Veneres uti observantur in gemmis antiquis. By Pierre d’Hancarville; 1771; in Naples.
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A book of Victorian hi-tech ghost conjuring which allows the reader to summon, as the sub-title proclaims, “ghosts everywhere and of any colour”. Accompanying the set of wonderfully gaudy images, are directions on how to use them, and a more detailed scientific description about how the illusion works. Also included in the latter is a declaration of at least one motive behind the book:
One thing we hope in some measure to further in the following pages, is the extinction of the superstitious belief that apparitions are actual spirits, by showing some of the many ways in which our senses may be deceived, and that, in fact, no so-called ghost has ever appeared, without its being referable either to mental or physiological deception, or, in those instances where several persons have seen a spectre at the same time, to natural objects, as in the case mentioned by Dr. Abercrombie, in his work on “The Intellectual Powers:” — “A whole ship’s company were thrown into the utmost consternation, by the apparition of a cook who had died a few days before. He was distinctly seen walking ahead of the ship, with a peculiar gait, by which he was distinguished when alive, from having one of his legs shorter than the other. On steering the ship toward the object, it was found to be a piece of floating wreck.”
The book plays with an optical phenomenon known as “afterimage“, in which the eye’s photoreceptors (the rods and cones) adapt to overstimulation and lose sensitivity, and so retain the image when no longer focusing on it.
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.
Regarding the aesthetic quality of the images, the author comments: “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.”