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stream; and many an awkward turn in our public roads would have been spared us, had the skewed arch only been earlier known.

After making allowance for the requirements of position and traffic, the form next must be considered, more particularly in relation to the stream. The stream principally affects the form, through prescribing the number of piers. Each pier takes up so much of the water-course, and thus narrows the effective passage of the water. The imme. diate consequence of narrowing the channel is to increase the velocity of the stream. As the velocity of the stream increases, it tends more and more to carry off the soil in the neighborhood of the piers, and finally, by deepening its course, to undermine them. From this consideration, the effect of too many piers will be obvious; but indeed this is not matter of speculation, for many bridges-among others, a B. of Smeaton's at Hexham-have been destroyed from this cause, thus falling from the very overabundance of support! To know how many piers may with safety be used, the volume of water that flows through the channel, both ordinarily and in winter-floods, must be ascertained, which can be done very nearly by calculating the mean of many soundings taken at different states of the river, and at a succession of points across its bed. There is another way in which the stream affects the form. If it is liable to floods, care must be taken to make the piers so high as to elevate the spring of the arches above the highest level attainable by the water. In connection with this part of the subject, it must be remembered, too, that floods are apt to carry down trees and other floating masses, which, if the arches do not afford them passage, become powerful levers for the destruction of the bridge.

The form of the B. being determined on, the remaining questions relate to its stabil. ity. This depends on the strength of the abutments and piers, and the balanced equi: librium of the arches. The importance of securing proper foundations for the abutments and piers cannot be over-estimated, and very frequently their foundations, owing to the nature of the soil, have to be artificially constructed. See PILES, COFFER-DAM, and CONCRETE. In considering the stability of the B., the first thing is to ascertain the forces which will act to destroy it. This is ascertained by calculating the extreme passing load, and also the weight of the structure above the arches, and of the arches themselves. A scientific and skilled engineer is then able to judge what amount of strain or destructive pressure will be exercised by these weights on the several parts of the structure, and thus to adapt the strength at every point to the strain. As to the passing load, it is usual to calculate on 240 lbs. per foot, superficial, of the whole area in ordinary bridges, and on 960 lbs. in railway bridges. The weight of the superstructure and arches is a question for practical measurement. As to the remaining pressure—viz., that of the stream-it must be ascertained for the highest floods. It is calculated from knowing the mean velocity of the stream, and the amount of surface exposed to it. The surface is readily observed by means of floats; and when this is under 10 ft. per second, the mean velocity is found to be about one fifth less. The stress of the stream on the bridge is diminished by the expedient known as a cut-water, which is an angular projection from the pier. The best form for a cut-water has practically been ascertained to be an equilateral prism, presenting an angle of 60° to the water-course. In all bridges, these are to be found on the sides of the piers presented to the stream; and in tidal rivers, they are built on the lower side as well.

After the conditions already mentioned are satisfied, taste has more to do with the form of the arches than anything else. The forms in use are the old semicircular, the elliptical-usually got at by putting together several circular arches of different radiiand the segmental arch. The semicircular arch was almost exclusively used in the more ancient bridges. This arch is the most solid and most easily constructed, as all the voussoirs may be worked from the same mold. It requires, however, high banking, as its height is equal half its breadth; and where the water-level greatly changes, it is particularly unsuitable, from the great height necessary to be given to the piers, to carry the intrados out of water-reach. The elliptical arch and the segmental of 60° are, besides, far more pleasing in appearance.

In possible extent of span, the masonic bridge is far exceeded by suspension and girder bridges. At Chester there is a stone arch with a span of 200 ft.; in the Britannia tubular bridge the span is 460 ft. ; in the suspension bridge over the Menai strait, 600 ft.; and in the suspension bridge at Freiburg, Switzerland, 870 feet. The railway bridgo across the Tay, near Dundee, partially destroyed in 1879, was 3450 yards long. See Tu. BULAR BRIDGE and SUSPENSION BRIDGES : CANTILEVER BRIDGE.

The principal objection to the wooden B. is its liability to decay, besides which it is liable to warping, through the swelling and contracting of its beams. The latter objec. tion applies also to iron bridges, but in their case, the contractions and expansions may be compensated for, as in the compensation balance of a watch, or the compensation pendulum.

