Using his spark-gap transmitter, a mild-mannered 31-year-old physics professor demonstrates electromagnetic phenomena to students in a dimly lit classroom at the University of Karlsruhe in Germany.

• 德国卡斯鲁大学灯光昏暗的教室里，一位温文儒雅的物理学教授，利用火花放电发送机，向学生示?电磁现象。