More than one hundred years ago, there 1 a great French scientist with the name Ampere. One day, Mr. Ampere went out for 2 in the street. There were 3 people and much traffic there. But all this was nothing to him. He was thinking about a maths 4 . He had no paper with him. 5 could he work it out? Then he saw a blackboard 6 him. He quickly walked up to it. He 7 a piece of chalk and wrote his problem on the blackboard. Then he started 8 on it. The blackboard moved a little, but he did not notice. The blackboard moved on, and Mr. Ampere walked after it. Then he started to run. But the blackboard moved faster and faster. At last he stopped 9 . What did he see? Why, the “ blackboard ” was 10 a blackboard. It was the back of a carriage ( 四 轮马车 ).