Encyclopaedia Britannica, 11th Edition, "Lightfoot, Joseph" to "Liquidation"
by Various · English · Gutenberg #41472 · 1,092,083 chars · public domain (US)
The Project Gutenberg eBook of Encyclopaedia Britannica, 11th Edition, "Lightfoot, Joseph" to "Liquidation"
This eBook is for the use of anyone anywhere in the United States and
most other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms
of the Project Gutenberg License included with this eBook or online
at www.gutenberg.org. If you are not located in the United States,
you will have to check the laws of the country where you are located
before using this eBook.
Title: Encyclopaedia Britannica, 11th Edition, "Lightfoot, Joseph" to "Liquidation"
Author: Various
Release date: November 24, 2012 [eBook #41472]
Most recently updated: October 23, 2024
Language: English
Other information and formats: www.gutenberg.org/ebooks/41472
Credits: Produced by Marius Masi, Don Kretz and the Online
Distributed Proofreading Team at http://www.pgdp.net
*** START OF THE PROJECT GUTENBERG EBOOK ENCYCLOPAEDIA BRITANNICA, 11TH EDITION, "LIGHTFOOT, JOSEPH" TO "LIQUIDATION" ***
Transcriber's notes:
(1) Numbers following letters (without space) like C2 were originally
printed in subscript. Letter subscripts are preceded by an
underscore, like C_n.
(2) Characters following a carat (^) were printed in superscript.
(3) Side-notes were relocated to function as titles of their respective
paragraphs.
(4) Macrons and breves above letters and dots below letters were not
inserted.
(5) [root] stands for the root symbol; [alpha], [beta], etc. for greek
letters.
(6) The following typographical errors have been corrected:
ARTICLE LIGHTHOUSE: "Examples of mercury floats are shown in figs.
41, 42, 43 and Plate I., figs. 54 and 55." 'and' amended from 'an'.
ARTICLE LIGHTHOUSE: "Electricity was substituted as an illuminant
for the then existing oil light at St Catherine's in 1888."
'Electricity' amended from 'Elctricity'.
ARTICLE LIGHTING: "They were, however, costly to install, so that
the flat flame burner retained its popularity in spite of the fact
that its duty was comparatively low ..." 'install' amended from
'instal'.
ARTICLE LIGHTING: "... the filament in the form of a lustrous and
dense deposit having an appearance like steel when seen under the
microscope." 'microscope' amended from 'miscroscope'.
ARTICLE LIMB: "... or to the subordinate members of the Cinque
Ports, attached to one of the principal towns; Pevensey was thus a
'limb' of Hastings." 'subordinate' amended from 'surbordinate'.
ARTICLE LIMON: "Its chief towns, after Limon, are Reventazon and
Matina, both with fewer than 3000 inhabitants." 'fewer' amended
from 'fever'.
ARTICLE LIMOUSIN: "Limousin takes its name from the Lemovices, a
Gallic tribe whose county was included by Augustus in the province
of Aquitania Magna." 'Aquitania' amended from 'Aquitanic'.
ARTICLE LIPSIUS, JUSTUS: "He then returned to Louvain, but was soon
driven by the Civil War to take refuge in Antwerp, where he
received, in 1579, a call to the newly founded university of
Leiden, as professor of history." 'Louvain' amended from 'Louvian'.
ARTICLE LIPSIUS, JUSTUS: "He died at Louvain on the 23rd of March
(some give 24th of April) 1606." 'Louvain' amended from 'Louvian'.
ENCYCLOPAEDIA BRITANNICA
A DICTIONARY OF ARTS, SCIENCES, LITERATURE
AND GENERAL INFORMATION
ELEVENTH EDITION
VOLUME XVI, SLICE VI
Lightfoot, Joseph to Liquidation
ARTICLES IN THIS SLICE:
LIGHTFOOT, JOSEPH BARBER LINDAU, PAUL
LIGHTHOUSE LINDAU
LIGHTING LINDEN
LIGHTNING LINDESAY, ROBERT
LIGHTNING CONDUCTOR LINDET, JEAN BAPTISTE ROBERT
LIGHTS, CEREMONIAL USE OF LINDLEY, JOHN
LIGNE, CHARLES JOSEPH LINDLEY, NATHANIEL LINDLEY
LIGNITE LINDLEY, WILLIAM
LIGONIER, JOHN LIGONIER LINDO, MARK PRAGER
LIGUORI, ALFONSO MARIA DEI LINDSAY (family)
LIGURES BAEBIANI LINDSAY (town of Canada)
LIGURIA LINDSEY, THEOPHILUS
LI HUNG CHANG LINDSTRÖM, GUSTAF
LILAC LINDUS
LILBURNE, JOHN LINE
LILIACEAE LINE ENGRAVING
LILIENCRON, DETLEV VON LINEN and LINEN MANUFACTURES
LILITH LINEN-PRESS
LILLE LINER
LILLEBONNE LING, PER HENRIK
LILLIBULLERO LING
LILLO, GEORGE LINGARD, JOHN
LILLY, WILLIAM LINGAYAT
LILOAN LINGAYEN
LILY LINGEN, RALPH ROBERT WHEELER LINGEN
LILYE, WILLIAM LINGEN
LIMA (Ohio, U.S.A.) LINGUET, SIMON NICHOLAS HENRI
LIMA (department of Peru) LINK
LIMA (capital of Peru) LINKÖPING
LIMAÇON LINLEY, THOMAS
LIMASOL LINLITHGOW, JOHN ADRIAN LOUIS HOPE
LIMB LINLITHGOW
LIMBACH LINLITHGOWSHIRE
LIMBER LINNAEUS
LIMBORCH, PHILIPP VAN LINNELL, JOHN
LIMBURG (feudal state) LINNET
LIMBURG (province of Belgium) LINSANG
LIMBURG (town of Germany) LINSEED
LIMBURG (province of Holland) LINSTOCK
LIMBURG CHRONICLE LINT
LIMBURGITE LINTEL
LIMBUS LINTH
LIME (exudation of holly-tree) LINTON, ELIZA LYNN
LIME (tree) LINTON, WILLIAM JAMES
LIMERICK (county of Ireland) LINTOT, BARNABY BERNARD
LIMERICK (city of Ireland) LINUS (Gregorian saint)
LIMERICK (form of verse) LINUS (Greek heroic figure)
LIMES GERMANICUS LINZ
LIMESTONE LION
LIMINA APOSTOLORUM LIONNE, HUGUES DE
LIMITATION, STATUTES OF LIOTARD, JEAN ETIENNE
LIMOGES LIP
LIMON LIPA
LIMONITE LIPAN
LIMOUSIN, LÉONARD LIPARI ISLANDS
LIMOUSIN LIPETSK
LIMPOPO LIPPE (river of Germany)
LINACRE, THOMAS LIPPE (principality of Germany)
LINARES (province of Chile) LIPPI
LINARES (town of Spain) LIPPSPRINGE
LINCOLN, EARLS OF LIPPSTADT
LINCOLN, ABRAHAM LIPSIUS, JUSTUS
LINCOLN (England) LIPSIUS, RICHARD ADELBERT
LINCOLN (Illinois, U.S.A.) LIPTON, SIR THOMAS JOHNSTONE
LINCOLN (Nebraska, U.S.A.) LIQUEURS
LINCOLN JUDGMENT, THE LIQUIDAMBAR
LINCOLNSHIRE LIQUIDATION
LIND, JENNY
LIGHTFOOT, JOSEPH BARBER (1828-1889), English theologian and bishop of
Durham, was born at Liverpool on the 13th of April 1828. His father was
a Liverpool accountant. He was educated at King Edward's school,
Birmingham, under James Prince Lee, afterwards bishop of Manchester, and
had as contemporaries B. F. Westcott and E. W. Benson. In 1847 Lightfoot
went up to Trinity College, Cambridge, and there read for his degree
with Westcott. He graduated senior classic and 30th wrangler, and was
elected a fellow of his college. From 1854 to 1859 he edited the
_Journal of Classical and Sacred Philology_. In 1857 he became tutor and
his fame as a scholar grew rapidly. He was made Hulsean professor in
1861, and shortly afterwards chaplain to the Prince Consort and honorary
chaplain in ordinary to the queen. In 1866 he was Whitehall preacher,
and in 1871 he became canon of St Paul's. His sermons were not
remarkable for eloquence, but a certain solidity and balance of
judgment, an absence of partisanship, a sobriety of expression combined
with clearness and force of diction, attracted hearers and inspired them
with confidence. As was written of him in _The Times_ after his death,
"his personal character carried immense weight, but his great position
depended still more on the universally recognized fact that his belief
in Christian truth and his defence of it were supported by learning as
solid and comprehensive as could be found anywhere in Europe, and by a
temper not only of the utmost candour but of the highest scientific
capacity. The days in which his university influence was asserted were a
time of much shaking of old beliefs. The disintegrating speculations of
an influential school of criticism in Germany were making their way
among English men of culture just about the time, as is usually the
case, when the tide was turning against them in their own country. The
peculiar service which was rendered at this juncture by the 'Cambridge
School' was that, instead of opposing a mere dogmatic opposition to the
Tübingen critics, they met them frankly on their own ground; and instead
of arguing that their conclusions ought not to be and could not be true,
they simply proved that their facts and their premisses were wrong. It
was a characteristic of equal importance that Dr Lightfoot, like Dr
Westcott, never discussed these subjects in the mere spirit of
controversy. It was always patent that what he was chiefly concerned
with was the substance and the life of Christian truth, and that his
whole energies were employed in this inquiry because his whole heart was
engaged in the truths and facts which were at stake. He was not diverted
by controversy to side-issues; and his labour was devoted to the
positive elucidation of the sacred documents in which the Christian
truth is enshrined."
In 1872 the anonymous publication of _Supernatural Religion_ created
considerable sensation. In a series of masterly papers in the
_Contemporary Review_, between December 1874 and May 1877, Lightfoot
successfully undertook the defence of the New Testament canon. The
articles were published in collected form in 1889. About the same time
he was engaged in contributions to W. Smith's _Dictionary of Christian
Biography_ and _Dictionary of the Bible_, and he also joined the
committee for revising the translation of the New Testament. In 1875 he
became Lady Margaret professor of divinity in succession to William
Selwyn. He had previously written his commentaries on the epistles to
the Galatians (1865), Philippians (1868) and Colossians (1875), the
notes to which were distinguished by sound judgment and enriched from
his large store of patristic and classical learning. These commentaries
may be described as to a certain extent a new departure in New Testament
exegesis. Before Lightfoot's time commentaries, especially on the
epistles, had not infrequently consisted either of short homilies on
particular portions of the text, or of endeavours to enforce foregone
conclusions, or of attempts to decide with infinite industry and
ingenuity between the interpretations of former commentators. Lightfoot,
on the contrary, endeavoured to make his author interpret himself, and
by considering the general drift of his argument to discover his meaning
where it appeared doubtful. Thus he was able often to recover the
meaning of a passage which had long been buried under a heap of
contradictory glosses, and he founded a school in which sobriety and
common sense were added to the industry and ingenuity of former
commentators. In 1879 Lightfoot was consecrated bishop of Durham in
succession to C. Baring. His moderation, good sense, wisdom, temper,
firmness and erudition made him as successful in this position as he had
been when professor of theology, and he speedily surrounded himself with
a band of scholarly young men. He endeavoured to combine his habits of
theological study with the practical work of administration. He
exercised a large liberality and did much to further the work of
temperance and purity organizations. He continued to work at his
editions of the _Apostolic Fathers_, and in 1885 published an edition of
the Epistles of Ignatius and Polycarp, collecting also a large store of
valuable materials for a second edition of Clement of Rome, which was
published after his death (1st ed., 1869). His defence of the
authenticity of the Epistles of Ignatius is one of the most important
contributions to that very difficult controversy. His unremitting
labours impaired his health and shortened his splendid career at Durham.
He was never married. He died at Bournemouth on the 21st of December
1889, and was succeeded in the episcopate by Westcott, his schoolfellow
and lifelong friend.
Four volumes of his _Sermons_ were published in 1890.
LIGHTHOUSE, a form of building erected to carry a light for the purpose
of warning or guidance, especially at sea.
1. EARLY HISTORY.--The earliest lighthouses, of which records exist,
were the towers built by the Libyans and Cushites in Lower Egypt, beacon
fires being maintained in some of them by the priests. Lesches, a Greek
poet (c. 660 B.C.) mentions a lighthouse at Sigeum (now Cape
Incihisari) in the Troad. This appears to have been the first light
regularly maintained for the guidance of mariners. The famous Pharos[1]
of Alexandria, built by Sostratus of Cnidus in the reign of Ptolemy II.
(283-247 B.C.) was regarded as one of the wonders of the world. The
tower, which took its name from that of the small island on which it was
built, is said to have been 600 ft. in height, but the evidence in
support of this statement is doubtful. It was destroyed by an earthquake
in the 13th century, but remains are said to have been visible as late
as 1350. The name Pharos became the general term for all lighthouses,
and the term "pharology" has been used for the science of lighthouse
construction.
The tower at Ostia was built by the emperor Claudius (A.D. 50). Other
famous Roman lighthouses were those at Ravenna, Pozzuoli and Messina.
The ancient Pharos at Dover and that at Boulogne, later known as _la
Tour d'Ordre_, were built by the Romans and were probably the earliest
lighthouses erected in western Europe. Both are now demolished.
The light of Cordouan, on a rock in the sea at the mouth of the Gironde,
is the earliest example now existing of a wave-swept tower. Earlier
towers on the same rock are attributed the first to Louis le Debonnaire
(c. A.D. 805) and the second to Edward the Black Prince. The existing
structure was begun in 1584 during the reign of Henri II. of France and
completed in 1611. The upper part of the beautiful Renaissance building
was removed towards the end of the 18th century and replaced by a
loftier cylindrical structure rising to a height of 207 ft. above the
rock and with the focal plane of the light 196 ft. above high water
(fig. 1). Until the 18th century the light exhibited from the tower was
from an oak log fire, and subsequently a coal fire was in use for many
years. The ancient tower at Corunna, known as the Pillar of Hercules, is
supposed to have been a Roman Pharos. The Torre del Capo at Genoa
originally stood on the promontory of San Berrique. It was built in 1139
and first used as a lighthouse in 1326. It was rebuilt on its present
site in 1643. This beautiful tower rises 236 ft. above the cliff, the
light being elevated 384 ft. above sea-level. A lens light was first
installed in 1841. The Pharos of Meloria was constructed by the Pisans
in 1154 and was several times rebuilt until finally destroyed in 1290.
On the abandonment of Meloria by the Pisans, they erected the still
existing tower at Leghorn in 1304.
In the 17th and 18th centuries numerous towers, on which were erected
braziers or grates containing wood or coal fires, were established in
various positions on the coasts of Europe. Among such stations in the
United Kingdom were Tynemouth (c. 1608), the Isle of May (1636), St
Agnes (1680), St Bees (1718) and the Lizard (1751). The oldest
lighthouse in the United States is believed to be the Boston light
situated on Little Brewster Island on the south side of the main
entrance to Boston Harbour, Mass. It was established in 1716, the
present structure dating from 1859. During the American War of
Independence the lighthouse suffered many vicissitudes and was
successively destroyed and rebuilt three times by the American or
British forces. At the third rebuilding in 1783 a stone tower 68 ft. in
height was erected, the illuminant consisting of four oil lamps. Other
early lighthouse structures on the New England coast were those at
Beaver Tail, near the entrance to Newport Harbour (1740), and the Brant
at the entrance to Nantucket Harbour (1754). A watch-house and beacon
appear to have been erected on Beacon or Lighthouse Island as well as on
Point Allerton Hill near Boston, prior to 1673, but these structures
would seem to have been in the nature of look-out stations in time of
war rather than lighthouses for the guidance of mariners.
2. LIGHTHOUSE STRUCTURES.--The structures of lighthouses may be divided
into two classes, (a) those on rocks, shoals or in other situations
exposed to the force of the sea, and (b) the more numerous class of land
structures.
[Illustration: FIG. 1.--Cordouan Lighthouse.]
_Wave-swept Towers._--In determining the design of a lighthouse tower to
be erected in a wave-swept position consideration must be given to the
physical features of the site and its surroundings. Towers of this
description are classified as follows: (1) Masonry and concrete
structures; (2) Openwork steel and iron-framed erections on pile or
other foundations; (3) Cast iron plated towers; (4) Structures erected
on cylinder foundations.
(1) _Masonry Towers._--Masonry or concrete towers are generally
preferred for erection on wave-swept rocks affording good foundation,
and have also been constructed in other situations where adequate
foundations have been made by sinking caissons into a soft sea bed.
Smeaton's tower on the Eddystone Rock is the model upon which most later
designs of masonry towers have been based, although many improvements in
detail have since been made. In situations of great exposure the
following requirements in design should be observed: (a) The centre of
gravity of the tower structure should be as low as possible. (b) The
mass of the structure superimposed at any horizontal section must be
sufficient to prevent its displacement by the combined forces of wind
and waves without dependence on the adhesion at horizontal joint faces
or on the dovetailing of stones introduced as an additional safeguard.
(c) The structure should be circular in plan throughout, this form
affording the least resistance to wave stroke and wind pressure in any
direction. (d) The lower portion of the tower exposed to the direct
horizontal stroke of the waves should, for preference, be constructed
with vertical face. The upper portion to be either straight with uniform
batter or continuously curved in the vertical plane. External
projections from the face of the tower, except in the case of a gallery
under the lantern, should be avoided, the surface throughout being
smooth. (e) The height from sea-level to the top of the tower should be
sufficient to avoid the obscuration of the light by broken water or
dense spray driving over the lantern. (f) The foundation of the tower
should be carried well into the solid rock. (g) The materials of which
the tower is built should be of high density and of resistant nature.
