lp »;^ V jmn. ^«^^> University of California • Berkeley A J .V'l ' /■ />i S^=i ^ ,», >? -i-^: J. *: >*.:^. &iif^# 1 raOK^TISPIB CE ABv^rS.S-.n- f/t c It li'teAtt.^, Co A isFiipn THE NEWTONIAN SYSTEM OF EXPLAINED BY FAMILIAR OBJECTS, IN" AN ENTERTAINING MANNER, FOR THE USE OF YOUNG LADIES &f GENTLEMEN, By TOM TELESCOPE, A. M. Illustrated with Copperplates and Cuts. SECOND PHILADELPHIA EDITION: WITH NOTES AND ALTERATIONS, By ROBERT PATTERSON. PROFESSOR OF MATHEMATICS, IN THE UNIVERSITY OF PENNSYLVANIA. PHILADELPHIA : PUBLISHED BY JOHNSON ^ WARNER, No. 147, MARKET STREET. 1808. Lydia R. Railey, PiuNTER, No. 10, Mrth Alley, DISTRICT OF PEJVKSYLVAJ^IJ, to wit: B, ^E it remembered* That on the eighteenth day of November, in the thirty-third year of the Independence of the United States of America, A D, 1808, Johmon and fVarnety 01 the sai; Dis- trict, have deposited in (his Office, the Title oJ a Book, the Right whereof they claim as Proprietors in the words follov<'ing, to tvit : The Newtonian System of Philosophy ; explained by familiar ob- jects, in an entertainiHg manner, for he use of Young Ladies and Gentlemen, by Tom Telescope, A.M. Illusttatcd with Copperplates and Cuts. Second Philadelphia Edition, with Notes and Alterations, by Robert Patterson, Professor of Mathematics, in he University of Pennsylvania. In conformity to the Act of Congress of the United States, enti- tled, "An Act for the Encouragement i>f Learning, by securing the Copies of Maps, Charts, and Books, to the Authors and Proprietors of such Copies during the Tunes therein mentioned." And also to the Act, entitled ** An Act supplementary to an Act, entitled, ** An Act for the Encouragement of Lea ning, by securing 'he Copies of Maps, Charts, and Books to the Authors aad Proprietors of such Copies during the I ime therein mentioned," and extending the Ben- ctits thereof to the Arts of designing, engraving, andetchmg historical; nd other Points." D. CALDWELL, Clerk of the District Court of Fenns^hania^ CONTENTS. INTRODUCTION, page 1. LECTURE 1. Of Matter and Motion. The Laws af Motion, page 5. At- traction and Gravitation, 8. Figure of the Earth, 9. Magnet or Load- stone, 11. Cohesion, 12. The Sphere of Attraction and of Repulsion, 13. LECTURE II. Of the Universe, and particularly of the Solar System. The Horizon, 15. The Reflecting Telescope, 17. The Refracting Te- lescope, 18. The Fixed Stars, 20. The Orrery, 22. The Sun and Pla- nets, 23. Comets, 25. Moon and Tides, 25. Eclipses of the Sim and Moon, 26. The Motion of the Earth, 32. The Armillary Sphere, 34. Ve- locity of Light, 36. LECTURE III. Of the Air, Atmos^ phere, and Meteors. The Four Elements, 39. The Air and Atmosphere, 42. The Triple Wea- ther-Glas, 43. Elasticity of the Air, 45. The Air-Gun, 47. Earthquakes. 48. Water, 49. Light and Sound, 50, Echo, 51. The Air-pump, 53. Ven- tilators, 57. The Air-Balloon, 59. Winds, 60. Mists, Fogs, Clouds, and Rain, 63. Thunder and Lightning, 2 Introduction. and cheating, that I abhor it; and have often Vr'ondered, when I have seen people, seem- mgly of years of discretion, so far mistake themselves and abandon common sense, as to lead a yonng gentleman, just put into jacket and trowsers, or a little lady in a frock dress up to a gaming table, to play and bet for shil- lings, crov/ns, and perhaps guineas, among a circle of sharpers. Parents, continued he, might almost as well teach their children to thieve as to game : for they are kindred em- ployments, and generally terminate in the ruin of both fortune and character.— Lady Twi- light, who is no friend to the modern modes of education, smiled atthisyoung gentleman's remark, and desired him to point out some diversion himself. 'Tis impossible for me, Madam, says he, to find out an amusement suitable to the taste of all the company pre- sent, unless I was perfectly acquainted w4th their dispositions ; but were I to choose, I should prefer those which not only divert the mind, but improve the understanding : and such are many of the diversions at the school where I am placed. We often play at sham Orations, comical Disputes, measuring of Land and Houses, taking the Heights and Distances of Mountains and Steeples solving Introduction. 3 Problems and Paradoxes on Orreries, Globes, and Maps, and sometimes at n itural Pliiloso- pby, which I think is very entertaining, and at the same time extremely useful ; for whether our knowledge is acquired by these amusements and reading little books, or by serious and elaborate study, what is obtained will be equally serviceable; nay, perhaps that wiiich is acquired in the entertaining manner may have the advantage ; for, as it is con- veyed to the mind with a train of pleasing ideas, it will be the m.ore permanent and last- ing, and the easier called up by the memory to our assistance. Mrs. Twilight was very desirous of know- ing what sort of diversion could be made of Natural Philosophy : and finding her young visitors in the same disposition, she conduct- ed them to Mr. Setstars, that they might have the use of proper instruments. As Mr. Set- star was engaged incompany, Lady Twilight though nearly related to him, would not dis- turb him, but led them through the saloon in- to a private parlour, where our little Philoso- pher, at the request of her Ladyship, imme- diately opened the Lecture, without making idle excuses, or waiting for f^irther solicitati- ons ; which he knew would be ill manners. .=^ec/Z^^^ c^t //2a/t^9^S(^^Lytcc TPTT^f^. LECTURE I. OF MATTER AND MOTION. BY Matter, my young friends, we mean the substance of all things, or that of which all bodies are composed, in whatever form or manner they may present themselves to our senses ; for this top, that ivory ball, the hill before us, and all things you see, are made of matter differently formed. As to Motion, I may save myself and you the trouble of explaining that; for every boy or girl who can whip his top, or wave a fan, knows what motion is. Matter, or Body, is indifferent to motion or rest. As for example, when I whip my top, it runs round, or is in motion ; but when I leave off whipping the top falls down, and is at rest. When a body is in motion, as much force is required to make it rest as was required while it v/as at rest, to put it in motion. Thus : Suppose a boy strikes a ball from a trap, and another stands close by to catch it, it will require as much strength or force to stop that ball, or reduce it to a state of rest, A 2 6 Of Matter and Motion. as the other exerted to put it in motion ; al- lowing for the distance the two boys stand apart. No body or part of matter can give itself either motion or rest: and therefore a body at rest will remain so for ever, unless it be put in motion by some external cause ; and a body in motion will move for ever, unless some external cause stops it. This seemed so absurd to Master Wilson, that he burst into aloud laugh. What ! says 'he, shall any body tell me that my hoop or my top will run for ever, when I know by daily experience, that they drop of themselves, without being touched by any body ? At this our little Philosopher was angry, and having requested silence; Don't expose your igno- rance, Tom Wilson, for the sake of a laugh, says he; if you intend to go through my course of Philosophy, and to make yourself acquainted with the nature of things, you must prepare to hear what is more extraor- dinary than this. When you say that no- thing touched the top or the hoop, you for- get the friction or rubbing against the ground it runs upon, and