This you have taken little notice of, because it is a school boy's action, and is seen every day; for indeed, we seldom trouble ourselves to reason about things that are so familiar; yet on this principle, my Lady, depends the force of a cannon; for it is not the gunpowder and fire that drives out the ball with such prodigious velocity; no, that force is occasioned by the fire's suddenly rarifying the air, which was contained in the chamber or breach of the cannon, and that generated by the powder itself. As proof of this, place the same ball, in the same quantity of powder in an open vessel, and when fired you will scarce see it move. But there have been guns lately invented, called wind-guns, which abundantly prove what I have advanced; for they are charged only with concentrated or condensed air and with ball, yet so contrived, that six or seven balls may be let off, one after the other, each of which would kill a buck or a doe at a very considerable distance.

You seem all amazed, and I don't wonder at it, since you have never yet considered the extraordinary properties of this element; and it must seem strange to you that[ 41 ]E 3that the air, which is so necessary for life, that without it we cannot breather, should be tortured into an instrument of destruction. You will however be more surprized when I tell you, that this is the cause of earthquakes; and that the noble city of Lisbon was lately destroyed by a sudden rarifaction of the air contained in some of the caverns of the earth, and perhaps under the sea. Tom Wilson gave a leer of impertinence, but was ashamed to shew his folly before such good company. All the rest stared at each other without speaking a word, except Lady Caroline, who protested she could not believe what he had said about earthquakes; for, says she, I remember to have read in the News Papers, that the flames burst out of the ground. That might be, my Lady, says the little Philosopher, for there could be no such sudden rarification of the air without fire. Fire, therefore, did contribute towards the earthquake, and fire might burn down a mountain composed of combustibles; but fire could never blow one up. No, my lady, that effect is the sole property of the air. This dispute would, in all probability, have taken up much time; but his[ 42 ]his Grace put an end to the controversy, by declaring it was true Philosophy.

In this property of being rarified and condensed, the air differs amazingly from water, which tho' composed of such small particles as not to be distinguished or seen separately with a microscope, and its readiness to rise or be evaporated with heat, and to be separated with a touch, cannot when confined, be at all concentrated or brought into a less compass. This experiment was once tried, by filling a golden globe full of water, then closing it up, and placing it in a screw press, which was pulled down with great force. In this situation it remained till the water sweated thro' the pores of the gold, and till that happened it would never give way.

Air is the medium which diffuses light to the world; for if there was no Atmosphere to refract the sun's rays round the globe, it would be almost as dark in the day time as in the night, and the Sun, Moon, and Stars, would only be visible. It is also the medium of sounds, which are conveyed by the tremulous motion of the air when agitated by any noise. Let me throw this peach stone into the moat, and you[ 43 ]you will perceive circles of small waves diffuse themselves by degrees to a great distance round it. Now as the air is fluid as well as the water, we may conclude that sound is conveyed somewhat in this manner, tho' as that is nearly a thousand times lighter than water, sounds are propagated at an amazing rate, some say after the rate of 1142 feet in a second of time; but, however that be, we may rest assured, that sound is conveyed in this manner. Only throw up the sash, and halloo, and the echo, which I spoke of in the beginning of the second Lecture, will return you the sound; that is, the waves or pulses of air, which are put in motion by the noise you make, will strike against the rocks, and return to you again; for echo is nothing but the reverberation of sound: and that there can be no sound conveyed with out air, is proved by experiment; for a bell struck in an exhausted receiver in an air pump, cannot be heard, that is, it has little or no sound.

