Every day we look in the mirror. We want to know how we look: whether we are well combed, whether we are neatly dressed. The mirror will not deceive: if it were not for this silent friend, we would never have known what color our eyes and hair are, what our eyebrows, nose and mouth are... And this is just a small part of what mirrors are capable of. People of various professions cannot do without them. For example, they help submariners, without surfacing, to see what is happening on the surface of the ocean, astronomers - to discover new stars, metallurgists - to smelt ultra-pure metals.