the resistance it meets with from the air in its course, which is very con- siderable though it has escaped your notice. Of Matter and Motion. ^ Somewhat too might be said on the gravity and attraction between the top, or the hoop, and the earth; but that you are not yet able to comprehend, and therefore we shall pro- ceed in our Lecture. A body in motion will always move on in a straight line, unless it be turned out of it by some external cause. Thus, we see that a marble shot upon the ice, if the surface be very smooth, will continue its motion in a straight line till it is stopt by the friction of the ice and air, and the force of attraction and gravitation. The swiftness of motion is measured by distance of place, and the length of time in which it is performed. Thus, if a cricket- ball andafivesball move each of them twenty yards in the same time, their motions are equally swift ; but if the fives-ball moves two yards while the cricket-ball is moving one, then is the motion of the fives-ball twice as swift as the other. But the quantity of motion is measured by the swiftness of motion, as above described, and the quantity of matter moved, consider- ed together. For instance : If the cricket- ball be equal in bulk and weight to the fives- ball, and move as swift, then it hath an equal 8 Of Matter and Motion. quantity of motion. But if the cricket-ball be twice as big and heavy as the fives-ball, and yet moves equally swift, it hath double the quantity of motion ; and so in proportion. All bodies have a natural tendency, attrac- tion, or gravitation towards each other. Here Tom Wilson, again laughing, told the com- pany that Philosophy was made up of nothing but hard words. — That is because you have not sense enough to enquire into, and retain the signification of words, says our Philoso- pher. All words, continued he, are difficult till they are explained ; and when that is done, we shall find that gravity or gravitation will be as easily understood as praise or commendati- on ; and attraction as easily as correction, which you deserve, Tom Wilson, for your impertinence. Gravity, my young friends, is that univer- sal disposition of matter which inclines or carries the lesser part lov/ards the centre of the greater part ; this is called weight or gravita- tion in the lesser body, but attraction in the greater, because it draws, as it were, the les- ser body towards it. — l^hus, all bodies in or near the earth's surface have a tendency, or seeming inclination, to descend towards its middle part or centre ; and but for this prin- Of Matter and Motion. 9 ciple in nature, the earth (considering its form and situation in the universe) could not subsist as it is; for we all suppose the earth to be nearly round (nay, we are sure it is so, for Captain Cook, and many other naviga- tors, you know, have sailed round it) ; and as it is suspended in such a mighty void or space, and always in motion, what should hinder the stones, water, and other parts of matter falling from the surface, but the al- mighty arm of God, or this principle or uni- versal law in nature, of attraction and gravi- tation, which he has established to keep the universe in order ! — -To illustrate and ex- plain what I have said, let us suppose the fol- lowing figure to be the earth and seas : let 10 Of Matter and Motion. Tom Wilson stand at this point of the globe of earth, where we are, and Harry Thomson at the opposite part of the earth, with his feet (as they must be) tow^ards us : if Tom drop an orange out of his hand, it will fall dowai towards Harry : and if Harry drop an orange, it will f;ill seemingly upAvards (if I may so express myself) towards Tom : and if these oranges had w^eight and powder sufficient to displace the other particles of matter, of which the earth is composed, so as to make way to the centre, they w^ould there unite together, and remain fixed ; and they w^ould then lose their power of gravitation, as being at the centre of gravity, and unable to fell, and only retain in themselves the power of attraction. This occasioned a general laugh ; and Tom Wilson starting up, asked how Master Thompson was to stand with his feet up- wards as here represented, without having any thing to support his head ? Have pati- ence, says the little Philosopher, and I w ill tell you, but pray behave with good manners, Master Wilson, and don't laugh at every thing you cannot comprehend. This difficul- ty is solved, and all the seeming confusion which you apprehend of bodies flying off from each other is removed, by means of this at- Of Matter and Motion, 1 1 traction and gravitation. Ask any of the sailors who have been round the world, and they will tell you that the people on the part of the globe over against us, do not walk upon their heads, though the earth is round ; and though their heels are opposite ours, they are in no more danger of falling into the mighty space beneath them, than we are of falling (or rather rising, I must call it here) up to the moon or stars. But besides this general law of attraction and gravitation, which affects all bodies equally and universally, there are particular bodies that attract and repel each other, as may be seen by this Magnet or Loadstone, which has the property of attracting or bring- ing iron to it with one end., and repelling or forcing it away with the other.* My knife, says Sam Jones, which was rubbed on a load- stone some years ago, still retains the power of picking up needles and small pieces of iron. This however, says Master Telescope, is but a small part of the virtues of the Load- stone ; for until its use was discovered, sail- * Both ends of the Magnet will attract small pieces of iron ; though the North end of one Magnet will attract the South end only of another Magnet.-^ii(/. 12 'Of Matter and Motion. ors never ventured with their ships out of sight of land. You certainly joke, Sir, says Harry Thompson, for it is impossible that a piece of iron like that can be of any service in navigating those large ships I ssiw some time ago. I am sorry, replies our Philoso- pher, that you, like most ignorant people > should think all things which you do not know the cause of impossible ; but I will soon prove to you, that it is very simple. They first procure a piece of steel, made something like a needle, but flat, about four inches long : this they rub with the Load- stone, and then balance it exactly on a point or pivet, so that it may turn round freely. One of the ends of the needle thus balanced, will always point towards the north. This needle, when put in a box, is called the ma-' riner's compass. Thus the sailors can steer to any part of the world ; which they could not do without the help of this piece of iron. When bodies are so attracted by each other as to be united or brought into close contact, they then adhere or cohere together, so as not to be easily separated; and this is called in Philosophy, the Power of Cohesion, and is undoubtedly that principle which binds the particles of large bodies together; for all large Of Matter and Motion. 