CHAPTER II.

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Q. What is the second chief source of heat?

A. Electricity.

Q. What is lightning?

A. Lightning is only an Electric Spark, taken from the clouds.

Q. What causes the discharge of an electric cloud?

A. When a cloud, overcharged with electric fluid, approaches another which is under-charged, the fluid rushes from the former into the latter, till both have the same quantity.

Q. Is there any other cause of lightning, besides the one just mentioned?

A. Yes; sometimes mountains, trees, and steeples, will discharge a lightning cloud floating near; and sometimes electric fluid rushes out of the earth, into the clouds.

Q. What produces electricity in the clouds?

A. 1st—The evaporation from the earth’s surface.

2ndly—The chemical changes perpetually going on: and

3rdly—Currents of air of unequal temperature, excite electricity by friction, as they pass by each other.

Q. How high are the lightning-clouds from the earth?

A. Electrical clouds are the lowest of all clouds; they are rarely more than 700 yards above the ground; and sometimes, they actually touch the earth with one of their edges.

Q. How high are the clouds generally?

A. In a fine day, the clouds are often 4 or 5 miles above our head; but the average height of the clouds is from 1-1/2 to 2 miles.

Q. Why is lightning sometimes forked?

A. When the lightning-cloud is a long way off, the resistance of the air is so great, that the electrical current is diverted into a zig-zag course.

Q. Why does the resistance of the air make the lightning zig-zag?

A. As the lightning condenses the air, in the immediate advance of its path; it keeps flying from side to side, in order to pass where there is the least resistance.

Q. How does lightning condense the air in the immediate advance of its path?

A. The air is condensed by the rapidity of the lightning-flash.

Q. Why is forked lightning more dangerous than a straight flash?

A. Whatever resists the flash, diverts its course; and when terrestrial objects offer resistance to the current, they are in great danger of being destroyed.

Q. Why are there sometimes two flashes of forked lightning at the same moment?

A. Sometimes (in very severe storms) a flash of lightning will divide into two or more parts; and then each branch assumes the zig-zag form.

Q. Why is the flash sometimes quite straight?

A. When the lightning-cloud hovers near the earth, as the flash meets with very little resistance, it is not diverted; or (in other words) the flash is straight.

Q. What is the cause of sheet lightning?

A. It is only the reflection of distant flashes, not distinctly visible: and sometimes several flashes (from different clouds) intermingle, and form one vast blaze or sheet of lightning.

Q. Which form of lightning is the most dangerous?

A. The ball of fire is by far the most dangerous; and the zig-zag lightning is next in danger. Sheet lightning is not often attended with danger.

Q. Why are balls of fire so very dangerous?

A. Because (whenever they fall) much mischief is occasioned by their bursting, which they always do, with an explosion like that of a cannon.

Q. Do these balls of lightning ever run along the ground?

A. Yes; they often run a considerable way along the ground, then stop for a little time, and burst in numberless pieces: sometimes each of these pieces will explode; and at other times, the whole ball will burst at once, producing most mischievous consequences.

Q. What mischief will these balls of fire produce?

A. They will set houses and barns on fire; and kill all cattle and human beings, which happen to be in their course.

Q. Why does lightning sometimes kill men and beasts?

A. When the electric current passes through a man or beast, it produces so violent an action upon the nerves, that it destroys life.

Q. When is a person struck dead by lightning?

A. Only when his body forms a part of the lightning’s path: i. e. when the electric fluid (in its way to the earth) actually passes through his body.

Q. Why are men sometimes maimed by lightning?

A. Because lightning strikes with amazing force, whatever opposes it: and if a man stand in the way, it strikes him such a blow, as to maim him.

Q. What is thunder?

A. Lightning parts the air through which it passes; and when the parted air closes again, the noise made by the concussion, is called Thunder.

Q. Why does lightning part the air through which it passes? It does not part a rod of iron.

A. Iron is a conductor, and therefore allows the fluid to go freely through it: but air being a non-conductor, resists the lightning; which, therefore, rips it open, in order to pass through it.

Q. Why is thunder sometimes one vast crash?

A. When the lightning-cloud is near the earth, as the flash is straight,—the whole volume of air (through which it passes) collapses at once; and produces one unbroken sudden crash.

