What makes a mirror reflect?
It is the brightness of the mirror surface that makes it reflect light.
It is the brightness of the mirror surface that makes it reflect light.
When light falls on a surface
some of the light may be reflected or thrown back, some absorbed and some
allowed to pass through. In a mirror the surface is made so bright that as much
light as possible is reflected and as little as possible absorbed.
The earliest mirrors consisted of thin discs of metal,
generally bronze, slightly convex and polished on one side.
The method of making mirrors by backing glass with thin
sheets of metal was known in the Middle Ages, and a guild of glass-mirror
makers existed in Nurnberg, Germany, in 1373. The commercial manufacture of
mirrors was developed in 16th Century Venice. Coated mirrors were made from
blown cylinders of glass which were slit, flattened on a stone, polished, and
their backs silvered by an amalgam of tin and mercury.
These mirrors had a high reflecting power, but a
considerable improvement came in France in 1691 when the art of making plate
glass was introduced. The chemical process of coating a glass surface with
metallic silver was discovered by Baron Justus von Liebig of Germany in 1835.
Mirror
surfaces are used inside lighthouses, lightships and searchlights, where it is
necessary to produce a high degree of reflection in order to throw the beam of
the light over a distance of several miles. Even a hand flashlight has a
slightly mirrored surface behind the bulb.
Comments
Post a Comment