Chord.

Chord. The chord of an arc is a straight line joining its two extremities; or, a chord, in a circle, ellipse, parabola, &c. is a straight line joining any two points in the curve. If we draw a series of parallel chords in any conic, the line through their middle points is called a diameter, and a line parallel to the chords which passes through the extremity of the diameter is a tangent to the curve. Hence in the circle (1) a diameter is perpendicular to the chords which it bisects, and also (2) to the tangent at its extremity; (3) the three chords of intersection of any three circles meet in a point. In any conic the tangents at the ends of any chord meet in the diameter which bisects the chord. A SCALE OF CHORDS on Mathematical Instruments is sometimes used for setting off angles, but has been mostly superseded by the Protractor (q.v.).