UNATTENDED LIGHTHOUSES
During the past fifty years engineering science as applied to
lighthouses has made remarkable advances. This has been due largely
to the indefatigable perseverance and ceaseless labour of the chemist
in regard to illumination. This wonder-worker has given us acetylene,
has evolved means whereby oil-gas may be compressed to a pressure
of several atmospheres with safety, and has discovered other gases
obtainable by inexpensive and simple means. The engineer has not
hesitated to profit from these developments, and has devised highly
ingenious apparatuses whereby these illuminating mediums may be stored
and used, so as to dispense with the human element almost entirely; in
fact, in these instances the latter factor has been reduced to such
a degree that it is only called upon to perform certain perfunctory
operations, such as the recharging of the storage vessels at long
intervals--three, six, or twelve months, according to circumstances.
This combination has provided the lighthouse engineer with a new,
powerful, and efficient means of overcoming abnormal difficulties.
Many a rock, reef, or stretch of uninhabited coastline has demanded
indication, but has defied such protection from motives of cost,
inaccessibility, or searching problems concerning the accommodation and
relief of the keepers. As I have shown in the course of this volume,
the erection of a first-class lighthouse is a costly undertaking,
and the shipping interests, which in the case of Great Britain and
a few other countries are called upon to pay the bill, naturally
demur, unless the rock or other obstacle is situate in the centre
of the marine thoroughfare, or the approach to a pitiless coast is
extremely hazardous, when the erection of the tower becomes absolutely
imperative. If one were to add up the costs of all the great lights
scattered throughout the seven seas, it would be found that several
millions sterling had been sunk in this humane effort, and yet,
relatively speaking, but a small area of danger in the aggregate is
safeguarded.
[Illustration: THE PLATTE FOUGÈRE LIGHTHOUSE UNDER CONSTRUCTION.
This automatic light marks a dangerous reef, off the Guernsey coast,
which is familiar to readers of Victor Hugo’s “Toilers of the Sea.”]
Then the human factor demands consideration. A colony of four or six
men scarcely could be found willing to suffer isolation from the world
at large and to be deprived of intercourse with their fellow-beings in
the interests of shipping, say, through the Straits of Magellan, around
Cape Horn, among the icy fastnesses of the Northern Labrador coast, or
in Hudson Bay. Life in the lighthouses which guard the busy steamship
lanes is monotonous and nerve-shattering enough, but to maroon men
in such remote places as those mentioned above would be to promote a
wholesale rush of inmates for the lunatic asylums.
This is where the chemist and the engineer in collaboration have
triumphed. By their joint efforts it is now possible to supply the
most inhospitable shore with a belt of lights equal in every respect
to those mounting sentinel over the more densely populated reaches of
coast in the civilized parts of the globe. The unattended lighthouse
is a modern development born of necessity, which has proved highly
serviceable, effective, and reliable. The passenger, as he lolls
against the taffrail of the steamer ploughing her way carefully through
the lane 375 miles long separating the mainland of South America from
Tierra del Fuego, and watches the faithful star twinkling upon the top
of a frowning cliff and urging the mariner to keep clear, may cherish
a feeling of pity for the man who has to keep that beam shining. But
his commiseration is misplaced. No human hands touch that beacon,
perhaps, for six months or more at a time. It is a triumph of automatic
operation. The same applies to the wicked shores of New Zealand, the
uninviting northern stretches of the Gulf of Bothnia, the iron-bound
coasts of Norway and Sweden, and many another unattractive mainland and
island.
All the great maritime nations possess several of these silent,
faithful lights, which, although upon their introduction they were
regarded with a certain amount of suspicion, owing to the urgent
necessity of a light never failing in its duty for the guidance of the
seafarer, yet have been proved by the convincing lesson of experience
to be as reliable in every respect as the light which is tended by
human hands.
So far as Great Britain is concerned, the unattended light has been
brought to a high stage of efficiency and utility by the efforts of
Messrs. David and Charles Stevenson, while in other parts of the world
the apparatus and methods perfected by Mr. Gustaf Dalén of Stockholm
are used extensively.
