鏡の歴史／The History of Mirrors

DENJIRO: Our topic for the day is mirrors, which we all use in our daily lives. I've made a mirror using an aluminum sheet and a tub. Aluminum tends to reflect light very well, so when we stretch it out over a tub... it turns into a mirror! Let me show you something even more interesting. There is a hole at the bottom of the tub. If we remove the air from this handmade mirror and make the aluminum sheet curve inward, it will turn into a concave mirror. The history of mirrors started with people using water to see a reflection. Later, mirrors using stones like obsidian were born. Next, we got mirrors made of metal. I've prepared a piece of metal. The surface is rough and has some small bumps, so I don't get a clear reflection of my face. Let me use a liquid abrasive to polish the surface. It's become a mirror! What's the difference between a piece of metal that reflects well and one that doesn't? Let me explain this using this model, where this bumpy piece of wood represents metal and this black ball represents light. When we roll the ball at the wood's bumpy side, it doesn't bounce straight back. The ball bounces irregularly and unpredictably. This is diffused reflection, and we don't get a clear image in the reflection. Now, let's try the same thing with a piece of wood that isn't as bumpy. The ball bounced back to the same direction at which it was thrown. This is the same state as a mirror. So by making the bumps of the surface of the mirror very small, it will reflect light very well and work as a mirror. Later on, mirrors made by silver-plated glass were invented. This is the most commonly used type of mirror nowadays. Recently, there are aluminum-plated mirrors as well. I hope energy will bring you all happiness. Our magic word is "Happy Energy!"