BUILDING A LIGHTHOUSE
Obviously, the task of erecting a lighthouse varies considerably with
the situation. On the mainland construction is straightforward, and
offers little more difficulty than the building of a house. The work
assumes its most romantic and fascinating form when it is associated
with a small rocky islet out to sea, such as the Eddystone, Skerryvore,
or Minot’s Ledge; or with a treacherous, exposed stretch of sand,
such as that upon which the Rothersand light is raised. Under such
conditions the operation is truly herculean, and the ingenuity and
resource of the engineer are taxed to a superlative degree; then he
is pitted against Nature in her most awful guise. Wind and wave,
moreover, are such formidable and relentless antagonists that for
the most momentary failure of vigilance and care the full penalty
is exacted. Then there are the fiercely scurrying currents, tides,
breakers, and surf, against which battle must be waged, with the odds
so overwhelmingly ranged against frail human endeavour that advance
can only be made by inches. The lighthouse engineer must possess the
patience of a Job, the tenacity of a limpet, a determination which
cannot be measured, and a perseverance which defies galling delays and
repeated rebuffs. Perils of an extreme character beset him on every
hand; thrilling escape and sensational incident are inseparable from
his calling.
The first step is the survey of the site, the determination of the
character of the rock and of its general configuration, and the takings
of levels and measurements for the foundations. When the rugged hump is
only a few feet in diameter little latitude is afforded the engineer
for selection, but in instances where the islet is of appreciable area
some little time may be occupied in deciding just where the structure
shall be placed. It seems a simple enough task to determine; one
capable of solution within a few minutes, and so for the most part it
is--not from choice, but necessity--when once the surface of the rock
is gained. The paramount difficulty is to secure a landing upon the
site. The islet is certain to be the centre of madly surging currents,
eddies, and surf, demanding wary approach in a small boat, while the
search for a suitable point upon which to plant a foot is invariably
perplexing. Somehow, the majority of these bleak, wave-swept rocks
have only one little place where a landing may be made, and that only
at certain infrequent periods, the discovery of which in the first
instance often taxes the engineer sorely.
Often weeks will be expended in reconnoitring the position, awaiting
a favourable wind and a placid sea. Time to the surveyor must be
no object. He is the sport of the elements, and he must curb his
impatience. To do otherwise is to court disaster. The actual operations
on the rock may only occupy twenty minutes or so, but the task of
landing is equalled by that of getting off again--the latter frequently
a more hazardous job than the former.
The west coast of Scotland is dreaded, if such a term may be used, by
the engineer, because the survey inevitably is associated with bitter
disappointments and maddening delays owing to the caprices of the
ocean. This is not surprising when it is remembered that this coastline
is of a cruel, forbidding character and is exposed to the full reach of
the Atlantic, with its puzzling swell and vicious currents. The same
applies to the west coast of Ireland and the open parts of the South
of England. The Casquets, off the coast of Alderney, are particularly
difficult of approach, as they are washed on all sides by wild races of
water. There is only one little cove where a landing may be effected
by stepping directly from a boat, and this place can be approached
only in the calmest weather and when the wind is blowing in a certain
direction. On one occasion, when I had received permission to visit
the lighthouse, I frittered away three weeks in Alderney awaiting a
favourable opportunity to go out, and then gave up the attempt in
disgust. As it happened, another month elapsed before the rock was
approachable to make the relief.
When the United States Lighthouse Board sanctioned the construction
of the Tillamook lighthouse on the rock of that name, off the Oregon
coast, the engineer in charge of the survey was compelled to wait
six months before he could venture to approach the island. In this
instance, however, his time was not wasted entirely, as there were many
preparations to be completed on the mainland to facilitate construction
when it should be commenced. Early in June, 1879, the weather
moderated, and the Pacific assumed an aspect in keeping with its name.
Stimulated by the prospect of carrying out his appointed task, the
engineer pushed off in a boat, but, to his chagrin, when he drew near
the rock he found the prospects of landing to be hopeless. He cruised
about, reconnoitring generally from the water, and then returned to
shore somewhat disgusted.
