Because the air in the chimney is of the same temperature as that in the room, and therefore will not ascend.

Because the air in the chimney, being warmed by the fire beneath, becomes lighter and ascends rapidly.

Because it is pressed upon by the cold air which always rushes towards a rarer atmosphere. It thus illustrates the development of storms.

Because the draught of air is not sufficient to supply the wants of the fire, and enable it to create an upward current.

Tubes built in the walls, communicating with the outer air, and terminating underneath the grates.

Because doors and windows may then be made air-tight, and draughts across rooms be prevented.

Because the wind, striking against the elevated object, flies back, and a part of it rushes downward.

Because the accumulation of the soot diminishes the size of the flue, and lessens the ascensive power of the draught, by reducing the quantity of warm air. It also obstructs the motion of the air, by the roughness of its surface.

Because the ascending air is suddenly chilled by gusts of damp and cold air, and driven down the chimney.

Because the air is still, and being dry and warm it does not chill the smoke, nor drive it out of its course.

Because the wind, striking at an angle upon the wings, forces them aside; and as there are four wings all upon the same angle, and fixed upon the same centre, the oblique pressure of the wind causes the centre to rotate.

There is a world of miniature phenomena which has never been fully recognised, in which we may see the mightier works of nature pleasingly and truthfully illustrated.

When the wind blows into the corner of a street, and whirling around, catches straw, dust, and feathers in its arms, and then wheels away, flinging the troubled atoms in all directions,—it is a miniature of the mightier whirlwind, which wrecks ships, uproots trees, and levels houses with the earth.

When a cloud of dust, on a hot summer's day, rises and flies along the thirsty road, making the passenger close his eyelids, and dusting the leaves of wayside vegetation,—it is a miniature of the terrible simoom, which blows from the desert sands, scattering death and devastation in its track.

When steam issues from the tea-urn, and becomes condensed in minute drops upon the window-pane,—the miniature is of the earth's heat, evaporating the waters, and the cold air of night condensing the vapours into dew.

When grass and corn bend before the wind, and are beaten down by its force; when the pond forgets its calm, and rises in troubled waves, casting the flotilla of natural boats that move upon its surface, in rude disorder upon its windward shore,—the little storm is but a miniature of those great hurricanes which wrecked a fleet in the Black Sea, and levelled the encampments of a mighty army.

When the snow that has gathered upon the house-top, warming beneath the smiles of the sun, slips from its bed, and drops in accumulated heaps from the roof,—it is a miniature of those terrible avalanches which in the Pyrenees bury villages in their icy pall, and doom man and beast to death.

When the rivulet hurries on its course, and meeting with obstructions, leaps over them in mimic wrath, overturning some little raft upon which, perchance, a weary fly has alighted,—it is a miniature of those rapids on whose banks the hippopotamus and the alligator yet live; and where, though rarely, man may be seen directing his raft over the troubled current, amid the rush of debris from forests unexplored.

A barometer is an instrument which indicates the pressure of the atmosphere, and which takes its name from two Greek words signifying measurer of weight.

Because it consists of a tube containing quicksilver, closed at one end and open at the other, so that the pressure of the air upon the open end balances the weight of the column of mercury (quicksilver), and when the pressure of the air upon the open surface of the mercury increases or decreases, the mercury rises or falls in response thereto.

Because changes in the weather are generally preceded by alterations in the atmospheric pressure. But we cannot perceive those changes as they gradually occur; the alteration in the height of the column of mercury, therefore, enables us to know that atmospheric changes are taking place, and, by observation, we are enabled to determine certain rules by which the state of the weather may be foretold with considerable probability.

Because a weight, which floats upon the open surface of the mercury, is attached to a string, having a nearly equal weight at the other extremity; the string is laid over a revolving pivot to which the hand is fixed, and the friction of the string turns the hand, as the mercury rises or falls.

Because the weight on the surface of the mercury frequently leans against the sides of the tube, and does not move freely. And, also, the mercury clings to the sides of the tube by capillary attraction; therefore, tapping on the face of the barometer sets the weight free, and overcomes the attraction which impedes the rise or fall of the mercury.

Dry air is heavier than air impregnated with vapours.

Because of the extreme tenuity of watery vapours, the density of which is less than that of atmospheric air.

Because it shows that as the air cannot support the full weight of the column of mercury, the atmosphere must be thin with watery vapours.

