Smeaton and Lighthouses Part 5

The foundation pit having a.s.sumed the appearance of a large even platform, and the tides being favourable, it was determined to lay down the first course, which consisted of a few irregular and detached stones for making up certain inequalities in the interior parts of the site of the building. Having taken the dimensions of the first or foundation stone, a model of its figure was made, and this was taken by the engineer in a fast-rowing boat to the work-yard at Arbroath: two men were immediately set to work upon one of the blocks from the Mylnefield quarry, and as the stone-cutters relieved each other, and worked without intermission, the stone was soon prepared, and sent off next day in one of the stone-lighters. On the 9th July the stone was placed in a praam-boat, decorated with colours for the occasion. Flags were also displayed upon the beacon and from the shipping in the offing. The stone was gently lowered into the water, which occupied the site of the building, amidst the cheering of all present. The stone was necessarily landed at high water, for want of a sufficient length of railway for conveying it along the rock at low water to the site of the building.

On the 10th July the sailors displayed their flags at all points, and as many as could be spared from the floating-light and the tenders landed to witness the long desired ceremony of laying the first stone of the lighthouse. The importance of the building was such, that but for the perilous and uncertain nature of any arrangement which could have been made for this ceremony, instead of its having been performed only in the presence of those immediately connected with the work, and a few casual spectators from the neighbouring sh.o.r.e, reckoning in all about eighty persons, many thousands would have attended upon an occasion which must have called forth the first dignitaries of the country in conferring upon it the highest honours of masonry.

At eleven o'clock the foundation stone was laid to hand. It was square in form, and contained about twenty cubic feet, and had no other inscription than the date 1808. The engineer, attended by his three a.s.sistants, applied the square, the level, and the mallet, and p.r.o.nounced the following benediction: 'May the Great Architect of the universe complete and bless this building.' Three hearty cheers were then given, and success to future operations drunk with the greatest enthusiasm. When the tide began to overflow the site the whole party returned to the ship; prayers were read, and every heart, doubtless, felt more than usually thankful.

The first continuous course was now landed on the rock and laid down.

Mr. Stevenson gives an enumeration of the various kinds and quant.i.ty of the work in this single course. Although only one foot in thickness it contained five hundred and eight cubic feet of granite in outward casing; eight hundred and seventy-six cubic feet of Mylnefield stone in the hearting; one hundred and four tons of solid contents; one hundred and thirty-two superficial feet of hewing in the face-work; four thousand five hundred and nineteen superficial feet of hewing in the beds, joints, and joggles; four hundred and twenty lineal feet boring of trenail holes; three hundred and seventy-eight feet lineal cutting for wedges; two hundred and forty-six oaken trenails; three hundred and seventy-eight oak-wedges in pairs.

In the work-yard about sixty men were employed in hewing and preparing the various courses of the solid part of the building. The second course, which contained some very weighty stones, was laid down upon the platform in the middle of the yard, each stone being carefully fitted and marked as it was to lie in the building.

By the end of this season the building was brought to a level with the highest part of the margin of the foundation pit, or about five and a half feet above the lower bed of the foundation-stone. The number of hours work upon the rock this season at low water amounted to about two hundred and sixty-five, of which number only eighty were employed in building.

The third season was commenced early in the spring of 1809. The first works consisted in laying down mooring-chains with floating-buoys, for mooring the stone-lighters and praam-boats; the beacon was also fitted out as a more permanent residence for the workmen, in order to lessen the amount of sickly motion which is so distressing to landsmen in a rough sea. By the end of June the men were able to work upon the masonry while the rock was under water; and on the 8th July, for the first time, the tide ceased to overflow the building at low water.

With considerable exertion the solid part of the building, which reached to the height of thirty feet, was completed by September. By continuing the works a month or two longer a much greater height might have been attained, but as the engineer foresaw that a diligent employment of the next season would suffice for the completion of the work, he deemed it advisable to leave the house in its present solid defensible posture, on which the sea had much less hold, than if part of the hollow portion had been built.

The winter months were occupied in preparing the upper courses; but in consequence of severe frosts, several excellent and valuable stones from the Mylnefield quarry were destroyed by absorption of moisture from the air, which moisture expanding in the act of freezing, split the stones, and rendered them useless. It was therefore determined to construct the cornice of the building, and the parapet of the light-room of the Liver Rock, of the Craig-Leith quarry, celebrated for its durability and beauty, and for its property of not being liable to be affected by the action of frost. These stones were prepared at Edinburgh during the winter, and the iron frame-work, and the several compartments of the light-room got ready.

