Encyclopaedia Britannica, 11th Edition, "Lightfoot, Joseph" to "Liquidation"

Chapter III: Front Matter (3)

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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.

_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.

_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.

_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.

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.

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.

_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.

TABLE IV.

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._

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Encyclopaedia Britannica, 11th Edition, "Lightfoot, Joseph" to "Liquidation"Chapter III: Front Matter (3)

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