See also:

• FOCAL

FOCAL See also:

• PLANE

PLANE  . (NTRAMCI See also:

• ROOM

ROOM . WA ? ER TANK . et See also:

• JAMES
• JAMES (Gr. 'IlrKw,l3or, the Heb. Ya`akob or Jacob)
• JAMES (JAMES FRANCIS EDWARD STUART) (1688-1766)
• JAMES, 2ND EARL OF DOUGLAS AND MAR(c. 1358–1388)
• JAMES, DAVID (1839-1893)
• JAMES, EPISTLE OF
• JAMES, GEORGE PAYNE RAINSFOP
• JAMES, HENRY (1843— )
• JAMES, JOHN ANGELL (1785-1859)
• JAMES, THOMAS (c. 1573–1629)
• JAMES, WILLIAM (1842–1910)
• JAMES, WILLIAM (d. 1827)

James See also:

• WALKER, FRANCIS AMASA (1840-1897)
• WALKER, FREDERICK (184o--1875)
• WALKER, GEORGE (c. 1618-169o)
• WALKER, HENRY OLIVER (1843— )
• WALKER, HORATIO (1858– )
• WALKER, JOHN (1732—1807)
• WALKER, OBADIAH (1616-1699)
• WALKER, ROBERT (d. c. 1658)
• WALKER, ROBERT JAMES (1801-1869)
• WALKER, SEARS COOK (1805—1853)
• WALKER, THOMAS (1784—1836)
• WALKER, WILLIAM (1824-1860)

Walker r86a J . N . See also:

• DOUGLASS, FREDERICK (1817-1895)

Douglass O.M.See also:

• POE, EDGAR ALLAN (18og-1849)

Poe 1874 See also:

• WOLF
• WOLF (Canis lupus)
• WOLF, FRIEDRICH AUGUST (1759-1824)
• WOLF, HUGO (1860-1903)
• WOLF, JOSEPH (1820-1899)

Wolf See also:

• ROCK
• ROCK (O.Fr. rake, Sp. rota, Ital. rocca; possibly from a Lat. form rupica, from rupes, rock)
• ROCK, DANIEL (1799–187t)

Rock . Dhu Heartach . FIG . 16.—Spectacle See also:

• REEF (1)

Reef . FIG . 17.—Ar'men .

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)

Bishop Rock and Eddystone towers has 1905); Jument d'Ouessant (See also:

• FRANCE
• FRANCE, ANATOLE (1844– )

France, 1907); and See also:

• ROCHE, SIR BOYLE, BART

Roche Bonne (France, See also:

• BUILDING

building 1910) . Jointing of Stones in Rock Towers.—Various methods of jointing the stones in rock towers are shown in See also:

• FIGS

figs . 6 and 22 . The See also:

• GREAT

great distinction between the towers built by successive See also:

• ENGINEERS, MILITARY

engineers to the 'Trinity See also:

• HOUSE
• HOUSE (O. Eng. hiss, a word common to Teutonic languages, cf. Dut. huis, Ger. Haus; in Gothic it is only found in gudhiss, a temple; it may be ultimately connected with the root of " hide," conceal)

House and other rock lighthouses is that, in the former the stones of each course are dovetailed together both laterally and vertically and are not connected by See also:

• METAL
• METAL (through Fr. from Lat. metallum, mine, quarry, adapted from Gr. µATaXAov, in the same sense, probably connected with ,ueraAAdv, to search after, explore, µeTa, after, aAAos, other)

metal or wooden pins and wedges and dowled as in most other cases . This See also:

• DOVE
• DOVE (Dutch duyve, Dan. due, Ice. dufa, Ger. Taube)

dove-tail method was first adopted at the Hanois Rock at the See also:

• SUGGESTION

suggestion of See also:

• NICHOLAS
• NICHOLAS (1841– )
• NICHOLAS (or NICLAES), HENRY (or HENDRIK) (c. 1501-C. 158o)
• NICHOLAS, SIR EDWARD (1593-1669)
• NICHOLAS, ST

Nicholas Douglass . On the upper See also:

• FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face, one See also:

• SIDE
• SIDE (mod. Eski Adalia)

side and at one end of each See also:

• BLOCK
• BLOCK (from the Fr. bloc, and possibly connected with an Old Ger. Block, obstruction, cf. " baulk ")
• BLOCK, MAURICE (1816–19or)

block is a dovetailed See also:

• PROJECTION

projection . On the under face and the other side and end, corresponding dovetailedeffect of waves on the been noted above . See also:

• LAND

Land Structures for Lighthouses.—The erection of lighthouse towers and other buildings on land presents no difficulties of construction, and such buildings are of See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary architectural See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character . It will therefore be unnecessary to refer to them in detail . See also:

• ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

Attention is directed to the Phare d'See also:

• ECKMUHL, or EGGMVRL

Eckmuhl at Penmarc'h (See also:

• FINISTERE, or FINISTERRE

Finistere), completed in 1897 . The cost of this magnificent structure, 207 ft. in height from the ground, was largely defrayed by a See also:

• BEQUEST (from 0. Eng. becwethan, to declare or express in words; cf. " quoth ")

bequest of £12,000 See also:

• LEFT

left by the See also:

• MARQUIS

marquis de Blocqueville . It is constructed entirely of See also:

• GRANITE (adapted from the Ital. granite, grained; Lat. granum, grain)

granite, and is octagonal in See also:

• PLAN
• PLAN (from Lat. planes, flat)

plan .

