TANGENT

(Lat. tangens; from tango, I touch.) In Geometry, the tangent to a curve is a straight line which meets or touches the curve without intersecting it. The nature of the tangent may be explained as follows: — Let A P B be an arc of a curve, and let the straight line T A B intersect it in two points, A and B. Conceive the i straight line to revolve about the point T. When it comes into the position Tab the intercepted arc a P b is shorter than A P B, or the points a and b have approximated. Let the motion of the line about T still be continued, and the length of the intercepted [s. 1219]