A GUIDE
TO THE
SCIENTIFIC KNOWLEDGE
OF
THINGS FAMILIAR;

A. The sensation of warmth.

A. When we touch a substance of higher temperature than ourselves, the warmer substance keeps parting with its heat, till both are of equal temperature.

A. Calo’ric. Caloric, therefore, is the matter of heat, which passes from body to body; but Heat is the sensation, of warmth, produced by the influx of Calo’ric.

[Pg 2]

A. 1.—The Sun. 2.—Electricity. 3.—Chemical Action: and 4.—Mechanical Action.

A. Expansion, Liquefaction, Vaporization, and Ignition.

A. The Sun.

A. The rays of the sun, collected by the Burning Glass, are all bent to one point, called the “focus;” thus the heat and light, (which should be diffused over the whole glass,) being gathered together into one point, are very greatly increased.

[Pg 3]

A. Because the rays of light, which should have fallen there, are bent into the focus, and the space around, (being deprived of these rays) is accordingly darkened.

A. No, not quite all: and, therefore, the rim round the focus is only slightly shadowed.

A. Electricity.

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

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.

[Pg 4]

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.

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.

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.

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.

[Pg 5]

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.

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.

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

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.

[Pg 6]

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.

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.

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.

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

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.

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

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

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.

[Pg 8]

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.

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.

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.

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.

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

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.

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

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

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.

[Pg 10]

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.

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

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

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

A. The echo.

[Pg 11]

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

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.

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

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

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.

[Pg 12]

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.

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.)

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.

A. Because a tall pointed object, [Pg 13](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.

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.

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

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.

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

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

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.

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

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.

[Pg 15]

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.

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

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.

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.

[Pg 16]

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.

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

A. When the clouds are 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.

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

[Pg 17]

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

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

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.

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.

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.

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.

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.

A. Each living body is a conductor of electricity; and a connected mass of such conductors is more likely to be[Pg 19] struck, than a single individual.

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

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

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.

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

[Pg 20]

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

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

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.

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

A. Because the electric fluid might run down the sides of the carriage; and (if a person were leaning against the[Pg 21] sides), would make choice of him for a conductor, and perhaps destroy life.

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.

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

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.

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.

[Pg 22]

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.

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.

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.”

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

A. Stout copper wire.

[Pg 23]

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.

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.

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.

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

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

[Pg 24]

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

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.

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

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.

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.

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

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.)

A. When different ingredients mingle [Pg 26]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.

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.

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

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.

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.

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.

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

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

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

[Pg 28]

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

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

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

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.

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

[Pg 29]

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.)

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

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.

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.

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.

A. Chemical Action.

A. Many things, when their chemical constitution is changed, (either by the abstraction of some of their gases, or by the combination of others not before united,) evolve heat, while the change is going on.

A. Water is cold, and sulphuric acid is cold; but if these two cold liquids be mixed together, they will produce boiling heat.

A. Because water (being lighter than sulphuric acid), is condensed by the heavier liquid; and its heat is squeezed out, as water from a sponge.

A. The heat is evolved by the chemical action, produced by the cold water combining with the lime.

[Pg 31]

A. It was in the water and lime before; but was in a latent state.

A. Yes. All bodies contain heat; the coldest ice, as well as the hottest fire.

A. Yes. But it is latent, (i. e. not perceptible to our senses).[4]

A. Thus:—Ice is 32° by the thermometer; but if ice be melted over a fire, (though 140° of heat are thus absorbed,) it will feel no hotter than it was before. (i. e. it will be only 32°, and not 172°)[5].

A. It is hidden in the water; or (to speak more scientifically) it is stored up in a latent state.

A. 1st—140° of heat are hidden in the water, when ice is melted by the sun or fire.

2ndly—1000° more of heat are secreted, when water is converted into steam. Thus, before ice is converted into steam, 1140° of heat become latent.[6]

A. Yes. Into a pint of snow put half as much salt; then plunge your hand into the liquid; and it will feel so intensely cold, that the snow itself will seem quite warm in comparison to it.

A. Yes, many degrees; and by [Pg 33]dipping your hand into the mixture first, and into snow afterwards, the mere snow will seem to be comparatively warm.

A. Combustion is another instance of heat, arising from chemical action.

A. Fuel and air.

A. As bread is a compound of flour, yeast, and salt; so fuel is a compound of hydrogen and carbon.

A. The air is a compound of oxygen and nitrogen mixed together; in the proportion of five gallons of nitrogen, to one of oxygen.

A. The solid part of fuel. It abounds also in all animal bodies, earths, and minerals.

A. Common charcoal, lamp-black, coke, black lead, and the diamond, are all varieties of carbon.

[Pg 34]

A. An inflammable gas. The gas used in our streets, is only the hydrogen gas driven out of coals by heat.

A. Though this gas itself will burn, yet a candle will not burn when immersed in it; nor can an animal live in it. Hydrogen gas is the lightest of all known substances.[7]

A. A gas, much heavier than hydrogen; which gives brilliancy to flame, and is essential to animal life.[8]

A. Nitrogen is another invisible gas. It will not burn, like hydrogen; and [Pg 36]an animal cannot live in it: it abounds in animal and vegetable substances, and is the chief ingredient of the common air.[9]

A. In order to dilute the oxygen. If the oxygen were not thus diluted, fires would burn out, and life would be exhausted too quickly.

A. Hydrogen gas, carbon, and oxygen gas; the two former in the fuel, and the last in the air which surrounds the fuel.

A. The hydrogen gas of the fuel being set free, and excited by a piece of lighted paper, instantly unites with the oxygen of the air, and makes a yellow flame: this flame heats the carbon of the [Pg 37]fuel, which also unites with the oxygen of the air, and produces carbonic acid gas.

A. Only carbon (or charcoal) combined with oxygen gas.

A. 1st—By liberating latent heat from the air and fuel: and

2ndly—By throwing into rapid motion the atoms of matter.

A. When the oxygen of the air combines with the hydrogen of the fuel, the two gases condense into water; and latent heat is squeezed out, as water from a sponge.

A. 1st—When hydrogen of fuel and oxygen of air condense into water, a vacuum is made; and the air is disturbed, as a pond would be, if a pail of water were taken out of it: and

2ndly—When the carbon of fuel and oxygen of air expand into carbonic acid[Pg 38] gas, the air is again disturbed, as it would be by the explosion of gunpowder.

A. The hydrogen of fuel and oxygen of air (liberated by combustion) combining together, condense into water.

A. The carbon of fuel and oxygen of air (combining together in combustion) expand into a gas, called carbonic acid.

A. When coals are heated throughout, the carbon is so completely mixed with the oxygen of the air, that the whole surface is in a state of combustion, and therefore red hot.

A. Carbon (being very solid) requires a great degree of heat to make it unite with the oxygen of the air. When fresh[Pg 39] coals are put on, their under surface is heated before the upper surface; and one is red (or in a state of combustion), while the other is black.

A. A blazing fire burns out the fuel quickest.

A. In red hot coals, only the mere surface is in a state of combustion, because the carbon is solid; but in a blazing fire, (where the gases are escaping), the whole volume of the coal throughout is in a state of decomposition.

A. Unconsumed parts of fuel (principally carbon), separated from the solid mass, and carried up the chimney by the current of hot air.

A. Carbon (being solid), requires a great degree of heat to make it unite with oxygen, (or, in other words, to bring it[Pg 40] into a state of perfect combustion): when coals are fresh laid on, more carbon is separated than can be reduced to combustion; and so it flies off in smoke.

A. When a fire is red hot, the entire surface of the coals is in a state of combustion; so a very little flies off unconsumed, as smoke.

A. Because the intensity of the combustion is greater in some parts of the fire, than it is in others.

A. Because the air flies to the fire in various and unequal currents.

A. Because the intensity of combustion is so unequal, (owing to the gusty manner in which the air flies to the fuel; and the various shades of red, yellow, and white heat mingling with the black of the[Pg 41] unburnt coal), produce strange and fanciful resemblances.

A. Merely because it is of a more fragile texture; and, therefore, its component parts are more easily heated.

A. Because it is not so solid; and, therefore, its elemental parts are more easily separated, and made hot.

A. Because paper (in consequence of its fragile texture), so very readily catches fire.

A. Because wood, (being more substantial), burns longer than paper; and, therefore, affords a longer contact of flame to heat the coals.

A. Because paper burns out so rapidly, that it would not afford sufficient contact of flame to heat the coals to combustion.

[Pg 42]

A. Because wood is too substantial to be heated into combustion, by the flame issuing from a mere match.

A. As every blaze tends upwards, if the paper were placed on the top of the fire, its blaze would afford no contact of flame to fuel lying below.

A. As every flame tends upwards, if the wood were above the coal, the flame would not rise through the coal to heat it.

A. As every flame tends upwards; when a flame is made at the bottom of a fire, it ascends through the fuel and heats it: whereas, if the fire were lighted from the top, the flame would not come into contact with the fuel piled below.

[Pg 43]

A. Because it is so very hard and compact, that it burns away very slowly.

A. Because they are more porous and less solid; and are, therefore, sooner reduced to a state of combustion.

A. Iron cinders are cinders saturated with oxygen; they are unfit for fuel, because they can imbibe no more oxygen, being saturated already.