(h) The stones used in the construction of the tower, at any rate those
on the outer face, should be dovetailed or joggled one to the other in
order to prevent their being dislodged by the sea during the process of
construction and as an additional safeguard of stability. Of late years,
cement concrete has been used to a considerable extent for maritime
structures, including lighthouses, either alone or faced with masonry.
(2) _Openwork Structures._--Many examples of openwork steel and iron
lighthouses exist. Some typical examples are described hereafter. This
form of design is suitable for situations where the tower has to be
carried on a foundation of iron or steel piles driven or screwed into an
insecure or sandy bottom, such as on shoals, coral reefs and sand banks
or in places where other materials of construction are exceptionally
costly and where facility of erection is a desideratum.
(3) _Cast iron Towers._--Cast iron plated towers have been erected in
many situations where the cost of stone or scarcity of labour would have
made the erection of a masonry tower excessively expensive.
(4) _Caisson Foundations._--Cylinder or caisson foundations have been
used for lighthouse towers in numerous cases where such structures have
been erected on sand banks or shoals. A remarkable instance is the
Rothersand Tower. Two attempts have been made to sink a caisson in the
outer Diamond Shoal off Cape Hatteras on the Atlantic coast of the
United States, but these have proved futile.
The following are brief descriptions of the more important wave-swept
towers in various parts of the world.
_Eddystone_ (_Winstanley's Tower_).--The Eddystone rocks, which lie
about 14 m. off Plymouth, are fully exposed to south-west seas. The
reef is submerged at high water of spring tides. Four towers have been
constructed on the reef. The first lighthouse (fig. 2) was polygonal
in plan and highly ornamented with galleries and projections which
offered considerable resistance to the sea stroke. The work was begun
by Henry Winstanley, a gentleman of Essex, in 1695. In 1698 it was
finished to a height of 80 ft. to the wind vane and the light
exhibited, but in the following year, in consequence of damage by
storms, the tower was increased in diameter from 16 ft. to 24 ft. by
the addition of an outer ring of masonry and made solid to a height of
20 ft. above the rock, the tower being raised to nearly 120 ft. The
work was completed in the year 1700. The lower part of the structure
appears to have been of stone, the upper part and lantern of timber.
During the great storm of the 20th of November 1703 the tower was
swept away, those in it at the time, including the builder, being
drowned.
_Eddystone_ (_Rudyerd's Tower_, fig. 3).--This structure was begun in
1706 and completed in 1709. It was a frustum of a cone 22 ft. 8 in. in
diameter at the base and 14 ft. 3 in. at the top. The tower was 92 ft.
in height to the top of the lantern. The work consisted principally of
oak timbers securely bolted and cramped together, the lower part being
filled in solid with stone to add weight to the structure. The
simplicity of the design and the absence of projections from the outer
face rendered the tower very suitable to withstand the onslaught of
the waves. The lighthouse was destroyed by fire in 1755.
_Eddystone_ (_Smeaton's Tower_, fig. 4).--This famous work, which
consisted entirely of stone, was begun in 1756, the light being first
exhibited in 1759. John Smeaton was the first engineer to use
dovetailed joints for the stones in a lighthouse structure. The
stones, which averaged 1 ton in weight, were fastened to each other by
means of dovetailed vertical joint faces, oak key wedges, and by oak
tree-nails wedged top and bottom, extending vertically from every
course into the stones beneath it. During the 19th century the tower
was strengthened on two occasions by the addition of heavy wrought
iron ties, and the overhanging cornice was reduced in diameter to
prevent the waves from lifting the stones from their beds. In 1877,
owing partly to the undermining of the rock on which the tower was
built and the insufficient height of the structure, the Corporation
of Trinity House determined on the erection of a new lighthouse in
place of Smeaton's tower.
[Illustration: FIG. 2. Winstanley 1699
FIG. 3. Rudyerd 1706
FIG. 4. Smeaton 1756
FIG. 5. Sir J. N. Douglass 1882
Lighthouses on the Eddystone.]
_Eddystone, New Lighthouse (J. N. Douglass)._--The site selected for
the new tower is 120 ft. S.S.E. from Smeaton's lighthouse, where a
suitable foundation was found, although a considerable section of the
lower courses had to be laid below the level of low water. The
vertical base is 44 ft. in diameter and 22 ft. in height. The tower
(figs. 5 and 6) is a concave elliptic frustum, and is solid, with the
exception of a fresh-water tank, to a height of 25 ft. 6 in. above
high-water level. The walls above this level vary in thickness from 8
ft. 6 in. to 2 ft. 3 in. under the gallery. All the stones are
dovetailed, both horizontally and vertically, on all joint faces, the
stones of the foundation course being secured to the rock by Muntz
metal bolts. The tower contains 62,133 cub. ft. of granite, weighing
4668 tons. The height of the structure from low water ordinary spring
tides to the mean focal plane is 149 ft. and it stands 133 ft. above
high water. The lantern is a cylindrical helically framed structure
with domed roof. The astragals are of gun-metal and the pedestal of
cast iron. The optical apparatus consists of two superposed tiers of
refracting lens panels, 12 in each tier of 920 mm. focal distance. The
lenses subtend an angle of 92° vertically. The 12 lens panels are
arranged in groups of two, thus producing a group flashing light
showing 2 flashes of 1½ seconds' duration every half minute, the
apparatus revolving once in 3 minutes. The burners originally fitted
in the apparatus were of 6-wick pattern, but these were replaced in
1904 by incandescent oil vapour burners. The intensity of the combined
beam of light from the two apparatus is 292,000 candles. At the time
of the completion of the lighthouse two bells, weighing 2 tons each
and struck by mechanical power, were installed for fog-signalling
purposes. Since that date an explosive gun-cotton fog signal has been
erected, the bells being removed. At a lower level in the tower are
installed 2 21-in. parabolic silvered reflectors with 2-wick burners,
throwing a fixed light of 8000 candle-power over a danger known as the
Hand Deeps. The work of preparing the foundation was begun on the 17th
of July 1878, the foundation stone being laid by the late duke of
Edinburgh on the 19th of August 1879. The last stone was laid on the
1st of June 1881, and the light was exhibited for the first time on
the 18th of May 1882. The upper portion of Smeaton's tower, which was
removed on completion of the new lighthouse, was re-erected on
Plymouth Hoe, where it replaced the old Trinity House sea mark. One of
the principal features in the design of the new Eddystone lighthouse
tower is the solid vertical base. This construction was much
criticized at the time, but experience has proved that heavy seas
striking the massive cylindrical structure are immediately broken up
and rush round to the opposite side, spray alone ascending to the
height of the lantern gallery. On the other hand, the waves striking
the old tower at its foundation ran up the surface, which presented a
curved face to the waves, and, unimpeded by any projection until
arriving at the lantern gallery, were partially broken up by the
cornice and then spent themselves in heavy spray over the lantern. The
shock to which the cornice of the gallery was exposed was so great
that stones were sometimes lifted from their beds. The new Eddystone
tower presents another point of dissimilarity from Smeaton's
structure, in that the stones forming the floors consist of single
corbels built into the wall and constituting solid portions thereof.
In Smeaton's tower the floors consisted of stone arches, the thrust
being taken by the walls of the tower itself, which were strengthened
for the purpose by building in chains in the form of hoops (fig. 7).
The system of constructing corbelled stone floors was first adopted by
R. Stevenson in the Bell Rock lighthouse (fig. 8).
[Illustration: FIG. 6.--Plan of Entrance Floor, Eddystone Lighthouse.]
[Illustration: FIG. 7.--Floor, Smeaton's Eddystone Lighthouse.]
_Bell Rock Lighthouse_ (fig. 9).--The Bell Rock, which lies 12 m. off
the coast of Forfarshire, is exposed to a considerable extent at low
water. The tower is submerged to a depth of about 16 ft. at high water
of spring tides. The rock is of hard sandstone. The lighthouse was
constructed by Robert Stevenson and is 100 ft. in height, the solid
portion being carried to a height of 21 ft. above high water. The work
of construction was begun in 1807, and finished in 1810, the light
being first exhibited in 1811. The total weight of the tower is 2076
tons. A new lantern and dioptric apparatus were erected on the tower
in 1902. The focal plane of the light is elevated 93 ft. above high
water.
[Illustration: FIG. 8.--Floor, Stevenson's Bell Rock Lighthouse.]
_Skerryvore Lighthouse_ (fig. 10).--The Skerryvore Rocks, 12 m. off
the island of Tyree in Argyllshire, are wholly open to the Atlantic.
The work, designed by Alan Stevenson, was begun in 1838 and finished
in 1844. The tower, the profile of which is a hyperbolic curve, is 138
ft. high to the lantern base, 42 ft. diameter at the base, and 16 ft.
at the top. Its weight is 4308 tons. The structure contains 9 rooms in
addition to the lantern chamber. It is solid to a height of 26 ft.
above the base.
_Heaux de Brehat Lighthouse._--The reef on which this tower is
constructed lies off the coast of Brittany, and is submerged at high
tide. The work was carried out in 1836-1839. The tower is circular in
plan with a gallery at a height of about 70 ft. above the base. The
tower is 156 ft. in height from base to lantern floor.
_Haut Banc du Nord Lighthouse._--This tower is placed on a reef at the
north-west extremity of the Île de Ré, and was constructed in
1849-1853. It is 86 ft. in height to the lantern floor.
_Bishop Rock Lighthouse._--The lighthouse on the Bishop Rock, which is
the westernmost landfall rock of the Scilly Islands, occupies perhaps
a more exposed situation than any other in the world. The first
lighthouse erected there was begun in 1847 under the direction of N.
Douglass. The tower consisted of a cast and wrought iron openwork
structure having the columns deeply sunk into the rock. On the 5th of
February 1850, when the tower was ready for the erection of the
lantern and illuminating apparatus, a heavy storm swept away the whole
of the structure. This tower was designed for an elevation of 94 ft.
to the focal plane. In 1851 the erection of a granite tower, from the
designs of James Walker, was begun; the light was first exhibited in
1858. The tower (fig. 11) had an elevation to the focal plane of 110
ft., the lower 14 courses being arranged in steps, or offsets, to
break up the force of the waves. This structure also proved
insufficient to withstand the very heavy seas to which it was exposed.
Soon after its completion the 5-cwt. fog bell, fixed to the lantern
gallery 100 ft. above high-water mark, was washed away, together with
the flagstaff and ladder. The tower vibrated considerably during
storms, and it was found that some of the external blocks of granite
had been split by the excessive stress to which they had been exposed.
In 1874 the tower was strengthened by bolting continuous iron ties to
the internal surfaces of the walls. In 1881, when further signs of
damage appeared, it was determined to remove the upper storey or
service room of the lighthouse, and to case the structure from its
base upwards with granite blocks securely dovetailed to each other and
to the existing work. At the same time it was considered advisable to
increase the elevation of the light, and place the mean focal plane of
the new apparatus at an elevation of 146 ft. above high-water mark.
The work was begun in 1883, and the new apparatus was first
illuminated on the 25th of October 1887. During the operation of
heightening the tower it was necessary to install a temporary light,
consisting of a cylindrical lightship lantern with catoptric
apparatus; this was raised from time to time in advance of the
structure as the work proceeded. The additional masonry built into the
tower amounts approximately to 3220 tons. Profiting by the experience
gained after the construction of the new Eddystone tower, Sir J. N.
Douglass decided to build the lower portion of the improved Bishop
Rock tower in the form of a cylinder, but with considerably increased
elevation (figs. 12 and 13). The cylindrical base is 40 ft. in
diameter, and rises to 25 ft. above high-water mark. The lantern is
cylindrical and helically framed, 14 ft. in diameter, the glazing
being 15 ft. in height. The optical apparatus consists of two
superposed tiers of lenses of 1330 mm. focal distance, the lenses
subtending a horizontal angle of 36° and a vertical angle of 80°. The
apparatus consists of 5 groups of lenses each group producing a double
flashing light of one minute period, the whole apparatus revolving
once in five minutes. The maximum aggregate candle-power of the flash
is 622,000 candles. A gun-cotton explosive fog signal is attached to
the lantern. The cost of the various lighthouses on the Bishop Rock
has been as follows:
1. Cast iron lighthouse £12,500 0 0
2. Granite lighthouse 34,559 18 9
3. Improved granite lighthouse 64,889 0 0
[Illustration: FIG. 9.--Bell Rock.
FIG. 10.--Skerryvore.
FIG. 11.--Bishop Rock.
FIG. 12.--Bishop Rock.]
_The Smalls Lighthouse._--A lighthouse has existed on the Smalls rock,
18½ m. off Milford Haven, since 1776, when an oak pile structure was
erected by Henry Whiteside. The existing structure, after the model of
the second lighthouse on the Bishop Rock, was erected in 1856-1861 by
the Trinity House and is 114 ft. in height from the foundation to the
lantern floor. A new optical apparatus was installed in 1907.
_Minot's Ledge Lighthouse._--The tower, which is 89 ft. in height, is
built of granite upon a reef off Boston Harbor, Mass., and occupied
five years in construction, being completed in 1860 at a cost of
£62,500. The rock just bares at low water. The stones are dovetailed
vertically but not on their horizontal beds in the case of the lower
40 ft. or solid portion of the tower, bonding bolts being substituted
for the horizontal dovetailed joints used in the case of the Wolf and
other English towers. The shape of the tower is a conical frustum.
_Wolf Rock Lighthouse._--This much exposed rock lies midway between
the Scilly Isles and the Lizard Point, and is submerged to the depth
of about 6 ft. at high water. The tower was erected in 1862-1869 (fig.
14). It is 116 ft. 6 in. high, 41 ft. 8 in. diameter at the base,
decreasing to 17 ft. at the top. The walls are 7 ft. 9½ in. thick,
decreasing to 2 ft. 3 in. The shaft is a concave elliptic frustum, and
contains 3296 tons. The lower part of the tower has projecting
scarcements in order to break up the sea.
_Dhu Heartach Rock Lighthouse._--The Dhu Heartach Rock, 35 ft. above
high water, is 14 m. from the island of Mull, which is the nearest
shore. The maximum diameter of the tower (fig. 15), which is of
parabolic outline, is 36 ft., decreasing to 16 ft.; the shaft is solid
for 32 ft. above the rock; the masonry weighs 3115 tons, of which 1810
are contained in the solid part. This tower occupied six years in
erection, and was completed in 1872.
_Great Basses Lighthouse, Ceylon._--The Great Basses lighthouse lies 6
m. from the nearest land. The cylindrical base is 32 ft. in diameter,
above which is a tower 67 ft. 5 in. high and 23 ft. in diameter. The
walls vary in thickness from 5 ft. to 2 ft. The tower, including the
base, contains about 2768 tons. The work was finished in three years,
1870-1873.
_Spectacle Reef Lighthouse, Lake Huron._--This is a structure similar
to that on Minot's ledge, standing on a limestone reef at the northern
end of the lake. The tower (fig. 16) was constructed with a view to
withstanding the effects of ice massing in solid fields thousands of
acres in extent and travelling at considerable velocity. The tower is
in shape the frustum of a cone, 32 ft. in diameter at the base and 93
ft. in height to the coping of the gallery. The focal plane is at a
level of 97 ft. above the base. The lower 34 ft. of the tower is
solid. The work was completed in 1874, having occupied four years. The
cost amounted to approximately £78,000.
_Chicken Rock Lighthouse._--The Chicken Rock lies 1 m. off the Calf of
Man. The curve of the tower, which is 123 ft. 4 in. high, is
hyperbolic, the diameter varying from 42 ft. to 16 ft. The tower is
submerged 5 ft. at high-water springs. The solid part is 32 ft. 6 in.
in height, weighing 2050 tons, the whole weight of the tower being
3557 tons. The walls decrease from 9 ft. 3 in. to 2 ft. 3 in. in
thickness. The work was begun in 1869 and completed in 1874.
_Ar'men Lighthouse._--The masonry tower, erected by the French
Lighthouse Service, on the Ar'men Rock off the western extremity of
the Île de Sein, Finistère, occupied fifteen years in construction
(1867-1881). The rock is of small area, barely uncovered at low water,
and it was therefore found impossible to construct a tower having a
base diameter greater than 24 ft. The focal plane of the light is 94
ft. above high water (fig. 17).
_St George's Reef Lighthouse, California._--This structure consists of
a square pyramidal stone tower rising from the easterly end of an oval
masonry pier, built on a rock to a height of 60 ft. above the water.
The focal plane is at an elevation of 146 ft. above high water. The
site is an exceedingly dangerous one, and the work, which was
completed in 1891, cost approximately £144,000.
_Rattray Head Lighthouse._--This lighthouse was constructed between
the years 1892 and 1895 by the Northern Lighthouse Commissioners upon
the Ron Rock, lying about one-fifth of a mile off Rattray Head,
Aberdeenshire. The focal plane is 91 ft. above high water, the
building being approximately 113 ft. in height. In the tower there is
a fog-horn worked by compressed air.