13 bodies are made up of atoms or particles in- conceivably small. And this cohesion will be always proportioned to the number of par- ticles or quantity of the surface of bodies that come into contact, or touch each other; for those bodies which are of a spherical form will not adhere so strongly as those that are flat or square, because they can only touch each other at a certain point ; and this is the reason why the particles of w^ater and quick- silver, which are globular or round, are so easily seperated with a touch, while those of metals and some other bodies, are not to be parted but with great force. To give a fa- miliar instance of this cohesion of matter, our Philosopher took two leaden balls, and filing a part off" each, so that the two flat parts might come into close contact, he gently pressed them together, and they united so firmly that it required some considerable force to get them asunder. The same force applied to two different bodies will always produce the same quan- tity of motion in each of them. To prove this, we put Master Jones into a boat, which (including his own weight) weighed ten hundred, on the Thames by the Mill-bank ; and on the Lambeth side, just opposite, we 14 Of Matter and Motion. placed another boat of one hundred weighty with a rope tied to it. This rope Master Jones pulled in the other boat ; and we ob- served, that as the boats approached each other, the small boat moved ten feet for every foot the other moved : which proves what I ha^ e before observed as to the quan- tity of motion. Attraction is the stronger, the nearer the attracting bodies are to each other : and in different distances of the same bodies it de- creases as the squares of the distances be- tween the centres of those bodies increase. For if two bodies at a given distance at- tract each other with a certain force, at half the distance they will attract each other with four times that force. —15— LECTURE IL OF THE UNIVERSE, AND PARTICULARLY OF THE SOLAR SYSTEM. THE last Lecture was read at Mr. Sct^ star's, who was so well pleased at these young gentlemen meeting thus to improve themselves, that he ordered them to be elegantly treated with tarts, sweetmeats, syllabubs, a.nd such other dainties as he thought were most proper for youth ; his Lady did them the honour of her company, and was particularly pleased with the con- versation of Master Telescope. As it was a moonlight night, Mrs. Setstar, after sup- per, led them to the top of the mansion, where there was an observatory, furnished with all the instrument's necessary for astro- nomical and philosophical observations. When the company were seated, our Phi- losopher thus began his second Lecture. Look round, my dear friends, said he; you see the earth seems to be bounded at an equal distance from us every way, and ap- pears to meet the sky Avhich forms this beau- tiful arch or concave over our heads. '' The 16 Of the Universe. Heavens declare the glory of God, and the finnament shewethhis handy-work," as the Psalmist beautifully expresses it. Now that distant round where we lose sight of the earth is called the horizon ; and w^hen the siui, moon, and stars emerge from beneath and com.e into our sight, we say they are risen or got above the horizon ; for all this glorious canopy bespangled with lights, that bedeck the Sky, and illuminate the Earth, as the Sun, the Fixed Stars, the Comets, and Planets (to which last our Earth and Moon belong) have all apparent motion, as may be perceived by the naked eye ; though, in fact, none move but the planets and comets; as will be proved her^- after. But besides the stars which we see, there are others not discernible by the naked eye, some of which are fixed stars, and some are bodies moving about the most distant planets, which were invisible and vmknown TO us before the discovery of Telescopes. Pray, hand me that Reflecting Telescope. The young Philosopher taking it, and placing it upon the table, gave the following description : Of the Universe. 17 This Telescope, from its construction, magnifies more than any other kind. It contains, within side, two metallic specu- lums, a large and a small one. These, with two glasses contained in the small tube, marked B, serve so to reflect and refract the rays of light issuing from the object, as to shew it under a magnified appearance. la using the Telescope, to adjust it exactly to your sight, you turn the long screw C on the side, while your eye is looking through at B, and the end A turned towards the object, till you can see the object you want to examine in the most perfect manner. BO ^^ Of the Universe, In the Refracting Telescope, which con- sists of glasses only, distant objects also seem to be both magnified and brought nearer to the sight. The large end must be placed pointing toward any distant object which we wish to see more distinctly. In the other end is a tube which slides within the Tele- scope, and is adjusted to the proper distance by gently drawing it outwards. Now, if you look through the glass at the end of this tube, to that part of the heavens to which I have pointed it, or indeed any other part, you will perceive more stars than you saw before with your eye alone. These are fixed stars, and are called fixed, because they al- ways keep the same distance from each other, and the same distance from the sun, which is also fixed; and were he placed at the immense distance they are at, would probably appear no bigger than one of them. — Hence some philosophers have con- cluded, and I think not without reason, that every fixed star is a sun that has a system of planets revolving round it, like our solar Of the Universe. 19 system. And if so, how immensely great, how wonderfully glorious is the structure of this universe, which contains many thousand worlds, large as ours, suspended in ether, rolling like the earth, round their several suns, and filled with animals, plants, and minerals, all perhaps different from ours, but all intended to magnify the Almighty Architect ; *' who weighed the mountains in his golden scales, who measured the ocean in the hollow of his hand, who drew out the heavens as a curtain, who maketh the clouds his chariot, and walketh on the wings of the wind." The fervor and air of piety with which he delivered this, silenced all his companions, and gave infinite satisfaction to Mrs. Setstar. Master Wilson, who had before been very impertinent, began now to consider himself a fool in comparison to our Philosopher: and as Master Telescope had mentioned the solar system, he begged that he would ex- plain it to him. That I will with pleasure, replied the Phi- , losopher : if you will be kind enough to hand me that Orrery that is in the corner of the observatory, and place it on the table: but first let me observe to you, that of these 20 Of the Universe. heavenly bodies some are luminous, and lend us their own light, as doth the Sun and Fixed Stars ; while others are opaque and have no light of their own to give us, but reflect to us a part of the light they receive from the sun. This is particularly the case with respect to the planets and comets of our solar system, which all give us a portion of the light they have received, and we in return reflect to them a portion of ours : for I make no doubt but those who inhabit the moon have as much of the sun's light re- fleeted to them from our earth, as we have reflected to us from the moon. The inhabitants of the moon ! says Master Lovelace, with some emotion; whither will you lead me? What! are the stories that have been told of the Man in the Moon, then, true ? I don't know what stories you have heard, replied the Philosopher ; but it is no extra- vagant conjecture to suppose that the moon is inhabited as well as the earth ; though what sort of inhabitants they are, we on earth are unable to discover. As to my part, I am lost in this boundless abyss. It appears to me that the sun, which gives life to the world, is only a beam of the glory of God, Of the Universe. 