Link 1, turning about fixed axis A, is connected by a sliding pair to link 3. Link 3 is connected by turning pair B to slider 4 which moves along fixed guides a-a whose axis is parallel to axis Ay. Cross-piece Bt of link 3 is connected by a sliding pair to slider 5 which, in turn, is connected by turning pair E to slider 2. Slider 2 moves along fixed guides d-d whose axis is also parallel to axis Ay. Centre A is placed at the focus of the parabola to be enveloped and the axis of guides d-d is made to coincide with the directrix of the parabola. When link 1 turns about axis .A, cross-pieces Bt and En of links 3 and 5 simultaneously envelop parabola q-q.
$1099$Lg,Ge$