Permalink Submitted by Anonymous on December 12, 2014

In fact Holmes, the circle with the chord S and tangent to line V has its center equidistant from the endpoints of the segment and from the line. Thus the center is on the locus of points equidistant from the line V and one of the endpoints of S (either will do), that is, on the parabola with focus the endpoint and directrix V.

## watson adds a detail

In fact Holmes, the circle with the chord S and tangent to line V has its center equidistant from the endpoints of the segment and from the line. Thus the center is on the locus of points equidistant from the line V and one of the endpoints of S (either will do), that is, on the parabola with focus the endpoint and directrix V.