Duchenne's physiognomy studies. Face of the primary model (an 'old toothless man') used by French neurologist Guillaume Duchenne (1806-1875) in his physiognomy experiments that induced facial expressions using electrical probes. Duchenne used the new technique of photography to record what he thought were idealised facial expressions that revealed the emotions of the soul. 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'.