A series of essays investigates purported supernatural phenomena and magical practices by showing how optical, acoustic, hydraulic, mechanical, chemical, and pharmacological principles produce illusions. The author analyzes visual apparitions as retinal and perceptual phenomena, examines historical uses of mirrors, lenses, and the magic-lantern to project spectres, and describes mechanical contrivances and fluid equilibria employed in religious deceptions. Case studies of spectral visions, ocular spectra, and phantasmagoric exhibitions illustrate physiological causes and technical methods behind supposed miracles, and the argument is advanced that knowledge of natural forces enabled authorities to fabricate the appearance of supernatural power.