Smeaton and Lighthouses Part 2

Of the other two light-keepers, one, named Henry Hall, had received injuries of a most serious nature; and his case is not a little extraordinary. At the time of the fire, there was, according to the usual custom, a tub of water standing in the lantern of the lighthouse; and when this man perceived the flames, he immediately exerted himself to the utmost in throwing buckets of water up into the roof of the cupola. As he was doing this, and looking upwards to see the effect of his endeavours, a quant.i.ty of lead, dissolved by the heat of the flames, suddenly rushed from the roof, and fell upon his head, face, and shoulders, burning him in a severe manner. At this moment his mouth happened to be open, and he persisted in declaring that some lead had gone down his throat, and was the cause of violent internal pain. When removed to his cottage at Stonehouse, he invariably told Dr. Spry, the medical man who attended him, and who constantly administered the proper remedies for the burns and injuries he had received, that if he would do anything effectual to his recovery, he must relieve his stomach of the lead, which he was sure it contained. This story appeared quite incredible to Dr. Spry, who did not believe that any human being could exist after receiving melted lead into the stomach; much less that he should afterwards be able to bear towing through the sea from the rock; and also the fatigue and inconvenience from the length of time employed in getting him ash.o.r.e, before any remedies could be applied. The man went on without much change for the better or for the worse. He took medicines, and swallowed many things both liquid and solid, until the tenth or eleventh day, when he suddenly grew worse, and on the twelfth day, being seized with cold sweats and spasms, he soon afterwards expired. On a subsequent examination of the stomach, Dr. Spry found, to his astonishment, a solid piece of lead of a flat oval form, which weighed seven ounces and five drachms. Smeaton saw this piece of lead, and observed that part of the coat of the stomach had firmly adhered to the convex side of it. Dr. Spry transmitted an account of this very singular case to the Royal Society: but it was not received with entire belief until he had, by subsequent experiments upon animals, borne out the fact that it is _possible_ for melted lead to be received into the stomach without the immediate death of the sufferer; though more probable that, in the great majority of cases, instant death would be the result.

But to return to the Eddystone rock. Notwithstanding every exertion was made to subdue the flames, the lighthouse was totally consumed, even to the ma.s.sive foundations, and nothing was left upon the rock but a number of the iron cramps and branches.

The value of a lighthouse on the Eddystone rock had now been so fully proved, that no time was to be lost in endeavouring to build a new one in the place of that which had been so unfortunately destroyed. An application was made to the President of the Royal Society, requesting him to point out a person who might appear worthy to be entrusted with the work. Lord Macclesfield (the then president) replied 'that there was one of their own body whom he could venture to recommend to the work; yet that the most material part of what he knew of him was his having within the compa.s.s of the last seven years recommended himself to the society by the communication of several mechanical contrivances and improvements; and though he had at first made it his business to execute things in the instrument way (without ever having been bred to the trade), yet on account of the merit of his performances he had been chosen a member of the society; and that for about three years past, having found the business of a philosophical instrument maker not likely to afford an adequate recompence, he had wholly applied himself to various branches of mechanics.' The earl went on to say that this person was then in Scotland, or in the north of England, and he should recommend the statement of the business to him, being fully confident that he would undertake nothing which he did not feel himself competent to perform.

The person thus referred to was John Smeaton, whose history, so far as the scanty materials will allow, shall here be given to the reader.

FOOTNOTES:

[Footnote 3: It was commonly said at the time, that during a hard gale the sea ran so high that it was very possible for a six-oared boat to be lifted by the waves, and driven through the open gallery of the lighthouse.]

CHAPTER IV.

BIOGRAPHICAL NOTICE OF SMEATON.

Birth of Smeaton--His early Character and Employments--Educated for an attorney--His dislike of that profession--Becomes Philosophical Instrument Maker--His Scientific Inquiries--Is appointed to build the Eddystone Lighthouse--His subsequent Employments--Public Works designed and completed by him--His Literary Works--His last Illness and Death--His Character-- Ill.u.s.trative Anecdotes.