Without air there would be no merchandize, for your ships could not sail to foreign climates; and without air the birds could not fly, since they would have nothing[ 44 ]nothing to support them, and their wings would be useless; for we know, that a feather falls with as much velocity as a guinea in an exhausted receiver. But above all, air is the principle which preserves life, both in plants and animals; there is no breathing without air, and you know, when our breath is stopt we die. This is one of those truths that are called self-evident, because it is universally known, and needs no confirmation; but if demonstration be thought necessary you may have it in a minute, by putting some living creature into the air pump; but it is cruel to torture a poor animal: so said Lady Caroline, and violently opposed this experiment's being tried; but as all the rest were for it, the Duke was willing to gratify their curiosity; and therefore told our Philosopher, that he might try the experiment with a rat, which they had caught in a trap, and if he survived it, give him his life for the pain they had put him to. This creature was accordingly put into the receiver, and when the air was partly exhausted, he appeared in great agony, and convulsed; and more air being pumped out, he[ 45 ]he fell on his side for dead; but fresh air being immediately admitted, it rushed into his lungs, which put them in motion again, and he recovered. The manner of the animal's recovery puts me in mind, says the Philosopher, of an accident which I once saw, and which I would have you all remember, for it may be of service to mankind.

Some time ago I was bathing, with several of my school-fellows, in a rover by the road-side. Master Curtis, who was an obstinate silly boy, would dastard the rest, as he called it; that is, he would foolishly exceed them in running into dangers and difficulties, and with this view, tho' he could swim no more than a stone, he plunged into a part of the river, which we told him was greatly above his depth, where he rose, and struggled to get out, but could not. We were all, you must imagine, in the utmost distress, and unable to assist him; for none of us could swim. At this instant came by some Gentlemen on horseback, who immediately dismounted, and got him out, but not till after he had sunk the third time. He was brought to shore with[ 46 ]without signs of life, and blooded without any effect; when one of the Gentlemen, who I have since heard was a great Philosopher, advised them to blow some air down his throat; this was done, and the elasticity of the air put his lung in motion, as I imagine, for a pulsation immediately ensued, and he recovered almost as soon as this animal. Now, from what I heard that Gentleman say, and from the instance before us, there is reason to believe, that the lives of many might be saved, who are supposed drowned, if this method was put in practice of conveying air to the lungs; for you are to consider, that unless the lungs are in motion, there can be no circulation, and it was for want of air, that their motion ceased in the water. Pray, Gentlemen, let this be remembered, for it is a matter of great importance.

We are to observe, Gentlemen, that air which has past thro' fire, or is become foul, or stagnated, and has lost its spring, is unfit for respiration. It was the want of fresh air, or, in other words, the being obliged to breathe air that was foul, and had lost its spring, or elastic force, that killed[ 47 ]killed so many of our poor country-men in the black hole at Calcutta, in the East Indies, as you have seen by the News Papers; and this breathing of foul air in inflammatory, putrid, and eruptive disorders, such, for instance, as the small-pox, and some fevers, has destroyed more than can be imagined. If therefore you should be seized with any of these disorders, advise the people about you to make us of their common sense, and not, because a man is ill, deprive him of that vital principle the air, without which he could not live, even in a state of health. Never suffer your curtains to be drawn close, or exclude the fresh air, when you sleep.

I am greatly mistaken, says Lady Caroline, if the air we are now in has not lost its spring; for I breathe with difficulty. Was that the case, Madam, replied the little Philosopher, you would not be able to breathe at all; but if your Ladyship finds the air so disposed, you should make use of the instrument that lies by you, which, by putting the air in motion, will in part recover its spring. What instrument, Sir? says the Lady. Your fan, Madam,[ 48 ]Madam, returned the Philosopher. Every fan is a philosophical instrument, and was originally contrived, we may suppose, for the purpose above-mentioned.

A bird dying in an Air-pump will be in some measure recovered by the convulsive fluttering of its own wings, because that motion alters the state of the air remaining in the receiver, and for a time renders if fit for respiration.

Motion is the only preservative for air and water; both of which become unwholsome if kept long in a state of rest; and both may be recovered and made salutary by being again put in motion.

If foul and stagnated air has such dire effects, how much are we obliged to the learned and ingenious Dr. Hales for discovering the Ventilator, and instrument which, in a little time, discharges the foul air from ships, prisons, and other close places, and supplies them with that which is fresh?

