Chapter IV (1)

SHIPPING.--IMPLEMENTS.--BUILDING MATERIALS,--AND PROGRESS OF THE BELL
ROCK WORKS IN THE YEAR 1808.

[Sidenote: 1808, January.]

After taking some notice of the preparations made during the winter months, or early part of the year 1808, it is proposed, in describing the progress of the works of this season, to adopt the form of a journal or diary, as in the preceding chapter. The last year’s operations being more of a preliminary nature, the implements and apparatus employed were few in number, and simple in their construction. But the facilities to be afforded by the erection of the Beacon were such, that not only the site of the building was expected to be prepared, but it was hoped that some of the courses of masonry would also be laid during the ensuing summer. It therefore became necessary to be provided with shipping, and every article, both of implements and building materials, however small the actual progress of the work might ultimately be.

_Shipping._

[Sidenote: The New Tender.]

It has already been noticed, in the course of last year’s operations, that much inconveniency, and no small degree of hazard, were experienced in making the numerous passages between the Bell Rock and the Floating-light, especially when the boats were crowded with artificers. Not having previously been so fully aware of these circumstances, and with a view to save expence, the Floating-light was likewise applied to the purpose of a tender. She was consequently moored at a more considerable distance from the rock, as will be understood from Plate V.; but as, from the nature of her tackling, she could not be cast loose upon any emergency, she was found to be but ill adapted to the uses of a tender.

[Sidenote: Is named The Sir Joseph Banks.]

The writer having represented this to the Light-house Board, was immediately authorised to provide a vessel, to be exclusively employed for the service of the rock. He accordingly purchased one upon the stocks at Arbroath, in such forwardness, that she was launched upon the 18th of January 1808. This vessel was built by a Mr Thomas Fernie, and was considered so complete in the mould or figure of her hull, that some of the best judges of shipping have described her as one of the handsomest vessels which perhaps had hitherto been built in Scotland. On account of the exertions of the late Sir Joseph Banks, in his capacity of one of the Lords of Trade, in procuring the loan from Government, for the use of the Bell Rock Light-house, already alluded to in the Introduction to this work, the writer suggested, as a mark of respect, that the new tender should be named “The Sir Joseph Banks,” to which the Light-house Board most readily acceded.

[Sidenote: Is rigged as a schooner.]

She was no sooner launched, than her rigging and equipment, in the best manner, were undertaken by professional people; but the inspection of the interior fitting and accommodations was kindly undertaken by the late Provost Balfour of Arbroath, a gentleman who took great delight in architectural pursuits, and who, upon all occasions, felt the most lively interest in the operations of the Bell Rock. In order that this vessel might stow two large boats upon deck, and be got as quickly as possible under sail, in the event of her breaking adrift, she was rigged as a schooner; and that, by the application of a tackle from each mast, the boats might be conveniently managed, in getting them in and out of the vessel. The Sir Joseph Banks being only 81 tons register, it was necessary to lay out the births, for the several departments of the service, with all possible attention to the economising of room. The forepeak was accordingly fitted up with a coboose for cooking; immediately aft of this birth, a compartment was set off for the ship’s company and the landing-master’s crew, with births for fifteen sailors. But _Jack_ is by no means ill to satisfy with his sleeping-place, and it was often found necessary to encroach upon the allotted number for this birth, according to the exigencies of the service. The waist or middle of the ship was set apart for the artificers, and was capable of containing forty men. Still proceeding aft, a small birth was set off for the mate and steward, which communicated both with the artificers’ birth, and also with the cabin for the engineer’s assistants, the landing-master, and the captain of the tender. In the sternmost part of the ship, a cabin was fitted up for the use of the writer; the whole being found extremely commodious and suitable. From the great proportion of the ship required for the birthage of seamen and artificers, the hold of this small vessel was much curtailed, there being hardly more room left than was sufficient for containing a stock of provisions, water and fuel, for any length of time, besides stowing two or three tiers of casks of lime, cement, and other necessaries for the use of the work.

[Sidenote: Praam-boats, or Stone-lighters.]

Continuing the description of the marine part of the establishment, we next notice three new praam-boats, or stone-lighters, built for conveying the building materials to the Bell Rock, from the vessels employed in bringing them from the work-yard at Arbroath. The term Praam-boat is applied to a certain description of Norwegian boats, having their stem and stem rounded after a peculiar fashion. The introduction of this phrase, in the Bell Rock service, was purely accidental, having been applied, by Captain Grindlay, Master of the Trinity-House of Leith, to the first or experimental stone-lighter, from its resemblance to the praams of Norway. Those now alluded to, however, were built of a more rounded form, after the Dutch manner. They measured over all, on deck, about 28 feet by 8 feet 6 inches, and their depth of hold may be stated at 2 feet, for, being built by different carpenters, they were not exactly of the same dimensions. They had a considerable spring or sheer, and were constructed for carrying their cargoes entirely upon deck, which formed a kind of _cockpit_ in the waist, having a high gunwale on each side, and a break, both fore and aft, as will be seen in Plate XI., the first tier of stones seldom reaching above the level of the gunwale. They had, consequently, little or no hold, having only what was sufficient for stowing some pig or cast iron ballast, a few empty casks, with the necessary warps, kedge-anchors, and grappling-irons.