John Smeaton was born the 28th of May, 1724, at Ansthorpe, near Leeds, Yorks.h.i.+re. Little is recorded of his parentage or early education: but we find that his father was a respectable attorney, and that the family lived in a house built by the grandfather of the younger Smeaton.

Smeaton seems to have been born an engineer. The originality of his genius and the strength of his understanding appeared at a very early age. His playthings were not the toys of children, but the tools men work with; and his greatest amus.e.m.e.nt was to observe artificers at work, and to ask them questions. Having watched some millwrights at work, he conceived the idea of constructing a windmill, and to the alarm of his friends was one day perceived on the top of his father's barn attempting to fix his model. On another occasion he accompanied some men who went to fix a pump at a neighbouring village, and observing them cut off a piece of bored pipe, he managed to procure it, and made a working model of a pump that raised water very well.

These anecdotes are related of him while he was yet a mere child in petticoats, and probably before he had attained his sixth year. At the age of fourteen or fifteen he had made for himself an engine to turn rose-work, and he made several presents to his friends of boxes in wood and ivory, as specimens of its operation.

In the year 1742, Mr. Holmes, afterwards his partner in the Deptford Water-works, visited Smeaton and could not conceal his astonishment at the mechanical skill displayed by the young engineer; he forged his iron and steel, and melted his metal; he had tools of every sort for working in wood, ivory, and metals. He had made a lathe, by which he had cut a perpetual screw in bra.s.s, a thing very little known at that day. All these resources were not furnished to him by rich and wealthy parents, nor had he the advantage of masters in his various pursuits; on the contrary, by the strength of his genius, and by indefatigable industry, he acquired at the age of eighteen an extensive set of tools, and the art of working in most of the mechanical trades, and Mr. Holmes, himself a good mechanic, says that few men could work better.

Astronomy was one of his most favourite studies, and he contrived and made several astronomical instruments for himself and friends. In later years, after fitting up an observatory at his house at Ansthorpe, he devoted much time to it when he was there, even in preference to engineering.

Smeaton's father being an attorney was desirous to educate his son for the same profession. He was therefore sent to London in 1742, where during a few terms he attended court; but finding the legal profession distasteful to him, and not to suit "the bent of his genius," he wrote a strong memorial on the subject to his father, who had the good sense to allow him from that time to pursue the path which nature pointed out to him. He continued to reside in London, and about the year 1750 he commenced the business of mathematical instrument maker. In 1751 he invented a machine to measure a s.h.i.+p's way at sea, and a compa.s.s of peculiar construction, touched by Dr. Knight's artificial magnet. He made two voyages in company with Dr. Knight for the purpose of ascertaining the merits of these contrivances.

In 1753 he was elected a fellow of the Royal Society, and his admirable papers inserted in the Transactions of that body sufficiently evince how highly he deserved that distinction. In 1759 he received by an unanimous vote their gold medal, for his paper ent.i.tled 'An Experimental Inquiry concerning the natural powers of wind and water to turn mills and other machines depending on a circular motion.' This paper was the result of experiments made on working models in 1752 and 1753, but not communicated to the society till 1759, by which time he had had abundant opportunity of applying these experiments to practice in a variety of cases, and for various purposes, so as to a.s.sure the society that he had found them to answer. He discovered by these means that wind and water could be made to do one third more than was before known. In the year 1754 he made a voyage to Holland, travelling for the most part on foot, or in the trekschuiten or drag-boats, the national conveyance of the country, and thus made himself acquainted with the most remarkable works of art in the low countries.

In December 1755 the Eddystone lighthouse was burnt down. Mr. Weston the chief proprietor, and others, were desirous of rebuilding it in the most substantial manner, and through the recommendation of the Earl of Macclesfield, whose friendly conduct to Smeaton we have already noticed, they were induced to appoint Smeaton as the most proper person to rebuild it.

Smeaton undertook the work, and completed it in the summer of 1759.

The history of this great undertaking belongs to another section of this notice. The completion of the work does not seem to have had the immediate effect of procuring him full employment as a civil engineer: in 1764, being in Yorks.h.i.+re, he offered himself a candidate for the office of one of the receivers to the Greenwich Hospital estates[4]; and on the 31st December in that year he was appointed, at a full board at Greenwich Hospital, in a manner highly flattering to himself.

