Mirror, a reflecting surface, usually made of glass lined at the back with a brilliant metal, so as strongly to reflect the image of any object placed before it. When mirrors were invented is not known, but the use of a reflecting surface would become apparent to the first person who saw his own image reflected from water; and probably for ages after the civilisation of man commenced the still waters of ponds and lakes were the only mirrors; but we read in the Pentateuch of mirrors of brass being used by the Hebrews. Mirrors of bronze were in very common use amongst the ancient Egyptians, Greeks, and Romans, and many specimens are preserved in museums. Praxiteles taught the use of silver in the manufacture of mirrors in the year 328 B.C. Mirrors of glass were first made at Venice in 1300; and judging from those still in existence—of which one may be seen at Holyrood Palace, in the apartments of Queen Mary—they were very rude contrivances, in comparison with modern ones. It was not until 1673 that the making of mirrors was introduced into England. It is now a very important manufacture; and mirrors can be produced of any size to which plate-glass can be cast. After the plate of glass is polished on both sides, it is laid on a perfectly level table of great strength and solidity, usually of smooth stone, made like a billiard-table with raised edges; a sheet or sheets of tinfoil sufficient to cover the upper surface of the glass are then put on, and rubbed down smooth, after which the whole is covered with quicksilver, which immediately forms an amalgam with the tin. The superfluous mercury is then run off, and a woollen cloth is spread over the whole surface, and square iron weights are applied. After this pressure has been continued a day and night, the weights and the cloth are removed, and the glass is removed to another table of wood, with a movable top, which admits of gradually increasing inclination until the unamalgamated quicksilver has perfectly drained away, and only the film of amalgam remains coating the glass, and perfectly adherent to it. Mirrors are also made by silvering glass with an ammoniacal solution of a silver salt to which tartaric acid and sugar-candy have been added.
Heat is reflected like light; so that a concave mirror may be used to bring rays of heat to a focus. In this way combustible substances may be set on fire at a distance from the reflector whence they receive their heat. Thus used, a mirror is called a Burning Mirror.
The mirror is one of the most characteristic features of Japanese life and legend. It is usually of bronze, convex, polished by mercurial amalgam, and engraved on the back. In a few specimens the mirror may be used as a mirror in the ordinary way, but bright light reflected from its polished surface on to a screen gives bright-lined images corresponding to the figures on the back. This property of the so-called Magic Mirror of Japan is (according to Professors Ayton and Perry) due to inequalities of curvature associated with inequalities of thickness, the thicker portions being the flatter.