The air, by some Philosophers, has been esteemed an universal menstruum, because, say they, it dissolves all bodies in time, and reduces their substances to a new form; as iron into rust, copper into verdigrease, &c. but this, I am inclined to think, is not so much owing to the air as to[ 49 ]F to certain saline or acid particles, which the air extracts from some bodies, and which afterwards cleave to other bodies, with which they have a closer affinity than with the air itself. But this I shall endeavour to explain in a future work.

We are now to speak of the Wind, which is only a stream or current of air, as a river is of water, and is occasioned by heat, eruptions of vapours, condensations, rarifactions, the pressure of clouds, the fall of rains, or some accident that disturbs the equilibrium of the air; for Nature abhors a vacuum, and for that reason, when the air is extremely rarified in one part, that which is more dense will immediately rush in to supply the vacant places, and preserve the equilibrium; as is the case with water and other fluid substances. Only raise a vessel of water suddenly out of a cistern, and see with what speed the other water will rush in, to fill up the space and preserve its level. And these rarefactions in the air may happen near the earth, or as much above it, and is the reason why clouds fly in contrary directions. This occasioned the loss of the great Kite, which we were a whole fortnight in making; for, tho' there was scarcely[ 50 ]scarcely wind in the Park sufficient to raise it, yet when lifted extremely high by the air, it was seized by a current of wind and torn in pieces.

Winds are violent, or gentle, in proportion to the rarifaction or disturbance there has been in the atmosphere. A violent wind in a great storm, flies after the rate of 50 or 60 miles in an hour, and is often so dense, or strong, as to bear down trees, houses, and even churches before it. What the sailors call a brisk wind flies after the rate of about 15 miles an hour, and is of great use in cooling the air, and cleansing it from poisonous and pestilentious exhalations.

The winds have various qualities, they are generally hot or cold, according to the quarter from whence they blow. I remember, some years ago, we had a South-West wind in February, which blew so long from that quarter, that it brought us the very air of Lisbon, and it was as hot as in summer. Winds from the North and North-East, which come off large tracts of land, are generally cold. Some winds moisten and dissolve, others dry and thicken; some raise rain, and others disperse it: Some winds blow constantly from one quarter,[ 51 ]F 2quarter, and are therefore called the general Trade Winds. These are met with on each side of the Equator, in the Atlantic, Ethiopic, and Pacific Oceans, between the Tropicks, and to near 24 degrees of latitude; and are occasioned by the Sun in his rotation round his axis, agitating the æther, or by the rarifaction of the air by the solar rays, and the denser air continually pouring in from the distant parts of each hemisphere to maintain the equilibrium. Some winds, again, blow constantly one for one half, or one quarter of the year, and then blow the contrary way. These are met with in the East-Indian Seas, and are called Monsoons, or periodical Trade Winds. But as these subjects are abstruse and difficult, and afford little entertainment, we shall defer an explanation of them till our next course of Lectures, and endeavour to give you some account of the Meteors that attend the air.

We have already observed, that besides pure air, the atmosphere contains minute particles of different sorts, which are continually arising in steams from the earth and waters, and are suspended and kept floating in the air.

The most considerable of these are the small[ 52 ]small particles of water, which are so separated as to be lighter than air, and are raised by the Sun's heat, or lifted up by the wind from the sea, rivers, lakes, and marshy or moist parts of the earth, and which descend again in Dews, Rain, Hail, and Snow.

When these small particles are by a rarified state of the air suffered to unite many of them together, and descend so as to render the hemisphere more opaque, and by its humidity to moisten bodies on the Earth, it is called a Mist. And on the contrary, those particles of water that arise after a hot day from rivers, lakes, and marshy places, and by filling the air moisten objects, and render them less visible, are called Fogs.

Clouds are the greatest and most beneficial of all the meteors, for they are borne about on the wings of the wind, and, as the Psalmist observes, distribute fatness to the Earth. Clouds contain very small particles of water, which are raised a considerable distance above the surface of the earth; for a cloud is nothing but a mist flying high in the air, as a mist is nothing but a cloud here below.