Public bridges are maintainable at the expense of the counties in which they are sit. uated; but in many cities and boroughs, the inhabitants have acquired by prescription a liability for this expense, and by the 13 and 14 Vict. c. 64, the management and control of such bridges is given to the council of the city or borough. If part of a public bridge be within one county or other place on which the liabilty rests, and the other part of the bridge be within another, each party or body shall repair that part of the bridge which

is within its own boundaries. Besides the bridge itself, the county liable is bound by the 22 Henry VIII. c. 5, to repair 300 ft. of the road either way from the bridge. And such is still the state of the law as to all bridges built prior to the passing of the highway act, 5 and 6 Will. IV. c. 50. But by that act it is provided that, in the case of all bridges thereafter to be built, the repair of the road itself passing over or adjoining to a bridge, shall be done by the parish, or other parties bound to the general repair of the highway of which it forms a portion-the county being still subject, however, to its former obligation as regards “the walls, banks, or fences of the raised causeways, and raised approaches to any bridge, or the land arches thereof." See Stephen's Com., vol. iii. p. 234. The neglect to make such repairs is treated in law books as a kind of negative offense; but there are positive offenses against bridges, which in the statutes are called nuisances, as to which, see the 43 Geo. III. c. 59. An act to amend the law in regard to the maintenance and management of roads and bridges in Scotland was passed in 1878, entitled “Roads and Bridges act." Private bridges are those erected and main. tained under contracts authorized by private acts of parliament. See Road.

BRIDGE (ante). The most important American bridge as regards construction is that over the East river between the cities of New York and Brooklyp, commonly known as the “ Brooklyn bridge.” The land approaches are of stone and brick in arches and piers, terminating at the river in the grand stone piers that rise 278 ft. above high-water. The following official account of dimensions and progress is down to the close of 1879: construction commenced Jan. 2, 1870; size of New York caisson, 172 X 102 ft.; size of Brooklyn caisson, 168 X 102 ft. ; timber and iron in caisson, 5253 cubic yards; concrete in well-holes, chambers, etc., 5669 cubic ft. ; weight of New York caisson, about 7000 tons; weight of concrete filling, about 8000 tons; New York tower contains 46,945 cubic yards of masonry; Brooklyn tower contains 38,214 cubic yards of masonry; length of river span 1595 ft. 6 in.; length of each land span, 930 ft.—1860 ft.; length of Brooklyn approach, 971 ft.; length of New York approach, 1562 ft. 6 in.; total length of bridge, 5989 ft., or 1.134 m.; width of bridge, 85 ft.; number of cables, 4; diameter of each cable, 15$ in.; first wire was run out May 20, 1877; cable-making really commenced June 11, 1877; length of each single wire in cables, 3578 ft. 6 in.; ultimate strength of each cable, 12,200 tons; weight of wire, 12 ft. per Ib.; each cable contains 5296 parallel (not twisted) galvanized steel, oil-coated wires, closely wrapped to a solid cylinder 154 in. in diameter; depth of Brooklyn tower foundation below high-water, 45 ft.; depth of New York tower foundation below high-water, 78 ft.; size of towers at high-water line, 140 X 59 ft.; size of towers at roof course, 136 X 53 ft.; total height of towers above high-water, 277 ft. ; clear beight of bridge in center of river span above high-water, at 90° Fah., 135 ft.; height of floor at towers above high-water, 119 ft. 3 in.; grade of roadway, 31 ft. in 100 ft.; height of towers above roadway, 159 ft.; size of anchorages at base, 129x119 ft.; size of anchorages at top, 117X104 ft.; height of anchorages, 88 ft. front and 85 ft. rear; weight of each anchor plate, 23 tons; total cost of bridge, exclusive of land, $14,627.379 ; total weight of suspended structure, 17,780 tons. Engineer, W. A. koebling. The bridge was opened, '83. 45,000 persons can cross hourly, supposing each to move at the rate of 200 ft. per minute, and 1440 vehicles.

