One quick way to change the way a mirror works is to curve it. Curved mirrors come in two basic flavors: convex and concave. A convex mirror, which bulges outward, reflects at a wider angle near its edges than at its center, creating a slightly distorted image that's smaller than actual size. Convex mirrors have many uses. The smaller size of the images means that you can see more with these surfaces, hence their use in safety mirrors. (This is why your passenger side mirror says that objects are closer than they appear.) Some department stores have reportedly placed convex mirrors in their dressing rooms. Why? Slight bends at the top and bottom make you look taller and thinner.
Concave or converging mirrors curve inward like a spoon (the side that holds soup). This gives these mirrors the ability to create an image when their curvature bounces light to a specific area in front of them. This area is called the focal point. From far away, objects will seem upside down, but as you get closer and pass the focal point, the image flips and magnifies. Concave mirrors are used in everything from shaving mirrors to lighting the Olympic torch.
Now that you know the basic mirror types, let's learn about other, more unusual types of mirrors. Here's a short list:
- Non-reversing mirrors: Patents for non-reversing mirrors go back as far as 1887, when John Derby created one by placing two mirrors perpendicular to each other [source: O'Mara].
- Acoustic mirrors: Acoustic mirrors are huge concrete dishes built to reflect and distribute sound instead of light. The English military used them before the invention of radar as an early warning system against air attacks.
- Two-way mirrors: These mirrors are made by coating one side of a sheet of glass with a very thin, very lightly reflective material. When the coated side faces a lighted room, some of the light reflects and some goes into a dark room behind the mirror, making it possible to see into the lighted room but not out. (If you've ever watched an interrogation scene on a police show, you've seen one of these mirrors.) Glass is also a mildly reflective material -- this is the same reason that seeing outside at night is difficult if you turn on the lights in your house.
Mirrors clearly play a role in our everyday lives, but what roles have they played in literature and folklore over the years? Find out on the next page.