sitely simple and beautiful mechanical contrivance perhaps ever invented. This contrivance is technically called trussing nothing can be more simple, yet nothing requires more care in its construction: it contains in itself both the germs of ruin and the sure and perfect cure for it. The inclined beams forming a truss would be violently striving to work the ruin of the building, by thrusting apart and throwing down its walls, were it not for the horizontal tie-beam restraining them: the inclined beams must not reach the walls; they must only come upon the tie-beams, then, while the tie-beam remains unbroken, the truss lies simply with its own weight upon the walls: there is then no thrust, no cross strain upon the walls. Such a mechanical contrivance is the most wonderful economiser of materials. It may be adopted more or less in a number of different ways: well applied it gives to every part of a building, however large its dimensions, that state of rest which the earliest buildings of antiquity possessed, while it enables us, with roof-beams, floors, galleries, hanging partitions, and platforms, to span enormous widths, which the ancients never could do without prodigious expense of material, and frequently not without great inconvenience in the interior. The principle is so exquisitely beautiful, so mathematical, so powerful, yet so simple and so cheap, that every person who calls himself a practical builder should be acquainted with it. His knowledge in this simple fact alone will save him, in the construction of buildings, an infinite deal more of outlay than he can previously conceive, while it would render his buildings infinitely better and more durable.*

The neglect of the study of the laws of force is a principal cause of the instability of modern edifices. The practitioner having had no grounding in this science performs almost everything in practical architecture by mere guess, assumption, tradition, or caprice; hence if his building hold together, it is oftentimes rather more from good fortune than from science; and while, in many cases, a large portion of the materials which are made use of perform no duty, in many cases another large portion of the materials not only do not afford any support or stability to the fabric, but really by the force of their gravity, work a positive injury to the other parts of the edifice.

DISSERTATION X.

A CAUTION ON LAYING FOUNDATIONS.

And " a foolish man built his house upon the sand; and the rain descended, and the floods came, and the winds blew, and beat upon that house, and it fell, and great was the fall thereof."-ST. MATTHEW'S GOSPEL.

The foundation of a building is that part of the walls which is laid under or below the surface of the earth, and which serves as a basis for the superstructure of the whole house that is raised above. It is the first thing to be considered in the commencement or erection of the house; and so much depends on the outset as to the stability of the fabric, that it cannot be too sufficiently regarded. The foundation of a building should be of such a nature that it will bear without compression or yielding the weight laid upon it: the best and most solid is that of rock, though that may sometimes be deceiving, if the upper layer be a loose slate much inclined in the stratification, or the cap in a state of decomposition. This we have noticed in the discourse on the substrata under

* It is to be regretted that the study of the laws of force and equilibriura is so much neglected, for while this neglect continues, the execution of every considerable work requiring science, such as bridges, (belonging to the architect's province,) will more and more pass away from the architect to the engineer, who, while he is in general better acquainted than the architect with gravitation and the law of force, not unfrequently is as destitute and careless about the principles of beauty in his designs as the architect is regardless of their soundness and durability. Thus we have works which are ab initio in shivers while others, such as provincial bridges, though generally sound, are from their offensive uncouthness, a satire upon that folly which should at so great an expense attempt for beauty that which to every eye is unsightly.—(A. B.)

the earth's crust. The next foundation in quality is that of compact gravel, which does not flow off and diminish in quantity from water percolating through it; and where gravel occurs, as we have observed in the disquisition on air, it is the most desirable, as it greatly contributes to the healthfulness of the place; although the substrata beneath may probably vary in solidity in different places and at different depths, and materially so from what appears above or uppermost.* It is therefore always advisable to sink or dig the well for the pump-water before the foundations are commenced; by this the architect will be able to ascertain the quality of the strata underneath the earth. It is however to be observed, that there is often an unsound matter directly beneath the different layers of earth, and in that case the strength and firmness of the superficial strata are but a decoy, and a dependence upon it will, in the end, cause the settlement of the building, which if it do not fall to the ground, will be sure to produce serious cracks in the wall, though the foundation may have a footing.†

Rock is the most solid foundation, but this is not everywhere to be found, for in many parishes in England none at all exists. A compacted gravel, as we have said, is the next in degree; but in order to judge of the nature of its excellence or solidity, where it is to be met with, we must observe and examine the thickness of the bed or its depth underneath, as there may be some other strata just below, such as blue clay imbedded with fossil shells, which will always be discovered in sinking the well. If the gravel be in a thick bed, and the under strata of a sound, hard, and firm consistency, there needs no assistance of art or auxiliary support for the walls, for this will bear any weight. If it prove to be the reverse we must then have recourse to art, either by adopting a concrete foundation, or piling and planking. The concrete in such case is to be composed of hard stony courses, such as the screenings of gravel and other equal-sized pebblestones, mixed up with hot lime and sand, which is to be poured on the stones, the same being first well rammed down; and if further substance is required, increased to three or four layers.

