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 ap. pears, 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 had 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 pitched roofs; they discharge the rain with greater rapidity; snow continues to lie a much shorter time on their surface, and they are less liable to be stripped by heavy winds.

Low roofs require large slates, and the utmost care in the execution; but they have, however, this advantage, that they are much cheaper, since they require shorter timbers, and consequently much smaller scantling; besides, they have less pressure on the walls. The roof is one of the principal ties to a building, when executed with judgment, as it binds the exterior walls together. There are a variety of forms in the vertical section of roofs, besides the simple and customary one above mentioned. The figure of the roof depends on two or more vertical and horizontal sections. A span, or pent roof, is that which stands upon walls of a quadrangular plan, and of which the transverse vertical section is every where a triangle throughout its length, and slopes from two opposite sides. A hipt, or Italian roof is that, the sides of which incline alike to the horizon, and terminate either in a point, line, or raised platform. Vitruvius calls a hipt roof, which rises from a rectangular plan, a testudinated roof, or simply a testudo. When the plan of a roof is a parallelogram, and when the vertical section across the two opposite walls, which have not a greater span than that across the other two walls,

consists of four sloping sides on the outside, each two forming an exterior angle, the roof is called a curb or mansard roof, whether there are gables on the other two sides of the building, or the different sides of the roof, equally inclined, all around, upon each respective wall.

Figures of roofs which rise from square, rectangular, and polygonal plans, forming only exterior angles on the outside, and which terminate in a point over the centre of the plan, are denominated from the base on which they rise, and from a vertical section passing through the apex perpendicular to any one of the sides of the base and to the horizon; that is, a roof standing upon a square pentagonal, or octagonal plan, having a triangular vertical section, is called a square pentagonal or octagonal pyramidal roof; when such a roof is said to be polygonal, the epithet only applies to the figure of the base. An octangular roof is one whose base is an octagon, whatever be the form of the vertical section. All roofs, the horizontal sections of which are similar figures, either polygons as above described, or circles or ellipses, and the vertical sections of which are segments of convex curves, such as of circles, ellipses, parabolas, &c. are called domes; hence a square dome is one that rises from a square plan; an octangular dome, from an octangular plan; a circular dome from a circular plan; and an elliptic dome from an elliptical plan. Domes upon circular plans are called cupolas. A circular or elliptical roof, the vertical section of which consists of two similar and equal concave curves meeting in the apex, is called a trumpet mouthed roof. When the roof is circular or elliptical, and the vertical section an isosceles triangle, the apex of which is that of the roof, the roof is simply called a conical or conoidal roof. When the vertical section of a circular dome is a parabola, hyperbola, or ellipsis, the dome is then called a paraboloidal dome, a hyperboloidal dome, or ellipsoidal dome, these epithets comprehending both the base of the figure and vertical section. All figures of roofs, which insist on the foregoing bases, whatever be the form of their vertical sections, are called by the general name of pavilion roofs, as they only cover one simple building. From the intersections of two or more simple roofs of the same or of different kinds, a multitude of complex figures will be formed: the plans of some of these are denominated by letters of the alphabet, as an ell roof

is one which rests upon a plan in the form of the letter L: a tee roof upon a plan in the form of the letter T; and an aitch roof upon a plan formed like the letter H; but when two common roofs, having their ridges parallel to each other, and a side of the one either joins one of the other, or these two sides intersect each other, and thereby leave a gutter above the roof; then the roof which is thus compounded of the two simple roofs is called an em roof, as the vertical section is in the form of the letter M: or rather an inverted Was M: this is an instance where the roof is denominated by the vertical section, and not by the plan. All roofs whatever are said to be truncated, whether they terminate in a plane or raised platform, or have a void at the top, bounded by a level curb.

When the side of a roof is a plane surface, except at the eaves, at which place it is concave, the roof is said to have a bell cast at that place.

The general names of the timbers are, straining pieces, tie pieces, and bearers; under straining pieces are included, principal rafters, camber beams, hip and valley rafters, collar beams, or straining beams, straining sills, struts, auxiliary rafters, or principal braces and studs.

Under the pieces are included, tie beams, diagonal ties, and truss posts; and under bearers are included plates, purlins, common rafters, small rafters, ridge pieces, boarding and dragon beams.

The sloping sides of roofs are of two kinds, single and double, or plain and carcase: single roofs are those which have one row of rafters upon the same side; double or carcase roofs are those which have two ties of rafters; the lower tie supporting the upper by the intervention of transverse pieces called purlins.

Stone Bridges. A stone bridge is a thick wall built across a hollow, with one, two, three, or a series of apertures, formed into arcades, which either serve to lighten the masonry, or to give passage to a stream of water, or both.