A fortnight later he was instructed to take up his position at Astoria,
to keep a sharp eye on the weather, to take the first chance that
presented itself of gaining the rock, and not to return to headquarters
until he had made a landing. He fretted and fumed day after day, and
at last pushed off with a gang of men when the sea where it lapped
the beach of the mainland was as smooth as a lake; but as they drew
near the Tillamook it was the same old story. A treacherous swell
was running, the waves were curling wickedly and fussily around the
islet; but the engineer had made up his mind that he would be balked
no longer, so the boat was pulled in warily, in the face of terrible
risk, and two sailors were ordered to get ashore by hook or by crook.
The boat swung to and fro in the swell. Time after time it was carried
forward to the landing spot by a wave, and then, just as the men were
ready to jump, the receding waters would throw it back. At last, as
it swung by the spot, the two men gave a leap and landed safely. The
next proceeding was to pass instruments ashore, but the swell, as if
incensed at the partial success achieved, grew more boisterous, and the
boat had to back away from the rock. The men who had landed, and who
had not moved a yard from the spot they had gained, became frightened
at this manœuvre, and, fearing that they might be marooned, jumped into
the sea, and were pulled into the boat by means of their life-lines,
without having accomplished a stroke.
[Illustration:
_By permission of the Lighthouse Literature Mission._
THE SANGANEB REEF LIGHTHOUSE IN THE RED SEA.
It indicates a treacherous coral reef, 703 miles from Suez. It is an
iron tower 180 feet high, with a white flashing light having a range of
19 miles.]
The engineer chafed under these disappointments, and himself determined
to incur the risk of landing at all hazards. With his tape-line in
his pocket, he set out once more a few days later, and in a surf-boat
pulled steadily into the froth and foam around the rock; while the men
sawed to and fro the landing-place, he crouched in the bow, watching
his opportunity. Presently, the boat steadying itself for a moment, he
made a spring and reached the rock. He could not get his instruments
ashore, so without loss of time he ran his line from point to point as
rapidly as he could, jotted down hurried notes, and, when the swell was
growing restive again, hailed the boat, and at a favourable moment, as
it manœuvred round, jumped into it.
The details he had secured, though hastily prepared, were sufficient
for the purpose. His report was considered and the character of the
beacon decided. There was some discussion as to the most favourable
situation for the light upon the rock, so a more detailed survey
was demanded to settle this problem. This task was entrusted to an
Englishman, Mr. John R. Trewavas, who was familiar with work under such
conditions. He was a master-mason of Portland and had been engaged
upon the construction of the Wolf Rock, one of the most notable and
difficult works of its kind in the history of lighthouse engineering.
He pushed off to the rock on September 18, 1879, in a surf-boat, only
to find the usual state of things prevailing. The boat was run in, and,
emulating the first engineer’s feat, he cleared the water and landed
on the steep, rocky slope; but it was wet and slippery, and his feet
played him false. He stumbled, and stooped to regain his balance, but
just then a roller curled in, snatched him up and threw him into
the whirlpool of currents. Life-lines were thrown, and the surf-boat
struggled desperately to get near him, but he was dragged down by the
undertow and never seen again. This fatality scared his companions,
who returned hastily to the mainland. The recital of their dramatic
story stirred the public to such a pitch that the authorities were
frantically urged to abandon the project of lighting the Tillamook.
Mr. David Stevenson related to me an exciting twenty minutes which
befell him and his brother while surveying a rock off the west coast
of Scotland. They had been waiting patiently for a favourable moment
to effect a landing, and when at last it appeared they drew in and
clambered ashore. But they could not advance another inch. The rock was
jagged and broken, while its surface was as slippery as ice owing to a
thick covering of slimy seaweed whereon boots could not possibly secure
a hold. Having gained the rock with so much difficulty, they were not
going away empty-handed. As they could not stand in their boots, they
promptly removed them, and, taking their line and levels, picked their
way gingerly over the jagged, slippery surface in their stockinged
feet. Movement certainly was exceedingly uncomfortable, because their
toes displayed an uncanny readiness to find every needle-point on the
islet; but the wool of their footwear enabled them to obtain a firm
grip upon the treacherous surface, without the risk of being upset and
having a limb battered or broken in the process. Twenty minutes were
spent in making investigations under these disconcerting conditions,
but the time was adequate to provide all the details required. When
they had completed the survey and had regained their boat--a matter of
no little difficulty in the circumstances--their feet bore sad traces
of the ordeal through which they had passed. However, their one concern
was the completion of the survey; that had been made successfully and
was well worth the toll exacted in the form of physical discomfort.
