When We Sing a Note to the Piano, Why Does it Answer?
If we put down the loud pedal of a piano (so raising the dampers), and then sing a steady note, we find that the piano also begins to sing. There is a very interesting reason why. We hear sounds because of blows on the drums of our ears. These eardrums are membranes stretched across the ear passage as parchment is stretched across a drum. If anything beats on this drum, the vibrations of the membrane are communicated to the brain and we hear sound.
Irregular vibrations of the air cause us to hear sounds we call noises, as, for example, when we knock over a chair. If the air is made to move in regular waves by regular vibrations, we hear a pleasing sound which we call a musical note. Thus, when a bow is drawn by an experienced hand across a violin string, the string vibrates regularly, and the air is set into a regular wave-motion. This wave-motion reaches our ears and causes the drums to vibrate accordingly. So it is with the piano string, which is set vibrating by being hit with a felt-covered hammer when we strike the appropriate key.
When we sing into the piano, we set up waves of sound in the air, and the particular string of the piano which is of a length to correspond with the note we sing begins to vibrate, and therefore to give out sound. But only the notes we sing will answer us. All the others remain silent, because their wave-length is not the wave-length we have set up. It is exactly the same principle that is used in wireless telegraphy, but in that case the waves are not sound-waves or airwaves, but electric waves in the ether.