_Fastnet Lighthouse._--In the year 1895 it was reported to the Irish
Lights Commissioners that the then existing lighthouse on the Fastnet
Rock off the south-west coast of Ireland, which was completed in 1854
and consisted of a circular cast iron tower 86 ft. in height on the
summit of the rock, was considerably undermined. It was subsequently
determined to proceed with the erection of a granite structure of
increased height and founded upon a sound ledge of rock on one side of
the higher, but now considerably undermined. portion of the reef.
This lighthouse tower has its foundation laid near high-water level.
The focal plane is at a level of 158 ft. above high-water mark. The
cost of the structure, which was commenced in 1899 and completed in
1904, was £79,000.
[Illustration: FIG. 13.--Bishop Rock Lighthouse.]
_Beachy Head Lighthouse._--A lighthouse has been erected upon the
foreshore at the foot of Beachy Head, near Eastbourne, to replace the
old structure on the cliff having an elevation of 284 ft. above
high-water mark. Experience proved that the light of the latter was
frequently obscured by banks of mist or fog, while at the lower level
the transparency of the atmosphere was considerably less impaired. The
Trinity House therefore decided in the year 1899 to proceed with the
construction of a granite tower upon the foreshore at a distance of
some 570 ft. from the base of the cliff (fig. 18). The foreshore at
this point consists of chalk, and the selected site just bares at low
water ordinary spring tides. The foundation course was laid at a depth
of 10 ft. below the surface, the area being excavated within a
coffer-dam. The tower, which is 47 ft. in diameter at the base, has an
elevation to the focal plane above high water of 103 ft., or a total
height from foundation course to gallery coping of 123 ft. 6 in. The
lower or solid portion of the tower has its face stones constructed in
vertical offsets or steps in a similar manner to that adopted at the
Wolf Rock and elsewhere. The tower is constructed with a facing of
granite, all the stones being dovetailed in the usual manner. The
hearting of the base is largely composed of concrete. The work was
completed in 1902 and cost £56,000.
_Maplin Lighthouse._--The screw pile lighthouse erected on the Maplin
Sand in the estuary of the river Thames in 1838 is the earliest of its
kind and served as a model for numerous similar structures in various
parts of the world. The piles are nine in number, 5 in. diameter of
solid wrought iron with screws 4 ft. diameter (fig. 19).
_Fowey Rocks Lighthouse, Florida._--This iron structure, which was
begun in 1875 and completed in 1878, stands on the extreme northern
point of the Florida reefs. The height of the tower, which is founded
on wrought iron piles driven 10 ft. into the coral rock, is 110 ft.
from high water to focal plane. The iron openwork pyramidal structure
encloses a plated iron dwelling for the accommodation of the keepers.
The cost of construction amounted to £32,600.
_Alligator Reef Lighthouse, Florida._--This tower is one of the finest
iron sea-swept lighthouse structures in the world. It consists of a
pyramidal iron framework 135 ft. 6 in. in height, standing on the
Florida Reef in 5 ft. of water. The cost of the structure, which is
similar to the Fowey Rocks tower, was £37,000.
_American Shoal Lighthouse, Florida._--This tower (fig. 20) is typical
of the openwork pile structures on the Florida reefs, and was
completed in 1880. The focal plane of the light is at an elevation of
109 ft. above high water.
_Wolf Trap Lighthouse._--This building was erected during the years
1893 and 1894 on Wolf Trap Spit in Chesapeake Bay, near the site of
the old openwork structure which was swept away by ice early in 1893.
The new tower is formed upon a cast iron caisson 30 ft. in diameter
sunk 18 ft. into the sandy bottom. The depth of water on the shoal is
16 ft. at low water. The caisson was filled with concrete, and is
surmounted by a brick superstructure 52 ft. in height from low water
to the focal plane of the light. A somewhat similar structure was
erected in 1885-1887 on the Fourteen Foot Bank in Delaware Bay, at a
cost of £24,700. The foundation in this case was, however, shifting
sand, and the caisson was carried to a greater depth.
_Rothersand Lighthouse._--This lighthouse, off the entrance to the
river Weser (Germany), is a structure of great interest on account of
the difficulties met with in its construction. The tower had to be
founded on a bottom of shifting sand 20 ft. below low water and in a
very exposed situation. Work was begun in May 1881, when attempts were
made to sink an iron caisson under pneumatic pressure. Owing to the
enormous scour removing the sand from one side of the caisson it
tilted to an alarming angle, but eventually it was sunk to a level of
70 ft. below low-water mark. In October of the same year the whole
structure collapsed. Another attempt, made in May 1883, to sink a
caisson of bi-convex shape in plan 47 ft. long, 37 ft. wide and 62 ft.
in height, met with success, and after many difficulties the structure
was sunk to a depth of 73 ft. below low water, the sides being raised
by the addition of iron plating as the caisson sank. The sand was
removed from the interior by suction. Around the caisson foundation
were placed 74,000 cub. yds. of mattress work and stones, the interior
being filled with concrete. Towards the end of 1885 the lighthouse was
completed, at a total cost, including the first attempt, of over
£65,000. The tower is an iron structure in the shape of a concave
elliptic frustum, its base being founded upon the caisson foundation
at about half-tide level (fig. 21). The light is electric, the current
being supplied by cable from the shore. The focal plane is 78 ft.
above high water or 109 ft. from the sand level. The total height from
the foundation of the caisson to the top of the vane is 185 ft.
Other famous wave-swept towers are those at Haulbowline Rock
(Carlingford Lough, Ireland, 1823); Horsburgh (Singapore, 1851); Bayes
d'Olonne (Bay of Biscay, 1861); Hanois (Alderney, 1862); Daedalus
Reef, iron tower (Red Sea, 1863); Alguada Reef (Bay of Bengal, 1865);
Longships (Land's End, 1872); the Prongs (Bombay, 1874); Little Basses
(Ceylon, 1878); the Graves (Boston, U.S.A., 1905); Jument d'Ouessant
(France, 1907); and Roche Bonne (France, building 1910).
[Illustration: FIG. 14.--Wolf Rock.
FIG. 15.--Dhu Heartach.
FIG. 16.--Spectacle Reef.
FIG. 17.--Ar'men.
FIG. 18.--Beachy Head.]
_Jointing of Stones in Rock Towers._--Various methods of jointing the
stones in rock towers are shown in figs. 6 and 22. The great distinction
between the towers built by successive engineers to the Trinity 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 metal or wooden pins and wedges and dowled as in most other
cases. This dovetail method was first adopted at the Hanois Rock at the
suggestion of Nicholas Douglass. On the upper face, one side and at one
end of each block is a dovetailed projection. On the under face and the
other side and end, corresponding dovetailed recesses are formed with
just sufficient clearance for the raised bands to enter in setting (fig.
23). The cement mortar in the joint formed between the faces so locks
the dovetails that the stones cannot be separated without breaking (fig.
24).
TABLE I.--_Comparative Cost of Exposed Rock Towers_.
+----------------------------------------------------------+--------------+--------+-----------+
| | | | Cost per |
| Name of Structure. | Total Cost. |Cub. ft.|cub. ft. of|
| | | | Masonry. |
+----------------------------------------------------------+--------------+--------+-----------+
| Eddystone, Smeaton (1759) |£40,000 0 0 | 13,343 | £2 9 11½ |
| Bell Rock, Firth of Forth (1811) | 55,619 12 1 | 28,530 | 1 19 0 |
| Skerryvore, west coast of Scotland (1844) | 72,200 11 6 | 58,580 | 1 4 7¾ |
| Bishop Rock, first granite tower (1858) | 34,559 18 9 | 35,209 | 0 19 7½ |
| Smalls, Bristol Channel (1861) | 50,124 11 8 | 46,386 | 1 1 7¼ |
| Hanois, Alderney (1862) | 25,296 0 0 | 24,542 | 1 0 7¼ |
| Wolf Rock, Land's End (1869) | 62,726 0 0 | 59,070 | 1 1 3 |
| Dhu Heartach, west coast of Scotland (1872) | 72,584 9 7 | 42,050 | 1 14 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 part reconstruction (1887)| 64,889 0 0 | 45,080 | 1 8 9 |
| Great Basses, Ceylon (1873) | 63,560 0 0 | 47,819 | 1 6 7 |
| Minot's Ledge, Boston, Mass. (1860) | 62,500 0 0 | 36,322 | 1 17 2 |
| Spectacle Reef, Lake Huron (1874) | 78,125 0 0 | 42,742 | 1 16 2 |
| Ar'men, France (1881) | 37,692 0 0 | 32,400 | 1 3 3 |
| Fastnet, Ireland (1904) | 79,000 0 0 | 62,600 | 1 5 5½ |
+----------------------------------------------------------+--------------+--------+-----------+
_Effect of Waves._--The 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 weight, were washed away
after having been set in cement at a height of 37 ft. above high water,
and similar damage was done during the construction of the Bell Rock
tower. The effect of waves on the Bishop Rock and Eddystone towers has
been noted above.
_Land Structures for Lighthouses._--The erection of lighthouse towers
and other buildings on land presents no difficulties of construction,
and such buildings are of ordinary architectural character. It will
therefore be unnecessary to refer to them in detail. Attention is
directed to the Phare d'Eckmühl at Penmarc'h (Finistère), completed in
1897. The cost of this magnificent structure, 207 ft. in height from the
ground, was largely defrayed by a bequest of £12,000 left by the marquis
de Blocqueville. It is constructed entirely of granite, and is octagonal
in plan. The total cost of the tower and other lighthouse buildings
amounted to £16,000.
[Illustration: FIG. 19.--Maplin Pile Lighthouse.]
The tower at Île Vierge (Finistère), completed in 1902, has an elevation
of 247 ft. from the ground level to the focal plane, and is probably the
highest structure of its kind in the world.
The brick tower, constructed at Spurn Point, at the entrance to the
Humber and completed in 1895, replaced an earlier structure erected by
Smeaton at the end of the 18th century. The existing tower is
constructed on a foundation consisting of concrete cylinders sunk in the
shingle beach. The focal plane of the light is elevated 120 ft. above
high water.
Besides being built of stone or brick, land towers are frequently
constructed of cast iron plates or open steel-work with a view to
economy. Fine examples of the former are to be found in many British
colonies and elsewhere, that on Dassen Island (Cape of Good 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. Recent examples are
the towers erected at Cape San Thomé (Brazil) in 1882, 148 ft. in height
(fig. 26), Mocha (Red Sea) in 1903, 180 ft. and Sanganeb Reef (Red Sea)
1906, 165 ft. in height to the focal plane.
[Illustration: FIG. 20.--American Shoal Lighthouse, Florida.]
3. 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 belt of light distributed
evenly around the horizon, condensation in the vertical plane only being
employed; (2) the concentration of the rays both vertically and
horizontally into a pencil or cone of small 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 horizontal plane in such a manner as to
concentrate the rays over a limited azimuth only.
Apparatus falling under the first category produce a fixed light, and
further distinction can be provided in this class by mechanical means of
occultation, resulting in the production of an occulting or intermittent
light. Apparatus included in the second class are usually employed to
produce flashing lights, but sometimes the dual condensation is taken
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 French 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 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 classification of apparatus depends on the resultant effect of
the optical elements. Another classification divides the 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 profile. _Dioptric_ elements are those in
which the light rays pass through the optical glass, suffering
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
internal reflexion at a second face and again refraction on emergence at
the third face (fig. 28).
The object of these several forms of optical apparatus is not only 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 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.
[Illustration: FIG. 21.--Rothersand Lighthouse.]
_Catoptric System._--Parabolic reflectors, consisting of small facets
of silvered glass set in plaster of Paris, were first used about the
year 1763 in some of the Mersey lights by Mr Hutchinson, then dock
master at Liverpool (fig. 29). Spherical metallic reflectors were
introduced in France in 1781, followed by parabolic reflectors on
silvered copper in 1790 in England and France, and in Scotland in
1803. The earlier lights were of fixed type, a number of reflectors
being arranged on a 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 in Sweden. Similar apparatus were installed at Cordouan
(1790), Flamborough Head (1806) and at the Bell Rock (1811). To
produce a revolving or flashing light the reflectors were fixed on a
revolving 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 general use vary from 21 in. to 24 in. diameter. These
instruments are still largely used for light-vessel illumination, and
a few important land lights are at the present time of catoptric type,
including those at St Agnes (Scilly Islands), Cromer and St Anthony
(Falmouth).
_Dioptric System._--The first adaptation of dioptric lenses to
lighthouses is probably due to T. Rogers, who used lenses at one of
the Portland lighthouses between 1786 and 1790. Subsequently lenses by
the same maker were used at Howth, Waterford and the North Foreland.
Count Buffon had in 1748 proposed to grind out of a solid piece of
glass a lens in steps or concentric zones in order to reduce the
thickness to a minimum (fig. 31). Condorcet in 1773 and Sir D.
Brewster in 1811 designed built-up lenses consisting of stepped
annular rings. Neither of these proposals, however, was intended to
apply to lighthouse purposes. In 1822 Augustin Fresnel constructed a
built-up annular lens in which the centres of curvature of the
different rings receded from the axis according to their distances
from the centre, so as practically to eliminate spherical aberration;
the only spherical surface being the small central part or "bull's
eye" (fig. 32). These lenses were intended for revolving lights only.
Fresnel next produced his cylindric refractor or lens belt, consisting
of a zone of glass generated by the revolution round a vertical axis
of a medial 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 lamp at a focal distance of 920 mm. To utilize the light,
which would otherwise escape above the lenses, Fresnel introduced a
series of 8 plain silvered mirrors, on which the light was thrown by a
system of lenses. At a subsequent period mirrors were also placed in
the lower part of the optic. The apparatus was revolved by clockwork.
This optic embodied the first combination of dioptric and catoptric
elements in one 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 account of the great
loss of light entailed by metallic reflection which is at least 25%
greater than the system described under. Before his death in 1827
Fresnel devised his totally reflecting or catadioptric prisms to take
the place of the silvered reflectors previously used above and below
the lens elements (fig. 28). The ray Fi falling on the prismoidal ring
ABC is refracted in the direction i r and meeting the face AB at an
angle of incidence greater than the 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 date, also applied to
flashing lights, in the first instance by T. Stevenson. Both the
dioptric lens and catadioptric 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.
[Illustration: FIG. 22.--Courses of various Lighthouse Towers.]
[Illustration: FIG. 23.--Perspective drawing of Dovetailed Stone (Wolf
Rock).]
[Illustration: FIG. 24.--Section of Dovetail.]
[Illustration: FIG. 25.--Dassen Island Lighthouse (cast iron).]
[Illustration: FIG. 26.--Cape San Thomé Lighthouse.]
[Illustration: FIG. 27.--Dioptric Prism.]
Fresnel also designed a 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 revolution
of the upright prisms periodically increased the power of the beam, by
condensation of the rays emergent from the fixed apparatus, in the
horizontal plane.
The lens segments in Fresnel's early apparatus were of polygonal form
instead of cylindrical, but subsequently manufacturers succeeded in
grinding glass in cylindrical rings of the form now used. The first
apparatus of this description was made by Messrs Cookson of Newcastle
in 1836 at the suggestion of Alan Stevenson and erected at Inchkeith.
[Illustration: FIG. 28.--Catadioptric or Reflecting Prism.]
In 1825 the French Commission des Phares decided upon the exclusive
use of lenticular apparatus in its service. The Scottish Lighthouse
Board followed with the Inchkeith revolving apparatus in 1835 and the
Isle of May fixed optic in 1836. In the latter instrument Alan
Stevenson introduced helical frames for holding the glass prisms in
place, thus avoiding 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 Devonshire, constructed in 1836.
Catadioptric or reflecting prisms for revolving lights were not used
until 1850, when Alan Stevenson designed them for the North Ronaldshay
lighthouse.
_Dioptric Mirror._--The next important improvement in lighthouse
optical work was the invention of the dioptric spherical mirror by Mr
(afterwards Sir) J. T. 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).
[Illustration: FIG. 29.--Early Reflector and Lamp (1763).]
_Azimuthal Condensing Prisms._--Previous to 1850 all apparatus were
designed to emit light of equal power in every azimuth either
constantly or periodically. The only exception was where a light was
situated on a stretch of coast where a mirror could be placed behind
the flame to utilize the rays, which would otherwise pass landward,
and reflect them back, passing through the flame and lens 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.
[Illustration: FIG. 30.--Modern Parabolic Reflector.]
_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
Premontré works, which have long been celebrated for the high quality
of optical glass produced. The early dioptric lights erected in the
United Kingdom, some 13 in all, were made by Messrs Cookson of South
Shields, who were instructed by Léonor Fresnel, the brother of
Augustin. At first they tried to mould the lens and then to grind it
out of one thick sheet of glass. The successors of the Cookson firm
abandoned the manufacture of lenses in 1845, and the firm of
Letourneau & Lepaute of Paris again became the monopolists. In 1850
Messrs Chance Bros. & Co. of Birmingham began the manufacture of
optical glass, assisted by M. Tabouret, a French expert who had been a
colleague of Augustin Fresnel himself. The first light made by the
firm was shown at the Great 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 German
constructors is made at Rathenow in Prussia and Goslar in the Harz.
The glass generally employed for lighthouse optics has for its
refractive index a mean value of µ = 1.51, the corresponding critical
angle being 41° 30'. Messrs Chance have used dense 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 = l.62 with
critical angle 38° 5'.
[Illustration: FIG. 31. Buffon's Lens.]
[Illustration: FIG. 32. Fresnel's Annular Lens.]
[Illustration: FIG. 33. Fresnel's Lens Belt.]
[Illustration: FIG. 34.--Fresnel's Revolving Apparatus at Cordouan
Lighthouse.]