[Illustration: THE ALCATRAZ LIGHTHOUSE UNDER CONSTRUCTION.
THE ALCATRAZ LIGHTHOUSE COMPLETED.
This tower off the Californian coast is one of the latest works of the
American Lighthouse Department. It has a range of 21 miles.]
As a rule, on a wave-swept rock which only shows itself at short
intervals during the day, the preparation of the foundations is not
an exacting task. A little paring with chisels and dynamite may be
requisite here and there, but invariably the engineer takes the exposed
surface as the basis for his work. The sea has eaten away all the
soft, friable material in its ceaseless erosion, leaving an excellent
foundation to which the superstructure can be keyed to become as solid
as the rock itself.
When the beacon is to be erected upon a sandy bottom, the engineer’s
work becomes more baffling, as he is compelled to carry his underwater
work down to a point where a stable foundation may be secured. When
the Leasowe lighthouse was built on the sandy Wirral shore, the
builders were puzzled by the lack of a suitable foundation for the
masonry tower. An ingenious way out of the difficulty was effected.
In the vicinity an incoming ship, laden with a cargo of cotton, had
gone ashore and had become a total wreck. The cotton was useless for
its intended purpose, so the bales were salvaged and dumped into the
sand at the point where the lighthouse was to be erected. The fleecy
mass settled into the sand, and under compression became as solid as a
rock, while its permanency was assured by its complete submersion. The
stability of this strange foundation may be gathered from the fact that
the tower erected thereon stood, and shed its welcome light regularly
every night, for about a century and a half, only being extinguished
two or three years ago as it was no longer required.
In the Old World, and, indeed, in the great majority of instances,
the lighthouse is what is described as a “monolithic structure,”
being built of courses of masonry, the blocks of which are dovetailed
together not only laterally, but also perpendicularly, so that, when
completed, the tower comprises a solid mass with each stone jointed
to its fellow on four or five of its six sides. This method was first
tried in connection with the Hanois lighthouse, off the Guernsey coast,
and was found so successful that it has been adopted universally in all
lighthouses which are exposed to the action of the waves.
The upper face and one end of each block are provided with projections,
while the lower face and the other end are given indentations.
Thus, when the block is set in position, the projections fit into
corresponding indentations in the adjacent blocks, while the
indentations receive the projections from two other neighbouring
pieces. The whole is locked together by the aid of hydraulic cement.
Consequently the waves, or any other agency, cannot possibly dislodge
a stone without breaking the dovetails or smashing the stone itself.
For the bottom layer, of course, the surface of the rock is pared away
sufficiently to receive the stone, which is bedded in cement adhering
to both the rock and the superimposed block. A hole is then drilled
through the latter deep into the rock beneath, into which a steel rod
or bolt is driven well home, and the hole is sealed up with cement
forced in under such pressure as to penetrate every interstice and
crevice.
The iron supports constitute the roots, as it were, of the tower,
penetrating deep into the heart of the rock to secure a firm grip,
while the tower itself resembles, in its general appearance, a
symmetrical tree trunk, this form offering the minimum of resistance to
the waves. The lower part of the tower is made completely solid by the
dovetailing of the integral blocks, and is cylindrical in shape up to a
certain predetermined level which varies according to the surrounding
conditions and the situation of the light. Some years ago the
lighthouse assumed its trunk-like shape at the bottom course, rising
in a graceful concave curve to the lantern; but this method has been
abandoned, inasmuch as, owing to the decreasing diameter of the tower
as it rose course by course above its foundations, the lowest outer
rings of masonry did not have to withstand any of the superimposed
weight, which naturally bears in a vertical line. By carrying the
lower part to a certain height in the form of a cylinder, and then
commencing the concave curve of the tower, the pressure of the latter
is imposed equally upon the whole of its foundations. The latter may be
stepped--_i.e._, one tier of stones may project a little beyond that of
the one immediately above--but this arrangement is adopted in order to
break the smashing force of the waves.
