No; they do not vibrate so rapidly in man as in woman. What kind of voice do rapid vibrations make? They make an acute voice; hence, woman can, when singing, raise her voice to a very high pitch. Where is the sensation of sound produced? The sensation of sound is produced on the ear. Do people vary in their ability to hear? Yes; they vary very much in their ability to hear. Is every person able to distinguish musical sounds? No; some persons cannot tell one musical note from another, and some cannot even tell one bird from another by its notes. Is the hearing of all animals alike? No; some can hear more acutely than others; a lion has more acute hearing than a man. What other animals have acute hearing? All such animals as hares, rabbits, and deer. Of what use is the acute hearing to these animals? It enables them quickly to hear the approach of their enemies, so that they may run away in time to escape the danger. Conduction of Sound. How does sound come to our ears? Sound is carried to our ears by the air. Is the air a conductor of sound? Yes; the _air_ is a _conductor_ of sound. Is there any sound where there is no air? No; there is not any sound where there is no air. How do we know this? When a bell is rung in a vacuum, no sound is heard. Can sounds be distinctly heard when the air is rare? No; the rarer the air the more poorly it conducts sound. What proof have we of this? On the top of a high mountain the human voice is heard only at a distance of a few yards; and a pistol when exploded sounds as faintly as the breaking of a stick. Can sounds be heard better when the air is dense? Yes; the denser the air, the better it conducts sound. What proof have we of this? The human voice sounds so distinctly in the dense air of deep mines, that conversation may be carried on in a whisper. Why are sounds heard better at night than in the day? Because the air at night is condensed by cold, and becomes a better conductor of sound; also, because the nights are stiller, and fewer sounds take our attention. Why is moist or damp air a better conductor of sound than dry air? Because the particles of water in the damp air increase its power of conduction. Why is sound heard farther when over the water? Because the damp air over the water is a better conductor, and because it contains fewer objects to obstruct the waves of sound. How far has the human voice been heard over the water? The words “all’s well” have been heard across the Strait of Gibraltar, a distance of _ten_ miles. How far has the human voice been heard over the land? It has been heard at the distance of _four_ miles. How does the wind affect sound? The wind carries the sound the way in which it is blowing, so that a noise may be heard much farther with the wind than against it. Why does water conduct sound faster than air?