was in ater times represented as descended from Aeneas, while others, preserving the legend more in its original purity, made no mention of its Trojan descent. The main features of the Roman legend which are preserved in Livy (1.3, &c.; Cic., De Republ., ii. 5; comp. Plut., Romul., 3, &c. Dionys. Hal., i., p. 61, &c.), are these: When Procas, king of Alba, died, he left two sons, Numitor and Amulius. The latter wrested the government from his elder brother, who yielded without a struggle, and lived as a private person in quiet retirement. But Amulius, fearing that the descendants of his brother might punish him for his usurpation, had the son of Numitor murdered, and made his daughter Silvia a priestess of Vesta, an office which obliged her to perpetual celibacy. One day however when Silvia went into the sacred grove to draw water from the well for the service of Vesta, an eclipse of the sun took place, and the maid, frightened by the appearance of a wolf, fled into a cave. Here she was overpowered by Mars, who promised her a glorious offspring. She was delivered of twins, but the god apparently forsook her, for she was condemned and put to death by Amulius, and it was determined that the two children should be drowned in the river Anio. But the river carried the cradle, with the children in it, into the Tiber, which at the time had overflowed its banks. The cradle was driven into shallow water to a wild fig-tree (Ficus Ruminalis) at the foot of the Palatine hill. A she-wolf, which came to the water to drink, heard the cries of the children, and suckled them, whilst a woodpecker, which was, like the wolf, an animal sacred to Mars, brought them other food whenever they wanted it. This marvellous spectacle was observed by Faustulus, the berdsman of the flocks of king Amulius, and he took the children and carried them to his wife Acca Laurentia or Lupa. Thus they grew up in the shepherd's straw huts on the Palatine; that in which Romulus was said to have lived was kept up to the time of the emperor Nero. The two youths became the stoutest and bravest among their comrades, with whom they shared their booty. The followers of Romulus were called Quinctilii, and those of Remus, Fabii. A quarrel one day broke out between the two brothers and the shepherds of the wealthy Numitor. Remus was taken by a stratagem, and led to Alba before Numitor, who, struck by his appearance and the circumstance of the age of the two brothers, ordered Romulus likewise to be brought before him. Faustulus now disclosed to the young men the secret of their birth, and with the assistance of the faithful comrades who had accompanied them to Alba, they slew Amulius, and their grandfather Numitor was restored to the government of Alba. | and Sabines to attend them with their daughters. In the midst of the solemnities the females were forcibly carried off: the number thus taken was said to have been thirty. The three nearest Latin towns, Antemnæ, Cænina, and Crustumerium, now took up arms against Rome, but Romulus defeated them successively, and having slain Acron, king of Canina, he dedicated the first spolia opima to Jupiter Feretrius. The Sabines, under their king Titus Tatius, likewise made war upon Rome, and the treachery of Tarpeia, a Roman woman, opened to them the gates of the fortress on the Capitol. The Sabines attempted to storm the city, and Romulus in this emergency vowed a temple to Jupiter Stator, in order to inspire his men with courage and to prevent them from flying before the enemy. The war was continued with doubtful success, and finally terminated by the Sabine women throwing themselves between the combatants, and thus restoring peace between their fathers and husbands. Romulus rewarded the women of Rome for their services by the grant of various privileges, and the thirty curiae were called after the names of the thirty Sabine women. The two nations, the Romans on the Palatine, and the Sabines on the Capitoline and the Quirinal, were united as one nation, though each continued to have its own king. The two kings and the citizens of the two states met in the valley between the Capitoline and Palatine (comitium) whenever it was necessary to transact business which was of importance to both nations. This union however did not last long, for Tatius was killed during a national sacrifice at Lavinium, and Romulus henceforth ruled alone over the two nations. During the period that Romulus was sole king, he is saia to have carried on two wars, one against Fidenae, and another against Veii. Fidena commenced the war from fear of the growing strength of its neighbour; but Romulus got a victory over them by stratagem, and took possession of their town. The war against Veii rose out of that against Fidenæ, for both were Etruscan towns. Veii was likewise humbled, but it obtained a truce of one hundred years, after surrendering part of its territory to Rome. Such are the fortunes and achievements which the old Roman legend ascribed