1905. Niches may be formed in brickwork. They constitute the most difficult part of the bricklayer's practice. The centre will be described under the section Carpentry. The difficulty in forming them arises from the thinness to which the bricks must be reduced at the inner circle, as they cannot extend beyond the thickness of one brick at the crown or top, it being the usual as well as much the neatest method to make all the courses standing. 1906. Tiling is the operation of laying the tiles on a roof for the covering of the building, and is effected with either plane tiles or pantiles, the former whereof is the most secure. Plane tiles are laid at different guages; when laid at a six-inch guage, 800 will cover a square; at a seven-inch guage, about 690. A plane tile weighs from 2 lbs. to 2 lbs.

1907. Pantiling is laid to a ten-inch guage; and 180 pantiles, weighing from 5 lbs. to 5 lbs. each, will cover a square. From the frequent repairs necessary to tiled roofs, slating has become the most useful covering, and is generally employed, except for the most common buildings.

1908. The tiler's tools are-the lathing hammer, with two guage marks on it, one at 7 inches, the other at 74 inches. The lathing staff, of iron, in the form of a cross, to stay the cross laths and clinch the nails. The tiling trowel, to take up the mortar and lay it on the tiles: it differs from the brick trowel, in being longer and narrower. The bosse, made of wood, with an iron hook, to hang on the laths or on a ladder, for holding the mortar and tiles. The striker, a piece of lath about 10 inches long, for separating and taking away the superfluous mortar at the feet of the tiles. The broom, to sweep the tiling after it is

struck.

SECT. III.

MASONRY.

1909. Masonry is the science of preparing and combining stones so as to tooth, indent, or lie on each other, and become masses of walling and arching for the purposes of building. The tools of the mason vary as the quality of the stone upon which they are to act. About the metropolis the value of stone is considerable; and it is accordingly cut into slips and scantlings by a saw moved horizontally backwards and forwards by a labourer. In those parts where stone is abundant, it is divided into smaller scantlings by means of wedges. The principal tools of the mason are the mallet and chisels, the latter being formed of iron, except at the steel end, and the cutting edge being the vertical angle. The end of the chisel struck by the mallet is a small portion of a spherical surface, and projects on all sides beyond the adjoining part or hand hold, which increases in magnitude towards the middle of the tool, to the entering or cutting edge. The other tools of the mason are a level, a plumb-rule, a square, a bevel, straight and circular rules of divers sorts, for trying surfaces in the progressive states of the work.

1910. In London, the tools used to work the face of a stone are, successively, the point, the inch tool, the boaster (the operation of working with which is called boasting, as that with the point is called pointing), and the broad tool. The use of the point leaves the stone in narrow furrows, with rough ridges between them, which are cut away by the inch tool, and the whole made smooth by the boaster. The point is from to of an inch broad, the boaster is 2 inches wide, and the broad tool 3 inches at the cutting edge, which in use is always kept perpendicular to the same side of the stone. It performs two sorts of operations. Thus, imagine the impression made by the whole breadth of the tool at the cutting edge to be called a cavity; in one operation, the successive cavities follow one another in the same straight line, until the breadth or length of the stone is exhausted; successive equidistant parallel lines are then repeated in the same manner, until the tool has passed over the whole surface. This operation produces a sort of fluted surface, and is called stroking. In the other operation, each successive cavity is repeated in new equidistant lines throughout the length or breadth of the stone; then a new series of cavities is repeated throughout the length and breadth of the stone; and thus until its whole length or breadth is gone through. This operation is called tooling. The tools for working the cylindrical and conical parts of mouldings are of all sizes, from of an inch upwards. Those for working convex mouldings are not less than half an inch broad, except the space be too confined to admit of such breadth.

1911. A stone is taken out of winding principally with points, and finished with the inch tool. In London, the squared stone used for facing buildings is usually stroked, tooled, or rubbed.

1912. In those parts of the country where the stone saved by the operation of sawing is not enough to compensate for the labour, the operation is altogether performed with the mallet and chisel.

