# DIRECTLY

, in Geometry: we say two lines lie directly
against each other, when they are parts of the
same right line. Also quantities are said to be directly
proportional, when the proportion is according to
the order of the terms; in contradistinction to *inversely,*
or *reciprocally* proportional, which is taking the proportion
contrary to the order of the terms.

In Mechanics, a body is said to strike or impinge
*directly* against another body, when the stroke is in a direction
perpendicular to the surface at the point of impact.

And a sphere in particular strikes directly against another, when the line of direction passes through both their centres.

DIRECTRIX. See Dirigent.

Directrix, in a Parabola, a line perpendicular to the axis produced, at the distance of the focus without the vertex.