus (1895). Fixed and Flashing Lights.—The use of these.lights, which show a fixed beam varied at intervals by more powerful flashes, is not to 9e recommended, though a large number were constructed in the earlier years of dioptric illumination and many are still in existence The distinction can be produced in one or other of three ways: (a) by the revolution of detached panels of straight condensing lens prisms placed vertically around a fixed light optic, (b) by utilizing (evolving lens panels in the See also:

• MIDDLE

Where the electric arc is employed it is often necessary to design the prisms so as to produce artificial divergence. The measure of the natural divergence for any point of the lens is the angle whose sine is the ratio of the diameter of the flame to the distance of the point from centre of flame. In the case of vertical divergence the mean height of the flame must be substituted for the diameter. The angle thus obtained is the total divergence, that is, the sum of the angles above and below the horizontal plane or to right and left of the medial section. In fixed dioptric lights there is, of course, no divergence in the horizontal plane. In flashing lights the horizontal divergence is a See also:

• MATTER

The early feux-eclairs, designed by the French engineers and others, had usually a flash of nth to 3rd of a second duration. As a result of experiments carried out in France in 1903-1904, A second has been adopted by the French authorities as the minimum duration for white flashing lights. If shorter flashes are used it is found that the reduction in duration is attended by a corresponding, but not proportionate, diminution in effective intensity. In the case of many electric flashing lights the duration is of necessity reduced, but the greater initial intensity of the flash permits this loss without serious detriment to efficiency. Red or green requires a considerably greater duration than do white flashes. The intervals between the flashes in lights of this character are also small, 2l seconds to 7 seconds. In group-flashing lights the intervals between the flashes are about 2 seconds or even less, with periods of 7 to 10 or 15 seconds between the groups. The flashes are arranged in single, double, triple or even quadruple groups, as in the older forms of apparatus. The See also:

• FEU

Mercury Floats.—It has naturally been found impracticable to revolve the optical apparatus of a light with its mountings, some-times weighing over 7 tons, at the high See also:

• RATE

54). Triform and quadriform apparatus have also been erected in Ireland; particulars of the Tory Island triform apparatus will be found in table VII. The adoption of the multi-form system involves the use of lanterns of in-creased height. Twin Apparatus.—Another method of doubling the power of a light is by mounting two complete and distinct optics side by side on the same revolving table, as I shown in fig. 43 of the Ile Vierge apparatus. Several such lights have been installed by the French Lighthouse Service. See also:

• PORT

The lantern may be placed at the See also:

• TOP (cf. Dan. top, Ger. Topf, also meaning pot)

Prisms. Hyper-Radial 1330 8o° 21° 57° 48° 1st order . 920 92°,80°,58° 21° 57° 48° 2nd „ 700 8o° 21° 57° 480 3rd ,, 500 8o° 210 57° 48° Small 3rd 375 8o° 210 57° 48° order 4th order . 250 80° 21° 57° 48° 5th „ . . 187 5 800 21° 57° 48° 6th 150 800 21° 57° 48° Lenses of small focal distance are also made for See also:

• BUOY

The resulting reduced values are termed " service " intensities. As has been explained above, the effect of a dioptric apparatus is to condense the light rays, and the measure of this condensation is the ratio between the vertical divergence and the vertical angle of the optic in the case of fixed lights. In flashing lights the ratio of vertical condensation must be multiplied by the ratio between the horizontal divergence and the horizontal angle of the See also:

• PANEL (O. Fr. panel, mod. panneau, piece of cloth, from Med. Lat. pannellus, diminutive of pannus, cloth)

4. ILLUMINANTS.—The earliest form of illuminant used for lighthouses was a See also:

• FIRE (in O. Eng. f j'r; the word is common to West German languages, cf. Dutch vuur, Ger. Feuer; the pre-Teutonic form is seen in Sanskrit pu, pavaka, and Gr. irup; the ultimate origin is usually taken to be a root meaning to purify, cf. Lat. purus)

9d. per gallon. See also:

• OLIVE (Olea europaea)

In 1878 cannel coal gas was adopted for the Galley Head lighthouse, with 1o8-jet Wigharn burners. Sir James Douglass introduced gas burners consisting of concentric rings, two to ten in number, perforated on the upper edges. These give excellent results and high intensity, 2600 candles in the case of the 10-ring burner with a flame diameter at the focal plane of 51 in. They are still in use at certain stations. The use of multiple ring and jet gas burners is not being further extended. Gas for light-house purposes generally requires to be specially made; the erection of gas works at the station is thus necessitated and a considerable outlay entailed which is avoided by the use of oil as an illuminant. Incandescent Coal Gas Burners.—The invention of the Welsbach See also:

• MANTLE

A small See also:

• RESERVOIR

Diameter of Mantle. Service Intensity. Consumption of oil. Pints per hour. 35 See also:

