Spiral gear, or Spiral wheel (Mach.), a gear resembling in general a
spur gear, but having its teeth cut at an angle with its axis, or so
that they form small portions of screws or spirals. -- Spiral gearing,
a kind of gearing sometimes used in light machinery, in which spiral
gears, instead of bevel gears, are used to transmit motion between
shafts that are not parallel. -- Spiral operculum, an operculum whih
has spiral lines of growth. -- Spiral shell, any shell in which the
whorls form a spiral or helix. -- Spiral spring. See the Note under
Spring, n., 4.
Spi"ral (?), n. [Cf. F. spirale. See Spiral, a.] 1. (Geom.) A plane
curve, not reëntrant, described by a point, called the generatrix,
moving along a straight line according to a mathematical law, while the
line is revolving about a fixed point called the pole. Cf. Helix.