to the founder of the city. Respecting his political institutions, see the article ROME. He is said to have died after a reign of thirty-seven years (716 B.C.). His death is represented in as marvellous a light as his birth. On the nones of Quinctilis, or on the Quirinalia, the king, while reviewing his people near the marsh of Capra, was taken up by his father Mars, and carried to heaven. The people in terror fled from the spot; but Romulus soon afterwards appeared as a glorified hero to Proculus Julius, and bade him inform his people that in future he would watch over them as the god Quirinus. The love of their humble home however drew the youths Such are the main features of the story of the founder of Rome, which was handed down by tradition, and commemorated in national songs to the time of Dionysius. (Dionys. Hal., i., p. 66.) Writers both antient and modern have attempted to elicit historical truth from this beautiful and in most parts truly poetical legend, or have struck out some parts of the narrative as altogether fabulous, and retained others which are more in accordance with the events of real history. The mischievous results of such perverse criticism have been clearly shown by Niebuhr (i., p. 235, &c.). The acts and institutions attributed to Romulus which are of any importance to the historian, and which from their connection with events of a more historical age, or with the general state of the nations of Italy, may be considered as The population of the new city being very small, the gates were thrown open to strangers. Exiles, robbers, runaway slaves, and criminals flocked to the city as an asylum, and found a welcome reception. The only thing they now wanted was women; but none of the neighbouring people were willing to form matrimonial connections with the new settlers. Romulus therefore had recourse to a stratagem; Le proclaimed that festive solemnities and games should be held in the city, and he invited his neighbours the Latins RONCES VALLES (French, Roncevaux) is the name of a valley formed by the Pyrenees of Navarre between Pampeluna and St. Jean Pié de Port, on the French frontier. It is also the name of a small village in that valley, remarkable only for an antient abbey (Nuestra Señora de Roncesvalles), where the tomb of Don Sancho el Fuerte (the strong), king of Navarre, is shown, as well as several antient relics bearing the name of Roland. According to tradition, this hero, and many others of Charlemagne's peers, who had invaded Spain in 778, whilst attempting to regain France, were surrounded by the Navarrese, commanded by Bernardo del Carpio, and put to death. This event however, which forms the subject of many Spanish romances and chivalrous chronicles, is far from being supported by historical evidence. RONDA, a city in the south of Spain, formerly belonging to the province of Malaga, is now the capital of a province | Pasquier, and others commended him highly; but mo so called since the late division of the Spanish territory. critics have judged him more severely. Boileau says t It is generally supposed, though erroneously, to occupy the Ronsard's language was a heterogeneous compound of site of the antient Arunda (Plin., iii. 1), which stood some rious languages and dialects, and that his muse spoke Gr miles to the south-west. It is an ascertained fact that it and Latin in French verses. Malherbe and La Bray was entirely built by the Moors, with the remains of Aci- have spoken of him in the same strain. Charles IX. nippo, or Ronda la Vieja (old Ronda), which is two leagues stowed on Ronsard an abbacy and other benefices. E to the north, and where the ruins of an amphitheatre, a moral conduct however is said not to have been strictly temple, aqueduct, and extensive walls are still standing. rical. He died in 1585, in one of his livings near T Ronda is situated in the midst of the lofty mountains of the and a solemn funeral service was celebrated in honou Sierra de Ronda, and is fourteen leagues from Gibraltar, him at Paris, in the chapel of the college of Boncour. R twenty from Cadiz, and about the same distance from Seville. sard had certainly poetical genius, but he was deficie It is considerably elevated above the sea, being built on a taste. He was in this respect in France what the sen hill, which terminates abruptly just below it to the west. tisti of the following century were in Italy and Spain. H The city is separated into two parts by a very narrow ravine poetical works are numerous; they consist of odes, byr of great depth, called El Tajo (the cut), through which flows eclogues, &c.: Mascarades, Combats, et Cartels faits & P the river Guadiaro. Though divided by nature, the city has et au Carnaval de Fontainebleau.' He also began a poem, L been united by means of a bridge of most stupendous dimen- Franciade,' which he left unfinished. His works are t sions, springing from the banks of the river on massive stone nearly forgotten. The most complete edition