In this appointment he was greatly a.s.sisted by his partner Mr. Walter, who managed the accounts, and left Smeaton leisure and opportunity to exert his abilities on public works, as well as to make many improvements in the mills, and in the estates of Greenwich Hospital.

By the year 1775 he had so much business as an engineer, that he wished to resign this appointment, but was prevailed upon to continue in the office about two years longer.

Among the many valuable public services of Smeaton a few only can be mentioned in this place. He completed the erection of new lighthouses at Spurn Head at the mouth of the Humber: he built the fine bridge over the Tay at Perth: he laid out the line of the great ca.n.a.l connecting the Forth and Clyde; and made the river Calder navigable; a work that required great skill and judgment, on account of its impetuous floods. On the opening of the great arch at London Bridge by throwing two arches into one, and the removal of a large pier, the excavation around and under the starlings was so considerable, that the bridge was thought to be in great danger of falling. Smeaton was then in Yorks.h.i.+re, but was sent for by express, and arrived with the utmost dispatch: on his arrival the fear that the bridge was about to fall prevailed so generally, that few persons would pa.s.s over or under it. Smeaton applied himself immediately to examine it, and to sound about the starlings as minutely as possible: his advice to the committee was to repurchase the stones which had been taken from the middle pier, then lying in Moorfields, and to throw them into the river to guard the starlings. This advice was adopted with the utmost alacrity, by which simple means the bridge was probably saved from falling, and time afforded for securing it in a more effectual manner.

'This method of stopping the impetuous ravages of water,' says Mr.

Holmes, 'he had practised before with success on the river Calder; on my calling on him in the neighbourhood of Wakefield, he shewed me the effects of a great flood, which had made a considerable pa.s.sage over the land; this he stopped at the bank of the river, by throwing in a quant.i.ty of large rough stones, which with the sand, and other materials washed down by the river, filling up their interstices, had become a barrier to keep the river in its usual course.'

In 1771 Smeaton and Holmes made a joint purchase of the water-works for supplying Deptford and Greenwich with water. On examining the books of the former proprietors, it appeared to have been a losing concern during many years; but the skill of Smeaton soon brought the undertaking into such a state as to be of general use to those for whom it was intended, and moderately profitable to himself and partner. In noticing this subject Mr. Holmes makes a few general remarks on the character of Smeaton:--'His language either in speaking or writing was so strong and perspicuous, that there was no misunderstanding his meaning, and I had that confidence in his abilities as never to consider any plan of improvement which he proposed, but only to see it executed with scrupulous exactness; at the same time, he was so open to reason in all matters, that during a constant communication of our opinions for upwards of twenty years, after we had laid them fully before each other we always agreed, and never had the slightest difference.'

It must be remembered that Smeaton lived before the time when the genius of Watt had rendered the steam-engine the useful and obedient servant of man; and consequently that much of the power now furnished by steam was then supplied by the wind. Hence the mechanics of windmills was an important study to the engineer, and Smeaton erected a vast variety of mills in which he turned to useful account the results of his experiments in 1752 and 1753. His usual habit was to confirm the conclusions of theory by direct experiment. He also erected a steam-engine at Ansthorpe, and made experiments thereon to ascertain the power of Newcomen's engine, which he improved and brought to a far greater degree of certainty both in its construction and powers.

During many years the opinion of Smeaton was held in such high esteem, that no great works were undertaken throughout the kingdom without first applying to him; he was constantly consulted in parliament, and was regarded as an ultimate reference on all difficult questions connected with his profession. It was his constant practice to make himself fully acquainted with every subject before he would engage in it, and then his known integrity and lucid powers of description secured the respect and attention of all. In the courts of law he was frequently complimented by Lord Mansfield and others for the new light he threw on difficult subjects.

