on."

JACK'S ALIVE. A once popular sea-port dance.

JACK-SCREW. A small machine used to cant or lift weighty substances, and
in stowing cotton or other elastic goods. It consists of a wooden frame
containing cogged iron wheels of increasing powers. The outer one, which
moves the rest, is put in motion by a winch on the outside, and is
called either single or double, according to its increasing force. The
pinions act upon an iron bar called the _spear_.

JACK-SHARK. A common sobriquet of the _Squalus_ tribe.

JACK-SHARP. A small fresh-water fish, otherwise known as _prickly-back_.

JACK'S QUARTER-DECK. The deck elevation forward in some vessels, often
called a top-gallant forecastle.

JACK-STAFF. A short staff raised at the bowsprit-cap, upon which the
union-jack is hoisted.

JACK-STAYS. Ropes, battens, or iron bars placed on a yard or spar and
set taut, either for bending the head of a sail to, or acting as a
traveller. Frequently resorted to for the staysails, square-sail yard,
&c.

JACOB'S LADDER. The assemblage of shakes and short fractures, rising one
above another, in a defective single-tree spar. Also, short ladders made
with wooden steps and rope sides for ascending the rigging.

JACOB'S STAFF, OR CROSS-STAFF. A mathematical instrument to take
altitudes, consisting of a brass circle, divided into four equal parts
by two lines cutting each other in the centre; at each extremity of
either line is fixed a sight perpendicularly over the lines, with holes
below each slit for the better discovery of distant objects. The cross
is mounted on a staff or stand for use. Sometimes, instead of four
sights, there are eight.

JACULATOR. A fish whose chief sustenance is flies, which it secures by
shooting a drop of water at them from its mouth.

JAG, TO. To notch an edge irregularly.--_Jagged_, a term applied to
denticulated edges, as in jagged bolts to prevent their coming out.

JAGARA, OR JOGGAREE. A coarse brown sugar of India.

JAGS. Splinters to a shot-hole.

JAIL-BIRD. One who has been confined in prison, from the old term of
_cage_ for a prison; a felon absurdly (and injuriously to the country)
sentenced to serve in the navy.

JALIAS. Small craft on the Arracan and Pegu coasts.

JAM, TO. Anything being confined, so that it cannot be freed without
trouble and force; the term is also applied to the act of confining it.
To squeeze, to wedge, to press against. (_See_ JAMBING.)

JAMAICA DISCIPLINE. The buc