SUBNORMAL

, in Geometry, is the subperpendicular AC, or line under the perpendicular to the curve BC, a term used in curve lines to denote the distance AC in the axis, between the ordinate AB, and the per- | pendicular BC to the curve or to the tangent. And the said perpendicular BC is the normal.

In all curves, the Subnormal AC is a 3d proportional to the subtangent TA and the ordinate AB; and in the parabola, it is equal to half the parameter of the axis.