1913. When stones, previous to the operation of hewing, are very unshapely, a stone axe, jedding axe, scabbling-hammer, or cavil, is used to bring the stone nearly to a shape; one end of the jedding axe is flat, and is used for knocking off the most protuberant angular parts, when less than right angles; the other end is pointed for reducing the different surfaces to nearly the intended form.

1914. In Scotland, besides the above described sorts of work, there are some other kinds termed droved, broached, and striped. Droving is the same as that called random tooling in England, or boasting in London. The chisel for broaching is called a punch, and is the same as that called a point in England. Broached work is first droved and then broached, as the work cannot at once be regularly done with the punch. Striped work must also be first droved and then striped. If broaching is performed without droving, which is sometimes done, it is never so regular, and the surface is full of inequalities. Of the three kinds of surfaces obtained, the droved is the cheapest.

1915. It is however to be observed, that the workman will not take the same pains to drove the face of a stone which is to be afterwards broached, as in that of which the droving is to remain the final finish. When the surface of stone is required to be perfectly smooth, it is accomplished by rubbing with sand or gritstone, and it is called rubbed work. In Aberdeen, where the stone is very hard, being a granite, they use the scabbling hammer, by which they pick the stone until the surface has nearly acquired the requisite form. This sort of work is called nidged-work, and the operation nidging.

WALLING.

1916. In stone walling the bedding joints are usually horizontal, and this should always, indeed, be so when the top of the wall is terminated horizontally. In building bridges, and in the masonry of fence walls upon inclined surfaces, the bedding joints may follow the general direction of the work.

The footings of stone walls should be constructed with stones as large as may be, squared and of equal thicknesses in the same course, and care should be had to place the broadest bed downwards. The vertical joints of an upper course are never to be allowed to fall over those below, that is, they must be made as it is called to break joint. If the walls of the superstructure be thin, the stones composing the foundations may be disposed so that their length may reach across each course from one side of the wall to the other. When the walls are thick, and there is difficulty in procuring stones long enough to reach across the foundations, every second stone in the course may be a whole stone in breadth, and each interval may consist of two stones of equal breadth, that is, placing header and stretcher alternately. If those stones cannot conveniently be had, from one side of the wall lay a header and stretcher alternately, and from the other side another series of stones in the same manner, so that the length of each header may be two thirds, and the breadth of each stretcher one third of the breadth of the wall, and so that the back of each header may come in contact with the back of an opposite stretcher, and the side of that header may come in contact with the side of the header adjoining the said stretcher. In foundations of some breadth, for which stones cannot be procured of a length equal to two thirds the breadth of the foundation, the works should be built so that the upright joints of any course may fall on the middle of the length of the stones in the course below, and so that the back of each stone in any course may fall on the solid of a stone or stones in the lower course.

1917. The foundation should consist of several courses, each decreasing in breadth as they rise by sets off on each side of 3 or 4 inches in ordinary cases. The number of courses is necessarily regulated by the weight of the wall and by the size of the stones whereof these foundations or footings are composed.

A wall which consists of unhewn stone is called a rubble wall, whether or not mortar is used. This species of work is of two kinds, coursed and uncoursed. In the former, the stones are guaged and dressed by the hammer, and thrown into different heaps, each containing stones of the same thickness. The masonry is then laid in horizontal courses, but not always confined to the same thickness. The uncoursed rubble wall is formed by laying the stones in the wall as they come to hand, without guaging or sorting, being prepared only by knocking off the sharp angles with the thick end of the scabbling hammer. 1918. Walls are most commonly built with an ashlar facing, and backed with brick or rubble work. In London, where stone is dear, the backing is generally of brickwork; which does not occur in the north and other parts, where stone is cheap and common. Walls faced with ashlar and backed with brick or uncoursed rubble are liable to become convex on the outside from the greater number of joints, and, consequently, from the greater quantity of mortar placed in each joint, as the shrinking of the mortar will be in proportion to the quantity; and therefore such a wall is inferior to one wherein the facing and backing are of the same kind, and built with equal care, even supposing both sides to be of uncoursed rubble, than which there is no worse description of walling. Where a wall

