COFFER

, in Fortification, denotes a hollow lodgment, athwart a dry moat, 6 or 7 feet deep, and 16 or 18 broad. The upper part of it is made of pieces of timber, raised 2 feet above the level of the moat; the elevation having hurdles laden with earth for its covering, and serving as a parapet with embrazures.

The coffer is nearly the same with the caponiere, excepting that this last is sometimes made beyond the counterscarp on the glacis, and the coffer always in the moat, taking up its whole breadth, which the caponiere does not.

It differs from the traverse and gallery, in that these are made by the besiegers, and the coffer by the besieged.

The besieged commonly make use of coffers to repulse the besiegers, when they endeavour to pass the ditch. And, on the other hand, the besiegers, to save themselves from the fire of these coffers, throw up the earth on that side towards the coffer.

COFFER-Dams, or Batardeaux, in Bridge-building, are inclosures formed for laying the foundation of piers, and for other works in water, to exclude the surrounding water, and so prevent it from interrupting the workmen.

These inclosures are sometimes single, and sometimes double, with clay rammed between them; sometimes they are made with piles driven close by one another, and sometimes the piles are notched or dove-tailed into one another; but the most usual method is to drive piles with grooves in them, at the distance of five or six feet from each other, and then boards are let down between them, after which the water is pumped out.

COGGESHALL's Sliding-Rule, an instrument used in Gauging, and so called from its inventor. See the description and use under Sliding-Rule.