The See also:

• TOTAL

total cost of the See also:

• TOWER (Lat. turris; Fr. tour, clocker; Ital. torre; Ger. Thurm)

tower and other See also:

• LIGHT

light-house buildings amounted to £16,000 . Name of Structure . Total Cost . Cub. ft . Cost per cub. ft. of See also:

• MASONRY

Masonry . Eddystone, See also:

• SMEATON, JOHN (1724–1792)

Smeaton (1759) . x,40,000 0 0 13,.343 £2 19 See also:

• ILI

Ili See also:

• BELL
• BELL, ALEXANDER MELVILLE (1819—1905)
• BELL, ANDREW (1753—1832)
• BELL, GEORGE JOSEPH (1770-1843)
• BELL, HENRY (1767-1830)
• BELL, HENRY GLASSFORD (1803-1874)
• BELL, JACOB (1810-1859)
• BELL, JOHN (1691-178o)
• BELL, JOHN (1763-1820)
• BELL, JOHN (1797-1869)
• BELL, ROBERT (1800-1867)
• BELL, SIR CHARLES (1774—1842)

Bell Rock, See also:

• FIRTH, CHARLES HARDING (1857– )
• FIRTH, MARK (1819-1880)

Firth of Forth (1811) . 55,619 12 I 28,530 119 0 Skerryvore, See also:

• WEST
• WEST, BENJAMIN (1738-1820)
• WEST, NICHOLAS (1461-1533)

west See also:

• COAST (from Lat. costa, a rib, side)

coast of See also:

• SCOTLAND
• SCOTLAND, CHURCH OF
• SCOTLAND, EPISCOPAL CHURCH OF

Scotland (1844) 72,200 I1 6 58,58o I 4 Bishop Rock, first granite tower (1858) 34,559 18 9 35,209 0 19 71 Smalls, See also:

• BRISTOL
• BRISTOL, EARLS AND MARQUESSES OF
• BRISTOL, GEORGE DIGBY, 2ND EARL OF1 (1612-1677)
• BRISTOL, JOHN DIGBY, 1ST EARL OF 6 (1580-1653)

Bristol Channel (1861) . 50,124 r1 8 46,386 I i 74 Hanois, See also:

• ALDERNEY (Fr. Aurigny)

Alderney (1862) . . 25,296 0 0 24,542 I 0 74 Wolf Rock, Land's End (1869) . 62,726 0 0 59,070 1 I 3 Dhu Heartach, west coast of Scotland (1872) 72,584 9 7 42,050 114 6 Longships, Land's End (1872) . 43,869 8 11 47,610 0 18 5 Eddystone, Douglass (1882) . 59,255 0 0 65,198 0 18 2 Bishop Rock, strengthening and See also:

• PART

part reconstruction (1887) 64,889 0 0 45,080 1 8 9 Great Basses, See also:

• CEYLON

Ceylon (1873) .

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

• MINOT, LAURENCE (fl. 1333—1352)

Minot's Ledge, See also:

• BOSTON
• BOSTON, THOMAS (1676-1732)

Boston, See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

Mass . (186o) . . 62,500 0 0 36,322 117 2 Spectacle Reef, See also:

• LAKE
• LAKE, GERARD LAKE, 1ST VISCOUNT (1744-1808)

Lake See also:

• HURON
• HURON (a French term, from huge', bristled, early used as an expression of contempt, signifying "lout ")

Huron (1874) 78,125 0 0 42,742 I 16 2 Armen, France (1881) 37,692 0 0 32,400 13 3 Fastnet, See also:

• IRELAND
• IRELAND, CHURCH
• IRELAND, CHURCH OF
• IRELAND, JOHN (1761-1842)
• IRELAND, JOHN (1838- )
• IRELAND, WILLIAM HENRY (1777-1835)

Ireland (1904) . 79,000 0 0 62,600 I 5 51 recesses are formed with just sufficient clearance for the raised bands to enter in setting (fig . 23) . The See also:

• CEMENT (from Lat. caementum, rough pieces of stone, a shortened form of caedimentum, from caedere, to cut)

cement See also:

• MORTAR

mortar in the See also:

• JOINT (through Fr. from Lat. junctum, jungere, to join)

joint formed between the faces so locks the dovetails that the stones cannot be separated without breaking (fig . 24) . Effect of 1Vaves.—The See also:

• WAVE

wave stroke to which rock lighthouse towers are exposed is often considerable . At the Dhu Heartach, during the erection of the tower, 14 joggled stones, each of 2 tons See also:

• WEIGHT

weight, were washed away after having been set in cement at a height of 37 ft. above high See also:

• WATER

water, and similar damage was done during the construction of the Bell Rock tower . The The tower at Ile See also:

• VIERGE, DANIEL (1851-1904)

Vierge (Finistere), completed in 1902, has an See also:

• ELEVATION

elevation of 247 ft. from the ground level to the See also:

• FOCAL

focal See also:

• PLANE

plane, and is probably the highest structure of its See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind in the See also:

• WORLD

world . The See also:

• BRICK (derived according to some etymologists from the Teutonic bricke, a disk or plate; but more authoritatively, through the French brique, originally a " broken piece," applied especially to bread, and so to clay, from the Teutonic brikan, to break)

brick tower, constructed at Spurn Point, at the entrance to the See also:

• HUMBER

Humber and completed in 1895, replaced an earlier structure erected by Smeaton at the end of the 18th See also:

• CENTURY (from Lat. centuria, a division of a hundred men)

century . The existing tower is constructed on a See also:

• FOUNDATION (Lat. fundatio, from fundare, to found)

foundation consisting of See also:

• CONCRETE
• CONCRETE (Lat. concretes, participle of concrescere, to grow together)

concrete cylinders sunk in the See also:

• SHINGLE

shingle See also:

• BEACH

beach .