A. Because their vapour, gases, and volatile parts, have been driven off by previous combustion.

A. Because they contain no hydrogen (or inflammable gas) like coals.

A. 1st—Because the moisture of the wet kindling prevents the oxygen of the air from getting to the fuel to form it into carbonic acid gas: and

[Pg 44]

2ndly—The heat of the fire is perpetually drawn off, by the conversion of water into steam.

A. 1st—Because no heat is carried away, by the conversion of water into steam: and

2ndly—The pores of dry wood are filled with air, which supply the fire with oxygen.

A. 1st—Because they help to entangle the heat of the passing smoke, and throw it on the fuel: and

2ndly—They help to entangle the air that passes over the fire, and create a kind of eddy or draught.

A. Salt contains water; and the cracking of the salt is owing to the sudden conversion of the water into steam.

A. Because any “al’kali” (such as potash) will arrest the hydrogen (as it escapes from the fuel), and prevent its combination with the oxygen of air.

A. The con’verse of an acid; as bitter is the con’verse of sweet, or insipid the con’verse of pungent.

A. The iron bars conduct heat to the interior of some lump of coal: and its volatile gas (bursting through the weakest part) is kindled by the glowing coals over which it passes.

A. When a lump of coals lies over the hot bars, or the coals below it are not red hot, the gas which bursts from the lump escapes unburnt, and is of a greenish colour.

A. Because neither the bars nor coals (over which it passes) are red-hot.

[Pg 46]

A. Gas from the hot coals at the bottom of the grate mixing with the carbon of the coals above, produces an inflammable gas (called carbonic oxide), which burns with a blue flame.

A. Because both the hydrogen and carbon of the fuel are in a state of perfect combustion. It is the white heat of the carbon, which gives the pale yellow tinge to the flaming hydrogen.

A. Rapid undulations of a fluid called ether, striking on the eye.

A. The atoms of matter (set in motion by heat) striking against this ether, produce undulations in it; as a stone thrown into a stream, would produce undulations in the water.

A. As sound is produced by undulations[Pg 47] of air striking on the ear; so light is produced by undulations of ether striking on the eye.

A. A very subtile fluid, which pervades and surrounds every thing we see.

A. When a fiddle-string is jerked suddenly, its rapid vibration produces a grey light; and when a carriage wheel revolves very quickly, it sends forth a similar light.

A. No: the heat of a stack of hay, or reeking dunghill, though very great, is not sufficient to produce light.

A. Because yellow rays always produce the greatest amount of light; though red rays produce the greatest amount of heat.

A. The intensity of fire-light depends upon the whiteness to which the carbon is reduced, by combustion. If the carbon be white hot, its combustion is perfect, and the light intense; if not, the light is obscured by smoke.

A. The flame of coals is made chiefly by hydrogen gas. As soon as this gas is consumed, the hot cinders produce only an invisible gas, called carbonic acid.

A. The fuel is decomposed (by combustion) into its simple elements, carbon and hydrogen gas. (see p. 33)

A. The air (being very cold) rushes to the fire so rapidly, that the coals burn out faster, and the inflammable gas is sooner consumed.

A. Because the volatile gases are[Pg 49] quickly consumed; and the solid carbon plentifully supplied with air, to make it burn bright and intensely.

A. Because the air is colder in winter, than in summer-time.

A. For two reasons: 1st—Because cold air being more condensed than hot air, contains a greater body: and

2ndly—Cold air rushes more quickly to the fire, and supplies more oxygen.

A. 1st—When the sun shines, the air is rarefied; and, therefore, flows more slowly to the fire.

2ndly—As the air is rarefied, even that which reaches the fire, affords less nourishment.

A. The greater the contrast (between the external air, and that which has[Pg 50] been heated by the fire) the more rapid will be the current of air towards that fire.

A. Because it is spread out, (like a piece of gold beaten into leaf); and as a square inch of gold leaf will not contain so much gold as a square inch of bullion—so, a square inch of rarefied air has less body, than a square inch of cold air.

A. 1st—Because the air out-of-doors is more dense, than the air in-doors: and

2ndly—Because air is more freely supplied to a fire out-of-doors.

A. Because the circulation is more free; and as soon as any portion has been rarefied, it instantly escapes, and is supplied by colder currents.

A. During a thaw, the air is filled with vapour; and, both moves too slowly, and is too much diluted to nourish the fire.

A. In windy weather the air is rapidly changed, and affords plentiful nourishment to the fire.

A. A pair of bellows, (like the wind), drives the air more rapidly to the fire; and the plentiful supply of oxygen soon makes the fire burn intensely.

A. As the flame of a candle is confined to a very small wick, it is severed from it by the breath; and (being unsupported) must go out.

A. The breath carries the air to it with great rapidity; and the oxygen of the air kindles the red hot wick, as it kindles charred wood.

[Pg 52]

A. Because oxygen is not supplied with sufficient freedom, unless it be blown to the wick.

A. In frosty weather; because the air contains more oxygen then, being condensed by the cold.

A. For two reasons. 1st—Because the poker concentrates the heat, and therefore increases it: and

2ndly—Because the poker arrests the air which passes over the fire, and produces a draught.

A. When there are two or three pieces of wood on a fire, the air (circulating round them) produces an eddy or draught, which draws up the fire.

A. In order that the air, on the lower part of the room, may be heated by the fire.

A. No; the heat of a fire has a very little effect upon the air below the level of the grate; and, therefore, every grate should be as near to the floor as possible.

A. As the fire consumes the air which passes over it, cold air rushes through the crevices of the doors and windows along the bottom of the room to supply the deficiency; and these currents of cold air, rushing constantly over our feet, deprive them of their warmth.

A. The carbon of a clear fire, being sufficiently hot to unite with the oxygen of the air, produces carbonic acid gas,[Pg 54] which soon envelops the paper laid flat upon the cinders: but carbonic acid gas will not blaze.

A. By blowing, or opening the door suddenly, the carbonic acid is dissipated, and the paper is instantly fanned into flame.

A. Water is composed of oxygen and hydrogen; when, therefore, the fire can decompose the water into its simple elements, it serves for fuel to the flame.

A. The hydrogen of the water will burn with a flame; and the oxygen of the water will increase the intensity of that flame.

[Pg 55]

A. Certainly. Unless the water be supplied so plentifully as to quench the fire, it will increase the intensity, like fuel.

A. When the supply is so rapid and abundant, that the fire cannot convert it into steam.

A. Yes, till it is converted into steam; but then it increases the intensity of fire, and acts like fuel.

A. As the wick is already very hot, a little extra heat will throw it into flame.

A. Because it again liberates the hydrogen of the tallow, and ignites it.

A. Yes; if a piece of wood be held near the fire for a little time it will blaze, even though it does not touch the fire.

[Pg 56]

A. The heat of the fire drives out the hydrogen gas of the wood; which is inflamed by contact with the red-hot coals.

A. The heat of the burning house sets at liberty the hydrogen gas of the neighbouring wood-work, which is ignited by the flames or red-hot bricks of the house on fire.

A. Coal freed from its volatile gases, by the action of artificial heat.

A. The fire is made of coke, which contains sulphur; and, whenever the draught is not rapid enough to drive the sulphur up the flue, it is emitted into the room.

A. Ignition produced by the action of one uninflamed body on another.

A. Goods packed in a warehouse will often catch fire of themselves; especially such goods as cotton, flax, hemp, rags, &c.

A. Because they are piled together in very great masses in a damp state or place.

A. The damp produces decay or the decomposition of the goods, and the great heat of the piled-up mass makes the decaying goods ferment.

A. During fermentation, carbonic acid gas is given off by the goods,—a slow combustion ensues,—till at length the whole pile bursts into flame.

A. Because compression squeezes out[Pg 58] heat, as water is squeezed from a sponge; and as the goods of a large pile are greatly compressed, much of their latent heat is squeezed out.

A. Either because the hay was got up damp, or because rain has penetrated the stack.

A. Damp hay soon decays, and undergoes a state of fermentation; during which, carbonic acid gas is given off, and the stack catches fire.

A. The heat of coffee is greatly increased by being roasted; and the carbon of the coffee uniting with the oxygen of the air, produces carbonic acid gas, and bursts into flame.

A. Because they very readily ferment, and (during fermentation) throw off exceedingly inflammable gases.

(N.B. Lamp-black mixed with linseed oil is more liable to spontaneous combustion, than anything that servants handle.)

A. As the air of the room passes over the fire, it becomes heated; and (being thus made lighter,) ascends the chimney, carrying the smoke with it.

A. Small particles of carbon, separated by combustion from the fuel, but not consumed.

A. Because they are moved in a right line, and then pushed on all sides; and this forces them into a circular motion.

[Pg 60]

A. When the hot air of the chimney has been cooled by the external air, it can no longer buoy up the solid smoke; so it falls to the earth in condensed flakes, called “blacks.”

A. The smoke of a railway engine consists chiefly of watery vapour, which dissolves in air, as sugar does in water; but the smoke of a common chimney consists of small fragments of unburnt fuel.

A. As the air, which supplies the copper hole, must pass through the furnace, it becomes exceedingly heated, and rushes up the chimney with great violence.

A. Air rushing rapidly through the crevices of the iron door, and up the chimney flue.

A. Because fresh air gets access to the fire more easily; and as the air is not so intensely heated, its motion is not so violent.