About the year 1785 Smeaton's health began to decline, and he then endeavoured to retire from business in order to gain time to publish an account of his inventions and works. This was one of the wishes nearest to his heart, for, as he often said, 'he thought he could not render better service to his country than by doing that.' He had just completed his account of the Eddystone lighthouse when he was prevailed on to continue his services as engineer to the trustees for Ramsgate harbour. The works at Ramsgate were begun in 1749, but had been conducted with very indifferent success until Smeaton was called in to superintend them in 1774. He completed the magnificent pier and harbour of this place in 1791, and thus established a secure and much needed place of shelter in the Downs.

A man whose life is so beneficially devoted to the service of the public can scarcely hope to enjoy leisure and retirement during which he may look back upon the past, and leave a written record of his exertions. Smeaton was so constantly and urgently employed that he could not achieve much with his pen. On the 16th September 1792, he was seized with an attack of paralysis induced by over-exertion, and this attack carried him to the grave on the 28th of the next month, in the 69th year of his age.

During his illness he dictated several letters to his old friend Mr.

Holmes. In one of them he describes minutely his health and feelings, and says, 'in consequence of the foregoing, I conclude myself nine-tenths dead, and the greatest favour the Almighty can do (as I think) will be to complete the other part, but as it is likely to be a lingering illness, it is only in His power to say when that is likely to happen.' His daughter, Mrs. d.i.c.kson, says that he always apprehended the attack which terminated his life, as it was hereditary in his family. He dreaded it only as it gave the melancholy possibility of outliving his faculties, or the power of doing good; or, to use his own words, 'lingering over the dregs after the spirit had evaporated.' Indeed, the decay of his mental faculties seems to have been that which he most dreaded. He would sometimes complain of slowness of apprehension, and would then excuse it with a smile, saying, 'it could not be otherwise, the shadow must lengthen as the sun went down.' When seized with paralysis he was resigned to the event, anxious to soften any alarm to his family, and was thankful that his intellect was spared. But his invariable wish was to be released. He expressed particular pleasure in seeing the usual occupations of his family resumed; and reading, drawing, music, and conversation excited the same interest and the same cheerful and judicious observations as ever. One evening he was requested to explain some phenomena respecting the moon, which was seen from the room s.h.i.+ning brightly. He gave a full explanation, then fixed his eyes full upon the object in question, and after regarding it stedfastly for some time, he observed, 'How often have I looked up to it with inquiry and wonder, and to the period when I shall have the vast and privileged views of an hereafter, and all will be comprehension and pleasure.'

We learn from his daughter Mrs. d.i.c.kson, that early in life Smeaton attracted the notice of the eccentric Duke and d.u.c.h.ess of Queensbury, on account of the strong personal likeness which he bore to their favourite Gay the poet. Their first acquaintance was made in a singular manner: it was at Ranelagh when walking with Mrs. Smeaton, he observed an elderly lady and gentleman gaze steadily upon him, they stopped and the d.u.c.h.ess said, 'Sir, I don't know who you are, or what you are, but so strongly do you resemble my poor dear Gay, that we _must_ be acquainted; you shall go home and sup with us, and if the minds of the two men accord as do the countenance, you will find two cheerful old folks who can love you well, and I think, (or you are an hypocrite) you can as well deserve it.' The invitation was accepted, and as long as the duke and d.u.c.h.ess lived the friends.h.i.+p was cordial and uninterrupted. During his visits cards were sometimes introduced.

Smeaton detested cards, and could not confine his attention to the game. On one occasion the stakes were already high, and it fell to Smeaton to double them when, neglecting to deal the cards, he was busily occupied in making some calculations on paper which he placed upon the table. The d.u.c.h.ess asked eagerly what it was, and Smeaton replied coolly, 'You will recollect the field in which my house stands may be about five acres three roods and seven perches, which, at thirty years' purchase, will be just my stake, and if your grace will make a duke of me, I presume the winner will not dislike my mortgage.'

The joke and the lesson had their effect, for they never played again but for the merest trifle.

Smeaton procured a situation in a public office for a clerk in whom he placed the greatest confidence, and jointly with another became security for him to a considerable amount. This man committed the crime of forgery, was detected and given up to justice. Mrs. d.i.c.kson says, 'The same post brought news of the melancholy transaction, of the man's compunction and danger, of the claim of the bond forfeited, and of the refusal of the other person to pay the moiety! Being present when he read his letters, which arrived at a period of Mrs.