To ascertain the solidity of a foundation, so as to know whether it is equal and every way sound after the trenches have been dug and cleared out, Palladio advises the throwing down of great

* If the soil under a building be of a soft nature, it will of necessity yield or compress beneath the weight placed upon it. If the building be uniform, and be well compacted and tied together, this compression may not lead to very serious consequences; but if any part of the building be loftier and more weighty than the other portions of it, as in the case of a church-tower or steeple, the soil beneath the extra weight will be more compressed than the other parts of the site, hence all that portion of this edifice will be sunk something into the ground, and in thus descending the masonry of the stone or brickwork will break away from the adjoining work, which remains more at its original level. This we find to be the case with the churches of St. James, Clerkenwell; St. Leonard, Shoreditch ; St. Martin-in-the-Fields, and in many other instances in the metropolis.-(A. B.)

+ In proportion as the soil is of a soft and yielding nature, the footings of a building should spread; for if a square yard of ground will bear a ton weight with a certain degree of compression, two separate square yards will bear two tons weight with the same degree of compression, or will bear one ton weight with only half the degree of compression, and perhaps less. On this principle, though a man in common shoes will sink by his weight in snow, yet with shoes with extended soles, which will meet with the resistance of a larger extent of snow, he can walk freely over the surface of it without sinking; and indeed upon a rolling soil, such as sand, a foundation of two united yards superficial will bear more than two separate yards superficial; for the soil can less readily roll away from the centre of a large plot than from the centre of a small one, for in the former instance it has further to move before it can escape and rise up at the sides.(A. B.)

Strong, hard, compact blue clay, like that in London, does not make a bad foundation. In a confined town shielded from the heat of the sun, it is very certain; but in open country situations during drought it is apt to split, and cause fractures in the building, unless the foundation be laid below the range of the fissures which occur in it. St. Paul's Cathedral, one of the very loftiest and weightiest buildings in the world, stands upon a layer of clay only from four to six feet thick, above a quicksand forty feet deep; yet from the breadth and compactness of its footing, the goodness of its masonry, the equipoise of its several parts, and the masterly skill with which it is joined together, it is freer from flaws and settlements than all other great buildings in the world, however good their foundations.-(Wren's Parentalia.) § Chalk is also a good and firm foundation for a building, and which commonly prevails in Wiltshire, Dorsetshire, and Berkshire. (B.)

NN

weights forcibly upon the ground, in those places which are suspected not to be so good as they should be; and then at the same time observing whether the ground shakes, trembles, or sounds hollow. This it appears was the method practised by the Italian architects, but with us a paviour's If the ground should appear to rammer is generally used, and in soft parts tried with the crowbar. shake, the trenches must then be sunk deeper; but if the substrata should after this prove partially faulty in places, piers may be built on each side of the defective part on that which is solid, and then arches turned over from one to the other; that is, over the loose foundation; but if the ground should not be very unsound, it may be made perfectly secure for sustaining the building by ramming down large stones closely packed together and well grouted in cement; if strong, then of lime and gravel-sand, laid in breadths at the bottom, proportioned to the intended thickness of the walls, including their footings. If the ground should prove to be insecure generally, then in all such cases it must be piled with oak or deal timber driven into the ground, and planked on the top to receive the intended superstructure.*

Lastly, it may be observed, that in partial loose foundations, where there are to be windows and doors in the buildings above, and where the piers stand on a firm foundation, it is an excellent method to introduce inverted or discharging segmental arches under such intended apertures. The beds or foundations of these piers, it is necessary to say, should all be as nearly as possible of the same depth, for although the bottoms of the trenches in one part may prove to be firm, yet if the piers should happen to be of different depths they will sink in the proportion thereto, according to the number of mortar-joints in them. Under these circumstances the deepest piers will sink more than those which are of a less depth, and thereby occasion great fractures in the upper parts of the edifice to which such foundations are applied.+ Annexed is a copy of a letter written in 1695, in the reign of William and Mary, by Sir H. Shere to Lord Nottingham—on the subject of a mansion which his lordship was then about to build-transcribed from the Sloane MSS. in the British Museum.

SOME DIRECTIONS FOR MY LORD NOTTINGHAM'S BUILDING.