of them is piers, and at the height of nearly 400 feet above the bed of by Richelet, 2 vols. fol., Paris, 1623. the river. The city of Ronda has a population of about 20,000 inhabitants. The streets are narrow, but clean. There is a public walk, called Alameda, well shaded with trees and shrubs; and a Plaza de Toros (bull-ring), built entirely of stone, and capable of holding eight or nine thousand persons. The Alcazar, or Moorish castle, one of the most extensive and best built in all Andalusia, is now a mass of ruins, having been blown up by the French on their evacuation of Ronda during the Peninsular war. It was considered impregnable as long as the Moors held it, and resisted several sieges, until it was finally reduced by Ferdinand in 1485, towards the close of the Moorish war. [MOORS.] With the exception of a few tan-yards, which are not in a very prosperous condition, Ronda has no trade whatever; the inhabitants occupy themselves chiefly in farming and raising fruits and vegetables for the consumption of Gibraltar. An annual fair, originally instituted for the sale of horses, but which now is not confined to that traffic, is held at Ronda. It is attended by merchants from almost every part of southern Spain. RONDEAU (Fr.), or RONDO (It.), a kind of air consisting of two or more strains, in which, after finishing the second strain, the first is repeated, and again after the third, &c., always returning to and concluding with the first. (Rousseau.) RONDELE TIA, a genus of plants of the natural family of Rubiacea, named after Rondelet, a French botanist of the sixteenth century. It is characterised by having a calyx with a subglobular tube. Corol superior, funnelshaped, ventricose at the throat. Segments four to five, ovate, obtuse, spreading. Anthers four to five, sessile within the corol. Ovary two-celled. Style filiform. Stigma bifid. Capsule round, crowned with the limb of the calyx. Seeds minute, numerous, or few when abortive. The genus, as formerly constituted, included many shrubby trees which occur in India (Roxb., Fl. Indica), but these have been referred by modern botanists to Adenosacme, Greenia, and Wendlandia. The present genus Rondeletia occurs chiefly in America and the West Indies. RÖNGEBIRGE. [GERMANY.] ROOD, the quarter of an acre. [ACRE.] ROOF, the covering of a house or other building. T name, in its most extended sense, embraces the exter covering itself, and the framework by which it is supporte but, as a term in carpentry, it is limited to the carcass rat or framing. J The importance of this part of a building can hardi overrated, since on its right construction depends not on.. the comfort of those for whose shelter it is designed, but as the safety and durability of the edifice itself. For t former of these purposes it is desirable that a roof shock exclude extremes of heat and cold, and be impervious: rain or snow. For the latter, the exclusion of water I equally necessary, and it is essential that the framework so disposed as to throw the least possible strain on the wais By a judicious arrangement in this particular, a roof may only be prevented from pressing on the walls in an in rious manner, but may be made to contribute greatly to stability of the whole structure. In order to the due cor bination of the requisite qualities, an intimate acqua ance with the principles of mechanical philosophy is ind pensable; and a correct knowledge of the strength different materials, when exposed to various kinds strain, is necessary to the economical adjustment of th dimensions of the several parts of a roof. A roof of iar span forms, indeed, one of the most interesting app cations of the science of carpentry, theoretical or o structive. In order to cover in a building ir which the space to spanned is greater than can be covered by single blocks stone extending from one point of support to another, it a necessary either to have recourse to the principle of th arch, as in vaults and domes of stone or brick, or to forta framework of timber to support the covering. The form plan is objectionable in the case of ordinary buildings ma its expense and weight, and from the great solidity requires in the walls, where they have to be used as the abutme of an arch. The principles on which such coverings of sonry are formed are explained under ARCH and DOME in this article the more usual kind of roof, that susta by a wooden framing, will be described. Such structu RONSA'RD, PIERRE DE, born in 1524, in the dis- occasionally partake of the character of an arch or do trict of old France called Vendômois, was the son of a but more usually consist of flat planes variously disposed maître-d'hôtel of Francis I., who made him a knight. Roofs formed of one level plane, which are extensively use Pierre studied for a short time in the college of Navarre at in eastern countries, are not adapted for buildings in wh Paris, but soon after he entered the service of the duke of a large space has to be