A Guide to the Scientific Knowledge of Things Familiar
CHAPTER II.
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 by_ "STRATA _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 the_ "VIBRATION _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_.