A. The vibration of some sonorous substance produces motion in the air called sound waves, which strike upon the drum of the ear, and give the sensation of sound.

A. Regular and uniform successions of vibrations, which are always pleasing to the ear.

A. About 13 miles in a minute, or 1142 feet in a second of time.

A. Light would go 8 times round the whole earth, while sound is going its 13 miles.

A. The sonorous quality of any substance depends upon its hardness and elasticity.

A. Copper and iron are hard and elastic; but as lead is neither hard nor yet elastic, it is not sonorous.

A. Of copper and tin in the following proportions:—In every 5 pounds of bell-metal, there should be 1 lb. of tin, and 4 lbs. of copper.

A. Because it is much harder and more elastic than either of the pure metals.

A. The weight of the finger stops the vibrations of the bell; and as soon as the bell ceases to vibrate, it ceases to make sound-waves in the air.

A. The split of the bell causes a double vibration; and as the sound-waves clash and jar, they impede each other’s motion, and produce discordant sounds.

A. The bow drawn across the string causes it to vibrate, and this vibration of the string sets in motion the sound-waves of the air, and produces musical notes.

A. The parchment head of the drum vibrates from the blow of the drum-stick, and sets in motion the sound-waves of the air.

A. Because the glasses vibrate as soon as they are struck, and set in motion the sound-waves of the air.

A. The breath of the performer causes the air in the flute to vibrate, and sets in motion the sound-waves of the air.

A. The keys of the piano (being struck with the finger) lift up a little hammer which knocks against a string; and the vibration thus produced, sets in motion the sound-waves of the air.

A. Slow vibrations produce bass or deep sounds; whereas, quick vibrations produce shrill or treble sounds.

A. Because the vibrations are too slow; in consequence of which, the sounds produced are not shrill or sharp enough.

A. Fogs, rain, and snow, obstruct the passage of sound; but when the air is cold and clear, sound is propagated more easily.

A. Because the falling rain interferes with the undulations of the sound-waves, and breaks them up.

A. Because the falling snow interferes with the undulations of the sound-waves, and stops their progress.

A. Because the air is most uniform then: there are not two currents of air (one up and one down) to interrupt the sound-waves.

A. Because the air is very cold and very clear; in consequence of which, there are not two currents of air (one up and one down) to interrupt the sound-waves.

Captain Ross heard the voices of his men in conversation, a mile and a half from the spot where they stood.

A. Because there are two currents of air; the current of hot air ascending from the earth, and the current of colder air falling towards the earth; and these two currents break up the sound-waves.

A. Because the mist diminishes the velocity of the sound-waves, and (by overburdening them with vapour) limits their length.

A. 1st—Night air is more uniform, because the ascending currents of air (raised by the action of the sun’s rays) cease as the evening advances; and

2ndly—Night is more still from the suspension of business, and the cessation of the hum of men.

A. The space between the laths (or canvass) should be filled with shavings or saw-dust; and then no sound would ever pass from one room to another.

A. Because there would be several different media for the sound to pass through: 1st—the air;

2ndly—the laths and paper;

3rdly—the saw-dust or shavings;

4thly—the air again: and every variety diminishes the strength of the sound-waves.

A. The ear trumpet restrains the spread of the voice, and limits the diameter of the sound-waves; in consequence of which, their strength is increased.

A. Because the air of mountains is very rarefied; and as the air becomes rarefied, sound becomes less intense.

A. If a bell be rung in the receiver of an air-pump, the sound becomes fainter and fainter as the air is exhausted, till at last it is quite inaudible.

A. Whenever a sound-wave strikes against any obstacle (such as a wall or hill), it is reflected (or thrown back); and this reflected sound is called an echo.

The same laws govern echo as light. (See p. 370.)

A. Caverns, grottoes, and ruined abbeys; the areas of antique halls; the windings of long passages; the aisles of cathedral churches; mountains, and ice-bergs.

A. 1st—Because the sound-waves cannot pass beyond the cavern or grotto, and must flow back:

2ndly—The return waves (being entangled by the cavern) are detained for a short time, and come deliberately to the ear.

A. Because the sound-waves cannot flow freely forward, but strike against the winding walls perpetually, and are beaten back.

A. Because they present a barrier to the sound-waves which they cannot pass; and are sufficiently elastic to throw them back.

A. Because sound travels with such velocity, that the echo is blended with the original sound, and produce but one impression on the ear.

Sound travels 13 miles in a minute.

A. Because the walls are so far off from the speaker, that the echo does not get back in time to blend with the original sound; and, therefore, each is heard separately.

A. The further the echoing body is distant, the more sound it will reflect. If, therefore, the echoing body be near, it will repeat but one syllable.

A. Because the echoing body is far off; and, therefore, there is time for one reflection to pass away before another reaches the ear.

A. 1st—Glass is sonorous; and the air communicates its vibrations to the glass, which echoes the same sound: and

2ndly—The window-frame is shaken by the sound-waves impinging against the window, and contributes to the noise.