21 and the air which supports that life, is, as it were, the breath of his rrostrils. Do thou, O God ! support me while I gaze with astonishment at thy wonderful producfions; since it is not idle impertinent curiosity that leads me to this enquiry, but a. fervent desire to see only the skirts of thy glory, that I may magnify thy power and thy mercy to mankind. ^2^2- OF THE SOLx\R SYSTEiM, NOW, by means of this Orrery, I will illustrate our Solar System; which contains the sun (marked a) in the centre, and the planets and comets moving about it. y db a c e g But how is it then, says Tom Wilson, that we daily see the sun rise and set? Your question, replies Master Telescope, is very natural / for it was an opinion held by the ancients some thousands of years, that the earth was the centre of the Universe, and that the sun and planets revolved round it ; but I think this is easily refuted by a Of the Solar System, 23 common occurrence in a kitchen ; I mean a small bird roasting on a spit before a large fire. Would not you think it very absurd if the cook should endeav^our to make the grate with a large fire move round the small bird on the spit ? Certainly I should, answers Tom Wilson; for surely it would be better for the bird to turn round before the fire, than the fire to turn round the bird. Very well, then, says our Philosopher, the sun being more than a million times larger than our earth, we have certainly reason to believe that it is the centre of our system, and that the earth and other planets move round it. But you will understand this better if you look at the plate I have draw^n of the sun and the planets, in their several orbits or circles, with their respective dis- tances from the sun, and from each other ; together with the orbit of a comet. The planets, as I have already observed, are bodies that appear like stars, but are opaque ; that is, they have no light in them- selves, but receive it from the sun, and re- flect it upon us. Of these there are two kinds : the one called Primary, and the other Secondary planets. 24 Of the Solar System. There are seven primary planets 5 and these are marked on the Orrery as follows •: Mercury b^ Venus c, the Earth r/, Mars e^ Jupiter yj Saturn ^5 and the Gcorgium Sidus (which being of such recent discovery, is not represented in this Orrery.) The last of these was discovered only a few years since by Dr. Herschel, and called by him, out of respect to his present majesty king George III. the Georgium Sidus, or Geor- gian. All these move round the sun, as you see by my turning the winch of the Orrery ; whereas the secondary planets move round other planets. — The Moon, you know (which is one of the secondary planets) moves round the Earth; four moons or sa- tellites, as they are frequently called, move round Jupiter ; five round Saturn ; and only two have yet been discovered to move- round the Georgian ; though we have great reason to believe there are more ; but fron^ the immense distance of that planet, we have not yet perceived them.* Thus has the Almighty provided light for those regions that lie at such an immense distance from the sun. * Saturn is now known to have seven satellites, and the Georgian six. — Ed, Of the Solar System. 25 I have here made out a table of the pe- riods, distances, and diameters of the seve- ral planets. Revolves round Distance from Diamctei the Sun in the Sun in in Eng. years, days, Eng. Miles. Miles. Mercury 88 36,000,000 3261 Venus 224 68,000,000 7699 Earth lor365 95,000,000 7920 Mars 1 &322 145,000,000 5312 Jupiter 11 — 314 494,000,000 90255 Saturn 29— ler 906,000,000 80012 Georgian 83—121 1812,200,000 34217 They all move round the sun from west to east; but in their progress do not describe a perfect circle, but an orbit a little mclining to an oval; the reason whereof I shall give you in a future Lecture. The knowledge we have of comets is very imperfect; it is a general supposition that they are planetary bodies forming a part of our system, for they revolve about the sun in extremely long elliptic curves, being some- times very near it, at others extending far be- yond the sphere of the Georgian. Th- period in revolving about the sun, of one which ap- peared in 1680, is computed to be 575 years. But let us quit these bodies, of which we know so little, and speak of our old compa- nion the Moon, with whom we ought to be 26 Of the Solar System. better acquainted: since she not only lights us home in the night, but lends her aid to get our ships out of the docks, and to bring in and carry out our merchandize; for without the assistance of Lady Luna you would have no tides. But more of this hereafter. — A little more now, if you please, says Tom Wilson. What then, does the moon pour down water to occasion the tides? I am at a loss to under- standyou. No, replied our Philosopher, the moon does not pour down water to occasion the tides; that were impossible : but she, by attracting the waters of the sea, raises them higher ; and that is the reason w^hy the tides are always governed by the moon. The Moon's diameter is 2,160 miles ; her distance from the earth is 240 thousand miles; she moves round it in the same manner as the earth does round the sun; she performs her synodical motion, as it is called, in 29 days, 12 hours, and 44 minutes, though the peri- odical is 27 days, 7 hours, and 43 minutes. By this motion of the moon are occasioned the eclipses of the sun and moon, and the different appearances, aspects, or phases she at different times puts on : for when the earth is so situated between the sun and the moon that we see all her enlightened parts, it is Full Of the Solar System. 27 Moon ; when the moon is so situated be- tween the sun and the earth, that her enlight- ened parts are hid or turned from us, it is New Moon ; and when her situation is such that only a portion of her enlightened part is hid from us, we see a Horned Moon, a Half Moon, or a Gibbous Moon, according to the quantity of the enlightened part we can per- ceive. But I will endeavour to explain this to you more clearly, says our Philosopher, taking an ivory ball suspended by a string, in his hand; we will suppose this ball to be the moon, the candle the sun, and my head the earth. When I place the ivory ball in a direct line between my eye and the candle, it appears all dark, because the enlightened part is opposite the candle ; but if I move the ball a little to the right, I perceive a streak of light, which is like the New Moon ; if the ball be moved further it presents the appearance of a Half Moon ; move it still further, until all the en- lightened part is seen, it appears like a Full Moon. I think it is extraordinarj^, says Tom Wilson, that the Moon which you say is so much smaller than the Sun, should appear to our sight equally large. 28 Of the Solar System. That is easily explained, replied our Phi- losopher, for if you consider that the sun is at 400 times a greater distance from us than the moon, your objection is answered ; but this I will explain furdier in treating of Eclipses. I have frequently observed, says Master Lovelace, that the moon appears much larger when just rising above the horizon, than she does afterw^ards ; I should like to know the cause of that. I thank you for your observa- tion, Sir, replies our Philosopher ; it is occa- sioned by the fogs or exhalations that arise from the earth, which always magnify ob- jects seen through them ; thus the moon, un- til she rises above these fogs, always appears larger.