Duchenne's physiognomy studies. Man with a facial expression induced by electrical probes applied by French neurologist Guillaume Duchenne (1806-1875). Duchenne used the new technique of photography to record idealised facial expressions thought to reveal the emotions of the soul. Here, the frontalis and platysma muscles are stimulated, with a dropping of the lower jaw. Photograph from the 1876 edition of Duchenne's 'Mecanisme de la physionomie humaine' (The Mechanism of Human Physiognomy, 1862). This work was subtitled: 'The Electro-Physiological Analysis of the Expression of the Passions, Applicable to the Practice of the Plastic Arts'.