Q. What is meant by the air collapsing?

A. When the rent air closes again, it is said to collapse.

Q. Why is the peal sometimes an irregular mangling broken roar?

A. When the lightning-cloud is a long way off, as the flash is zigzag, the air does not collapse all at once; and as we hear the concussion of one part after another, the peal is broken, protracted, and irregular.

Q. Which part of the collapsing air do we hear first?

A. That part nearest the earth; then the strata above; and last of all, that in the immediate vicinity of the cloud.

Q. What is meant bystrata of air?

A. If a board were laid upon the earth, and several other boards were piled upon it, this pile would represent strata of wood.

Q. How does this illustration apply to the air?

A. A layer of air covers the earth; another layer rests upon it; and thus layer is piled upon layer, for 50 miles in height. Each layer is a “stratum” of air; and the plural of stratum is strata.

Q. Why do we hear the collapsing of the air nearest the earth first?

A. Because sound takes a whole second of time to travel 380 yards; but the air is ripped from top to bottom instantaneously: if, therefore, the cloud were 1000 yards off, we should hear the collapsing of the lowest strata nearly three seconds, before we heard that in the immediate vicinity of the cloud.

Q. Why is the thunder sometimes like a deep growl?

A. When the storm is far distant, the thunder sounds like a deep growl.

Q. Does not scenery affect the sound of thunder?

A. Yes; the flatter the country, the more unbroken the peal: Mountain scenery breaks the peal, and makes it harsh and irregular.

Q. What is the cause of rolling thunder?

A. The rolling is produced by the reverberation of the thunder along the massive clouds.

Q. What is meant by the reverberation?

A. The echo.

Q. Why is a flash of lightning generally followed by a pouring rain?

A. The cloud collapses, as soon as the electric fluid has left it; and the water it contained is squeezed out.

Q. Why is a flash of lightning generally followed by a gust of wind?

A. The flash rent the air asunder through which it darted; and when the two parts collapse, a rapid motion is produced, which we call wind: the vibration of the thunder contributes also to agitate the air.

Q. What is meant by thevibration of the thunder?”

A. The quivering motion it gives to the air, by its loud sound.

Q. Why is there no thunder to what is called summer lightning?

A. Because the lightning-clouds are so far off, that the sound of the thunder is lost, before it reaches the earth.

Q. Do thunder-bolts ever drop from the clouds?

A. No; the notion of thunder-bolts falling from the clouds, arises from the globular form, that is sometimes assumed by a flash of lightning.

Q. Why is the thunder often several moments after the flash?[1]

A. The flash travels nearly a million times faster than the thunder; if, therefore, the thunder has far to come, it will not reach the earth till a considerable time after the flash.

[1] The speed of lightning is so great, that it would go 480 times round the earth in one minute: whereas, thunder would go scarcely 13 miles in the same space of time.

Q. Can we not tell the distance of a thunder-cloud, by observing the interval which elapses between the flash and the peal?

A. Yes; the flash is instantaneous, but the thunder will take a whole second of time to travel 380 yards: hence, if the flash is 5 seconds before the thunder, the cloud is 1900 yards off.

(i. e. 380 × 5 = 1900 yards.)

Q. What places are most dangerous to be in, during a storm?

A. It is very dangerous to be near a tree, or lofty building; it is dangerous also, to be near a river, or any running water.

Q. Why is it dangerous to be near a tree, or lofty building, during a thunder-storm?

A. Because a tall pointed object, (like a tree or spire,) will frequently discharge a lightning-cloud; and then the electric fluid will pass down it, in its way to the earth.

Q. How can a tree or spire discharge a lightning-cloud?

A. A lightning-cloud (floating over a plain) may be too far off to be discharged by it; but as a tree, or spire, would shorten the distance between the cloud and its conductor, it might no longer be too far off a conductor to be discharged.

Q. Is not air a conductor of lightning?

A. No; dry air is not a conductor of lightning; and therefore, the flash rends it in twain, to get to some conductor.

Q. Why would it be dangerous to stand near a tree or spire, while lightning is passing down it?

A. Because the electric fluid (called lightning) always rushes down the outside of the tree or spire; and if any one were standing near, might pass through him, and kill or maim him.