"Sir, "You command me to give you my opinion touching some general rules for building, which if you had digested into I therefore shortly observe, that the bottom on which queries on that subject, I should have known how to obey you. your foundation is to rest ought to be uniform, viz., all rock or all gravel, for wherever any part of the bottom is defective or unequal it will be seen in the building, and 'tis hardly in the power of art to mend the defect; for which reason the

* If the intended foundation be for a building of great magnitude, then the following system should be adopted. Lay a course of Yorkshire landings all round in the trenches close to each other, each stone being about sixteen inches wider than the walls: then on that lay another course of stones, each being about eight inches narrower than the lower course; these must break the joints below. Now, if the building be a public one and extremely large, where expense must give way to strength and durability, a six-inch chain-bond, well charred, should be laid on the top of the upper course of stones, along the middle, carried all round, and spiked together at the junctions and angles. The Venetians are supposed to be the first in modern times who adopted the method of charring timber, which was done by exposing the piece to a strong fire, in the flame of which it was continually turned round by an engine, till it was completely covered with a black coaly crust, when it was taken out and fit for use. By this means it became so hardened as to resist the effects of earth, air, and water, even for centuries. The beams of the theatre at Herculaneum were converted into charcoal by the lava which overflowed that city; and after a lapse of more than seventeen hundred years, the charcoal is as perfect as if it had been formed but yesterday.-(R. B.)

+ There is less pressure upon the foundation directly under the windows, which stand over each other in a house, than under the piers between them; consequently the foundations of those parts are not so considerable. The greatest pressure and greatest weight are at the angles of the building, and the most likely here to fail if the foundation has not been well In doubtful foundations it is best therefore to go deeper at the external angles of the considered and guarded against. building than that of the other parts, and allow some few weeks for the mortar in those angle-piers to harden before proceeding with the several parts of the walling; but if time will not allow of it, then those external angle-piers should be built in cement.-(R. B.) It is necessary to observe, that all stone and brick walls must have footings in the foundations from three to five courses, formed on each side of the wall like steps, and that the joints of mortar in these courses should always be laid thin to avoid much settlement of mortar; for this reason it is that you frequently see the two first courses of brickwork generally laid dry and then grouted.—(A.)

Italians, who give us the best examples in this science, go any depth and scruple no expense to obtain an equal uniform seat for their buildings. We have in England often buildings on clay, which is the worst bottom of all others, which when necessity urges and you cannot avoid it, the safest course is to lay your foundation on a good thickness of timber, in good lengths, (not cross) alongst, and according to the range of your work. The use of this timber under your foundation I approve almost in all buildings that have weight, except rock, chalk, or gravel, but principally on a clay bottom, which being always moist is apt to yield and sink under the burthen that is laid on it. This defect becomes often very mischievous in great buildings, where you are under a necessity of charging the foundation with different weights of matter, as, namely, in great stacks of chimney-piers, where you have great openings, towers, pavilions, and the like. I say these differing weights pressing and treading heavier and lighter on the foundation while your masonry is green, makes different impressions on the vielding bottom, which breaks the bondage, cracks your walls, brings your work out of square, and becomes a great cause of the decay of most of our great buildings here in England, where we have over and above the worst materials and workmen for the masonry part in the whole world. Now laying of timber in the manner I have proposed for your foundation, will be a means of giving these burthensome parts of your building an ample footing, by which means it treads lighter on the bottom, by transferring the weight beyond its perpendicular gravitation, and so gives a proportional share of the building to those parts of the foundation which without such preventive applications would produce those ill effects I have noticed where your bottom is unsound.

"Burying timber likewise in the walls under the jaumbs of your windows and all openings, carries the burthen and sustains the weight by carrying a share of the pressure into the voids, which often prevents cracks and flaws in your walls, which we see almost everywhere in ill-performed structures, where the openings are wide and the piers are little. Now 'tis to be noted, that this use of timber in your foundation, and elsewhere, is only of a temporary service, and does its office while the work is green, by uniting the strength and bondage these parts have to sustain, which by that time the timber is decayed on which it rests, becomes solid and compact, and of strength sufficient to bear its own burthen without any foreign aids, as timber or any other matter whatever that is substituted, (as I may say,) to supply a present weakness, and is not of a piece and of the like duration with the rest of the matter whereof your masonry is composed.

