堰池的组成是什么？

     "If you want to see a thing well, reach out (伸出手) and touch it!"
      That may seem a strange thing to say. But touching things can help you to see them better. Your eyes
can tell you that a glass ball is round. But by holding it in your hands, you can feel how smooth (光滑) and
cool the ball is. You can feel how heavy the glass is. When you feel all these about the ball, you really see it.
With your skin, you can feel better. For example, your fingers can tell the difference between two coins in
your pocket. You can feel a little drop of water on the back of your hand, too.
      All children soon learn what "Don't touch!" means. They hear it often. Yet most of us keep on touching
things as we grow up. In shops, we touch things as we might buy: food, clothes. To see something well,
we have to touch it.
      There are ways of learning to see well by feeling. One way is to close your eyes and try to feel
everything that is touching your skin. Feel the shoes on your feet, the clothes on your body, the air on your
skin. At first, it is not easy to feel these things. You are too used to (习惯于) them! 
      Most museums are just for looking. But today some museums have some things to touch. Their signs
say, "Do touch!" There you can feel everything on show. If we want to see better, reach out and touch it.
Then you will really see!