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ARTS, SCIENCES, HISTORY,
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JOHN CLARK RIDPATH, LL.D.
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ON SPECIAL SUBJECTS
over the Trent, at Newark, Eng. ; Blackfriar's, London ; Bridge Bateau', a floating-bridge, something similar to the Tower B., London ; Clifton Suspension-B., England; over a pontoon-bridge, supported by bateaux. the Eipel, Hungary; over the Rhine, at Strasburg; over the Saar, at Freiburg ; over the Lahn, at Coblentz; over the Thames, at Windsor; over the Orne, France ; over the Ohio, at Benwood; over the Hudson, at Poughkeepsie, and over the Harlem River, New York. Some of the most important Bs. ever constructed have been built within a few yrs. past. One is over the Duoro River, at Bordeaux, finished
w 1886. The necessary extreme length of this B. is 1,278 ft.,
Thi and it has only one span. The outward thrust of the enormous arch is tremendous, and the height of the areh, 240 ft. above low-water, offers an immense leverage for the high winds. The span of the arch is the greatest in existence, 566 ft.
The thickness of the arch at the key is 26 ft., about of the span, and the thickness increases downward until it reaches 55 ft. at the piers. Over the Forth, at Queensferry, near Edinburgh, is one of the most remarkable Bs. in the world. A suspension-B. was begun here in 1878, but when the Tay disaster occurred the work was abandoned and recommenced on the cantilever plan in 1883. The breadth of the Forth at Queensferry is rather
a, a, a, a, bateaux; b, b, b, b, balks ; c, c, chesses. more than a mile, but as the viaduct is continued over land on the end shores for several hundred yards the whole Bridge-build'ing Broth'erhoods were religious socilength of the B. is about 1} m., including two 1,700-ft. eties that originated in France in the latter half of the spans, two 675-ft. spans, fifteen 168-ft. spans, and five 25-ft. 12th c. Their purpose was to establish hospices at the spans. The clear headway under the center of the B. is most frequent fords of large rivers, to keep up ferries, and 150 ft. above high-water. The three main piers of the to build bridges. The Church during the Middle Ages restructure are known respectively as the Fife pier, the Inch- garded the making of streets and bridges as meritorious reGarvie pier, and the Queensferry pier, upon each of which ligious services. The fraternity was sanctioned by Pope is built a huge cantilever. The piers comprise four columns Clemens III. in 1189 ; its internal organization was similar carried down to the rock, one of them more than 90 ft. to that of the knightly orders, and the members wore as below high-water. The caissons are filled with concrete up their badge or insignia a pick-hammer on the breast. to low-water mark, above which cylindrical masonry piers, Bridge-head, or Tete-du-pont, in Military Engineer. 55 ft. in diameter at the bottom and 36 ft. h., are carried | ing, is a fortified post intended to defend the passage of a
river over a bridge. It is a field-work, open at the gorge or in the rear, and having its two flanks on the banks of the river. The most favorable position is at a re-entering sinuosity of the river, where the guns can work better with the supporting batteries opposite. Bs, are usually temporary works, hastily constructed. Their most frequent use is to aid a retiring army to cross the river in order, and to check an enemy pressing upon it. Openings are left to allow the retiring army, with guns and carriages, to file through without confusion; and parapets are so disposed as to flank and defend these openings.
Bridge, Mil'itary, is a temporary construction to facilitate the passage of rivers by troops, cannon, and military wagons. The most efficient are described under Pontoons, (q. v.;) but there are many other kinds. A B. 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 bulks
of timber, resting on trestles, form a continThe Clifton Suspension Bridge, England.
uous road from boat to boat across the whole
breadth of the river; the boats ought to be of up, 48 heavy steel bolts holding down the bed-plates and such size that, when fully laden, the gunwales or upper edges the superstructure of the main spans. One of the leading shall not be less than 1 ft. above the water. Rope-Bs. are features in the design of the superstructure is the tubular sometimes, but not frequently, used by military engineers. struts of hitherto unequaled length, of which nearly 6 m. A boat and rope B. consists of cables resting on boats, and are required for the completed B., some of which are 12 ft. supporting a platform or road of stout timber. A cask-B. in diameter. The whole work is on a magnificent scale. consists of a series of timber-rafts resting on casks; the During the last 40 yrs. many suspension-Bs. have been casks are grouped together in quadrangular masses ; at cerbuilt in Europe and the U.S. The first one of importance tain intervals timbers are laid upon them to form rafts, and was erected over the Ohio at Wheeling 1848, and was broken several such rafts form a B.; it is an inferior kind of pondown by the wind in 1854. Its span was 1,010 ft. The toon-B. A trestle-B. is sometimes made for crossing a small Bellevue B. at Niagara, built 1848, had a span of 759 ft. stream in a hilly country; it consists of trestles hastily made This was removed in 1854 and its cables incorporated in up in any rough materials that may be at hand, with plankanother B. constructed by John A. Roebling, whose name is ing or fascines to form a flooring, cables to keep the trestles now familiar to most Americans as the builder of the B. at in a straight line, and heavy stones to prevent them from Niagara, the one at Cincinnati over the Ohio, and as the floating. Raft-Bs. consist of planks lashed together. designer of the B. between New York and Brooklyn, Bridge'north, town of Salop, or Shropshire, Eng. ; pop. perhaps the most notable engineering feat of the c. A 7,317. The town, which at one time was called Bruges or notable structure is the Niagara cantilever B., finished in Brug, is said to be of Saxon origin. In the beginning of 1883. It is a double-track R.R. B., about 300 ft. farther up the 12th c. the Earl of Shrewsbury defended the town unsucthe stream than the R.R. suspension-B., and was built for cessfully against Henry I. It was besieged in the same c. by the Michigan Central R.R. It is constructed on the cantilever Henry II.; and during the civil wars it resisted the Parliaprinciple, (q. v.) See East River Bridge.
mentary forces for three weeks