consists of an ashlar facing outside, and the inside is coursed rubble, the courses at the back should be as high as possible, and the beds should contain very little mortar. In Scotland, where there is abundance of stone, and where the ashlar faces are exceedingly well executed, they generally back with uncoursed rubble; in the north of England, where they are not quite so particular with their ashlar facings, they are much more particular in coursing the backings. Course rubble and brick backings admit of an easy introduction of bond timber. In good masonry, however, wooden bonds should not be continued in length; and they often weaken the masonry when used in great quantity, making the wall liable to bend where they are inserted. Indeed, it is better to introduce only such small pieces, and with the fibres of the wood perpendicular to the face of the wall, as are required for the fastenings of battens and dressings.

1919. In ashlar facing, the stones usually rise from 28 to 30 inches in length, 12 inches in height, and 8 or 9 inches in thickness. Although the upper and lower beds of an ashlar, as well as the vertical joints, should be at right angles to the face of the stone, and the face, bed, and vertical joints at right angles to the beds in an ashlar facing; yet, when the stones run nearly of the same thickness, it is of some advantage, in respect of bond, that the back of the stone be inclined to the face, and that all the backs thus inclined should run in the same direction; because a small degree of lap is thus obtained in the setting of the next course, whereas, if the backs are parallel to the front, no lap can take place when the stones run of an equal depth in the thickness of the wall. It is, moreover, advantageous to select the stones so that a thicker one and a thinner one may follow each other alternately. The disposition of the stones in the next superior course should follow the same order as in the inferior course, and every vertical joint should fall as nearly as possible in the middle of the stone below.

1920. In every course of ashlar facing in which the backing is brick or rubble, bond, or, as they are called in the country, through stones should be introduced, their number being proportioned to the length of the course; every one of which stones, if a superior course, should fall in the middle between every two like stones in the course below. And this disposition should be strictly attended to in all long courses. Some masons, in carrying

up their work, to show that they have introduced a sufficient number of bond stones into their work, choose their bond stones of greater length than the thickness of the wall, and knock or cut off their ends afterwards. But this is a bad practice, as the wall is liable to be shaken by the force used in reducing, by chiselling or otherwise cutting away the projecting part, and sometimes with the chance even of splitting the bond stone itself.

1921. In piers, where the jambs are coursed with ashlar in front, every alternate jamb stone should go through the wall, with its beds perfectly level. If the jamb stones are of one entire height, as is often the case when architraves are wrought upon them, and also upon the lintel crowning them, of the stones at the ends of the courses of the pier which are to adjoin the architrave jamb, every alternate stone should be a bond stone; and if the piers be very narrow between the apertures, no other bond stones will be necessary in such short courses. When the piers are wide, the number of bond stones is to be proportioned to the space. Bond stones, too, must be particularly attended to in long courses above and below windows. They should have their sides parallel, and of course perpendicular to each other, and their horizontal dimension in the face of the work should never be less than the vertical one. The vertical joints, after receding about three quarters of an inch from the face of the work with a close joint, should widen gradually to the back, so as to form hollow wedge-like figures for the reception of mortar and packing. The adjoining stones should have their beds and vertical joints filled with oil-putty, from the face to about three-quarters of an inch inwards, and the remaining part of the beds with well-prepared mortar. Putty cement is very durable, and will remain prominent when many stones are in a state of dilapidation, through the action of the atmosphere upon them. The use of the oil-putty is at first disagreeable, from the oil spreading over the surface of the contiguous stones; but after a time this unpleasant look disappears, and the work seems as though of one piece.

1922. All the stones of an ashlar facing ought to be laid on their natural beds. From inattention to this circumstance, the stones often flush at the joints; and, indeed, such a position of the lamina much sooner admits the destructive action of the air to take place.

