找两把同样的雨伞,一块手表,两段粗铁丝。先将一把伞撑开放在空地上,用铁丝把它支起来(如图)。你把耳朵伸进去听一听声音,你会发现,各处的声响略有不同,沿着伞柄你会找到声音最响的一个位置。在这个位置挂上那块机械手表,它不停地发出滴嗒声。 Find the same two umbrellas, a watch, two sections of thick wire. First open an umbrella in the open space, with wire to support it (Figure). When you put your ear in and listen to the sound, you find that there is a slight difference in sound everywhere, and along the umbrella handle you will find the loudest place. Hanging the mechanical watch in this position, it keeps ticking.