The fall of the mercury in the long arm of the tube would cause the weight F to be pressed upwards. This would release the string to which the weight W is attached; it would, therefore, fall, and turn the hand down to Rain or Much Rain.

Because the external air becoming dense, and free from highly elastic vapours, presses with increased force upon the mercury upon which the weight F floats; that weight, therefore, sinks in the short tube as the mercury rises in the long one, and in sinking turns the hand to Change, Fair, &c.

Because, as the barometer is carried up a mountain, there is a less depth of atmosphere above to press upon the mercury; it therefore falls, and by comparing various observations, it has been found practicable to calculate the height of mountains by the fall of the mercury in a barometer.

It may vary as much as a pound and a half to the square inch at the level of the sea.

When there is a duration of frost, or when north-easterly winds prevail.

Because the atmosphere is exceedingly dry and dense, and fully balances the weight of the column of mercury.

When a thaw follows a long frost; or when south-west winds prevail.

Because much moisture exists in the air, by which it is rendered less dense and heavy.

It causes the mercury to fall, by evaporating moisture into the air.

It causes the mercury to rise, by checking evaporation, and increasing the density of the air.

"For so the Lord said unto me, I will take my rest, and I will consider in my dwelling place like a clear heat upon herbs, and like a cloud of dew in the heat of harvest."—Isaiah xviii.

In noting barometrical indications, more attention should be paid to the tendency of the mercury at the time of the observation, than to the actual state of the column, whether it stands high or low. The following rules of barometric reading are given as generally accurate, but liable to exceptions:—

The thermometer is an instrument in which mercury is employed to indicate degrees of heat. Its name is derived from two Greek words, meaning heat measurer.

Because it expands readily with heat, and contracts with cold; and as it passes freely through small tubes, it is the most convenient medium for indicating changes of temperature.

"When ye see a cloud rise out of the west straightway ye say, There cometh a shower; and so it is. And when ye see the south wind blow, ye say there will be heat; and it cometh to pass."—Luke xiii.

Because their inventors, after whom they are named, adopted a different system of notation, or thermometrical marks; and as their thermometers have been adopted by various countries and authors, it is now difficult to dispense with either of them.

In the thermometer the column of mercury is much smaller than in the barometer, and is sealed from the air; while in the barometer the column of mercury is open at one end to atmospheric influence.

It varies more in the winter than in the summer season.

Because the temperature of our climate differs more from the temperature of the torrid zones in the winter than it does in the summer, and the inequalities of temperature cause frequent changes in the degree of prevailing heat.

The same remarks (714, 715,) apply to the barometer.

Sound is an impression produced upon the ear by vibrations of the air.

The atoms of elastic bodies being caused to vibrate by the application of some kind of force, the vibrations of those atoms are imparted to the air, and sound is produced.

If we take a tuning fork, and hold it to the ear, we hear no sound. If we move it rapidly through the air, or if we blow upon it, it produces no sound; but if we strike it, a sound immediately occurs; the vibration of the fork may be seen, and felt by the hand that holds it; and as those vibrations cease, the sound dies away.

When a bell is struck, the force of the blow gives an instant agitation to all its particles. The air around the bell is driven back by the impulse of the force, and thus a vibration of compression is imparted to the air; but the air returns to the bell, by its own natural elasticity, thus producing a vibration of expansion—when it is again struck, and thus successive vibrations of compression and expansion are transmitted through the air.

They travel at a rate of rather more than a quarter of a mile in a second, or twelve miles and three-fourths in a minute.

All sounds, whether strong or weak, high or low, musical or discordant, travel with the same velocity.

Because the contact of the finger stops the vibration of the atoms of the metal and glass, which therefore cease to impart vibrations to the air.

Because the connection between the atoms of the bell being broken, their vibrations are not uniform: some of the atoms vibrate more intensely than the others; the vibrations imparted to the air are therefore jarring and discordant.

Because the sounds proceeding from different distances, reach our ears in varying periods of time.

C or Do, 480 vibrations in a second; B or Si, 450 vibrations; A or La, 400 vibrations; G or Sol, 360 vibrations; F or Fa, 320 vibrations; E or Mi, 300 vibrations; D or Re, 270 vibrations; C or Do, 240 vibrations. It is thus seen that the more rapid the vibrations, the higher the note, and vice versa.

