Among the most gripping photographs of the 19th century, plates from Duchenne de Boulogne’s Mechanism of Human Physiognomy occupy a unique place at the intersection of art, science, and sentiment. A pioneering neurologist and physiologist as well as an amateur aesthetician, Duchenne de Boulogne conducted a series of experiments aimed at eliciting expressions of the principal emotions through the electrical stimulation of facial muscles. His goal was to publish an updated version of earlier treatises on the “passions of the soul”—attention, aggression, pain, joy, lasciviousness, sadness, surprise—this time based in science and recorded accurately with photography for use by artists.