Smeaton's declining health, so entirely did the command of himself second his anxious attention to her, that no emotion was visible on their perusal, nor, till all was put into the best train possible, did a word or look betray the exquisite distress it occasioned him. In the interim, all which could soothe the remorse of a prisoner, every means which could save (which did, at least from public execution,) were exerted for him, with a characteristic benevolence, active and un.o.btrusive.'

Smeaton was a man of indefatigable industry and great moral probity.

With ample opportunity of ama.s.sing wealth, he rendered its acquisition but a secondary object on all occasions; his first aim always being to execute the task intrusted to him in the most skilful and perfect manner. Had his object been to ama.s.s a fortune, he might have received many lucrative appointments besides those which he actually held. The empress Catherine of Russia attempted to secure his services for her own country by most magnificent offers; but Smeaton preferred to dedicate his time and talents to the service of his country. 'The disinterested moderation of his pecuniary ambition,' says his daughter, 'every transaction in private life evinced; his public ones bore the same stamp; and after his health had withdrawn him from the labours of his profession, many instances may be given by those whose concerns induced them to press importunately for a resumption of it; and when some of them seemed disposed to enforce their entreaties by further prospects of lucrative recompense, his reply was strongly characteristic of his simple manners and moderation. He introduced the old woman who took care of his chambers in Gray's Inn, and showing her, a.s.serted 'that her attendance sufficed for all his wants.' The inference was indisputable, for money could not tempt that man to forego his ease, leisure, or independence, whose requisites of accommodation were compressed within such limits!' Before this, the princess Daschkaw made an apt comment upon this trait of his character; when, after vainly using every persuasion to induce him to accept a carte blanche from the empress of Russia as a recompense for directing the vast projects in that kingdom--she observed 'Sir, you are a great man, and I honour you! you may have an equal in abilities, perhaps, but in character you stand single. The English minister, Sir Robert Walpole, was mistaken, and my sovereign has the misfortune to find one man who has not his price.'

In all the social duties of life Smeaton was most exemplary; and he was a lover and encourager of real merit in whatever station of life he found it. To strangers his mode of expression appeared warm and even harsh; but Mr. Holmes refers it to the intense application of his mind, which was always in the pursuit of truth, or engaged in investigating difficult subjects: hence, when anything was said that did not tally with his ideas, he would sometimes break out hastily. As a friend, he was warm, zealous, and sincere; as a companion, always entertaining and instructive, and none could spend their time in his company without improvement. In his person Smeaton was of middle stature, but broad and strong-made, and possessed of an excellent const.i.tution. He was remarkable for the plainness and simplicity of his manners.

After his death, his papers consisting of plans, reports, and treatises, on almost every branch of engineering, were published by the Society of Civil Engineers.

FOOTNOTES:

[Footnote 4: This was the Derwent.w.a.ter Estate which was forfeited in the year 1715, and its revenues applied by Parliament towards the funds of Greenwich Hospital. It consists of mines of lead, containing much silver, as well as lands. It required careful management, and the knowledge of mining details to make it profitable. Smeaton contrived more efficient machines and better modes of working the mines and managing the estate.]

CHAPTER V.

THE EDDYSTONE AS A TYPE OF ENGLISH LIGHTHOUSES.

A Stone Lighthouse proposed--Smeaton's first Visit to the Rock--Operations of the First Season--Second Season--Structure of the Foundation--Ingenious Mode of securing the Stones--Third Season--State of the Work--Progress and Description of the Work--Accidents to the Engineer--Proposal to exhibit a Light before the completion of the Building refused--Fourth Season-- Completion of the Work--Appearance of the Lighthouse during a Storm--Situation of the Light-keepers.

