We must be near the place in which the sound is made. What kind of waves will make a faint sound? Small waves in the air make a faint sound. Will these waves extend as far away as larger ones? No; as all waves of sound decrease in size as they recede, the smallest ones will soonest disappear. Why will a loud sound be heard farther than a fainter sound? Because the waves in the air from the loud sound will extend farther away than those from the fainter one. How are sounds produced? Sounds are produced by striking solid bodies together. How else may sound be produced? By striking a solid body against a liquid, as a stick struck against the water. In what other way may sound be made? Sound may be made by causing a substance to move rapidly through the air. When a piece of wood attached to a string is swung rapidly around, what kind of a noise is made? It makes a humming noise. When lightning passes through the air, what noise is made? A noise which we call thunder. How can a murmur be produced? When sounds, too faint to be heard separately, are united, they produce a murmur. Where may we hear a murmur? We may hear a murmur from the brook, as its waves flow over the pebbles, and from the wind, as it passes through the trees. When a sound is heard but once, what is it called? It is called a noise. When sounds are made at irregular intervals, what are they called? They are called noises. When sounds are repeated at regular intervals, what do they become? They become musical sounds. Upon what do the high and low sounds in music depend? They depend upon the rapidity with which the waves are produced in the air. When the waves are repeated rapidly, what sound is made? They make a high or acute sound. When they are repeated more slowly, what sound is made? They make a low or grave sound. How small a number of vibrations or waves in the air can be heard? _Sixteen_ vibrations in a second of time, will produce the gravest sound that can be heard. How large a number of vibrations in the air can be heard? Twenty-four thousand vibrations in a second of time, make the most acute sound that can be heard. How is the human voice made? It is made by means of the vocal chords at the upper part of the larynx. What is the larynx? The upper part of the windpipe is called the larynx. How do these chords produce the voice? When the air is forced out of the lungs, it causes these chords to vibrate, so as to produce the voice. Are these chords the same in all persons? No; they are larger and coarser in some persons than in others. In whom are they larger and coarser? They are usually larger and coarser in men, and they are smaller and finer in women. What kind of a voice is made by the large and coarse chords? They make a rough, coarse voice. What kind of voice is made by the finer chords? They make a finer and more delicate voice. Do these chords vibrate so rapidly in man as in woman?