Spiral
in geometry, a curve which may be generated by a point moving along a straight line, in the same direction, according to any law, while the straight line revolves uniformly about a fixed point, always continuing in the same plane. The portion generated during one revolution is called a spire.
The moving point is the generatrix of the curve, the fixed point is the pole of the spiral, and the distance from the pole to any position of the generatrix is the radius vector of that point. The law according to which the generatrix moves along the revolving line is the law of the spiral, and determines the nature of the curve. Any position of the revolving line, assumed at pleasure, is called the initial line. Spirals are known by the names of their inventors, or by terms derived from the properties by which they are characterized; as, the spiral of Archimedes, hyperbolic spirals, logarithmic spirals, parabolic spirals, etc. Also a helix or curve which winds round a cylinder like a screw.
SPIRES. See SPEYER.