Having during two seasons landed and built upwards of one thousand four hundred tons of stone upon the rock, while the work was low down in the water, and before the beacon was habitable; and finding that it did not now require more than about seven hundred tons to complete the masonry, there was every prospect of finishing the lighthouse during the season. But as the success of the work depended wholly upon the stability of the beacon, every possible attention was bestowed upon it, and visits made to the rock during the winter months when the weather would allow.

On the 10th of May operations for the season were commenced. The building to the height of fifteen feet above the rock was found to be thickly covered with fuci: on the east side the growth of sea-weed was observed to the full height of thirty feet, and even on the top or upper bed of the last-laid course it had grown so as to render walking somewhat difficult. The men therefore set to work to sc.r.a.pe off the sea-weed, in order to apply the moulds of the first course of the staircase. The engineer had also to fix the position of the entrance-door, which was regulated chiefly by the appearance of the growth of the sea-weed on the building, indicating the direction of the heaviest seas, on the opposite side of which the door was placed.

The artificers now took permanent possession of the beacon, and were all heartily rejoiced at getting rid of the trouble of boating, and the sickly motion of the tender. The beacon, which has been so often named, and which proved a source of so much comfort to the men, and of benefit and dispatch to the work, stood well during the five years that its services were required. In its present complete form it consisted of three floors, one of which was occupied as the cook-house and provision store; the second, which was much enc.u.mbered by the meeting of the princ.i.p.al beams, formed only two cabins, one for the engineer, and the other for the foreman. In the third compartment were three rows or tiers of beds, capable of accommodating about thirty men. Below these three floors was the temporary floor at the height of twenty-five feet above the rock, used for preparing mortar and for the smith's workshop. The beacon was connected with the building by a gangway, or bridge of timber.

Mr. Stevenson has given an interesting description of his cabin in the beacon, where he had pa.s.sed many weeks 'in a kind of active retirement, making practical experiment of the fewness of the positive wants of man.' This cabin measured not more than four feet three inches in breadth on the floor; and though, from the oblique direction of the beams of the structure, it widened towards the top, yet it did not admit of the full expansion of his arms when he stood on the floor, while its length was little more than sufficient for suspending a cot-bed during the night. This was tied up to the roof during the day, thus leaving free room for the admission of occasional visitants.

'His folding-table was attached with hinges immediately under the small window of the apartment, and his books, barometer, thermometer, portmanteau, and two or three camp-stools, formed the bulk of his moveables. His diet being plain, the paraphernalia of the table were proportionably simple, though every thing had the appearance of comfort, and even of neatness, the walls being covered with green cloth formed into panels with red tape, and his bed festooned with curtains of yellow cotton-stuff. If, in speculating upon the absolute wants of man in such a state of seclusion, one was reduced to a single book, the Sacred Volume, whether considered for the striking divinity of its story--the morality of its doctrine--or the important truths of its Gospel, would have proved by far the greatest treasure.'

As the building rose in height the action of the sea upon it was regarded with much interest. When the wind was blowing, accompanied with a heavy surf upon the rock, the appearance towards high water is described as being very grand and wonderful. Waves of considerable magnitude rose as high as the solid or level of the entrance-door which was to the leeward; but on the windward side the sprays flew like lightning up the sloping sides of the building, occasionally wetting the artificers, and interrupting their operations on the top of the walls.

In the early part of July, the works being nearly completed, great interest was excited by a visit from Mrs. d.i.c.kson, the only daughter and surviving relative of Mr. Smeaton. She was conveyed to the building on board the 'Smeaton,' which had been thus spontaneously named by the engineer from the sense of the obligation which a public work of the description of the Bell Rock owed to the labours and abilities of Mr. Smeaton. Mrs. d.i.c.kson seemed to be quite overcome with the many concurrent circ.u.mstances which tended in a peculiar manner to revive and enliven the memory of her departed father.

