odditiesThe Public Domain Review1865 · London, England
An 1865 Victorian book taught readers to conjure ghosts with afterimages to debunk spirits
Spectropia, published in London in 1865, is a book of coloured plates designed to produce ghostly images in the reader's eye. The reader stares at a dot on a plate for about twenty seconds, then looks at a blank wall or a white sheet, and a spectre appears. The phenomenon is an afterimage, which happens when the light-sensitive cells in the retina, the rods and cones, become fatigued by strong stimulation and temporarily lose sensitivity. The author's stated aim was to show that apparitions were caused by the senses and the mind, not by spirits. The illustrations were chosen for how well they worked rather than for artistic taste.
It shows that a supposed ghost can be produced by ordinary eye physiology, which helped Victorian readers understand how perception can fool them. The same principle still explains why you see a bright patch after a camera flash.
The colours of an afterimage are complementary to the original, so staring at a red patch leaves a green ghost.
Image: The Public Domain Review
