Old Linkages 2 Perpendicular Straight Line Point

Description

From the book "How to Draw a Straight Line; A Lecture on Linkages", by A.B. Kempe, London, 1877. This is a series of linkage mechanisms, very old, but still interesting and useful. In this mechanism, one point (blue) describes a straight line movement, perpendicular to a reference (red). Scheme at https://br.pinterest.com/pin/479070479118547611.