The 29th of July was a day of great rejoicing at the Bell Rock. The last stone was landed, and that it might lose none of its honours, the same praam-boat with which the first stone of the building had been landed was appointed also to carry the last. The weather being remarkably fine, all the ships and the craft hoisted flags; the praam which carried the stone was towed by the seamen in gallant style to the rock, and on its arrival cheers were given as a finale to the landing department. On the next day, the ninetieth or last course of the building having been laid, the lintel of the light-door room, being the finishing stone of the exterior walls, was laid with due formality by the engineer, who at the same time p.r.o.nounced the following benediction, 'May the Great Architect of the Universe, under whose blessing this perilous work has prospered, preserve it as a guide to the mariner.'

The remaining details, referring chiefly to the completion of the interior of the lighthouse, are not of general interest. They were so far advanced by the end of the year 1810, that the light was advertised to the public to be exhibited every night from the 1st of February 1811. The advertis.e.m.e.nt stated the following particulars:--'The light will be from oil, with reflectors placed at the height of about one hundred and eight feet above the medium level of the sea. To distinguish this light from others on the coast, it is made to revolve horizontally, and to exhibit a bright light of the natural appearance, and a red-coloured light alternately, both respectively attaining their greatest strength, or most luminous effect, in the s.p.a.ce of every four minutes; during that period the bright light will, to a distant observer, appear like a star of the first magnitude, which after attaining its full strength is gradually eclipsed to total darkness, and is succeeded by the red-coloured light, which in like manner increases to full strength and again diminishes and disappears.

The coloured light, however, being less powerful, may not be seen for a time after the bright light is first observed. During the continuance of foggy weather and showers of snow, a bell will be tolled by machinery, night and day, at intervals of half a minute.' By this management the light was found to be so powerful as to be seen and readily distinguished at the distance of six or seven leagues in a clear atmosphere. On the exhibition of this light the floating light was discontinued.

Having thus traced the building through some of its princ.i.p.al stages, a brief view in its complete state may here be desirable. This lighthouse is a circular building, forty-two feet in diameter at the base and thirteen feet in diameter at the top. The masonry is one hundred feet high, and the whole structure, with the light-room, measures one hundred and fifteen feet. The ascent from the rock to the entrance-door is by a kind of trap-ladder, which is a difficult mode for any but the light-keepers, who are accustomed to it. Other persons are generally hoisted up in a chair by a moveable crane. From the entrance a circular stair leads to the first apartment, which contains the water, fuel, &c. The communication with the other apartments is by means of wooden steps. The three lower apartments have two windows each, and the upper rooms four windows each. All the windows have double sash-frames, glazed with plate-gla.s.s, besides storm-shutters of timber. The light-room is octagonal, twelve feet across and fifteen feet high. It is framed of cast iron and glazed with polished plate-gla.s.s, each plate measuring two feet six inches by two feet three inches, and being one-fourth of an inch thick. It is covered with a dome and terminates in a ball. It is also furnished with a lightning-conductor. In the year 1816, the whole exterior surface having become much discoloured by the sprays of the sea, was painted in oil of one uniform tint.

In the course of the first winter some interesting observations were made upon the action of the weather and the general appearance of the lighthouse. During rough weather a tremulous vibratory motion was found to affect the whole house. The tremour was especially felt in leaning against the walls in the upper apartments when the wind was blowing fresh, or when the house was struck by a sea or by a boat coming suddenly against it, and might be compared to that which is perceptible in a common house upon the slamming of particular doors, or when a carriage makes a rattling noise in pa.s.sing along the streets. But this effect is attended with no real danger. The late eminent Professor Robison told Mr. Stevenson that when he visited the Eddystone Lighthouse, something having forcibly struck the building, he was sensible of a vibratory motion in one of the rooms in which he was then sitting; but instead of producing any alarm in his mind, he a.s.sured his friends that it was to him the strongest proof of the unity and connection of the fabric in all its parts.

During the storms of winter, Mr. Stevenson says that from the Forfarshire coast 'the lighthouse appeared in one of its most interesting aspects, standing proudly among the waves while the sea around it was in the wildest state of agitation. The light-keepers did not seem to be in motion, but the scene was by no means still, as the noise and dashing of the waves were unceasing. The seas rose in the most surprising manner to the height of about seventy feet above the rock, and after expending their force in a perpendicular direction, fell in great quant.i.ties round the base of the lighthouse, while considerable portions of the spray were seen adhering, as it were, to the building, and gathering down its sides in the state of froth as white as snow. Some of the great waves burst and were expended upon the rock before they reached the building; while others struck the base, and embracing the walls, met on the western side of the house, where they dashed together and produced a most surprising quant.i.ty of foam.'