"You tell me, my lord, you purpose this house entirely of stone, which I am sorry for, having, I think, very good reason to prefer brick to any other material whatsoever; I mean for the case or carcase of the building, not refusing any ornament or clothing of stone you may be supposed to give it. My grounds for this opinion is, first, from observation, that all works wrought in brick being more durable than in stone; the greater edifices and monuments of antiquity now in the world being of that material; and not to multiply instances of the truth of this remark, I take notice that the Pantheon at Rome, built by Agrippa in the first century, continues to this day perfect in all its strength, and certainly without the least appearance of defect or decay. The walls of this structure are twenty feet thick; the core, or solid part thereof is brick, and covered only with a shell of marble, whereof the ornaments are composed. Now if I am asked a reason for this superior strength and durability of works in brick, I answer first, the mortar, a cement which is the virgula that binds and holds the parts together, is allowed to be harder and more pure in works of brick than of any other material, and forasmuch as the decay of all buildings takes beginning at the mortar or cement, which is the least durable part, it follows that where that is hardest and most durable, the building must be most lasting and longer endures the weather and assaults of time.§ Now I say, that as the cement in brick-work rests better and is harder than in stone, being found in fact to corrode; the reason of which I will endeavour to give you, which I take to be this, namely, that bricks, as everything doth that is made by fire, acquire a warmth by that element that does not presently forsake it; which adventitious heat too partaking with the petrifying quality of the mortar, bakes and hardens it to a greater perfection than in stone, and so begets a finer and more durable consistency of the mass. Furthermore, brick hath the advantage of stone in point of figure, being cast and finished in such a fashion by art, both for length, breadth, and thickness, as consists with that bandage and union which is necessary to all works that are to be made into a mass, and compiled out of divers and lesser parts whereof the whole is to be composed. Bricks are likewise formed straight, flat, and with right-angles, which gives them an easy and firm seat one upon another, by which means they will rest and stand fair on their bases without the help of cement.

"This advantage is not to be had in stone-work, where the irregular figure of the stones is supplied by the addition of mortar, wherein they are pinned and sustained without any principle of stability but from the mortar that upholds it, and without which it would fall and forsake the place to which it is assigned in the building. Now of the cement, whereof there is a much greater proportion used in stone than in brick-work, so the weakest and least durable material in the mass; the more there is used thereof in compoing your work the weaker it will prove proportionably; where likewise brick-work becomes more durable than stone, and this not only from the necessity you are under of using more of the weaker material, but in regard of the figure, brick standing on a firm basis of its own without helps, but stone when the mortar decays, having nothing but that for the most part to sustain it, necessarily falls of itself and drops out of the building, which brick will not do; and thus a stone wall drops, moulders, and decays by faster degrees than brick. It is further advantageous, brick being lighter than stone by twenty per cent., that will bear to be wrought thinner and with less dimensions; the pile when finished then containing a lighter burthen to the foundation, is another help towards the strength and permanence of the structure.

"This may suffice touching the reasons of the preference of brick to stone-work, with respect to the strength and duration of the structure. Let us see now what further motives there are for the choice of brick rather than stone in buildings that are designed especially for habitations; and I hold the argument to be much stronger here in England in favour of brick than in France, Spain, Italy, or any of those warmer climates where the purity of the air and vicinity of the sun,

* Timber so used should be charred, the charcoal rendering it indestructible.-(Author.)

Some of the pyramids at Egypt, built during the dynasties of the Pharaohs, about 2200 years B.C., are of brick.— (Manetho.)

Walls of mansions built of brick and cased externally with freestone, are the noblest.—(Author.)

§ Mr. Buckingham found bricks at Babylon united by bitumen mortar, that was impossible to separate without breaking the bricks.-(B.)

brings all sorts of masonry to a quicker perfection than our northern moist country. Now if a healthy situation be essential in the choice of a seat, whenever you would build a house, the next best choice you can make is to build a healthy house in a healthy place, which I undertake to say cannot be obtained here in England, especially if your edifice be composed entirely of stone. When in great buildings that required proportionable thickness in the walls, it is a doubt whether the mortar towards the centre becomes even thoroughly set and cemented. This at least we are sure of, that stone-work ripens (dries) by so slow degrees in comparison with brick, that the one in a year or two may afford a tolerable habitation, while the other in third the time will continue green, moist, cold, and unfit to dwell in; greatly pernicious to the health of the inhabitants, and prejudicial and destructive to all sorts of furniture whatsoever that shall be lodged therein; for as your walls must be thicker in stone than brick-work, which exacts a larger space for the setting of the work, so the stone itself being a material chiefly moist, and ministering nothing to the hardening of the cement, the work will, I say, for aught I know, never be thoroughly set towards the centre, by which means, in all hot seasons especially, unwholesome vapours will break out and perpetually affect the health of the inhabitants. And this is among my reasons why in point of health, and for the preservation of the ornaments, goods, and household-stuff that go to the establishment of great buildings, which for the most part are very chargeable, I would give the preference to brick buildings.