Some other American bridges may be brietly described. One of the earliest of note is that over the Schuylkill at Philadelphia, which Fanny Kemble poetically described as “a scarf rounded by the wind and thrown over the river.” It was accidentally burned in 1838. The railroad bridge at Bellows Falls, built in 1850, las a span of 250 feet. The Susquehanna bridge (of the Wilmington and Baltimore railroad) is 3500 ft. long, with 13 piers and 2 guard piers at the draw. The spans are 250 ft. long, and the draw-span 176 feet. The Niagara Suspension bridge has a span from center to center of towers of 821 ft., and is 245 ft. above the river. The bridge (suspension) over the Ohio between Cincinnati and Covington has a span of 1067 ft., and is 91 ft. above low-water. The Clifton bridge (over Niagara river just below the falls and above the suspension bridge) is 1190 ft. from bank to bank, and 1268 ft. between the points of suspension on the towers, and is 193 ft. above the water. The Victoria tubular bridge over the St. Lawrence at Montreal has a length of tube of 6600 ft., carried over 25 openings of 240 ft. each, and one of 330 ft.; with the approaches this bridge is 9084 ft. long. The Quincy bridge over the Mississippi (draw) has 17 spans, two of 250 ft., three of 200, 11 of 137, and a drawspan of 360 feet. The bridge over the Missouri at Omaha is 2800 ft. Jong in 11 spans. The bridge of the New York Central railroad over the Hudson at Albany is 1740 ft. long, in 15 spans and a draw. But the most noteworthy of railroad bridges is that over the Mississippi at St. Louis. It is in three immense snaps, those at the end being 497 ft. each, and the middle one 515 feet. Over the railroad floor is a carriage and foot roadway 34 ft. wide between the foot-walks, which are each 8 ft. wide.

The terrible disaster of the fall of the Tay bridge in Scotland, the center portion of which went down in a furious gale on the night of the 27th Dec., 1879, justities a brief description of that structure. It was the largest iron bridge in the world, crossing the river, or arm of the sea, a mile and a quarter w. of Dundee, with a length from shore to shore of 10,320 ft. (only 240 ft. less than two miles). Commencing at the s. or Fife shore there were three spans of 60 ft., two of 80 ft., 22 of 120 ft., 14 of 200 ft., 16 of 120 ft., 25 of 66 ft., one of 160 ft., and six of 27 ft.-in all 89 spans, the rails being 88 ft. above the water. The portion which fell consisted of 12 spans somewhere near the middle of the bridge. A train of six passenger cars and the brakemen's van either went down with the bridge or ran into the vacancy in the dark, and not one person survived. There were over 90 lives lost.

The following statement comprises a list of the most important railway bridges and viaducts constructed by European and American railway companies. There are stone, wood, and iron structures, all of which appear under a separate head:

Stone Bridges and Viuducts.—Ballochmoyle viaduct, Glasgow, and S. W., width of span, 181 ft.; viaduct at Nogent, S. M., near Paris, 164 ft.; Durham Junction viaduct, 160 ft.; bridge bear Wolmsdorf, Silesià, 150 ft.; bridge near Maidenhead, built by Brunel, 1835, 129 feet. There are three or four structures to be added to the foregoing, whose widths of openings exceed 100 feet. This includes the bridge at the Point-du-Jour, at Paris; the viadúct near Loebau, in Saxony, and the bridge at Point-de-Pille, on the line between Orleans and Bordeaux. The highest arches are principally found in Germany, and in the second line in various parts of France.

Viaducts of Stone and Brick.-Height of arch; over the Goeltz valley, in Saxony, 256 ft.; over the Elster valley, in Saxony, 223 ft.; over the Riofredo, in Austria, 197 ft.; at Diedenmuhle, near Chemnitz, Saxony, 170 ft.; at Chaumont, Paris to Mulhouse, 164 ft.; at Kalte Rinne, Semmering, Austria, 151 ft.; at Fure, near Grenoble, 135 ft.; at Comelle, near Creil, Paris, 131 ft.; at Wagnergraben, Semmering, Austria, 128 ft.; at Combe-Bouchard, Paris-Lyons railway, 128 feet. In addition to these there are several other bridges and viaducts whose height varies from 100 to 125 feet. Among the principal are: the viaduct over the Tranz valley, in Austria; bridge across the river Fulda, near Kragenhof, Hanover; the Goel viaduct at Aix-la-Chapelle; viaduct at Mireville, on the line between Havre and Rouen; four more are in Saxon Switzerland; the rest in various parts of France. The longest viaducts and bridges are to be found in England; notably the viaduct on the line from London to Greenwich; the system of the Southwestern, South-eastern, Chatham and Dover, Great Eastern, and of other lines serving the metropolis. The next importance attaches to the bridge spanning the Lagoons and running into Venice, the bridge and viaduct over the river Elbe, at Dresden, and a few others.