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)

stone or brick, land towers are frequently constructed of See also:

• CAST (from the verb meaning " to throw "; the word is Scand. in origin, cf. Dan. kaste, and Swed. kasta; " cast " in Middle Eng. took the place of the A.S. weor pan, cf. Ger. werf en)

cast See also:

• IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron plates or open See also:

• STEEL, FLORA ANNIE (1847– )

steel-See also:

• WORK

work with a view to See also:

• ECONOMY

economy . See also:

• FINE

Fine examples of the former are to be found in many See also:

• BRITISH

British colonies and elsewhere, that on Dassen See also:

• ISLAND (O.E. ieg =isle, +land')

Island (Cape of See also:

• GOOD, JOHN MASON (1764-1827)

Good See also:

• HOPE, ANTHONY
• HOPE, THOMAS (c. 1770-1831)

Hope), 105 ft. in height to the focal plane, being typical (fig . 25) . Many openwork structures up to 200 ft. in height have been built . See also:

• RECENT

Recent examples are the towers erected at Cape See also:

• SAN

San See also:

• THORNE

Thorne (See also:

• BRAZIL
• BRAZIL, or BRASIL

Brazil) in 1882, 148 ft. in height (fig . 26), Mocha (Red See also:

• SEA (in O. Eng. sae, a common Teutonic word; cf. Ger. See, Dutch Zee, &c.; the ultimate source is uncertain)
• SEA, COMMAND OF THE

Sea) in 1903, 18o ft. and Sanganeb Reef (Red Sea) 1906, 165 ft. in height to the focal plane . 3 . See also:

• OPTICAL

OPTICAL APPARATUS.—OptiCal apparatus in lighthouses is required for one or other of three distinct purposes: (1) the concentration of the rays derived from the light source into a See also:

• BELT (a word common to Teutonic languages, the Old Ger. form being bale, from which the Lat. balteus probably derived)
• BELT, THOMAS (1832-1878)

belt of light distributed evenly around the See also:

• HORIZON (Gr. 6pfTwv, dividing)

horizon, condensation in the See also:

• VERTICAL (from Lat. vertex, highest point)

vertical plane only being employed; (2) the concentration of the rays both vertically and horizontally into a See also:

• PENCIL (Lat. penicillus, brush, literally little tail)

pencil or See also:

• CONE (Gr. Kwvos)

cone of small See also:

• ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

angle directed towards the horizon and caused to revolve about the light source as a centre, thus producing a flashing light; and (3) the condensation of the light in the vertical plane and also in the See also:

• HORIZONTAL

horizontal plane in such a manner as to concen- trate the rays over a limited See also:

• AZIMUTH (from the Arabic)

azimuth only . Apparatus falling under the first See also:

• CATEGORY (Gr. Karrlyopia, " accusation ")

category produce a fixed light, and further distinction can be provided in this class by See also:

• MECHANICAL

mechanical means of See also:

• OCCULTATION (from Lat. occultare, the frequentative of occulere, to hide)

occultation, resulting in the See also:

• PRO

pro- duction of an occulting or intermittent light . Apparatus included in the second class are usually employed to produce flashing See also:

• LIGHTS, CEREMONIAL USE OF

lights, but sometimes the dual condensation is taken See also:

• ADVANTAGE

advantage of to produce a fixed pencil of rays thrown towards the horizon for the purpose of marking an isolated danger or the limits of a narrow channel . Such lights are best described by the See also:

• FRENCH
• FRENCH, DANIEL CHESTER (1850– )
• FRENCH, NICHOLAS (1604-1678)

French See also:

• TERM

term feux de direction .

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)

beam of light over a wider azimuth than can be conveniently covered by an apparatus of the second class, and for reinforcing the beam of light emergent from a fixed apparatus in any required direction . The above See also:

• CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification of apparatus depends on the resultant effect of the optical elements . Another classification divides the See also:

• INSTRUMENTS

instruments themselves into three classes: (a) catoptric, (b) dioptric and (c) catadioptric . Catoptric apparatus are those by which the light rays are reflected only from the faces of incidence, such as silvered mirrors of plane, spherical, parabolic or other See also:

• PROFILE

profile . Dioptric elements are those in which the light rays pass through the optical See also:

• GLASS
• GLASS (O.E. glees, cf. Ger. Glas, perhaps derived from an old Teutonic root gla-, a variant of glo-, having the general sense of shining, cf. " glare," " glow ")
• GLASS, STAINED

glass, suffering See also:

• REFRACTION
• REFRACTION (Lat. refringere, to break open or apart)

refraction at the incident and emergent faces (fig . 27) . Catadioptric elements are combined of the two foregoing and consist of optical prisms in which the light rays suffer refraction at the incident face, total See also:

• INTERNAL

internal reflexion at a second face and again refraction on emergence at the third face (fig . 28) . The See also:

• OBJECT

object of these several forms of optical apparatus is notonly to produce characteristics or distinctions in lights to enable them to be readily recognized by mariners, but to utilize the light rays in directions above and below the horizontal plane, and also, in the See also:

• CASE
• CASE, JOHN (d. 1600)

case of revolving or flashing lights, in azimuths not requiring to be illuminated for strengthening the beam in the direction of the mariner . It will be seen that the effective condensation in flashing lights is very much greater than in fixed belts, thus enabling higher intensities to be obtained by the use of flashing lights than with fixed apparatus . Catoptric See also:

• SYSTEM

System.—Parabolic reflectors, consisting of small facets of silvered glass set in See also:

• PLASTER

plaster of See also:

• PARIS
• PARIS (also called ALEXANDROS)
• PARIS, ALEXIS PAULIN (1800-x881)
• PARIS, BRUNO PAULIN GASTON (1839-1903)
• PARIS, FRANCOIS DE (169o-1727)
• PARIS, LOUIS PHILIPPE ALBERT
• PARIS, TREATIES OF (1814-1815)

Paris, were first used about the See also:

• YEAR

year 1763 in some of the See also:

• MERSEY

Mersey lights by Mr See also:

• HUTCHINSON
• HUTCHINSON, ANNE (c. 1600-1643)
• HUTCHINSON, JOHN (1615-1664)
• HUTCHINSON, JOHN (1674-1737)
• HUTCHINSON, SIR JONATHAN (1828– )
• HUTCHINSON, THOMAS (1711-1780)

Hutchinson, then See also:

• DOCK

dock See also:

• MASTER (Lat. magister, related to tnagis, more, as the corresponding minister is to minus, less; the English form is due partly to the O. Eng. maegister, and partly to O. Fr. maistre, mod. maitre; cf. Du. meester, Ger. Meister, Ital. maestro)

master at See also:

• LIVERPOOL
• LIVERPOOL, EARLS
• LIVERPOOL, EARLS OF

Liverpool (fig .