1923. Where walls or insulated pillars of very small dimensions are to be carried up, every stone should be carefully bedded level, and be without conçavity in the middle. If the beds should be concave, as soon as the superimposed weight comes to be borne by the pier or pillar, the joints will in all probability begin to flush; and it is moreover better, if it be possible, to make every course in the masonry of such a pier or pillar in one stone. 1924. When large columns are obtained in a single block, their effect, from that circumstance alone, is very striking; but as this is not very often to be accomplished, the next point is to have as few and as small joints as possible; and the different stones, moreover, ought to be selected with the view, as much as possible, of concealing the joints, by having

the blocks as much of the same colours as possible. It will immediately, of course, occur to the reader, that vertical joints in columns are inadmissible.

COLUMNS.

1925. The stones for an intended column being procured, and the order in which they are to be placed upon one another having been determined, we must correctly ascertain the exact diameter for the two ends of each of them. To effect this, draw an elevation of the column proposed to its full size, divide it by lines parallel to the base into as many heights as the column is intended to contain stones, taking care that none of the heights exceed the lengths the stones will produce; the working of the stones to the diameters thus obtained then becomes easy. The ends of each stone must first be wrought so as to form exactly true and parallel planes. The two beds of a stone being thus formed, find their centres, and describe a circle on each of them; divide these circles into the same number of equal parts, which may, for example, amount to six or eight; draw lines across each end of the stone, so that they will pass through the centre and through the opposite divisions of the same end. The extremities of these lines are to regulate the progress of the chisel along the surface of the stone; and therefore, when those of one end have been drawn, those of the other must be made in the same plane, or opposite to them respectively. The cylindrical part of the stones must be wrought with the assistance of a straight edge; but for the swell of a column, a diminishing rule, that is, one made concave to the line of the column, must be employed. This diminishing rule will also serve to plumb the stones in setting them. If it be made the whole length of the column, the heights into which the elevation of the column is divided should be marked upon it, so that it may be applied to give each stone its proper curvature. But as the use of a very long diminishing rule is inconvenient when the stones are in many and short lengths, rules or rods may be employed corresponding in length to the different heights.

STAIRS.

1926. Nothing to perplex will occur in carrying up stairs which are supported by a wall at both ends, because the inner ends of the steps may either terminate in a solid newel, or be tailed into a wall surrounding an open newel. Where elegance is not required, and where the newel does not exceed 2 feet 6 inches, the ends of the steps may be conveniently supported by a solid pillar; but when the newel is thicker, a thin wall surrounding the newel would be cheaper. In stairs to basement stories, where geometrical stairs are used above, the steps next to the newel are generally supported upon a dwarf wall.

1927. In geometrical stairs, the outer end of each step is fixed in the wall, and one of the edges of every step supported by the edge of the step below, and formed with joggled joints, so that no step can descend in the inclined direction of the plane nor in a vertical direction; the sally of every joint forms an exterior obtuse angle on the lower part of the upper step, called a back rebate, and that on the upper part of the lower step of course an interior one, and the joint formed of these sallies is called a joggle, which may be level from the face of the risers to about one inch within the joint. Thus the plane of the tread of each step is continued one inch within the surface of each riser; the lower part of the joint is a narrow surface, perpendicular to the inclined direction or soffit of the stair at the end next to the newel.

1928. With most sorts of stone the thickness of every step at the thinnest place need not exceed 2 inches for steps of 4 feet in length; that is, measuring from the interior angle of every step perpendicular to the rake. The thickness of steps at the interior angle should be proportioned to their length; but allowing that the thickness of the steps at each of the interior angles is sufficient at 2 inches, then will the thickness of them at the interior angles be half the number of inches that the length of the steps is in feet; for instance, a step 5 feet long would be 2 inches at that place.