The most interesting example of the Stevenson unattended lighthouse is
provided in the English Channel, indicating the entrance to the strait
which leads to the Guernsey capital of St. Peter Port. This was one of
the first of its character to be erected, but the type is now being
adopted widely owing to the success of this initial undertaking. The
Channel Islands have achieved an unsavoury reputation in marine annals,
as they form a graveyard of the Channel; they have claimed their
victims, during recent years at any rate, mostly from the ranks of the
heavy cross-Channel traffic.
[Illustration: THE PLATTE FOUGÈRE LIGHTHOUSE.
This beacon, designed by Messrs. D. and C. Stevenson, probably is the
finest unattended lighthouse in existence. On the top of the tower is
the automatically controlled acetylene light.]
The Russell Channel, leading to St. Peter Port from the north, is
exceedingly dangerous, the sea being littered with granite rocks both
submerged and exposed, of which the Grande Braye, Barsier, and Platte
Fougère, form the outer rampart. Readers of Victor Hugo may gather some
realistic idea of the perilous nature of these waters by perusing “The
Toilers of the Sea,” in which these rocks figure very prominently,
particularly the Platte Fougère. The menace of this corner of the
channel is accentuated by the velocity of the tidal currents which
swing and swirl round the reefs, together with the extreme range of
the tides, which averages about 30 feet. Formerly, in thick weather,
vessels found it almost impossible to pick up the Russell, and often
a captain, by the rip and crash of metal being torn, to his dismay
learned that he had swung too far to the westward.
[Illustration: SETTING THE COMPRESSED-AIR RESERVOIR AT FORT DOYLE.
The Platte Fougère automatic light is supplemented by a land station on
the island of Guernsey a mile away.]
The companies engaged in this traffic repeatedly petitioned the
authorities to mark the entrance to the strait by some adequate means.
A light was not required so keenly as a sound-signal, because in clear
weather navigation was tolerably safe. The proposal was discussed
time after time, but no solution appeared to be forthcoming. To erect
a lighthouse on the outer fringe of the barrier would have entailed
prodigious expenditure, which the island authorities could ill afford,
even if such a scheme were practicable.
The question was taken up boldly by General Campbell during his
occupation of the post of Governor-General of the Island of
Guernsey, and he pressed forward the scheme vigorously in a resolute
determination to bring about a diminution in the number of maritime
disasters at this point. He approached Messrs. David and Charles
Stevenson, who had considerable experience of similar conditions
around the Scottish coasts, and they, after an elaborate survey of the
site, recommended the erection of a light and fog-signal station upon
the Platte Fougère, which should be controlled from the land a mile
distant. They agreed that the erection of a tower similar to those
generally planted on sea-rocks would be a formidable undertaking and
enormously expensive, owing to the conditions prevailing, but the
station they suggested was quite practicable, and would serve the
purposes equally well.
Instead of a massive, gracefully-curving tower, measuring some 40
feet in diameter at the base, these engineers suggested a building of
irregular octagonal shape, measuring 14½ and 17 feet across the faces,
80 feet in height, and carried out in ferro-concrete. They advocated
its erection upon the Platte Fougère, because there the fog-signal
would be brought into the most serviceable position for shipping. A
narrow or thin building was advised, to offer the minimum of surface
to the waves, which break very heavily on these ridges. The wisdom of
this design has been revealed very convincingly since the tower has
been in service. The seas fall on either side, divide and rush round
the building, so that it does not experience the full brunt of their
heavy, smashing blows. As the engineers pointed out, “It is better to
avoid heavy sea pressures, where feasible, in preference to courting
them.”
Still, the Platte Fougère was not an ideal rock from the engineers’
point of view, although it is a solid knot of granite. Its head is
visible only at low-water spring-tides, while it is difficult to
approach, even in the smoothest weather, owing to the tides and
currents. Much of the foundation work had to be carried out under
water. The season was unavoidably limited, as the days when both the
wind and the sea are calm in this part of the channel are very few and
far between.