The conditions attending the actual building operations upon the
rock, which may be accessible only for an hour or two per day in calm
weather, prevent the blocks of granite being shaped and trimmed upon
the site. Accordingly, the lighthouse in the first place is erected
piecemeal on shore. A horizontal course of stones is laid to see that
each dovetail fits tightly and dead true. The next course is laid upon
this, and so on for perhaps eight or ten courses, the trimming and
finicking being accomplished as the work proceeds. Each projection has
to be only just big enough to enter its relative indentation, while
the latter must be exactly of the requisite dimensions to receive the
projection, and no more. Each stone is then given an identification
mark, so that the masons on the rock may perceive at a glance its
precise position in a course, and to what ring of stones it belongs.
Therefore the mason at the site has no anxiety about a stone fitting
accurately; he has merely to set it in position upon its bed of cement.
On shore--generally in the quarry yard--when a series of courses
have been temporarily built up in this manner and have received the
critical approbation of the resident engineer, the topmost course is
removed and retained, while the other blocks are despatched to the
site. This topmost course forms the bottom ring in the next section
of the lighthouse which is built up in the yard, and the topmost
course of this section in turn is held to form the bottom course of
the succeeding part of the tower, and so on from foundation to lantern
parapet.
During the past two or three years reinforced concrete has been
employed to a certain extent for lighthouse construction, but granite
of the finest and hardest quality still remains the material _par
excellence_ for towers erected in exposed, sea-swept positions. The
Russian lighthouse authorities have adopted the ferro-concrete system
in regard to one or two shore lights, especially on the Black Sea,
while another fine structure upon this principle was built by the
French _Service des Phares_ in 1905 at the entrance to the River
Gironde. The system has also been adopted by the Canadian lighthouse
authorities; one or two recent notable lights under their jurisdiction
have been constructed in this material, although on somewhat different
lines from those almost invariably followed, so far as the general
design is concerned.
While the masonry or monolithic structure is the most durable and
substantial structure, it is also the most expensive. In many parts of
the world, notably along the Atlantic coastline of the United States,
what are known as “screw-pile lighthouses” are used. These buildings
vary in form, some resembling a huge beacon, such as indicates the
entrance to a river, while others convey the impression of being
bungalows or pavilions on stilts. The legs are stout, cylindrical, iron
members, the lower ends of which are shaped somewhat after the manner
of an auger, whereby they may be screwed into the sea-bed--hence the
name. This system has been employed for beacons over dangerous shoals;
and while they are somewhat squat, low-lying lights, they have proved
to be highly serviceable.
Iron has been employed also for lighthouse constructional work,
the system in this case being a combination of the screw pile
and the tower, the latter, extending from a platform whereon the
living-quarters are placed and mounted clear of the water, on piles,
being a huge cylindrical pipe crowned by the lantern. One of the
most interesting and novel of these iron lighthouses is the Hunting
Island tower off the coast of South Carolina. In general design it
resembles the ordinary lighthouse wrought in masonry, and it is 121½
feet in height from the ground to the focal plane. It is built of iron
throughout, the shell being in the form of panels, each of which weighs
1,200 pounds.
This type of tower was selected owing to the severe erosion of the sea
at the point where it is placed. When it was erected in 1875, at a cost
of £20,400, or $102,000, it was planted a quarter of a mile back from
the sea. This action was severely criticized at the time, it being
maintained that the light was set too far from the water’s edge to
be of practical value; but the hungry ocean disappointed the critics,
because in the course of a few years the intervening strip of shore
disappeared, and the necessity of demolishing the light and re-erecting
it farther inland arose. On this occasion the engineers determined to
postpone a second removal for some time. The tower was re-erected at
a point one and a quarter miles inland, and the sum of £10,200, or
$51,000, was expended upon the undertaking. The iron system, which
was adopted, proved its value in this work of removal piece by piece,
because, had the tower been carried out in masonry, it would have been
cheaper to set up a new light, as was done at Cape Henry.
