MIRROR, a name for a looking-glass, or any polished body, the use of which is to form the images of distant objects, by reflection of the rays of light.
Mirrors are either plane, convex, or concave. The plane reflect the rays of light in a direction exactly similar to that in which the latter fall upon them, and therefore represent bodies of their natural magnitude. The convex make the rays diverge much more than before reflection, and therefore greatly diminish the images of objects; whilst the concave, by collecting the rays into a focus, not only magnify objects, but burn very fiercely when exposed to the rays of the sun, and hence such specula are commonly known by the name of burning mirrors. See BURNING MIRRORS.
In ancient times mirrors were made of some kind of metal; and from a passage of the Mosaic writings we learn that those mirrors used by the Jewish women were made of brass. The Jews certainly had been taught to use that kind of mirrors by the Egyptians; and hence it is probable that brazen mirrors were the first kind used in the world. Any kind of metal, indeed, when well polished, reflects powerfully; but of all others silver reflects the most, though it has been in all countries too expensive a material for common use. Gold is also a very powerful reflector; and metals, or even wood when gilded and polished, act as burning mirrors. Polished ivory, or straw nicely plaited together, forms mirrors capable of burning, if constructed upon a large scale.
Since the invention of glass, and the application of quicksilver thereto, became generally known, it has been universally employed for such plane mirrors as are used for ornaments to houses.