_Occulting Lights._--During the last 25 years of the 19th century the
disadvantages of fixed lights became more and more apparent. At the
present day the practice of installing such, except occasionally in
the case of the smaller and less important of harbour or river lights,
has practically ceased. The necessity for providing a distinctive
characteristic for every light when possible has led to the conversion
of many of the fixed-light apparatus of earlier years into occulting
lights, and often to their supersession by more modern and powerful
flashing apparatus. An occulting apparatus in general use consists of
a cylindrical screen, fitting over the burner, rapidly lowered and
raised by means of a cam-wheel at stated intervals. The cam-wheel is
actuated by means of a weight or spring clock. Varying characteristics
may be procured by means of such a contrivance--single, double, triple
or other systems of occultation. The eclipses or periods of darkness
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 £300. With apparatus
illuminated by 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 ball bearings or carried upon a small mercury
float. The usual driving mechanism employed is a spring clock. "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 blind, and operated by mechanical means.
_Leading Lights._--In the case of lights designed to act as a 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 Gage Roads,
Fremantle, West Australia (fig. 38). The occulting bright light covers
the fairway, and is flanked by sectors of occulting red and green
light marking dangers and intensified by vertical condensing prisms. A
good example of a holophotal 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 180°
horizontal angle and 157° vertical, with a mirror of 180° at the back.
The lens throws a red beam of about 4½° amplitude in azimuth, and
50,000 candle-power over a narrow channel. The illuminant is an
incandescent 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 separate towers for leading
lights unnecessary.
If two distinct lights are employed to indicate the line of 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 rear or landward one.
_Coloured Lights._--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 and for harbour lighting
purposes. The use of coloured lights as alternating flashes for
lighthouse lights is not to be commended, on account of the unequal
absorption of the coloured and bright rays by the atmosphere. When
such distinction has been employed, as in the Wolf Rock apparatus, the
red and 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 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.
[Illustration: FIG. 35.--Fixed Apparatus at Chassiron Lighthouse
(1827).]
[Illustration: FIG. 36.--Vertical Section. Prism of Dioptric Spherical
Mirror.]
_High-Angle Vertical Lenses._--Messrs Chance of Birmingham have
manufactured lenses having 97° of vertical amplitude, but this result
was only attained by using dense flint glass of high refractive index
for the upper and lower elements. It is doubtful, however, whether the
use of refracting elements for a greater angle than 80° vertically is
attended by any material corresponding advantage.
[Illustration: FIG. 37.--Chance's Dioptric Spherical Mirror.]
_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 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, 10 seconds, the sequence being completed in a period
of, say, 15 seconds. In 1874 Dr John Hopkinson introduced the very
valuable improvement of dividing the lenses of a dioptric 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
Tampico, Mexico and the Little Basses lighthouse, Ceylon (double
flashing). The Casquets apparatus (triple flashing) was installed in
1877. A group-flashing catoptric light had, however, been exhibited
from the "Royal Sovereign" light-vessel in 1875. A sectional plan of
the quadruple-flashing first order apparatus at Pendeen in Cornwall
is shown in fig. 39; and fig. 55 (Plate 1.) illustrates a double
flashing first order light at Pachena Point in British Columbia.
Hopkinson's system has been very extensively used, most of the
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 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 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
Galley Head, Co. 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 focus of each tier of lenses he produced the
group-flashing distinction. The light showed, instead of one prolonged
flash at intervals of one minute, as would be produced by the
apparatus in the absence of a gas occulter, a group of 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 device was adopted at other
gas-illuminated stations in Ireland at subsequent dates. The
quadriform apparatus and gas installation at Galley Head were
superseded in 1907 by a first order bi-form apparatus with
incandescent oil vapour burner showing five flashes every 20 seconds.
[Illustration: FIG. 38.--Gage Roads Direction Light.]
[Illustration: FIG. 39.--Pendeen Apparatus. Plan at Focal Plane.]
_Flashing Lights indicating Numbers._--Captain F. A. Mahan, late
engineer secretary to the United States Lighthouse Board, devised for
that service a system of flashing lights to indicate certain numbers.
The apparatus installed at Minot's Ledge lighthouse near Boston
Harbour, 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 successive members of
a group. The flashes in a group indicating a figure are about 1½
seconds apart, the groups being 3 seconds apart, an interval of 16
seconds' darkness occurring between each repetition. Thus the number
is repeated every half minute. Two examples of this system were
exhibited by the United States Lighthouse Board at the Chicago
Exhibition in 1893, viz. the second-order apparatus just mentioned and
a similar light of the first order for Cape Charles on the Virginian
coast. The lenses are arranged in a somewhat similar manner to an
ordinary group-flashing light, the groups of lenses being placed on
one side of the optic, while the other is provided with a catadioptric
mirror. This system of numerical flashing for lighthouses has been
frequently proposed in various forms, notably by Lord Kelvin. The
installation of the lights described is, however, the first practical
application of the system to large and important coast lights. The
great cost involved in the alteration of the lights of any country to
comply with the requirements of a numerical system is one of the
objections to its general adoption.
[Illustration: PLATE I.
FIG. 54.--FASTNET LIGHTHOUSE--FIRST ORDER SINGLE-FLASHING BIFORM
APPARATUS.
FIG. 55.--PACHENA POINT LIGHTHOUSE, B.C.--FIRST ORDER DOUBLE-FLASHING
APPARATUS.]
[Illustration: PLATE II.
FIG. 56.--OLD EDDYSTONE LIGHTHOUSE.
FIG. 57.--EDDYSTONE LIGHTHOUSE.
FIG. 58.--ILE VIERGE LIGHTHOUSE.
FIG. 59.--MINOT'S LEDGE LIGHTHOUSE.]
[Illustration: FIG. 40.--Sule Skerry Apparatus.]
_Hyper-radial Apparatus._--In 1885 Messrs Barbier of Paris constructed
the first hyper-radial apparatus (1330 mm. focal distance) to the
design of Messrs D. and C. Stevenson. This had a height of 1812 mm. It
was tested during the South Foreland experiments in comparison with
other lenses, and found to give excellent results with burners of
large focal diameter. Apparatus of similar focal distance (1330 mm.)
were subsequently established at Round Island, Bishop Rock, and Spurn
Point in England, Fair Isle and Sule Skerry (fig. 40) in Scotland,
Bull Rock and Tory Island in Ireland, Cape d'Antifer in France, Pei
Yu-shan in China and a lighthouse in Brazil.
The light erected in 1907 at Cape Race, Newfoundland, is a fine
example of a four-sided hyper-radial apparatus mounted on a mercury
float. The total weight of the revolving part of the light amounts to
7 tons, while the motive clock weight required to rotate this large
mass at a speed of two complete revolutions a minute is only 8 cwt.
and the weight of mercury required for flotation 950 lb. A similar
apparatus was placed at Manora Point, Karachi, India, in 1908 (fig.
41).
The introduction of incandescent and other burners of focal
compactness and high intensity has rendered the use of optics of such
large dimensions as the above, intended for burners of great focal
diameter, unnecessary. It is now possible to obtain with a
second-order optic (or one of 700 mm. focal distance), having a
powerful incandescent petroleum burner in focus, a beam of equal
intensity to that which would be obtained from the apparatus having a
10-wick oil burner or 108-jet gas burner at its focus.
_Stephenson's Spherical Lenses and Equiangular Prisms._--Mr C. A.
Stephenson in 1888 designed a form of lens spherical in the horizontal
and vertical sections. This admitted of the construction of lenses of
long focal distance without the otherwise corresponding necessity of
increased diameter of lantern. A lens of this type and of 1330 mm.
focal distance was constructed in 1890 for Fair Isle lighthouse. The
spherical form loses in efficiency if carried beyond an angle
subtending 20° at the focus, and to obviate this loss Mr Stephenson
designed his equiangular prisms, which have an inclination outwards.
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 be
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
revolving lens panels in the middle portion of the optic to produce
the flashing light, the upper and lower sections of the apparatus
being fixed zones of catadioptric or reflecting elements emitting a
fixed belt of light, and (c) by interposing panels of fixed light
section between the flashing light panels of a revolving apparatus. In
certain conditions of the atmosphere it is possible for the fixed
light of low power to be entirely obscured while the flashes are
visible, thus vitiating the true characteristic of the light. Cases
have frequently occurred of such lights being mistaken for, and even
described in lists of light as, revolving or flashing lights.
_"Cute" and Screens._--Screens of coloured glass, intended to
distinguish the light in particular azimuths, and of sheet iron, when
it is desired to "cut off" the light sharply on any angle, should be
fixed as far from the centre of the light as possible in order to
reduce the escape of light rays due to divergence. These screens are
usually attached to the lantern framing.
_Divergence._--A dioptric apparatus designed to bend all incident rays
of light from the light source in a horizontal direction would, if the
flame could be a point, have the effect of projecting a horizontal
band or zone of light, in the case of a fixed apparatus, and a
cylinder of light rays, in the case of a flashing light, towards the
horizon. Thus the mariner in the near distance would receive no light,
the rays, visible only at or near the horizon, passing above the level
of his eye. In practice this does not occur, sufficient natural
divergence being produced ordinarily owing to the magnitude of the
flame. 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 matter of
considerable importance, determining as it does the duration or length
of time the flash is visible to the mariner.
_Feux-Éclairs or Quick Flashing Lights._--One of the most important
developments in the character of lighthouse illuminating apparatus
that has occurred in recent years has been in the direction of
reducing the length of flash. The initiative in this matter was taken
by the French lighthouse authorities, and in France alone forty lights
of this type were established between 1892 and 1901. The use of short
flash lights rapidly spread to other parts of the world. In England
the lighthouse at Pendeen (1900) exhibits a quadruple flash every 15
seconds, the flashes being about ¼ second duration (fig. 39), while
the bivalve apparatus erected on Lundy Island (1897) shows 2 flashes
of 1/3 second duration in quick succession every 20 seconds. Since
1900 many quick flashing lights have been erected on the coasts of the
United Kingdom and in other countries. The early _feux-éclairs_,
designed by the French engineers and others, had usually a flash of
(1/10)th to (1/3)rd of a second duration. As a result of experiments
carried out in France in 1903-1904, 3/10 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, 2½ 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 _feu-éclair_
type of apparatus enables a far higher intensity of flash to be
obtained than was previously possible without any corresponding
increase in the luminous power of the burner or other source of light.
This result depends entirely upon the greater ratio of condensation of
light employed, panels of greater angular breadth than was customary
in the older forms of apparatus being used with a higher rotatory
velocity. It has been urged that short flashes are insufficient for
taking bearings, but the utility of a light in this respect does not
seem to depend so much upon the actual length of the flash as upon its
frequent recurrence at short intervals. At the Paris Exhibition of
1900 was exhibited a fifth-order flashing light giving short flashes
at 1 second intervals; this represents the extreme to which the
movement towards the reduction of the period of flashing lights has
yet been carried.
_Mercury Floats._--It has naturally been found impracticable to
revolve the optical apparatus of a light with its mountings, sometimes
weighing over 7 tons, at the high rate of speed required for
_feux-éclairs_ by means of the old system of roller carriages, though
for some small quick-revolving lights ball bearings have been
successfully adopted. It has therefore become almost the universal
practice to carry the rotating portions of the apparatus upon a
mercury float. This beautiful application of mercury rotation was the
invention of Bourdelles, and is now utilized not only for the
high-speed apparatus, but also generally for the few examples of the
older type still being constructed. The arrangement consists of an
annular cast iron bath or trough of such dimensions that a similar but
slightly smaller annular float immersed in the bath and surrounded by
mercury displaces a volume of the liquid metal whose weight is equal
to that of the apparatus supported. Thus a comparatively insignificant
quantity of mercury, say 2 cwt., serves to ensure the flotation of a
mass of over 3 tons. Certain differences exist between the type of
float usually constructed in France and those generally designed by
English engineers. In all cases provision is made for lowering the
mercury bath or raising the float and apparatus for examination.
Examples of mercury floats are shown in figs. 41, 42, 43 and Plate I.,
figs. 54 and 55.
[Illustration: FIG. 41.--Manora Point Apparatus and Lantern.]
_Multiform Apparatus._--In order to double the power to be obtained
from a single apparatus at stations where lights of exceptionally high
intensity are desired, the expedient of placing one complete lens
apparatus above another has sometimes been adopted, as at the Bishop
Rock (fig. 13), and at the Fastnet lighthouse in Ireland (Plate I.,
fig. 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 multiform system involves the
use of lanterns of increased 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 Île Vierge apparatus.
Several such lights have been installed by the French Lighthouse
Service.
_Port Lights._--Small self-contained lanterns and lights are in common
use for marking the entrances to harbours and in other similar
positions where neither high power nor long range is requisite. Many
such lights are unattended in the sense that they do not require the
attention of a keeper for days and even weeks together. These are
described in more detail in section 6 of this article. A typical port
light consists of a copper or brass lantern containing a lens of the
fourth order (250 mm. focal distance) or smaller, and a single wick or
2-wick Argand capillary burner. Duplex burners are also used. The
apparatus may exhibit a fixed light or, more usually, an occulting
characteristic is produced by the revolution of screens actuated by
spring clockwork around the burner. The lantern may be placed at the
top of a column, or suspended from the head of a mast. Coal gas and
electricity are also used as illuminants for port lights when local
supplies are available. The optical apparatus used in connexion with
electric light is described below.
_"Orders" of Apparatus._--Augustin Fresnel divided the dioptric
lenses, designed by him, into "orders" or sizes depending on their
local distance. This division is still used, although two additional
"orders," known as "small third order" and "hyper-radial" respectively
are in ordinary use. The following table gives the principal
dimensions of the several sizes in use:--
TABLE II.
+-------------+---------+-------------------------------------+
| | | Vertical Angles of Optics. |
| | | (Ordinary Dimensions.) |
| | Focal +-------------+-----------------------+
| Order. |Distance,| | Holophotal Optics. |
| | mm. | Dioptric +-------+-------+-------+
| | | Belt only. | Lower | Lens. | Upper |
| | | |Prisms.| |Prisms.|
+-------------+---------+-------------+-------+-------+-------+
| Hyper-Radial| 1330 | 80° | 21° | 57° | 48° |
| 1st order | 920 |92°, 80°, 58°| 21° | 57° | 48° |
| 2nd " | 700 | 80° | 21° | 57° | 48° |
| 3rd " | 500 | 80° | 21° | 57° | 48° |
| Small 3rd | | | | | |
| order | 375 | 80° | 21° | 57° | 48° |
| 4th order | 250 | 80° | 21° | 57° | 48° |
| 5th " | 187.5 | 80° | 21° | 57° | 48° |
| 6th " | 150 | 80° | 21° | 57° | 48° |
+-------------+---------+-------------+-------+-------+-------+
Lenses of small focal distance are also made for buoy and beacon
lights.
[Illustration: FIG. 42.--Cape Naturaliste Apparatus.]
[Illustration: FIG. 43.--Île Vierge Apparatus.]
_Light Intensities._--The powers of lighthouse lights in the British
Empire are expressed in terms of standard candles or in "lighthouse
units" (one lighthouse unit = 1000 standard candles). In France the
unit is the "Carcel" = .952 standard candle. The powers of burners and
optical apparatus, then in use in the United Kingdom, were carefully
determined by actual photometric measurement in 1892 by a committee
consisting of the engineers of the three general lighthouse boards,
and the values so obtained are used as the basis for calculating the
intensities of all British lights. It was found that the intensities
determined by photometric measurement were considerably less than the
values given by the theoretical calculations formerly employed. A
deduction of 20% was made from the mean experimental results obtained
to compensate for loss by absorption in the lantern glass, variations
in effects obtained by different men in working the burners and in the
illuminating quality of oils, &c. 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 panel. The loss
of light by absorption in passing through the glass and by refraction
varies from 10% to 15%. For apparatus containing catadioptric elements
a larger deduction must be made.
The intensity of the flash emitted from a dioptric apparatus, showing
a white light, may be found approximately by the empirical formula I =
PCVH/vh, where I = intensity of resultant beam, P = service intensity
of flame, V = vertical angle of optic, v = angle of mean vertical
divergence, H = horizontal angle of panel, h = angle of mean
horizontal divergence, and C = constant varying between .9 and .75
according to the description of apparatus. The factor H/h must be
eliminated in the case of fixed lights. Deduction must also be made in
the case of coloured lights. It should, however, be pointed out that
photometric measurements alone can be relied upon to give accurate
values for lighthouse intensities. The values obtained by the use of
Allard's formulae, which were largely used before the necessity for
actual photometric measurements came to be appreciated, are
considerably in excess of the true intensities.
[Illustration: FIG. 43A.--Île Vierge Apparatus and Lantern. Plan at
focal plane.]
_Optical Calculations._--The mathematical theory of optical apparatus
for lighthouses and formulae for the calculations of profiles will be
found in the works of the Stevensons, Chance, Allard, Reynaud, Ribière
and others. Particulars of typical lighthouse apparatus will be found
in tables VI. and VII.
4. ILLUMINANTS.--The earliest form of illuminant used for lighthouses
was a fire of coal or wood set in a brazier or grate erected on top of
the lighthouse tower. Until the end of the 18th and even into the 19th
century this primitive illuminant continued to be almost the only one in
use. The coal fire at the Isle of May light continued until 1810 and
that at St Bees lighthouse in Cumberland till 1823. Fires are stated to
have been used on the two towers of Nidingen, in the Kattegat, until
1846. Smeaton was the first to use any form of illuminant other than
coal fires; he placed within the lantern of his Eddystone lighthouse a
chandelier holding 24 tallow candles each of which weighed 2/5 of a
lb. and emitted a light of 2.8 candle power. The aggregate illuminating
power was 67.2 candles and the consumption at the rate of 3.4 lb. per
hour.