The regulations observed in attending the Bell-Rock may be briefly stated. The nearest town to the lighthouse is that of Aberbrothock, or Arbroath, in Forfarshire, about eleven miles distant. A handsome cutter, called 'The Pharos,' is stationed here as a tender to the lighthouse. This vessel goes off to the rock every fortnight, or in the course of each set of spring-tides, to relieve the light-keepers and to supply the house with fuel, provisions, &c. There are four lighthouse-keepers, three of whom are always on duty, while one is ash.o.r.e. If the weather offers no impediment, the light-keepers are each six weeks at the rock and a fortnight ash.o.r.e with their families. The salaries are from fifty to sixty guineas per annum, with a stated allowance for each man of bread, beef, b.u.t.ter, oatmeal, vegetables, and small-beer, with fourpence a day extra for tea, &c.

They have also a suit of uniform clothes every third year. Mr.

Stevenson says that the light-keepers were, upon the whole, pleased with their situation, and talked in a feeling manner of the hardships of mariners whom they often saw tossed about during the storms of winter.

According to the present system of Northern lighthouses, the watches in the light-room are as regularly relieved as on ship-board. The keeper is liable to immediate dismissal if he leave the light-room before being regularly relieved; and for securing order and regularity in this respect a time-piece is placed in each light-room, and bells are hung in the bed-rooms of the dwelling-houses. At some of the stations the light-room and the bed-rooms are connected by a set of tubes, by blowing gently into which the keepers on watch can sound an alarum-bell in the room below, and rouse his comrade to change guard.

The man below answers this call by a counterblast through the tubes, and a small index in the light-room is thereby raised to signify that the signal has been obeyed.

At Arbroath suitable buildings are erected for the light-keepers'

families, with each a piece of enclosed ground, and a seat in the parish-church. Connected with these buildings are store-houses, a room for the master and crew of the attending vessels, and a signal-tower fifty feet high, at the top of which is a small observatory furnished with an excellent achromatic telescope, a flag-staff, and a copper signal-ball measuring eighteen feet in diameter. By means of this and a corresponding ball at the lighthouse, daily signals are kept up to signify when _all is well_. Should the ball at the rock be allowed to remain down, as is the case when anything is particularly wanted, or in the event of sickness, the tender immediately puts out to sea.

The expense of this great national undertaking, together with the buildings at Arbroath, the attending vessel, and the first year's stores, amounted to about sixty-one thousand three hundred and fifty pounds.

We cannot close this notice of the Bell Rock lighthouse without recording a curious accident which occurred on the night of the 9th February, 1832, about 10 o'clock. A large-herring gull struck one of the south-eastern mullions of the light-room with such force, that two of the polished plates of gla.s.s measuring about two feet square and a quarter of an inch thick, were shivered to pieces, and scattered over the floor, to the great alarm of the keeper on watch, and the other two inmates, who rushed instantly into the light-room. It happened fortunately, that although one of the red shaded sides of the reflector-frame was pa.s.sing in its revolution at the moment, the pieces of broken gla.s.s were so minute, that no injury was done to the valuable red gla.s.s. The gull was found to measure five feet between the tips of the wings. In its gullet was found a large herring, and in its throat a piece of plate-gla.s.s about an inch in length.

While the Bell-Rock lighthouse was in progress, Mr. Stevenson was often struck with the frequent and distressing occurrence of shipwrecks at the Carr Rock. The Carr forms the seaward termination of a reef of sunken rocks which appear at low water, extending about a mile and three quarters from the sh.o.r.e of Fifeness, on the northern side of the entrance of the Frith of Forth. The very dangerous position of this rock, as a _turning point_ in the navigation of the northern-bound shipping of the Frith, required that this rock, in connection with the several lighthouses of the Bell Rock, Isle of May, and Inchkeith, should be made as easily distinguishable to the mariner as possible. In the course of nine years no fewer than sixteen vessels had been either lost or stranded on the Carr Rocks. Therefore, in 1809, moorings were laid down for a floating buoy, 'but owing to the heavy swell of sea and the rocky sand-stone bottom on this part of the coast, it was found hardly possible to prevent the buoy from occasionally drifting, even although it had been attached to part of the great chain made from bar-iron an inch and a half square, with which the Bell-Rock floating-light had been moored for upwards of four years without injury. The moorings of the Carr Rock buoy, from the continual rubbing upon the sand-stone bottom, were worn through with the friction in the course of ten months; and during the four years which it rode here, though regularly examined and replaced in the proper season of the year, it was no less than five times adrift, to the great inconvenience and hazard of shipping.'