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)

copper in 1790 in See also:

• ENGLAND
• ENGLAND, THE CHURCH OF

England and France, and in Scotland in 1803 . The earlier lights were of fixed type, a number of reflectors being arranged on a See also:

• FRAME

frame or stand in such a manner that the pencils of emergent rays overlapped and thus illuminated the whole horizon continuously. in 1783 the first revolving light was erected at Marstrand inSweden . Similar apparatus were installed at Cordouan (1790), Flamborough See also:

• HEAD (in 0. Eng. heafad; the word is common to Teutonic languages; cf. Dutch hoofd, Ger. Haupt, generally taken to be in origin connected with Lat. caput, Gr. KerbOvi7)
• HEAD, SIR EDMUND WALKER, BART
• HEAD, SIR FRANCIS BOND, BART

Head (18o6) and at the Bell Rock (1811) . To produce arevolving or flashing light the reflectors were fixed on a revolving See also:

• CARRIAGE

carriage having several faces . Three or more reflectors in a face were set with their axes parallel . A type of parabolic reflector now in use is shown in fig . 30 . The sizes in See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general use vary from 21 in. to 24 in. See also:

• DIAMETER (from the Cr. &a, through, µErpov, measure)

diameter . These instruments are still largely used for light-See also:

• VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel See also:

• ILLUMINATION

illumination, and a few important land lights are at the See also:

• PRESENT

present See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time of catoptric type, including those at St See also:

• AGNES, SAINT

Agnes (Scilly Islands), See also:

• CROMER
• CROMER, EVELYN BARING, 1ST EARL (1841– )

Cromer and St See also:

• ANTHONY, SAINT
• ANTHONY, SUSAN BROWNELL (1820-1906)

Anthony (See also:

• FALMOUTH

Falmouth) . Dioptric System.—The first See also:

• ADAPTATION (from Lat. adaptare. to fit to)

adaptation of dioptric lenses to light-houses is probably due to T . See also:

• ROGERS, HENRY DARWIN (18o8—1866)
• ROGERS, JAMES EDWIN THOROLD (1823-1890)
• ROGERS, JOHN (1627–c. 1665)
• ROGERS, JOHN (1829-1904)
• ROGERS, JOHN (c. 1500-1555)
• ROGERS, ROBERT (1727-1784?)
• ROGERS, S
• ROGERS, SAMUEL (1763-1855)
• ROGERS, WILLIAM (1819-1896)

Rogers, who used lenses at one of the See also:

• PORTLAND
• PORTLAND, EARL OF
• PORTLAND, ISLE OF
• PORTLAND, WILLIAM BENTINCK, EARL
• PORTLAND, WILLIAM HENRY CAVENDISH BENTINCK

Portland lighthouses between 1786 and 1i90 .

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

• HOWTH

Howth, See also:

• WATERFORD

Waterford and the See also:

• NORTH
• NORTH, BARONS
• NORTH, MARIANNE (1830—1890)
• NORTH, ROGER (1653-1734)
• NORTH, SIR THOMAS (1535?-16o1?)

North See also:

• FORELAND, NORTH

Foreland . See also:

• COUNT (Lat. comes, gen. comitis, Fr. comte, Ital. conte, Span. conde)

Count See also:

• BUFFON, GEORGE LOUIS LECLERC, COMTE DE (1707-1788)

Buffon had in 1748 proposed to grind out of a solid piece of glass a See also:

• LENS
• LENS (from Lat. lens, lentil, on account of the similarity of the form of a lens to that of a lentil seed)

lens in steps or concentric zones in See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order to reduce the thickness to a minimum (fig . 31) . See also:

• CONDORCET, MARIE JEAN ANTOINE NICOLAS CARITAT, MARQUIS DE (1743-1794)

Condorcet in 1773 and See also:

• SIR

Sir D . See also:

• BREWSTER, SIR DAVID (1781–1868)
• BREWSTER, WILLIAM (c. 1566–1644)

Brewster in 1811 designed built-up lenses consisting of stepped See also:

• ANNULAR, ANNULATE

annular rings . Neither of these proposals, however, was intended to apply to lighthouse purposes . In 1822 Augustin See also:

• FRESNEL, AUGUSTIN JEAN (1788-1827)

Fresnel constructed a built-up annular lens in which the centres of curvature of the different rings receded from the See also:

• AXIS (Lat. for " axle ")

axis according to their distances from the centre, so as practically to eliminate spherical See also:

• ABERRATION (Lat. ab, from or away, errare,, to wander)

aberration; the only spherical See also:

• SURFACE

surface being the small central part or " See also:

• BULL
• BULL, GEORGE (1634–1710)
• BULL, JOHN (c. 1562–1628)
• BULL, OLE BORNEMANN (18ro-188o)

bull's See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye " (fig . 32) . These lenses were intended for revolving lights only . Fresnel next produced his cylindric refractor or lens belt, consisting 2o.—See also:

• AMERICAN

American Shoal Lighthouse, See also:

• FLORIDA

Florida . 7- 22-Om . of a See also:

• ZONE (Gr. 'WV77, a girdle, from 'wvvLvay to gird)

zone of glass generated by the revolution See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round a vertical axis of a medial See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section of the annular lens (fig .