_Oil._--Oil lamps with flat wicks were used in the Liverpool
lighthouses as early as 1763. Argand, between 1780 and 1783, perfected
his cylindrical wick lamp which provides a central current of air
through the burner, thus allowing the more perfect combustion of the
gas issuing from the wick. The contraction in the diameter of the
glass chimney used with wick lamps is due to Lange, and the principle
of the multiple wick burner was devised by Count Rumford. Fresnel
produced burners having two, three and four concentric wicks. Sperm
oil, costing 5s. to 8s. per gallon, was used in English lighthouses
until 1846, but about that year colza oil was employed generally at a
cost of 2s. 9d. per gallon. Olive oil, lard oil and coconut oil have
also been used for lighthouse purposes in various parts of the world.
_Mineral Oil Burners._--The introduction of mineral oil, costing a
mere fraction of the expensive animal and vegetable oils,
revolutionized the illumination of lighthouses. It was not until 1868
that a burner was devised which successfully consumed hydrocarbon
oils. This was a multiple wick burner invented by Captain Doty. The
invention was quickly taken advantage of by lighthouse authorities,
and the "Doty" burner, and other patterns involving the same
principle, remained practically the only oil burners in lighthouse use
until the last few years of the 19th century.
The lamps used for supplying oil to the burner are of two general
types, viz. those in which the oil is maintained under pressure by
mechanical action and constant level lamps. In the case of single
wick, and some 2-wick burners, oil is supplied to the burner by the
capillary action of the wick alone.
The mineral oils ordinarily in use are petroleum, which for lighthouse
purposes should have a specific gravity of from .820 to .830 at 60° F.
and flashing point of not less than 230° F. (Abel close test), and
Scottish shale oil or paraffin with a specific gravity of about .810
at 60° F. and flash point of 140° to 165° F. Both these varieties may
be obtained in England at a cost of about 6½d. per gallon in bulk.
_Coal Gas_ had been introduced in 1837 at the inner pier light of
Troon (Ayrshire) and in 1847 it was in use at the Heugh lighthouse
(West Hartlepool). In 1878 cannel coal gas was adopted for the Galley
Head lighthouse, with 108-jet Wigham 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 5(5/8) 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 lighthouse 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 mantle
placed at the disposal of the lighthouse authorities the means of
producing a light of high intensity combined with great focal
compactness. For lighthouse purposes other gaseous illuminants than
coal gas are as a rule more convenient and economical, and give better
results with incandescent mantles. Mantles have, however, been used
with ordinary coal gas in many instances where a local supply is
available.
[Illustration: FIG. 44.--"Chance" Incandescent Oil Burner, with 85 mm.
diameter mantle.]
_Incandescent Mineral Oil Burners._--Incandescent lighting with
high-flash mineral oil was first introduced by the French Lighthouse
Service in 1898 at L'Île Penfret lighthouse. The burners employed are
all made on the same principle, but differ slightly in details
according to the type of lighting apparatus for which they are
intended. The principle consists in injecting the liquid petroleum in
the form of spray mixed with air into a vaporizer heated by the mantle
flame or by a subsidiary heating burner. A small reservoir of
compressed air is used--charged by means of a hand pump--for providing
the necessary pressure for injection. On first ignition the vaporizer
is heated by a spirit flame to the required temperature. A reservoir
air pressure of 125 lb. per sq. in. is employed, a reducing valve
supplying air to the oil at from 60 to 65 lb. per sq. in. Small
reservoirs containing liquefied carbon dioxide have also been employed
for supplying the requisite pressure to the oil vessel.
The candle-power of apparatus in which ordinary multiple wick burners
were formerly employed is increased by over 300% by the substitution
of suitable incandescent oil burners. In 1902 incandescent oil burners
were adopted by the general lighthouse authorities in the United
Kingdom. The burners used in the Trinity House Service and some of
those made in France have the vaporizers placed over the flame. In
other forms, of which the "Chance" burner (fig. 44) is a type, the
vaporization is effected by means of a subsidiary burner placed under
the main flame.
Particulars of the sizes of burner in ordinary use are given in the
following table.
+--------------------+------------------+-------------------+
| Diameter of Mantle.|Service Intensity.|Consumption of oil.|
| | | Pints per hour. |
+--------------------+------------------+-------------------+
| 35 mm. | 600 candles. | .50 |
| 55 mm. | 1200 " | 1.00 |
| 85 mm. | 2150 " | 2.25 |
|Triple mantle 50 mm.| 3300 " | 3.00 |
+--------------------+------------------+-------------------+
The intrinsic brightness of incandescent burners generally may be
taken as being equivalent to from 30 candles to 40 candles per sq. cm.
of the vertical section of the incandescent mantle.
In the case of wick burners, the intrinsic brightness varies,
according to the number of wicks and the type of burner from about 3.5
candles to about 12 candles per sq. cm., the value being at its
maximum with the larger type of burner. 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 argument applies to the case of multiple ring and
multiple jet gas burners which, notwithstanding their large total
intensity, have comparatively small intrinsic brightness. The economy
of the new system is instanced by the case of the Eddystone bi-form
apparatus, which with the concentric 6-wick burner consuming 2500
gals. of oil per annum, gave a total intensity of 79,250 candles.
Under the new régime the intensity is 292,000 candles, the oil
consumption being practically halved.
_Incandescent Oil Gas Burners._--It has been mentioned that
incandescence with low-pressure coal gas produces flames of
comparatively small intrinsic brightness. Coal gas cannot be
compressed beyond a small extent without considerable injurious
condensation and other accompanying evils. Recourse has therefore been
had to compressed oil gas, which is capable of undergoing compression
to 10 or 12 atmospheres with little detriment, and can conveniently be
stored in portable reservoirs. The burner employed resembles the
ordinary Bunsen burner with incandescent mantle, and the rate of
consumption of gas is 27.5 cub. in. per hour per candle. A reducing
valve is used for supplying the gas to the burner at constant
pressure. The burners can be left unattended for considerable periods.
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 costs about £800. The
annual expenditure for gas lighting in France does not exceed £72 per
light where works are installed, or £32 where gas is supplied from
elsewhere. In the case of petroleum vapour lighting the annual cost of
oil amounts to about £26 per station.
_Acetylene._--The high illuminating power and intrinsic brightness of
the flame of acetylene makes it a very suitable illuminant for
lighthouses and beacons, providing certain difficulties attending its
use can be overcome. At Grangemouth an unattended 21-day beacon has
been illuminated by an acetylene flame for some years with
considerable success, and a beacon light designed to run unattended
for six months was established on Bedout Island in Western Australia
in 1910. Acetylene has also been used in the United States, Germany,
the Argentine, China, Canada, &c., for lighthouse and beacon
illumination. Many buoys and beacons on the German and Dutch coasts
have been supplied with oil gas mixed with 20% of acetylene, thereby
obtaining an increase of over 100% in illuminating intensity. In
France an incandescent burner consuming acetylene gas mixed with air
has been installed at the Chassiron lighthouse (1902). 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 60 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 Dungeness lighthouse, where it
remained in service until the year 1874 when oil was substituted for
electricity. The earliest of the permanent installations now existing
in England is that at Souter Point which was illuminated in 1871.
There are in England four important coast lights illuminated by
electricity, and one, viz. Isle of May, in Scotland. Of the former St
Catherine's, in the Isle of Wight, and the Lizard are the most
powerful. Electricity was substituted as an illuminant for the then
existing oil light at St Catherine's in 1888. The optical apparatus
consisted of a second-order 16-sided revolving lens, which was
transferred to the South Foreland station in 1904, and a new second
order (700 mm.) four-sided optic with a vertical angle of 139°,
exhibiting a flash of .21 second duration every 5 seconds substituted
for it. A fixed holophote is placed inside the optic in the dark or
landward arc, and at the focal plane of the lamp. This holophote
condenses the rays from the arc falling upon it into a pencil of small
angle, which is directed horizontally upon a series of reflecting
prisms which again bend the light and throw it downwards through an
aperture in the lantern floor on to another series of prisms, which
latter direct the rays seaward in the form of a sector of fixed red
light at a lower level in the tower. A somewhat similar arrangement
exists at Souter Point lighthouse.
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.
[Illustration: FIG. 45.--Isle of May Apparatus.]
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 10°, and the
remainder of the vertical section consisting of reflecting prisms.
In France the old south lighthouse at La Hève was lit by electricity
in 1863. This installation was followed in 1865 by a similar one at
the north lighthouse. In 1910 there were thirteen important coast
lights in France illuminated by electricity. In other parts of the
world, Macquarie lighthouse, Sydney, was lit by electricity in 1883;
Tino, in the gulf of Spezia, in 1885; and Navesink lighthouse, near
the entrance to New York Bay, in 1898. Electric apparatus were also
installed at the lighthouse at Port Said in 1869, on the opening of
the canal; Odessa in 1871; and at the Rothersand, North Sea, in 1885.
There are several other lights in various parts of the world
illuminated by this agency.
Incandescent electric lighting has been adopted for the illumination
of certain light-vessels in the United States, and a few small harbour
and port lights, beacons and buoys.
Table VI. gives particulars of some of the more important electric
lighthouses of the world.
_Electric Lighthouse Installations in France._--A list of the thirteen
lighthouses on the French coast equipped with electric light
installations will be found in table VI. It has been already mentioned
that the two lighthouses at La Hève were lit by electric light in 1863
and 1865. These installations were followed within a few years by the
establishment of electricity as illuminant at Gris-Nez. In 1882 M.
Allard, the then director-general of the French Lighthouse Service,
prepared a scheme for the electric lighting of the French littoral by
means of 46 lights distributed more or less uniformly along the
coast-line. All the apparatus were to be of the same general type, the
optics consisting of a fixed belt of 300 mm. focal distance, around
the outside of which revolved a system of 24 faces of vertical lenses.
These vertical panels condensed the belt of fixed light into beams of
3° amplitude in azimuth, producing flashes of about ¾ sec. duration.
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, Sunderland. The
intensities obtained were 120,000 candles in the case of fixed lights
and 900,000 candles with flashing lights. As a result of a nautical
inquiry held in 1886, at which date the lights of Dunkerque, Calais,
Gris-Nez, La Canche, Baleines and Planier had been lighted, in
addition to the old apparatus at La Hève, it was decided to limit the
installation of electrical apparatus to important landfall lights--a
decision which the Trinity House had already arrived at in the case of
the English coast--and to establish new apparatus at six stations
only. These were Créac'h d'Ouessant (Ushant), Belle-Île, La Coubre at
the mouth of the river Gironde, Barfleur, Île d'Yeu and Penmarc'h. At
the same time it was determined to increase the powers of the existing
electric lights. The scheme as amended in 1886 was completed in
1902.[2]
All the electrically lit apparatus, in common with other optics
established in France since 1893, have been provided with mercury
rotation. The most recent electric lights have been constructed in the
form of twin apparatus, two complete and distinct optics being mounted
side by side upon the same revolving table and with corresponding
faces parallel. It is found that a far larger aggregate candle-power
is obtained from two lamps with 16 mm. to 23 mm. diameter carbons and
currents of 60 to 120 amperes than with carbons and currents of larger
dimensions in conjunction with single optics of greater focal
distance. A somewhat similar circumstance led to the choice of the
twin form for the two very powerful non-electric apparatus at Île
Vierge (figs. 43 and 43A) and Ailly, particulars of which will be seen
in table VII.
Several of the de Meritens magneto-electric machines of 5.5 K.W., laid
down many years ago at French electric lighthouse stations, are still
in use. All these machines have five induction coils, which, upon the
installation of the twin optics, were separated into two distinct
circuits, each consisting of 2½ coils. This modification has enabled
the old plants to be used with success under the altered conditions of
lighting entailed by the use of two lamps. The generators adopted in
the French service for use at the later stations differ materially
from the old type of de Meritens machine. The Phare d'Eckmühl
(Penmarc'h) installation serves as a type of the more modern
machinery. The dynamos are alternating current two-phase machines, and
are installed in duplicate. The two lamps are supplied with current
from the same machine, the second dynamo being held in reserve. The
speed is 810 to 820 revolutions per minute.
The lamp generally adopted is a combination of the Serrin and Berjot
principles, with certain modifications. Clockwork mechanism with a
regulating electromagnet moves the rods simultaneously and controls
the movements of the carbons so that they are displaced at the same
rate as they are consumed. It is usual to employ currents of varying
power with carbons of corresponding dimensions according to the
atmospheric conditions. In the French service two variations are used
in the case of twin apparatus produced by currents of 60 and 120
amperes at 45 volts with carbons 14 mm. and 18 mm. diameter, while in
single optic apparatus currents of 25, 50 and 100 amperes are utilized
with carbon of 11 mm., 16 mm. and 23 mm. diameter. 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 compressor, siren, &c., but not buildings, amounts
approximately to £5900.
_Efficiency of the Electric Light._--In 1883 the lighthouse
authorities of Great Britain determined that an exhaustive series of
experiments should be carried out at the South Foreland with a view to
ascertaining the relative suitability of electricity, gas and oil as
lighthouse illuminants. The experiments extended over a period of more
than twelve months, and were attended by representatives of the chief
lighthouse authorities of the world. The results of the trials tended
to show that the rays of oil and gas lights suffered to about equal
extent by atmospheric absorption, but that oil had the advantage over
gas by reason of its greater economy in cost of maintenance and in
initial outlay on installation. The electric light was found to suffer
to a much larger extent than either oil or gas light per unit of power
by atmospheric absorption, but the infinitely greater total intensity
of the beam obtainable by its use, both by reason of the high luminous
intensity of the electric arc and its focal compactness, more than
outweighed the higher percentage of loss in fog. The final conclusion
of the committee on the relative merits of electricity, gas or oil as
lighthouse illuminants is given in the following words: "That for
ordinary necessities of lighthouse illumination, mineral oil is the
most suitable and economical illuminant, and that for salient
headlands, important landfalls, and places where a very powerful light
is required electricity offers the greater advantages."
5. MISCELLANEOUS LIGHTHOUSE EQUIPMENT. _Lanterns._--Modern lighthouse
lanterns usually consist of a cast iron or steel pedestal, cylindrical
in plan, on which is erected the lantern glazing, surmounted by a
domed roof and ventilator (fig. 41). Adequate ventilation is of great
importance, and is provided by means of ventilators in the pedestal
and a large ventilating dome or cowl in the roof. The astragals
carrying the glazing are of wrought steel or gun-metal. The astragals
are frequently arranged helically or diagonally, thus causing a
minimum of obstruction to the light rays in any vertical section and
affording greater rigidity to the structure. The glazing is usually
¼-in. thick plate-glass curved to the radius of the lantern. In
situations of great exposure the thickness is increased. Lantern roofs
are of sheet steel or copper secured to steel or cast-iron rafter
frames. In certain instances it is found necessary to erect a grille
or network outside the lantern to prevent the numerous sea birds,
attracted by the light, from breaking the glazing by impact. Lanterns
vary in diameter from 5 ft. to 16 ft. or more, according to the size
of the optical apparatus. For first order apparatus a diameter of 12
ft. or 14 ft. is usual.
_Lightning Conductors._--The lantern and principal metallic structures
in a lighthouse are usually connected to a lightning conductor carried
either to a point below low water or terminating in an earth plate
embedded in wet ground. Conductors may be of copper tape or
copper-wire rope.
_Rotating Machinery._--Flashing-light apparatus are rotated by
clockwork mechanism actuated by weights. The clocks are fitted with
speed governors and electric warning apparatus to indicate variation
in speed and when rewinding is required. For occulting apparatus
either weight clocks or spring clocks are employed.
_Accommodation for Keepers, &c._--At rock and other isolated stations,
accommodation for the keepers is usually provided in the towers. In
the case of land lighthouses, dwellings are provided in close
proximity to the tower. The service or watch room should be situated
immediately under the lantern floor. Oil is usually stored in
galvanized steel tanks. A force pump is sometimes used for pumping oil
from the storage tanks to a service tank in the watch-room or lantern.
6. UNATTENDED LIGHTS AND BEACONS.--Until recent years no unattended
lights were in existence. The introduction of Pintsch's gas system in
the early 'seventies provided a means of illumination for beacons and
buoys of which large use has been made. Other illuminants are also in
use to a considerable extent.
_Unattended Electric Lights._--In 1884 an iron beacon lighted by an
incandescent lamp supplied with current from a secondary battery was
erected on a tidal rock near Cadiz. 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
Bénard et Turenne of Paris, and supplied with current from batteries
of Daniell cells, with electric clockwork mechanism for occulting the
light. These apparatus have been fitted to beacons and buoys, and are
generally arranged to automatically switch off the current during the
day-time. They run unattended for periods up to two months. Two
separate lenses and lamps are usually provided, with lamp changer,
only one lamp being in circuit at a time. In the event of failure in
the upper lamp of the two the current automatically passes to the
lower lamp.
[Illustration: FIG. 46.--Garvel Beacon.]