Such being the case, it was resolved, however difficult and perilous the undertaking, to erect a beacon of masonry upon the rock. The length of the Carr Rock, from north to south, measures seventy-five feet, but its greatest breadth, as seen at low-water of spring-tides, is only twenty-three feet; hence it was not possible to obtain a base for a building of greater diameter than eighteen feet. The surface of the rock was also so rugged that it was necessary to excavate part of the foundation-pit of the building to the depth of seven feet. The difficulties were still further increased on account of the foundation being partly under the level of the lowest tides, so that a coffer-dam was required. It was further necessary, after each tide's work, to remove and carry ash.o.r.e part of this coffer-dam; so that on the return of the workmen at ebb-tide much time was lost in readjusting the coffer-dam, and in pumping the water out of the foundation-pit.

Some idea may be formed of the difficulties attending the early stages of this work, from the fact that during the whole of the first season, or summer of 1813, the workmen could not command more than forty-one hours' work upon the rock; during the second season the time was only fifty-three hours. These two years were entirely occupied in excavating and preparing the foundation, and in laying ten stones, or the half course of masonry, which brought the foundation to a uniform level for the first entire course of the building. Mr. Stevenson contrasts this slow progress with that made at the Bell Rock during the first two seasons. Although this building was situated twelve miles from the sh.o.r.e, three courses were erected, the diameter of the base being forty-two feet, besides the erection of a beacon-house or barrack for the workmen. 'The establishment for the works at the Bell Rock was of course on a much larger scale than that of the Carr Rock; but still the latter was equally effective, and the same apparatus, artificers, and seamen, were employed at both.'

During the third year's work, the second course of the masonry was completed upon the Carr; and nine stones of the third course were laid by the 3rd of October, when a heavy ground-swell obliged the workmen precipitately to leave the rock and take to their boats. Before the cement was fixed, the surge of the sea had washed it out; the oaken trenails were wrenched off, and the whole of the nine blocks of stone swept off the rock and lost in deep water, though they had been completely dove-tailed and fitted on the same principles as the masonry of the Bell-Rock lighthouse, where not a single stone was lost during the whole progress of the work.

During the fourth season, the operations were r.e.t.a.r.ded by several untoward accidents. The wind and the waves sometimes destroyed in a moment the labour of weeks; but by dint of skill and untiring patience and industry, they succeeded by the month of November in completing the sixteenth course, which raised the building to the height of about twenty feet.

The fifth year was particularly unfortunate. The whole of the masonry having been completed, the coast was visited in November with a gale of wind, accompanied with a heavy swell of sea, which washed down the upper part of the building, and reduced it to the height of the fifth course, which formed part of the fourth year's work. It was therefore determined to modify the original design of the work. Instead of completing this beacon with masonry, and providing the machine and large bell, which was to have measured five feet across the mouth, to be tolled by the alternate rise and fall of the tide, it was now determined to erect six columns of cast iron upon the remaining courses of masonry, to terminate in a cast iron ball of the diameter of three feet, formed in ribs, elevated about twenty-five feet above the medium level of the sea. This beacon was completed in September 1821.

FOOTNOTES:

[Footnote 5: Lines written by Sir Walter Scott in the Alb.u.m of the Bell-Rock Lighthouse, when he visited it in 1814.]

CHAPTER VIII.

LIGHTHOUSES ON SAND AND CAST-IRON LIGHTHOUSES.

Floating Lights--Objections to--Mitch.e.l.l's Screw-moorings-- Experiments on the Maplin Sand--Foundation--Erection of Screw-pile Lighthouse--Details of the Wyre Lighthouse--Proposed Lighthouse on the Goodwin Sands--Metallic Lighthouses--Advantages of Metal over Stone--Details of Cast-iron Lighthouse at Morant Point, Jamaica.

Those dangerous approaches to a coast which, from the nature of the soil, have not till very lately admitted of the erection of a permanent lighthouse, are usually indicated to the navigator by floating lights; but these being nothing more than large lanterns suspended in the rigging of a vessel, necessarily possess but feeble illuminating power. This power is still further diminished in a gale of wind, when it is most wanted, by the pitching and floundering about of the vessel: every now and then she is submerged in the trough of the sea, covered with spray and drift, or, what is most to be dreaded, she is liable to be blown away from her moorings; an accident which has been productive of the most disastrous consequences to life and property.