The tower is solid for a height of 46 feet above the rock, and the base
is formed of Portland cement placed in iron moulds, with iron bars
driven into the solid rock to anchor the concrete firmly. On the side
to which the building is exposed to the heaviest seas, massive beams
of rolled steel are driven into the rock, so as to impart additional
strength to the part of the tower where the greatest strains are likely
to be set up.
On the entrance level is a compartment containing an electric motor and
air-compressor, while on the floor immediately above is a duplicate
installation. The siren projects through the top of the tower, the
trumpet being so turned as to throw the sounds in a horizontal
direction over the water. On the top of the tower is a small automatic
acetylene gas plant and light, such as the engineers have employed
so successfully in their unattended Scottish light-stations, two
air-receivers, and a water-tank. A new type of burner is used, and a
clockwork mechanism is incorporated to extinguish the light at dawn and
to ignite it at dusk, with a special arrangement to allow for the short
summer nights and the long periods of darkness during the winter.
[Illustration: THE FORT DOYLE SIREN.
This installation on the island is maintained so as to take the place
of the automatic lighthouse a mile out to sea, in the remote event of
the latter breaking down.]
As mentioned above, the station is controlled electrically from a point
on shore. In deciding the latter, it was necessary to discover the most
favourable landing-place for the submarine cable in relation to its
route, and Doyle Fort was selected as meeting all requirements in this
direction. Here a two-floor dwelling has been erected for the keepers,
together with an adjoining engine-house, which measures 32 feet in
length by 20 feet wide. The tower being a mile distant, the designers
had to meet the possibility of the machinery therein breaking down.
Accordingly, at the shore station there is an auxiliary fog-siren and
air-compressing plant, which is brought into use when the sea apparatus
is deranged.
[Illustration:
_By courtesy of Messrs. D. and C. Stevenson._
AN UNATTENDED BEACON LIGHT PLACED UPON A WILD PART OF THE SCOTTISH
COAST.
These lights will run for several months without any human attention,
and, by means of ingenious mechanism, light and extinguish themselves
automatically.]
The machinery includes two oil-engines which drive three-phase
alternators, and an air-compressor for working the land siren when
required. One of the greatest difficulties arose in connection with the
submarine cable which connects the land-station with the sea-tower.
Owing to the broken, rocky nature of the sea-bed, the viciousness of
the currents, and the heavy seas, the cable had to be of exceptional
strength; indeed, it had to be made specially for the purpose. It is
a double-sheathed, steel-armoured cable of the heaviest “rock” type,
being 11 inches in circumference, and weighing 45 tons per nautical
mile. As the current used is three-phase, there are three conductors,
which weigh 1,100 pounds per mile, protected by a thick layer of
gutta-percha averaging 450 pounds per mile. In the centre of the core
are two other wires for switching and telephone purposes respectively.
The laying of the cable was a peculiar and exacting task in itself;
6,504 feet had to be paid out. But by waiting for a very calm day
and slack water this task was achieved without mishap. In the tower
there is a simple switch operated by an electro-magnet, whereby the
motor-driven air-compressors are thrown in and out of action. The
two compressors are used alternately, so as to keep them in thorough
working order; and as they have to be left sometimes for months without
being examined, special attention has been devoted to their lubrication.
A visit to this lighthouse is a somewhat curious experience. Climbing
the ladder and entering the building, one finds it apparently
abandoned. Not a sound beyond the murmuring of the waves playing about
the rocks below disturbs a silence which is uncannily tense. Suddenly
there is an almost imperceptible click. The keeper at the light-station
has moved his switch, and simultaneously that in the tower has
closed. The electric motors instantly commence to revolve, with a low
grunt at first, but rising quickly to a loud humming as they settle
down to their stride, driving the air-compressors. Then comes the
ear-splitting, deep-toned roar from the siren overhead, attended by
the whirr of machinery in motion. The humming of the motors and the
compressors dies down, and in a few seconds absolute stillness prevails
once more. The sensation is decidedly eerie. It seems impossible that a
silence so intense as to be felt should be interrupted by a click--the
result of a slight movement by an unseen hand a mile away--which gives
forth such a nerve-shattering din as to convey the idea that Bedlam
had been let loose. At the land-station the experience is similarly
weird. The keeper moves his switch which brings the tower machinery
into action. Presently there is the sharp tinkle of an electric bell.
