Part 65

The best bricks must not be made of any earth that abounds with sand or gravel, not of such as is gritty or stony; but of a greyish marle, or yellow clay, or at least of reddish earth. But if there is a necessity to use that which is sandy, choice should be made of that which is tough and strong.

The best season for making bricks is the spring; because they are subject to crack, when made in the summer: the loam should be well steeped or soaked, and wrought with water. They are shaped in a mould, and, after some drying in the sun or air, are burnt to a hardness. This is our manner of making bricks; but whether they were always made in this manner admits a doubt. We are not clear what was the use of straw in the bricks for building in Egypt, or why in some part of Germany they mix saw-dust in their clay for bricks.

We are in general tied down by custom to one form, and one size; which is truly ridiculous: 8 or 9 inches in length, and 4 in breadth, is the general measure: but beyond doubt there might be other forms, and other sizes, introduced very advantageously.

Compass BRICKS, are of a circular form; their use is for steening of walls; we have also concave, and semi-cylindrical, used for different purposes.

Grey-Stocks, are made of the purest earth, and better wrought: they are used in front in building, being the strongest and handsomest of this kind.

Place-BRICKS, are made of the same earth, or worse, and being carelessly put out of hand, are therefore weaker and more brittle, and are only used out of sight, and where little stress is laid on them.

Red Stocks, are made of a particular earth, well wrought, and little injured by mixtures: they are used in fine work, and ornaments.

Hedgerly BRICKS, are made of a yellowish colored loam, very hard to the touch, containing a great quantity of sand: their particular excellence is, that they will bear the greatest violence of fire without hurt.

BRICOLE, an improved kind of traces used by the French in drawing and manœuvring artillery; analogous to the old drag rope, but having the addition of a leather strap or girdle with a buckle, to which the drag is affixed; and an iron ring and hook at the end to drag by.

BRIDGES. Manner of laying a pontoon bridge across a river.

The bank on each side, where the ends of the bridge are to be, must be made solid and firm, by means of fascines, or otherwise. One end of the cable must be carried across the river; and being fixed to a picket, or any thing firm, must be drawn tight by means of a capstan, across where the heads of the boats are to be ranged. The boats are then launched, having on board each two men, and the necessary ropes, &c. and are floated down the stream, under the cable, to which they are lashed endwise, by the rings and small ropes, at equal distances, and about their own breadth asunder; more or less, according to the strength required. If the river be very rapid, a second cable must be stretched across it, parallel to the first, and at the distance of the length of the boats; and to which the other ends of the boats must be lashed. The spring lines are then lashed diagonally from one boat to the other, to brace them tight; and the anchors, if necessary, carried out, up the stream, and fixed to the cable or sheer line across the river. One of the chesses is then laid on the edge of the bank, at each end of the bridge, bottom up; these serve to lay the ends of the baulks upon, and as a direction for placing them at the proper distances, to fit the chesses that cover the bridge. The baulks should then be laid across the boats, and keyed together: their numbers proportioned to the strength required in the bridge. If the gangboards are laid across the heads and sterns of the boats from one side of the river to the other, they will give the men a footing for doing the rest of the work. Across the baulks are laid the chesses, one after another, the edges to meet; and the baulks running between the cross pieces on the under side of the chesses. The gangboards are then laid across the ends of the chesses on each edge of the bridge.

Precautions for passing a bridge of boats.

Whatever size the bridge may be, infantry should never be allowed to pass at the same time with carriages or cavalry. The carriages should always move at a certain distance behind each other, that the bridge may not be shook, by being overloaded. The horses should not be allowed to trot over the bridge; and the cavalry should dismount and lead their horses over. Large flocks of cattle must not be allowed to cross at once.

For the dimensions, weight, and equipage of a pontoon, see the word Pontoon.

When bridges are made to facilitate the communication between different parts of the approaches at a siege, they should, if possible, be placed above the town; or the besieged will take advantage of the current to float down large trees, or other bodies, in order to destroy the bridge. Two of such bridges should always be placed close to each other, in order to prevent the confusion of crossing and recrossing on the same bridge; the one being intended to pass over one way, and the other to return. Pontoon bridges will generally not support a greater weight than 4 or 5,000 pounds. Pontoons, when united as a bridge, will no doubt bear more in proportion, than when acted upon separately: but the weight which a pontoon will bear may be easily ascertained, by loading it with water till it sinks to any required depth, and then by calculating the number of cubic feet of water it contains, ascertain the number of pounds required to sink it to that particular depth.

BRIDGES, in military affairs, are of several sorts and denominations, viz.

Rush-BRIDGES, are made of large bundles of rushes, bound fast together, over which planks are laid, and fastened: these are put in marshy places, for an army to pass over on any emergency.

Pendant or hanging BRIDGES, are those not supported by posts, pillars, or butments, but hung at large in the air, sustained only at the two ends; as the new bridge at the Falls of Schuylkill, five miles from Philadelphia, 1809.

Draw-BRIDGE, that which is fastened with hinges at one end only, so that the other may be drawn up (in which case the bridge is almost perpendicular) to hinder the passage of a ditch, &c. There are others made to draw back and hinder the passage; and some that open in the middle; one half of which turns away to one side, and the other half to the other, and both again join at pleasure.

Flying-BRIDGE, is generally made of two small bridges, laid one over the other, in such a manner that the uppermost stretches, and runs out by the help of certain cords running through pullies placed along the sides of the upper bridge, which push it forwards, till the end of it joins the place it is intended to be fixed on. They are frequently used to surprise works, or out-posts that have but narrow ditches. There is a curious bridge of this kind on the Ohio, worthy of attention.

BRIDGE of boats, is a number of common boats joined parallel to each other, at the distance of 6 feet, till they reach across the river; which being covered with strong planks, and fastened with anchors and ropes, the troops march over.

BRIDGE of communication, is that made over a river, by which two armies, or forts, which are separated by that river, have a free communication with one another.

Floating-BRIDGE, a bridge made use of in form of a work in fortification called a redoubt; consisting of two boats, covered with planks, which are solidly framed, so as to bear either horse or artillery. Bridges of this kind are frequently used.

Floating bridges made of large logs of light timber bound together with a floor along them are common in the United States.

Ponton-BRIDGE, a number of tin or copper boats placed at the distance of 7 or 8 feet asunder, each fastened with an anchor, or a strong rope that goes across the river, running through the rings of the pontons. They are covered with baulks, and then with chests or planks, for the army to march over. See PONTON.

Cask, or Barrel BRIDGE, a number of empty casks that support baulks and planks, made as above into a bridge, where pontons, &c. are wanting. Experience has taught us that 5 ton of empty casks will support above water 9000 pounds: hence any calculation may be made.

BRIDGES are made of carpentry or masonry. The number of arches of a bridge is generally made odd; either that the middle of the stream or chief current may flow freely without interruption of a pier; or that the two halves of the bridge, by gradually rising from the ends to the middle, may there meet in the highest and largest arch; or else, for the sake of grace, that by being open in the middle, the eye in viewing it may look directly through there as we always expect to do in looking at it, and without which opening we generally feel a disappointment in viewing it.

If the bridge be equally high throughout, the arches, being all of a height, are made all of a size, which causes a great saving of centering. If the bridge be higher in the middle than at the ends, let the arches decrease from the middle towards each end, but so that each half have the arches exactly alike, and that they decrease in span proportionally to their height, so as to be always the same kind of figure. Bridges should rather be of few and large arches, than of many and small ones, if the height and situation will allow of it.