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"I am not against carrying up a great building with stone to the top of the ground, but from thence upwards I would by all means build with brick. The Italians work their brick-work always wet, their mortar being much more liquid than ours, which makes much better work, thereby having smaller joints, driving down every brick with the handle of their trowel till in some part or other it touches the brick under it. The best way of preparing mortar in the world is what I have already imparted to you; but it is very hard to put workmen out of their road.‡

"All great openings and little piers are to be avoided, for ashlinds and lintels do not suffice to protect the damage that attends such errors, for wheresoever a great weight rests upon a little foot, it will be hardly possible to prevent the parting and cracking of the walls; for wherever great weights rest upon a little foot the materials under it cripple and yield to the burthen. For roofing I prefer oak everywhere, because it is stiff and a timber of long duration, and you are at liberty in the framing to design your work by all the strength of art you please.§ But in flooring, where your timber is laid horizontal, bearing its own burthen, and you have no help or principle to sustain it, I prefer fir, as being lighter and which will sink less by its own weight in great length than oak.||

"In all doorways or openings that adjoin to chimneys, towers, turrets, or any other burthensome part of the building, remember to let your lintels be higher towards that part than elsewhere, because in a short space all such openings will otherwise become out of square, by reason of the settlement of those weighty parts of the building more than the rest, which this will obviate. Avoid, as much as may be, all sorts of burthens to your building that have not a principle to sustain them; as turrets¶ and lantern-lights framed in the roof over staircases and the like, for such weights as are not sustained from the bottom, and hang, as I may say, by the nail, will, at a long run, sink, settle, and prove prejudicial to the roof, shaking and disordering the covering, begetting leakage and decay in the structure.

"All doorways and openings on the outside of your buildings ought to be of stone and not of timber, not only because there is no solidity or union to be made betwixt timber and masonry, and therefore in time those two materials will part and leave an opening where they were joined together, and so let in the air and the weather; but forasmuch also as the jambs and head-pieces being put in where the work is green do very often share a part of the burthen, and therefore ought to be of a like durable matter with the rest of the building, lest by being of timber, which in time must decay, the taking down the same to repair them may be of ill consequence to the work which it may chance to rest on.

"Chimneys void smoke better by a flank than a back draught, by which means a good deal of weight may be avoided, which in these burthensome parts of the building cannot be too carefully shunned. All plastering upon beams in the ceiling begets cracks. I propose therefore, to avoid these cracks thus, your joists should drop an inch and a half, or thereabouts, below the bottom of your girders,* ,** and then join the ends of your joist with a piece nailed up to the girders of the same thickness with your joist, on which to tack your laths, by which means, the plastering not touching the solid timber of the girder, the cracks will be avoided.

"It is not safe to build too fast; many inconveniences happen by overcharging a green foundation.++ In terrace-walks that are designed to be covered with slate paving-stone,‡‡ the earth is to be made everywhere equal, and then to be well rammed and to stand a winter; then let it be levelled for your purpose, and pitched with good pebbles or flints, being well rammed. This done, lay your flat stones, bedded in good mortar and well jointed, no other way will prevent its being perpetually out of repair. Caution must be had too, that your stone be of a quarry that frost will not touch, otherwise that

To counteract this, all good houses built with stone have their walls now battened and lathed, on which the plaster is laid.-(B.)

+ A house in the south-west corner of Hanover-square in London was built in this way; it is the best and most noted in the metropolis.—(B.)

We find that the best of our houses in England in the reign of the Tudors were built of brick material, out of which all their carved mouldings were formed. See their ornamental clustered chimneys, many of which are existing to the present day. (Author.)

§ Anterior to this period chestnut was much used.—(Ibid.)

Trussing girders I believe was at this time undiscovered.—(Ibid.)

¶ It is not an unfrequent case to see those objects reclining on one side.--(Ibid.)

** This is the method now practised, but this thickness is sufficient.—(Ibid.)

++ This is a good caution, and it is always advisable to let the carcase of a house, after being covered in, stand for some months to season, exposed to the sun and wind, before the internal joiners' work is begun.—(Ibid.)

Terraces not gravelled are now either covered with York-paving or Asphalte composition, from a mineral rock of Pyrimont Seyssel, a bituminous mountain on the eastern side of the Jura. This substitute, which is manufactured by Mr. Claridge, near Westminster-bridge, has been tried in numerous places and under every disadvantage, with great success, which the author considers to be a great desideratum in architecture, on the account of great expense of lead where flat roofs have been required.