_Oil-gas Beacons._--In 1881 a beacon automatically lighted by
Pintsch's compressed oil gas was erected on the river Clyde, and large
numbers of these structures have since been installed in all parts of
the world. The gas is contained in an iron or steel reservoir placed
within the beacon structure, refilled by means of a flexible hose on
the occasions of the periodical visits of the tender. The beacons,
which remain illuminated for periods up to three months are charged to
7 atmospheres. Many lights are provided with occulting apparatus
actuated by the gas passing from the reservoir to the burner
automatically cutting off and turning on the supply. The Garvel beacon
(1899) on the Clyde is shown in fig. 46. 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 Sweden. Many lights of this type have
subsequently been placed in different parts of the world. The volatile
spirit lamp burns day and night. Occultations are produced by a screen
or series of screens rotated round the light by the ascending current
of heated air and gases from the lamp acting upon a horizontal fan.
The speed of rotation of the fan cannot be accurately adjusted, and
the times of occultation therefore are liable to slight variation. The
lights run unattended for periods up to twenty-one days.
_Benson-Lee Lamps._--An improvement upon the foregoing is the
Benson-Lee lamp, in which a similar occulting arrangement is often
used, but the illuminant is paraffin consumed in a special burner
having carbon-tipped wicks which require no trimming. The flame
intensity of the light is greater than that of the burner consuming
light spirit. 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 deposit of carbonized tar on its exposed upper
surface. This crust prevents further charring of the wick after
ignition, the oil becoming vaporized from the under side of the crust.
Many fixed, occulting and flashing lights fitted with these burners
are established in France and other countries. In the case of the
occulting types a revolving screen is placed around the burner and
carried upon a miniature mercury float. The rotation is effected by
means of a small Gramme motor on a vertical axis, fitted with a speed
governor, and supplied with current from a battery of primary cells.
The oil reservoir is placed in the upper part of the lantern and
connected with the burner by a tube, to which is fitted a constant
level regulator for maintaining the burning level of the oil at a
fixed height. In the flashing or revolving light types the arrangement
is generally similar, the lenses being revolved upon a mercury float
which is rotated by the electric motor. The flashing apparatus
established at St Marcouf in 1901 has a beam intensity of 1000
candle-power, and is capable of running unattended for three months.
The electric current employed for rotating the apparatus is supplied
by four Lalande and Chaperon primary cells, coupled in series, each
giving about 0.15 ampere at a voltage of 0.65. The power required to
work the apparatus is at the maximum about 0.165 ampere at 0.75 volt,
the large surplus of power which is provided for the sake of safety
being absorbed by a brake or governor connected with the motor.
_Wigham Beacon Lights._--Wigham introduced an oil lamp for beacon and
buoy purposes consisting of a vertical container filled with ordinary
mineral oil or paraffin, and carrying a roller immediately under the
burner case over which a long flat wick passes. One end of the wick is
attached to a float which falls in the container as the oil is
consumed, automatically drawing a fresh portion of the wick over the
roller. The other end of the wick is attached to a free counterweight
which serves to keep it stretched. The oil burns from the convex
surface of the wick as it passes over the roller, a fresh portion
being constantly passed under the action of the flame. The light is
capable of burning without attention for thirty days. These lights are
also fitted with occulting screens on the Lindberg system. The
candle-power of the flame is small.
7. LIGHT-VESSELS.--The earliest light-vessel placed in English waters
was that at the Nore in 1732. The early light-ships were of small size
and carried lanterns of primitive construction and small size
suspended from the yard-arms. 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.
Depth moulded 13 ft. to 15 ft. 6 in.
Tonnage 155 to 280.
The larger vessels are employed at outside and exposed stations, the
smaller ships being stationed in sheltered positions and in estuaries.
The moorings usually consist of 3-ton mushroom anchors and 1(5/8) open
link cables. The lanterns in common use are 8 ft. in diameter,
circular in form, with glazing 4 ft. in height. They are annular in
plan, surrounding the mast of the vessel upon which they are hoisted
for illumination, and are lowered to the deck level during the day.
Fixed lanterns mounted on hollow steel masts are now being used in
many services, and are gradually displacing the older type. The first
English light-vessel so equipped was constructed in 1904. Of the 87
light-vessels in British waters, including unattended light-vessels,
eleven are in Ireland and six in Scotland. At the present time there
are over 750 light-vessels in service throughout the world.
Until about 1895 the illuminating apparatus used in light-vessels was
exclusively of catoptric form, usually consisting of 21 in. or 24 in.
silvered parabolic reflectors, having 1, 2 or 3-wick mineral oil
burners in focus. The reflectors and lamps are hung in gimbals to
preserve the horizontal direction of the beams.
The following table gives the intensity of beam obtained by means of a
type of reflector in general use:
_21-in. Trinity House Parabolic Reflector_
Service Intensity
of Beam.
Burners 1 wick "Douglass" 2715 candles
" 2 " (Catoptric) 4004 "
" 2 " (Dioptric) 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 Thames in 1837. Group-flashing characteristics can be
produced by special arrangements of the reflectors. Dioptric apparatus
is now being introduced in many new vessels, the first to be so fitted
in England being that stationed at the Swin Middle in 1905, the
apparatus of which is gas illuminated and gives a flash of 25,000
candle-power.
Fog signals, when provided on board light-vessels are generally in the
form of reed-horns or sirens, worked by compressed air. The
compressors are driven from steam or oil engines. The cost of a modern
type of English light-vessel, with power-driven compressed air siren,
is approximately £16,000.
In the United States service, the more recently constructed vessels
have a displacement of 600 tons, each costing £18,000. They are
provided with self-propelling power and steam whistle fog signals. The
illuminating apparatus is usually in the form of small dioptric lens
lanterns suspended at the mast-head--3 or more to each mast, but a few
of the ships, built since 1907, are provided with fourth-order
revolving dioptric lights in fixed lanterns. There are 53
light-vessels in service on the coasts of the United States with 13
reserve ships.
_Electrical Illumination._--An experimental installation of the
electric light placed on board a Mersey light-vessel in 1886 by the
Mersey Docks and Harbour Board proved unsuccessful. The United States
Lighthouse Board in 1892 constructed a light-vessel provided with a
powerful electric light, and moored her on the Cornfield Point station
in Long Island Sound. This vessel was subsequently placed off Sandy
Hook (1894) and transferred to the Ambrose Channel Station in 1907.
Five other light-vessels in the United States have since been provided
with incandescent electric lights--either with fixed or occulting
characteristics--including Nantucket Shoals (1896), Fire Island
(1897), Diamond Shoals (1898), Overfalls Shoal (1901) and San
Francisco (1902).
_Gas Illumination._--In 1896 the French Lighthouse Service completed
the construction of a steel light-vessel (Talais), which was
ultimately placed at the mouth of the Gironde. The construction of
this vessel was the outcome of experiments carried out with a view to
produce an efficient light-vessel at moderate cost, lit by a dioptric
flashing light with incandescent oil-gas burner. The construction of
the Talais was followed by that of a second and larger vessel, the
Snouw, on similar lines, having a length of 65 ft. 6 in., beam 20 ft.
and a draught of 12 ft., with a displacement of 130 tons. The cost of
this vessel complete with optical apparatus and gasholders, with
accommodation for three men, was approximately £5000. The vessel was
built in 1898-1899.[3] A third vessel was constructed in 1901-1902 for
the Sandettié Bank on the general lines adopted for the preceding
examples of her class, but of the following increased dimensions:
length 115 ft.; width at water-line 20 ft. 6 in.; and draught 15 ft.,
with a displacement of 342 tons (fig. 47). Accommodation is provided
for a crew of eight men. The optical apparatus (fig. 48) is dioptric,
consisting of 4 panels of 250 mm. focal distance, carried upon a
"Cardan" joint below the lens table, and counter-balanced by a heavy
pendulum weight. The apparatus is revolved by clockwork and
illuminated by compressed oil gas with incandescent mantle. The
candle-power of the beam is 35,000. The gas is contained in three
reservoirs placed in the hold. The apparatus is contained in a 6-ft.
lantern constructed at the head of a tubular mast 2 ft. 6 in.
diameter. A powerful siren is provided with steam engine and boiler
for working the air compressors. The total cost of the vessel,
including fog signal and optical apparatus, was £13,600. A vessel of
similar construction to the Talais was placed by the Trinity House in
1905 on the Swin Middle station. The illuminant is oil gas. Gas
illuminated light-vessels have also been constructed for the German
and Chinese Lighthouse Service.
_Unattended Light-vessels._--In 1881 an unattended light-vessel,
illuminated with Pintsch's oil gas, was constructed for the Clyde, and
is still in use at the Garvel Point. The light is occulting, and is
shown from a dioptric lens fitted at the head of a braced iron lattice
tower 30 ft. above water-level. The vessel is of iron, 40 ft. long, 12
ft. beam and 8 ft. deep, and has a storeholder on board containing oil
gas under a pressure of six atmospheres capable of maintaining a light
for three months. A similar vessel is placed off Calshot Spit in
Southampton Water, and several have been constructed for the French
and other Lighthouse Services. The French boats are provided with deep
main and bilge keels similar to those adopted in the larger gas
illuminated vessels. In 1901 a light-vessel 60 ft. in length was
placed off the Otter Rock on the west coast of Scotland; 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 balance and "Cardan" joint as in the Sandettié light-vessel.
The illuminant is oil gas, with an occulting characteristic. The
storeholder contains 10,500 cub. ft. of gas at eight atmospheres,
sufficient to supply the light for ninety days and nights. A bell is
provided, struck by clappers moved by the roll of the vessel. The cost
of the vessel complete was £2979. The Northern Lighthouse
Commissioners have four similar vessels in service, and others have
been stationed in the Hugli estuary, at Bombay, off the Chinese coasts
and elsewhere. In 1909 an unattended gas illuminated light-vessel
provided with a dioptric flashing apparatus was placed at the Lune
Deep in Morecambe Bay. It is also fitted with a fog bell struck
automatically by a gas operated mechanism.
[Illustration: FIG. 47.--Sandettié Lightship.]
[Illustration: FIG. 48.--Lantern of Sandettié Lightship.]
_Electrical Communication of Light-vessels with the
Shore._--Experiments were instituted in 1886 at the Sunk light-vessel
off the Essex coast with the view to maintaining telephonic
communication with the shore by means of a submarine cable 9 m. in
length. Great difficulties were experienced in maintaining
communication during stormy weather, breakages in the cable being
frequent. These difficulties were subsequently partially overcome by
the employment of larger vessels and special moorings. Wireless
telegraphic installations have now (1910) superseded the cable
communications with light-vessels in English waters except in four
cases. Seven light-vessels, including the four off the Goodwin Sands,
are now fitted for wireless electrical communication with the shore.
In addition many pile lighthouses and isolated rock and island
stations have been placed in electrical communication with the shore
by means of cables or wireless telegraphy. The Fastnet lighthouse was,
in 1894, electrically connected with the shore by means of a
non-continuous cable, it being found impossible to maintain a
continuous cable in shallow water near the rock owing to the heavy
wash of the sea. A copper conductor, carried down from the tower to
below low-water mark, was separated from the cable proper, laid on the
bed of the sea in a depth of 13 fathoms, by a distance of about 100
ft. The lighthouse was similarly connected to earth on the opposite
side of the rock. The conductor terminated in a large copper plate,
and to the cable end was attached a copper mushroom. Weak currents
were induced in the lighthouse conductor by the main current in the
cable, and messages received in the tower by the help of electrical
relays. On the completion of the new tower on the Fastnet Rock in 1906
this installation was superseded by a wireless telegraphic
installation.
8. DISTRIBUTION AND DISTINCTION OF LIGHTS, &c.--_Methods of
Distinction._--The following are the various light characteristics which
may be exhibited to the mariner:--
_Fixed._--Showing a continuous or steady light. 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 shipping or other
shore lights.
_Flashing._[4]--Showing a single flash, the duration of darkness always
being greater than that of light. This characteristic or that
immediately following is generally adopted for important lights. The
French authorities have given the name _Feux-Eclair_ to flashing lights
of short duration.
_Group-Flashing._--Showing groups of two or more flashes in quick
succession (not necessarily of the same colour) separated by eclipses
with a larger interval of darkness between the groups.
_Fixed and Flashing._--Fixed light varied by a single white or coloured
flash, which may be preceded and followed by a short eclipse. This type
of light, in consequence of the unequal intensities of the beams, is
unreliable, and examples are now seldom installed although many are
still in service.
_Fixed and Group-Flashing._--Similar to the preceding and open to the
same objections.
_Revolving._--This term is still retained in the "Lists of Lights"
issued by the Admiralty and some other authorities to denote a light
gradually increasing to full effect, then decreasing to eclipse. At
short distances and in clear weather a faint continuous light may be
observed. There is no essential difference between revolving and
flashing lights, the distinction being merely due to the speed of
rotation, and the term might well be abandoned as in the United States
lighthouse list.
_Occulting._--A continuous light with, at regular intervals, one sudden
and total eclipse, the duration of light always being equal to or
greater than that of darkness. 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.
_Group Occulting._--A continuous light with, at regular intervals,
groups of two or more sudden and total eclipses.
_Alternating._--Lights of different colours (generally red and white)
alternately without any intervening eclipse. This characteristic is not
to be recommended for reasons which have already been referred to. Many
of the permanent and unwatched lights on the coasts of Norway and Sweden
are of this description.
_Colour._--The colours usually adopted for lights are white, red and
green. White is to be preferred whenever possible, owing to the great
absorption of light by the use of red or green glass screens.
[Illustration: FIG. 49.--Otter Rock Light-vessel.]
_Sectors._--Coloured lights are often requisite to distinguish cuts or
sectors, and should be shown from fixed or occulting light 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 cover the dangers, white light being shown over the fairway
with sufficient margin of safety between the edges of the coloured
sectors next the fairway and the dangers.
_Choice of Characteristic and Description of Apparatus._--In
determining the choice of characteristic for a light due regard must
be paid to existing lights in the vicinity. No light should be placed
on a coast line having a characteristic the same as, or similar to,
another in its neighbourhood unless one or more lights of dissimilar
characteristic, and at least as high power and range, intervene. In
the case of "landfall lights" the characteristic should differ from
any other within a range of 100 m. In narrow seas the distance between
lights of similar characteristic may be less. Landfall lights are, in
a sense, the most important of all and the most powerful apparatus
available should be installed at such stations. The distinctive
characteristic of a light should be such that it may be readily
determined by a mariner without the necessity of accurately timing the
period or duration of flashes. For landfall and other important coast
stations flashing dioptric apparatus of the first order (920 mm. focal
distance) with powerful burners are required. 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 geographical range in clear weather. On the other hand there are
many harbour and other lights which do not meet this condition.
The distances given in lists of lights from which lights are
visible--except in the cases of lights of low power for the reason
given above--are usually calculated in nautical miles as seen from a
height of 15 ft. above sea-level, the elevation of the lights being
taken as above high water. Under certain atmospheric conditions, and
especially with the more powerful lights, the glare of the light may
be visible considerably beyond the calculated range.
TABLE III.--_Distances at which Objects can be seen at Sea,
according to their Respective Elevations and the Elevation of the
Eye of the Observer._ (A. Stevenson.)
+--------+------------+---------------------+
| |Distances in| |Distances in|
|Heights |Geographical|Heights |Geographical|
|in Feet.|or Nautical |in Feet.|or Nautical |
| | Miles. | | Miles. |
+--------+------------+--------+------------+
| 5 | 2.565 | 110 | 12.03 |
| 10 | 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 |
| 60 | 8.886 | 500 | 25.65 |
| 65 | 9.249 | 550 | 26.90 |
| 70 | 9.598 | 600 | 28.10 |
| 75 | 9.935 | 650 | 29.25 |
| 80 | 10.26 | 700 | 30.28 |
| 85 | 10.57 | 800 | 32.45 |
| 90 | 10.88 | 900 | 34.54 |
| 95 | 11.18 | 1000 | 36.28 |
| 100 | 11.47 | | |
+--------+------------+--------+------------+
EXAMPLE: A tower 200 ft. high will be visible 20.66 nautical miles
to an observer, whose eye is elevated 15 ft. above the water; thus,
from the table:
15 ft. elevation, distance visible 4.44 nautical miles
200 " " 16.22 "
-----
20.66 "
_Elevation of Lights._--The elevation of the light above sea-level
need not, in the case of landfall lights, exceed 200 ft., which is
sufficient to give a range of over 20 nautical miles. One hundred and
fifty feet is usually sufficient for coast lights. Lights placed on
high headlands are liable to be enveloped in banks of fog at times
when at a lower level the atmosphere is comparatively clear (e.g.
Beachy Head). No definite rule can, however, be laid down, and local
circumstances, such as configuration of the coast line, must be taken
into consideration in every case.
_Choice of Site._--"Landfall" stations should receive first
consideration and the choice of location for such a light ought never
to be made subservient to the lighting of the approaches to a port.
Subsidiary lights are available for the latter purpose. Lights
installed to guard shoals, reefs or other dangers should, when
practicable, be placed seaward of the danger itself, as it is
desirable that seamen should be able to "make" the light with
confidence. Sectors marking dangers seaward of the light should not
be employed except when the danger is in the near vicinity of the
light. Outlying dangers require marking by a light placed on the
danger or by a floating light in its vicinity.
[Illustration: FIG. 50.--Spar Gas Buoy.]