The details already given will convey some notion of the difficulty and danger of planting a lighthouse on the solid rock in a stormy sea; we may naturally suppose that this difficulty and danger must be enormously increased in erecting a permanent residence on the shifting sands. Such, however, is by no means the case; one of the recent triumphs of engineering has proved that it is not always folly to build a house upon the sand.

This remarkable result has been accomplished chiefly by means of Mitch.e.l.l's screw-mooring, an instrument which consists essentially of an enormous cast-iron screw of about one turn and a half, having a hollow cylindrical centre; a wrought-iron spindle pa.s.ses through the cylindrical socket; it is somewhat tapering in form, and when driven up tight is fixed thereto by a forelock pa.s.sing through both; it is formed with a square head to receive the key for s.c.r.e.w.i.n.g it into the ground. It is also furnished with a collar of wrought iron fitted so as to turn freely on the upper part of the shaft of the spindle below the collar.

The attention of the Trinity House having been called to this instrument, it was considered applicable to the establishment of lighthouses on sands; and accordingly a series of experiments was undertaken at the cost of that honourable body. The spot selected for the purpose was on the verge of the Maplin Sand lying at the mouth of the Thames, about twenty miles below the Nore, forming the north side of the Swin or King's Channel, which, on account of its depth, is much frequented by large ships, as also by colliers and other vessels from the north sea. The sand is shifting, and is dry at low water spring-tides, and hitherto a floating light has been maintained upon it. On this spot it was proposed to erect a fixed lighthouse of timber framing, with a lantern and residence for the attendants.

In the month of August 1838, operations were commenced by inserting nine of Mitch.e.l.l's patent mooring-screws, each four feet and a half in diameter, and furnished with shafts of wrought iron about twenty-five feet in length and five inches thick. One of these screws served as a centre to the remainder, which occupied the angles of an octagon forty-two feet in diameter. The screws were turned into the sands to the depth of twenty-one feet and a half, the upper extremities being left standing about five feet above the surface of the sands. For the purpose of fixing the screws, a stage or raft of timber, thirty feet square, was floated over the spot, with a capstan in the centre, which was made to fit on the top of the iron shaft, and firmly keyed to it.

A power of about thirty men was employed for driving the screws, and their labours were continued until their united force could scarcely turn the capstan. This stage or raft, which had been formed in two thicknesses crossing each other at right angles, and bolted at their intersection, was, as a precautionary measure, allowed to remain. It covered the whole site within the piles, and also extended some distance beyond them. A curb about eighteen inches high was raised round this stage; on its surface was arranged a quant.i.ty of brushwood, and then about two hundred tons of rough stone, which sunk the stage into the sand and prevented it from being displaced. Between the s.p.a.ces of the stage and the brushwood the sand was allowed to wash its way, and it soon filled the interstices of the stone. The whole ma.s.s soon became embedded below the surface of the sand, and gave considerable lateral support to the piles, and formed a solid body for the water to wash upon.

In this state the whole was allowed to remain for about two years, during which time every change in the surface of the sand was observed, and although early in the year 1839 violent storms occurred, yet the screw-piles stood firmly, and the sand at no time was lowered more than three feet. In August 1840 the raft was found to have completely settled down, the piles were as firm as if they had been screwed into clay; a lighthouse was therefore erected within the short s.p.a.ce of three months; and on the 16th February, 1841, a dioptric fixed light was exhibited off this dangerous spot, and was visible ten miles off in all directions.

But while the preparatory steps for this lighthouse were being taken, a screw-pile lighthouse was begun and completed at Port Fleetwood on the Wyre, near Lancaster; which being the first of the kind ever constructed, deserves particular notice.

The preparatory stages were of a similar nature to those already described. The foundation was formed of seven screw-piles, six occupying the angles of a hexagon forty-six feet in diameter, and the seventh being placed in the centre. From each screw proceeded a pile fifteen feet in length, at the upper end of which was another screw for securing a wooden column. These columns were prepared of Baltic timber; the one in the centre was fifty-six feet, and each of the remainder forty-six feet in length, bound firmly round with iron hoops and coated with pitch.