[Sidenote: Precautions taken for rendering them water-tight and buoyant.]

These lighters were built of uncommonly strong materials, both in their timbers, outward planks, and ceiling or lining, which last was caulked and secured in a manner similar to that described for the Floating-light, so that although the outward skin were damaged, by striking or rubbing on the rock, there would still be an additional defence against sinking. Such, however, was the presentiment of danger attached to the landing-department, that besides the precaution of a water-tight lining, each praam was provided with twelve strong empty casks, which were stowed in the hold, and were sufficient to float and render her buoyant, in case of accident. The praams, therefore, became so many life-boats moored in the neighbourhood of the rock.

[Sidenote: Method of mooring the Praam-boats.]

These praams had but one hawse-hole, and that they might ride more easily at their moorings in the open sea, it was placed amid-ships, and as low or near the water-line as possible. The chain-hawsers with which they were connected to their respective floating-buoys and mushroom-anchors, were made of rod-iron, one-half inch in diameter, turned into as short links as possible. This piece of chain was about five fathoms in length, and was attached to the praam by a strong hook, connected with her _bits_, the farther end being made permanently fast to the mooring-chain of the mushroom-anchor. From the lowness of the hawse-hole, and its central position in the praam, and from having only a short piece of chain to carry, which connected the boat to the mooring-buoy, may be attributed the astonishing ease and safety with which these boats rode at anchor. So remarkable was this, that while the tender, and the other vessels in the service, were tossed about, and shipping a great deal of sea, and even at times obliged to slip their moorings, the praams floated with an easy undulating motion, and were generally as dry upon deck during a gale, though loaded with ten tons of stone, as if, to use a sailor’s phrase, they had been riding in a mill-pond. The facility, also, with which the praams were attached and disengaged from their moorings, was another very great conveniency to the work. In unmooring them, all that became necessary was to unhook the hawser-chain from the bits, and throw it overboard, with a small floating-buoy attached to it, for the purpose of suspending the hawser-chain for the time. In the same manner, in making the praams fast to their moorings, this chain was simply to be laid hold of, by taking the small floating-buoy on board. The chain was then slipped into the hawse-hole, by a corresponding slit in the stem of the praam, and then attached to the bits, when the process was complete. By inspecting the diagrams in Plate XI., this process will be better understood.

[Sidenote: Attending Boats.]

The two cutters or boats employed last year for transporting the artificers from the Floating-light to the Bell Rock, were found to be rather too small in rough weather. They measured 16 feet in length of keel, 5 feet 3 inches in breadth, on the mid-ship thwart or seat, and 2 feet 6 inches in depth. These boats were of as large dimensions as the floating-light could stow, after making the necessary allowance for _ranging_ her cables on deck. They had square sterns, were rowed with four oars, and accommodated twelve sitters, including sailors. But the Sir Joseph Banks being entirely fitted as a tender for the works, the stowing of large landing-boats became a principal object. Her boats were therefore made as large as possible, due regard being had to their convenient management and fitness for the small creeks or landing-places at the rock. After a careful consideration of these circumstances, it was resolved that the two new attending-boats should measure 20 feet in length of keel, 5 feet 8 inches in breadth, and 2 feet 10 inches in depth. They were rowed with eight oars, double banked, or two upon each thwart, and could accommodate eighteen sitters each. They were round in the stern, fitted with a backboard and a convenient seat for the cockswain, who steered with a _yoke_ and lines, instead of a _tiller_.

[Sidenote: Life-Boat.]

One of these boats was called The Mason, the other The Seaman. The latter was fitted up as a Life-boat, somewhat after Greathead’s method, being lined and girded with cork, to the depth of three streaks below the gunwale. In case of accident, therefore, by the bilging of either boat upon the rock, she was rendered more buoyant by the cork lining and sheathing. They were built in Leith, and before being sent to the rock, the buoyancy of the Life-boat was tried, when it was found that she would float with thirty people on board.

_Implements._

[Sidenote: Railways.]

From the wasting effects of the sea, the Bell Rock is formed into numerous benches and gullies, and its surface is consequently extremely rough and irregular. The site of the Light-house being in a central position on the rock, it became necessary to make some provision for conveying the large blocks of stone speedily from the respective landing-places to the site of the building; or at least within the range of the cranes or machinery to be employed in laying them. In ordinary situations, the most obvious method would have been to clear away the inequalities of the rock; but here, from the lowness of its position in the water, such an operation would have been extremely tedious and difficult. Besides, every portion of the Bell Rock was held sacred, excepting in so far as it was absolutely necessary to excavate or remove part of it, in fixing the Beacon-house, and in preparing the foundation of the Light-house. Instead, therefore, of quarrying the rock, the writer found that the most advisable process would be, to lay cast-iron railways round the site of the Light-house, projecting to the several landing-places, on which waggons could easily be wheeled in all directions, as will be seen by tracing the dotted lines on Plate VI.