9. ILLUMINATED BUOYS.--_Gas Buoys._ Pintsch's oil gas has been in use
for the illumination of buoys since 1878. In 1883 an automatic
occulter was perfected, worked by the gas passing from the reservoir
to the burner. The lights placed on these buoys burn continuously for
three or more months. The buoys and lanterns are made in various forms
and sizes. The spar buoy (fig. 50) may be adopted for situations where
strong tides or currents prevail. Oil gas lights are frequently fitted
to Courtenay whistling (fig. 51) and bell buoys.
In the ordinary type of gas buoy lantern the burner employed is of the
multiple-jet, Argand ring, or incandescent type. Incandescent mantles
have been applied to buoy lights in France with successful results.
Since 1906, and more recently the same system of illumination has been
adopted in England and other countries. The lenses employed are of
cylindrical dioptric fixed-light form, usually 100 mm. to 300 mm.
diameter. Some of the largest types of gas-buoy in use on the French
coast have an elevation from water level to the focal plane of over 26
ft. with a beam intensity of more than 1000 candles. A large gas-buoy
with an elevation of 34 ft. to the focal plane was placed at the
entrance to the Gironde in 1907. It has an incandescent burner and
exhibits a light of over 1500 candles. Oil gas forms the most
trustworthy and efficient illuminant for buoy purposes yet introduced,
and the system has been largely adopted by lighthouse and harbour
authorities.
There are now over 2000 buoys fitted with oil gas apparatus, in
addition to 600 beacons, light-vessels and boats.
_Electric Lit Buoys._--Buoys have been fitted with electric light,
both fixed and occulting. Six electrically lit spar-buoys were laid
down in the Gedney channel, New York lower bay, in 1888. These were
illuminated by 100 candle-power Swan lamps with continuous current
supplied by cable from a power station on shore. The wear and tear of
the cables caused considerable trouble and expense. In 1895
alternating current was introduced. The installation was superseded by
gas lit buoys in 1904.
_Acetylene and Oil Lighted Buoys._--Acetylene has been extensively
employed for the lighting of buoys in Canada and in the United States;
to a less extent it has also been adopted in other countries. Both the
low pressure system, by which the acetylene gas is produced by an
automatic generator, and the so-called high pressure system in which
purified acetylene is held in solution in a high pressure gasholder
filled with asbestos composition saturated with acetone, have been
employed for illuminating buoys and beacons. Wigham oil lamps are also
used to a limited extent for buoy lighting.
_Bell Buoys._--One form of clapper actuated by the roll of the buoy
(shown in fig. 52) consists of a hardened steel ball placed in a
horizontal phosphor-bronze cylinder provided with rubber buffers.
Three of these cylinders are arranged around the mouth of the fixed
bell, which is struck by the balls rolling backwards and forwards as
the buoy moves. Another form of bell mechanism consists of a fixed
bell with three or more suspended clappers placed externally which
strike the bell when the buoy rolls.
[Illustration: FIG. 51.--Courtenay's Automatic Whistling Buoy.
A, Cylinder, 27 ft. 6 in. long.
B, Mooring shackle.
C, Rudder.
D, Buoy.
E, Diaphragm.
F, Ball valves.
G, Air inlet tubes.
H, Air (compressed outlet tube to whistle).
I, Compressed air inlet to buoy.
K, Manhole.
L, Steps.
N, Whistle.]
10. FOG SIGNALS.--The introduction of coast fog signals is of
comparatively recent date. They were, until the middle of the 19th
century, practically unknown except so far as a few isolated bells and
guns were concerned. The increasing demands of navigation, and the
application of steam power to the propulsion of ships resulting in an
increase of their speed, drew attention to the necessity of providing
suitable signals as aids to navigation during fog and mist. In times
of fog the mariner can expect no certain assistance from even 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 a sea fog
of even moderate density, at a distance of less than a ¼ m. from the
shore. The careful experiments and scientific research which have been
devoted to the subject of coast fog-signalling have produced much that
is useful and valuable to the mariner, but unfortunately the practical
results so far have not been so satisfactory as might be desired,
owing to (1) the very short range of the most powerful signals yet
produced under certain unfavourable acoustic conditions of the
atmosphere, (2) the difficulty experienced by the mariner in judging
at any time how far the atmospheric conditions are against him in
listening for the expected signal, and (3) the difficulty in locating
the position of a sound signal by phonic observations.
[Illustration: FIG. 52.--Buoy Bell.]
_Bells and Gongs_ are the oldest and, generally speaking, the least
efficient forms of fog signals. Under very favourable acoustic
conditions the sounds are audible at considerable ranges. On the other
hand, 2-ton bells have been inaudible at distances of a few hundred
yards. The 1893 United States trials showed that a bell weighing 4000
lb. struck by a 450 lb. hammer was heard at a distance of 14 m. across
a gentle breeze and at over 9 m. against a 10-knot breeze. Bells are
frequently used for beacon and buoy signals, and in some cases at
isolated rock and other stations where there is insufficient
accommodation for sirens and horns, but their use is being gradually
discontinued in this country for situations where a powerful signal
is required. Gongs, usually of Chinese manufacture, were formerly in
use on board English light-ships and are still used to some extent
abroad. These are being superseded by more powerful sound instruments.
_Explosive Signals._--Guns were long used at many lighthouse and
light-vessel stations in England, and are still in use in Ireland and
at some foreign stations. These are being gradually displaced by other
explosive or compressed air signals. No explosive signals are in use
on the coasts of the United States. In 1878 sound rockets charged with
gun-cotton were first used at Flamborough Head and were afterwards
supplied to many other stations.[5] The nitrated gun-cotton or tonite
signals now in general use are made up in 4 oz. charges. These are
hung at the end of an iron jib or pole attached to the lighthouse
lantern or other structure, and fired by means of a detonator and
electric battery. The discharge may take place within 12 ft. of a
structure without danger. The cartridges are stored for a considerable
period without deterioration and with safety. This form of signal is
now very generally adopted for rock and other stations in Great
Britain, Canada, Newfoundland, northern Europe and other parts of the
world. An example will be noticed in the illustration of the Bishop
Rock lighthouse, attached to the lantern (fig. 13). Automatic hoisting
and firing appliances are also in use.
_Whistles._--Whistles, whether sounded by air or steam, are not used
in Great Britain, except in two instances of harbour signals under
local control. It has been objected that their sound has too great a
resemblance to steamers' whistles, and they are wasteful of power. In
the United States and Canada they are largely used. The whistle
usually employed consists of a metallic dome or bell against which the
high-pressure steam impinges. Rapid vibrations are set up both in the
metal of the bell and in the internal air, producing a shrill note.
The Courtenay buoy whistle, already referred to, is an American
invention and finds favour in the United States, France, Germany and
elsewhere.
_Reed-Horns._--These instruments in their original form were the
invention of C. L. Daboll, an experimental horn of his manufacture
being tried in 1851 by the United States Lighthouse Board. 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
Professor Holmes, and many examples from his designs are now in use in
England and America. At the Trinity House experiments with fog signals
at St Catherine's (1901) several types of reed-horn were experimented
with. The Trinity House service horn uses air at 15 lb. pressure with
a consumption of .67 cub. ft. per second and 397 vibrations. A small
manual horn of the Trinity House type consumes .67 cub. ft. of air at
5 lb. pressure. The trumpets of the latter are of brass.
_Sirens._--The most powerful and efficient of all compressed air fog
signals is the siren. The principle of this instrument may be briefly
explained as follows:--It is well known that if the tympanic membrane
is struck periodically and with sufficient rapidity by air impulses or
waves a musical sound is produced. Robinson was the first to construct
an instrument by which successive puffs of air under pressure were
ejected from the mouth of a pipe. He obtained this effect by using a
stop-cock revolving at high speed in such a manner that 720 pulsations
per second were produced by the intermittent escape of air through the
valves or ports, a smooth musical note being given. Cagniard de la
Tour first gave such an instrument the name of siren, and constructed
it in the form of an air chamber with perforated lid or cover, the
perforations being successively closed and opened by means of a
similarly perforated disk fitted to the cover and revolving at high
speed. 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 Helmholtz introduced many improvements, and
Brown of New York patented, about 1870, a steam siren with two disks
having radial perforations or slots. The cylindrical form of the siren
now generally adopted is due to Slight, who used two concentric
cylinders, one revolving within the other, the sides being perforated
with vertical slots. To him is also due the centrifugal governor
largely used to regulate the speed of rotation of the siren. Over the
siren mouth is placed a conical trumpet to collect and direct the
sound in the desired direction. In the English service these trumpets
are generally of considerable length and placed vertically, with bent
top and bell mouth. Those at St Catherine's are of cast-iron with
copper bell mouth, and have a total axial length of 22 ft. They are 5
in. in diameter at the siren mouth, the bell mouth being 6 ft. in
diameter. At St Catherine's the sirens are two in number, 5 in. in
diameter, being sounded simultaneously and in unison (fig. 53). 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 admission of
air to the siren can be delayed until the cylinder is rotating at full
speed, and a much sharper sound is produced than in the case of the
automatic type. The Scottish trumpets are frequently constructed so
that the greater portion of the length is horizontal. The Girdleness
trumpet has an axial length of 16 ft., 11 ft. 6 in. being horizontal.
The trumpet is capable of being rotated through an angle as well as
dipped below the horizon. It is of cast-iron, no bell mouth is used,
and the conical mouth is 4 ft. in diameter. In France the sirens are
cylindrical and very similar to the English self-driven type. The
trumpets have a short axial length, 4 ft. 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 mushroom trumpet nor the twin siren is used the
single bent trumpet is arranged to rotate through a considerable
angle. Table IV. gives particulars of a few typical sirens of the most
recent form.
[Illustration: FIG. 53.--St Catherine's Double-noted Siren.]
TABLE IV.
+-----------------------+----------------------+----------+---------+----------------+--------------------+
| | | |Sounding |Cub. ft. of air | |
| | |Vibrations|Pressure |used per sec. of| |
| Station. | Description. | per sec. |in lb per| blast reduced | Remarks. |
| | | | sq. in. | to atmospheric | |
| | | | | pressure. | |
+-----------------------+----------------------+-----+----+---------+-------+--------+--------------------+
| | |High.|Low.| | High. | Low. | |
|St Catherine's (Trinity|Two 5-in. cylindrical,| 295 | 182| 25 | 32 | 16 |The air consumption |
| House) | automatically driven| | | | | | is for 2 sirens. |
| | sirens | | | | | | |
|Girdleness (N.L.C) |7-in. cylindrical | 234 | 100| 30 | 130 | 26 | |
| | siren, motor driven | | | | | | |
|Casquets (Trinity |7-in. disk siren, | .. | 98| 25 | .. | 36 | |
| House) | motor driven | | | | | | |
|French pattern siren |6-in. cylindrical | 326 | .. | 28 | 14 | .. |A uniform note of |
| | siren, automatically| | | | | | 326 vibrations per|
| | driven | | | | | | sec. has now been |
| | | | | | | | adopted generally |
| | | | | | | | in France. |
+-----------------------+----------------------+-----+----+---------+-------+--------+--------------------+
Since the first trial of the siren at the South Foreland in 1873 a
very large number of these instruments have been established both at
lighthouse stations and on board light-vessels. In all cases in Great
Britain and France they are now supplied with air compressed by steam
or other mechanical power. In the United States and some other
countries steam, as well as compressed air, sirens are in use.
_Diaphones._--The diaphone is a modification of the siren, which has
been largely used in Canada since 1903 in place of the siren. It is
claimed that the instrument emits a note of more constant pitch than
does the siren. The distinction between the two instruments is that in
the siren a revolving drum or disk alternately opens and closes
elongated air apertures, while in the diaphone a piston pulsating at
high velocity serves to alternately cover and uncover air slots in a
cylinder.
_The St Catherine's Experiments._--Extensive trials were carried out
during 1901 by the Trinity House at St Catherine's lighthouse, Isle of
Wight, with several types of sirens and reed-horns. Experiments were
also made with different pattern of trumpets, including forms having
elliptical sections, the long axis being placed vertically. The
conclusions of the committee may be briefly summarized as follows: (1)
When a large arc requires to be guarded two fixed trumpets suitably
placed are more effective than one large trumpet capable of being
rotated. (2) When the arc to be guarded is larger than that
effectively covered by two trumpets, the mushroom-head trumpet is a
satisfactory instrument for the purpose. (3) A siren rotated by a
separate motor yields better results than when self-driven. (4) No
advantage commensurate with the additional power required is obtained
by the use of air at a higher pressure than 25 lb. per sq. in. (5) The
number of vibrations per second produced by the siren or reed should
be in unison with the proper note of the associated trumpet. (6) When
two notes of different pitch are employed the difference between these
should, if possible, be an octave. (7) For calm weather a low note is
more suitable than a high note, but when sounding against the wind and
with a rough and noisy sea a high note has the greater range. (8) From
causes which cannot be determined at the time or predicted beforehand,
areas sometimes exist in which the sounds of fog signals may be
greatly enfeebled or even lost altogether. This effect was more
frequently observed during comparatively calm weather and at no great
distance from the signal station. (It has often been observed that the
sound of a signal may be entirely lost within a short distance of the
source, while heard distinctly at a greater distance and at the same
time.) (9) The siren was the most effective signal experimented with;
the reed-horn, although inferior in power, is suitable for situations
of secondary importance. (No explosive signals were under trial during
the experiments.) (10) A fog signal, owing to the uncertainty
attending its audibility, must be regarded only as an auxiliary aid to
navigation which cannot at all times be relied upon.
_Submarine Bell Signals._--As early as 1841 J. D. Colladon conducted
experiments on the lake of Geneva to test the suitability of water as
a medium for transmission of sound signals and was able to convey
distinctly audible sounds through water for a distance of over 21 m.,
but it was not until 1904 that any successful practical application of
this means of signalling was made in connexion with light-vessels.
There are at present (1910) over 120 submarine bells in service,
principally in connexion with light-vessels, off the coasts of the
United Kingdom, United States, Canada, Germany, France and other
countries. These bells are struck by clappers actuated by pneumatic or
electrical mechanism. Other submerged bells have been fitted to buoys
and beacon structures, or placed on the sea bed; in the former case
the bell is actuated by the motion of the buoy and in others by
electric current, transmitted by cable from the shore. In some cases,
when submarine bells are associated with gas buoys or beacons, the
compressed gas is employed to actuate the bell striking mechanism. 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 hull plating. The signals are audible by the aid of ear
pieces similar to ordinary telephone receivers. Not only can the bell
signals be heard at considerable distances--frequently over 10 m.--and
in all conditions of weather, but the direction of the bell in
reference to the moving ship can be determined within narrow limits.
The system is likely to be widely extended and many merchant vessels
and war ships have been fitted with signal receiving mechanism.
The following table (V.) gives the total numbers of fog signals of
each class in use on the 1st of January 1910 in certain countries.
TABLE V.
+----------------------------+-------+------+--------------+------+---------+-----+------+------+------+-------+
| | | | Horns, | |Explosive| | | |Subm- | |
| |Sirens.| Diap-| Trumpets, &c.| Whis-| Signals |Guns.|Bells.|Gongs.|arine |Totals.|
| | | hone.+------+-------+ tles.| (tonite,| | | |Bells.| |
| | | |Power.|Manual.| | &c.). | | | | | |
+----------------------------+-------+------+------+-------+------+---------+-----+------+------+------+-------+
| 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 | 1 | .. | 1 | .. | 25 | .. | 2 | 48 |
| United States (excluding | | | | | | | | | | | |
| inland lakes and rivers) | 43 | .. | 35 | 15 | 59 | .. | .. | 218 | 1 | 36 | 407 |
| British North America | | | | | | | | | | | |
| (excluding inland lakes | | | | | | | | | | | |
| and rivers) | 6 | 66 | 5 | 79 | 16 | 8 | .. | 24 | .. | 11 | 215 |
+----------------------------+-------+------+--------------+------+---------+-----+------+------+------+-------+
When two kinds of signal are employed at any one station, one being
subsidiary, the latter is omitted from the enumeration. Buoy and
unattended beacon bells and whistles are also omitted, but local port
and harbour signals not under the immediate jurisdiction of the
various lighthouse boards are included, more especially in Great
Britain.
11. LIGHTHOUSE ADMINISTRATION. The principal countries of the world
possess organized and central authorities responsible for the
installation and maintenance of coast lights and fog signals, buoys and
beacons.
_United Kingdom._--In England the corporation of Trinity House, or
according to its original charter, "The Master Wardens, and Assistants
of the Guild Fraternity or Brotherhood of the most glorious and
undivided Trinity and of St Clement, in the Parish of Deptford Strond,
in the county of Kent," existed in the reign of Henry VII. as a
religious house with certain duties connected with pilotage, and was
incorporated during the reign of Henry VIII. In 1565 it was given
certain rights to maintain beacons, &c., but not until 1680 did it own
any lighthouses. Since that date it has gradually purchased most of
the ancient privately owned lighthouses and has erected many new ones.
The act of 1836 gave the corporation control of English coast lights
with certain supervisory powers over the numerous local lighting
authorities, including the Irish and Scottish Boards. The corporation
now consists of a Master, Deputy-master, and 22 Elder Brethren (10 of
whom are honorary), together with an unlimited number of Younger
Brethren, who, however, perform no executive duties. In Scotland and
the Isle of Man the lights are under the control of the Commissioners
of Northern Lighthouses constituted in 1786 and incorporated in 1798.
The lighting of the Irish coast is in the hands of the Commissioners
of Irish Lights formed in 1867 in succession to the old Dublin Ballast
Board. The principal local light boards in the United Kingdom are the
Mersey Docks and Harbour Board, and the Clyde Lighthouse Trustees. The
three general lighthouse boards of the United Kingdom, by the
provision of the Mercantile Marine Act of 1854, are subordinate to the
Board of Trade, which controls all finances.