Timber-built Bridges and Viaducts.—The most prominent structures are the following: Over the river Mista, on the Moscow and St. Petersberg railway, nine openings, each 200 ft. wide; over the river Elbe, at Wittenberg, with 14 openings, varying in width from 140 to 100 ft.; bridge near Woltenhofen, on the road from Lindau to Augsburg, Bavaria, one opening, 170 ft. wide; bridge near Kempten, on the same line as the fore. going, with five openings, varying in width from 85 to 140 ft. each. There are two wooden bridges on the North Shields, Newcastle line, one with seven, the other with five openings, the widest of which spans about 135 feet. The United States possess wooden bridges in very large numbers, and of much greater dimensions than are found on European roads. Among those noteworthy is the bridge over the Delaware river, on the Erie road, with two openings, each of a width of about 260 feet. The next structure of importance is a bridge over the Susquehanna river, near Columbia, with 29 openings, each about 200 ft. wide. There are two bridges crossing the Connecticut river, with spans of 174 feet. These are the most prominent bridges; but there are numerous other very remarkable structures, which, though of smaller dimensions, give evidence of great engineering skill.

Iron Bridges and Viaducts. The following list comprises structures of this class of the greatest extent in length:

Feet.
Parkersburg bridge, West Virginia, U. S.
St. Charles bridge, Missouri, Ü. S........

6,536
Over the river Ohio, near Louisville, Ky., U. S.

5,310 Over the river Delaware, Pennsylvania, U. S......

4,920 Over the East river, New York...................

5,000 Victoria bridge, St. Lawrence river, Canada.......

4,980 Over the river Rhine, at Mayence, Germany.......

3.380 Over the river Tongabudda, Bombay, Madras .....

3,730 Over the river Mississippi, near Quincy, U. S...

3,200 Over the river Missouri, near Omaha, U. S.........

2,790 Over the river Vistula, near Dirschau, Germany........

.750 Over the river Danube, near Stadlau, Austria.

,520

2,485 Over the river Tamar, near Saltash ..........

. 2,190 Over the river Lek, near Kuilenburg...

.2,185 Over the river Mississippi, near Dubuque, U. S.........

.. 1,758 Over the river Sorai, in British India................... .... 1,745 The foregoing comprises a list of the longest bridges constructed of iron, but it does not include all the most important works from an engineering point of view. The bridges which have the widest or the most numerous openings are given in the subjoined list, and comprise all the great marvels which engineering skill and ingenuity have produced: Britannia bridge, Menai straits: four openings, each 460 ft., and two openings,