That these vapours are raised in the air, in[ 53 ]F 3in the manner abovementioned, may be readily conceived; for it is an action that is seen every day in common distillations; but how these invisible particles, which float in the air, are collected into clouds in order to bring the water back again, is not so easy to determine. Perhaps, says the Marchioness, who had just before entered the room, it may be occasioned by the winds driving the clouds together and uniting the particles, which may by that means become specifically heavier than the air, and therefore fall down. There is reason, my Lady, in what you say, replied the Philosopher, but I would wish to know how these clouds are sometimes all of a sudden collected. It frequently happens, Madam, that you go abroad when the sky is so serene and clear, that not a cloud is to be see, and before your Ladyship has taken a turn round the Park, you shall see clouds gather round, and all the hemisphere overcast, and the drops begin to fall. How happens this? There were no clouds for the winds to drive against each other, nor could the aqueous vapours arise from the Earth, and descend at the same instant of time. Whence then could they come? I am afraid, Madam, says the Duke,[ 54 ]Duke, this young gentleman has shaken your Ladyship's Philosophy; for the question he has put is not to be answered without some knowledge of Chemistry, which is, I think, too little studied in this kingdom. I am not uneasy about it, my Lord Duke, says the Marchioness, he is the Lecturer, and let him account for it if he can. — I shall get little honour by solving this question, says the Philosopher, since his Grace has pointed out the only method, by which it can be done, that is to say, by Chemistry; for that action of bodies which the Chemists call precipitation, will answer it in all respects; but the explanation of it is a task so difficult, that I must defer it till another opportunity. Some idea, however, I will endeavour to give these young Gentlemen of precipitation, if your Ladyship will favour me with the tincture of bark which I saw in your hand this morning. The bark, Gentlemen, at least the resinous part of the bark, is here suspended in spirits of wine; and so suspended that you see it perfectly bright. Now in order to precipitate this bark, I must find out a body which has a closer affinity or relation with the spirits of wine, than the bark has (for things inanimate have all[ 55 ]all their relations when chemically considered;) that body is water, which when I add to the tincture, you will perceive it grow foul; for the spirits of wine will immediately let go the bark to lay hold of the water, which will occupy the space the bark before filled, and that will fall to the bottom. This perhaps may be the case in the atmosphere; some substance may brought into the air, to which it is nearer allied than to the water, that it suspended before in such a pellucid manner, as not to be seen, but which water becomes obvious, when the air lets it go to embrace its nearer ally, and by uniting first into small drops, then into larger, becomes too heavy to be suspended by the air, and falls down in rain.

But all clouds are not composed of watery vapours only; they are sometimes impregnated with sulphureous and even saline particles, which are exhaled from the earth; for the Chemists will tell you by experience, that volatile bodies will volatilize some fixed bodies, and carry them off: And this happens to be the case here, as may be particularly seen in Thunder and Lightning, which is occasioned, we may suppose, by the sulphureous and[ 56 ]and nitrous particles taking fire, and bursting the cloud with a tremendous noise, which is preceded by a flash of fire, much resembling that of lighted gunpowder, only more penetrating, which is owing, perhaps, to its extreme volatility. — But look, there is a cloud rising before us, which seems replete with that electrical matter, and may by and by discover, in a more sensible manner, these effects to you which I have been endeavouring to describe.

That there are some sort of nitrous particles, or a substance very much like it raised in the air, is, I think, evident, from that nourishment which rain (and particularly that rain which is attended with thunder) gives to vegetables, above common water; and from the quantities of nitre which have been found in heaps of earth that were exposed to the air, at the same time that it was kept from the rain.

Snow seems to be the small particles of water frozen in the air before they had united into drops, and hail seems to be drops of rain frozen in their fall. From the regular figures which snow and hail put on in their descent, some have been inclined to[ 57 ]to think, that they contain particles of salt mixed with the water, and which occasioned them to shoot and unite in certain angles; but an experiment should, I think, be tried before this is admitted as true Philosophy, and it might be done by boiling the snow and hail over the fire, till it put on a pellicle or scum at the top, and then setting it in a cold place, for the salts to crystallize, or shoot to the bottom.

