The sounds we make when we talk are produced in exactly the same way with the exception of the little hammers. In our throats are two cords which we call our vocal cords. When we talk we cause these cords to vibrate and thus we make the sounds of our voices. The most wonderful part of this voice of ours is that with only two vocal cords or wires, we can produce practically all the notes that can be made with a piano, which has a wire or cord for every note, excepting that we cannot make so many at one time. The human throat is so wonderfully constructed that we can lengthen or shorten our vocal cords at will and produce, with two strings, in our throats as many notes as it takes the piano many more strings to produce. Why Does the Sound Stop When We Touch a Gong that Has Been Sounded? When we touch the gong we stop the sound waves which the gong gives off when it is struck. These sound waves continue after the gong has been struck in continuous vibrations until something stops them. When you touch the vibrating gong, you stop its vibrating. If you only touch your finger to the vibrating gong you can feel the vibrations which cause a little tickling sensation. Naturally when you stop these vibrations you stop the air waves which the vibrations cause, and thus also the sound of these air waves striking your ear are stopped and the sound ceases. How Can Sound Come Through a Thick Wall? A sound will come through a thick or thin wall only if the wall is a good conductor of sound. Some things are good conductors of sound and others are not, just as some things are good conductors of electricity and others are not. If a wall is built of materials all of which are good conductors of sound, the sound will come through it no matter how thick. Wood is an especially good conductor of sound. It is even better than air. You can stand at one end of a long log and have another person at the other end hold up his watch in the air, and you cannot hear the watch tick, but if the watch is “going” as we say, and you ask the person holding it to put the watch against his end of the log, and you then put your ear to the other end, you can hear the watch ticking almost as well as if you had it to your own ear. In like manner you can hear the scratching of a pin at the other end of the log. When you put your ear against a telegraph pole you can hear the hum of the wires while you cannot hear it through the air. All sound is produced by sound waves and many solids are better conductors of sound waves than the air. Sound waves, however, will sometimes not be heard as plainly through a wall, because of the fact that the wall may be made of materials which are not equally good conductors of sound. When a sound wave strikes a poor conductor it loses some of its power and the sound, although it may be heard through the wall, will be fainter. What Is Meant by Deadening a Floor or a Wall?