Beethoven was a famous German musician in the 19th century. He devoted his life to symphony creation and composed a large number of world-renowned musical works. These works still have endless charm today. However, you may not have thought that this great musician became deaf after middle age - a serious illness caused him to lose his hearing. Even so, Beethoven did not interrupt his creative activities. It is said that after Beethoven became deaf, he used a steel rod to "listen" to music: he touched one end of the steel rod to the piano and held the other end between his teeth. As his beating fingers kept hitting the keyboard of the piano, he miraculously heard the beautiful notes one by one.

Why was Beethoven able to "hear" the sound of music using the above method even after he became deaf? There is a certain scientific reason for this. It turns out that this wonderful thing called "sound" can not only propagate in the air, but also in solid or liquid. Have you ever noticed this phenomenon: when eating, especially when chewing dry hard food, you often "hear" loud chewing sounds. If you cover your ears at this time, the chewing sound will not weaken at all, indicating that the sound is not heard with your ears. So where does this chewing sound come from? Careful study shows that it is the vibration emitted during chewing that is transmitted to the auditory nerve through the skull (solid) and then to the brain, thereby causing people to feel sound. The same principle applies to Beethoven listening to music with a steel rod: when playing the piano, the vibration of the strings is transmitted to the steel rod, and then transmitted to the tooth bone through the steel rod, and then transmitted from the tooth bone through the skull to the auditory nerve and spread. to the brain, so the sound of music was "heard" by Beethoven.

Human beings have known the principle of sound transmission in solids or liquids for a long time, and it has been widely used. In ancient times, when the two armies were fighting, soldiers often put their ears to the ground and used sound transmission from the ground to detect the movements of enemy troops and horses in the distance. Under the lighthouse standing in the ocean, there is a heavy bell. On a foggy night, the strong sound emitted by the bell can be transmitted to far away places by using sea water (liquid). Ships sailing in the ocean can use special listening devices to receive the bells, and then they can bypass the reefs and sail safely on the waterway.