spanned over, nor to resist the perOrléans, son of Francis I., in the quality of page. He after-tration of water; and are therefore unsuitable for clima's wards attended, in the same capacity, James Stuart, king of Scotland, who had come to Paris to marry Marie de Lorraine, and he accompanied James on his return to Scotland, where he remained three years. On his return to France he resumed his post with the duke of Orléans, who sent him on several missions to Scotland, Ireland, and other countries. He was afterwards sent by Francis I. on a mission to Piedmont. In these several journeys he suffered much, in consequence of which he became deaf. On withdrawing from active life he retired to the college of Coqueret, where he studied the classics under Turnèbe, became a good Greek scholar, and took orders as a priest. He also began writing French poems, and was crowned in the floral games at Toulouse. [CLEMENCE, ISAURE.] He was considered as the successor of Marot, and the chief of the French poets of the time. [MAROT.] Montaigne, De Thou, Scaliger, Muret, in which rain and snow are common. A simple inele plane is well adapted to resist injury from weather, but, it is scarcely more favourable to an economical disposit of the timbers than a flat roof, it is only suited for s buildings, and is seldom used except as a lean-to. Anoth objection to its use on a large scale is the disproportar height it requires in one side of the building. The b figure for a simple roof is that formed of two inclined planes rising from the two opposite walls that approach nearest" each other, and meeting over the centre of the edifice, s to form a ridge. By this form, supposing the same slope? be maintained, one half of the height of the single inch plane is avoided; and, the length of the timbers be diminished one half, their scantling may be considerab reduced. Fig. 1 represents a plan, with side and end viess of such a roof, which is called a common or gable-ended roj he sides and ends. Where a hipped roof covers a perfectly quare building, the faces all meet in a point, and form a yramid; but when, as in the diagram, the plan of the roof oblong, the planes rising from the nearest opposite walls neet in a ridge. Sometimes the inclined faces are not connued upwards till they meet, but the roof is completed by horizontal plane. Such a roof is called a truncated, rrace, or cut roof, and may have two, three, or four in lined faces. Fig. 3 represents a truncated roof hipped at ne end, and terminating at the other in a vertical wall, ke the gable-ended roof. Fig. 3. This arrangement is useful in diminishing the height of a of, the level platform being covered with lead to compenite for the want of slope. It should be observed however at even this part is not perfectly level, the centre being ightly elevated to throw off water. A similar saving of eight is frequently obtained by means of a roof in which ch sloping face consists of two planes of different degrees of clination. This form, which is denominated a curb roof or, from its inventor, a Mansarde roof), is very common in London, because it affords more space for the formation of drooms in the roof than the simpler forms. A curb roof may be hipped or not, according to circumstances. Fig. 4 presents it hipped at one end only, as the last figure, showg, like the previous diagrams, the plan, and side and end Fig. 4. Levations. tween roofs with dripping eaves, and those in which the water is collected in gutters. In the former case the roof projects several inches, or even feet, beyond the walls, and the water running from the roof either drops at once on the ground, or is collected in troughs fixed under the margin of the eaves, and conducted by them to descending pipes. This arrangement has a clumsy appearance, and is perhaps unnecessary where a sufficient projection is given to the eaves, though it is essential to the dryness of the walls when they are of the diminutive size often adopted by modern builders. In gutter roofs the timbers do not extend to the outside of the walls, which are carried up as parapets, of a reduced thickness, to such a height as to conceal the roof either wholly or partially. The gutters, which are troughs of wood covered with lead or other metal, are laid at the bottom of the slopes, just within the parapets, and have a gentle inclination (usually about an inch in ten feet), to cause water to run freely towards the pipes. In extensive the elevated end of the gutter may cover as little of the roof roofs it is well to use two or more falls instead of one, that as need be. Similar troughs are often used in the valleys. Gutters are generally made wide enough for a man to walk risk of overflowing during a sudden heavy fall of rain. along them, and should be sufficiently capacious to avoid all The degree of slope given to the inclined faces of a roof varies according to the covering material employed, as well as to the climate. The antient Grecian temples had