A. If fresh air is not admitted into a room, as fast as it is consumed by the fire, a current of air will rush down the chimney to supply the deficiency, and bring the smoke along with it.

A. Leather and curtains round the doors; sand-bags at the threshhold and on the window-frames; and other contrivances to keep out the draught.

A. If water be taken with a pail out of a river, other water will rush towards the hole, as soon as the pail is lifted out; and if air be taken from a room, (as it is, when some of it goes up the chimney) other air will rush towards the void to fill it up.

A. Because if doors and windows are all made air-tight, it can get to the room in no other way.

A. The speediest remedy is to open the door or window: but by far the best remedy is to carry a small tube from the hearth into the external air.

A. Because the fire will be plentifully supplied with air by the tube; the doors and windows may all remain air-tight; and we may enjoy a warm fireside, without the inconvenience of draughts and cold feet.

A. If it were not so, it would smoke; as all funnels do which are too short.

A. That part of a chimney through which the smoke passes, is called the funnel, or flue.

A. Because the draught of a short flue is too slack to carry the smoke up the chimney.

A. For many reasons. 1st—The fire is always dull and sluggish if the chimney be too short.

2ndly—The smoke rolls out of the chimney, before it has acquired its full velocity.

3rdly—The wind, rain, and air, have more influence over a short funnel, than over a long one.

A. Because the draught is so bad: and as the rarefied air passes up the chimney very tardily, fresh air flows as tardily towards the fire, to supply it with oxygen.

A. The intensity of fire is always in proportion to the quantity of oxygen with which it is supplied.

[Pg 64]

A. Because the higher smoke ascends in a flue, (provided it be clear and hot) the faster it goes; (as a stone falls faster and faster the lower it descends): if, therefore, a funnel be very short, the smoke never acquires its full velocity.

A. Yes. The more quickly hot air flies up the chimney, the more quickly cold air will rush towards the fire to supply the place; and, therefore, the longer the flue, the greater the draught.

A. Because the higher smoke ascends, the faster it goes; (as a stone falls faster and faster, the nearer it approaches to the earth): if, therefore, a funnel be long, the smoke acquires great velocity, and the draught is great.

A. To contract the opening of the chimney contiguous to the stove.

A. As all the air (which enters the chimney) must pass near the fire, it will become greatly heated, and rise rapidly through the funnel; and this increase of heat will compensate for the shortness of the flue.

A. Because the fiercer fire will exhaust the most air; and draw from the smaller one, to supply its demand.

A. Whenever the door between the two rooms is opened, air will rush from the chimney of the inferior fire, to supply the other; and both rooms will be filled with smoke.

A. Let a tube be carried from the hearth of each stove, into the external[Pg 66] air; and then each fire will be so well supplied, that neither will need to borrow from the other.

A. Because the wind (striking against the steeple) is reflected back; and tumbles down the vestry chimney, forcing the smoke into the room.

A. Those from the north-east or south-east; according to the position of the vestry.

A. Because they strike against the steeple, and bound back to the vestry chimney: but western winds cannot rebound over the roof of a church.

(N. B. The steeple of a church is always due west, and the other end of the church due east; if, therefore, a western wind rebound, it would rebound to the west, or away from the church, and not towards it.)

A. Because the wind (striking against[Pg 67] the surrounding hills) rebounds back again upon the chimney, and destroys its draught.

A. To fix a cowl on the chimney top, to turn like a weather-cock, and present its back to the wind.

A. If the wind be strong, it will keep the opening of the cowl towards the steeple or hill; and then the reflected wind will blow into the cowl, and down the chimney.

A. If the chimney flue can be carried higher than the steeple or hills, no wind can enter the flue.

A. Because the reflected wind would strike against the sides of the chimney-flue, and not pass over the opening at all.

A. If both door and chimney be placed on the same side of a room, the chimney will often smoke.

A. Because when the door is opened, a current of air will blow into the chimney-place, and drive the smoke into the room.

A. The door must be set opposite to the chimney, or nearly so; and then the draught from the door will blow the smoke up the chimney, and not into the room.

A. Because the obstruction in the chimney (presented by the loose soot, to the free passage of the smoke) delays its current, and prevents the draught.

A. 1st—Because the loose mortar and bricks obstruct the smoke: and

[Pg 69]

2ndly—The cold air (oozing through the chinks) chills the air in the chimney, and prevents its ascent.

A. Because the cold air (which gets through the joints) chills the air in the flue, and prevents its ascent.

A. Because the opening is so very large, that much of the air which goes up the chimney, has never passed near the fire; and this cold air mixing with the other, so reduces its temperature, that it ascends very slowly, and the draught is destroyed.

A. Because, unless the current of air up the chimney be very powerful, it cannot buoy the smoke up through the flue.

A. The chimney-place must be contracted.

[Pg 70]

A. As the air will then pass nearer the fire, it will be more heated, and fly up the chimney much faster.

A. The gust (blowing the air away from the top of the chimney) removes (for a time) all resistance to the smoke: but when the wind lulls again, the resistance of the air suddenly returns—the draught is checked—and a puff of smoke rushes into the room.

A. When the opening of a chimney is large, the top must be contracted by a chimney-pot, in order to increase the draught.

A. As the same quantity of hot air has to escape through a much smaller opening, it must pass through more quickly.

A. Because they compel the air to go through the fire, and not over it; therefore the fire is well supplied with oxygen, and the draught greatly increased.

A. As all the air which enters the chimney has to pass through the fire, it is much hotter, and ascends the chimney very fast; and the faster the air flies up the chimney, the faster it rushes towards the fire also.

A. The air in the chimney (being colder than the air in the parlour) descends into the room, and leaves a disagreeable smell of soot behind.

A. The heated air ascending, carries the dust and fine soot to the ceiling; where the hot air escapes through the plaster, and leaves the soot and dust behind.

[Pg 72]

A. As the air cannot penetrate the thick joists of the ceiling, it passes by those parts, and deposits its soot and dust on those which are more penetrable.

A. Wood which has been exposed to a red heat, till it has been deprived of all its gases and volatile parts.

A. Because so large a quantity of water has been abstracted from the fuel, by the red heat to which it has been already exposed.

A. Because it absorbs all odoriferous effluvia, whether they arise from putrefying animal or vegetable matter.

A. Charcoal absorbs the impurities of the water, and removes all disagreeable tastes and smells, whether they arise from animal or vegetable matter.

[Pg 73]

A. Charring the inside of the cask reduces it to a kind of charcoal; and charcoal (by absorbing animal and vegetable impurities) keeps the liquor sweet and good.

A. The surface of the bread is reduced to charcoal by being burnt; and the charcoal surface of the bread abstracts all the impurities of the water, and makes it palatable.

A. The surface of the bread being reduced to charcoal by being burnt, prevents the water from being affected by the impurities of the sick room.

A. Charcoal undergoes no change by exposure to air and water; therefore timber will resist weather much longer, after it has been charred.

A. Principally of carbon and hydrogen gas. The solid part is carbon, the volatile part is gas.

A. A solid substance, generally of a black colour; well known under the forms of charcoal, lamp-black, coke, black-lead, &c.

A. The principal ingredient of water. It is well known in the form of common coal gas: it burns so readily that it used to be called “inflammable air.”[10]

A. The heat of the lighted wick decomposes the tallow into its elementary [Pg 75]parts of carbon and hydrogen; and the hydrogen of the tallow, combining with the oxygen of the air, produces flame.

A. 1st—Because the flame liberates latent heat from the air and tallow: and

2ndly—It throws into rapid motion the atoms of matter.

A. When the hydrogen of the tallow and oxygen of the air combine, they condense into water; and much of their latent heat is squeezed out.

A. 1st—When the hydrogen of the tallow and oxygen of the air condense into water, a vacuum is made; and the air is disturbed, as a pond would be, if a pail of water were taken out.

2ndly—When the carbon of tallow and oxygen of the air expand into carbonic acid gas, the air is again disturbed; in a similar way as by the explosion of gunpowder.

[Pg 76]

A. The chemical changes made by combustion, excite undulations of ether, which (striking the eye) produce light. (see p. 46.)

A. Only the outer coat of the flame is yellow; the lower part of the flame is violet; and the inside of the flame is hollow.

A. Because the carbon of the tallow (being in a state of perfect combustion) is made white-hot.

A. The bottom part of the flame is overladen with hydrogen, raised from the tallow by the burning wick; and this half-burnt gas gives a purple tinge to the flame.

A. Because it is filled with vapour, raised from the candle by the heat of the wick.

[Pg 77]

A. The flame consists of three cones. The innermost cone is hollow; the intermediate cone of a dingy purple hue; and the outside cone is yellow.

A. Because the gases are not in a state of perfect combustion; but contain an excess of hydrogen, which gives this cone a purple tinge.

A. Because the outer cone prevents the oxygen of the air from getting freely to the middle of the cone; and without the free access of oxygen gas, there is no such thing as complete combustion.

A. The flame heats the surrounding air, which (being hot) rapidly ascends, and drives the flame upwards at the same time.

A. The upper part of a flame is more volatile than the lower parts; and as it affords less resistance to the air, is reduced to a mere point.

A. The lower parts of the flame are laden with unconsumed gas and watery vapour; which present considerable resistance to the air.

