Mirror

Mirror, Magic. In China and Japan small mirrors are nearly always made of metal, highly polished, and often slightly convex on their reflecting face, and with figures or signs in relief ornamenting the back. Some of these mirrors are found to exhibit a curious phenomenon, when a beam of light is reflected from the face on to a white screen. A more or less distinct image of the carving on the back of the mirror is produced. Such mirrors were termed "magic," and have been for many centuries prized far more than the ordinary reflectors in those countries. This peculiarity has been found to be due to an irregularity in the convexity of the front face yvhicb is produced in the process of manufacture. The metal on the front face is cut by a tool which is not equally resisted by all parts of the mirror, the thin portions yvhere there is no relief ornament bending in front of the tool, and then afterwards rebounding into a rather more convex form than the thicker parts assume. A strong beam of light is therefore unequally reflected from the different portions, and an image appears on the screen. It has further been found that if a mould be taken of the face of the mirror, and this be coated electrically with a thin piece of metal, the polished metal surface of the mould will throw the same image on the screen, proving that the face of the mirror is unevenly curved.