-* The apparent magnitude of a celestial body or the an- gle it subtends at the eye, when near the horizon, is not greater but indeed somewhat less than when it is in the zenith ; and that it should seem to be greater is a mere optical deception from its apparent greater distance. To this deception the fogs or exhalations near the horizon will no doubt J in some measure, contribute. — >Ed, Of the Solar System. 29 The total or longest eclipse of the moon happens when the earth is directly between the sun and the moon, and prevents the light of the sun from falling upon and being reflected by the moon; as you will under- stand by looking at the figure I have here drawn. We will suppose the candle a to be the Sun ; the cricket-ball 6, to be the Earth ; and the fives-ball r, to be the Moon, A string being tied to each of the balls, I tie them up to the ceiling, or any other support, in a di- rect line from the light of the candle ; the cricket-ball about eight inches from the can- dle, and the fives-ball about two inches from the cricket.ball. Whenever the earth and moon come in the position of these balls, a total eclipse of the moon ensues ; because the lightof the candle (or sun) shining on the C 2 30 Of the Solar System. cricket-ball (or the earth) totally obscures or eclipses the fives-ball (or the moon); but if we move the fives-ball a little higher up, or lower down, so that the light from the can- dle may pass by the cricket-ball, it will of course be only partially eclipsed. An Eclipse of the Sun is occasioned by the moon's being between the sun and the earth, and preventing the light of the sua from coming to that part of the earth we in- habit. This may be explained by changing the places of the balls; for when the fives-ball is placed between the cricket-ball and the candle, it will shew a total eclipse of the sun; but if the cricket-ball is moved a small de- gree higher up or lower down, so that the light from the candle shines a little upon it, it will shew only a partial eclipse. But I should be glad to be informed, says Master Lovelace, how the sun which is so much larger than the moon, can be totally eclipsed from our sight, by the moon coming between us and it ? That is what I intended to explain to you, replied Master Telescope, If you place your cricket-ball in a direct line between your eye and the sun, it will entirely hinder you from Of the Solar System. 3i seeing it, although your ball is much smal- ler than the sun. An eclipse of the sun never happens but at new moon ; nor one of the moon but when she is at the full. The surface of the Moon consists of Moun- tains and Vallies, not unlike our Earth, and appears very beautiful when seen through the Telescope I shewed you some time ago. The livid spots and bright streaks of light are supposed to be the mountainous parts ; and the same parts being constantly turned towards the earth, she always pre- sents the same side to us. The dark parts were formerly imagined to be seas ; but from later observation it is proved, that 32 Of the Solar System. they are hollow places or caverns, which do not reflect the light of the sun. The Earth, by its revolution about the sun in 365 days, 5 hours, and 49 minutes^ measures out that space of time which wc call a year; and the line described by the earth in this annual revolution about the sun, is called the Ecliptic. By an inspec- tion of this Armillary Sphere you will have a perfect idea of this and other circles ne- cessary to be known. The annual motion of the earth round the sun is from west to east, or, to speak more philosophically, it is according to the order of the signs of the Zodiac ; which "we shall hereafter explain. T]ie Solar ^y ^ Syl teixi Of the Solar System. 33 But besides this annual motion or revo- lution about the sun in the line of the Eclip- tic, the earth turns round upon its own axis in about 24 hours ; so that it hath two mo- tions at one and the same time. Mrs. Setstar, whose curiosity had kept her there during the Lecture, desired to have this explained. — That shall be done, Madam, in a minute, says the little Philo- sopher ; and I can never have a better op- portunity ; for I see Mr. Galaxy coming on a visit to your Ladyship : hi^ coach is iu^t entermg the iron gates, and will" presently wheel round the circle, or rather oval, be- fore the Portico. Pray, Madam, fix your eyes on one of the wheels (which you may do as it is moon-light) and you will per- ceive it turn round upon its ow^n axis, at the same time that it runs round the oval before the house. This double motion of the wheel very fitly represents the two mo- tions of the earth. 34 Of the Solar System, i^i^^r By mL....:3 of this Terrestrial Globe I shall explain more interesting astronomical principles. Your t:iadyship knows perfectly that the earth, turning on its own axis, makes the succession of day and night ; you will therefore give me leave, Madam, to ad- dress my discourse to these young gentle- men and ladies, who may be ignorant of this branch of philosophy. That the turning of the earth on its own axis, makes the succession of day and night is most certain : for in those parts of the earth which are turned toward the sun it will be day ; and of course it must be night in those which are turned from it. Of the Solar System. 35 But the length of days and nights, and the variations of the seasons, are occasion- ed by the annual revolution of the earth about the sun in the Ecliptic ; for, as the earth in this course keeps its axis equally inclined every where to the plane of the ecliptic and parallel to itself, the earth in this direction has sometinaes one of its poles nearest the sun, and sometimes the other. Hence heat and cold, summer and winter, and length of days and nights. Yet not- withstanding these effects of the sun, which gives us light and heat, his distance from us is so great, that a cannon-ball would be twenty-five years coming from thence to the earth, even if it flew with the same velocity as it does when it is first discharged from the mouth of a cannon. Here they were all amazed ; and Lady Caroline said this doctrine could not be true ; for if the sun were at that immense distance, his light could not reach us every morning in the manner it does. I beg your pardon, Madam, replied the Philoso- pher, your Ladyship's mistake arises from your not knowing, or at least not consider- ing the amazing velocity of light, which although coming from the sun, which is 56 Of the Solar System, more than 95 millions of miles distant, reaches us in the space of seven minutes and a half, it must in consequence travel at the rate of about 212,000 miles in one se- cond of time. But if you are so surprised at the sun's distance, Madam, what think you of the fixed stars, which are so far remote from us, that a cannon-ball, flying with the same velocity as when first discharged, would be 700,000 years in coming to the earth? Yet many of these stars are seen even without the use of Telescopes. There are other things observable in our Solar System, which, if attended to, will excite our admiration : such as the dark spots which are seen on the Sun's sur- face, and which often change their place, number, and magnitude. Such also is the amazing ring which encompasses the body of the planet Saturn : and such are the belts that gird the body of Jupiter : — concerning all which there are various conjectures; but conjectures in philosophy are rarely to be admitted. ( 37 ) LECTURE III. OF THE AIR, ATMOSPHERE, AND