mooth. This is usually called an Americanism, but is a very old
sea-term. In the _Book for Boys and Girls_, 1686, it is aptly
illustrated:

"The mole's a creature very smooth and slick,
She digs i' th' dirt, but 'twill not on her stick."

SLIDE-VALVE CASING. A casing on one side of the cylinder of an engine,
which covers the nozzles or steam-ports, and confines the slide-valves.

SLIDE-VALVE ROD. A rod connecting the slide-valves of an engine, to
both of which it is joined; it passes through the casing cover, the
opening of which is kept steam-tight.

SLIDE-VALVES. The adaptations used in a marine-engine to change the
admission of the steam into, and its eduction from, the cylinder, by the
upper and lower steam-ports alternately.

SLIDING BAULKS, OR SLIDING-PLANKS. Those timbers fitted under the bottom
of a ship, to descend with her upon the bilge-ways when launched.

SLIDING BILGE-BLOCKS. Those logs made to slide under the bilge of a ship
in order to support her.

SLIDING GUNTERS. Masts fitted for getting up and down with facility
abaft the mast; generally used for _kites_, as royals, skysails, and the
like.

SLIDING-KEEL. A contrivance to prevent vessels from being driven to
leeward by a side-wind; it is composed of planks of various breadths,
erected vertically, so as to slide up and down, through the keel.

SLING, TO. To pass the top-chains round the yards when going into
action. Also, to set any large article, in ropes, so as to put a tackle
on, and hoist or lower it. When the clues are attached to a cot or
hammock, it is said to be slung; also water-kegs, buoys, &c., are slung.

SLING-DOGS. In timber lifting, a dog is an iron implement with a fang at
one end, and an eye at the other, in which a rope may be made fast for
hauling anything along. Two of these fastened together by a shackle
through the eyes are called sling-dogs. (_See_ DOG.) Also, an ancient
piece of ordnance. (_See_ SLYNG.)

SLING-HOOP. That which suspends the yard from the mast, by which it is
hoisted and lowered.

SLINGS. A rope fitted to encircle any large article, and suspend it
while hoisting and lowering. Also, leather straps made fast to both ends
of a musket, serving for the men to hang them by on their shoulders,
that both hands may be free.--_Boat-slings._ Strong ropes, furnished
with hooks and iron thimbles, whereby to hook the tackles to keel, stem,
and stern bolts, in order to hoist the boats in or out of the
ship