gent to the curve may be drawn at any point M by drawing MO parallel to the axis and bisecting the angle OMF. MT is the required tangent at the point M.

Since the angle T'MR is equal to the angle TMF, it follows that MR would be the direction of a ray of light emitted from the focus F and reflected from the parabola at M.

Having given the abscissa VB, and the ordinate BE in Fig. 130. Draw AE parallel and equal to VB. Divide AE and BE into the same number of equal parts. From the divisions on BE draw parallels to the axis and from the divisions on AE draw lines converging to the vertex V. The intersection of these lines, 1 and 1, 2 and 2, etc., will determine points in the required curve. In like manner obtain the opposite side.