When a stone bridge is resolved upon, the first consideration is its place in this several particulars should be taken into consideration, and the advantages compared to the disadvantages. As the height of the bridge depends on the banks of the river, the expense will be increased according to their height: therefore a convenient situation should be chosen, where the banks will be adequate in height to that necessary for the bridge, though the expense will be increased by the length of the bridge. In most cases, where the

river runs in a valley, a wide part of the stream must be preferred to a narrow part, as the water at this narrower part has not only a greater degree of velocity of itself, but the velocity would also be increased by the piers of the bridge; in times of heavy floods it would be liable to be thrown down, and in a navigable river the navigation would be impeded. As the expense depends on the bed of the river, it must also be taken into the account.

These being settled, the form and height of the arches come next under consideration; the height of the arches, which determine that of the bridge, depends on the rise of the water in time of floods; and whether there is to be a navigation, and what kind of vessels there are to pass.

Stone bridges ought to be constructed with as few arches as possible, which will not only give greater beauty, but will require fewer foundations, piers, and centerings, and also easier passage for craft. The piers ought to be so proportioned as to enable them to withstand the thrust of the adjacent arches, though the rest were thrown down. The number of arches ought to be odd, in order that one may stand in the middle, where the stream has its greatest velocity.

When the passage-way along the top of the bridge is a convex curve, the arches should diminish from the n iddle towards each extreme, so as to be similar to the middle one; this will allow a more free passage to the water, the velocity being greatest in the middle. With respect to the choice of arches, the elliptical, cycloidal, and equilibrated arches, are not only convenient, in allowing more room for the passage of ships at the hanches, but they require fewer materials than most other curves of the same dimensions.

When the extrados is convex, and the height of the arch small in proportion to the span, a segment of a circle may be used with success: in this case the arch should not exceed 60 degrees.

These particulars being fixed, the practice is as follows:-When the foundation of a stone bridge is to be laid in a river which is not very deep a single or double inclosure of wood is formed, and the intervening space is rammed well with clay or chalk, to prevent the water from coming in. These inclosures are either made with piles driven closely together, and dovetailed at their jointings, or by piles driven at certain distances from one another, and grooved on the sides oppo

site each other, and the intervals are shut with boards let in between the grooves. This kind of fence against the water is called a batterdeaux, or coffer-dam. The batterdeaux, or coffer-dam, requires a good foundation of solid earth or clay. If the bed of the river be of a loose consistence, the water will ooze through it in too great abundance. The sides of the inclosure must be made very strong, and well braced within, to prevent the ambient water from forcing its way into the batterdeaux.

Where the water is deep, but having a sound bottom, a strong chest, called a caisson, must be formed, so that the sides may easily be disengaged from the bottom of the river, being bevelled where the pier is to be built, and the caisson properly placed over it, and kept in this situation by ropes: begin to build, and as the work advances it will sink gradually, and at the same time keep continually bracing the sides with timber, to prevent the ambient water from crushing it together, and thereby not only spoiling the work, but drowning the workmen. When the pier is of such height as to be deeper than the water, the sides may be disengaged, and the bottom of the caisson will remain under the pier, as a footing on which it is to rest: for this purpose the bottom of the caisson should be made very strong. Where the foundation is not firm, recourse must be had to piling, as in other such foundations.

With regard to the superstructure of a stone bridge, the arch stones sometimes terminate in a curve parallel to the intrados, and sometimes the joints of the arch stones are continued through the spandrils, observing to break joints sideways; at other times, the upper ends of the arch stones terminate so as to fit the beds and upright joints of every course of stone. The joints of the arch stones are sometimes joggled with plugs,in order to prevent them from passing each other. The piers are generally solid pieces of masonry from the foundation till they come to the spring, or above the spring of the arch; thence arches, or complete cylindrical vaults, are sometimes thrown, in order to lighten the bridge, and brace every two adjacent arches between which they are placed. When the abutments are deep, and extend considerably along the road-way at each end, walls on each side of the road-way should be built, similar to those used in aquatic piers, and either strengthened with counterforts, or vaulted under and across the road-way. When there is a heavy pres

sure of earth between the side of the abutments, these sides should be both concave in any vertical, and also in any horizontal sections.

In stone bridges, when the extrados is a curve, and when the work is coursed, the intersection of the bedding joint of every two courses on the face of the masonry ought to be parallel to the intersection of the extrados with this face, as this position of the joints is not only more beautiful, but is also more agreeable to the laws of strength, than those bedding joints which have their intersections in horizontal planes.

BULB, or BLBOUS root, in the anatomy of plants, expresses a root of a round or roundish figure, and usually furnished with fibres at its base. See BOTANY.

BULBOCODIUM, in botany, a genus of the Hexandria Monogynia class and order. Liliaceous plants. Order Spathacea: Narcissi, Jussieu. Essential character: corolla funnel-form, hexapetalous, with a narrow claw bearing the stamens; capsule superior. There is but one species, viz. B. vernum, spring flowering bulbocodium, resembles the common colchicum in shape, though much smaller; it is covered with a dark brown skin. About the middle of February, according to the season, the flowers spring up, inclosed within three brownish green leaves, opening themselves as soon almost as they are out of the ground, and shew their buds for flowers within them very white, before they open far; though sometimes purplish at first appearing. There is frequently but one flower, and never more than two; they are smaller than those of colchicum. After the flowers are past, the leaves grow to the length of a finger, and in the middle of them rises up the seed vessel, which is smaller, shorter, and harder than that of colchicum, and contains many small brown seeds. It is a native of Spain and of Russia, in mountainous situations.

