tical circular rings, or conic surfaces, having the same common axis with the intrados. Stone walls are those Stone Walls. built of stone, with or without cement in the joints; the bedding joints have most commonly a horizontal position in the face of the work; and this ought always to be the case, when the top of a wall terminates in a horizontal plane or line. In bridge building, and in the masonry of fence walls, upon inclined surfaces, the bedding joints on the face sometimes follow the direction of the top or terminating surface. The footings of stone walls ought to be The following are methods practised in In broad foundations, where stones can- thirds of the foundation, then build them Walls faced with squared stones, hewn By these means, the facing and backing are toothed together, and unquestionably had been parallel to the front surface of stronger than if the back of each ashler the wall; as the stones are mostly raised in quarries of various thicknesses, in an ashler facing, it would greatly contribute B to the strength of the work to select the stones in each course, so that every alternate ashler may have broader beds than those of every ashler placed in each alternate interval. In every course of ashler facing bond stones should be introduced, and their number should be proportioned to the length of the course. This should be strictly attended to in long ranges of stones, both in walls without apertures, and in the courses that form wide piers; when they are wide, every bond stone of one course should fall in the middle of every two bond stones in the course below. In every pier where the jambs are coursed with the ashler, and also in every pier where the jambs are one entire height, every alternate stone next to the aperture in the former case, and every alternate stone next to the jambs in the latter case, should bond through the wall; and also every other stone should be placed lengthwise, in each return of an angle, not less than the average length of an ashler. Bond stones should have no taper in their beds; the end of every bond stone, as well as the end of every return stone, should never be less than a foot. There should be no such thing as a closer permitted, unless it bond through the wall. All the uprights, or joints, should be square, or at right angles to the front of the wall, and may recede about ths of an inch from the face, from thence gradu. ally widen to the back, and thereby make hollow, wedge-formed figures, which will give sufficient cavities for the reception of packing and mortar. Both the upper and lower beds of every stone should be quite level, and not form acute angles, as is often the case; the joints from the face to about ths of an inch within the wall should be either cemented with fine mortar, or with a mix. ture of oil, putty, and white lead: the former is the practice both in London and Edinburgh, and the latter in Glasgow. The putty cement will stand longer than most stones, and will be prominent when the face of the stones has been corroded with age. The whole of the ashler, except that mentioned of the joints toward the face of the wall, the ruble work, and the core, should be set and laid in the best mortar, and every stone laid on its natural bed. All wall-plates should be placed upon a number of bond stones, and particularly those of the roof; by which means they may either be joggled upon the bonds, or fastened to them by iron and lead. In building walls or insulated pillars of very short horizontal dimensions, not exceeding a length of stones that can be easily procured, every stone should be quite level on the bed, without any degree of concavity, and should be one entire piece between every two horizontal joints. This should be particularly attended to on piers, where the insisting weight is great, otherwise the stones will be in danger of splintering and crushing to pieces, and perhaps occasion a total demolition of the fabric. Vitruvius has left us an account of the manner of the construction of the walls of the ancients, which were as follows the reticulated is that wherein the joints run in parallel lines, making angles of 45° each with the horizon in contrary ways, and consequently the faces of the stones form squares, of which one diagonal is horizontal, and the other vertical. This kind of wall was much used by the Romans in his time. The incertain wall was formed of stones, of which the one direction of the joints was horizontal, and the other vertical; but the vertical joints of the alternate courses were not always arranged in the same straight line: all that they regarded was to make them break joint. This manner of walling was used by the Romans in times antecedent to the time of Vitruvius. Vitruvius directs, that in both the reticulated and incertain walls, instead of filling up the spaces between the sides with ruble promiscuously, they should be strengthened with abutments of hewn stone or bricks, or common flints, built in walls two feet high, and bound to the front with cramps of iron. The emplection consisted of two sides or shells of squared stone, with alternate joints, and a ruble core in the middle. The walls of the Greeks were of three kinds, named isodomum, pseudosodomum, and emplection. The isodomum had the courses all of an equal thickness; but the pseudosodomum had them unequally thick; in both these walls, wherever the squared work was discontinued, the interval or core was filled up with common hard stones, laid in the manner of brick, with alternate joints. The emplection was constructed wholly of squared stones; in these bond stones were placed at regular intervals, and the stones in the intermediate distance were laid with alternate joints, in the same manner as those of the face; so that this manner of Greek walling must have been much stronger than the emplection of the Roman villagers. This is a most strong and durable manner of walling, and in modern times it may be practised with the utmost Stone Columns. Stone columns should circle draw a straight line, parallel to any one of the lines drawn through the cen tre and circumference of the former; also from the point in the circumference of the last drawn circle, where the line drawn through the centre cuts this cirsame number of equal parts as that of the cle, divide the circumference into the circle formerly drawn; then draw lines from the centre to each of the points so divided, and these lines will be respectively parallel to those of the former circle; the extremities of each pair of parallel lines, in each circumference, will regulate the chissel draught, which is to be wrought along the surface of the column. The corresponding draught being made from each pair of parallels, the spaces between will be more easily wrought down; then, if the number of pieces which compose the column exceed seven or nine, a straight edge may be applied, the side of which always be ing in a plane passing through the axis; but if fewer pieces are used, make a diminishing rule, that is, to the line of the column: on the side of the diminishing rule draw a straight line parallel to the axis; this rule will serve to plumb the convex surface of each stone: prepare stones in setting them, and to work the stone having its edge straight the same another rule, equal in length to that of a