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 depressor anguli oris and corrugator supercilii muscles are stimulated. 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'.