Duchenne's physiognomy studies. Woman with different facial expressions (left and right) involving coquetry (flirting) induced by electrical probes applied by French neurologist Guillaume Duchenne (1806-1875). 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'.