as the diminishing rule. The cement used in setting each column stone is either oil-putty, or white lead, or white lead mixed with chalkputty, or fine mortar, or milled lead rolled rolled lead be used, it needs only to form very thin. If the column be large, and a ring half an inch distant from the edge of the joint, and let the joint at the edge be filled with oil-putty. Stone Stairs. When stairs are supported by a wall at both ends, nothing difficult can occur in the construction; in ther terminate into a solid newal, or be this the inner ends of the steps may einewal. Where elegance is not required, tailed into a wall surrounding an open and where the newal does not exceed two feet six inches, the ends of the steps may be conveniently supported by a solid thin wall surrounding the newal would be pillar; but when the newal is thicker, a where there is a geometrical stair above, cheaper. In the stairs of a sunk story, Geomethe steps next to the newal are generally supported upon a dwarf wall. trical stairs have the outer end fixed in the wall, and one of the edges of every step supported by the edge of the step below, and constructed with sally-formed joints; so that they cannot descend in the inclined direction of the stair, not yet in a vertical direction; the upper sally of every step forms an interior obtuse angle, called a back rebate, and the lower, of course, an exterior one; and the joint formed of these sallies is called a joggle. The upper part of the joint may be level from the face of the risers, to about one inch within the joint. This is the plane of the tread of each step, continued one inch within the surface of each riser; the lower part of the joint is a narrow surface, perpendicular to the rake of the stair, at the end next to the newal. In stairs constructed of most kinds of stone, the thickness of every step, at the thinnest place of the end next to the newal, has no occasion to exceed two inches, for steps of four feet in length, that is, by measuring from the interior angle of every step perpendicular to the rake. The thickness of steps at the interior angle should be proportioned to the length of the step; but allowing that the thickness of the steps at each interior angle is sufficient at two inches, then will the thickness of the steps at the interior angles be half the number of inches that the length of the steps has in feet; thus a step five feet long would be two inches and a half at that place. The stone platform of geometrical stairs, viz. the landing half spaces, and quarter spaces, are constructed of one, two, or several stones, according to the difficulty of procuring them. When the platform consists of two or more stones, the first platform stone is laid upon the last step that is set, and the one end wedged in the wall the next platform stone is joggled, or rebated, into the one next set, and the end again fixed in the wall, as that and the preceding steps are, and every stone in succession, till the platform is completed. If there is occasion for another flight of steps, the last platform becomes a spring stone for the next step; the joint is to be joggled, as well as all the succeeding steps, in the same manner as the first flight. Geometrical stairs, executed in stone, depend on the following principle: that every body must at least be supported by three points, placed out of a straight line, and, consequently, if two edges of a body in different directions be secured to another, the two bodies will be immoveable in respect to each other. This last is the case in a geometrical stair; one end of a stair stone is always tailed into the wall, and one edge either rests on the ground itself, or on the edge of the preceding stair stone, whether the stair stone be a plat or step. The stones forming a platform are generally of the same thickness as those forming the steps. Roofs. Roof is that part of a building raised upon the walls, and extending over all the parts of the interior, which consists not only of the covering or exterior part, but of all the necessary supports of that part, for protecting its contents from inclement seasons. There are many forms of roofs, the most simple of which is that which has only one plane, and is called a shed roof; but the form which has always been, and still continues to be, in most general use, wherever the nature of climate requires it to be raised, is that, the vertical section of which consists of two sloping sides, is consequently triangular, and called a span or pediment roof. Here it will be proper to say something of the changes of inclination or pitch which have prevailed in this simple form, among different nations, from time to time, arising as well from the nature of the climate as the caprice of the people, and as transmitted down to the present age. The ancient Egyptians, Babyloni. ans, and Persians, as well as other eastern nations, and also the present inhabitants of those climates where rain seldom appears, make their roofs quite flat. The ancient Greeks, perceiving the inconvenience of this, raised them in the middle, with a gentle inclination towards the sides; the height from the middle to the level of the walls not exceeding oneninth or one-eight part of the span; as may be seen by many ancient temples still remaining in that country. The Romans made the height from one-fifth to two-ninth parts of the span. After the decline of the Roman empire, high pitched roofs began to be in general request all over Europe, and the vertical section of that which most generally prevailed seems to have been an equilateral triangle, which was considered as the standard. In Germany, this has been remarkable from very remote antiquity, as appears from Vitruvius: the equilateral pitch, and that of a higher one, appears to have Continued as long as pointed architecture prevailed. When Grecian and Roman architecture was first introduced into this country from Italy, roofs began to be made lower, and the rafters were three-fourths of the breadth of the building: this was called true pitch, and subsequently the square seems to have been considered as the true pitch. In these several gradations of changes, the material for the covering has been supposed to be impervious stone or slates; and the roofs themselves to be those which cover ordinary dwellings; for, after the Italian architecture began to prevail in the last century, platform roofs, and those of a pediment pitch, were introduced in many sumptuous mansions and public edifices; but the material employed for covering was lead. At the present day, when good slates are to be bad in abundance, we can execute roofs to the Grecian declivity; but with regard to the general practice, the pitch of the roof depends on the style of architecture introduced in the buildings; the proportion of the pitch, in ordinary dwellings, is between one-third and one fourth part of the span; mansions and public buildings are executed in every style that has prevailed in different times and among different people; and the proportion of the roof, as well as other parts, are rigidly adhered to; this consequently produces a great diversity in the heights. There are some advantages in high Low roofs require large slates, and the consists of four sloping sides on the out- Figures of roofs which rise from square, |