[Illustration: FIG. 1.--SECTIONAL DIAGRAM OF THE AR-MEN LIGHTHOUSE,
SHOWING YEARLY PROGRESS IN CONSTRUCTION.
It guards the “Bay of the Dead,” off Cape Finisterre. Commenced in
1867, it was not finished until 1881.]
Some of the American coast lights are of the most primitive and
odd-looking character, comprising merely a lofty skeleton of ironwork.
The lamp is a head-light, such as is carried by railway engines, fitted
with a parabolic reflector. Every morning the lamp is lowered, cleaned,
and stored in a shack at the foot of the pyramid, to be lighted and
hauled into position at dusk. This is the most economical form of
lighthouse which has been devised, the total cost of the installation
being only about £2,500, or $12,500, while the maintenance charges
are equally low. Lights of this description are employed for the most
part in connection with the lighting of waterways, constituting what
is known as the “back-light” in a range or group of lights studded
along the river to guide the navigator through its twists and shallows,
instead of buoying of the channel.
The task of constructing a sea-rock lighthouse is as tedious and
protracted an enterprise as one could conceive, because the engineer
and his workmen are entirely at the mercy of the weather. Each great
work has bristled with its particular difficulties; each has presented
its individual problems for solution. Few modern lighthouses, however,
have so baffled the engineer and have occupied such a number of years
in completion, as the Ar-men light off Cape Finisterre. This tower
was commenced in 1867, but so great and so many were the difficulties
involved in its erection that the light was not first thrown over the
Atlantic from its lantern until 1881.
This light is situated at one of the most dreaded parts of a sinister
coast. At this spot a number of granite points thrust themselves
at times above the water in an indentation which has received the
lugubrious name Bay of the Dead. The title is well deserved, for it
is impossible to say how many ships have gone down through fouling
these greedy fangs, or how many lives have been lost in its vicinity.
The waters around the spot are a seething race of currents, eddies,
and whirlpools. It is an ocean graveyard in very truth, and although
mariners are only too cognizant of its terrible character, and
endeavour to give this corner of the European mainland a wide birth,
yet storms and fogs upset the calculations of the most careful
navigators.
[Illustration: THE THIMBLE SHOALS LIGHT.
A typical example of the American iron screw pile system. A vessel ran
into this beacon and wrecked it; the ruins caught fire, and the keepers
only escaped in the nick of time.]
As the streams of traffic across the Bay of Biscay grew denser and
denser, it became imperative to provide a guardian light at this
spot, and the engineers embarked upon their task. They knew well that
they were faced with a daring and trying enterprise, and weeks were
spent in these troubled waters seeking for the most favourable site.
As a result of their elaborate surveys, they decided that the rock
of Ar-men offered the only suitable situation; but what a precarious
foundation upon which to lift a massive masonry tower! The hump is only
25 feet wide by 50 feet in length; no more than three little pinnacles
projected above the sea-level, and at low-tide less than 5 feet of the
tough gneiss were exposed. Nor was this the most adverse feature. The
rock is in the centre of the bad waters, and is swept from end to end,
under all conditions of weather, by the furious swell. Some idea of the
prospect confronting the engineers may be gathered from the fact that a
whole year was spent in the effort to make one landing to take levels.
When construction was taken in hand the outlook was even more
appalling. It was as if the sea recognized that its day of plunder was
to draw to a close. The workmen were brought, with all materials
and appliances, to the nearest strategical point on the mainland,
where a depot was established. Yet in the course of two years the
workmen, although they strove day after day to land upon the rock,
only succeeded twenty-three times, while during this period only
twenty-six hours’ work was accomplished! It is not surprising that,
when the men did land, they toiled like Trojans to make the most of the
brief interval. The sum of their work in this time was the planting
of the lighthouse’s roots in the form of fifty-five circular bars,
each 2 inches in diameter and spaced 3¼ feet apart at a depth of about
12 inches in the granite mass. By the end of 1870 the cylindrical
foundation had crept a few feet above the highest projection; this
plinth was 24 feet in diameter, 18 feet in height, and was solid
throughout. A greater diameter was impossible as the wall was brought
almost to the edge of the rock.
