The Project Gutenberg EBook of Spectropia; or, Surprising Spectral Illusions, by J. H. Brown
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Title: Spectropia; or, Surprising Spectral Illusions Showing Ghosts Everywhere, and of Any Colour
Release Date: November 22, 2020 [EBook #63842]
Produced by: Tim Lindell, Chuck Greif and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.)
*** START OF THE PROJECT GUTENBERG EBOOK SPECTROPIA; OR, SURPRISING SPECTRAL ILLUSIONS
***_Designed by J. H. Brown, and Published Decʳ. 19ᵗʰ. 1863, by Griffith & Farran, Sᵗ. Paul’s Church Yard, London._]
First Series. WITH SIXTEEN ILLUSTRATIONS.
LONDON: GRIFFITH AND FARRAN, SUCCESSORS TO NEWBERY AND HARRIS, CORNER OF ST. PAUL’S CHURCHYARD. H. & C. TREACHER, BRIGHTON. MDCCCLXV.
The following Illusions are founded on two well-known facts; namely, the persistency of impressions, and the production of complementary colours, on the retina.
The explanations are divided into two Parts. The FIRST consists of directions for seeing the spectres. The SECOND, a brief and popular, as well as a scientific, description of the manner in which the spectres are produced, and is intended for the use of those who may wish to know more of this subject than is contained in the first Part.
As an apology for the apparent disregard of taste and fine art in the plates, such figures are selected as best serve the purpose for which they are intended.
To see the spectres, it is only necessary to look _steadily_ at the dot, or asterisk, which is to be found on each of the plates, for about a _quarter_ of a minute, or while counting about twenty, the plate being well illuminated by either artificial or day light. Then turning the eyes to the ceiling, the wall, the sky, or better still to a white sheet hung on the wall of a darkened room (not totally dark), and looking rather steadily at any one point, the spectre will soon begin to make its appearance, increasing in intensity, and then gradually vanishing, to reappear and again vanish; it will continue to do so several times in succession, each reappearance being fainter than the one preceding. Winking the eyes, or passing a finger rapidly to and fro before them, will frequently hasten the appearance of the spectre, especially if the plate has been strongly illuminated.