To return to the history of the Eddystone Lighthouse. When the proposal relating to the rebuilding of this edifice was made to Smeaton, and when he had duly weighed the subject in his own mind, he delivered his decided opinion that the building ought to be constructed _entirely of stone_. Some opposition was at first raised against this idea, but the proprietors were at length so well satisfied with the plans submitted to their inspection, and with the plain, straightforward reasoning of Smeaton on the matter, that they left the whole affair in his hands. Their chief objection had arisen from the opinion, supported by that of the best judges, that the safety and continuance of Rudyerd's lighthouse during so many years, had in a great measure depended on the elasticity of the materials of which it was composed, which enabled it to give way to the shocks of the sea. Indeed it was affirmed, that in violent storms the motion of that wooden edifice was so great that trenchers and other articles were thrown from the shelves in the upper rooms. Smeaton answered to this, that the great agitation of the late building arose from its want of _weight_, as well as want of strength; that the edifice he had in view would be much _heavier_ and much stronger, so that the building would not give way to the sea, but the sea would give way to the building.

In the spring of 1756 Smeaton first visited and examined the Eddystone rock, proving, as his predecessors had done, the extreme difficulty of gaining a landing, or of remaining long enough on the rock to carry on his observations. These difficulties suggested to him the important and valuable expedient of keeping a vessel fixed within a quarter of a mile of the rock, which should be capable of lodging the workmen and their tools, and thus enable them to take immediate advantage of any favourable opportunity of putting out their boat and conveying materials at once to the Eddystone, instead of having to take the voyage from Plymouth on each occasion.

The first actual work done on the rock was in August, 1756. Two companies of workmen were employed, each remaining at the work a week, that every opportunity might be made the most of, and the men relieved by visits to the sh.o.r.e. A sloop, a large yawl with sails and oars, and a boat, were employed to expedite the work. The sloop formed the lodging for the company working at the rock, and was anch.o.r.ed at a short distance from it. The sloop was afterwards replaced by a larger store vessel, called the Neptune Buss. The weather from the 27th of August to the 14th of September happened to be favourable to the work, so that the companies were employed on it at every tide. After this, unsettled weather began to prevail, so that Smeaton was obliged to be satisfied with the progress already made, which consisted in the mere preparation of the House-rock for the intended edifice, by cutting two new steps in the lowest part of the sloping side of the rock, and forming anew the five steps which remained of the efforts of Rudyerd.

Dove-tailed recesses were also cut in all these steps for the reception of the stone-work. The remaining part of the autumn was spent in expediting necessary work on sh.o.r.e, such as completing the work-yard with its machinery and conveniences, and then preparing the granite and Portland stone, of which the lighthouse was to be made.

The desirability of doing as much of the work as possible on sh.o.r.e, became more and more apparent, as experience showed the dangers and accidents likely to occur at the rock. During this winter Smeaton began seriously to consider the great importance to his work, of getting the most perfect cement possible, to resist the extreme violence of the sea. He found that nothing of the resinous or oily kind would answer, as it was impossible to get a dry surface at the rock. He therefore went through a complete set of experiments on cements with a view to produce one which would, in despite of water almost continually driven against it with every degree of violence, become so firm in its consistence and adhesion to the stone, that it should compose one even regular surface with the stone, without needing hoops of iron or copper to surround the horizontal joints. In this endeavour he considered himself at length completely successful.

At the beginning of June, 1757, Smeaton renewed his work at the Eddystone rock. The first proceedings were to fix some timbers to the east side of the rock merely as a defence to the boats, which were frequently damaged by running against the sharp edges; and also to erect shears, windla.s.s, &c. The first stone was laid in its place on the 12th of June. This stone weighed two tons and a quarter, though the ordinary weight of the stones did not exceed one ton each. The first course consisting of four stones was finished during the next day. By Smeaton's plan the stones were most ingeniously dove-tailed together and into the rock, so that when once fixed, it was impossible for one stone to be separated from the rest. The second course of stones was not completed until the 30th of the same month; several accidents having occurred to hinder the progress of the work; yet Smeaton was in no wise disheartened, for in establis.h.i.+ng these two courses he considered the most difficult and arduous part of the work to be already accomplished, since these courses brought him up to the same level where his predecessor Mr. Rudyerd had begun. On the 11th of July the third course, consisting of twenty-five pieces, was completed, and on the 31st the fourth course of twenty-three pieces.