"I know nothing of Crystallizations, says Lady Caroline, nor shall I ever turn Chemist; therefore, good Sir, give us something more entertaining. Pray can you tell me what occasioned those terrible lights in the air which we had last week."

The Aurora Borealis, or northern lights, says he, are occasioned, Madam, by certain nitrous and sulphureous vapours, which are thinly spread through the atmosphere above the clouds, where they ferment, and taking fire, the explosion of one portion kindles the next, and the flames succeed one another, till all the vapour is set on fire, the streams whereof seem to converge towards the zenith of the spectator, or that point of the heavens, which is immediately over his head.

At this instant up started Master Long, and[ 58 ]and told her Ladyship, if she had done, he would be glad to ask a question: Sir, says she, with a smile, it was you made the compliment, I should be glad to hear your question, for, I dare say, it will be a sensible one. I wish you may find it so, replied he; but what I want to have an account of, is this same Jack with a Lanthorn, which so haunts my Lord Marquis's park, and t'other day led my friend Tom Wilson into a large pond. Master Wilson, you are to understand, had been at his uncle's,where he had staid rather too late, and therefore his uncle ordered the Footman to light him home; but Tom being a very courageous fellow, and a little obstinate, would walk home alone, and in the dark; but just as he came into the marshy meadow, who should he almost overtake but this same Gentleman, this Jack with the Lanthorn, who he mistook for Goody Curtis, the chare-woman, and thought she was lighting her way home from work. Tom ran to overtake Dame Curtis, but Mr. Jack with his Lanthorn still kept out of reach, and led my friend Tom out of the path, which he did not perceive till he had lost himself; on which Tom ran, and Jack ran; Tom halloo'd, and Jack would not[ 59 ]not answer; at last souse came Tom into Duckweed Pond, where he might have lain till this time, if Mr Goodall had not heard him call out as he was riding by, and ran to his assistance. This put all the company in good humour, and Tom had good nature and good sense enough to join them in the laugh, which being subsided, our Philosopher thus proceeded in his Lecture.

The Ignis Fatuus, Jack with a Lanthorn, or Will with the Wisp, as it is frequently called, says he, is supposed to be only a fat, unctuous, and sulphureous vapour, which in the night appears lucid, and being driven about by the air near the earth's surface, is often mistaken for a light in a lanthorn, as my friend Master Wilson can testify. Vapours of this kind are in the night frequently kindled in the air, and some of them appear like falling stars, and are by ignorant people so called.

It may be here necessary to mention that beautiful phenomenon the Rainbow, since it has the appearance of a meteor, though, in reality, it is none; for the Rainbow is occasioned by the refraction or reflection of the sun's beams from the very small drops of a cloud or mist seen in a cer[ 60 ]a certain angle made by two lines, the one drawn from the sun, and the other from the eye of the spectator, to those small drops in the cloud which reflect the sun's beams: so that two persons looking on a Rainbow at the same time, do not, in reality, see the same Rainbow.

There are other appearances in the atmosphere which ought to be taken notice of, and these are the halo's, or circles, which sometimes seem to encompass the sun and moon, and are often of different colours. These always appear in a rimy or frosty season, and are therefore, we may suppose, occasioned by the refraction of light, in the frozen particles in the air.

Here the Lecture would have ended, but a sudden clap of thunder brought on fresh matter for meditation; some of the company, and particularly the Ladies, endeavoured to avoid the lightning; but Master Telescope, after the second clap, threw up the sash, and assured the Ladies and Gentlemen there was no danger, for that the clouds were very high in the air. The danger in a thunder-storm, says he, is in proportion to the violence of the tempest and the distance of the clouds; but this tempest is not violent, and that the[ 61 ]Gthe cloud is at a great distance, or high in the air, you may know by the length of time there is between your seeing the flash of lightning, and hearing the clap of thunder. Look, see how the sky opens, to emit the fire, presently you will hear the thunder; for you know we see the fire from a gun long before we hear the report! There it is! and how tremendous! These tempests always put me in mind of that beautiful passage in Shakespear's King Lear; where when the good old King is out in a storm, and obliged to fly from his unnatural children, he says,