[Fr. miroir.] A plate of glass lined at the back with a brilliant metal, so as to reflect the image of any object placed before it. Mirrors are made by coating the back of a sheet of plate-glass with an amalgam of mercury and tin-foil. In ancient times mirrors were made of polished metal. Ordinary mirrors have flat surfaces, but there are also convex mirrors, which cause the rays of light to diverge and decrease the size of the reflected image, and concave mirrors, in which the rays are reflected to a focus and the image magnified. Beyond the focus it is inverted.