Because the shorter the string the more rapid are its vibrations when struck.

Because when the string or wire is tight, a touch communicates vibrations to all its particles; but when it is loose the vibrations are imperfectly communicated.

Because the vibrations of musical strings vary from 32 vibrations in a second, which produces a soft and deep bass, to 15,000 vibrations in a second, which produces the sharpest treble note.

Because the vibrations are confined to the air within the tube, and are not interfered with by other vibrations or movements in the air; the tube itself is also a good conductor of sound.

Air is a good conductor, but water is a better conductor than air; wood, metals, the earth, &c., are also good conductors.

For various reasons: because the smooth surface of water is a good conductor; because there are fewer noises, or counter vibrations, to interfere with the transmission of sound; and because there are no elevated objects to impede the progress of the vibrations.

Because what may be called expended vibrations always exist in air where various sounds are occurring. These tremblings of the air are received upon the thin covering of the shell, and thus being collected into a focus, are transmitted to the ear.

Because there the air, being cold and dense, is a very good conductor; and the smooth surface of the ice also favours the transmission of sound.

Because the earth is a good conductor of sound. For this reason, also, persons working under ground in mines can hear each other digging at considerable distances.

Because the density of dry air improves the sound-conducting power of the atmosphere. The transmission of sounds is also assisted by the direction of the winds.

"The morning is come unto thee, O thou that dwellest in the land: the time is come, the day of trouble is near, and not the sounding again of the mountains."—Ezekiel vii.

Because ear-trumpets collect the vibrations of the air into a focus, and make the sounds produced thereby more intense.

Because, being suspended over, and a little behind, the speaker, they collect the vibrations of the air, and reflect them towards the congregation.

Echoes are sounds reflected by the objects on which they strike.

Because the reflecting surface is very near; therefore the sound returns immediately.

Because they are at a considerable distance, and the sound takes time to travel to it, and an equal time to return.

Because the reflecting surface, having vibratory qualities of its own, mingles its own vibrations with that of the sound.

Sounds are doubtless reflected by walls and ceilings around us. But we do not perceive the echoes, because they are so near that they occur at the same moment with the sound. In lofty buildings, however, there is frequently a double sound, making the utterance of a speaker indistinct. This arises from the echo following very closely upon the sound.

Because the sounds of our voices are immediately reflected. And as a gas reflector increases the intensity of light, so a sound reflector will increase the apparent strength of our voices.

There are many places where remarkable echoes occur. On the banks of the Rhine, at Lurley, if the weather be favourable, the report of a rifle, or the sound of a trumpet, will be repeated at different periods, and with various degrees of strength, from crag to crag, on opposite sides of the river alternately. A similar effect is heard in the neighbourhood of some of the Lochs in Scotland. There is a place at Woodstock, in Gloucestershire, which is said to echo a sound fifty times. Near Rosneath, a few miles from Glasgow, there is a spot where, if a person plays a bar of music upon a bugle, the notes will be repeated by an echo, but a third lower; after a short pause, another echo is heard, again in a lower tone; then follows another pause, and a third repetition follows in a still lower key. The effect is very enchanting. The whispering galleries of St. Paul's, of the cathedral church of Gloucester, and of the Observatory of Paris, owe their curious effects to those laws of the reflection of sound, by which echoes are produced; but in these cases the effect is assisted by the elliptical form of the edifice, each person being in the focus of an ellipse.

Water is a fluid composed of two volumes of hydrogen to one of oxygen, or eight parts by weight of oxygen to one of hydrogen. It is nearly colourless and transparent.

Because the heat of the fire passes into the water, and drives its atoms apart, making those of them that rise quickly to the surface lighter than the air, upon which they consequently rise.

Because the latent heat of the water passes away from between its atoms into the air; the atoms, therefore, draw closer together.

Because, when the atoms of water are congealing, they do not form a compact mass, but arrange themselves in groups of crystal points, which occupy greater space. Water contracts when freezing until it sinks to 40 deg., and then it expands as ice is formed.

32 deg. is said to be the freezing point, but it should be called the frozen point.

Because heat, entering into the lower portions of the water, expands it; the heated portions are then specifically lighter than those that are cooler; the hot water therefore rises upward, and forces the cooler water down.

There are about one hundred and forty seven millions of square miles of water, to forty-nine and a half millions of square miles of land.

