Boats ought to be added to the remarks on page 58, or to the first section of the second chapter (pp. 109-12), for primitive man got his first boats from Nature. The earliest were floating branches and trees on which men sat astride, drifting with the current of rivers; the later were trees hollowed out by decay, which became models for dug-outs. “Between the primitive dug-out and a modern man-of-war there is, apparently, an impassable gulf; but yet the two are connected by an unbroken chain of successive improvements all registering greater efficiency in mechanical skill. Each of those intermediate increments constitutes a numbered milestone in the history and development of navigation.”—Dr. Robert Munro.

Boats, Bridge of, at Cologne, 1. It will be remembered that Julius Cæsar frequently made use of boat-bridges, and that Xerxes, four hundred and eighty years before the Birth of Christ, made a bridge of boats across the narrowest part of the Hellespont, between the ancient cities of Sestus and Abydus. So the boat-bridge at Cologne, like the wooden pontoon, has an old and fascinating lineage, yet a modern bridge was going to displace it when the present Great War began. “Kultur” cancels history.

Brackets, below the parapet of the Pont Neuf at Paris, 321. Brackets are ornamental projections from the face of a wall, to support statues and other objects. Some are adorned only with mouldings, while many are carved into angels, or foliage, or heads, or animals. Parker says: “It is not always easy to distinguish a bracket from a corbel; in some cases, indeed, one name is as correct as the other.” See Brangwyn’s drawing of the Pont Neuf facing page 320.

Bradford-on-Avon, Wiltshire, the bridge there has a tiny oratory, 231-2, which was profaned after the Reformation, becoming a “lock-up,” and then a powder magazine, 232. The bridge has nine arches; the two pointed ones uniting the oratory to the bankside have ribbed vaults, and the others are round-headed arches with double rings of voussoirs, 305 footnote. Originally the bridge was a narrow one for packhorses, but it was widened in 1645, or thereabouts. A hospital used to stand at one end of the bridge, and doles of charity for it may have been collected in the little place of prayer. Leland admired this bridge, and noted its nine fair arches of stone, and a fair large parish church standing beneath the bridge on Avon ripe.

Bridge built with Arches, its anatomy. Professor Fleeming Jenkin says: “An arch may be of stone, brick, wood, or metal. The oldest arches are of stone or brick. They differ from metal and from wooden arches, inasmuch as the compressed arc of materials called the ring is built of a number of separate pieces having little or no cohesion. Each separate stone used in building the ring has received the name of voussoir, or archstone. The lower surface of the ring is called the soffit of the arch. The joints, or bed-joints, are the surfaces separating the voussoirs, and are normal to the soffit. A brick arch is usually built in numerous rings, so that it cannot be conceived as built of voussoirs with plane joints passing straight through the ring. The bed-joints of a brick arch may be considered as stepped and interlocked. This interlocking will affect the stability of the arch only in those cases where one voussoir tends to slip along its neighbour. The ring springs from a course of stones in the abutments, called quoins. The plane of demarcation between the ring and the abutment is called the springing of the arch. The crown of an arch is the summit of the ring. The voussoirs at the crown are called keystones. The haunches of an arch are the parts midway between the springing and the crown. The upper surface of the ring is sometimes improperly called the extrados, and the lower surface is more properly called the intrados. These terms, when properly employed, have reference to a mathematical theory of the arch little used by engineers. The walls which rest upon the ring along the arch, and rise either to the parapet or to the roadway, are called spandrils. There are necessarily two outer spandrils forming the faces of a bridge; there may be one or more inner spandrils. The backing of an arch is the masonry above the haunches of the ring; it is carried back between the spandrils to the pier or to the abutment. If the backing is not carried up to the roadway, as is seldom the case, the rough material employed between the backing and the roadway is called the filling. The parapet rests on the outer spandrils.”

Bridge-Wreckers, 352, 355. It is worth noting that the King of the Belgians in the present Great War has used a cyclist corps of bridge-wreckers, whose work is described in the Daily Mail, December 14, 1914, page 4. “The cyclists led the way. The explosives followed in a car. The charge was fixed to the girders under the bridges, an electric wire affixed, you touched a button and the near span of the bridge was in a moment no more than a gap. Their greatest achievement ... was a railway bridge between Courtrai and Audenarde. It needed two charges.” The cyclists regarded their work as “fun,” because no bridge was at all difficult to destroy.

Centres or Centring, the curved scaffolding upon which arches are built. The voussoirs rest on the centres while the ring is in process of being constructed. When the centres are not rigid enough, arches sink a good deal while the masons are at work and after the scaffolding is carefully struck. In Perronet’s bridge at Neuilly-sur-Seine, for example, the sinking amounted to twenty-three inches, 338; thirteen inches while the centre was in its place, and ten inches after the centre was removed. On the other hand, when the centres of Waterloo Bridge were taken down, no arch sank more than 1½ inches. There is reason to believe that modern centres are more complicated than were the mediæval. See page 264 and page 286.