This notifies the keeper that the blast on the tower has been given,
but conclusive evidence of this fact does not arrive until five seconds
later, when the baying of the siren comes rolling over the water.
A complete check is kept upon the isolated station out at sea. If the
electric bell does not ring out at the appointed period, to notify
the keeper that the siren has emitted its warning note, he knows that
something is amiss. The land-station is brought into service without
delay, the intimation to the mariner to stand clear being thrown from
Doyle Fort once every ninety seconds. The men on shore take it in turns
to mount watch for fog both day and night, and their vigil is checked.
There is an electric alarm, which maintains silence only so long as the
man on duty fulfils his appointed task and records this fact upon his
mechanical register at scheduled intervals. Should he fail to perform
this function, there is a frenzied clanging by the alarm-bell, which
summons the second keeper to duty.
[Illustration: THE GASFETEN LIGHT: A LONELY BEACON IN SWEDISH WATERS.
This was the first tower to be fitted with the Dalén “sun-valve” in
conjunction with the Dalén flasher. Several automatic lights of this
type are used to show the way through the Panama Canal.]
Apparently, the weakest point in the installation is the submarine
cable, but the engineers entertain no apprehensions on this score. It
is too stoutly made and too heavily armoured to rupture very readily.
Experience has proved its efficiency and reliability, while a long
life is anticipated for it. The Platte Fougère unattended lighthouse
has opened up new possibilities for protecting wild coasts. It has
proved conclusively that there is no difficulty in maintaining such
a station and controlling it from a distance so long as automatic
apparatus which has proved its worth is employed. This practical
application should serve to solve many peculiar problems. No longer can
the bogie of expense be put forward as an argument against safeguarding
a notoriously evil length of shoreline or isolated rock, even if the
latter is exposed to the heaviest seas known. The Guernsey installation
was completed for £8,500, or $42,500, and is as serviceable as the
ordinary type of tower, which in this instance would have cost at least
£60,000, or $300,000, to build and equip. From the maintenance point
of view it is equally convincing and economical, inasmuch as only two
keepers are required in the place of the four who otherwise would have
been necessary.
[Illustration: THE DALÉN “SUN-VALVE,” THE MOST WONDERFUL INVENTION OF
MODERN LIGHTHOUSE ENGINEERING.
Depending upon the action of daylight alone, it automatically ignites
and extinguishes the light at dusk and dawn respectively.]
The system which has been devised by Mr. Gustaf Dalén of Stockholm,
and which is exploited by the Gas Accumulator Company of the Swedish
capital, operates with dissolved acetylene. The first light in
Scandinavian waters to be brought into action upon the “Aga” principle,
as it is called, was installed in the Gasfeten tower, an exceedingly
isolated beacon which offered every means of testing it thoroughly.
The idea follows the broad lines of that adopted in connection
with lightships, and, the Gasfeten experiments proving completely
successful, it has been adopted extensively since, not only by the
Swedish authorities for the lighting of lonely waters in the Baltic
Sea and Gulf of Bothnia, but by various other Powers. The Straits of
Magellan are protected in this way, and when one recalls the sparse
population which dwells upon the banks of this short-cut between the
Atlantic and Pacific Oceans, and bears in mind the fact that the lights
have to be left to their own automatic action for some months on end,
then one may realize the perfection and reliability of the invention.
The failure of a light in such treacherous waters would be notified
speedily to the authorities responsible for the illumination of this
sea-lane, but no such complaints appear to have been received from
passing vessels. These lonely lights for the most part are of a very
simple character, a result due to local conditions. As a rule they are
planted on lofty eminences--not at too high an elevation, as thereby
they might be rendered useless by headland fogs--at a height varying
between 150 and 250 feet. The base of the tower forms a space for the
accommodation of the gas-accumulators, wherein the illuminating medium
is stored under pressure, surmounted by the lantern which carries the
requisite optical apparatus, and the flasher whereby the characteristic
visual warning is given.