For this purpose, patterns were prepared in the course of the winter, from which castings of the several compartments of the railways were made by Mr John Baird, of the Shotts Iron Works. These rails were cast in lengths of four feet, and supported upon props and frames of cast-iron, varying in height from six inches to five feet, according to the inequalities of the rock, that the whole might be laid upon one level. Besides the tracks for the wheels of the waggons, it was necessary also to provide a tracking-path of the same metal, which was formed of ribbed work, rested upon the supports of the rails, as will be understood from the diagrams in Plate X. The waggon-tracks were of the form technically termed Plate-rails, which were found convenient for making the necessary fixtures. The edge-rail is less liable to friction, and is certainly greatly preferable to the plate-rail, where the track is liable to be impeded with dust, and other adventitious matters; objections which do not apply at the Bell Rock, where the rails were every tide considerably under water.

[Sidenote: Waggons.]

It was necessary that every thing intended to be left on the Bell Rock during the working season, should have as little buoyancy as possible, and as it would have been extremely inconvenient to have removed the waggons from the rock, which were to be employed in conveying the blocks of stone from the landing-places to the Light-house, they were constructed entirely of iron, excepting two pieces of oak timber, which were bolted upon the top, to form a seat for the stones. These waggons, represented in Plate X., moved upon four trucks or wheels of cast-iron, measuring one foot two inches in diameter, placed two feet six inches asunder, being the length of the axle, and breadth of the railway. Each waggon was provided with a handle, which shifted at pleasure to either end, for the conveniency of reversing the motion, without the necessity of turning the vehicle. But what was more peculiar to these waggons, was a joint in the middle of the perch or double frame, connecting the wheels, by means of which they were made applicable to the circular tracks of the railway round the site of the building.

[Sidenote: Triangular Crane.]

Connected with the cast-iron railways, preparations were also made at the eastern landing place, for lifting the stones by means of cranes or other machinery from the Praam-boats, and laying them upon the waggons to be conveyed to the building. After a good deal of consideration, patterns were prepared for an apparatus consisting chiefly of six pieces of cast-iron, four of which measured 12 feet in length, and of a corresponding strength. As will be seen in Plate XI., these bars met at the top in the form of two sets of sheers, but their lower ends were placed about 9 feet asunder. Connected with these, a pair of sheers were set up, which were moveable upon a bolt, and worked with a crab or winch machine, the whole being strongly batted to the rock. When the moveable pair of sheers, with their attached chain and hook, were suspended outwards over the stone to be lifted from the praam, the chain was hooked to the Lewis-bat, previously inserted into the block. The sheers were then raised till they were brought to a perpendicular position, when the motion of the winch was reversed, and the sheers were lowered inwards upon the wharf, and the stone thus laid upon the waggon. The chain was then unhooked, and the sheers were ready for lifting another stone, as will be better understood by referring to Plate XI., with its letter-press description.

[Sidenote: Crane with moveable Beam.]

Having, in the foregoing article, described the implement employed in landing the stones on the Bell Rock during the year 1808, we are now to notice the crane employed in laying or building them. It appears from Mr Smeaton’s Narrative, that the implements chiefly used for building at the Edystone, were a pair of moveable sheer-poles and a set of triangles, most ingeniously applied to their respective purposes. But such implements must have come far short of the expedition which the writer had conceived to be necessary at the Bell Rock, both on account of the much greater extent of the building, and also from its foundation being so much lower in the water. After considering the subject, and making minute inquiries into the practice at various public works, he found no implement of the description, which he considered applicable to his purpose. The common sheer-poles, still chiefly in use, were recommended as having upon the whole been successfully employed at the Edystone. In some instances, the common crane, with the beam fixed at the top, at right angles to the shaft, was applied for laying heavy materials. The writer, however, laid it down as a proposition to himself, That a more effective mode of building must be adopted at the Bell Rock than had hitherto been in use, by which all the stones at any time likely to be landed in the course of a tide, might be built and secured before the artificers left the rock.

The chief difficulties attending the application of the common crane in such a situation, consisted in the laying the stones perpendicularly into their respective places, as they were all of a dove-tail or angular form, as will be seen from Plate XIII. The fixed beam of the common crane was further objectionable, from its being more liable to interfere with the guy ropes. It would also have been difficult to have lifted it either laterally or perpendicularly upon the building, from one course to another. To these may also be added the great obstruction which the beam would have presented to the waves of the sea at high water. All these objections, however, were in a great measure got over, by substituting a moveable beam to work upon a bolt at the foot or lower end of the upright shaft, instead of a fixed beam at the top in the usual manner. But as we shall have occasion again to notice this machine in the operation of building, we shall here refer to Plate XIV. with its letter-press description. Three of these cranes, with moveable beams, were prepared for the work, in the course of the winter, one with an upright shaft of 28 feet in length, for laying the prepared stones upon the platform in the work-yard at Arbroath, and other two, with shafts of 21 feet, for building at the rock.

[Sidenote: Sling Cart.]

