Letters on natural magic, addressed to Sir Walter Scott, bart (1834)
Brewster, David, 1781-1868. n 84239125 · London : J. Murray · leaf 115
next the light, and the shadow of a protuberance on- the side opposite to the light; but if the object is the raised impression of a seal upon wax, I have found that, when inverted, it still seemed raised to the three youngest of six per- sons, while the three eldest were subject to the deception.… … appears raised, and let an opaque and unpolished pin A be placed on one side of the seal. Its sha- dow will be of course op])osite the candle as at B. In this case the seal, which had become a cameo by its inversion, will now sink down into a cavity by the introduction of the pin and its shadow ;…
Scientific recreations
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