Q. Does lightning go through the inside or outside of a tree?

A. It rolls down the outside of a tree; but passes through the inside of a man.

Q. Why does lightning pass down the outside of a tree?

A. Lightning always makes choice of the best conductors; and the outside of a tree is a better conductor than the inside.

Q. Why does lightning pass through the inside of a man?

A. As the fluids of the human body make a better conductor than the skin, therefore lightning passes through a man, and not down the skin.

Q. Why is it dangerous to be near a deep river, or any other running water, during a thunder-storm?

A. Because running water is a good conductor; and lightning always takes in its course the best conductors.

Q. Why is it dangerous for a man to be near water, in a thunder-storm?

A. Because the height of a man may be sufficient to discharge a cloud: and (if there were no taller object nigh) the lightning might make the man its conductor to the water.

Q. Why is it dangerous to ring church-bells during a thunder-storm?

A. For two reasons: 1st—Because the steeple may discharge the lightning-cloud, in consequence of its mere height.

2ndly—The swinging of the bells causes a current of air, which collects electric fluid.

Q. Why is it unsafe to run or drive fast during a thunder-storm?

A. The rapid motion of running causes a current of air, which collects electric fluid, and is often fatal.

Q. What parts of a dwelling are most dangerous during a thunder-storm?

A. The fire-place, (especially if the fire be lighted); the attics and cellar. It is also dangerous to sit close by the walls; to ring the bell; or to bar the shutters, during a thunder-storm.

Q. Why is it dangerous to sit before a fire, during a thunder-storm?

A. Because the heated air and soot are conductors of lightning; especially when connected with such excellent conductors as the stove, fender, and fire-irons.

Q. Why are the attics and cellar dangerous, during a thunder-storm?

A. Lightning sometimes passes from the clouds to the earth, and sometimes from the earth to the clouds; and therefore, the middle story of a house is always the safest to be in, during a thunder-storm.

Q. When does lightning pass from the earth to the clouds?

A. When the clouds are in a “negative” state of electricity.

Q. When does lightning pass from the clouds to the earth?

A. When the clouds are in a “positive” state of electricity.

Q. What is meant by the clouds being in a “positive state of electricity?”

A. When the clouds contain more electric fluid than they generally do, they are said to be in a positive state of electricity.

Q. What is meant by the clouds being in a “negative state of electricity?”

A. When the clouds contain less electric fluid than they ought to do, they are said to be in a negative state of electricity.

Q. Does the flash proceed from a negative or positive body?

A. Always from a positive body, or one over-burdened with electric fluid.

Q. When lightning flashes from the earth to the clouds, what is the flash called?

A. It is called the “returning stroke;” because the earth (being over-burdened with electric fluid) returns the surplus quantity to the clouds.

Q. Why is it dangerous to lean back against a wall during a thunder-storm?

A. Because the electric fluid sometimes runs down the wall of a house or room; and (as a man is a better conductor than a brick wall), would make him its path, and injure him.

Q. Why is it dangerous to ring a bell during a thunder-storm?

A. Bell-wire is an excellent conductor; and (if a person were to touch the bell-handle), the electric fluid, passing down the wire, might run through his hand and injure it.

Q. Why would the lightning run through a man touching a bell-handle?

A. Because the human body is a better conductor than the wall (between the bell-handle and the floor); and as lightning always chooses the best conductors for its path, it would (in this case) pass through the man, and injure him.

Q. Why is it dangerous to bar a shutter during a thunder-storm?

A. The iron shutter-bar is an excellent conductor; and (if a person were touching the bar), the electric fluid passing down it, might run from the bar through the person touching it, and injure him.

Q. Why is it dangerous to be in a crowd during a thunder-storm?

A. For two reasons. 1st—Because a mass of people form a better conductor than an individual: and

2ndly—The vapour from a crowd increases the danger of such a place.

Q. Why is a mass of bodies a better conductor than a single body?

A. Each living body is a conductor of electricity; and a connected mass of such conductors is more likely to be struck, than a single individual.

Q. Why is the danger increased by the vapour which rises from a crowd?

A. Vapour is a conductor, and therefore, may determine the shock; especially when connected with so many living bodies.

Q. Why is a theatre dangerous, during a thunder-storm?

A. Because the crowd assembled there, and the great vapour arising from so many living bodies, render a theatre an excellent conductor of lightning.