Though none of the stones of the Bell Rock Light-house were likely to exceed two tons in weight, in their finished state; yet, in their undressed state, they were much more ponderous. From the waste attending their dove-tailed form, and the working them square on all their sides, the blocks from the quarry were greatly reduced; in many instances, to one-half of the cubical contents of their quarry dimensions, before they were brought to the size of the moulds. The stones had not only to be conveyed from the harbour of Arbroath to the work-yard, a distance of from two to three hundred yards, but also required to be frequently lifted from place to place; as, for example, when in a hewn or dressed state, they were removed to the circular platform, in the middle of the work-yard, to be tried and marked;--they were again shifted from this position, and ultimately carried to the harbour to be shipped for the rock. From the various movements which each stone had thus to undergo, it became an object of importance to the facility and economy of the work, to consider how this could be most conveniently accomplished. Had a cart or carriage, with four wheels of the ordinary construction for great loads, been employed, it would have been extremely troublesome, in all the operations of loading, turning and moving from place to place. To have attempted to avoid this by the use of waggons with low wheels, and the introduction of railways along the quays and public streets of Arbroath, would also have been objectionable, especially as the object could be much more conveniently obtained by the use of what is called the Woolwich Sling-cart, represented in Plate X. By this machine, the weight is simply raised off the ground with a wheel and pinion apparatus fixed upon the frame of the cart, and in this manner, the stone, instead of being lifted upon the body of the carriage, had only to be suspended at the necessary height for overcoming the inequalities of the road. This vehicle had long been used with great advantage by military engineers, in moving ordnance; but was probably first employed at Mylnefield Quarry, and the Bell Rock works, in transporting blocks of stone.

[Sidenote: Carpenter’s Jack.]

Another implement prepared, in the course of the winter, for the Bell Rock work-yard, was the Carpenter’s jack, used for raising ships upon the blocks or props for the purposes of repair. This machine, which is simple in its construction, and direct in its application, consists of a rack and pinion, enclosed in a frame of oak timber, strongly bound with iron, as represented in Plate X. By working the handle of the jack, the stone-cutter is enabled, without the assistance of his fellow workmen, to turn and lay the heaviest stone to his hand. This apparatus the writer first saw used to much advantage, by the quarriers at Portland Island, in the year 1801; and though it had not perhaps at that time been put into the hands of the stone-cutter, it was obvious that it might also be applied to his purpose with equal effect.

It may further be noticed, regarding this useful implement, as strongly marking the prejudices of habit, that Mr Mylne, the proprietor of Mylnefield Quarry, who, with enlightened views, furnished his works with machinery of the very best description, among other articles, provided a number of these jack-machines for his quarriers, but, for a long time, they could not be induced to make use of them. One of the men, however, happening, of his own accord, to apply the jack in turning a heavy block, its utility soon became apparent; and Mr Allan the manager, who had previously taken considerable pains to get the jack introduced, was at length not a little pleased to find it, after having been laid up in store as useless, in much request throughout that extensive quarry.

[Sidenote: Lewis Bat.]

A Lewis Bat, of some form, for lifting large stones, is believed to have been known to the ancients. But that now in common use is generally understood to have been at least improved by the French engineers, who, in honour of their Sovereign, gave it the name of Lewis. This useful implement is so universally known in practice, for its great utility in building with heavy materials, that it is hardly necessary to do more than simply allude to it. It consists of five pieces of iron, three of which, forming a dovetail, like an inverted wedge or the keystone of an arch, are inserted into a corresponding hole cut in the stone. The fourth is the bolt connecting the shackle-piece, by which the weight is suspended, as will be better understood by referring to the sketch or diagram illustrative of it in Plate XI. Of this implement, it became necessary to furnish several dozens, as well from the variety in the weight, as from the figure of the stones, many of them requiring two Lewises to produce a proper balance. But the number was more particularly encreased, from the different sets required for the workyard, the stone-lighters, and for the Bell Rock, where it was necessary to provide against loss, to which this service was so peculiarly liable.

[Sidenote: Moulds.]

As the whole of the stones of each course or tier of this building were connected or let into one another, by a system of dovetails, diverging from the centre to the circumference, after the manner of the Edystone Light-house, as will be seen from Plate XIII., each particular stone required to be cut with accuracy, to fit its precise place in the building; and as even the form into which the blocks of granite were made, often depended upon the adventitious produce of the quarries, it became a very considerable operation to prepare the necessary moulds or patterns for the respective courses. When, therefore, the thickness was ascertained that a lot of these stones would admit being dressed, a plan of the particular course was first drawn upon paper by the Clerk of Works; a certain compartment of the course was then protracted of the full size, upon a platform of polished pavement, measuring 70 feet in length, and 25 feet in breadth, and occupying part of the ground floor of the workmen’s barrack. From this enlarged draught, Mr James Slight, the principal mould-maker, took his dimensions in making the moulds of the full size of the ground-plan of each stone, on which were marked the necessary directions for the stone-cutter, both as to the thickness of the course, and the position of the connecting joggle-holes, trenails and wedges.

These moulds being made with great precision, were carefully marked and numbered with oil paint, according to the positions which the respective stones were to occupy. They were made of well seasoned fir timber, and dressed clean in the form of open frame-work, measuring from three to four inches in breadth, and from one-half to three-fourths of an inch in thickness. At the angles and joints, thin plates of iron were screwed upon these frames, to strengthen and preserve them, while the workmen were making their draught-lines, and in their numerous applications of them in the process of hewing the stones. Each course of the solid part of the building required from three to five moulds, of the form delineated in Plate X., which were carefully laid aside in sets, till the particular course to which they belonged should be landed upon the rock, and secured in the building. In a work of this kind, such a precaution was indispensably necessary; for, in case of loss or accident to any of the stones, in landing them at the Rock, it would then only have been necessary to send to the work-yard, referring to the particular number of the mould, from which another stone could speedily have been prepared.

