Ben Franklin grasped the concept long ago and mounted a metal rod atop the roof of his home, then ran a wire to the ground, thereby inverting the lightning rod.

• 很久以前，本富兰克林就已经认识到了这一点。他在自家屋顶上安了一根金属棒，从上面接了根金属线到地上，有此发明了避雷针。