METEORS. WHAT was said by Mrs. Galaxy and Lady Caroline in favour of Master Tele- scope, excited Mr. Galaxy's curiosity to see him ; and the next morning he came into the Observatory just as the Lecture began. The presence of so great a personage put the young gentleman into some confusion, and several of them offered to go away ; which Mr. G. observing, prevented by step- ping into the next room ; and Master Teles ■ cope took this opportunity to correct their folly. Gentlemen, says he, I am amazed at your meanness and ill manners. What ! because the gentleman does you the honor of a visit, will you run away from him ? — There is nothing betrays a mean spirit and low edu- cation so much as this ridiculous awe and dread which some people shew in the compa- ny of their superiors : and besides, it is trou- blesome ; for the uneasiness one person is in, communicates itself to the rest of the D 38 Of the Air, Atmosphere^ ^c, company, and abridges them of a portion of their pleasure. The easier you appear in the company of the great, the more po- lite you will be esteemed. None but a clown hangs down his head, and hides his face ; for a gentleman always looks in the face of his superior when he talks to him, and behaves with openness and freedom. I venerate Mr. Galaxy for his virtues and amiable character, as highly as any of you ; and this inclines me to wish for his compa- ny, rather than to avoid it. Fortune, and what the world ridiculously calls high- birth, are merely accidental, and may often be found in persons of the most worthless description ; whilst on the other hand, we sometimes find in persons of mean parent- age, (as it is called) and without any of the tinsel of fortune, those amiable virtues, and that nobleness of soul, which justly claim our highest veneration and esteem. This r^proof^ and these remarks had their proper effect ; for they all sat down, and Mr. Galaxy having returned, accompa- nied by his Lady, our Philosopher began his lecture on the nature and properties of the air, atmosphere, and meteors contained therein. Of the Airy AtmospherCy feV. 39 We have already considered the Earth as a planet, says he, and observed its diurnal and annual motion ; we are now to speak of the materials of which it is composed, and of the Atmosphere, and the Meteors that surround and attend it. In order to explain these effectually, says Mr. Galaxy, you should, I think, Sir, begin with an account of the first principles of the four Elements, which are Fire, Air, Earth, and Water, and then shew how they affect each other, and by their mutual aid give motion, life and spirit to all things ; for without fire, the water would assume a different form, and become solid ice; without water, the fire would scorch up the earth, and destroy both animals and plants ; without air, the fire per- haps would be unable to execute its office ; nor without air, could the water, though ex- haled by the sun into clouds, be distributed over the earth for the nourishment of plants and animals. Nor is the earth inactive, but lends her aid to the other elements ; for she, by reflecting the sun's beams, occasions that warmth which nourishes all things on her surface ; but which would be very inconsi- derable and scarcely felt, if a man was placed on the highest mountain, above tlVe 40 Of the AtTy Atmosphere^ bV. common level of the earth, and m such a situation as to be deprived of her reflection. All this, Sir, I have considered, replied the Philosopher ; and had thoughts of car- rying it farther, and shewing how those ele- ments pervade and are become indeed con- stituent parts of the same body; for Fire, Air, Earth, and Water, are to be drawn even from a dry stick of wood. That two sticks rubbed violently together will prp- duce fire, is very well known ; for coach or waggon-wheels frequently take fire when not properly clouted with iron, and suppli- ed with grease ; and if pieces of wood, seemingly dry, be put into a glass retort over a furnace, you'll obtain both air and water: and then if you burn the wood to ashes, and wash out the salts with water, as the good women do when they make lye, the remaining part will be pure earth : and thus we can at any time draw the four elements out of a stick of wood. But as these spe-. culations are above the comprehension of some of the young gentlemen whom I have the honor to instruct, I shall defer the consideration of such minute and abstruse matters till another opportunity. Science is to be taught as we teach children the Of the Air, Atmosphere, ^c. 41 use of their legs ; they are at first shown how to stand alone; after this, they are taught to walk with safety, and then suf- fered to run as fast as they please : and I beg you will be so good as to permit me to pursue this method in the course of my Lectures. Mr. Galaxy gave his assent with a nod ; and our philosopher thus pro- ceeded : The Air is a light, thin, elastic or springy body, which may be felt, but not seen : it is fluid, and runs in a current like water (as you may perceive by opening the win- dow ; ) but it cannot, like water, be con- gealed into ice ; and the Atmosphere is that great body or shell of air which sur- rounds the earth, and which reaches many miles above its surface, as is known by considering the elasticity or springiness of the air and its weight together ; for a column of air is of equal weight with a column of quicksilver of between 29 and 30 inches high. Now quicksilver being near four times heavier than water, if the air was as heavy as water, the atmosphere would be about fourteen times higher than the column of quicksilver, or about 34 feet ; but the air is near 1000 times lighter than water , there- D 2 42 Of the Ah\ Atmosphere^ U'c. fore, the atmosphere must be many miles high, even at this rate of computing. And when with this you consider the elasticity of the Air, which, when the pressure of the incumbent Atmosphere is taken off, will dilate itself so as to fill more than 150 times the space it occupied before, you will perceive that the height of the Atmosphere must be very great. For as the Air is a springy body, that part next the earth must be more dense than the upper part, as be- ing pressed down by the air above it. Look at that hay-stack yonder, which the groom is cutting, and you'll perceive that the hay at the bottom is much closer and harder to cut than that at the top, because it has been pressed into a less space than it otherwise would have occupied, by the other hay above it; and had not the whol^ stack been trodden and pressed down by the men who made it, the difference would have been still more considerable. The air, however, even near the earth, is not always in the same state. It is some- times rarefied, and becomes lighter than at other times, as appears by the quicksilver's falling in the barometer, and the rains de- scending on the earth. Of the Ab\ Atmosphere^ ^c. 43 It may be acceptable here, says the young Phi- losopher, to explahi the construction of that triple weather-glass that I see hanging up before me. So walking up to it, he described it in the follow- ing manner : The upper- most instrument contain- ed in the round brass box, is called the Hygrometer, (marked a). It consists of a brass plate, divided into degrees both ways, right and left, from to 180. To the left is engraved Moist y and to the right Dr^, In the centre of the plate is fixed the beard of a wild oat, with a piece of straw glued to it, as an in- dex. The index is first set to of the di- visions, so