JACK -- A flag flawn at the
bow of a ship.
JACK BOX -- A box containing switches or connexions for
changing circuits.
JACKET -- An outer casing or cover constructed round a
cylinder or pipe, the space being filled with a fluid for either cooling or
heating the contents, or with insulating material for keeping the contents at
substantially constant temperature, e.g., the water jackets of an I.C.
engine.
JACK SHAFT -- An intermediate shaft used in locomotives having
collective drive; the jack shaft is geared to the motor shaft and carries
cranks which drive the coupling rod on the driving wheels.
JERK-PUMP -- A timed fuel-injection pump in which a cam-driven
plunger overruns a spill port, thus causing the abrupt pressure rise necessary
to initiate injection through the atomizer.
JACOBS'S LADDER -- Vertical belt conveyor with cups or
buckets.
JET CONDENSER -- A condenser in which exhaust steam is
condensed by jets of cooling water introduced into the steam space.
JET PUMP -- A pump working by entraining a fluid in a jet of
steam. See
injector,
ejector.
JOINT COMPOUNDS -- Non-hardening materials used on pipe
threads to insure a proper seal.
JOINT EFFICIENCY -- The ratio, expressed in per cent, of the
strength of a section of riveted or welded joint to the strength of an
analogous section of solid plate.
JOULE -- J. The SI unit of work or energy, equal to the work
done by a force of one newton when its point of application moves through a
distance of one meter in the direction of the force.
JOULE EFFECT -- Production of heat solely arising from current
flow in a conductor.
JOURNAL -- That part of a shaft that is in contact with, and
supported by, a bearing.
JUMPER -- A wire used to connect two electrical terminals or
nearby rails.
JUNK RING -- A metal ring attached to a steam-engine piston
for confining soft packing materials; or for similarly holding a cast-iron
piston-ring in position.
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