A. As the flame of a candle is attached to a very small wick, a puff of breath severs the flame from the wick; and it goes out for want of support.

A. The hydrogen of the tallow combining with the oxygen of the air, produce a “watery vapour,” which is condensed by the cold glass held above the flame.

A. Because the hot gases and air (in their ascent) come in contact with the hand placed above the flame: but when the hand is placed below the flame, or on one side, it only feels heat from radiation.

A. As the rush wick is smooth and hard, the mere motion of the air (produced by carrying the candle from one place to another,) is sufficient to sever the flame from the rush.

A. The cotton wick is quite full of small threads or filaments, which help to hold the flame on the wick, like the roots of a tree.

A. Because the air in the extinguisher is soon exhausted of its oxygen by the flame: and when there is no oxygen to support it, the flame goes out.

A. 1st—Because the flame very soon exhausts the little oxygen contained in the paper extinguisher: and

2ndly—The flame invests the inside of the paper extinguisher with carbonic acid gas, which prevents it from blazing.

A. Because it is bent by its own weight.

A. The knotty or flowery appearance of the top of a wick arises from an accumulation of particles partly separated, but still loosely hanging to the wick.

A. Because the length of the wick so diminishes the heat of the flame, that it is not hot enough to burn it off.

A. The wick is divided into two parts, each of which bends outward to the outside of the flame; where the end is intensely heated, and separated from[Pg 81] the wick by the current of air up the candle.

A. Because the heat of the flame is not sufficient to consume the wick; and the longer the wick grows, the less heat the flame produces.

A. The wick of wax candles is made of very fine thread, which the heat of the flame is sufficient to consume: but the wick of tallow candles is made of coarse cotton, which is too substantial to be consumed by the heat of the flame, and must be cut off by snuffers.

A. Because a pin (being a good conductor), carries away the heat of the flame from the wick, and prevents the combustion of the tallow.

A. Solid particles of carbon separated from the wick and tallow, but not consumed.

[Pg 82]

A. The combustion of the carbon depends upon its combining with the oxygen of the air: but as the outer surface of the flame prevents the access of air to the interior parts, therefore much of the carbon of those parts passes off in smoke.

A. Either because the wick is cut unevenly, or else because it is turned up too high.

A. 1st—Because the points of the jagged edge (being very easily separated from the wick,) load the flame with more carbon than it can consume: and

2ndly—As the heat of the flame is greatly diminished by these bits of wick, it is unable to consume even the usual quantity of smoke.

A. Because more carbon is separated from the wick than can be consumed by the flame.

[Pg 83]

A. Because a current of air passes through the middle of the flame; and therefore the carbon of the interior is consumed, as well as that in the outer coating of the flame.

A. Because it both concentrates and reflects the heat of the flame; in consequence of which, the heat is so greatly increased, that very little carbon escapes unconsumed.

A. Animal heat is produced by the combustion of hydrogen and carbon in the capillary veins.

[Pg 84]

A. Veins as small as hairs running all over the body; so called from the Latin word “capilla’ris” (like a hair).

A. Yes. Whenever blood flows from a wound, some vein must be divided; and as you cannot insert a needle into any part of the body without bringing blood, therefore these little veins must run through every part of the human frame.

A. The food we eat is converted into blood, and blood contains both hydrogen and carbon.

A. The carbon of the blood combines with the oxygen of the air we breathe, and forms into carbonic acid gas.

A. Some of it is thrown off by the breath; and the rest of it is absorbed by the blood, to keep up the animal heat.

[Pg 85]

A. The carbon of fuel unites with the oxygen of the air, and forms carbonic acid gas.

A. The carbon of the oil or tallow unites with the oxygen of the air, and forms carbonic acid gas.

A. The piled-up goods ferment from heat and damp; and (during fermentation) carbonic acid gas is formed, as in the two former cases.

A. Yes, precisely. The carbon of the blood, combining with the oxygen of air inhaled, produces carbonic acid gas, which is attended with combustion.

A. It actually does so. Every muscle, nerve, and organ of the body, actually[Pg 86] wastes away like a burning candle; and (being reduced to air and ashes) is rejected from the system as useless.

A. It would be so, unless the parts destroyed were perpetually renewed: but as a lamp will not go out, so long as it is supplied with fresh oil; neither will the body be consumed, so long as it is supplied with sufficient food.

A. First the fat, because it is the most combustible; then the muscles; last of all the brain; and then the man dies, like a candle which is burnt out.

A. After the fat and muscles of the body have been consumed by animal combustion, the brain is next attacked; and (unless the patient dies) madness must ensue from starvation.

A. A starved man shrinks just as a fire does, unless it be supplied with sufficient fuel.

A. Food is the fuel of the body; and the carbon of the food mixing with the oxygen of the air, evolves heat in the same way that a fire or candle does.

A. As the capillary veins run through every part of the human body, and the combustion of blood takes place in the capillary veins, therefore every part of the body is warm.

A. When we run, we inhale air more rapidly; and the rapidity with which we inhale air fans the combustion of our body, as a pair of bellows quickens the flame of a common fire.

A. As the combustion of the blood is more rapid, (in consequence of the introduction of more oxygen from the[Pg 88]air), therefore the blood is more heated, and every part of the body is warmer also.

A. Because it produces quicker respiration; by which means a larger amount of oxygen is introduced into the lungs, and the capillary combustion increased. Hunger is the notice (given by our body) to remind us, that our food-fuel must be replenished.

A. Singing increases respiration; and as more oxygen is introduced into the lungs, our food-fuel is more rapidly consumed.

A. Reading aloud increases respiration; and as more oxygen is introduced into the lungs, our food-fuel is more rapidly consumed.

A. As we breathe more slowly during sleep, therefore, less oxygen is introduced into the lungs to consume our food-fuel.

[Pg 89]

A. 1st—Because the night is generally colder than the day.

2ndly—As our respiration is slower, our animal combustion is slower also; in consequence of which, our bodies are more cold.

A. The pores of the body are like the safety valves of a steam-engine; when the heat of the body is too great, the combustible gas and grease flow out in perspiration, instead of burning in the blood.

A. Animal food contains great nourishment, and produces a desire for active occupations; but when the body is not supplied with strong food, this desire for muscular action ceases, and the person grows slothful.

A. Hard bodily labour in the open air causes much oxygen to be conveyed into the lungs by inspiration; the combustion of the food is carried on quickly; animal heat increased; and need for nutritious food more quickly indicated by craving hunger.

A. 1st—The air they inhale is not so pure, because its oxygen is partly exhausted: and

2ndly—Their respiration is neither so quick nor strong, and therefore the combustion of their food is carried on more slowly.

A. Strong meat and grease contain large portions of hydrogen, which (when burned in the blood) produce a larger amount of heat than any other kind of food.

A. In cold weather the body requires more fuel to keep up the same amount of[Pg 91] animal heat; and as we put more coals on a fire on a cold day to keep our room warm, so we eat more food on a cold day to keep our body warm.

A. 1st—The air contains more oxygen in cold weather; and as fires burn fiercer, so animal combustion is more rapid: and

2ndly—We are more active in cold weather; and increased respiration acts like a pair of bellows on the capillary combustion.

A. This is a wise providence to keep our bodies in health; in order that the body itself may not be consumed, it gives notice (by hunger) that the capillary fires need replenishing.

A. 1st—Because activity increases the warmth of the body, by fanning the combustion of the blood: and

2ndly—The strong food we eat creates a desire for muscular exertion.

[Pg 92]

A. Oil and blubber contain a very large amount of hydrogen, which is exceedingly combustible; and as these people live in climates of intense cold, the heat of their bodies is increased by the greasy nature of their food.

A. Strong meat and grease contain so much hydrogen, that they would make us intensely hot; and therefore we refuse them in hot weather.

A. Fruits and vegetables contain less carbon than meat, and therefore produce less blood: instead of blood, they combine into water as they are digested, and keep the body cool.

A. 1st—Because they deprive the blood of carbon, which is the chief cause of animal heat: and

[Pg 93]

2ndly—These gases coalesce into water, which greatly tempers the animal heat.

A. 1st—Because muscular activity would increase the heat of the body, by quickening the respiration: and

2ndly—The food we eat in hot weather, not being greasy, naturally abates our desire for bodily activity.

A. Rice and fruit by digestion are mainly converted into water, and (by cooling the blood) prevent the tropical heat from feeling so oppressive.

A. 1st—Cleanliness increases hunger; and as poor people are generally ill-fed, they are averse to cleanliness.

2ndly—Dirt is warm, (thus pigs who love warmth, are fond of dirt); and as poor people are generally ill-clad, they like the warmth of dirt.

[Pg 94]

A. 1st—Because ventilation increases the oxygen of the air,—the combustion of food,—and the cravings of appetite: and

2ndly—Ventilation cools the air of our rooms: poor people, therefore, (who are generally ill-clad) love the warmth of an ill-ventilated apartment.

A. Flannel and warm clothing do not make us warm, but merely prevent the body from becoming cold.

A. Flannel (being a bad conductor) will neither carry off the heat of the body into the cold air, nor suffer the cold of the air to come into contact with our warm bodies; and thus it is that flannel clothing keeps us warm.

A. Because they consume so little air; and without a plentiful supply of air, combustion is so slow, that very little animal heat is evolved.