that any change of the air which happens afterwards in the room to Moist or Dri/y the beard by twisting or untwist- ing itself from the action of the air, will by the index point it out accordingly on tlie scale. The open square part next below, is called the Barometer, (marked 6). It consists of a 44 Of the Air ^ Atmosphere^ ^e. glass tube about 32 inches long, closed at the top, first filled with quicksilver, and then in- verted on a reservior, or leather bag below, of quicksilver. By this means the quick- silver in the tube subsides to its proper height, as acted upon by the pressure of the air, or atmosphere ; for it is the dense state, or heaviness of the air that raises the quick- silver in the barometer, and prevents the clouds from distilling through the air in rain; and, on the contrary, its lightness that ad- mits the fall in showers, &c. Barometers are also used to determine the heights of mountains. Sec. because as we as- cend, the quicksilver sinks in proportion ; the weight of the atmosphere which presses on it being less. But what is the use of that screw at the bottom of the instrument? says Master Wil- son. I thank you for the question, says the Philosopher ; for many a young ignoramus has totally spoiled a good barometer, by fool- ishly playing with that screw till he forced it up, broke the bag, and let out all the quick^- silver. Let it be particularly known, that this screw is only provided by the instru- ment-maker, to force upthe quicksilver in its tube in a gentle manner, so that in convey- Of the Jir, Atmosphere^ &V. 43 ingthe instrument iiitothe country or abroad, it is thus made quite portable, and not liable to have the tube broken by the con- cussion of the quicksilver against the top of the tube. The next instrument below is called the Thermometer (marked c). It con- tains a long glass tube, partly filled with quicksilver, and screwed down to a brass scale, on which are marked divisions and terms of various degrees of heat and cold, from boiling water down to freezing, found and adjusted by actual trial of the maker. The freezing point is marked 32, and the boiling water 212. This is called Fahren- heit's Scale, as being the name of the inven- tor. I'he heat of the air expands the quick- silver in the ball ; and it accordingly rises in the tube ; whereas, on the contrary, cold contracts the quicksilver, and it of course falls, so that at any time by mere inspection, the change of the temperature of the air is immediately shewn. The elastic principle in the air, which renders it so capable of being rarefied and condensed, has been productive of the most wonderful effects. But before you proceed farther, says Lady Caroline, pray do me the favour. Sir, to convince me, by some expe- 46 Of the Atr^ Atmosphere^ ^e* riment, that the air is endowed With this wonderful quality., — That he cannot do, re- plied Mr. Setstar, without the use of proper instruments. — Almost any thing will do, says the Philosopher. — Little Master's pop- gun that lies in the window, is sufficient for my purpose. Do me the honor to step this way, Lady Caroline. You see here is a pel- let in the top of this tube, made of hemp or brown paper. With this piece of paper I will make another pellet, and put it into the other end. Now with the gun-stick drive it forward. There you have forced the pellet some p^rt of the way with ease ; but it will be more difficult to get it farther, because the air, being compressed &nd made more dense or compact, will make more resist- ance ; and when you have pressed it so close that its force overpowers the resistance which the pellet makes at the other end, that pellet will fly off with a bounce, and be thrown by the spring of the air to a consi- derable distance. There, see with what force it is thrown ! This you have taken little notice of, be- cause it is a school-boy's action, and is seen everyday; for indeed we seldom trouble our- selves to reason about things that are so fa- Of the Jir, Atmosphere, feV. 47 miliar; yet on this principle, my Lady, de- pends the force of a cannon ; for it is not the gun-powder and fire that drives out the ball with such prodigious velocity ; no, that force is occasioned by the fire's suddenly rarefy- ing the air which was contained in the cham- ber or breach of the cannon, and that gene- rated by the powder itself. As a 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 in- vented, called Air-guns, which abundantly prove what I have advanced ; for they are charged only with concentrated or condensed air. Here is one, I perceive, hanging over my head, where you are to observe that the ball, which is pre- viously filled by a syringe with the condensed air, is screwed under the back, and by pulling the trigger, a valve is pushed in the ball by a pin ; the air rushes from thence, through the back, into the barrel, against 48 Of the Atr^ Atmosphere^ ^c the bullet, and drives it to a great distance ; and the air in the ball is sufficient to dis- charge six or seven balls, 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 the air, which is so necessary for life, that without it we cannot breathe, should be tortured into an instrument of destruction. You will, however, be more surprised when I tell you that this is probably the cause of earth- quakes ; and that the noble city of Lisbon was some years ago destroyed by a sudden rarefaction of the air contained in some of the caverns of the earth, and perhaps under the sea. Tom Wilson gave a leer of imper- tinence, 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 Of the Aii\ Atmosphere^ ^c. 49 there could be no such sudden rarefaction 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 Mr. Setstar put an end to the contro- versy, by declaring it was true Philosophy. In this property of being rarefied and con- densed, the air differs amazingly from water, which, though composed of such small par- ticles as not to be distinguished or seen se- parately w^ithamicroscope, and notwithstand^ ing its readiness to rise or be evaporated wath heat, and to be separated with a touch, cannot, when confined, be at all concentrated or brought into a less compass. I have already intimated that heat is the efficient cause of all fluidity, and that ice may therefore be termed the natural state of water; the utility of which to man, as well in diluting his food as in increasing his en- joyments in various modes, it would be te- dious and useless minutely to describe to you ; containing a quantity of air, it is the medium by which aquatic animals respire. So Of the Air J AtiJiosphere^ ^c. It is also, if not the principal, at least a con- siderable part of the food of Vegetables ; which I will afterv^ards explain to you. By increasing the heat, water is rendered elastic and volatile ; that is, it is converted into vapour, the force of which, when con- fined is almost incredible; this force has been applied to the use of Mechanics in the Steam Engines, by which, it is said, that a single drop of water, converted into vapour, is capable of raising several hundred weight* The construction of these engines is so very complicated, that it is impossible for me to explain them without a model. 