Mirror
July 25, 2007 – 8:30 pm
It is the irony of life that this ‘I’ is so very strong in us and yet we cannot see it without the help of the mirror. In Greek Mythology Narcissus saw his reflection in the water and fell in love with it! It is only through the reflection in the mirror that we can get nearest to the self in us. A mirror must have a smooth surface for an image to be impressed upon it. The most common type is the plain mirror.
The mirror is a must in everyday use. It is an article no home is without. Apart from seeing and grooming yourself, the mirror is used for purposes of decoration.
The reflections formed on a plane ordinary or spherical mirror are called virtual images. The reflected image is the same size as that of the original. The parallel light changes direction as a whole but still remains parallel. In concave mirrors the parallel light turns into a convergent ones. In convex mirrors parallel beams diverge. Due to spherical aberration none of these three types of mirrors focus on a single point. Parabolic reflectors do this. For example the light from a star far away in the sky is focused on to a tiny spot. Thus parabolic mirrors are not suitable for reflections of objects that are close by.
Long time ago mirrors were nothing but sheets of metal that were highly polished. Silver and copper were commonly used. The mirrors that we see today consist of aluminum layer lining the back of piece of glass. This layer is known as Tain.
For optical purposes the coating is done on the front surface of the mirror to get rid of the reflection from the glass. Metal films on the front are usually covered with a coating that is thin and transparent to prevent corrosion. The coating is generally silica. It also helps to increase reflectivity.
Mirrors that are used for special applications like lasers and other high-grade optical devices use an optical coating, which consists of different layers of various dielectric stuff.
Vehicles like cars and bicycles, motorbikes, always used rear-view mirrors to see what is sneaking up from behind. Some helmets have a Multiple Reflective Optic System built into them. There are also sunglasses whose left and right extremes serve the purpose of rear view mirrors.
A convex mirror allows for a much wider view than the ordinary flat variety. These are often fixed at crossroads and parking lots to allow drivers to look around corners. In security systems these play a very important part. It makes it possible for a single video camera to probe more than one angle at one point of time.
Another type of mirror is the corner reflector, which uses three ordinary mirrors to reflect light back towards its place of origin. These are used for many emergency purposes including scientific work related to the study of the Moon.
Keeping the Sun as the source of light the mirror was used for purposes of signaling over long distances. The Native Americans used to make use of this technique. The signal could be sent on a cloud free day to a distance of even about 60 kilometers.
One-way mirrors allow reflection of some amount of light while allowing the rest to pass. It is used between a room that is dark and another that is brightly lit. Those on the lighted side see their own images like any ordinary mirror. But those on the dark side see through it like peering through something that is transparent. Generally it is used to scrutinize criminals without being observed.
Another type of mirror is the microscopic model that is the core of many of the biggest televisions and sophisticated video projectors. Telescopes and other fine precision instruments use first surface mirrors. Mirrors are also invaluable in the science of astronomy. A technique called adaptive optics is used to measure image distortions.
A combination of lens and mirrors that are concave is called a mangin mirror and is in use for manufacture of optical instruments as well as cameras. In military fields x-ray mirrors are used in the manufacture of thermonuclear weapons. In history it is said that Archimedes used a number of mirrors to burn the ships of Rome.
Mirrors can even change the weather – darkness can turn to sunlight. Viganella, in Italy hardly gets any sunlight during winter because of its location on the steep side of a valley. In 2006 computer controlled mirror was set up to reflect sunlight into the centre of the town. Switzerland is planning to apply the same technique in 2007 to light up the village of Bodo.
Mirrors have always been part of fun and decoration. In Feng Shui mirrors are used to bring harmony to the home. In amusement parks the hall of mirrors is a great attraction wherein the images of the viewer are distorted to ridiculous proportions. Magicians take the help of mirrors to confuse and amuse. Disco balls covered with tiny mirrors cast spotlights on the dance floor. Kaleidoscopes create a fantasy with mirrors.
Mirrors are very much of part of our beliefs and superstitions interwoven in our legends and literature. Do not break a mirror. It will be followed up with seven years of bad luck. Perseus killed Medusa by using a mirrored shield so that he did not have to directly gaze at her fearsome form as he slew her. Had he done so he would have been turned into stone. Tennyson’s Lady of Shallot frees herself from a curse when a mirror breaks. The reflection of Count Dracula would never fall on a mirror, because he was a ghost. The wicked Queen in Snow White used the mirror to tell her the truth about her beauty.
The greatest wonder of all about mirrors is that although the majority of animals do not know its virtues there are some who can recognize their own images. Among them are the elephants, great apes and dolphins.