The fifth course was closed in on the 5th of August. When the sixth course was completed, which was on the 11th of that month, Smeaton had the satisfaction to find that the sea did not now invariably wash over every part of their work at each tide, which had always. .h.i.therto been the case in the course of laying the previous courses. The greatest difficulties were now considered to be successfully surmounted, as each succeeding course gave them more time and more room, and they had brought their work to a level with the highest part of the rock.

Up to this point all the courses had been begun by the stones that were securely dove-tailed into the rock, and further made fast by oak-wedges and cement. To receive these wedges, two grooves were cut in the waist of each stone, from the top to the bottom of the course, of an inch in depth and three inches in width. The care with which the foundation-work was carried on may be gathered from Smeaton's description of the manner of laying each stone. 'The stone to be set being hung in the tackle, and its bed of mortar spread, was then lowered into its place, and beat with a heavy wooden maul, and levelled with a spirit level; and the stone being accurately brought to its marks, it was then considered as set in its place. The business now was to retain it exactly in that position, notwithstanding the utmost violence of the sea might come upon it, before the mortar was hard enough to resist it. The carpenter now dropped into each groove two of the oaken wedges, one upon its head, the other with its point downwards, so that the two wedges in each groove would lie heads and points. With a bar of iron about two inches and a half broad, a quarter of an inch thick, and two feet and a half long, the ends being square, he could easily (as with a rammer) drive down one wedge upon the other; very gently at first, so that the opposite pairs of wedges being equally tightened, they would equally resist each other, and the stone would therefore keep place. A couple of wedges were also, in like manner, pitched at the top of each groove; the dormant wedge, or that with the point upward, being held in the hand, while the drift-wedge, or that with its point downward, was driven with a hammer. The whole of what remained above the upper surface of the stone was then cut off with a saw or chisel: and generally, a couple of thin wedges were driven very moderately at the b.u.t.t-end of the stone; whose tendency being to force it out of its dove-tail, they would, by moderate driving, only tend to preserve the whole ma.s.s steady together, in opposition to the violent agitation that might arise from the sea.' In addition to this, a couple of holes having been bored through every piece of stone, one course was bound to another by oak trenails driven stiffly through, and made so fast that they could more easily be torn asunder than pulled out again. 'No a.s.signable power,' says Smeaton, 'less than what would by main stress pull these trenails in two could lift one of these stones from their beds when so fixed, exclusive of their natural weight, as all agitation was prevented by the lateral wedges.' The stone being thus fixed, a proper quant.i.ty of mortar was liquefied; and the joints having been carefully pointed, up to the upper surface, this mortar or cement was poured in with iron ladles so as to occupy every void s.p.a.ce. The more consistent parts of this cement naturally settled to the bottom, and the watery parts were absorbed by the stone: the vacancy thus left at the top was repeatedly refilled, until all remained solid; the top was then pointed, and, when necessary, defended by a coat of plaster. When the whole of the foundation was in this manner brought to a level, some other means was necessary of attaining the like degree of security. For this purpose the central stone of the sixth course had a hole of one foot square cut quite through the middle. Eight other depressions of one foot square and six inches deep were also sunk at equal distances in the circ.u.mference. A plug of strong hard marble, from the rocks near Plymouth, one foot square and twenty-two inches in length, was set with mortar in the central cavity, and fixed firmly therein with their wedges. This course was thirteen inches in height, so that the marble plug, which reached through it, stood nine inches above the surface. Upon this the centre-stone of the seventh course was fixed, having a similar hole made in its centre, bedded with mortar and wedged as before. By this means no force of the sea acting horizontally upon the centre-stone, less than what was capable of cutting the marble plug in two, was able to move it from its place; and to prevent the stone the more effectually from being lifted, in case its bed of mortar should happen to be destroyed, it was fixed down by four trenails. The stones surrounding the central stone were dove-tailed to it in the same manner as before, and thus the courses proceeded with no other interruption than arose from the nature of the situation.