A machine invented in 1789 by Gilles Louis Chretien for tracing a portrait subject's profile. It was used in the 18th and early 19th centuries when silhouettes were popular. Among artists working in America who used the device were Charles Saint-Memin (1770-1852). Source: Peter Falk, "Who Was Who in American Art"; Ralph Mayer, "A Dictionary of Art Terms and Techniques" (LPD)