The pressure of the sea, at the depth of 1,100 yards, is equal to 15,000 lbs. to the square inch.

Oxygen, which forms so large a part of water. Of animal substances, oxygen forms three-fourths; of vegetable substances it forms four-fifths; of mineral substances it forms one-half; it forms eight-ninths of the waters and one-fifth of the atmosphere; and aggregating the whole creation, from one-half to two-thirds consists of oxygen.

Man eats, drinks, breathes, and burns it, in various proportions and combinations. It is estimated that the human race consume in those various ways 1,000,000,000 lbs. daily; that the lower animals consume double that amount; and that, in the varied works of nature, no less than 8,000,000,000 lbs. of oxygen are used daily.

Because the atoms of water are very minute; they therefore permeate the pores, or spaces, between the atoms of those bodies, and overcoming their attraction for each other, cause them to separate.

Because the heat assists to repel the particles of the substance undergoing solution, and gives the water a freer passage between the atoms.

Because, in passing through the earth, it has become impregnated with mineral matters, usually the sulphate and carbonate of lime.

Because it is derived from vapours which, in ascending to the clouds, could not bear up the mineral waters with them. It therefore became purified or distilled.

Because the soap unites with the mineral matters in the water, and being neutralised thereby, cannot dissolve the dirt which we desire to cleanse away.

Because salt is a mineral which prevails largely in the earth, and which, being very soluble in water, is taken up by the ocean.

Lakes and rivers, also, even those that are considered fresh, hold in solution some degree of saline matters, which they contribute to the ocean.

As, in the evaporations from the sea, the salt remains in it, while the vapours fall as rain, and again wash the earth and carry some of its mineral properties to the ocean, the greater saltness of the sea, as compared with rivers, is accounted for.

By some persons the opinion is entertained that the sea has been gradually getting salter ever since the creation of the world. This, they say, arises from the evaporation of water free from salt, and the returns of the water to the sea, taking with it salt from the land.

The amount of common salt in the various oceans is estimated at 3,051,342 cubic geographical miles, or about five times more than the mass of the mountains of the Alps.

The extreme depth has not, probably, been ascertained. But Sir James Ross took soundings about 900 miles west of St. Helena, whence he found the sea to be nearly six miles in depth. Now, if we take the height of the highest mountain to be five miles, the distance from that extreme rise of the earth, to the known depth of the sea, will be no less than eleven miles.

Because the water contains a large proportion of oxygen, some of which combines with the iron and forms an oxide of iron, which is rust.

Because the large amount of oxygen which it contains accelerates the decomposition of dead animal and vegetable substances that accumulate in it.

No danger arises from the living creatures in water; but putrefactive matters may produce serious diseases.

By obtaining water from the purest sources, and by filtering it before drinking, by which nearly all extraneous matters would be separated from it.

Attraction is the tendency of bodies to draw near to each other. It is called attraction, from two Latin words signifying drawing towards.

There are five principal kinds of attraction:—

Because they are influenced by the attraction of gravitation, by which all bodies are drawn towards the centre of the earth.

Because the air, being a denser body, obeys the law of attraction, and in doing so displaces lighter bodies that interfere with its gravitation.

Because they are influenced by the attraction of cohesion.

Cohesion.—The act of sticking together.

Because the iron of the knife attracts the oxygen of the water, by chemical affinity; and the two substances form a thin coating of oxide of iron.

Affinity.—Attraction between dissimilar particles through which they form new compounds.

Because they are moved by the attraction of electricity.

Because the water is conveyed up through the towel, by capillary attraction. The atoms of the water are attracted by the threads of the towel, and drawn up into the small spaces between the threads.

Capillary.—Resembling a hair, small in diameter.

Because the attractive power of a large body is greater than that of a small one. As each atom of matter has inherent power of attraction, it follows that a large aggregation of particles must attract in proportion to the number of those particles.

Because they are attracted by the mountains.

Because the masses of stone of which the church is built would attract the lead.

By observing what is called the deflection of small bodies when brought within given distances of larger bodies, the degree of attraction exercised by the large body upon the smaller one becomes known. This attraction of the large body exercised over the smaller body is an opposing influence, acting against the earth's attraction of the small body, which is drawn out of its course: it constitutes a natural balance between the influence of the earth and another body, acting in opposition to it. Founded upon these, and some other data, man can weigh the earth, and give a morally certain result!