By dint of great effort this part of the work was completed by the end
of 1874, which year, by the way, showed the greatest advance that had
been attained in a single twelvemonth. As much of the foundations was
completed in this year as had been achieved during the three previous
years. Although the heavy gales pounded the structure mercilessly, so
well was the masonry laid that it offered quite effective resistance.
Upon this plinth was placed the base of the tower. This likewise is 24
feet in diameter, and about 10 feet in height. It is also of massive
construction, being solid except for a central cylindrical space which
is capable of receiving some 5 tons of coal.
[Illustration:
_By permission of Messrs. Bullivant & Co., Ltd._
SETTING THE LAST STONE OF THE BEACHY HEAD LIGHTHOUSE.]
The base was completed in a single year, and in 1876 the erection
of the tower proper was commenced, together with the completion of
the approaching stairway leading from the water-level to the base of
the structure. The latter, divided into seven stories, rises in the
form of a slender cone, tapering from a diameter of 21½ feet at the
bottom to 16½ feet at the top beneath the lantern. Some idea of the
massive character of the work which was demanded in order to resist
the intense fury of the waves may be realized when it is mentioned
that the wall at the first and second floors is 5½ feet in thickness,
leaving a diameter of 10 feet for the apartment on the first floor,
which is devoted to the storage of water, and of 7 feet for that on
the second floor, which contains the oil reservoirs for the lamps.
The living-rooms have a diameter of 11 feet, this increased space
being obtained by reducing the thickness of the wall to 2½ feet. The
erection of the superstructure went forward steadily, five years being
occupied in carrying the masonry from the base to the lantern gallery,
so that in 1881 for the first time powerful warning was given of a
danger dreaded, and often unavoidable, from the time when ships first
sailed these seas. Fifteen years’ labour and peril on the part of the
engineers and their assistants were crowned with success.
Whereas the Ar-men light off Cape Finisterre demanded fifteen years
for its completion, the construction of the Beachy Head lighthouse off
the South of England coast was completed within a few months. It is
true that the conditions were vastly dissimilar, but the Sussex shore
is exposed to the full brunt of the south-westerly and south-easterly
gales. This lighthouse thrusts its slender lines from the water,
its foundations being sunk into the chalk bed of the Channel, 550
feet from the base of the towering white cliffs, which constitute a
striking background. This beacon was brought into service in 1902, its
construction having occupied about two years. The light formerly was
placed on the crown of the precipice behind, but, being then some 285
feet above the water, was far from being satisfactory, as its rays
were frequently blotted out by the ruffle of mist which gathers around
Beachy Head on the approach of evening.
Indeed, this is one of the great objections to placing a light upon a
lofty headland. In such a position it does not serve as an aid, but
more often than not as a danger, to navigation, owing to the light
being invisible at the time when its assistance is required and sought
most urgently. Consequently lighthouse engineers endeavour to set their
towers at such a level that the light is not raised more than from
160 to 200 feet above the water. In the case of Beachy Head, a further
reason for a new structure was the disintegration of the cliff upon
which the light stood, under the terrific poundings of the sea, huge
falls of chalk having occurred from time to time, which imperilled the
safety of the building.
When the new lighthouse was taken in hand, investigation of the
sea-bed revealed an excellent foundation in the dense hard chalk, and
accordingly a hole 10 feet deep was excavated out of the solid mass
to receive the footings of the building. As the site is submerged to
a great depth at high-tide, the first operation was the erection of
a circular dam carried to a sufficient height to enable the men to
toil within. By this arrangement the working spells were lengthened
considerably, labour only being suspended at high-tide. When the sea
ebbed below the edge of the dam, the water within was pumped out,
leaving a dry clear space for the workmen. Excavation had to be carried
out with pickaxe and shovel, blasting not being permitted for fear of
shattering and splitting up the mass forming the crust of the sea-bed.