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)

lamp at a focal distance of 920 mm . To utilize the light, Dhu Heal wen, 1st Course . Chickens, 6th Course . sCA.C~oF n+E COUA$CS., e which would otherwise See also:

• ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

escape above the lenses, Fresnel introduced a See also:

• SERIES (a Latin word from serere, to join)

series of 8 See also:

• PLAIN (O. Fr. plain, from Lat. plenum)

plain silvered mirrors, on which the light was thrown by a system of lenses . At a subsequent See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period mirrors were also placed in the See also:

• LOWER

lower part of the optic . The apparatus was revolved by See also:

• CLOCK

clock-work . This optic embodied the first See also:

• COMBINATION (Lat. combinare, to combine)

combination of dioptric and catoptric elements in one See also:

• DESIGN (Fr. desiin, drawing; Lat. designare, to mark out)

design (fig . 34) . In the following year Fresnel designed a dioptric lens with catoptric mirrors for fixed light, which was the first of its kind installed in a lighthouse .

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)

account of the great Stone (Wolf Rock). of Dovetail . loss of light entailed by metallic reflection which is at least 25% greater than the system described under . Before his See also:

• DEATH

death in 1827 Fresnel devised his totally reflecting or catadioptric prisms to take the See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place of the silvered reflectors previously used above and below the lens elements (fig . 28) . The See also:

• RAY (Lat. raia)
• RAY (or WRAY, as he wrote his name till 1670), JOHN (1628-1705)

ray Fi falling on the prismoidal See also:

• RING (O.E. hring; a word common to Teutonic languages; and probably cognate with the Lat. circus, Gr. KtpKOS or KpLKOS, Skt'. chakra, wheel, circle, cf. also " harangue "); in art, a band of circular shape of varying sizes, made of any material and used f

ring See also:

• ABC

ABC is refracted in the direction i r and See also:

• MEETING (from " to meet," to come together, assemble, 0. Eng. metals ; cf. Du. moeten, Swed. mota, Goth. gamotjan, &c., derivatives of the Teut. word for a meeting, seen in O. Eng. Wit, moot, an assembly of the people; cf. witanagemot)

meeting the face AB at an angle of incidence greater than the See also:

• CRITICAL (in alphabetical order of authors)

critical, is totally reflected in the direction r e emerging after second refraction in a horizontal direction . Fresnel devised these prisms for use in fixed light apparatus, but the principle was, at a later 0 I date, also applied to flashing lights, in the first instance by T . See also:

• STEVENSON, ADLA1 EWING (1835- )
• STEVENSON, ROBERT (1772-1850)
• STEVENSON, ROBERT LEWIS BALFOUR (1850-1894)

Stevenson . Both the dioptric lens and catadioptric See also:

• PRISM (Gr. rrpivµa, properly a thing sawn, Irpii"ety, to saw)

prism invented by Fresnel are still in general use, the mathematical calculations of the great French designer still forming the basis upon which lighthouse opticians work . Fresnel also designed a See also:

• FORM (Lat. forma)

form of fixed and flashing light in which the distinction of a fixed light, varied by flashes, was produced by placing panels of straight refracting prisms in a vertical position on a revolving carriage outside the fixed light apparatus . The revolu- tion of the upright prisms periodically in- creased the See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power of the beam, by condensa- tion of the rays emergent from the fixed apparatus, in the See also:

• SUE, EUGENE [JosEPH MARIE] (1804—1857)

sue' horizontal plane .

The lens segments in Fresnel's See also:

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

early appara- FIG . 27.-Dioptric Prism . tus were of polygonal form instead of cylindrical, but subsequently manufacturers succeeded in grinding glass in cylindrical nags of the form now used . The first apparatus of this description was made by Messrs Cookson of See also:

• NEWCASTLE
• NEWCASTLE, DUKES OF

Newcastle in 1836 at the suggestion of Alan Stevenson and erected at Inchkeith . In 1825 the French See also:

• COMMISSION (from Lat. commissio, committere)

Commission See also:

• DES

des Phares decided upon the exclusive use of lenticular apparatus in its service . Br The Scottish Lighthouse -E -e See also:

• SPY
• SPY (from " to spy " or " espy"; 0. Fr. espie, espier, to spy, watch; cf. Ger. spdhen, Lat. specere, to look; the Fr. term " espionage "is of course from the same source)

spy . See also:

• BOARD (O. Eng. bord)

Board followed with the Inchkeith revolving apparatus in 1835 and the Isle of May fixed optic in 1836 . In the latter See also:

• INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

instrument Alan Stevenson introduced helical frames for holding the glass prisms in place, thus avoiding See also:

• COMPLETE

complete obstruction of the light rays in any azimuth . The first dioptric light erected by the Trinity House was that formerly at Start Point in See also:

• DEVON, EARLS OF

Devon-See also:

• SHIRE

shire, constructed in 1836 . Catadioptric or reflecting FIG . 28.-Catadioptric or Reflecting prisms for revolving lights Prism . were not used until 185o, when Alan Stevenson designed them for the North Ronaldshay lighthouse .

