Movement No. 172 demonstrates a linkage mechanism designed to trace an egg-shaped curve — a path that resembles an ellipse but is not mathematically true to one. Unlike the precise Trammel-based ellipsograph (No. 152), this mechanism uses a different arrangement of pivoted links and constrained points to generate its characteristic asymmetric, ovoid path: rounder and wider at one end, narrower and more pointed at the other — much like the profile of an actual egg. As the input crank or driving link rotates, the constrained tracing point follows this egg-shaped trajectory continuously. Such asymmetric curve-generating linkages were valued in decorative arts, engraving, and ornamental turning, where the natural, organic egg-shape provided an aesthetically pleasing alternative to a perfect circle or true ellipse, and could be used to guide cutting or engraving tools along this distinctive path.
172. A mode of obtaining an egg-shaped elliptical movement.