Beside the site a substantial iron staging was erected, and from
this point to the top of the cliffs behind a Bullivant cableway was
stretched, up and down which the various requirements were carried,
together with the workmen. This cableway, designed by Mr. W. T. H.
Carrington, M.I.C.E., consulting engineer to Messrs. Bullivant and Co.,
Ltd., facilitated rapid and economical construction very appreciably.
The span was about 600 feet between the erecting stage and the cliff
summit, and there were two fixed ropes stretched parallel from point
to point. One rope, 6 inches in diameter, had a breaking strain of 120
tons; the second, 5½ inches thick, had a breaking strain of 100 tons.
At the seaward end the cables were anchored into the solid chalk.
Everything required for the constructional operations was handled by
this carrying system, and when it is recalled that some of the blocks
for the lower courses weighed from 4½ to 5 tons, it will be recognized
that such a method of handling these ungainly loads, with the care
that was demanded to preserve the edges and faces from injury, solved
an abstruse problem completely.
The base of the tower, the diameter of which is 47 feet, is solid to
a height of 48 feet, except for a central circular space for storing
drinking water. It was designed by Sir Thomas Matthews, M.I.C.E., the
Engineer-in-Chief to the Trinity Brethren, and is a graceful building,
the tower rising in a curve which is described as a “concave elliptic
frustum.” From the base to the lantern gallery is 123½ feet, and 3,660
tons of Cornish granite were used in its construction. The over-all
height to the top of the lantern is 153 feet. The building is provided
with eight floors, comprising the living and sleeping quarters for
the keepers, storage of oil, and other necessaries. The light, of
the dioptric order, is of 83,000 candle-power, and the two white
flashes given every fifteen seconds are distinguishable for a distance
of seventeen miles, which is the average range of modern British
lighthouses.
Although the constructional work was frequently interrupted by rough
weather, every advantage was taken of calm periods. While from the
point of daring engineering it does not compare with many of the other
great lights of the world, yet it certainly ranks as a fine example
of the lighthouse builder’s skill. Owing to the elaborate precautions
observed, the achievement was not marred by a single fatality, although
there were many thrilling moments, the sole result of which, however,
was the loss of tools and sections of the plant, which in the majority
of cases were recovered when the tide fell. The most serious accident
was a crushed toe, which befell one of the masons when a stone was
being bedded.
Although the lighthouse is subjected to the full fury of wind and wave,
if skilfully erected it will withstand the ravages of both without
creating the slightest apprehensions in the engineer’s mind. The stones
are prepared so carefully that they fit one another like the proverbial
glove, while the cement fills every nook and cranny. Occasionally,
however, the cement will succumb to the natural disintegrating forces,
and, becoming detached, reveal a point vulnerable to attack. The air
within the interstice becomes compressed by the surging water, and
thereby the fabric is liable to be shattered. Some years ago one or
two of the lighthouses guarding the Great Lakes of North America
were found to have become weakened from this cause. A novel remedy
was evolved by an ingenious engineer. He provided each tottering
lighthouse with an iron overcoat, enveloping it from top to bottom.
The metal was not laid directly upon the masonry, but was so placed
as to leave about a quarter of an inch between the inner face of the
metal and the surface of the masonry. Liquid cement was then admitted
under pressure--“grouting” it is called--into this annular space,
and penetrating every crack and crevice in the masonry, and adhering
both to the metal and the stonework, it practically formed another
intermediate jacket, binding the two so firmly together as to make them
virtually one. This novel procedure absolutely restored the menaced
building to its original homogeneity and rigidity, so that it became as
sound as the day on which it was built.
Nowadays, owing to the skill in designing and the workmanship
displayed, one never hears of a modern lighthouse collapsing. Expense
is no object; the engineer does not endeavour to thwart the elements,
but follows a design wherein the minimum of resistance is offered to
them.