[Pg 95]

A. Air is no longer conveyed to the lungs after respiration has ceased; and, therefore, animal heat is no longer evolved by combustion.

A. 1.—By Percussion. 2.—By Friction. 3.—By Condensation.

A. The act of striking; as when a blacksmith strikes a piece of iron on his anvil with his hammer.

A. Beating the iron condenses the particles of the metal; and squeezes out its latent heat, as water from a sponge.

A. Yes; every thing contains heat; but when a thing feels cold, its heat is latent.

A. Heat not perceptible to our feeling. When anything contains heat without feeling the hotter for it, that heat is called “latent.” (See p. 31.)

A. Yes; and when a blacksmith compresses the particles of the iron by his hammer, he squeezes out this latent heat, and makes the iron red-hot.

A. They used to place a soft iron nail upon their anvil; strike it two or three times with a hammer; and the point became sufficiently hot to light a brimstone match.

A. As the particles of the nail are compressed by the hammer, it cannot contain so much heat as it did before; so some of it flies out (as water flows from a sponge when it is squeezed).

A. The blow condenses those parts of the flint and steel which strike together, and squeezes out their latent heat.

A. A very small fragment (either of the steel or flint) is knocked off red-hot, and sets fire to the tinder on which it falls.

A. Because blowing the tinder, drives the oxygen of the air towards it.

A. The air itself is composed of two gases (nitrogen and oxygen) mixed together.

(Every 5 lbs. of common air contain 4 lbs. of nitrogen, and 1 lb. of oxygen.)

[Pg 98]

A. Oxygen gas supports combustion; and lighted tinder is quickened by the breath, in the same way as a dull fire is revived by a pair of bellows.

A. When iron horse-shoes strike against the flint-stones of the road, very small fragments (either of the shoe or stones) are knocked off red-hot, and look like sparks.

A. The percussion condenses the part struck, and squeezes out its latent heat.

A. The act of rubbing two things together; as the Indians rub two pieces of wood together to produce fire.

[Pg 99]

A. They take a piece of dry wood (sharpened to a point), which they rub quickly up and down a flat piece, till a groove is made; and the saw-dust (collected in this groove) soon catches fire.

A. The latent heat of the wood is developed by friction; because the particles of the wood are squeezed closer together, and the heat pours out, as water from a sponge.

(The best woods for this purpose are box-wood against mulberry, or laurel against poplar or ivy.)

A. Yes; if the wheels be dry,—or fit too tightly,—or revolve very rapidly,—they often catch fire.

A. The friction of the wheels against the axle-tree is so great, that their latent heat is disturbed, and produces ignition.

[Pg 100]

A. The grease lessens the friction; and (by diminishing the friction) the latent heat is less disturbed.

A. 1st—Because the air on a mountain is less compressed, than the air in a valley.

2ndly—It is more rarefied: and

3rdly—It is less heated by reflection.

A. As the air in a valley is more compressed (by the mass of air above) than that on the top of a mountain, therefore more heat runs out; just as more water runs from a sponge, the closer it is squeezed together.

A. As the air is more rarefied, its heat is diffused over a larger space and is less intense; just as a candle would show less light in a large room, than in a small one.

[Pg 101]

A. Air is not heated by the sun, but by reflection from the surface of the earth; and as there is no earth round a mountain-top to reflect heat, therefore the air there is intensely cold.

A. Chiefly because the friction excites the latent heat of our hands and faces, and makes it sensible to our feeling.

A. The vital heat of the body (which had become latent by the action of the water) is again developed by friction: and, as soon as this animal heat can be excited, the vital powers of the body are restored.

A. Ice contains 140 degrees of latent heat, and (when two pieces are rubbed[Pg 102] together) their particles are compressed, and this latent heat rolls out and melts the ice.

A. Yes; when two branches or trunks of trees (blown about by the wind) rub violently against each other, their latent heat is developed, and sets fire to the forest.

A. The act of bringing parts nearer together; as a sponge is compressed by being squeezed in the hand.

A. Yes; if a piece of German tinder be placed at the bottom of a glass tube, and the air in the tube compressed by a piston,[11] the tinder will catch fire.

A. Because the air is compressed; and its latent heat being squeezed out, sets fire to the tinder at the bottom of the tube.

A. 1.—Expansion. 2.—Liquefaction. 3.—Vaporization. 4.—Evaporation; and 5.—Ignition.

A. Yes; if a bladder (partially filled with air) be tied up at the neck, and laid before the fire, the air will swell till the bladder bursts.

A. Because the heat of the fire gets between the particles of air, and drives them further apart from each other; which causes the bladder to expand.

[Pg 104]

A. Chestnuts contain a great deal of air, which is expanded by the heat of the fire; and, as the thick rind prevents the air from escaping, it violently bursts through, slitting the rind, and making a great noise.

A. 1st—The sudden bursting of the rind makes a report, in the same way as a piece of wood or glass would do, if snapped in two: and

2ndly—The escape of hot air from the chestnut makes a report also, in the same way as gunpowder, when it escapes from a gun.

A. As the attraction of the parts is suddenly overcome, a violent jerk is given to the air; this jerk produces rapid undulations in the air, which (striking upon the ear) give the brain the sensation of sound.

[Pg 105]

A. Because a quantity of air (suddenly let loose) pushes against the air around, in order to make room for itself; and as the air of the chestnut slaps against the air of the room, a report is made, (as when I slap a book or table).

A. Because the heated air of the chestnut can freely escape through the slit in the rind.

A. An apple contains a vast quantity of air, which (being expanded by the heat of the fire) bursts through the peel, carrying the juice of the apple along with it.

A. Yes, much more. There is as much condensed air in a common apple, as would fill a space 48 times as big as the apple itself.

[Pg 106]

A. The inside of an apple is made up of little cells (like a honey-comb), each of which contains a portion of the air.

A. When an apple is roasted, the air in the cells next to the fire is expanded and flies out; the cells are broken, and their juices mixed together; so the apple collapses (from loss of air and juice), and feels soft in those parts.

A. The plumpness gives way, and the apple becomes flabby and shrivelled.

A. The air in the wood (expanded by the heat), forces its way through the pores of the log; and carries along with it the covering of the pore, which resisted its passage.

A. Very small holes in the wood, through which the sap circulates.

[Pg 107]

A. Very small pieces of wood red hot, separated from the log by the force of the air, as it bursts from its confinement.

A. The pores of deal are very large, and contain much more air than wood of a closer grain.

A. In green wood the pores are filled with sap, and therefore contain very little air; but in dry wood the sap is dried up, and the pores are filled with air instead.

A. Because the pores of dry wood are filled with air, which supports combustion; but the pores of green or wet wood are filled with vapour, which extinguishes flame.

A. Combustion is produced by the chemical action which takes place, while the carbon of fuel unites with the oxygen of air, and forms “carbonic acid gas.” (See p. 36.)

A. The air in the stones (expanded by the heat of the fire), meets with great resistance from the close texture of the stone; and, therefore, bursts forth with great violence, tearing the stone to atoms, and forcing the fragments into the room.

A. Yes. All the dreadful effects of gunpowder are merely the results of the sudden expansion of air.

[Pg 109]

A. If the bottle be not quite full, there will be air between the liquor and the cork; this air (expanded by the heat of the fire) forces out the cork.

A. The froth of ale or porter depends upon the pressure to which it is subjected; and as the air (between the liquor and the cork) is expanded by the heat, it presses against the liquor, and increases the quantity of froth.

A. Because the liquor absorbs carbonic acid so long as it is under pressure; and the moment that the pressure is removed, the carbonic acid escapes in foam or froth.

A. The air inside the balloon is expanded by the flame, till the whole balloon is blown out without a crumple.

[Pg 110]

A. The same quantity of air is expanded to three or four times its original volume; and is made so much lighter than common air, that even when all the paper, wire, and cotton are added, it is still lighter bulk for bulk.

A. If the balloon be 3 square feet in size, it is lighter (when inflated) than 3 square feet of common air, and therefore floats through it; as a cork (at the bottom of a tub of water) would rise to the surface.

A. The heat of the fire expands the air in the chimney; and (being thus made lighter than the air around), it rises up the chimney, and carries the smoke in its current.

A. Because air rises faster and faster the higher it ascends in a chimney flue;[Pg 111] the same as a stone falls faster and faster the nearer it approaches to the ground.

A. If the fire be not pretty fierce, its heat will not be sufficient to rarefy all the air in the chimney; and then the chimney will smoke.

A. Because the cold air (condensed in the upper part of the flue), will sink from its own weight, and sweep the ascending smoke back with it into the room.

A. The cowl acts as a screen against the wind, to prevent it from blowing into the chimney.

A. 1st—It would prevent the smoke from getting out: and

2ndly—The cold air (introduced into[Pg 112] the chimney by the wind) would fall down the flue, and drive the smoke with it back into the room.

A. The current of hot air up the chimney, striking against the oblique vanes of the smoke-jack, drives them round and round; in the same way as the sails of a wind-mill are driven round by the wind.

A. As heat enters any substance, it drives its particles further asunder; and a solid (like ice) becomes a liquid; and a liquid (like water) becomes a gas.

A. The particles of water near the bottom of the kettle (being formed into steam sooner than the rest) shoot upwards; but are condensed again (as they rise) by the colder water, and produce what is called “simmering.”

