  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. Those who use gaslight will find it convenient, after having looked at the plate as above described, to extemporise a darkened room by having the gaslight turned low; or one end of the room may be darkened by placing a screen before the gas, lamp, or candle light. The spectres may be easily made to appear life-sized or colossal, by having the plate nearer the eyes while receiving the impression, and by increasing the distance between the observer and the surface against which they are seen. As a general rule, the observer should be about eight to twenty feet from the surface. When the spectres are seen against opposite houses, the sky, and other distant surfaces, they will appear colossal. Should any one not be able to see the spectre’s features, the reason will be, either that the eyes have been allowed to wander, or the head to move, while looking at the plate. Many persons will see some one coloured spectre better than the others, in consequence of their eyes not being equally sensitive to all colours. The colours in the plate will be found to reverse themselves in the spectres, as explained elsewhere, the spectres always appearing of the complementary colour to that of the plate from which it is obtained. Thus, blue will appear orange, and orange blue, |
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