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each 230 feet; built by Robert Stephenson and Fairbank, 1846–50. Conway bridge, Menai straits: one opening, 400 feet; built by Stephenson, 1847-48. Victoria bridge, crossing the St. Lawrence river at Montreal: one opening 330 ft., and 24 openings, each 240 feet; built by Stephenson. Bridge over the Garonne, near Langon, on the Bordeaux-Cette line: one opening of 245 fi., and two each of 210 feet. Over the Aire, near Brothertop: one opening of 225 feet. Over the Trent, near Gainsborough, on the Manchester, Sheffield and Lincoln line: two openings, each 150 ft. wide. Over the river Lek, a branch of the Rhine, near Kuilenburg, Holland: one opening of 150 ft., one of 80 ft., and seven of 57 feet: built 1868-70. Over the river Ohio, near Lonisville, U. S.; one opening of 400 ft.; one of 370 st.; six, each of 236 ft.; 14, varying in width from 210 ft. to 140 ft.; one of 100 ft., and two, each of 50 feet; built in 1868. Over the Vistula, near Dirschau, Berlin-Königsberg line-built 1850-57, by Lentze: six openings, 350 ft. each. Over the Waal, near Lommel, Belgium: three openings of 400 ft. each, and eight of 190 ft. each. Over the Rhine, near Griethausen: one opening of 330 ft., and 20 of 60 ft. each; built in 1863-64, by Monie. Over the Rhine, near Hamm: four openings, each of 330 feet; built in 1868-70, by Pichier. Over the Dieppe, pear Moerdyk, Holland: 14 openings, each of 330 ft., and two of 51 feet. This structure resembles in a measure the unfortunate Tay bridge. It was completed in 1871. Over the Rhine, near Cologne: four openings of 320 ft. each; built, 1856-60, by Lohse and Wiedman. Over the Nogat, near Marienburg, Baltic: two openings of 312 ft. each. ()ver the Wye, near Chepstow: one opening of 300 ft., and three, each of 100 feet; built by Brunel, 1850 -52. Over the Rhine, near Mannheim: three openings of 295 feet. Over the Boyne, near Drogheda: one opening of 270 ft., and two each of 140 feet ; built by Barton, 1855. Over the Danube canal, near Vienna: one opening 260 ft. wide; built in 1860 by Koestlin. Over the Danube, near Stadlau, Austria : five openings each of 250 ft., and 10 each of 110 feet ; built by Ruppert, 1868–70. Over the Trent, near Newark: one opening of 240 feet; built by Fox and Henderson, 1851. Over the Thames, Blackfriars: one opening of 205 ft., two of 195 ft., and two of 170 feet ; built 1863-64. Over the Kinzig, near Offenburg, Germany: one opening of 190 feet. Over the Eipel, Hungary: one opening of 185 ft., and three of 145 feet. Over the Rhine, near Strasburg: three openings of 185 feet. Over the Grau, in Hungary: one opening of 166 ft., and three of 144 ft, caclı, built by Ruppert, 1858. Over the Saar, near Freibourg: five openings, each of 160 ft., and two of 142 feet. Crumlin Viaduct, Newport-Abergavenny line: 10 openings each of 160 ft. width; built by Liddle and Gordon, 1853. Over the Lahn, near Coblentz: one opening, 150 ft. wide. Over the Thames, near Windsor: one opening of 200 feet ; built by Brunel, 1819. Over the Weser, near Corvey, Germany: four openings, each of 185 feet; built by Schwedler, 1863-64. Over the Orne, near Caen, France: one opening of 145 feet. Built by Maier, 1858. On the Blackwall line: one opening, 120 feet. Over the Tamar, at Saltash: two openings of 450 ft., and 17 openings varying from 70 to 90 feet; built by Brunel. Over the Rhine, at Mayence: four openings, each of 335 ft., six of 115 ft., and 22 openings varying in width from 50 to 80 feet. Over the Isar, near Hesselohe, Germany: two openings, each of 170 ft., and two each of 85 feet. Over the Elbe, at Hamburg: seven openings, each of 335 ft. , and three openings of 310 feet; built by Lohse, 1870. Over the Yssel, near Zutphen, Holland: one opening of 320 ft., and two of 55 feet. Over the Ohio, near Benwood, United States: one opening of 320 feet. Over the Mersey, near Runcorn, London and North-western railway: three openings of 300 ft. each. Over the Missouri, near Omaha, United States: 11 openings, each of 270 feet; built by Dodge, 1860-61. Over the Danube, near Manthausen, Austria: five openings of 260 ft., and two of 90 feet. Over the Danube, at Vienna, North-western line: four openings of 260 ft., and 14 openings of 95 feet; built by Hellwag and Gerlish, 1870-72.

The railway suspension bridge over the Forth at Queensferry will be, when completed, the most remarkable application of the suspension principle in the world. The breadth of the Forth at Queensferry is rather more than a mile; but, as the viaduct is to be continued overland on the n. shore for several hundred yards, the whole length of the bridge will be about one mile and one third. This, however, gives no fair idea of the breadth of span to which the physical conditions require the suspension principle to be applied. In the midst of the firth, but rather nearer to the northern than to the southern shore, rises the rocky islet of Incligarvie. On either side of this island the bed of the river sinks to a depth which is impracticable for engineering purposes. On the n. side the bed sinks to a depth of 210 ft., on the s. side to 180 ft, below the water-mark; and it is there, for a breadth of 1600 it. on either side, that no practicable bottom can be found for piers, and therefore that the suspension principle has perforce to be resorted to. Between the deep furrow on the s, side of Inchgarvie and the southern shore there is a reach of comparatively shallow water, with a maximum depth of 30 ft., but within which foundations may be found for some 12 or 15 piers. Viewed in profile from the bosom of the tirth, the bridge will thus present to view five distinct sections. First, there is a shallow-water section on the s. side, covering some 2000 ft., and supported on 16 piers; then there is the deep-water section, s. of Inchgarvie, traversed by a suspension bridge; next there is the island of Inchgarvie itself, over which the viaduct will be carried on two or three piers; then there is the deep-water section n. of Inchgarvie, spanned by a second suspension bridge; and, lastly, there is the northern shoreward section, which carries the