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)

Mirror.—The next important improvement in lighthouse I intervals . The See also:

• CAM (CAO), DIOGO (fl. 1480-1486)

cam-See also:

• WHEEL (0. Eng. hweol, hweohl, &c., cognate with Icel. hjol, Dan. hiul, the Indo-European root is seen in Sanskrit chakra, Gr. r in Aos, circle, whence " cycle ")
• WHEEL, BREAKING ON THE

wheel is actuated by means of a weight or optical work was the invention of the dioptric spherical mirror by Mr (afterwards Sir) J . T . See also:

• CHANCE (through the O. Fr. cheance, from the Late Lat. cadentia, things happening, from cadere, to fall out, happen; cf. " case ")

Chance in 1862 . The zones or prisms are generated round a vertical axis and divided into segments . This form of mirror is still in general use (figs . 36 and 37) . Azimuthal Condensing Prisms.—Previous to 185o all apparatus were designed to emit light of equal power in every azimuth either constantly or periodic- ally . The only excep- tion was where a light was situated on a • stretch of coast where a mirror could be placed behind the See also:

• FLAME (Lat. flamma; the root flag- appears in flagrare, to burn, blaze, and Gr. d, XEryew)

flame to utilize the rays, which would otherwise pass land-See also:

• WARD
• WARD, ADOLPHUS WILLIAM (1837- )
• WARD, ARTEMUS
• WARD, EDWARD MATTHEW (1816-1879)
• WARD, ELIZABETH STUART PHELPS (1844-1911)
• WARD, JAMES (1769--1859)
• WARD, JAMES (1843– )
• WARD, JOHN QUINCY ADAMS (1830-1910)
• WARD, LESTER FRANK (1841– )
• WARD, MARY AUGUSTA [MRS HUMPHRY WARD]
• WARD, WILLIAM (1766-1826)
• WARD, WILLIAM GEORGE (1812-1882)

ward, and reflect them the ack, flpassmeing and rol ns in a seaward direction .

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

works, which have See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long been celebrated for the high quality of optical glass produced . The early dioptric lights erected in the See also:

• UNITED

United See also:

• KINGDOM

Kingdom, some 13 in all, were made by Messrs See also:

• COOK
• COOK, ALBERT STANBURROUGH (1853– )
• COOK, EDWARD DUTTON (1829–1883)
• COOK, ELIZA (1818–1889)
• COOK, JAMES (1728-1779)
• COOK, THOMAS (1808-1892)

Cook-son of See also:

• SOUTH
• SOUTH, ROBERT (1634–1716)

South See also:

• SHIELDS, JAMES (181b-1879)

Shields, who were instructed by Leonor Fresnel, the See also:

• BROTHER

brother of Augustin . At first they tried to See also:

• MOULD

mould the lens and then to grind it out of one thick See also:

• SHEET

sheet of glass . The successors of the Cookson See also:

• FIRM

firm abandoned the manufacture of lenses in 1845, and the firm of Letourneau & Lepaute of Paris again became the monopolists . In 185o Messrs Chance Bros . & Co. of See also:

• BIRMINGHAM

Birmingham began the manufacture of optical glass, assisted by M . Tabouret, a French See also:

• EXPERT (Lat. expertus, from experiri, to try)

expert who had been a colleague of Augustin Fresnel himself . The first light made by the firm was shown at the Great See also:

• EXHIBITION

Exhibition of 1851, since when numerous dioptric apparatus have been constructed by Messrs Chance, who are, at this time, the only manufacturers of lighthouse glass in the United Kingdom . Most of the glass used for apparatus constructed in France is manufactured at St Gobain .

Some of the glass used by See also:

• GERMAN
• GERMAN, DUTCH AND SCANDINAVIAN

German constructors is made at See also:

• RATHENOW

Rathenow in See also:

• PRUSSIA
• PRUSSIA (Ger. Preussen; Lat. Borussia)

Prussia and See also:

• GOSLAR

Goslar in the Harz . The glass generally employed for lighthouse See also:

• OPTICS

optics has for its refractive See also:

• INDEX

index a mean value of µ=1.51, the corresponding critical angle being 41 ° 30' . Messrs Chance have used dense See also:

• FLINT
• FLINT, AUSTIN (1812-1886)
• FLINT, or FLTNTSHTRE (sir Gallestr)
• FLINT, ROBERT (1838- )
• FLINT, TIMOTHY (1780-1840)

flint glass for the upper and lower refracting rings of high angle lenses and for dioptric mirrors in certain cases . This glass has a value of µ=1.62 with critical angle 38° 5' . Occulting Lights.—During the last 25 years of the 19th century the disadvantages of fixed lights became more and more apparent . At the present See also:

• DAY (O. Eng. dreg, Ger. Tag; according to the New English Dictionary, " in no way related to the Lat. dies")
• DAY, JOHN (1574-1640?)
• DAY, THOMAS (1748-1789)

day the practice of installing such, except occasionally in the case of the smaller and less important of See also:

• HARBOUR (from M.E. hereberge, here, an army; cf. Ger. Heer and -beorg, protection or shelter. Other early forms in English were herberwe and haiborow, as seen in various place names, such as Market Harborough.. The French auberge, an inn, derived through

harbour or See also:

• RIVER

river lights, has practically ceased . The See also:

• NECESSITY (Lat. necessitas)

necessity for providing a distinctive characteristic for every light when possible has led to the See also:

• CONVERSION (Lat. conversio, from convertere, to turn or ,change)

conversion of many of the fixed-light apparatus of earlier years into occulting lights, and often to their supersession by more See also:

• MODERN

modern and powerful flashing apparatus . An occulting apparatus in general use consists of a cylindrical See also:

• SCREEN (usually, but very doubtfully, connected with Lat. scrinium, a box for holding books, from scribere, to write; a connexion with Ger. Schranke, barrier, has been suggested)

screen, fitting over the burner, rapidly lowered and raised by means of a cam-wheel at stated See also:

• SPRING (from " to spring," " to leap or jump up," " burst out," O. Eng., springau, a common Teut. word, cf. Ger. springer, possibly allied to Gr. QnrFpxecOac, to move rapidly)

spring clock . Varying characteristics may be procured by means of such a contrivance—single, See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)

double, triple or other systems of occultation . The eclipses or periods of darkness See also:

• BEAR
• BEAR, BLACK
• BEAR, BROWN
• BEAR, GRIZZLY
• BEAR, ISABELLINE
• BEAR, WHITE

bear much the same relation to the times of illumination as do the flashes to the eclipses in a revolving or flashing light . In the case of a first-order fixed light the cost of conversion to an occulting characteristic does not exceed £250 to f300 . With apparatus illuminated by See also:

• GAS

gas the occultations may be produced by successively raising and lowering the gas at stated intervals .