[Sidenote: Cofferdam.]

In the first designs for the Bell Rock Light-house, the writer had modelled a cofferdam, five feet in height, intended to have been erected of cast-iron, round the site of the building, that the work in its early stages might be continued for a longer period, both during the ebb and flood tides. The experience of last season’s work, however, shewed that the erection of the proposed cofferdam would have been attended with considerable difficulty; and, to have rendered such an apparatus equally useful during ebb-tide as flood-tide, would have required the pumping of water by machinery more complicated and powerful than the situation of the Bell Rock would have admitted.

[Sidenote: Pumps.]

This idea was therefore laid aside, and two Pumps, of a simple construction, were prepared, for clearing the foundation-pit of water. They measured about twelve feet in length, and were of a square form, both externally and internally, having each a void of ten inches. They were made of fir timber, three inches in thickness, strongly jointed, and put together with white-lead paint, having also a number of cross bars and bolts of iron, to strengthen them for withstanding the atmospheric pressure upon so considerable a surface. These pumps were furnished with a wooden spear or rod, having a cross head or handle at one end, and a leathern valve attached to the other. This valve was of a very simple construction; it collapsed when plunged into the water, and was inflated by the return draught delivering a quantity of water equal to the cubical contents of the void or chamber of the pump.

[Sidenote: Winch-machines.]

There were four Crabs or Winch-machines prepared for working the different purchases required in the various departments of the work, as, for example, in lifting the stones from the praam-boats, as represented in Plate XI. Another of these machines was fixed on the temporary wooden bridge of communication, erected between the Beacon-house and Light-house, as will be seen in Plate IX. Other two of these machines are likewise represented for raising the stones from stage to stage upon the building, as will be more particularly described in the letter-press description of this Plate. These machines were made wholly of iron, excepting the bushes for the gudgeons working in, which were of bell-metal. They were calculated to work with what is called _double and single purchases_, according to the weight of the stones to be lifted. They were very powerful in their operation: the winch or barrel being twelve inches in diameter, gave the single purchase a power of about fifteen to one, and the double purchase about sixty to one. These machines were calculated to work with five tons. The weight of the largest size was altogether about 10 cwt., so that they were not easily shifted by the impulse of the sea, when batted to the rock, as represented in Plate XI.

_Building Materials._

[Sidenote: Stone.]

The Commissioners of the Northern Light-houses, as before noticed, having finally resolved that the erection upon the Bell Rock should be of stone, constructed upon principles similar to the Edystone Light-house, it became a question of importance in the economy of the work, to fix the quality and description of stone to be used. Considering this subject in reference to the Edystone Light-house, it appears that the hearting or interior of the solid part is of sandstone from Portland Island, and that the exterior of that building is of Cornish granite, both of which were highly suitable in quality, and were fortunately procurable from quarries the most contiguous to Plymouth, where these works were situate.

[Sidenote: Mineralogy of the southern and eastern shores of Britain.]

It may farther be noticed, that granite is perhaps the only stone upon the coast of England, which possesses durability for withstanding the effects of the weather in a situation so exposed, or strength sufficient for undergoing the process of landing the stones when in their prepared state. In Scotland, however, the case is widely different, for here, the country abounds with excellent building materials of almost every description; and excepting in those districts which produce granite, that stone is rarely had recourse to for buildings of any description. It is curious to observe, and it may here not be out of place to remark, in looking into the mineralogy of the British coast, on the great scale, that we find the shores of the whole southern parts of the kingdom, or from Portland Island in Dorsetshire, to Flamborough Head in Yorkshire, consist chiefly of chalk, limestone, clay, and beds of gravel. But if we continue our course from thence northward, to Stonehaven in Kincardineshire, including the Firth of Forth, the strata, with little exception, are sandstone, greenstone, limestone and coal. The Aberdeenshire coast is chiefly of granite, syenite, and gneiss, while a part of Banffshire consists of serpentine and porphyry: but here the sandstone again makes its appearance, and stretches along the northern shores of the Moray Firth , Caithness and Sutherland, nearly as far to the westward as Cape Wrath. To this great extent of sandstone country, may also be added the islands of Orkney and Shetland, with some considerable exceptions, however, in so far as regards Shetland; but, in Orkney, these are confined to comparatively small portions of gneiss with granite veins, which occur in Pomona or the Mainland, and in the Island of Græmsay.

From this state of the mineral strata, it naturally follows, that those who inhabit the sandstone districts employ that beautiful, easily worked, and, in many instances, highly durable stone, in architecture; and so of the other districts, according to the predominating species of their stone. For a building, therefore, in a country situate like that of the Bell Rock, abounding with sandstone of the first quality, this description of stone obviously presented itself, both as the most accessible and economical. But when the importance of this work came to be fully considered in all its relations, a little additional expence was not to be allowed to regulate a point so essential, without a due regard to what might ultimately prove the most durable and permanent fabric.

[Sidenote: The use of granite and sandstone is resolved upon.]