Q. Why is a flock of sheep in greater danger than a smaller number?

A. Because each sheep is a conductor of lightning, and the greater the number, the better its conducting power; besides, the vapour arising from a flock of sheep increases its conducting power, and its danger.

Q. Why is a herd of cattle in danger during a storm?

A. 1st—The number of living bodies increases the conducting power of the animal fluids: and

2ndly—The vapour arising from a herd is also a good conductor.

Q. If a person be abroad in a thunder-storm, what place is the safest?

A. Any spot about 20 or 30 feet from some tall tree or building; unless that spot be near to running water.

Q. Why would it be safe to stand 20 or 30 feet from some tall tree, in a thunder-storm?

A. Because the lightning would always choose the tall tree as a conductor, rather than the shorter man; and he would not be sufficiently near the tree, to be injured by the electric current passing down it.

Q. If a person be in a carriage in a thunder-storm, in what way can he travel most safely?

A. He should not lean against the carriage; but sit upright, without touching any of the four sides.

Q. Why should not a person lean against the carriage in a storm?

A. Because the electric fluid might run down the sides of the carriage; and (if a person were leaning against the sides), would make choice of him for a conductor, and perhaps destroy life.

Q. If a person be in a house during a thunder storm, what place is safest?

A. Any room in the middle story. The middle of the room is best; especially if you place yourself on a mattrass, bed, or hearth-rug.

Q. Why is the middle story of a house safest in a thunder-storm?

A. Because (even if the fluid struck the house), its strength would be exhausted before it reached the middle story.

Q. Why is the middle of the room more safe, than any other part of it, in a thunder-storm?

A. Because, if the lightning came into the room at all, it would come down the chimney or walls of the room; and therefore, the further distant from these, the better.

Q. Why is a mattrass bed, or hearth-rug a good security against injury from lightning?

A. Because they are all non-conductors; and, as lightning always takes in its course the best conductors, it would not select such things as these.

Q. Is it better to be wet or dry during a storm?

A. To be wet: if a person be in the open field, the best thing he can do, is to stand about 20 feet from some tree, and get completely drenched to the skin.

Q. Why is it better to be wet than dry?

A. Because the wet clothes would form a far better conductor than the fluids of our body; and, lightning would roll down the wet clothes, without touching our body at all.

Q. What is the safest thing a person can do to avoid injury from lightning?

A. He should draw his bedstead into the middle of his room, commit himself to the care of God, and go to bed; remembering that our Lord has said, “The very hairs of your head are all numbered.”

Q. What is a lightning-conductor?

A. A metal rod fixed in the earth, running up the whole height of a building, and rising in a point above it.

Q. What metal is the best for this purpose?

A. Stout copper wire.

Q. Why is copper wire better than iron?

A. 1st—Because copper is a better conductor than iron:

2ndly—It is not so easily fused or melted: and

3rdly—It is not so much injured by weather.

Q. What is the good of a lightning-conductor?

A. Metal wire is a most excellent conductor; and as the lightning makes choice of the best conductors, it would run down the metal wire, rather than the bricks of the building.

Q. How far will the beneficial influence of a lightning-conductor extend?

A. It will protect a circumference all round, the diameter of which is (at least) 4 times as long as that part of the rod, which rises above the building.

Q. Give me an example.

A. If the rod rise 2 feet above the house, it will protect the building for (at least) 8 feet all round.

Q. Why are not lightning-conductors more generally used?

A. Because they are often productive of more harm than good.

Q. How can lightning-conductors be productive of harm?

A. If the rod be broken by weather or accident, the electric fluid (being obstructed in its path) will rend the building into fragments.

Q. Is there any other evil to be apprehended from a lightning rod?

A. Yes; if the rod be not big enough to conduct the whole current to the earth, the lightning will fuse the metal, and greatly injure the building.

Q. How stout is it needful for the copper wire to be, that it may conduct the fluid safely to the earth?

A. It should be (at least) one inch in diameter.

Q. Why does lightning sometimes knock down houses and churches?

A. The steeple, or chimney is first struck; the lightning then darts to the iron bars and cramps employed in the building; and (as it darts from bar to bar) shatters to atoms the bricks and stones, which oppose its progress.

Q. Can you tell me how St. Bride’s Church (London) was nearly destroyed by lightning, about 100 years ago?

A. The lightning first struck the metal vane, and ran down the rod; it then darted to the iron cramps, employed to support the building; and (as it flew from bar to bar) smashed the stones of the church, which lay between.