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- )

ball See also:

• BEARINGS

bearings or carried upon a small See also:

• MERCURY
• MERCURY (MERCU1uus)
• MERCURY (symbol Hg, atomic weight = 2oo)

mercury See also:

• FLOAT (in O. Eng. floc and flota, in the verbal form f eotan; the Teutonic root is flut-, another form of flu-, seen in " flow," cf. " fleet "; the root is seen in Gr. a-M e, to sail, Lat. pluere, to rain; the Lat, fluere and fluctus, wave, is not connect

float . The usual See also:

• DRIVING (from " to drive," i.e. generally to propel, force along or in, a word common in various forms to the Teutonic languages)

driving mechanism employed is a spring clock . " See also:

• OTTER
• OTTER (0. Eng. ate, otor, a common Teutonic word, cf. Dutch and Ger. Otter, Dan. odder, Swed. utter; it is to be referred to the root seen in Gr. 6&ep, water)
• OTTER, SEA

Otter " screens are used in cases when it is desired to produce different periods of occultations in two or more positions in azimuth in order to differentiate sectors marking shoals, &c . The screens are of sheet metal blacked and arranged vertically, some what in the manner of the laths of a venetian See also:

• BLIND, MATHILDE (1841—1896)

blind, and operated by mechanical means . Leading Lights.—In the case of lights designed to See also:

• ACT (Lat. actus, actum)

act as a See also:

• LEAD
• LEAD (pronounced iced)

lead through a narrow channel or as direction lights, it is undesirable to employ a flashing apparatus . Fixed-light optics are employed to meet such cases, and are generally fitted with occulting mechanism A typical apparatus of this description is that at See also:

• GAGE
• GAGE, LYMAN JUDSON (1836– )
• GAGE, THOMAS (1721–1787)

Gage Roads, See also:

• FREMANTLE

Fremantle, West See also:

• AUSTRALIA

Australia (fig . 38) . The occulting See also:

• BRIGHT, JOHN (1811-188g)
• BRIGHT, SIR CHARLES TILSTON

bright light covers the See also:

• FAIR

fair-way, and is flanked by sectors of occulting red and See also:

• GREEN, A
• GREEN, ALEXANDER HENRY (1832—1896)
• GREEN, DUFF (1791—1875)
• GREEN, JOHN RICHARD (1837—1883)
• GREEN, MATTHEW (1696-1737)
• GREEN, THOMAS HILL (1836-1882)
• GREEN, VALENTINE (1739–1813)
• GREEN, WILLIAM HENRY (.1825–1900)

green light marking dangers and Plan intensified by vertical See also:

• CON

con- densing prisms . A good FIG . 34.—Fresnel's Revolving example of a holophotal Apparatus at Cordouan Lighthouse. direction light was exhibited at the 1900 Paris Exhibition, and afterwards erected at Suzac lighthouse (France) . The light consists of an annular lens 500 mm. focal distance, of 18o° horizontal angle and 157° vertical, with a mirror of 18o° at the back .

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

• AMPLITUDE (from Lat. amplus, large)

amplitude in azimuth, and 50,000 See also:

• CANDLE (Lat. candela, from candere, to glow)

candle-power over a narrow channel . The illuminant is an incandesce It See also:

• PETROLEUM (Lat. Petra, rock, and oleuin, oil)

petroleum vapour burner . Holophotal direction lenses of this type can only be applied where the sector to be marked is of comparatively small • angle . Silvered metallic mirrors of parabolic form are also used for the purpose . The use of • single direction lights frequently renders the construction of See also:

• SEPARATE

separate towers for leading lights unnecessary . If two distinct lights are employed to in. dicate the See also:

• LINE

line of See also:

• NAVIGATION (from Lat. navis, ship, and agere, to move)

navigation through a channel or between dangers they must be sufficiently far apart to afford a good lead, the front or seaward light being situated at a lower elevation than the See also:

• REAR

rear or landward one . Coloured Lights.—See also:

• COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

Colour is used as seldom as possible as a distinction, entailing as it does a considerable reduction in the power of the light . It is necessary in some instances for differentiating sectors over dangers See also:

• ANT
• ANT (O. Eng. aemete, from Teutonic a, privative, and maitan, cut or bite off, i.e. " the biter off "; aemete in Middle English became differentiated in dialect use to (mete, then amte, and so ant, and also to emete, whence the synonym " emmet," now only u

ant for harbour See also:

• LIGHTING

lighting purposes . The use of coloured lights as alternating flashes for lighthouse lights is not to be come mended, on account of the unequal absorption of the coloured section at Pendeen in See also:

• CORNWALL

Cornwall is shown in fig . 39; and fig . 55 (See also:

• PLATE

Plate I.) illustrates a double flashing first order light at Pachena Point in British See also:

• COLUMBIA

Columbia . See also:

• HOPKINSON, FRANCIS (1737–1791)
• HOPKINSON, JOHN (1849-1898)

Hopkinson's system has been very extensively used, most of the See also:

• GROUP

group-flashing lights shown in the accompanying tables, being designed upon the general lines he introduced .

