Working during the height of the Enlightenment, the so-called “Age of Reason,” the Swiss-English painter Henry Fuseli (born Johann Heinrich Füssli) instead chose to depict darker, irrational forces in his famous painting The Nightmare. In Fuseli’s startling composition, a woman bathed in white light stretches across a bed, her arms, neck, and head hanging off the end of the mattress. An apelike figure crouches on her chest while a horse with glowing eyes and flared nostrils emerges from the shadowy background.