very low, or pediment roofs, varying from about 120 to about 160, the height being from one-ninth to one-seventh of the span. In Roman buildings the inclination is somewhat greater, being usually 23° or 24°, or from one-fifth to two-ninths of the span. The general introduction of the pointed style of architecture led to the use of very high-pitched roofs, a very common proportion being that in which the length of the rafters is the same as the span, so that they formed an equilateral triangle. In comparatively modern domestic architecture in this country, it has been considered desirable for and an angle of 45° is still considered by some to be the best the length of the rafters to be three-fourths that of the span, pitch when plain tiles are used. As builders can, in the may be made of any required degree, down to the low present day, obtain excellent covering materials, the pitch Grecian pediment, and it therefore depends on the style of architecture and the taste of the builder; the most common height being from one-fourth to one-third of the span. High roofs discharge rain the most rapidly, and do not retain snow so much as those of low pitch; but where they have gutters they are liable to become choked by snow sliding into them, and to overflow from water running into them faster than the pipes can convey it away. Steep roofs may be covered with small slates, and are less likely to be stripped by violent winds. Low roofs, in consequence of their superior lightness, are less expensive, the timbers not only being shorter, but of proportionately smaller scantling, and they press less injuriously on the walls. The following table, extracted from Tredgold's 'Elementary Principles of Carpentry,' shows the proper angle for roofs covered with the materials specified in the first column, the last column indicating the comparative weight of each kind of covering:Height of roof Weight upon a Covering. in parts of square of the span. Copper or lead ... Inclination to the horizon. 3° 50' ..... 22° 26° 33' 29° 41' 29° 41' Fig. 6. Stone slate Plain tiles roofing. copper 100 {lead... 700 1120 900 to 500 2380 1780 650 -r the junction of two planes in such a manner as to Form hollows the reverse of hips. When two faces of a of join so as to form an angle similar to a valley, but in an orizontal instead of an inclined position, the term gutter is =pplied instead of valley. A further distinction, which it may be well to mention beCore entering upon the details of construction, is that be In describing the timber-work of an ordinary roof, each of the planes of which it is composed may be considered to be bounded by a frame, the parts of which have the general name of bordering pieces. Those which join the wall are the wall-plates; that at the meeting of two faces, parallel to the wall-plates, is the ridge-piece; and the inclined bars extending from the wall-plates to the ridge-piece are rafters, those which form the salient angles in hipped roofs being distinguished as hip-rafters. The support necessary for the external covering is given by a series of rafters or inclined bars, extending from the wall-plates to the ridge-piece, and placed • A square of roofing contains 100 square feet. parallel with each other at equal distances. In a hipped roof, the rafters near the ends, being parallel with the others, are necessarily diminished in length, extending from the wall-plate to the hip-rafter instead of the ridge-piece. All such pieces, being shorter than the length between the wallplate and the ridge-piece, are called jack rafters. It is not usual to vary the scantling, or transverse dimensions of rafters, in any considerable degree, on account of their various lengths; nearly the same scantling being used in all buildings, and the required strength being obtained by introducing intermediate supports between the wallplates and ridge-piece where the size of the roof renders such necessary. This additional support is supplied by horizontal rectangular bars called purlins, placed under the rafters in such a manner as to divide their length into two or more equal parts, the ends of the purlins being fixed to the sides of the bordering frame. Like the rafters, the purlins are not much varied in thickness according to the strain upon them, but they are in turn supported by a series of bars placed equidistant from each other, and parallel with the rafters, but with their upper face in the same plane as the lower face of the purlins. These are called principal rafters, or, for brevity, principals, to distinguish them from the first described, or common rafters. Where it is desirable to save room by reducing the thickness of a roof, the purlins may, as shown in fig. 15, be notched I the principals and common rafters, but this practice # to be recommended, as it weakens the timbers. Wh principals are used, their lower ends are mortised into ends of a tie-beam, which stretches across the building, z rests upon the wall-plates. This