ampart; which latter, being finished exteriorly at the natural slope of
the earth, remains effective after the destruction of the wall by a
besieger. It was at first intended, being kept low and covered by a near
counterguard, to offer extraordinary difficulties to the besieger's
breaching batteries; but improved artillery has nullified that supposed
advantage.

DETACHED WORKS. Works included in the scheme of defence of a fortress,
but separated from it, and beyond the glacis.

DETACHMENT. A force detached from the main body for employment on any
particular service.

DETAIL OF DUTY. The captain's night orders.

DETENTION OF A VESSEL: on just ground, as supposed war, suspicious
papers, undue number of men, found hovering, or cargo not in conformity
with papers or law.

DETONATING HAMMER. A modern introduction into the Royal Navy for firing
the guns. With the aid of an attached laniard, it is made to descend
forcibly upon the percussion arm of the tube, and fires the piece
instantaneously. It is, however, already generally superseded by the use
of the _friction-tube_ (which see).

DEVIATION. A voluntary departure from the usual course of the voyage,
without any necessary or justifiable cause: a step which discharges the
insurers from further responsibility. Liberty to touch, stay, or trade
in any particular place not in the usual course of the voyage must be
expressly specified in the contract, and even this is subordinate to the
voyage. The cases of necessity which justify deviation are--1, stress of
weather; 2, urgent want of repairs; 3, to join convoy; 4, succouring
ships in distress; 5, avoiding capture or detention; 6, sickness; 7,
mutiny of the crew. It differs from a _change_ of voyage, which must
have been resolved upon before the sailing of the ship. (_See_
CHANGE.)--_Deviation_ is also the attraction of a ship's iron on the
needle. It is a term recently introduced to distinguish a sort of second
variation to be allowed for in iron vessels.

DEVIL. A sort of priming made by damping and bruising gunpowder.

DEVIL-BOLTS. Those with false clenches, often introduced into
contract-built ships.

DEVIL-FISH. The _Lophius piscatorius_, a hideous creature, which has
also obtained the name of fish-frog, monk-fish, bellows-fish, sea-devil,
and other appellatives significant of its ugliness and bad manners.
There is also a powerful _Raia_, which grows to an immense size in the
tropics, known as the devil-fish, the