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piers, operate as a solid body. Whereas, if this expedient ofinverted arches be not adopted, the low piece of wall underthe aperture, not having a sufficient vertical dimension, willgive way by the resistance of the ground upon its base, andnot only fracture the brickwork between the apertures, butalso the window-sills. Hence it is evident that these archesshould be turned with the greatest exactness, and should bein height at least half their width. The parabolic curve willbe found most effectual in resisting the reaction of theground; it being the form most adapted to the laws ofuniform pressure.

The bed of the piers ought to be of equal solidity through-out ; for though the bottom of the trench may be firm enough,yet if there be any difference in substance, the settlement willbe partial, the amount thereof varying according to the soft-ness of the ground; consequently the piers on the softer groundwill settle more than those on the firmer, and occasion a ver-tical fracture in the superstructure.

Should the solid parts of the trench be found under theintended apertures, and the softer parts where piers are to bebuilt, the reverse of the above practice must be resorted to,viz.: build piers on the firm ground, and suspend arches, notinverted, between them ; in performing which, attention mustbe paid to the insisting pier, whether it will cover the arch,or not; for if the middle of the pier rest over the middle ofthe summit of the arch, the narrower the pier is, the greatershould be the curvature of the arch at its apex. When sus-pended arches are used, the intrados ought to be clear, thatthe arch may have its full effect. Here also, as before, theground on which the piers are erected should be of equalfirmness, lest the building be injured by an unequal settling,which is attended with much more mischievous consequencesthan where the ground, from being uniformly soft, permitsthe piers to descend equally, in which case the building isseldom or never damaged.

When it is necessary to ram foundations, the stones, beingpreviously chopped or hammer-dressed, so as to have them aslittle taper as possible, should be laid of a breadth propor-tioned to the weight intended to be rested on them, andrammed closely together with a heavy rammer. In ordinarycases, the lower bed of stones may project about a foot oneach side of the wall, on which another course may be laid,so as to bring the upper bed of stones upon a general levelwith that of the trench, projecting about eight inches oneither side of the wall, or receding four inches on each sidewithin the lower course. Care should be taken that thejoints of every upper course fall as nearly as possible uponthe middle of the stones in the course immediately beneathit; a principle also to be strictly adhered to in every kind ofwalling ; for in all the modes, various as they are, of layingstones or bricks, the uniform object is to obtain the greatestlap one upon the other.

The directions for preparing a solid foundation, refer tothe general practice amongst builders before the introductionof concrete. The now almost universal use of the latter, asa certain, convenient, and ready means of obtaining a securefoundation, has rendered it necessary to give a description ofthe mode in which this material is generally used.

The ground having been examined as described in the firstpart of this article, a sufficient depth must be excavated inthe bottom of the trenches, to allow of throwing in a quan-tity of concrete, varying in breadth and depth, according tothe size and character of the building to be erected, and thenecessary width of the footings.

The concrete is composed of different materials, and pro-portions of those materials, as the qualities of sand, lime, &c.,are most conveniently obtained in the locality of the building.

The concrete used in and near London is generally composedof Thames ballast and fresh-burned stone-lime, (ground topowder without slacking,) in the proportions of from one-fifthto one-ninth of lime to one of the ballast. These ingredientsshould be well blended together dry, and as small a quantityof water added as will bring them to the consistency of mor-tar ; and then, after turning over the materials with theshovel once or twice, thrown as quickly as possible into thefoundation, from a height of several feet. It sets veryquickly, so that it is desirable that the mixture should bemade at, or close to the height from which it is thrown, andthen spread and brought to a level as expeditiously as pos-sible. See Concrete.

Having premised thus much on foundations, we proceedto the operation of walling; the first object in which is thedue preparation of the cementing material.

Mortar is most commonly used in modern brick buildings.It is composed of lime, gray or white, but gray or stone-limeis the better, mixed with river-sand, or road-sand, in theproportion of one of gray lime to two and a half of sand, andone of white or chalk-lime to two of sand.

In slacking the lime, no more water should be used than isbarely sufficient to reduce it to powder; and it should becovered with a layer of sand, in order to prevent the gas,wherein is the virtue of the lime, from flying off. It is bestto slack the lime in small quantities, about a bushel at a time,in order to secure its qualities in the mortar, which wouldevaporate were it to remain slacked any length of time beforebeing used. See Mortar.

The mortar, vlien about to be used, should be beaten threeor four times, and turned over with the beater, so as toincorporate the lime and sand, and break the knots that passthrough the sieve: this not only renders the texture moreuniform, but by admitting the air into the body and pores ofthe mortar, makes it much stronger. Should the mortarstand any length of time after this operation, without beingused, it must be beaten again : it should be observed, that inthese beatings very little water should be used; though inhot and dry weather the mortar may be kept considerablysofter than in winter.

In dry weather, and for firm work, the best mortar mustbe used, and the bricks should be wetted, or dipped in wateras they are laid; but in damp weather, the latter precautionwill be unnecessary. The wetting of the bricks causes themto adhere to the mortar, which they will never do if laid dry,and covered with sand or dust, as they may be removed with-out the adhesion of a single particle of the mortar. .

In laying the foundations of walls, the first courses arealways laid broader than the wall intended to be carried up 5these courses are called the footings, and the projections arecalled set-off’s; there are generally two inches in each pro-jection.

In working up the wall, not more than four or five feetof any part should be built at a time; for as all walls shrinkimmediately after building, the part which is first broughtup will settle before the adjacent part is brought up to it 5and the shrinking of the latter will consequently cause thetwo parts to separate. Unless it be to accommodate thecarpenter, &e., no part of a wall should be carried higherthan one scaffold, without having its contingent parts addedto it. In carrying up any particular part, the ends shouldbe regularly sloped off, so as to receive the bond of theadjoining parts, on the right and left.

In laying bricks, there are four kinds of Bond; vi*->English -bond, Flemish-bond, Herring-bond, and Garden*wall-bond. The two first are principally used in modernbrickwork, the others only occasionally.