The attention of the Commissioners was consequently directed to the use of granite, as combining the greatest number of properties for such a building. Some doubts, however, having existed, as to the certainty of procuring blocks of that stone of sufficient dimensions, it became a matter of importance to determine this point, and also to ascertain the quality of the sandstone, of which it had been proposed to form at least the hearting of the solid part. The Commissioners, therefore, in the month of November 1806, required a special opinion from Mr Rennie and the writer upon this subject; who accordingly visited the sandstone quarry of Mylnefield near Dundee, and the granite quarries in the neighbourhood of Aberdeen, and made a report to the Board, which is given in the Appendix, No. IV.

[Sidenote: Report of Mr Rennie and Mr Stevenson.]

This report sets forth, that many granite quarries were found in activity at Aberdeen, some of which were capable of producing larger blocks of stone than are usually met with, but that still it was doubtful, whether any single quarry would be found to produce a sufficient number of large blocks for this work in any reasonable time. Upon the quality of the stones respectively; the report states, that “the granite of Aberdeen is very strong and durable in its nature, and having been used in works where the sea has acted upon it for time immemorial, no doubt can possibly be entertained as to its adaptation to a work of this kind. There is also every reason to believe that the Mylnefield stone resists the sea and weather equally well, but we have not been able to collect such positive proof of this as of the other; for, although a great number of Mylnefield stones have been used in the piers of the harbour of Dundee, yet, as these works consist of stones from other quarries, having the same appearance, and nearly the same composition, there is no possibility of our saying whether some of the stones that appear in a wasting state, may not have been from that quarry, although we have great reason to believe they have not. However, where facts cannot be positively ascertained doubts exist, and we think that a Light-house upon the Bell Rock is too important a work to permit the leaving of the slightest doubt about the durability of the materials. We have, therefore, no hesitation in recommending that the outer part of the building, at least as high as the first apartment, should be of granite; and as this is the great bulk of the work, it may be as well to complete the outer course of granite.”

The Reporters then go on to state, from a review of the several quarry prices, that, for the outer casing, the sum of about L. 2,500 would be saved by the use of sandstone from Mylnefield, instead of granite from Aberdeen; and that, for the hearting of the solid part, an additional saving of about L. 1000 would further be made, if the sandstone of the Redhead quarries, in the immediate neighbourhood of Arbroath, instead of the Mylnefield stone, was used. On considering this subject, however, in all its bearings, the Commissioners resolved that measures should be taken for procuring granite for the whole outward casing of the Light-house, and that the Mylnefield sandstone should be used for the interior work. To the other properties of these stones, one of some consideration for a work of this description was their ponderosity, there being only about 13½ cubic feet of Rubislaw granite to the ton, and 15 feet of Mylnefield stone, while the more common kinds of sandstone contain about 15½ feet to the ton.

These, and other matters of minor importance alluded to in this report, having been adjusted by the Light-house Board, the writer took the necessary measures for entering into contracts and agreements for the supply of stones from these quarries. The difficulties which subsequently attended the procuring of a regular supply of stones for the work have already been alluded to; and to this subject we shall again have occasion to recur, as it was ultimately found necessary to restrict the use of granite to the outward casing of the first thirty feet or solid part of the building.

[Sidenote: Mortar of the ancients.]

The best composition for building-mortar appears to have been a problem from the earliest history of the arts. Vitruvius, who lived about 130 years before the Christian æra, seems to have been practically, as well as scientifically, acquainted with the whole subject of architecture. But, although he, and other eminent authors who followed him, have minutely treated of the composition of mortar, stating, no doubt, all that was known of the practice of the ancients; yet, it has always been a favourite maxim to maintain, that the secret of compounding mortar has at some period of its history been irrecoverably lost. It is certainly true, that many of the works of ancient times exhibit wonderful specimens of the excellency of their building materials. It may, however, be drawn no less conclusively from the writings of intelligent travellers, that many of their finest edifices have been subject to premature decay, which affords a proof that at least no systematic rule was universally observed in the preparation of their calcareous cements; but that, like the artists of the present day, the quality of their materials depended much upon those adventitious circumstances which too often regulate the views of their successors, by an over-anxious desire for economy, without keeping duly in view the permanency of their works.

[Sidenote: Attention of the moderns to this subject.]

In Great Britain, the composition of mortar does not seem to have occupied much of the attention of the learned, prior to the beginning of the 18th century, or the time of Sir Christopher Wren. And, indeed, the subject was not pursued with much intelligence and effect, till after the great discoveries of Dr Black, about the year 1754, which unfolded the principles of latent caloric, and the expulsion of fixed air, by which limestone loses about one-half of its weight in the process of calcination. These discoveries were succeeded by the excellent treatise of Dr Higgins on Water Cements, published in 1780; and in 1793, Mr Smeaton’s Narrative of the Edystone Light-house appeared, containing, not only an account of the preparation of the mortar for that celebrated building, but also of his experience for thirty-six years, as an engineer of the most extensive practice of his day. The composition of mortar has also occupied the attention of several French authors, as Belidor, Loriot, Viccat and others, but without perhaps adding much to our stock of practical knowledge.

[Sidenote: Experience of the writer.]