Although adoption of the flasher enabled the consumption of gas to
be reduced very appreciably, there was one noticeable drawback: the
light had to burn both night and day, unless clockwork mechanism were
introduced to extinguish the light at sunrise and to ignite it at
twilight. Some authorities, however, do not place trust in clockwork
mechanism. Certainly it is liable to fail at a critical moment, and in
the case of an isolated light, several hundred miles from the nearest
base, this would be a serious calamity, intimation of the fact not
being available until several weeks after the disability had been
observed.
In order to overcome the fallibility of clockwork, and to insure a
still further marked decrease in the consumption of gas, Mr. Gustaf
Dalén devoted his energies to the perfection of a device which
should achieve the self-same end, but be operated by Nature herself.
His efforts were crowned with complete success by the invention of
the “light-valve,” but which has become more widely known as the
“sun-valve.”
[Illustration: THE GAS ACCUMULATORS EMPLOYED IN THE DALÉN AUTOMATIC
SYSTEM.
The size of the storage cylinder varies according to the work,
character, and position of the beacon.]
This device is based upon a well-known principle. If two objects,
fashioned from the same metal, and identical in every respect except
that one is made light-absorbing and the other light-reflecting, are
exposed to daylight, while the former will expand, the latter will
remain unaffected. This result is due to the fact that the one which
absorbs light transforms it into energy. The acting part of the
“sun-valve” therefore is a light-absorber. It consists of a central
rod, the surface of which is coated with lampblack, so that its
light-absorbing qualities are enhanced as much as possible. The lower
part of this rod is connected to a small lever, which opens and shuts
an orifice through which the gas passes to the flasher in the lantern
above. Around this central black copper rod are three other copper
rods, disposed equidistantly. They resemble the former in every respect
except that they have no light-absorbing qualities, but they are given
polished gold surfaces, so that their light-reflecting properties are
raised to the maximum.
This sun-valve is exposed. At the break of dawn, under the gathering
intensity of daylight, the central black rod absorbs the luminosity,
the amount of which is increased by the light thrown from the
gold-burnished outer rods, and, converting it into energy, expands
longitudinally. In so doing it forces the lever at the base downwards,
closing the opening through which the gas flows to the flasher. In a
short while, when the day has broken fairly and there is no further
need for the beacon’s services, the gas-feed is cut off entirely, only
the pilot burner remaining alight, the gas-supply to this not being
affected by the sun-valve. In order to bring the greatest possible
pressure upon the lever, the blackened rod is so arranged that it can
expand only in one direction--namely, downwards.
Upon the approach of evening, owing to the daylight becoming weaker,
the blackened rod contracts, and, the pressure upon the lever being
released, the gas commences to flow once more to the burner. It is a
small stream at first, but as the darkness gathers, and the shrinking
continues, the valve opens wider and wider, until at last, when night
has settled down and the copper central rod has fully contracted, the
gas-valve is opened to its fullest extent, permitting the greatest
pressure of gas to flow to the burner, so that the beacon throws its
most brilliant light. This automatic action continues infallibly every
dawn and dusk, and is the simplest and at the same time most reliable
means of economizing gas during the day that has yet been devised.
There is another feature of this system which must not be overlooked.
Suppose, for some reason or other, that the sea becomes shrouded in
suffused light, such as might arise from the obscuring of the sun by
an overhanging bank of fog or smoke, the beacon comes automatically
into service, as the cutting off of the daylight must bring about a
contraction of the blackened copper rod controlling the valve.
The central rod can be adjusted to any degree of sensitiveness, by
means of a screw, while protection of the vital parts is insured by
enclosure within a heavy glass cylinder. The first apparatus of this
character was tested by the Swedish authorities in 1907, and proved
so successful that it is now in service at all the exposed unattended
lighthouses in Swedish and Finnish waters; while it has been adopted,
also, very extensively by the United States, more particularly for the
lighting of the lonely stretches of the Alaskan coastline and of the
Panama Canal.