1929. The stone platforms of geometrical stairs, that is, the landings, half paces, and quarter paces, are constructed of one or more stones, as they can be procured of sufficient size. When the platform consists of two or more stones, the first of them is laid on the last step that is set, and one end tailed in and wedged into the wall; the next stone is joggled or rebated into the one just set, and the end also fixed into the wall, as that and the preceding steps also are; and every stone in succession, till the platform is completed. When another flight of steps is required, the last or uppermost platform becomes the spring stone for the first step of it, whose joint is to be joggled, as well as that of each succeeding step, similarly to those of the first flight. The principle upon which stone geometrical stairs are constructed is, that every body must be supported by three points placed out of a straight line; and therefore, that if two edges of a body in different directions be secured to another body, the two bodies will be immoveable in respect to each other. This last case occurs in the geometrical staircase, one end of each stair stone being tailed into the

wall so as to be incapable of tilting, and another edge resting either on the ground itself, or on the edge of the preceding stair stone or platform, as the case may be. The stones which form a platform are generally of the same thickness as those forming the steps.

ON THE SCIENTIFIC OPERATIONS OF STONE CUTTING.

1930. The operations by which the forms of stones are determined, so as to combine them properly in the various parts of an edifice, are founded on strictly geometrical principles, and require the greatest care and exactness in execution. It is only by a thorough know. ledge of the nature of these operations that the master mason is able to cut and carve the parts which, when joined together, compose the graceful arch, the light tracery of the Gothic vault, or the graceful and magnificent dome. The method of simple walling, and

its general principles, have been given in this book, chap. sect. x. In what follows we propose to confine ourselves, 1st, to the leading operations necessary to set out the simple arch or vault, and the groins formed by it; 2d, to the forms produced by vaults with plain and curved surfaces intersecting; 3d, and lastly, to dome vaulting; giving such examples as will so initiate the student that he may, we trust, have little, if any, difficulty in resolving any case that may occur, and reminding him that if he well understand the section already submitted to him on Descriptive Geometry, his labour will be much abridged, not only in what immediately follows, but in that section which treats hereafter on Carpentry.

1931. I. OF THE CONSTRUCTION OF ARCHES AND SIMPLE VAULTS, AND THE GROINS FORMED BY THEIR INTERSECTION. In arches and simple vaults we have to ascertain the exact form of the arch in all its parts, and the direction of its joints; both which points are dependent on the geometrical properties of the curve used for the arch.

1932. To find the joints of a flat arch without using the centre of the circle of which the arch is a part. Divide the arch AB (fig. 619.)

e f

C

3

4

5

6

A

Fig. 619.

into as many equal parts as there are intended to be arch stones, at the points 1, 2, 3, &c. From A, with any convenient radius, describe an arc at a, and from 2, with the same radius, describe another arc, crossing the first at a, and join al; then 1 is the first joint from A. To find the joint passing through 2; with the same radius as before, from the joints 1 and 3 as centres, describe arcs cutting each other at b, and draw 2b; then 26 is the second joint. In the same manner all the other joints between A and B will be found. To find the skew backs, or abutting joints AC and DB; with a radius equal to la, from the centre A describe an arc at C; from the centre 1, with the radius Aa, describe an arc cutting the former at C, and draw the line AC, which will be the springing bed of the arch. In the same manner the joint BD may be found.

1933. The joints of any arch may be drawn with considerable accuracy by setting off at equal distances a point in the curve on each side of the place for the joint, and from these points, as centres, with any radius, arcs to intersect, through whose intersections lines being drawn, will give the directions of the joints.

1934. To draw an elliptical arch to any two dimensions by circular arcs. Draw the straight line AB (fig. 620.). Bisect AB in C by the perpendicular Dg, make CA and CB each

Bisect #D

equal to half the span of the arch, and make CD equal to the height, and Aj parallel and equal to CD. In Cg make Ch equal to CD. Divide Aj and AC each into two equal parts. Through 1 in AC draw kn, and through 1 in Aj draw 1D, cutting kn at n. by the perpendicular lg, and from g with the radius gn or gD describe the arc n Dih. Draw gh parallel to AB, and join hB, and produce hB to meet the arc n Dh in i. Join gi cutting AB in f and make Ce equal to Cf. Join ge, and produce it to meet the arc n Dh in n. From ƒ with the radius fi describe the arc i B, and from e with the radius eA describe the arc Amn. Then Am DiB is the arch required.

1935. An elliptical arch ADB (fig. 621.) being given, to draw the joints for a given number