A. A gentle tremor or undulation on[Pg 113] the surface of the water. When water simmers, the bubbles collapse beneath the surface, and the steam is condensed to water again: but when water boils, the bubbles rise to the surface, and steam is thrown off.

A. Because the air (entangled in the water) escapes by fits and starts through the spout of the kettle; which makes a noise like a wind instrument, when it is blown into.

A. As all the water is boiling hot, the steam meets with no impediment, but freely escapes in a continuous stream.

A. When it is set on a hob to boil.

A. When the kettle is set on the hob to boil, the heat is applied very partially: one side is hotter than the other, and therefore the steam is more entangled.

[Pg 114]

A. Because the upper surface cools first; and the steam (still rising from the lower parts of the kettle) is again entangled, and escapes fitfully.

A. Water (like air) expands by heat. The heat of the fire drives the particles of water further apart from each other; and (as they are not packed so closely together) they take up more room; or (in other words) the water swells.

A. Water is composed of little globules, like very small grains of sand; the heat drives these particles away from each other; and (as they then require more room) the water swells.

A. Water contains air; and (as the water is heated) the air is driven out, and raises a bubble in that part of the water which resists its escape.

[Pg 115]

A. Liquids expand very much by heat; if, therefore, a kettle be filled with cold water, some of it must run over as soon as it is expanded by heat.

A. If a fire be very fierce, the air is expelled so rapidly, that the bubbles are very numerous; and (towering one above the other) reach the top of the kettle, and fall over.

A. When the water was swelled by boiling heat, it filled the pot even to overflowing; but as soon as the water is condensed by cold, it contracts again, and occupies a much less space.

A. Because the steam cannot escape so fast as it is formed, and (being confined in the kettle) presses on the water[Pg 116] with great power, and forces it out of the spout.

A. In the same manner as the pressure of air on the mercury of a barometer, forces the quicksilver up the glass tube.

A. The steam (seeking to escape) forces up the lid of the boiler, and the weight of the lid causes it to fall back again: this being done frequently, produces a rattling noise.

A. If the lid fitted so tightly, that the steam could not raise it up, the boiler would burst into fragments, and the consequences might be fatal.

A. Steam is really invisible; and the half-inch (between the spout and the[Pg 117] “stream of mist”) is the real steam, before it has been condensed by air.

A. As the steam comes in contact with the colder air, the invisible particles (being condensed), roll one into another, and look like a thick mist.

A. After it is condensed into mist, it is dissolved by the air, and dispersed abroad as invisible vapour.

A. Being lighter than air, it ascends to the upper regions, where (being again condensed) it contributes to form clouds.

A. The metal spoon (being an excellent conductor) carries off the heat from the water; and (as heat is carried off by the spoon) the water takes a longer time to boil.

[Pg 118]

A. Because water can never be heated above the boiling point: all the heat absorbed by the water after it boils, is employed in converting the water into steam.

A. The moment the water in the larger pot is boiling hot (or 212°), steam is formed, and carries off some of its heat; therefore, 212 deg^s. of heat can never pass through it, to raise the inner vessel to the same heat.

A. Because they have a tendency to fix water by chemical attraction; and therefore retard its conversion into steam.

A. Immerse the pot (containing the water you want to boil) in a saucepan containing strong brine, or sugar.

[Pg 119]

A. Though water boils at 212 deg^s. of heat, yet brine will not boil till raised to 218 or 220 deg^s. Therefore, 212 deg^s. of heat may easily pass through brine to raise the vessel immersed in it to boiling heat, before any of it is carried off by steam.

A. Because both liquids will impart heat till they boil, and then they can impart heat no longer.

A. Because all extra heat is spent in making steam. Hence water will not boil a vessel of water immersed in it, because it cannot impart to it 212 deg^s. of heat: but brine will, because it can impart more than 212 deg^s. of heat, without being converted itself into steam.

Any liquid which boils at a lower degree can be made to[Pg 120] boil if immersed in a liquid which boils at a higher degree. Thus a cup of ether can be made to boil in a saucepan of water. A cup of water in a saucepan of brine or syrup. But a cup of water will not boil if immersed in ether; nor a cup of syrup in water.

A. 1st—Because the air (expanded by heat) drives them higher up: and

2ndly—The clouds themselves are lighter, and therefore more buoyant.

A. Because their mists are either absorbed by the dry air, or vapourized by the hot sun.

A. Its principal use is to hold the crust up, and prevent it from sinking, when the cooked fruit gives away under it.

A. No, by no means; it would rather tend to make it boil over, than otherwise.

A. As soon as the pie is put into the[Pg 121] oven, the air in the cup will begin to expand, and drive every particle of juice from under it; the pie dish, therefore, will have a cup-full less room to hold its fruit, than if the cup were taken out.

A. Immediately the pie is drawn, the air in the cup begins to condense again, and occupy a smaller space; in consequence of which, there is no longer enough air to fill the cup, and so juice rushes in to fill up the deficiency.

A. As the external air presses upon the surface of the juice, it rushes into the cup unobstructed; as mercury rises through the tube of a barometer through similar pressure.

A. Yes; every thing (that man is acquainted with) is expanded by heat.

A. 1st—As iron expands by heat, the hoops will be larger when they are red-hot; and will, therefore, fit more easily on the tub: and

2ndly—As iron contracts by cold, the hoops will shrink as they cool down, and girt the tub with a tighter grasp.

A. 1st—That they may fit on more easily: and

2ndly—That they may girt the nave more tightly.

[Pg 123]

A. As iron expands by heat, the hoops will be larger when they are hot; and (being larger) will go on the nave more easily.

A. As iron contracts by cold, the hoops will shrink as they cool down; and, therefore, girt the nave with a tighter grasp.

A. That it may stick the closer, when it has contracted by cold.

A. The iron stove expands by heat, and (as it swells) the parts rub both against each other, and against the bricks around, driving them further off; and this produces a cracking noise.

A. The iron stove contracts again,[Pg 124] as soon as the fire is removed; and (as it shrinks into a smaller space) the parts rub against each other again, and the bricks are again disturbed; and this produces a cracking noise.

A. When the fire is lighted, the iron-work (which expands more than the brick-work and plaster) pushes away the bricks and plaster: but when the fire is put out, the metal shrinks again, and leaves the “setting” behind.

A. As a chink is left (between the “setting” and the stove), the plaster will frequently fall away from its own weight.

A. As the heat of the fire varies, the size of the iron stove varies also; and this swelling and perpetually contracting, keeps up such a constant disturbance about the plaster, that it cracks and falls off, leaving the fire-place very unsightly.

A. Heat expands the metal; and as the metal is increased in bulk, it occupies a larger space, (or, in other words, rises higher in the tube.)

A. Because the inside of the glass is expanded by the hot water, and not the outside; so the glass snaps for want of flexibility.

A. Glass is a non-conductor of heat; and, therefore, breaks before the heat of the inner surface is conducted to the outside.

A. Glass is expanded by heat; and as the inner surface expands, it stretches the outer surface till it snaps.

A. China is a non-conductor; and, as the inner surface expands by the heat, before the outer one, it forms an arch, and pulls the parts of the cup asunder.

[Pg 126]

A. Glass is a non-conductor; and, as the bottom of the glass (from the warmth of the hot stove) expands, before the sides are heated, the two parts separate the one from the other.

A. The state of being melted; as ice is melted by the heat of the sun.

A. The heat of the sun (entering the solid ice) forces its particles asunder, till their attraction of cohesion is sufficiently overcome, to convert the solid ice into liquid. (See p. 112.)

[Pg 127]

A. The heat of the fire (entering the solid metal) forces its particles asunder, till their attraction of cohesion is sufficiently overcome, to convert the solid metal to a liquid.

A. The heat of the fire (entering the water) divides its globules into very minute bubbles, which (being made lighter than air) fly off from the surface in the form of steam.

A. Because the heat of the fire decomposes the wood into gas, smoke, and ashes; and the different parts separate from each other.

A. The conversion of liquid into vapour; as water is converted into vapour by the heat of the sun.

A. Moisture evaporated from the earth, and collected in the upper regions of the air.

[Pg 128]

A. Clouds and fogs differ only in one respect. Clouds are elevated above our heads: but fogs come in contact with the surface of the earth.

A. 1st—The vapour of clouds is composed of very minute bubbles (called ves’cicles), which float like soap bubbles: and

2ndly—Warm air (between the bubbles) keeps them apart, and makes the mass lighter; and the currents of air (which constantly ascend from the warm earth) buoy them up.

A. When the surface of the earth is warmer than the air, the vapour of the earth (being condensed by the chill air) becomes mist or fog. But when the air is warmer than the earth, the vapour rises through the air, and becomes cloud.

[Pg 129]

A. No. They vary greatly in density, height, and colour.

A. The changes of the wind.

A. If a cold current of wind blows suddenly over any region, it condenses the invisible vapour of the air into cloud or rain: but if a warm current of wind, blows over any region, it disperses the clouds, by absorbing their vapour.

A. Those where the winds are most variable, as Britain.

A. Those where the winds are not variable, as Egypt.

A. Some thin light clouds are elevated above the highest mountain-top; some heavy ones touch the steeples, trees, and[Pg 130] even the earth: but the average height is between one and two miles.