viaduct on 10 or 11 piers from the brink of the tide to the dead level of the Fife shore. The great features of the architectural design, as seen from the firth, will be the four pairs of lofty towers on which the massive steel chains which are to support the two suspension bridges will be hung, and the two pairs of landward buttresses to which the suspending chains will be anchored. Of the towers, two pairs will rise from the island of Inchgarvie, and will reach the imposing height of 596 ft. Two pairs on the shore of n. Queensferry, and other two on the brink of deep water on the southern chan. nel, will attain to a height of 584 feet. The two pairs of buttresses on the n. and the s. side respectively will be, of course, less lofty; but they will be bold and striking masses of masonry. Those parts of the bridge, n. and s., which rest on piers, with a solid foundation, will consist of a single permanent way 25 ft. broad, and carrying a double set of rails. But the intervening portions carried by the suspension bridges will consist of two distinct and parallel branches, each 15 ft. broad, each carrying a single line of rails, and 100 ft. apart. These branches will be tightly braced together; and this arrangement has been adopted in order to give greater breadth, and therefore greater stability, to the whole structure. Seen from above, the outline of the design has the appearance of a shuttle with elongated points. The divergence of the branches begins at the massive piers, two on each side, to which the suspension chains will be anchored, and the maximum of divergence, 100 ft., will be attained before the lofty towers are reached. While the bridge throughout the greater part of its extent makes pecessarily a straight course, the shoreward part at either end forms a gentle curve. From each shore to the beginning of the suspension bridge the line rises with a gradient of 1 in 100. In the shoreward sections, and in that over Inchgarvie, the permanent way rests on the upper members of the lattice-girders; but in the two suspension sections it rests on the lower members. By this contrivance here, as in the case of the Tay bridge, the full height of 150 ft. above the high-water mark is confined to the central sections only. It will be evident that each of the deep-water channels n. and s. of the island of Inchgarvie will be spanned by a double suspension bridge. Each of these double bridges will consist of four parallel and enormous lattice-girderstwo for each branch. These girders will be 1600 ft. long. Seen in profile, their upper members will form an arched outline, with a maximum height of 50 ft. and a minimum of 19 ft. besides the towers. On these towers, of course, their ends will rest; but they will derive their main support from four immense steel chains, one for each girder, which will be slung over the towers and fastened to the anchoring piers at either end. The girders will be attached to the chains by stout wrought-iron rods at intervals of 50 ft. See adjoining illus.; also ENGINEERING, vol. V., p. 426.

BRIDGE, MILITARY, is a temporary construction, to facilitate the passage of rivers by troops, cannon, and military wagons. The most efficient are described under PonTOON; but there are many other kinds. A bridge of boats is formed by small-craft, especially cargo-boats, collected from various places up and down the river; trestles are placed in them to bring their tops to one common level; the boats are anchored across the river, and baulks of timber, resting on the trestles, form a continuous road from boat to boat across the whole breadth of the river; the boats ought to be of such size that, when fully laden, the gunwales or upper edges shall not be less than one foot above the water. Rope-bridges are sometimes but not frequently used by military engi. neers. Alboat-and-rope bridge consists of cables resting on boats, and supporting a platform or road of stout timber. A cask-bridge consists of a series of timber-rafts resting on casks; the casks are grouped together in quadrangular masses; at certain intervals, timbers are laid upon them to form rafts, and several such rafts form a bridge; it is an inferior kind of pontoon-bridge. A trestle-bridge is sometimes made for crossing a small stream in a hilly country; it consists of trestles hastily made up in any rough materials that may be at hand, with plapking or fascines to form a flooring, cables to keep the trestles in a straight line, and heavy stones to prevent them from floating. Raft-bridges, consisting of planks lashed together, are easily made of any rough materials that may be found on the spot; but they have little buoyancy, and are not very manageable. A swing-flying bridge consists of a bridge of boats, of which one end is moored in the center of the river, and the other end left loose; this loose end is brought to the proper side of the river, the boats are laden, and they make a semicircular sweep across the river by means of rudders and oars, until the loose end of the bridge reaches the other bank. A trail-flying bridge is a boat or raft, or a string of boats or rafts, which is drawn across a river by ropes, in a line marked out and limited by other ropes.

BRIDGE, NATURAL. See NATURAL BRIDGE.

BRIDGE-BUILDING BROTHERHOODS (Fr. Frères pontifes; Lat. Fratres pontifices) were religious societies that originated in the s. of France in the latter half of the 12th century. Their purpose was to establish hospices at the most frequented fords of large rivers, to keep up ferries, and to build bridges. The church during the middle ages regarded the making of streets and bridges as meritorious religious service. Whether or not the herdsman Benezet, subsequently canonized, was the founder or only a member of this fraternity, is as uncertain as the tradition which attributes to him the completion of the bridge over the Rhone at Avignon in 1180. The fraternity was sanctioned by pope Clemens III. in 1189; its internal organization was similar to that of the knightly

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