beam keeps the lower tremities of the principals from separating, and dischar the weight of the roof on the walls in a vertical direct relieving them entirely from the lateral thrust of t rafters. The triangular frame formed by the two princ and a tie-beam, with any bars it may comprise for addit strength, is called a truss, and such frames being placed regular intervals, the timber-work between any two. them is called a bay of roofing. The lower extremities? the common rafters, being elevated by this arrangem above the wall-plates, are supported by pole-plates, or p of timber parallel to the wall-plates, resting on the ends the tie-beams. The supporting frame-work altogether called a carcass-roof. Fig. 7, which represents a small carcass-roof supparel by four trusses, and having one purlin only between the wall-plate and ridge-piece, may assist the reader in com prehending the arrangement of the parts enumerated; and their names will be found more distinctly by referring : the representation of a more complicated truss at fig. In this figure the common rafters are represented on one half of the roof only, that the trusses may be more distinctly seen; and the end walls are omitted for the same reason. The proper construction of the trusses of a roof, with reference to the size of the building and the weight of the covering, is a matter requiring much scientific knowledge. For the want of this it is not unusual to encumber trusses with much more timber than is necessary or useful; and the disadvantage of this is not confined to the increased weight and cost of the roof, as superabundant timbers frequently occasion injurious strains, and the increased number of joints adds to the risk of derangement by the shrinking and warping common to all timber constructions. The general principles to be acted upon may be illustrated by a few diagrams; but in the limited space devoted to this article no attempt can be made to describe all the modifications required by the ever-varying forms of buildings; in the design of which it is too common, instead of assigning its due importance to the roof, to treat it as an unsightly feature, to be concealed as much as possible from view. In a roof formed as shown in fig. 8, consisting simply of two inclined planes abutting on the walls, it is evident that the weight of the rafters ab and bc, as well as that of the covering sustained by them, will have a tendency to thrust out the walls. This tendency ordinary walls have not the of the rafters, relieves the walls of lateral strain: If th tension of the tie-beam ac be sufficient to resist the extre ing force of the rafters without sensible elongation, the effect that such a roof can have upon the walls is a vertirs pressure on each, equal to half its weight; and it can fall without the tie-beam, which acts the part of a cond chain, being pulled asunder, or the rafters being crushe If the materials were perfectly rigid, no additional para would be required; but as they are not so in practice. becomes necessary, when the timbers are of conside length, to provide means for counteracting their tenden sinking, or sagging. By adding a bar shaped like bd 10), the centre of the tie-beam may be suspended from crown of the roof. This piece is called a king-post, but a Fig. 10. b d name is perhaps not a good one, as, though it appears! a post to support the ridge or crown of the roof, it reality a tie, supported by it, and sustaining, instead resting upon, the centre of the tie-beam. By cutt the king-post out of a piece of wood of larger scantling th the shank of the post itself, projections of the shapes cated in the cut may be formed at its ends. These are car joggles, and those at the upper end form a wedge betw the heads of the rafters, like the key-stone of an arcb. It evident that a weight pressing on the projecting joggles the base of the king-post will be by it transmitted to the trown of the roof. These therefore form fixed points, from which support may be obtained, by means of struts or braces, e and f, for the centre of each rafter. Where purlins are added, they rest on those points of the principal rafters that are thus supported by struts, as may be seen by reference to fig. 7. It may be observed that this truss consists of two pieces (the tie-beam and king-post) in a state of tension, and four (the two rafters and the two struts) in a state of compression; and that in every well-contrived truss, however the number of its component parts may be increased, every bar is in one or other of these states. Those parts which are in a state of tension, acting merely as cords to bind the truss together, may be and sometimes are formed of slender rods of wrought-iron; but the others, needing stiffness as well as cohesion, require bars of considerable substance, and are therefore mostly formed of wood or cast-iron. Sometimes the king-post is dispensed with, and its office performed by two similar posts, called queen-posts, at equal