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)

atmosphere . When such distinction has been employed, as in the Wolf Rock apparatus, the red and See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white beams can be approximately equalized in initial intensity by constructing the lens and prism panels for the red light of larger angle than those for the white beams . Owing to the absorption by Section . the red colouring, the power of a red beam is only 40% of the intensity of the corresponding white light . The corresponding intensity of green light is 25 % . When red or green sectors are employed they should invariably be reinforced by mirrors, azimuthal condensing prisms, or other means to raise the coloured beam to approximately the same intensity as the white light . With the introduction of group-flashing characteristics the necessity for using colour as a means of distinction disappeared . High-Angle Vertical Lenses.—Messrs Chance of Birmingham have manufactured lenses having 97° of vertical amplitude, but this I. result was only attained by using --- dense flint glass of high refractive revolving light with the panels of reflecting prisms above and below them, setting them at an angle to produce the group-flashing characteristic . The first apparatus of this type constructed were those now in use at See also:

• TAMPICO

Tampico, See also:

• MEXICO
• MEXICO (Span. Mejico, or Mexico,)
• MEXICO, FEDERAL DISTRICT OF
• MEXICO, GULF OF

Mexico and the Little Basses light-house, Ceylon (double flashing) . The Casquets apparatus (triple flashing) was installed in 1877 . A group-flashing catoptric light had, however, been exhibited from the " Royal See also:

• SOVEREIGN

Sovereign ' light-vessel in 1875 .

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

Dublin, who obtained it in the case of a revolving apparatus by alternately raising and lowering the flame . The first apparatus in which this method was employed was erected at See also:

• GALLEY (derived through the 0. Fr. galee, galie, from the Med. Lat. galea, Ital. galea, Port. gale, of uncertain origin; from the Med. Lat. variant form galera are derived the Mod. Fr. galere, Span. and Ital. galera)

Galley Head, Co . See also:

• CORK
• CORK (perhaps through Sp. corcha from Lat. cortex, bark, but possibly connected with quercus, oak)
• CORK, RICHARD BOYLE

Cork (1878) . At this lighthouse 4 of Wigham's large gas burners with four tiers of first-order revolving lenses, eight in each tier, were adopted . By successive lowering and raising of the gas flame at the See also:

• FOCUS (Latin for " hearth " or " fireplace ")

focus of each tier of lenses he produced the group-flashing distinction . The light showed, instead of one prolonged flash at intervals of one See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute, as would be produced by the apparatus in the See also:

• ABSENCE (Lat. absentia)

absence of a gas occulter, a group of See also:

• SHORT, FRANCIS JOB (1857– )

short flashes varying in number between six and seven . The uncertainty, however, in the number of flashes contained in each group is found to be an objection to the arrangement . This See also:

• DEVICE

device was adopted at other gas-illuminated stations in Ireland at subsequent See also:

• DATES

dates . The quadriform apparatus and gas See also:

• INSTALLATION

installation at Galley Head were superseded in 1907 by a first order biform apparatus with incandescent oil vapour burner showing five flashes every 20 seconds .

Flashing Lights indicating See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

Numbers.—See also:

• CAPTAIN (derived from Lat. ca put, head, through the Low Lat. capitanus)

Captain F . A . See also:

• MAHAN, ALFRED THAYER (1840- )

Mahan, See also:

• LATE

late engineer secretary to the United States Lighthouse Board, devised for that service a system of flashing lights to indicate certain numbers . The apparatus in-stalled at Minot's Ledge lighthouse near Boston Harbour, See also:

• MASSACHUSETTS (an Indian name, originally applied to a tribe of Indians)

Massachusetts, has a flash indicating the number 143, thus: the dashes indicating short flashes . Each group is separated by a longer period of darkness than that between succes- FIG . 39.—Pendeen Apparatus . sive members of Plan at Focal Plane . a group . The flashes in a group indicating a figure are about 11 seconds apart, the See also:

• GROUPS
• GROUPS, THEORY

groups being 3 seconds apart, an See also:

• INTERVAL

interval of 16 seconds' darkness occurring between each repetition . Thus the number is repeated every See also:

• HALF

half minute . Two examples of this system were exhibited by the United States Lighthouse Board at the See also:

• CHICAGO
• CHICAGO, UNIVERSITY OF

Chicago Exhibition in 1893, viz, the second-order apparatus just mentioned and a similar light of the first order for Cape See also:

• CHARLES
• CHARLES (1270-1325)
• CHARLES (1421-1461)
• CHARLES (1525-1574)
• CHARLES (c. 1319-1364)
• CHARLES (Fr. Charles; Span. Carlos; Ital. Carlo; Ger. Karl; derived from O.H.G. Charal,latinized as Carolus, meaning originally " man ": cf. Mod.Ger., Kerl," fellow," A.S. ceorl, Mod. Eng. " churl ")
• CHARLES (KARL EITEL ZEPHYRIN LUDWIG; in Rum. CAROL)
• CHARLES [KARL ALEXANDER] (1712-1780)
• CHARLES, ELIZABETH (1828-1896)
• CHARLES, JACQUES ALEXANDRE CESAR (1746-1823)
• CHARLES, THOMAS (1755-1814)

Charles on the Virginian coast . The lenses are arranged in a somewhat - --' f index for t h e — upper and lower elements .

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)

eclipse . Thus two, three or more flashes of, say, half second duration or less follow each other at intervals of about 2 seconds and are succeeded by an eclipse of, say, to seconds, the sequence being completed in a period of, say, 15 seconds . In 1874 Dr See also:

• JOHN
• JOHN (1167–1216)
• JOHN (1290-c. 1320)
• JOHN (1296-1346)
• JOHN (1371–1419)
• JOHN (1468-1532)
• JOHN (1801-1873)
• JOHN (Heb. llni')
• JOHN (ZAPOLYA) (1487-1540)
• JOHN, 4TH MARQUESS OF TWEEDDALE (c. 1695-1762)
• JOHN, DON (1545-1578)
• JOHN, DON (1629–1679)
• JOHN, GOSPEL OF ST
• JOHN, or HAYS (1513–1571)
• JOHN, THE APOSTLE
• JOHN, THE EPISTLES OF