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the flute to vibrate; and this vibration sets in motion the sound-waves of the air.

Q. Why are some notes bass, and some treble?

A. Because slow vibrations produce bass or deep sounds; but quick vibrations produce shrill or treble ones.

Q. Why is an instrument flat, when the strings are unstrung?

A. Because the vibrations being too slow, the sounds produced are not shrill or sharp enough.

Q. Why can persons, living a mile or two from a town, hear the bells of the town-church sometimes and not at others? A. Because fogs, rain, and snow, obstruct the passage of sound; but when the air is cold and clear, sound is propagated more easily.

Q. Why can we not hear sounds (as those of distant church bells) in rainy or snowy weather, so well as in fine weather? A. Because falling rain or snow interferes with the undulations of the sound-waves, and stops their progress.

Q. Why can we hear distant clocks most distinctly in clear cold weather?

A. Because the air is of more uniform density, and there are fewer currents of air of unequal temperature to interrupt the sound-waves.

Q. Why can persons (near the poles) hear the voices of men in conversation a mile distant in winter time?

A. Because the air is very cold, clear, and still; in consequence of which, there are but few currents of air of unequal temperature to interrupt the sound-waves.1

Q. Why are not sounds (such as those of distant church bells) heard so distinctly on a hot day, as in frosty weather? A 1st-Because the density of the air is less uniform in very hot weather:

2ndly-It is more rarefied; and consequently, a worse conductor of sound: and,

3rdly-It is more liable to accidental currents, which impede the progress of sound.

Q. Why can we not hear sounds (such as those of distant clocks) so distinctly in a thick mist or haze, as in a clear night?

1 Captain Ross heard the voices of his men in conversation a mile and a half from the spot where they stood: and Lieutenant Foster held a conversation with a man across the harbour of Port Bowen, (in the North Sea,) a distance of a mile and a quarter.

A. Because the air is not of uniform density, when it is laden with mist; in consequence of which, the sound-waves are obstructed in their progress.

Q. Why do we hear sounds better by night than by day? A. 1st-Because night air is of more uniform density, and less liable to accidental currents: and,

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

Q. Why is the air of more uniform density by night, than it is by day?

A. Because the breezes (created by the action of the sun's rays) generally cease at night-fall.

Q. How should partition walls be made to prevent the voices in adjoining rooms from being heard?

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

Q. Why would shavings, or saw-dust, prevent the transmission of sound from room to room?

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-lath and paper again; 5thly-the air again: and every change of medium resists the progress of the sound-waves.

Q. Why can deaf people hear through an ear-trumpet? A. Because it restrains the spread of the voice, and limits the diameter of the sound-waves; in consequence of which, their strength is increased.

Q. Why are mountains noiseless and quiet?

A. Because the air of mountains is very rarefied; and rarefied air is a bad medium for conducting sound.

Q. How do you know that the rarity of air diminishes the intensity of sound?

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 almost inaudible.

Q. What is the cause of echoes?

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.

Q. What places are most famous for echo?

A. Caverns, grottoes, and ruined abbeys; the areas of

halls; the windings of long passages; the aisles of cathedral churches; mountains and icebergs.

Q. Why are caverns and grottoes famous for echoes?

A. Because the sound-waves which cannot pass through the cavern or grotto, are driven back again from their sides. Q. Why are halls, winding passages, ruins, and cathedral aisles, famous for echoes?

A. Because the sound-waves cannot flow freely forward in them; but strike against the opposing walls and are beaten. back.

Q. Why are mountains and ice-bergs, famous for echoes? A. Because they present an insurmountable barrier to the sound-waves, and throw them back again.

Q. Why do not the walls of an ordinary room or small church produce perceptible echo?

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

Q, Why do very large buildings (as cathedrals), often reverberate the voice of the speaker?

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.

Q. Why do some echoes repeat only one syllable? A. Because the echoing body is very near. The farther the echoing body is off, the longer the sound it will reflect: If, therefore, it be very near, it will repeat but one syllable. Q. Why does an echo sometimes repeat two or more syllables?

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

ear.

Q. Why are two or more echoes sometimes heard?

A. Because separate reverberating surfaces receive the sound, and reflect it in succession.1

Q. Why do windows rattle, when carts pass by a house? A. 1st-Because glass is sonorous; and the air communi

1 17 miles above Glasgow, near a mansion called Rosneath, is a very remarkable echo. If a trumpeter plays a tune, the echo will begin the same tune and repeat it all accurately:-as soon as this echo has ceased, another will echo the same tune in a lower tone; and after the second echo has ceased, a third will succeed with equal fidelity, though in a much feebler tone.

At the Lake of Killarney in IRELAND, there is an echo, which plays an excellent "second" to any simple tune played on a bugle.

cates its vibrations to the glass, which echoes the same sound; 2ndly-The window-frame being shaken, contributes to the noise. Brewer's Guide to Science.

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ASTRONOMY, teaches us the magnitudes and distances of the heavenly bodies, their arrangements, their various motions and phenomena, and the laws by which their movements are regulated. It presents to our view, objects the most wonderful and sublime; whether we consider the vast magnitude of the bodies about which it is conversant-their immense number-the velocity of their motions-the astonishing forces requisite to impel them in their rapid career through the regions of the sky-the vast spaces which surround them, and in which they perform their revolutions-the magnificent circles they describe the splendour of their appearance-or the important ends they are destined to serve in the grand system of the universe.

When we lift our eyes towards the sky, we perceive an apparent hollow hemisphere, placed at an indefinite distance,

and surrounding the earth on every hand. In the day time, the principal object which appears in this hemisphere is the sun. In the morning, we see him rise above the distant mountains, or from the extremity of the ocean: he gradually ascends the vault of heaven, and then declines, and disappears in the opposite quarter of the sky. In the northern parts of the globe, where we reside, if, about the 21st of March, we place ourselves on an open plain, with our face towards the south, the sun will appear to rise on our left, or due east, about six in the morning, and about the same hour in the evening he will set due west. In the month of June, he rises to our left, but somewhat behind us, in a direction towards the north-east, ascends to a greater height at noon than in the month of March, and after describing a large arc of the heavens, sets on our right and still behind us, in the northwestern quarter of the sky. In the month of December, if we stand in the same position, we may observe, without turning ourselves, both his rising and setting. He rises in the south-east, ascends to a small elevation at noon, and sets in the south-west, after having described a very small arc of the heavens. Every day he appears to move a little towards the east, or contrary to his apparent diurnal motion; for the stars which are seen to the eastward of him, appear every succeeding day to make a nearer approach to the place in which he is seen. All the variety of these successive changes is accomplished within the period of 365 days 6 hours, in which time he appears to have made a complete revolution round the heavens from west to east.

The moon is the next object in the heavens which naturally attracts our attention; and she is found to go through similar variations in the course of a month. When she first becomes visible at new moon, she appears in the western part of the heavens, in the form of a crescent, not far from the setting sun. Every night she increases in size, and removes to a greater distance from the sun, till at last she appears in in the eastern part of the horizon, just as the sun disappears in the western; at which time she presents a round full-enlightened face. After this she gradually moves farther and farther eastward, and her enlightened part gradually decreases, till at last she seems to approach the sun as nearly in the east as she did in the west, and rises only a little before him in the morning, in the form of a crescent.

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