ided on being passed through a prism.

SPEED-INDICATOR. A modification of Massey's log.

SPELL. The period wherein one or more sailors are employed in particular
duties demanding continuous exertion. Such are the spells to the
hand-lead in sounding, to working the pumps, to look out on the
mast-head, &c., and to steer the ship, which last is generally called
the "trick at the wheel." _Spel-ian_, Anglo-Saxon, "to supply another's
room." Thus, _Spell ho!_ is the call for relief.

SPENCER. The fore-and-main trysails; fore-and-aft sails set with gaffs,
introduced instead of main-topmast and mizen staysails.

SPENT. From _expend_: said of a mast broken by accident, in
contradistinction to one shot away.

SPENT SHOT. A shot that has lost its penetrative velocity, yet capable
of inflicting grave injury as long as it travels.

SPERM WHALE. Otherwise known as the cachalot, _Physeter macrocephalus_.
A large cetacean, belonging to the division of delphinoid or toothed
whales. It is found in nearly all tropical and temperate seas, and is
much hunted for the valuable sperm-oil and spermaceti which it yields.
When full grown, it may attain the length of 60 feet, of which the head
occupies nearly one-third.

SPERONARA. A Mediterranean boat of stouter build than the _scampavia_,
yet rowed with speed: in use in the south of Italy and Malta.

SPHERA NAUTICA. An old navigation instrument. In 1576 Martin Frobisher
was supplied with a brass one, at the cost of L4, 6_s._ 8_d._

SPHERE. The figure formed by the rotation of a circle. A term
singularly, but very often, misapplied in parlance for orbit.

SPHERICAL CASE-SHOT. _See_ SHRAPNEL SHELL.

SPHERICAL TRIANGLE. That contained under three arcs of great circles of
a sphere.

SPHEROID. The figure formed by the rotation of an ellipse, differing
little from a circle.

SPICA, OR {a} VIRGINIS. The lucida of Virgo, a standard nautical star.

SPIDER. An iron out-rigger to keep a block clear of the ship's side.

SPIDER-HOOP. The hoop round a mast to secure the shackles to which the
futtock-shrouds are attached. Also, an iron encircling hoop, fitted with
belaying pins round the mast.

SPIDER-LINES. A most ingenious substitution of a spider's long threads
for wires in micrometer scales, intended for delicate astronomical
observations.

SPIKE-NAILS. _See_ DECK-NAILS.

SPIKE-PLANK. (_Speak-plank?_) In Polar voyages, a platform projecting
across the vessel before the mizen-mast, to