Aids for perspective drawing

Perspective drawing aids are described, including (a) A parallel linkage arrangement (Fig. 2) having a pointer pivoted to a fixed point on one arm of the linkage, and to a fitting selectably positionable along the mutually parallel arm (exact indication of "vanishing point"). (b) A pair of equal length arms pivoted to respective ends of a link, the other ends of the arms being pivoted at mutually adjustable positions to a support, and the pointer being attached to the link perpendicular thereto (Fig. 3). (c) A pair of intersecting linear tracks mutually pivotable about the point of intersection, and a link having its ends slidable along respective tracks, the pointer being attached to the link perpendicular thereto (Fig. 4) ((c) and (d) give only an approximate indication of "vanishing point"). Various "3-axis" devices are described which are based upon the above, notably devices derived from (a) above in which the parallelism of the arms is maintained by (i) an elongate inextensible flexible element (Figs. 5-8) (ii) an arrangement of links.