到过上海的人,外滩是不能不去的。那里有一道中国罕见的防汛墙。今天,我们只讲防汛墙而引发的科学思考,从中得出一个科学方法——共变觅因法。我60年代在上海读书,常去外滩。那时的防汛墙并不高,潮水上涨,几可在岸边洗脚。从那以后,每隔几年防汛墙就加高一次,如今已成了一堵真正的又高又大的水泥墙 For people who have been to Shanghai, the Bund cannot but go. There is a rare flood wall in China. Today, we only talk about the scientific thinking triggered by the flood wall and draw a scientific method from it—covariation and causation. I studied in Shanghai in the 60s and often went to the Bund. At that time, the flood prevention wall was not high, and the tide was rising. It was possible to wash feet on the shore. Since then, the flood wall has been raised once every few years, and it has now become a real high and large cement wall.