(Streaky curling clouds, like hair, are often five or six miles high.)

A. Those that are most highly electrified: lightning clouds are rarely more than about 700 yards above the ground; and very often actually touch the earth with one of their edges.

A. Some clouds are 20 square miles in surface, and above a mile in thickness; while others are only a few yards or inches.

A. As the tops of high mountains are generally above the clouds; therefore, travellers (who climb the mountains) may pass quite through the clouds, into a clear blue firmament, when they may see the clouds beneath their feet.

A. The shape of clouds depends upon two things:—Their state of electricity, and the wind.

[Pg 131]

A. If one cloud be full of electricity, and another not, they will be attracted to each other, and either coalesce,—diminish in size,—or vanish altogether.

A. Those that are the most highly electrified.

A. They sometimes absorb them entirely: sometimes increase their volume and density; and sometimes change the position of their parts.

A. A warm dry wind will convert the substance of the clouds into invisible vapour, and carry it in its own current.

A. A cold current of wind will condense the invisible vapour of the air, and add it to the clouds as it passes by.

[Pg 132]

A. Because clouds are so voluble and light, that every breath of wind changes the position of those ves’cicles or bubbles.

A. White and grey, when the sun is above the horizon: but red, orange, and yellow, at sun-rise and sun-set.

The blue sky cannot be considered as clouds at all.

A. Because red rays are the least refrangible of all; and, therefore, are the last to disappear.

A. Being less able to be bent. Blue and green rays being very easily bent (by the resistance of the air) are thrown off from the horizon; but red rays not being bent back in the same way, give a tinge to the evening clouds.

A. Because red rays are the least refrangible of all, and not being bent back by the air (like blue and green), strike upon the horizon, and give a tinge to the morning clouds.

A. Because their size, density, and situation in regard to the sun, vary perpetually; so that sometimes one colour is reflected, and sometimes another.

A. The motion of the clouds is generally directed by the winds; but sometimes electricity will influence their motion also.

A. Because we often see in calm weather small clouds meeting each other from opposite directions.

A. Because clouds often meet from opposite directions; and (after they have[Pg 134] discharged their opposite electricities into each other) vanish altogether.

A. Into three classes:—viz. Simple, Intermediate, and Compound.

A. 1.—Cirrus. 2.—Cum’ulus; and 3.—Stra’tus.

A. Clouds like fibres, loose hair, or thin streaks, are called cirrus clouds.

A. From the Latin word, cirrus (“a lock of hair, or curl”): they are the most elevated of all clouds.

A. When the streamers point upwards, the clouds are falling, and rain is at hand: but when the streamers point downwards, expect easterly wind or drought.

A. Cum’ulus clouds are lumps like great sugar-loaves,—volumes of smoke,—or mountain towering over mountain.

[Pg 135]

A. From the Latin word, cum’ulus (a mass or pile).

A. When these piles of cloud are fleecy, and sail against the wind, they indicate rain; but when their outline is very hard, and they come up with the wind, they foretell fine weather.

Cumulus clouds should be smaller towards evening than they are at noon. If they increase in size at sun-set, a thunder-storm may be expected in the night.

A. Creeping mists, especially prevalent in a summer’s evening: these clouds rise at sun-set in low damp places, and are always nearer the earth, than any other sort of cloud.

A. From the Latin word, stra’tus (“laid low,” or “that which lies low”).

A. Into two sorts. 1.—The Cirro-Cum’ulus; and 2.—The Cirro-Stra’tus.

[Pg 136]

A. When cirrus clouds spring from a massy centre; or when heavy masses of cloud terminate at their edges in long streaks, or what are called “mares’ tails.”

A system of small round clouds may be called cirro-cum’ulus.

A. Continued drought, or hot dry weather.

A. They compose what is generally called a “mackarel sky.” This class of clouds always indicate rain and wind; hence the proverb—

A. Compound clouds are also sub-divided into two sorts. 1.—The Cum’ulo-stra’tus; and 2.—The Nimbus.

A. Those clouds which assume all[Pg 137] sorts of gigantic fancy forms; such as vast towers and rocks,—huge whales and dragons,—scenes of battle,—and cloudy giants. This class of clouds is the most romantic and strange of all.

A. A change of weather; either from fine to rain, or from rain to fine weather.

A. Nimbus is the Latin word for “clouds which bring a storm;” and all clouds from which rain falls are so named.

A. The cum’ulus cloud becomes stationary, and cirrus streaks settle upon it, forming cumulo-stratus clouds; which are black at first, but afterwards of a grey colour.

A. Because (as they float along) they dash against the mountains; and (being arrested in their motion) collect round the top.

A. 1st—They act as screens to arrest the radiation of heat from the earth:

2ndly—They temper the heat of the sun’s rays: and

3rdly—They are the great store-houses of rain.

A. When a dry wind travels over sea, and accumulates more vapour than the air can sustain, it relinquishes a part (as it flies along) in the form of clouds.

A. When wind travels over dry climes or thirsty deserts, it becomes so dry itself, that it absorbs vapour from the clouds, and disperses them.

A. Because the vapour of the air is not actually condensed into clouds, but only on the point of being condensed; in which state it bends the red rays of the sun towards the horizon, where they are reflected at sun-set.

[Pg 139]

A. Because (notwithstanding the cold of sun-set) the vapours of the earth are not condensed into clouds. Our Lord referred to this prognostic in the following words: “When it is evening ye say, it will be fair weather, for the sky is red.” (Matt. xvi. 2.)

A. Because the vapour of the air is actually condensed into clouds; in which case it “refracts” (or bends) the yellow rays of the sun towards the horizon, where they are reflected at sun-set.

A. Because the vapours of the air are already condensed into clouds; rain, therefore, may be shortly expected.

A. Vapour in the upper region of the air just on the point of being condensed.

A. Because the higher regions of the air are laden with vapour, on the very point of condensation, which the rising sun cannot disperse. Hence our Lord’s observation, “In the morning (ye say) it will be foul weather to-day, for the sky is red and lowering.” (Matt. xvi. 3.)

A. Because that air alone contiguous to the earth is damp and full of vapour. There are no vapours in the higher regions of the air to reflect red rays; and hence the morning-light looks grey.

A. In a grey sunrise, only that portion of air contiguous to the earth is filled with vapour; all the rest is clear and dry. But in a red sunrise the air in the upper regions is so full of vapour that the rising sun cannot disperse it.

A. If the air on the surface of the earth be very damp at sunset, it is a[Pg 141] proof that the air is saturated with vapour, and wet may be expected: hence the proverb—

A. A rainbow can only be formed when the clouds (containing or dropping rain) are opposite the sun: a morning rainbow, therefore, is always in the west, and indicates that bad weather is on the road to us.

A. Because our heavy rains are usually brought by west or south-west winds; and, therefore, clouds which reflect the colour of the rainbow in the west, are coming up with the wind, bringing rain with them.

A. As a rainbow is always opposite to[Pg 142] the sun, therefore a rainbow at night is in the east, and indicates that bad weather is leaving us.

A. As west and south-west winds bring rain, if the clouds have been driven from the west to the east, they have passed over us, and are going away from us.

A. A luminous white cloud in the north of the sky at night-time. Sometimes streaks of blue, purple, and red,—and sometimes flashes of light, are seen also.

In our island this phenomenon generally rises from a dark cloud (running from the north to the east and west) elevated about 10 or 20 degrees above the horizon: above this dark bed of clouds the luminous white light appears.

A. Electricity in the clouds.

A. Because the electric fluid passes[Pg 143] through air extremely rarefied: and whenever electric fluid passes through air much rarefied, it always produces a white light.

A. Because the electric fluid passes through air of different densities. The most rarefied air produces a white light; the most dry air, red; and the most damp produces yellow streaks.

A. When its corruscations are very bright, it is generally followed by stormy moist unsettled weather.

A. Because the haze is caused by very fine rain falling in the upper regions of the air; when this is the case, a rain of 5 or 6 hours continuance, may be expected.

A. Because the halo is caused by fine rain falling in the upper regions of the air. The larger the halo the nearer the rain-clouds, and the sooner may rain be expected.

A. The mist is black, because it is overshadowed by dense clouds or masses of vapour; and, therefore, it forebodes wet.

A. The mist is white, because no clouds blacken it with their shadow; and (as the sky is cloudless) fine weather may be expected.

A. Because the heat of the earth (being unable to escape into the upper region of the air, in consequence of the clouds) floats, like a sea of heat, on the surface of the earth.

A. Because the heat of the earth can readily escape into the upper regions of the air, and is not confined and pent-in by thick clouds.

A. 1st—Because when the air is laden with vapour, it has less oxygen.

2ndly—The air being lighter than usual, does not balance the air in our body: and

3rdly—Moist air has a tendency to relax the nervous system.

A. The human body is filled with air of the same density as that around: if, therefore, we ascend into purer air, or descend into denser air, the balance is destroyed, and we feel oppressed and suffocated.

A. If the air around be more dense, it will squeeze our body in by its weight:[Pg 146] if it be less dense, the air in our body will blow us out.

A. Because the air in the upper regions is more rare than the air in their bodies; and (till the equilibrium is restored) great pain is felt in all the more sensitive parts of the body.

A. Because the air in the sea is more dense than the air in their bodies; and (till the equilibrium is restored) great pain is felt in all the more sensitive parts of the body.

