trees of life bearing the golden fruits of immortality among all the nations of the earth. This mighty river, so deep, so broad, so far-reaching in its many branches, we may trace back to the tears of that little girl. Behold, what a great fire a little matter kindleth!

Read's Hand of God in History.

captain when he swore such a horrid oath? 14. What effect had his words on Captain Haldane?

15. What has this Captain Haldane become?

16. What good has his brother done in Geneva ?

17. Name the good men whom Robert Haldane has been the means of turning to the Lord.

18. What great reformer once lived in Geneva ?

19. Why did the Welsh girl weep when asked by the clergyman to name the text? 20. What did this "small matter" lead to?

21. How many copies of God's Word, that best of all books, has the British and Foreign Bible Society distributed?

22. Did the effects of the "child's tears" terminate with the British Bible Society? 23. Seeing that God rules all things, ought not both teachers and pupils ever to pray to God in the name of Christ, for the Holy Spirit, that they may be fitted for Heaven, and brought there when they die?

QUESTION. How is sound1 produced?

Answer. The vibration of some sonorous substance produces

1 The Science which treats of the nature, properties, and laws of sound, is called Acoustics; a word derived from the Greek Akouo, I hear.

L

wave-like motion in the air, which strikes upon the drum of the ear, and gives the sensation of sound.

Q. What are musical sounds?

A. Regular and uniform successions of vibrations.
Q. How fast does sound travel?

A. About 13 miles in a minute, or 1142 feet in a second of time. 1

Q. Why are some things sonorous, and others not?

A. The sonorous quality of any substance, is connected with its hardness and elasticity.

Q. Why are copper and iron sonorous, and not lead? A. Because copper and iron are hard and elastic; but as lead is neither hard nor yet elastic, it is not sonorous. Q. Of what is bell-metal made?

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

Q. Why is this mixture of tin and copper used for bellmetal?

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

Q. Why is the sound of a bell stopped, by touching the bell with our finger?

A. Because 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.

Q. Why does a split bell make a hoarse disagreeable sound?

A. Because 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.

Q. Why do fiddle-strings give musical sounds?

A. Because the bow causes them to vibrate: and this vibration sets in motion the sound-waves of the air, and produces musical notes.

Q. Why does a drum sound?

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

Q. Why do flutes, &c., produce musical sounds?

A. Because the breath of the performer causes the air in

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

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 from one room to another.

pass

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.