Spectropia; or, Surprising Spectral Illusions: Showing Ghosts Everywhere, and of Any Colour

"Spectropia; or, Surprising Spectral Illusions" by J. H. Brown is a scientific publication written during the mid-19th century. The book explores optical illusions and the phenomenon of seeing "ghosts" through the manipulation of light and the physiology of the eye. It aims to demystify the occurrence of spectral visions, presenting a rational and scientific explanation for these optical experiences that were often attributed to the supernatural. The content of "Spectropia" is divided into directions for witnessing spectral illusions and descriptions of the underlying scientific principles. Brown provides detailed instructions for creating spectral images by gazing at particular illustrations, whereby observers can see complimentary color spectres upon turning their gaze to a blank surface. He explores how the human eye perceives colors and how the brain can be deceived, arguing that many ghosts perceived throughout history are merely the result of visual phenomena rather than actual apparitions. The book also critiques spiritualism and witchcraft trends of the time, aiming to educate readers about the scientific explanations for what they might perceive as supernatural events.