distances from the centre of the truss. În order to keep these in their right position, a short horizontal beam, called a collar-beam, is inserted between their upper extrem ties, and another, termed a straining-sill, between their lower ends. This arrangement is explained by fig. 11, which also shows the position of other parts of a truss. One side is represented as a gutter-roof, and the other with eaves. aa, Wall-plates. b, Tie-beam. cc, Principal rafters. dddd, Purlins. ee, Pole-plates. ff. Common rafters. g, King-post. The auxiliary or cushion rafters, m, m, are pieces occasionally added, in large roofs, to strengthen the principals; and they, with the collar-beam, &c., form a complete truss within them. The trusses of truncated roofs are formed in this manner, the collar-beam forming, as it were, the keystone of the arch, and being surmounted by a camber-beam, the upper edge of which is formed into two slightly inclined planes, to give the necessary slope to the lead covering. In such a roof, pieces of wood resembling ridge-pieces are inserted at the angles formed by the meeting of the rafters with the horizontal bars that support the flat. The following representation of a very simple truss, from Nicholson's Carpenter and Joiner's Companion,' illustrates the use of slender king-posts and queen-posts of wroughtiron, and shows how the stress of every part of the roof may be brought to bear on the ridge. The lower ends of the struts rest in stirrups attached to the vertical rods, and the weight Fig. 12. bearing on the strut a is imparted, through b and c, to the king-post. The tie-beam is suspended by bolts from each of the vertical rods, and the ends of the rafters are secured to the tie-beam by iron straps passing round them, and bolted to the beam at d, d. Trusses on the same principle may be made of timber only. In curb roofs the upper rows of rafters are called curbrafters, and the horizontal bars that receive the upper ends of the lower rafters, and the feet of the curb-rafters, are known as curb-plates. The proper position of equilibrium for the rafters of a curb-roof may be ascertained by very simple means, within the reach of persons not possessed of sufficient mathematical knowledge for determining it by calculation. If the rafters are to be equally loaded, as in a roof entirely covered with one material, this position will be xactly the reverse of that which they would take by gravity, were they suspended in a chain or festoon, the joints being flexible. If they are framed together in this position of equilibrium, they will balance each other like the stones of an arch; and the tie-beams, posts, and braces will have no cther office to perform than that of resisting such irregular strains as might tend to alter their arrangement. rafters thus suspended would fall into the position abcde, Ag. 13, a line drawn through the angles being a catenarian P. C., No. 1249. The curve; and a' b'c' d' e', in the same figure, represents the corresponding position in which they should be placed in an equally loaded roof. If the rafters b'c' and c'd' are to a Fig. 13. Fig. 14. e a bear a greater weight than a'b' and d'e', they will, if proportionately loaded when suspended in a curve, fall in such a way as to increase the angles abc and cde, and diminish bcd, thereby indicating their proper position in the roof. When the roof is to be loaded unequally, and more on one side of the ridge than the other, as it would be if b'c' were to be covered with lead, and the other planes with slates, a corresponding weight added to the centre of gravity of be will cause the bars to arrange themselves as abcde, fig. 14, the angles of which, being transferred to the roof, give the position of equilibrium a'b'c' d'e'. This practical method of finding the proper angles of a curb-roof may be applied under all circumstances, the dimensions of the experimental bars being proportionate to those of the rafters, and their centres of gravity being loaded according to the pressure to be sustained by each plane of the roof. The great advantage of curb-roofs consists in the space they afford for chambers in the roof, such chambers being lighted by dormer windows in the lower inclined faces. When the trusses of the roof form partitions between the bed-rooms, their posts and braces are so arranged as to leave one or more doorways for communication between them. In roofs of very large span it is often desirable, in order to avoid running up to a great height, to form two or more ridges. When intermediate support can be obtained from partition walls, such constructions may be regarded as combinations of two or more distinct roofs placed side by side. Fig. 15 is an example of a roof of large span without any intermediate support, and having a large available space between the tie and collar beams. It represents the form of the trusses, which were placed fifteen feet apart, of a roof of eighty feet span, erected over Drury-Lane Theatre in |