• MIN

The luminous intensity of a beam from a dioptric apparatus is, ceteris paribus, proportional to the intrinsic brightness of the luminous source of flame, and not of the total luminous intensity. The intrinsic brightness of the flame of oil burners increases only slightly with their focal'diameter, consequently while the consumption of oil increases the efficiency of the burner for a given apparatus decreases. The illuminating power of the condensed beam can only be improved to a slight extent, and, in fact, is occasionally decreased, by increasing the number of wicks in the burner. The same See also:

• ARGUMENT

The system was first adopted in France, where it is installed at eight lighthouses, among others the Ar'men Rock light, and has been extended to other parts of the world including several stations in Scotland and England. The mantles used in France are of 35 mm. diameter. The 35 mm. mantle gives a candle-power of 400, with an intrinsic brightness of 20 candles per sq. cm. The use of oil gas necessitates the erection of gas works at the lighthouse or its periodical supply in portable reservoirs from a neighbouring station. A complete gas works plant See also:

• COSTS

The French Lighthouse Service has perfected an incandescent acetylene burner with a 55 mm. mantle having an intensity of over 2000 candle-power, with intrinsic brightness of 6o candles per sq. cm. Electricity.—The first installation of electric light for lighthouse purposes in England took place in 1858 at the South Foreland, where the Trinity House established a temporary plant for experimental purposes. This installation was followed in 1862 by the adoption of the illuminant at the See also:

• DUNGENESS

The apparatus installed at the Lizard in 1903 is similar to that at St Catherine's, but has no arrangement for producing a subsidiary sector light. The flash is of • 13 seconds duration every 3 seconds. The apparatus replaced the two fixed electric lights erected in 1878. The Isle of May lighthouse, at the mouth of the Firth of Forth, was first illuminated by electricity in 1886. The optical apparatus consists of a second-order fixed-light lens with reflecting prisms, and is surrounded by a revolving system of vertical condensing prisms which split up the vertically condensed beam of light into 8 separate beams of 3° in azimuth. The prisms are so arranged that the apparatus, making one complete revolution in the minute, produces a group characteristic of 4 flashes in quick succession every 30 seconds (fig. 45). The fixed light is not of the ordinary Fresnel section, the refracting portion being confined to an angle of to°, and the See also:

• REMAINDER, REVERSION

Electric apparatus were also installed at the lighthouse at Port Said in 1869, on the opening of the See also:

• CANAL
• CANAL (from Lat. canalis, " channel " and " kennel " being doublets of the word)

To illuminate the near sea the vertical divergence of the lower prisms of the fixed belt was artificially increased. These optics are very similar to that in use at the Souter Point lighthouse, See also:

• SUNDERLAND
• SUNDERLAND, CHARLES SPENCER, 3RD EARL OF (c. 1674-1722)
• SUNDERLAND, ROBERT SPENCER, 2ND EARL OF (1640-17o2); English politician, was the only son of Henry Spencer (162o--1643)

Several of the de Meritens magneto-electric See also:

• MACHINES

In England fluted carbons of larger diameter are employed with correspondingly increased current. Alternating currents have given the most successful results in all respects. Attempts to utilize continuous current for lighthouse arc lights have, up to the present, met with little success. The cost of a first-class electric lighthouse installation of the most recent type in France, including optical apparatus, lantern, dynamos, engines, air See also:

• COMPRESSOR

Adequate See also:

• VENTILATION (Lat. ventilare, from ventus, wind)

The clocks are fitted with speed See also:

• GOVERNORS

A 28-day clock was arranged for eclipsing the light between sunrise and sunset and automatically cutting off the current at intervals to produce an occulting characteristic. Several small dioptric apparatus illuminated with incandescent electric lamps have been made by the firm of Barbier Benard et See also:

• TURENNE, HENRI DE LA TOUR

The burner has 7 jets, and the light is occulting. Since 1907 incandescent mantle burners for oil gas have been largely used for beacon illumination, both for fixed and occulting lights. Acetylene has also been used for the illumination of beacons and other unattended lights. Lindberg Lights.—In 1881–1882 several beacons lighted automatically by volatile petroleum spirit on the Lindberg-Lyth and Lindberg-Trotter systems were established in See also:

• SWEDEN
• SWEDEN [Sverige]
• SWEDEN, NORWAY AND

The introduction of paraffin also avoids the danger attending the use of the more volatile spirit. Many of these lights are in use on the Scottish coast. They are also used in other parts of the United Kingdom, and in the United States, Canada and other countries. Permanent Wick Lights.—About 1891 the French Lighthouse Service introduced petroleum lamps consuming ordinary high-flash lighthouse oil, and burning without attention for periods of several months. The burners are of special construction, provided with a very thick wick which is in the first instance treated in such a manner as to cause the formation of a See also:

• DEPOSIT (Lat. depositurn, from deponere, to lay down, to put in the care of)

The electric current employed for rotating the apparatus is supplied by four See also:

• LALANDE, JOSEPH JEROME LEFRANCAIS DE (1732-1807)

Modern light-vessels are of steel, wood or composite construction. Steel is now generally employed in new ships. The wood and composite ships are sheathed with Muntz metal. The dimensions of English light-vessels vary. The following may be taken as the usual limits: Length 80 ft. to 114 ft. Beam 20 ft. to 24 ft. See also:

• DEPTH

The moorings usually consist of 3-ton See also:

• MUSHROOM

. 6722 „ 3 . . . 7528 „ In revolving flashing lights two or more reflectors are arranged in parallel in each face. Three, four or more faces or groups of reflectors are arranged around the lantern in which they revolve, and are carried upon a turn-table rotated by clockwork. The intensity of the flashing beam is therefore equivalent to the combined intensities of the beams emitted by the several reflectors in each face. The first light-vessel with revolving light was placed at the Swin Middle at the entrance to the See also:

• THAMES

They are provided with self-propelling power and steam See also:

• WHISTLE

The vessel was built in 1898-1899.1 A third vessel was constructed in 1901–1902 for the Sandettie See also:

• BANK

The total cost of the vessel, including fog See also:

• SIGNAL

In 190I a light-vessel 6o ft. in currents were induced in the lighthouse conductor by the main length was placed off the Otter Rock on the west coast of Scotland; current in the cable, and messages received in the tower by the help ' .3Sm. Lonpiudinot Section - - - - ----- ----- it is constructed of steel, 24 ft. beam, 12 ft. deep and draws 9 ft. of water (fig. 49). The focal plane is elevated 25 ft. above the water-line, and the lantern is 6 ft. in diameter. The optical apparatus is of 500 mm. focal distance and hung in gimbals with a pendulum See also:

• BALANCE (derived through the Fr. from the Late Lat. bilantia, an apparatus for weighing, from bi, two, and lanx, a dish or scale)

Electrical Communication of Light-vessels with the See also:

• SHORE

Seldom used in modern lighthouses and generally restricted to small port or harbour lights, A fixed light is liable to be confused with lights of See also:

• SHIPPING

This characteristic is usually exhibited by fixed dioptric apparatus fitted with some form of occulting mechanism. Many lights formerly of fixed characteristic have been converted to occulting. 1 For the purposes of the mariner a light is classed as flashing or occulting solely according to the duration of light and darkness and without any reference to the apparatus employed. Thus, an occulting apparatus, in which the period of darkness is greater than that of light, is classed in the Admiralty " List of Lights " as a " flashing " light. Group Occulting.—A continuous light with, at regular intervals, groups of two or more sudden and total eclipses. Alternating.—Lights of different See also:

• COLOURS, MILITARY

In countries where the atmosphere is generally clear and fogs are less prevalent than on the coasts of the United Kingdom, second or third order lights suffice for landfalls having regard to the high intensities available by the use of improved illuminants. Secondary coast lights may be of second, third or fourth order of flashing character, and important harbour lights of third or fourth order. Less important harbours and places where considerable range is not required, as in estuaries and narrow seas, may be lighted by flashing lights of fourth order or smaller size. Where sectors are requisite, occulting apparatus should be adopted for the main light : or subsidiary lights, fixed or occulting, may be exhibited from the same tower as the main light but at a lower level. In such cases the vertical distance between the high and the low light must be sufficient to avoid commingling of the two beams at any range at which both lights are visible. Such commingling or blending is due to atmospheric aberration. Range of Lights.—The range of a light depends first on its elevation above sea-level and secondly on its intensity. Most important lights are of sufficient power to render them visible at the full See also:

• GEOGRAPHICAL

Miles. 5 2.565 110 12.03 IO 3.628 120 12.56 15 4'443 130 13.08 20 5.130 140 13.57 25 5'736 150 14.02 30 6.283 200 16.22 35 6.787 250 18.14 40 7.255 300 19.87 45 7.696 350 21.46 50 8.112 400 22.94 55 8'509 450 24'33 6o 8.886 500 25.65 65 9.249 550 26.90 70 9'598 600 28.10 75 9'935 65o 29.25 8o Io•26 700 30.28 85 10'57 800 32.45 90 so•88 900 34'54 95 11.18 woo 36.28 100 11.47 apparatus and not from flashing apparatus. In marking the passage through a channel, or between sandbanks or other dangers, coloured light sectors are arranged to See also:

• COVER (from the Fr. convert, from couvrir, to cover, Lat. cooperire)

No definite rule can, however, be laid down, and local circumstances, such as configuration of the coast line, must be taken into See also:

• CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

The spar buoy (fig. 50) may be adopted for situations where strong tides or currents pre- vail. Oil gas lights are frequently fitted to See also:

• COURTENAY
• COURTENAY, RICHARD (d. 1415)
• COURTENAY, WILLIAM (c. 1342—1396)

Oil gas forms the most See also:

• TRUST

52) consists of a hardened steel ball placed in a horizontal phosphor-See also:

• BRONZE

the most efficient system of coast lighting, since the beams of light from the most powerful electric lighthouse are frequently entirely dispersed and absorbed by the particles of moisture, forming (3) the difficulty in Buoy. locating the position A, Cylinder, 27 ft. H, Air (compressed of a sound signal by 6 in. long. outlet tube to phonic observations. B, Mooring shackle. whistle. Bells and Gongs are C, See also:

• RUDDER (O.E. Rather, i.e. rower)

N, Whistle. very favourable powerful signal is required. Gongs, usually of Chinese manufacture, were formerly in use on board English lightships and are still used to some extent abroad. These are being superseded by more powerful sound instruments. Expldsive Signals.—Guns were long used at many lighthouse and light-vessel stations in England, and are still in use in Ireland and at some See also:

• FOREIGN

An example will be noticed in the See also:

• ILLUSTRATION

In 1862 the Trinity House adopted the instrument for seven land and light-vessel stations. For compressing air for the reed-horns as well as sirens, caloric, steam, gas and oil engines have been variously used, according to local circumstances. The reed-horn was improved by See also:

• PROFESSOR (the Latin noun formed from the verb profiteri, to declare publicly, to acknowledge, profess)

The perforations being cut at an angle, the disk was self-rotated by the oblique pressure of the air in escaping through the slots. H. W. Dove and See also:

• HELMHOLTZ, HERMANN LUDWIG FERDINAND VON (1821-1894)

Each siren is provided with ports for producing a high note as well as a low note, the two notes being sounded in quick succession once every minute. The trumpet mouths are separated by an angle of 120° between their axes. This double form has been adopted in certain instances where the angle desired to be covered by the sound is comparatively wide. In Scotland the cylindrical form is used generally, either automatically or motor driven. By the latter means the See also:

• ADMISSION

6 in., and are of brass, with bent bell mouth. The Trinity House has in recent years reintroduced the use of disk sirens, with which experiments are still being carried out both in the United Kingdom and abroad. For light-vessels and rock stations where it is desired to distribute the sound equally in all directions the mushroom-head trumpet is occasionally used. The Casquets trumpet of this type is 22 ft. in length, of cast-iron, with a mushroom top 6 ft. in diameter. In cases where neither the See also:

• MUSH

The St Catherine's Experiments.—Extensive trials were carried out dqring 1901 by the Trinity House at St Catherine's lighthouse, Isle of Wight, with several types of sirens and reed-horns. Experiments Plan Double-noted Siren. Station. Description. Vibrations See also:

• SOUNDING (for derivation see SOUND above)

98 25 .. 36 7-in. disk siren, motor House) driven 326 .. 28 14 . . A See also:

• UNIFORM

(7) For See also:

• CALM

To take full advantage of the signals thus provided it is necessary for ships approaching them to be fitted with special receiving mechanism of telephonic character installed below the water line and in contact with the See also:

• HULL
• HULL (in O.Eng. hulu, from helan, to cover, cf. Ger. Hiille, covering)
• HULL (officially KINGSTON-UPON-HULL)
• HULL, ISAAC (1775-1843)

Since that date it his gradually See also:

• PURCHASED

. . . 1217 87 289 19 Some small harbour and river lights of subsidiary character are not included in the above total. United States.—The United States Lighthouse Board was constituted by act of See also:

• CONGRESS (Lat. congressus, coming together, from congredi; cum, with, and gradus, step)

94 Fog signals operated by steam or oil engines. 228 Fog signals operated by clockwork, &c 205 Submarine signals 43 See also:

• POST

M O 5 .- C U u Power. Manual. W ? C7 v F England and Channel Islands 44 , . 27 31 2 15 48 10 16 193 Scotland and Isle of Man 35 6 2 5 .. 16 3 67 Ireland 12 . . 2 6 .. 11 3 11 .. 3 48 France . . . 12 .. 7 I ..

1 .. 25 2 48 United States (excluding in- 43 . . 35 15 59 • • .. 218 I 36 407 land lakes and rivers) . . British North America (ex- 6 66 5 79 16 8 .. 24 .. II 215 cluding inland lakes and rivers) . . Candle- Ratio of Elevation Year o Duration Focal Angular a o0 Electric above - Remarks. E stab- Name. Characteristic. of Flash power Distance Breadth of Generators. Lamps.

Engines. High (Service Intensity) of Lens. Panel to u .° U Water, Whole Circle.