Were the writer permitted to state the result of his professional observations for the last twenty years, he might notice, that no error is more commonly met with in water buildings, than that of employing house or common mortar in the erection of sea-walls. It may also be stated, generally, in compounding mortar, that the cheapest article is too apt to be made use of in the greatest proportion. We accordingly find, that lime is not unfrequently made too _rich_, as it is technically termed when a small proportion of sand is applied to the mixture; an error, which is attended even with worse consequences than when the lime is made _poor_, or when too great a proportion of sand is used. But, perhaps, the worst of all mortar is that wherein very fine _pit-sand_, containing a portion of earthy matters, is used, and when the whole is mixed up with impure water. So little attention is often paid to the quality of mortar, in common buildings, that one would imagine it were applied, as if intended more to prevent the sifting winds from penetrating the walls, than as the medium by which they were ultimately to be bound or formed into a compact fabric.

It is not possible to give any formula for the composition of mortar which will apply generally; so much depends upon the quality of the limestone, the mode of its treatment in burning, the use of clean sharp sand and pure water. When these ingredients are judiciously selected, duly apportioned, and well beaten together, they will immediately form a paste of some tenacity, which will ultimately take bond and give a consistency to the work. From all the experiments that have been made, it seems to be essential to the composition of the best water-cements, that the limestone should contain about one-seventh of alumine or clayey matter. But as this description of limestone admits of a less proportion of sand in the mortar compounded of it, than that which is more purely calcareous, it is not so much in request for the common operations of building, as being less economical. It may, however, be stated, as a pretty general maxim, that where comparatively pure calcareous matter is met with, at least three measures of clean sharp sand, free of earthy particles, mixed with one of burned lime, in the state of powder, and a due portion of pure water, well beaten together, will form good mortar for common use.

[Sidenote: Mortar of the Edystone.]

From the similarity of the situations and the buildings upon the Edystone and Bell Rocks, and from Mr Smeaton’s celebrity as an engineer, his Narrative of the former work became a text-book to the writer in the erection of the latter. In considering the importance of this subject, with a view to the erection of the Bell Rock Light-house, the judicious remarks, and numerous experiments, of Dr Higgins on water cement, were carefully examined, and they will always be consulted with interest by the professional reader. The composition of the Edystone mortar consisted of equal portions, by measure, of Aberthaw lime and Pozzolano earth, both in the state of powder, mixed up with sea-water. When the writer first visited Plymouth in the year 1801, the Edystone Light-house had been erected about 42 years; and he was informed by Mr Tolsher, agent for the establishment, that the original pointing of the joints of that building had never required repair.

[Sidenote: Bell Rock Mortar.]

Of the ingredients of the Bell Rock mortar, as the pozzolano was not only the most expensive, but, from the distracted state of Europe, during the progress of the works, could hardly be procured at any price, it became an object to be as independent of that article as possible. A train of experiments was therefore undertaken by the writer, when it was ultimately found, that pozzolano and lime, in the state of a dry impalpable powder, and clean sharp sand, in equal proportions by measure, mixed with sea-water, formed a mortar equally good in all respects as when no sand was added. Under favourable circumstances, this mixture did not seem to be more tardy in fixing, than when the sand was excluded, while nothing could exceed the compact and indurated state of the composition. The writer accordingly built some small rubble-walls with it within sea-mark, which were allowed to stand for a few months, and when pulled down, they appeared like so many pieces of conglomerated rock, the mortar being as hard and compact as the sandstone of good quality with which these little walls were built. From the excellency of the Bell Rock mortar, it may not be amiss to go a little farther into detail, by noticing each of the ingredients of which it was composed.

[Sidenote: Lime.]

In the course of investigating this subject, specimens of lime, from the counties of Edinburgh, Haddington, Fife and Forfar, were subjected to various trials with mixtures of pozzolano and sand. The results were not a little curious, as the experimental balls, made with different proportions of these limes, did not set or harden; but, on the contrary, the particles seemed to repel each other as the mixture became heated, and ultimately crumbled into its constituent ingredients. From these experiments, it was found advisable to bring a cargo of limestone from Aberthaw in Wales, being the same as that used for the Edystone Light-house. This lime is found imbedded in a clayey matrix, in the state of water-worn nodules, varying in size from a cubic inch to that of a cubic foot. This limestone is of a bluish or beautiful French grey colour, of the specific gravity of 2.70. It is easily calcined, and in that state is reducible to the finest powder. It is the mountain or first flœtz limestone of geologists; and, when broken, it pretty generally displays the _Cornua ammonis_, and many other curious animal remains. This limestone is found in great abundance on the sea-shore at Aberthaw, where the softer matters being washed away from the lower stratum of certain high cliffs, containing these rounded masses, the upper parts fall in great quantities, from which the succeeding tides wash away the earthy matters, leaving the limestone upon the beach in the state of debris. When a vessel is to load limestone here, she is grounded on the shore at about half-tide, and loaded when the water recedes. The price paid to the proprietor for a cargo is at the rate of one shilling _per_ ton, as a lordship.

[Sidenote: Pozzolano.]

