after the waterloo campaign, napoleon was banished (流放) onto a lonely island named st helena in south atlantic. he became a prisoner for life. facing the vast sea, he always thought of escaping from the island, but that was impossible. he knew nothing about the topography (地形) of the island!
once a good friend of his went to see him. since there wa always someone keeping watch on them, they talked about only the old days. when they parted, the friend took out a set of chess made of tusk and nephrite (软玉), and said to napoleon, "i give this to you. maybe it will be of some help." napoleon liked it very much. he used to play with the chessmen (棋子) and study chess manuals (棋谱), to pass the last days of his life.
after his death, many of the things he had ever used were auctioned (拍卖). the set of chess was also sold and resold several times at very high prices. finally it was the national museum in france. when the staff members were cleaning the chessmen, they found the bottom of black king could be twisted off (拧开). they opened it and, to their great surprise, in it there was a detailed map about how to escape from the island. it was a great pity that napoleon had never discovered the secret, and thus he nulified (使......无用) his friend' s effort.