A. The density of the air (just previous to a storm) is very suddenly diminished, but the air in the sea is not so quickly affected; therefore the sea heaves and sighs in its effort to restore an equilibrium.

A. Because the air is suddenly and very greatly rarefied; and (as the density of the air is diminished) its power to transmit sound is diminished also.

A. Because the sound of a bell (in the receiver of an air-pump) cannot be heard at all, after the air has been partially exhausted; and a pistol fired on a high mountain would not sound louder than a common cracker.

A. 1st—Because there is more oxygen in the air on a fine frosty morning, than there is on a wet day: and

2ndly—A brisk and frosty air has a tendency to brace the nervous system.

A. 1st—Because the air does not contain its full proportion of oxygen: and

2ndly—Because the damp relaxes their nervous system, and makes them drowsy.

[Pg 148]

A. 1st—As the air does not contain its full proportion of oxygen, they feel a difficulty in breathing: and

2ndly—As damp relaxes their nerves, they feel languid and uneasy.

A. As the air contains less oxygen in wet weather, the heat of fire is less intense: and the flame is blue, because the fuel is not thoroughly consumed.

A. Because (when the air is laden with vapour) the rays of light are more dispersed, and produce a larger reflection; objects, therefore, seen at a distance, appear larger.

A. Because the fog or mist diminishes the light reflected from the object; and as the object becomes more dim, it seems to be further off.

[Pg 149]

A. Because the rays pass through more of the vapoury atmosphere which surrounds the earth; and this vapoury atmosphere acts like a magnifying glass.

It is very manifest that the lines D C are shorter than the lines E C: if, therefore, A be the earth, and D G E the boundary of the atmosphere round the earth, then the rays M E C (at the horizon) will pass through more of the atmosphere, than the rays S D C, which are more elevated.

A. Because the rays pass through more of the vapoury atmosphere which surrounds[Pg 150] the earth; and this vapoury atmosphere magnifies the moon, just like a magnifying glass.

A. Either because the air is full of vapour, and its humidity (piercing between the hair of the cat) produces an itching sensation; or more probably, because the air is overcharged with electricity.

A. If the air is overcharged with electricity, the hair of the cat is overcharged also; and this makes her feel as if she were covered with cobwebs.

A. Her hair will not lie smooth, but has a perpetual tendency to become turgid and ruffled; so the cat keeps rubbing her coat and ears, to smooth the hair down, and brush away the feeling of cobwebs.

A. Probably because the air is overcharged with electricity; and, therefore, a sensation (like that of cobwebs) irritates the skin, and produces an itching.

A. Because the air is filled with vapour, and water is a better conductor of sound than dry air.

A. Because the air is filled with vapour, and vapour is a better conductor of sound than dry air.

A. Because the air is filled with vapour, which (penetrating into the pores of the wood) forces the parts further apart, and swells the door.

A. Because the moisture is absorbed from the wood; and, as the particles are brought closer together, the size of the door is lessened, (or in other words, the wood shrinks).

[Pg 152]

A. Because the volatile parts, (which rise from dunghills, sewers, &c.), being laden with vapour, are unable to rise so readily, as when they are rarefied by a bright sun.

A. Because the volatile parts (which constitute the perfume of flowers) are laden with vapour; and (being unable to rise) are confined to the lower regions of the air.

A. Because they smell the odour of plants and hay, and delight to snuff in their fragrance.

A. The air being less dense in wet weather, cannot buoy up smoke so readily, as when more dry and heavy.

A. Because the insects (of which they are in pursuit) have fled from the cold upper regions of the air, to the warm air near the earth: and as their food is low, the swallows fly low.

A. Because they are forced downward, by some current of cold air which drives them down.

A. Because it condenses the warm vapour; which then descends in rain.

A. In cold stormy weather, one magpie alone will leave its warm snug nest in search of food, while the other stays with the eggs or young ones; but in fine mild weather (when their brood will not be injured by cold) both the magpies will fly out together.

A. Because when magpies fly abroad singly, the weather is cold and stormy; but when both birds fly out together, the weather is warm and mild, which is favourable for fishing.

A. Because they live upon fish, which are found near the surface of the sea in fine weather.

A. Because the fish (on which they live) leave the surface of the sea in stormy weather, and go down too deep for the gulls to get at them; they are obliged, therefore, to feed on the worms and larvæ which are driven out of the ground at such times.

A. Because the petrel lives upon sea insects, which are always to be found in abundance about the spray of swelling waves.

(The Petrel is a bird of the duck-kind, which lives in the[Pg 155] open sea. They run on the top of the sea, and are called Petrels, or rather Peter-els, from “St. Peter,” in allusion to his walking on the sea, to go to Jesus.)

A. Because the air is filled with vapour, and the humidity penetrates the wick; where (being formed into steam) it expands suddenly, and produces a little explosion.

A. If the iron be very hot indeed, the bottom of the drop is turned into vapour, before the drop can evaporate; and the vapour thus formed buoys the drop up, without allowing it to touch the iron at all.

A. The current of air (which is always passing over the heated surface) drives it along.

A. If the saliva sticks to the box and[Pg 156] is evaporated, the box is not hot enough; but if the saliva runs along the box, it is.

A. If the saliva runs along the box, the iron is hot enough to convert the bottom of the drop of spittle into vapour; but if the saliva will not roll, the box is not hot enough to convert the bottom of the drop of spittle into vapour.

A. The dissipation of liquid by its being converted into vapour.

A. The liquid vaporized absorbs heat from the body whence it issues; and the body deprived of the liquid by evaporation, loses heat thereby.

[Pg 157]

A. The saliva quickly evaporates; and (as it evaporates) absorbs heat from the finger, which makes it feel cold.

A. Ether very rapidly evaporates; and (as it evaporates) absorbs heat from the burning head, producing a sensation of cold.

A. Because it requires less heat to convert it into vapour; and therefore it evaporates much more quickly.

(Ether is converted into steam with 104 deg^s. of heat, but water requires 212 deg^s. of heat to convert it into steam.)

A. Because it evaporates very rapidly; and (while it is converted into vapour) carries off the heat of the burn.

A. As the wet of our shoes or clothes[Pg 158] evaporates, it keeps absorbing heat from the body, which makes it feel cold.

A. Because the evaporation absorbs heat from the body so abundantly, that it is lowered below its natural standard; and therefore health is injured.

A. Because the heat of the body is continually absorbed in converting the damp of the sheets into vapour; and as heat is abstracted from the body, its temperature is reduced below the healthy standard.

A. The macintosh prevents evaporation, because the steam cannot escape through the air-tight fabric; and (as the wet cannot evaporate from the clothes) no heat is absorbed from our bodies.

A. The salt of the sea retards evaporation; and (as the heat of the body is drawn off very gradually) the sensation of cold is prevented.

A. The heat of the room causes a rapid evaporation of the sprinkled water; and as the water evaporates, it absorbs heat from the room, and cools it.

A. The hot streets and roads part with their heat to promote the evaporation of the water sprinkled on them.

A. The earth (being wet with the rain) parts with its heat to promote evaporation; and as the earth is cooled, it cools the air also.

A. The air (blowing over the linen) promotes evaporation, by removing the vapour from the surface of the wet linen, as soon as it is formed.

[Pg 160]

A. Because the particles of vapour are more rapidly removed from the surface of the linen by evaporation.

A. Because the great evaporation (carried on through the wet summer) reduces the temperature of the earth lower than usual, and produces cold.

A. Because it is better drained and better cultivated.

A. Because it diminishes evaporation; in consequence of which less heat is abstracted from the earth.

A. 1st—Because hedges and belts of trees are multiplied;

2ndly—Because the land is better drained;

3rdly—Because the land is dug and ploughed; and

[Pg 161]

4thly—Because the vast forests are cut down.

A. Because they retard evaporation, by keeping off the wind.

A. 1st—Because they detain and condense the passing clouds:

2ndly—They prevent the access of both wind and sun:

3rdly—The soil of forests is always covered with long damp grass, rotting leaves, and thick brushwood: and

4thly—There are always many hollows in every forest full of stagnant water.

A. Because they are always damp; and the evaporation which they promote, is constantly absorbing heat from the earth beneath.

A. Digging and ploughing help to[Pg 162] pulverize the soil, by admitting air into it, and this increases its mean temperature.

A. Chiefly because their vast forests have been cut down; and the soil is better drained and cultivated.

A. Ponds and tubs in summer-time are often left dry, because their water is evaporated by the air.

A. The air contains heat, and changes the surface of the water into vapour; this vapour (blending with the air) is soon wafted away; while fresh portions of air blow over the water, and produce a similar evaporation; till the pond or tub is left quite dry.

A. To carry off the heat (arising from the rapid motion of the wheels) by evaporation, as soon as it is developed.

[Pg 163]

A. Because (when the moisture of the mould has been evaporated by the sun) the earthy particles come into closer contact, and the mass becomes more solid.

A. If the soil did not become crusty and hard in dry weather, the heat and drought would penetrate the soil, and kill both seeds and roots.

A. Because evaporation is increased by increasing the surface; and as tea in a saucer presents a much larger surface to the air, its heat is more rapidly carried off by evaporation.

(The subject of “convection” will be treated of in a future chapter, and would scarcely be understood in this place.)