Deflection.—The act of turning aside.

The planets exercise as certain an influence upon each other as do two pieces of wood floating upon a basin of water. As the planetary bodies fly through their prescribed orbits, and approach nearer to, or travel further from, each other, they are observed to deviate from that course which they must have pursued but for the increase or the decrease of some influence of attraction. By making observations at various times, and by comparing a number of results, it is possible to weigh any planetary body, however vast, or however distant.

By making observations at different seasons of the year, when the earth is in opposite positions in her orbit; and by recording, by instruments constructed with the greatest nicety, the angle of sight, at which the planetary body is viewed; by noticing, also, the various eclipses, and estimating how long the first light after an eclipse has ceased reaches the earth, it is possible to estimate the distances of heavenly bodies, no matter how far in the depths of the universe those orbs may be.

The diameter of the sun is 770,800 geographical miles, or 112 times greater than the diameter of the earth; its volume is 1,407,124 times that of the earth, and 600 times greater than all the planets together; its mass is 359,551 times greater than the earth; and 738 times greater than that of all the planets. A single spot seen upon its surface has been estimated to extend over 77,000 miles in diameter, and a cluster of spots have been estimated to include an area of 3,780,000 miles.

The earth has a circumference of 25,000 miles, and is estimated to weigh 1,256,195,670,000,000,000,000,000 tons.

It is its weight estimated relatively to the weights of other bodies.

Generally speaking, their specific gravity, which is proportionate to the density, or compactness of the atoms of which they are composed.

"Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding."

Repulsion is that property in matter by which it repels or recedes from, those bodies for which it has no attraction or affinity.

Because it repels the air, and the substances of the leaves upon which it rests. Because, also, its own particles cohere.

Because they repel the particles of dust; and also because their own particles have a stronger attraction for each other than for the particles of dust.

Because the needle and the water mutually repel each other.

Because the caloric repels the particles of the water.

Because, besides being specially lighter than water, the particles of the oil and the water mutually repel each other.

Carbonic acid is a mixture of carbon and oxygen, in the proportion of 3 lbs. of carbon to 8 lbs. of oxygen.

"Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it?"

Pure carbonic acid may exist in the solid, the liquid, or the æriform state. In the solid state it is produced only by artificial means, and it is then a white crystallised body, in appearance like snow; in the liquid state it is a heavy colourless fluid; in the æriform state it is a pungent, heavy, colourless gas, and is known as carbonic acid gas.

Because, by the fermentive process, carbonic acid has been developed in the porter, and is held in liquid solution; but it always has a strong tendency to escape, and directly the pressure is removed, it evolves into gas, by which it occupies much greater space, and forces the porter in millions of small bubbles out of the bottle.

Because carbonic acid gas is forced into the water by pressure. Pressure alters the gas into a liquid, and directly the pressure ceases, the liquid again evolves into gas.

Because it contains carbonic acid.

Because the carbonic acid has been driven off by boiling.

Because its carbonic acid has escaped as carbonic acid gas.

Because, in the places where the bubbles are formed, the liquid carbonic acid is evolving into carbonic acid gas.

Because, when the formation of gas once begins, and bubbles ascend, there is less pressure in the line of the column of bubbles; the carbonic acid, therefore, draws towards those points as the easiest channel of escape.

These explanations equally apply to the "working" of beer, by which yeast is produced; to the effervescence of various waters, acidulated drinks, ginger beer, &c., and also to the "sponging" of bread, &c.

Gunpowder is made of a very intimate mechanical mixture of nitrate of potash, charcoal, and sulphur. When these substances are heated to a certain degree, the nitrate of potash is decomposed, and its oxygen combines with the charcoal and sulphur, instantaneously forming large volumes of carbonic acid gas and nitrogen, which, seeking an escape, produce an explosion.

"Thus saith the Lord, Let not the wise man glory in his wisdom, neither let the mighty man glory in his might, let not the rich man glory in his riches."—Jeremiah ix.

Because the carbon readily absorbs, and combines with various gases, neutralising their offensive odours, and destroying their unhealthy properties.

Let us now pause for a few moments to consider the importance of those two great divisions of nature, Air and Water, and to reflect upon the wisdom of some of those laws which are connected with the phenomena thereof, and which have not yet been sufficiently explained.