BULIMY, a disease in which the patient is affected with insatiable and perpetual desire of eating; and unless he is indulged, he often falls into fainting fits. It is also called fames canina, canine appetite.

In the third volume of the "Memoirs of the Medical Society of London" is inserted the history of a case of bulimy, accompanied with vomiting, wherein 379lbs. of meat and drink were swallowed in the space of six days; yet the patient lost flesh rapidly. A cure was effected by giving food boiled down to a jelly, frequently, and in small quantities. In this

form the food was retained, and the body being duly supplied with nourishment, the stomach and rest of the system recovered their proper tone and energy. But the most extraordinary instance of bulimy, which perhaps ever occurred, is that recorded in the third volume of the "Medical and Physical Journal," communicated by Dr. Johnson, commissioner of sick and wounded seamen, to Dr. Blane, formerly physician to the navy. The subject was a Polish soldier, named Charles Domery, in the service of the French, on board of the Hoche frigate, which was captured by the squadron under the command of Sir John Borlase Warren, off Ireland, in 1799. He was 21 years of age, and stated that his father and brothers had been remarkable for their voracious appetites. He began when he was 13 years of age. He would devour raw and even live cats, rats, and dogs, besides bullock's liver, tallow candles, and the entrails of animals. One day (viz. September 7th, 1799) an experiment was made of how much this man could eat in one day. This experiment was made in the presence of the before-mentioned Dr. Johnson, Admiral Child, and Mr Forster, agent for prisoners at Liverpool, and several other gentlemen. He had breakfasted at 4 o'clock in the morning on 4lbs. of raw cow's udder; at half past nine o'clock there were set before him 5lbs. of raw beef and 12 tallow candles of 1b weight, together with 1 bottle of porter; these he finished by half past

ten o'clock; at one o'clock there were put before him 5lbs. more of beef, 1lb. of candles, and three bottles of porter; he was then locked up in the room, and centries were placed at the windows, to prevent his throwing away any of his provi. sions. At two o'clock he had nearly finished the whole of the candles and great part of the beef; but without having had any evacuations by vomiting, stool, or urine. His skin was cool, pulse regular, and spirits good. At a quarter past six he had devoured the whole, and declared he could eat more; but the prisoners on the outside having told him that experiments were making upon him, he began to be alarmed.

BULK heads are partitions made athwart the ship with boards, by which one part is divided from the other; as the great cabin, gun-room, bread-room, and several other divisions. The bulk head afore is the partition between the forecastle and gratings in the head.

BULK breaking. See BREAKING.
BULL. See Bos.

BULL finch. See LOXIA.

BULL, among ecclesiastics, a written letter dispatched by order of the Pope, from the Roman chancery, and sealed with lead, being written on parchment, by which it is partly distinguished from a brief. See BRIEF.

BULL, golden, an edict or imperial constitution, made by the Emperor Charles IV. reputed to be the magna charta, or the fundamental law of the German empire.

It is called golden, because it has a golden seal, in the form of a pope's bull, tied with yellow and red cords of silk: upon one side is the Emperor represented sitting on his throne, and on the other the capital of Rome. It is also called Caroline, on Charles IV's account Till the publication of the golden bull, the form and ceremony of the election of an emperor were dubious and undetermined, and the number of the electors not fixed.

This solemn edict regulated the functions, rights, privileges, and pre-eminen ces of the electors. The original, which is in Latin, on vellum, is preserved at Frankfort; this ordinance, containing thirty articles or chapters, was approved of by all the princes of the empire, and remains still in force.

BULLA, in natural history, a genus of insects of the Vermes Testacea. Animal a limax; shell univalve, convolute, unarmed with teeth; aperture a little entire at the base; pillar oblique, smooth. straightened, oblong, longitudinal, very There are nearly sixty species. B. lignaria is found on European coasts, and is about three inches long. The shell is thin, of a dirty colour, but within it is white. The inhabitants of this species, and, according to Gmelin, those of most of the genus, are furnished with an organ resembling the gizzard of a fowl, and which they appear to use for the purpose of masticating their food.

BULLET, an iron or leaden ball, or shot, wherewith fire-arms are loaded. Bullets are of various kinds; viz. red-hot bullets, made hot in a forge, intended to set fire to places where combustible matters are found. Hollow bullets, or shells made cylindrical, with an aperture and fuse at one end, which giving fire to the inside when in the ground, it bursts, and has the same effect with a mine. Chainbullets, which consist of two balls, joined by a chain three or four feet apart. Branch-bullets, two balls joined by a bar of iron, five or six inches apart. Twoheaded bullets, called also angles, two