Of course, the saving of gas which is rendered possible by the use of
the sun-valve varies according to the season of the year. During the
winter, when the nights are long, the saving may not be very marked,
but in the summer, when darkness does not last more than four or five
hours, the economy is very noticeable. According to the experience of
the Swedish authorities, the average saving of gas during the year
varies from 35 to 40 per cent., as compared with similar lights not
fitted with this device.
But there is another factor which is influenced to a very appreciable
degree by the utilization of the sun-valve. By cutting off the light
when it is not required, the capacity of--_i.e._, the duration of
service upon--one charge is lengthened, and this in the case of an
isolated light is a very important consideration. In fact, with the
“Aga” system wherein the sun-valve is combined with the flasher, it is
possible for the light to work a round twelve months without the least
control or necessity for intermediate inspection, and at as low an
annual charge as £2 15s., or about $14.
[Illustration: THE LAGERHOLMEN LIGHTHOUSE.
It marks a lonely dangerous rock in the Baltic Sea, and operates
upon the Aga unattended automatic system, with Dalén flasher and
“sun-valve.”]
One of the latest unattended installations which have been carried out
upon these lines is the Lagerholmen lighthouse, marking a dangerous
rock in the Baltic Sea. It is a cylindrical tower, with the focal
plane 56 feet 4 inches above sea-level, and the flashing light, with
sun-valve control, has a range of eighteen miles. The geographical
range, however, is only thirteen miles, owing to the comparatively low
height of the tower.
An interesting and ingenious automatic unattended light has also been
established in an isolated part of the Bristol Channel. It was designed
by Sir Thomas Matthews, the engineer to the Brethren of Trinity House.
This is purely and simply a clockwork-controlled apparatus in which
extreme care has been taken to eliminate the disadvantages incidental
to such mechanism. This type of light was designed to fulfil three
conditions--to give a flashing light; to light up and go out at
the proper times; and to require attention only at long intervals.
Acetylene is the illuminant used, the gas being stored in a reservoir
under high pressure. The gas as it emerges from the supply cylinder is
expanded, so that the pressure at the burner does not exceed 2 pounds
per square inch.
The outstanding feature of this apparatus is that the clockwork
control cutting off and turning on the gas does not require to be
wound by hand, but is actuated by the mechanism which revolves the
lenses, through a simple set of gearing. The gas as it issues from the
reservoir passes into one of two cylinders. Each of these is provided
with an inlet and an exhaust valve, while the upper end is closed
with a lid of leather, covering the top like the vellum of a drum.
To each leather cover is attached a circular piece of metal, smaller
than the leather diaphragm, and from this in turn extends a vertical
rod, the upper end of which is connected to one end of a centrally
pivoted rocking arm. When the gas enters one cylinder, naturally in
expanding it forces the leather lid upwards, and with it the vertical
rod. This elevates the corresponding end of the rocking arm, and
simultaneously drives down the rod attached to the opposite end
of the beam, which in turn drives down the leather lid of the second
cylinder, and forces out any gas that may be therein. The apparatus
consequently is something like a double pump, owing to the rocking arm
having a seesaw motion. This reciprocating action serves to wind up
the clock, and also to revolve the lenses through spurs and pinions.
The mechanism, however, is controlled completely by the clock whereby
the light is started, inasmuch as without this the apparatus cannot
be set in motion. There are two dials, one of which is divided into
twenty-four divisions, corresponding to the hours of the day, and the
other into twelve divisions, representing the twelve months of the
year. The clocks work together, and the time of lighting up is advanced
or retarded, according to the time of the year, through the clock train
wheels.
The apparatus is very compact, highly ingenious, and has proved
efficient in service. Although this is the first application of the
idea for rotating the lenses by the gas which feeds the burners,
so far as England is concerned, it has been employed under similar
circumstances in Germany with conspicuous success, in combination
with the Pintsch oil-gas apparatuses, but it lacks the simplicity and
reliability of the sun-valve.
[Illustration: AN UNATTENDED BEACON LIGHTING THE STRAITS OF MAGELLAN.
This warning, fitted with Dalén flasher and sun-valve, is visited once
in six months.]