Q. Why did the lightning fly about from place to place, and not pass down in a straight course?

A. Because it always takes in its course the best conductors; and will fly both right and left, in order to reach them.

Q. Why does lightning turn milk sour?

A. Lightning causes the gases of the air (through which it passes) to combine, and thus produces a poison, called nitric acid; some small portion of which, mixing with the milk, turns it sour.[2]

(N. B. Sometimes, the mere heat of the air, during the storm, turns milk sour.)

[2] The air is composed of two gases, called oxygen and hydrogen, mixed together, but not combined. If oxygen is combined with nitrogen, it produces five deadly poisons, viz.—nitrous oxide, nitric oxide, hyponitrous acid, nitrous acid, and nitric acid, according to the proportion of each gas in the combination.

Q. What is the difference between combining and mixing?

A. When different ingredients mingle without undergoing any chemical change, they are said to be mixed; but when the natural properties of each are altered by the union, then those ingredients are said to be combined.

Q. Give me an example.

A. If different coloured sands be shaken together in a bottle, the various grains will mix together, but not combine: but if water be poured on quick lime, the water will combine with the lime, and not mix with it.

Q. Why are the different grains of sand said to be mixed, when they are shaken together?

A. Because they are mingled together, but the property of each grain remains the same as it was before.

Q. Why is water poured on lime, said to combine with it?

A. Because the properties, both of the water and the lime, are altered by the mixture: the lime alters the character of the water, and the water alters the character of the lime.

Q. Do oxygen and nitrogen combine, or only mix together, in common atmospheric air?

A. They only mix together, as grains of sand would do, when shaken in a bottle. When oxygen and nitrogen combine, they do not constitute air, but acid poisons.

Q. Why does lightning turn beer sour, although contained in a close cask?

A. If the beer be new, and the process of fermentation not complete, lightning will so accelerate the process, as to turn the liquor sour.

Q. Why is not old beer and strong porter made sour by lightning?

A. Because the fermentation is complete already; and, therefore, is not affected by electrical influence.

Q. Why is metal sometimes fused by lightning?

A. Because the dimension of the metal is too small, to afford a path for the electric current.

Q. Why does lightning purify the air?

A. For two reasons: 1st—Because the oxygen and nitrogen of the air combine,[3] and produce “nitric acid:”

2ndly—Because the agitation of the storm stirs up the air.

[3] The oxygen and hydrogen are not combined, but simply mixed in the ordinary air; but the lightning causes the mixed elements to combine.

Q. How does the production of nitric acid purify the air?

A. Nitric acid acts very powerfully in destroying exhalations, arising from putrid vegetable and animal matters.

Q. Why is lightning more common in summer and autumn, than in spring and winter?

A. The heat of summer and autumn produces great evaporation; and the conversion of water to vapour, always develops electricity.

Q. Why does a thunder-storm generally follow very dry weather, and rarely succeeds continued wet?

A. The clouds are always charged with electricity; but dry air (being a non-conductor), will not conduct the surplus fluid from the clouds to the earth: so it violently rends the dry air with a flash, in order to relieve the cloud, and reach the earth.

Q. What is the general direction of a thunder-storm?

A. Either from east to west; or else from north to south.

Q. Why is electricity excited by friction?

A. Electricity, like heat, exists in all matter; but is often in a latent state: friction disturbs it, and brings it into active operation. (see p. 31.)

Q. Why is a tree sometimes scorched by lightning, as if it had been set on fire?

A. Lightning scorches it by its own positive heat, just the same as fire would.

Q. Why is the bark of a tree often ripped quite off by a flash of lightning?

A. As the lightning runs down the tree, it develops the latent heat so rapidly, that it carries the bark of the tree along with it, while it seeks to escape.

Q. Why are boughs of trees broken off by lightning?

A. The mechanical force of lightning is very great; and when the flash strikes a tree, it will often break off the boughs by the force with which it strikes against it.

Q. Why is an electric shock felt most at the elbow joint?

A. Because the path of the fluid is obstructed by the joint: and the shock felt at the elbow is caused by the fluid leaping from one bone to another.


                                                                                                                                                                                                                                                                                                           

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