Pozzolano, the second mentioned ingredient of the Bell Rock mortar, is a kind of earthy lava, of a brownish red or greyish colour. It contains in the hundred parts, silica 55, alumina 20, lime 5, and oxide of iron 20. It was not so easily procured as the limestone from Aberthaw. It is very abundant on the coast of Italy and shores of Sicily, where it is found in considerable masses, and is usually imported in a crude earthy state, requiring to be pounded, or beat in a mill, to fit it for the finer purposes of mortar. It is generally brought to this country as ballast; and, in time of peace, when the ports are open, is sold for about L. 5 _per_ ton. During the progress of the Bell Rock works, however, from the long continued and almost universal restrictions upon British trade with foreign ports, as much as L. 15 _per_ ton has been paid for pozzolano for the use of these works. The writer having had great difficulty in procuring a supply of it for commencing the works, got a quantity of Tarras from Holland, the Dutch ports being, at this time, open to British vessels. Tarras or Trass is found near Andernach, and is brought down the Rhine to Holland. It is very similar in its nature and properties to pozzolano, and, like it, is of a reddish or greyish colour. It contains 37 parts silica, 28 alumina, 6.5 lime and 8.5 iron. Its property of setting in water is very remarkable, and, when good, it admits even a greater proportion of lime in the composition of mortar than pozzolano. The Dutch are very attentive in ascertaining the quality of the trass before using it in building their dikes. The following simple experiment is always employed. A small vessel, made of a mixture of lime and trass, is filled with water, and if at the end of three days the water does not filter through the vessel, the trass is considered good; if, on the contrary, water passes through, the trass is rejected as bad.

[Sidenote: Sand.]

According to Dr Higgins, the sand used for mortar should be free of earthy particles, and have as many sharp angular points as possible. The writer having accordingly examined the shores in the neighbourhood of Arbroath, for sand answerable to this description, he found it of excellent quality about a mile and a half westward from that place. Upon examining this sand with a magnifying-glass, its appearance was like so many small shining crystals shooting into numerous points.--It is often a difficult question with mineralogists, to account for the production of sand in many situations upon the coast; but here the question involves no perplexity, as St Andrew’s Bay, which is generally understood to extend from Fifeness to the Redhead, a distance of about 25 miles, is not only bounded by sandstone, but forms the embouchure of the river Tay, and of several other considerable streams, which fall into the sea upon its shores.

[Sidenote: Water.]

It usually forms a condition in the Specification of mortar for house-building, that it shall be mixed with pure water, free of earthy or saline particles. In situations where water is scarce, many impurities are apt to be mixed with it, which injure and even destroy the adhesive quality of the mortar. The use of sea or salt water is guarded against in these cases, from its liability to produce an efflorescence on the walls; when the saline particles deliquesce with the changes of the weather, and produce the appearance of dampness.

To have attempted to avoid the use of salt-water in the preparation of the mortar for the Bell Rock Light-house,--which was all prepared on the spot,--independently of the risk of deteriorating the mortar, would have been attended with much additional trouble and expence. Besides the practice at the Edystone, the writer had previously ascertained, that the use of sea-water produced no bad effect upon the tenacity or adhesive quality of the mortar into which it was introduced, and the object of avoiding the appearance of dampness in this building was extremely trifling. The stones were to be very correctly jointed, and the whole of the interior walls to consist of polished masonry, so that the fine lines of the joints exposed to the action of the air were so inconsiderable, as hardly to be taken into account. Salt-water was, therefore, uniformly used in the preparation of the Bell Rock mortar.

[Sidenote: Cement.]

The recent discovery of a very excellent water-cement, for which Mr Parker of London obtained a patent, under the title of “Roman Cement,” became another matter of importance to the Bell Rock works. This substance is produced from calcined nodules of argillaceous limestone, found upon the southern shores of England. It is of a brownish colour, and from its excellent property of setting in water, when good and fresh, its application as a mortar, for the lower courses of the Light-house, demanded attention. But, for general use as a mortar, it would not only have been expensive, but often highly inconvenient in building, from the speedy manner in which it hardens. It is also of too brittle a nature to be suitable for the general purposes of common mortar; though it forms a paste of great value for _lipping_ or pointing the outward joints of water buildings, not only by preserving the mortar till it gets into a fixed state, but also as forming a durable joint. A considerable supply of this cement was accordingly used throughout the building, for pointing the exterior joints. This cement is sold at the rate of five shillings per Winchester bushel, in the state of powder, packed into casks, lined with paper, to prevent it, in some measure, from imbibing humidity from the atmosphere, by which its adhesive properties are destroyed.

[Sidenote: Oaken Trenails and Wedges.]

Following out the principle of the Edystone Light-house in most of its details, the oaken trenail and wedge were used for fixing the stones, till the mortar took band, and a superincumbent weight was got upon them to prevent the sea from sweeping them away. These being also introduced into all the lower courses of the Bell Rock Light-house, a sufficient quantity was procured for the probable number of courses that might be built during the ensuing season. The precise lengths of the trenails and wedges could not be fixed, from the uncertainty of the granite quarries, which regulated the thickness of the courses of the building; but, for the present, the trenails were provided of the length of 2 feet, and 1¼th inch in diameter. The wedges were of the length of 18 inches, measuring 3 inches in breadth, 1 inch in thickness at the top, and tapering to ¼th of an inch in thickness at the point, as will be seen in Plate X. Figs. 10. and 11. But when we come to speak of the process of building, their respective uses will be described.

[Sidenote: 1808, March.]

[Sidenote: The writer visits the Bell Rock.]