[Illustration: AN AUTOMATIC LIGHT-BOAT.
This novel warning was constructed for installation at the mouth of a
Swedish river owing to the extreme velocity of the current. Such a boat
may be left unvisited for a year if desired.]
A different system, which has been adopted widely throughout the
East and in Australian waters, is the Wigham petroleum beacon. This
system possesses many notable features, the most important being
that well-refined petroleum oil is employed. In many parts of the
world carbide of calcium is not readily obtainable, and, moreover, is
somewhat expensive, whereas, on the other hand, oil is comparatively
cheap and available in unlimited quantities. The principle of working
is somewhat novel. The wick is not burned in the manner generally
followed in regard to lamps--viz., at the end, which within a short
time becomes carbonized and brings a marked diminution of the
illuminating power--but it is moved so that the same part is not
exposed continuously to the action of the heat arising from combustion.
It is caused to travel horizontally over a small roller, in a
specially-constructed burner, combustion taking place, therefore, on
its flat side. It is moved slowly and continuously over this roller,
so that it cannot burn through, and in this manner the flame, being
constantly emitted from a fresh surface, is of uniform intensity.
[Illustration: THE WIGHAM THIRTY-ONE DAY UNATTENDED PETROLEUM LIGHT.
The type at left shows the lamp carried upon a cast-iron pillar; while
on the right it is mounted upon a lattice tower.]
The lamp comprises three main parts. There is the lantern, with the
lens and the projecting panes of plate-glass, in the focus of which
the burner is fixed. Then there is the burning-oil reservoir, which
feeds the wick as it moves towards the burner. This reservoir is
circular in shape, somewhat shallow, and serves as a deck on which
the lantern is built up. The third part is the float cylinder, made
of copper, which is attached to the underside of the oil reservoir.
This cylinder is filled with oil, which is kept quite distinct from
the burning oil, and thereon floats a weighted copper drum, to which
one end of the wick is secured by means of a hook. At the lower end of
this cylinder is a micrometer valve, which when opened permits the oil
to drip away at a certain speed. This causes the float to fall with
the oil in the cylinder, and to drag the wick over the burner roller
and down the float cylinder after it, so that a fresh surface of the
wick is presented continuously for combustion. The lamps themselves may
be divided into two broad classes--the single-wick and the three-wick
respectively. The latter obviously emits the more brilliant light, and
is the type which is coming into more extensive use at the present
time. In the latest type a duplex burner is employed, and this has
been found to give a very powerful light with a comparatively low oil
consumption.
The light is generally carried at the top of a lattice-work steel
tower. A support of this character can be taken to pieces, packed
within small compass, and transported without difficulty, while
erection is simplified and facilitated. Seeing that a large number
of these beacons have been erected on headlands along the wildest
stretches of the African continent and the loneliest coasts of
Australia, where the methods of transport are restricted to coolies
or mules, this method of packing is distinctly advantageous. The lamp
is secured to the top of the tower, with the float cylinder of the lamp
depending from the centre. In this arrangement, as a rule, a small tank
is provided into which a drain-pipe empties the oil dropping from the
drip-valve. In this way the oil may be drawn off, filtered, and used
again in the float cylinder. In some instances the lamp is mounted upon
a cast-iron column, in which case the float cylinder and the oil-drip
tank are placed within the tube, access thereto being obtained through
a door.
The length of service on one charge varies according to the situation
of the light. If in a very exposed and inaccessible place, it may be
required to burn for two or three months without attention. Taken
on the average, however, a monthly charge has been found to offer
the greatest advantages. But in some places the longer interval is
unavoidable. For instance, the Wigham light which is mounted upon the
extremity of the Manora breakwater at Karachi cannot be approached for
three months at a time during the monsoon. Under these circumstances a
one-hundred-day service is imperative.
The lenses are of the dioptric order, consisting of six elements built
up into a strong gun-metal framework. The internal diameter naturally
varies with the size and number of the wicks, and ranges from 10 inches
for a 1-1/8 inch single wick, to 15 inches in the case of a 1-5/8 inch
three-wick lamp. In the larger sizes a curved plate-glass pane is
fitted outside the lens as a protection from the action of the weather.