On the 1st of January 1910 the lights, fog signals and submarine bells
in service under the control of the several authorities in the United
Kingdom were as follows:
+----------------------------------+-------+--------+--------+---------+
| |Light- | Light- | Fog |Submarine|
| |houses.|vessels.|Signals.| Bells. |
+----------------------------------+-------+--------+--------+---------+
| Trinity House | 116 | 51 | 97 | 12 |
| Northern Lighthouse Commissioners| 138 | 5 | 44 | .. |
| Irish Lights Commissioners | 93 | 11 | 35 | 3 |
| Mersey Docks and Harbour Board | 16 | 6 | 13 | 2 |
| Admiralty | 31 | 2 | 6 | .. |
| Clyde Lighthouse Trustees | 14 | 1 | 5 | .. |
| Other local lighting authorities | 809 | 11 | 89 | 2 |
| +-------+--------+--------+---------+
| Totals | 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 Congress in 1852. The Secretary of Commerce and Labor is the
ex-officio president. The board consists of two officers of the navy,
two engineer officers of the army, and two civilian scientific
members, with two secretaries, one a naval officer, the other an
officer of engineers in the army. The members are appointed by the
president of the United States. The coast-line of the states, with the
lakes and rivers and Porto Rico, is divided into 16 executive
districts for purposes of administration.
The following table shows the distribution of lighthouses,
light-vessels, &c., maintained by the lighthouse board in the United
States in June 1909. In addition there are a few small lights and
buoys privately maintained.
Lighthouses and beacon lights 1333
Light-vessels in position 53
Light-vessels for relief 13
Gas lighted buoys in position 94
Fog signals operated by steam or oil engines 228
Fog signals operated by clockwork, &c. 205
Submarine signals 43
Post lights 2333
Day or unlighted beacons 1157
Bell buoys in position 169
Whistling buoys in position 94
Other buoys 5760
Steam tenders 51
Constructional Staff 318
Light keepers; and light attendants 3137
Officers and crews of light-vessels and tenders 1693
_France._--The lighthouse board of France is known as the Commission
des Phares, dating from 1792 and remodelled in 1811, and is under the
direction of the minister of public works. It consists of four
engineers, two naval officers and one member of the Institute, one
inspector-general of marine engineers, and one hydrographic engineer.
The chief executive officers are an Inspecteur Général des Ponts et
Chaussées, who is director of the board, and another engineer of the
same corps, who is engineer-in-chief and secretary. The board has
control of about 750 lights, including those of Corsica, Algeria, &c.
A similar system has been established in Spain.
TABLE VI.--_Electric Lighthouse Apparatus._
+--------------------------+-----------------+-----+----------+-----------+----------+-------------+-------+----+--------+--------------------------+----------+--------+---------+-------+---------------------------------------------------+
| | | P | | | | | C | V | C | | | | | | |
| | | e | | | | Ratio of | u | o | a | | | | | | |
| | | r | | Candle- | Focal | Angular | r | l | r | | | |Elevation| Year | |
| Name. | Characteristic. | i | Duration | power | Distance | Breadth of | r | t | b | Electric | Lamps. |Engines.| above | Estab-| Remarks. |
| | | o | of Flash.| (Service | of Lens. | Panel to | e | a | o | Generators. | | | High |lished.| |
| | | d | |Intensity).| |Whole Circle.| n | g | n | | | | Water. | | |
| | | . | | | | | t | e | s | | | | | | |
| | | | | | | | . | . | . | | | | | | |
+--------------------------+-----------------+-----+----------+-----------+----------+-------------+-------+----+--------+--------------------------+----------+--------+---------+-------+---------------------------------------------------+
| | | | | Standard | | | | | | | | | | | |
|UNITED KINGDOM-- | |Secs.| Secs. | Candles. | mm. | | Amps. | | mm. | | | | Feet. | | |
| Souter Point | Single flash | 30 | 5 | | 500 | 1 : 8 | .. | 40 | 17 | Holmes machines, | Serrin | Steam | 150 | 1871 |Fixed light apparatus, with revolving vertical |
| (Durham) | | | |\ C n | | | | | | alternating (400 revs.) | | | | | condensing lenses in eight panels. |
| South Foreland | Single flash | 2.5| .35 || a o d | 700 | 1 : 16 | .. | 40 | 26 | do. | Serrin | Steam | 374 | 1904 |Lens elements only; 97° vertical angle. |
| (Kent) | | | || n t e | | | | | | | | | | | (This apparatus was in use at St Catherine's, |
| | | | || d t | | | | | | | | | | |1888 to 1904, and replaced the two fixed electric |
| | | | || l o e | | | | | | | | | | |lights established in 1872.) |
| Lizard | Single flash | 3 | .13 || e f r | 700 | 1 : 4 |145 for| 40 | 50 and | De Meritens alternators | Modified | Oil | 230 | 1903 | Mercury rotation; vertical angle, 139°. Replaced |
| (Cornwall) | | | | > - f m | | | 50 mm.| | 60 | (600 revs.) | Berjot- | engines| | | the two fixed electric lights erected in |
| | | | || p i i | | |carbons| | fluted | | Serrin | | | | 1878. |
| St Catherine's | Single flash | 5 | .21 || o c n | 700 | 1 : 4 |145 for| 40 | 50 and | do. | do. |2 Steam,| 136 | 1904 |Mercury rotation; vertical angle, 139°. |
| (Isle of Wight) | | | || w i e | | | 50 mm.| | 60 | | | each 50| | | |
| | | | || e a d | | |carbons| | fluted | | | h.p. | | | |
| Isle of May | 4 flash | 30 | .4 || r l . | 700 | 1 : 8 | 220 | 40 | 40 | do. | Berjot- | Steam | 240 | 1886 |Fixed light apparatus, with revolving vertical |
| (Firth of Forth) | | | || l | (Fixed | | | | | | Serrin | | | | condensing lenses. |
| | | | |/ y |apparatus)| | | | | | | | | | |
|FRANCE-- | | | | | | | | | | | | | | | |
| Dunkerque | 2 flash | 10 | .2 to .4 | 3,500,000 | 300 | 1 : 12 | 30 | 45 | 14 and |2 De Meritens alternators,| Improved | 2 Semi-| 193 | 1902 |Twelve panels in groups of two. |
| (Strait of Dover) | | | | to | | | and | | 18 | each of 5.5 k.w. | Serrin |portable| | | (This apparatus was in use at Barfleur, 1893 |
| | | | | 6,500,000 | | | 60 | | | (550 revs.) | | steam, | | |to 1902.) |
| | | | | | | | | | | | | each 30| | | |
| | | | | | | | | | | | | i.h.p. | | | |
| Calais | 4 flash | 15 | .75 | 900,000 | 300 | 1 : 24 | 60 | 45 | 18 | do. | French | do. | 190 | 1883 |Fixed light apparatus, with revolving vertical |
| (Strait of Dover) | | | | | | | | | | | Service | | | | condensing prisms. |
| [Les Baleines (1882) | | | | | | | | | | | pattern | | | | |
| similar] | | | | | | | | | | | (1902) | | | | |
| | | | | | | | | | | | | | | | |
| Cap Gris-nez | Single flash | 5 |.10 to .14| 15,000,000| 300 | 1 : 4 | 60 | 45 | 18 and | do. | do. | Steam | 233 | 1899 |Twin optic, mercury rotation. |
| (Strait of Dover) | | | | to | | | to | | 28 | | | | | | (This light superseded a triple-flashing electric|
| | | | | 30,000,000| | | 120 | | | | | | | |light, with intermediate red flash, of the Calais |
| | | | | | | | | | | | | | | |type, established in 1885. The first installation |
| | | | | | | | | | | | | | | |of the electric light at this station was in 1869.)|
| La Canche | 2 flash | 10 |.10 to .14| 15,000,000| 300 | 1 : 4 | 30 | 45 | 14 and | do. | do. | do. | 174 | 1900 |Twin optic, mercury rotation. |
| (Strait of Dover) | | | | to | | | to | | 18 | | | | | | (This light superseded a fixed electric light |
| | | | | 30,000,000| | | 60 | | | | | | | |established in 1884.) |
| Cap de la Hève | Single flash | 5 |.10 to .14| 10,000,000| 300 | 1 : 4 | 60 | 45 | 18 and | De Meritens alternators | Improved | do. | 397 | 1893 | Mercury rotation. |
| (Havre, English | | | | to | | | to | | 28 | (550 revs.) | Serrin | | | | (The first installation of electric light at this|
| Channel) | | | | 20,000,000| | | 120 | | | | | | | |lighthouse was in 1863.) |
| [Île d'Yeu in the Bay | | | | | | | | | | | | | | | |
| of Biscay (1895) | | | | | | | | | | | | | | | |
| similar] | | | | | | | | | | | | | | | |
| Créac'h d'Ouessant | 2 flash | 10 |.10 to .14| 15,000,000| 300 | 1 : 4 | 60 | 45 | 18 and |2 De Meritens alternators,| French | do. | 225 | 1901 |Twin optic, mercury rotation. |
| (Ushant) | | | | to | | | to | | 28 | each of 5.5 k.w. | Service | | | | (This light superseded a double-flashing |
| [Barfleur (English | | | | 30,000,000| | | 120 | | | (550 revs.) | pattern | | | |electric light, similar to that now at Dunkerque, |
| Channel) 1903, La | | | | | | | | | | | (1902) | | | |established in 1888.) |
| Coubre (Bay of | | | | | | | | | | | | | | | |
| Biscay) 1905, and | | | | | | | | | | | | | | | |
| Belle Île (Bay | | | | | | | | | | | | | | | |
| of Biscay) 1903, | | | | | | | | | | | | | | | |
| similar] | | | | | | | | | | | | | | | |
| Penmarc'h (Phare | Single flash | 5 |.10 to .14| 15,000,000| 300 | 1 : 4 | 30 | 45 | 14 and | Two-phase Labour alter- | do. | do. | 197 | 1897 |Twin optic, mercury rotation. |
| d'Eckmühl) | | | | to | | | and | | 18 |nators (810 to 820 revs.) | | | | | |
| (Finistère) | | | | 30,000,000| | | 60 | | | | | | | | |
| Planier | Single flash | 5 |.10 to .14| 15,000,000| 300 | 1 : 4 | 30 | 45 |14 to 18| De Meritens alternators | do. | do. | 207 | 1902 |Twin optic, mercury rotation. |
| (near Marseilles) | | | | to | | | to | | | (550 revs.) | | | | | (This light superseded an electric light estab- |
| | | | | 30,000,000| | | 60 | | | | | | | |lished in 1881, showing a group of three white |
| | | | | | | | | | | | | | | |flashes separated by one red flash of the Calais |
|ITALY-- | | | | | | | | | | | | | | |type.) |
| Tino | 3 flash | 30 | 1.25 | Undeter- | 700 | 1 : 24 | 50 | 50 | 15 | do. | Berjot- | do. | 384 | 1885 |Eight panels of three lenses each, no mirror. |
| (Gulf of Spezia) | | | | mined. | | | 110 | | 25 | (830 revs.) | Serrin | | | | |
| | | | | | | | 200 | | 35 | | | | | | |
|AMERICA-- | | | | | | | | | | | | | | | |
| Navesink | Single flash | 5 | .08 | About | 700 | Nearly 1 : 2| Max. | 50 | 23 | Alternating dynamos | Modified | Oil, | 246 | 1898 |Mercury rotation. Bivalve of 165°. |
| (Entrance to New | | | | 60,000,000| | | 100 | | | (800 revs.) | Serrin | each | | | |
| York Bay) | | | | | | | | | | | (Ciolina)| 25 h.p.| | | |
| | | | | | | | | | | | | | | | |
|AUSTRALIA-- | | | | | | | | | | | | | | | |
| Macquarie | Single flash | 60 | 8 | 5,000,000 | 920 | 1 : 16 | 55 | 50 | 15 | De Meritens alternators | Serrin | Gas | 345 | 1883 |16-panel revolving apparatus, with 180° fixed |
| (Sydney, N.S.W.) | | | | | | | 110 | | 25 | (600 revs.) | | | | | mirror. |
+--------------------------+-----------------+-----+----------+-----------+----------+-------------+-------+----+--------+--------------------------+----------+--------+---------+-------+---------------------------------------------------+
TABLE VII.--_Typical Non-Electric Lighthouse Apparatus._
+----------------+-------------------+--------------+-------+--------+------------+---------+-------------+-------------+------------------+----------+-------+----------+-------------------------------------------------------------+
| | | | | | Candle- | | Ratio of | | | | | | |
| | | | | | Power in | | Angular | | | Service | Height| | |
| Name. | Locality. | Character- |Period.|Duration| Standard | Focal | Breadth of | Illuminant. | Burner. | Candle- | above | Year | Remarks. |
| | | istic. | | of | Candles |Distance | Panel to | | | power | High | Estab- | |
| | | | |Flashes.| (Service |of Lens.|Whole Circle.| | |of Burner.| Water.| lished.* | |
| | | | | | Intensity).| | | | | | | | |
+----------------+-------------------+--------------+-------+--------+------------+---------+-------------+-------------+------------------+----------+-------+----------+-------------------------------------------------------------+
| | | | Secs. | Secs. | | mm. | | | | | Feet. | | |
|Casquets | Channel Islands | 3 flash | 30 | 1.5 | 185,000 | 920 | 1 : 9 | Incandescent| "Matthews" 3-50 | 3300 | 120 | 1877 |Dioptric holophote, 126½° vertical angle; 3 sides of 3 |
| | | | | | | | | petroleum | mm. dia. mantles | | | | panels in each. |
| | | | | | | | | vapour | | | | | |
|Eddystone | South Devon | 2 flash | 30 | 1.5 | 292,000 | 920 | 1 : 12 | do. | do. | 3300 | 133 | 1882 |Biform apparatus, lens elements only, 92° vertical angle; |
| | | | | | | | | | | | | | 6 sides of 2 panels each. |
|Bishop Rock | Scilly Isles | 2 flash | 60 | 4.0 | 622,000 | 1330 | 1 : 10 | do. | do. | 3300 | 134 | 1886 |Biform apparatus, lens elements only, 80° vertical angle; |
| | | | | | | | | | | | | | 5 sides of 2 panels each. |
|Spurn Point | Yorkshire | Single flash | 20 | 1.5 | 519,000 | 1330 | 1 : 6 | do. | do. | 3300 | 120 | 1895 |Lens elements only, 80° vertical angle. |
|Lundy Island | Bristol Channel | 2 flash | 20 | .33 | 374,000 | 920 | Nearly 1 : 4| do. | do. | 3300 | 165 | 1897 |Mercury rotation, 4-panel bivalve. |
| | | | | | | | | | | | | | [St. Mary's Isle, Northumberland (1898), is similar.] |
|Pendeen | Cornwall | 4 flash | 15 | .25 | 190,000 | 920 | 1 : 8 | do. | do. | 3300 | 195 | 1900 |80° vertical angle lens, 2 sides of 4 panels each, mercury |
| | | | | | | | | | | | | | rotation. |
|Roker Pier | Sunderland | Single flash | 5 | .10 | 175,000 | 500 | Nearly 1 : 2| do. | "Chance" 55 mm. | 1200 | 83 | 1903 |Mercury rotation; univalve 164° in azimuth, with 164° |
| | | | | | | | | | dia. mantle | | | | dioptric mirror in rear. |
|Bell Rock | Near Firth of Tay | Red and white| 60 | .50 | 392,000 | 920 and | White about | do. | "Chance" 55 mm. | 1200 | 93 | 1902 |Combined hyper-radial and first-order light with back |
| | |flashes alter-| | | | 1330 | 1 : 9 | | dia. mantle | | | | prisms in white and mirrors in red. Revolves in 60 |
| | |nately every | | | | | red about | | | | | | secs. |
| | | 30 secs. | | | | | 1 : 2.2 | | | | | |[Holy Island, 1905 (Lamlash), similar, flash every 15 secs.] |
|Kinnaird's Head | Aberdeenshire | Single flash | 15 | .50 | 881,000 | 920 and | 1 : 2.2 | do. | do. | 2150 | 120 | 1903 |Composite apparatus; panels of 1330 mm. and 920 mm. |
| | | | | | | 1330 | | | | | | | focal distance; 2 faces. |
|Tarbet Ness | Dornoch Firth | 6 flash | 30 | .50 | 89,000 | 700 | 1 : 12 | do. | "Chance" 55 mm. | 1200 | 175 | 1892 |6 panels (lens) of 30° with 180° mirror. |
| | | | | | | | | | dia. mantle | | | | [Douglas Head (Isle of Man) similar.] |
|Sule Skerry | West of Orkneys | 3 flash | 30 | 1.0 | 378,000 | 1330 | 1 : 9 | do. | "Chance" 85 mm. | 2150 | 113 | 1895 |Equiangular lenses. |
| | | | | | | | | | dia. mantle | | | | |
|Pladda | South end of Arran| 3 flash | 30 | .50 | 597,000 | 1330 | 1 : 6 | do. | do. | 2150 | 130 | 1901 |3 equiangular lens panels with mirror in rear; side panels |
| | Island | | | | | | | | | | | | eccentric. |
| | | | | | | | | | | | | | [Hyskin Rocks (1904) similar.]
Showing first 200,000 characters. Full text: gutenberg.org/ebooks/41472