Television pictures fool your eyes. When you look at a picture, your brain （大脑）holds the picture for one tenth of a second （秒） then you must look again. So when the brain has to hold more than ten pictures a second, it puts them together as moving pictures. You can see this yourself by drawing a lot of pictures of the same person, one on each page of a notebook. Then turn the pages of the notebook very quickly. The person will seem to move.
A television picture uses a series of lines （一系列线） across the screen. The lines change the picture many times each second and make moving pictures. We call this kind of television "analogue （模拟的） television".
Now we have digital（数字的）television. It has no lines. Both sound and pictures are in numbers. When the numbers on a digital television change, only the differences between the old picture and the new one change. So the change is very fast and the picture and sound are very good.