These storm-panes are set in copper doors, so that the glasses may be
easily cleaned and polished when the lamp is being retrimmed.
[Illustration: WILLSON GAS AND WHISTLING FLOATING LIGHT OFF EGG ISLAND,
NOVA SCOTIA.]
[Illustration: THE WILLSON “OUTER AUTOMATIC,” HALIFAX, NOVA SCOTIA.]
The maintenance charges are guided by the local market values
of materials and labour, the item of repairs and renewals being
practically negligible. So far as oil consumption per month is
concerned, this fluctuates according to the type of lamp used,
ranging from 1-1/5 pints per twenty-four hours, or 4·8 gallons per
month, in the case of a 1-1/8-inch single-wick burner, to 2¼ pints
per twenty-four hours, or 8¾ gallons of oil per month, in the case
of the latest 1-5/8-inch duplex-wick burner. American petroleum-oil,
of a specific gravity of about 0·795, gives the best results and
the brightest and clearest flame. Russian and other heavier oils
generally used in lighthouses are unsuitable. In view of the world-wide
operations of the Standard Oil Company, however, no difficulty is
experienced in procuring adequate supplies of this oil anywhere between
the two Poles.
The oil used in the float cylinder, as mentioned previously, is quite
distinct from the burning oil, and is used only to support the float to
which the wick is attached. As the oil escapes through the drip-valve,
it may be allowed to run to waste, or, what is far preferable, it may
be caught, filtered, and used again for this purpose, to bring about a
reduction in the cost of upkeep. The float cylinder of a thirty-one-day
light, irrespective of the number of wicks, requires the same quantity
of oil for the float cylinder--9½ gallons.
The advantages of the unattended, automatic light have been appreciated
by the various maritime Powers, and their application is being
developed rapidly. They are inexpensive in first cost, and their
maintenance charges are very low. In Sweden a second-order light,
consuming 6 cubic feet of acetylene gas per hour, throwing a fixed
white light of 4,000 candle-power, and visible for seventeen miles in
clear weather, costs about £15, or $75, per annum; while the smaller
lights, with a 300-millimetre lens and a 12-inch burner emitting 360
candle-power, may be run for £2, or $10, per annum, the low cost in
this instance being attributable to use of the Dalén flasher and
sun-valve.
The cost of the acetylene gas averages ¾d., or 1½ cents, per cubic
foot, a result attributable to the fact that Scandinavia is the world’s
largest producer of carbide of calcium.
The Wigham petroleum system has proved similarly economical and
reliable, and has been installed in some of the wildest corners of
the globe. The Congested Districts Board for Ireland have established
a number of these beacons on the rugged west coast to assist the
fishermen in making their harbours at night. Many are placed in very
exposed positions on headlands, where they are frequently swept by the
full force of the Atlantic gales. The Austrian Government has adopted
the principle for lighting the dangerous coasts of the Adriatic near
Trieste, while the shoreline of Jamaica is safeguarded by more than
sixteen lights of this type. Many of these lights suffered severely
from the effects of the earthquake which overwhelmed the island a few
years ago, but others withstood all the shocks successfully. In this
instance, had expensive and massive lighthouses of the usual type been
erected, the loss would have been considerable, in view of the severity
of this seismic disturbance and the widespread destruction which was
wrought. These lights play a very prominent part in the guarding of
the southern ocean, the Australian shores being protected by over
sixty such beacons, many of which are established in very exposed and
isolated positions off the mainland.
While the day is still far distant when expensive graceful towers,
carrying immensely powerful lights, will be no longer constructed, the
perfection and utility of the unattended light, in one or other of
its many forms, are assisting tangibly in the solution of the problem
of lighting busy shorelines adequately and inexpensively. Structures
costing tens of thousands sterling in future will be restricted to
important places, especially in connection with sea-rocks, such as
landfalls, or to those some distance from the land, where a fog-signal
station must be maintained, unless the example of the Platte Fougère
land-controlled station becomes adopted.