*To show the Transmission of Sound.*—1. Vibrate a tuning fork and press the stem against a table or desk. The vibrations which are reënforced in this way will be heard in all parts of the room. Now press one end of a wooden rod, as a broom handle, against the table, and bring the stem of the vibrating fork against the other end. The vibrations now move down the stick to the table, from whence they are communicated to the air. Observe that the sound waves, to reach the ear, must pass through the rod, the table, and the air. 2. Fasten the tuning fork to a flat piece of cork by pressing the stem into a small hole in the center. Vibrate the fork and let the cork rest on the surface of water in a half-filled tumbler on the table. The sound will, as before, pass to the table and then to the air. Observe that in this case the vibrations are transmitted by a liquid, a solid, and by the air. Compare this action with the transmission of sound waves by different portions of the ear. *To show Effects of Sound Waves.*—1. Place two large tuning forks of the same pitch, and mounted on thin boxes for reënforcing their vibrations, near each other on a table. Vibrate one of the forks for a moment and then stop it by means of the hand. Observe that the other fork has been set in vibration. (This experiment does not work with forks of different pitch.) 2. While holding a thin piece of paper against a comb with the open lips, produce musical tones with the vocal cords. These will set the paper in vibration, producing the so-called "comb music." 3. Examine the disk in a telephone which is set in vibration by the voice. Observe that it is a thin disk and, like the membrane of the ear, has air on both sides of it. *To show the Reënforcement of Sound.*—1. Vibrate a tuning fork in the air, noting the feebleness of the tone produced. Then hold the stem against a door or the top of a table, noting the difference. 2. Hold a vibrating tuning fork over a tall jar, or bottle, and gradually add water. If the vessel is sufficiently tall, a depth will be reached where the air in the vessel reënforces the sound from the fork. 3. Hold a vibrating fork over the mouth of a small fruit jar, partly covered with a piece of cardboard. By varying the size of the opening, a position will be found where the sound is reënforced. If not successful at first, try bottles and jars of different sizes.