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 Avould 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 medi- xmi 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 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 Of the Ai)% Atmosphere^ ^e. 5 1 in this manner ; though 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 man- ner :— Only throw up the sash and halloo, and the echo will return you the sound ; that is, the v/aves 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 the echo is nothing but the reverberation of sound. And that there can be no sound conveyed without air, is proved by experi- ment ; for a bell, struck in an exhausted receiver of an air-pump, cannot be heard; that is, it has little or no sound. Without air there w^ould be no merchan. dize ; for your ships could not sail to foreign climates ; and without air the birds could not fly, since they would have nothing to sup^ port 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 of an air pump. 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 ^^2 Of the Air J Atmosphere^ ^c. slopt, we die. This is one of those truths that are called self-evident ; because' it is universall-y known, and needs no confirma- tion ; but if demonstration be thought ne- cessary, you may have it in a minute, by put- ting some living animal into an air-pump. — But, said Lady Caroline, it is cruel to tor- ture a poor animal ; and violently opposed this experiment being tried ; but as the rest v/ere for it, Mr. Setstar was willing to gratify their curiosity, and therefore told our Phi- losopher 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. Master Tele-^ scope, after placing the air-pump on the lable proceeded as follows : Of the Ah\ Atmosphere, fcV. '60 By the help of this machine, all that I have spoken concerning the weight and elas- ticity of the air, is demonstrated in the most simple and elegant manner. For by work- ing the handle (marked A) all the air that is contained within the glass receiver (marked B) is pumped out; and if any living animal is put within the receiver, all the air in its body is pumped out likewise: then, as I mentioned before, air being the principle which pre- serves life, the animal dies, unless fresh air be immediately admitted^ which may be done by turning a screw (at C). Our Phi- losopher then put the rat into the receiver ; E 2 54 Of the Ah\ Atmosphere^ ^c. and when the air was nearly exhausted, it appeared in great agony, and convulsed ; and more air being pumped out, it fell on its side for dead ; but fresh air being imme- diately admitted, it rushed into its lungs, which put them in motion again, and he re- covered. The maimer of the animal's re- covery puts me in mind, eays the Philoso- pher of an accident which I once seen, and which I would have you all remember ; for it may be of service to mankind. Some time ago I was bathing with se- veral of my school-fellows in a river by the road-side. Master Curtis, who was an ob- stinate silly boy, would dastard the rest, as he called it ; that is, he would foolishly ex- ceed them in running into dangers and dif- ficulties ; and with this view, though he could swim no more than a stone, he plunged into a part of the river, which we told him was greatly beyond his depth, where he rose and struggled to get out, but could not. We were all in the utmost distress^ and unable to assist him„ for none of us could swim. At this instant some gentle- men on horseback came up, who immedi- ately dismounted, and got him out; but not till he had sunk the third time. — He Of the Ah\ Atmosphere^ ^c, 55 was brought to the shore without signs of life, and blooded w ithout 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 lungs in motion, as I imagine, for a pulsation immediately ensued ; he reco- vered 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 remem- bered, for it is a matter of great impor- tance. We are to observe, gentlemen, that air which has passed through fire, or is become foul or stagnated, and has lost its spring,*' is unfit for respiration. It was the want of * Air is not rendered noxious, or unfit for respiration, by any loss of sfirvig^ or elasticity, but by that of its vital principle, which the modem chemists tcrni cxy-- §cn gas — Ed, 56 Of the Jir, Atmosphere^ ^c. fresh air, or, in other words, the being obliged to breath air that was foul, and had lost its spring, or elastic force, that some years ago killed so many poor Englishmen in the black hole at Calcutta, in the East- Indies : and this breathing of foul air in in- flammatory, 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 use 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, even when you sleep. I am greatly mistaken, says Lady Caro- line, 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 ? Of the Ai)\ Atmosphere^ ^c. 57 says the Lady. Your fan, Madam, return- ed the Philosopher, Every fan is a philo- sophical instrument, and was originally contrived, wc may suppose, for the purpose above-mentioned. A bird dying in an air-pump will be in some measure recovered by the convulsive flutterings of its own wings ; because that motion alters the state of the air remaining in the receiver, and for a time renders it fit for respiration. Motion is the only preservative for air and water ; both of which become unwhole- some 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 disco- vering the Ventilator : an 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 researches of our modern Philoso- phers, says eur Lecturer, have been the means of many new discoveries in regard to air. They now produce and prove the existence of many different sorts of air ; 58 Of the Air^ Atmosphere^ Wc. such as our common air, inflammable air, nitrous air, mephitic air, more technically denominated by them gases, or elastic flu- ids. But it would be difficult to give you clear ideas upon this subject, unless you had some previous knowledge of Chemis- try. I must therefore beg leave to dispense with the account of these now, and only to advise my hearers to a study of Chemistry, as now improved, as a science that will afibrd them much pleasure, and informa- tion in Nature's wonderful operations. When you mentioned inflammable air, says master Wilson, I thought you would ha\^e mentioned the Balloon ; which, of all the wonders, I think the greatest. I pro- test it perplexes me to account how in na- ture it is possible for any large hollow sub- stance, even although filled with air, to float in fhe almosphere, particularly when weighed down with a boat and two men in it, as represented in this picture hung near me ; which records the memorable event of Mr. Blanchard and Dr. Jefferies crossing the English channel from Dover to France. Of the Ah\ Atmosphere^ ^c. 59 I am surprised at so simple a question, says our Philosopher. Why, surely, you never considered the reason of those balls that I have seen you make by soap and wa- ter beat to a lather, and blown out of the bowl of a tobacco-pipe. The air, by which they are blown, issuing from your lungs, is specifically lighter than the common air ; even when contained in that thin watery globe. Now, inflammable air is about ten times lighter than common air, so that a large hollow silk balloon, filled with inflam- mable air, although loaded with a boat, two men, and sundries, is lighter in its bulk than common air ; and consequently, when 60 Of the Air^ Atmospliere^ &V. released from the cords that fasten it to the ground, it rises majestically, and soars along, in and above the clouds, according to the direction of the wind. 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, ^rarefactions, the pressure of clouds, the fall of rains, or some other accident that dis- turbs the equilibrium of the air : for Nature abhors a vacuum, and for that reason, when the air is extremely rarefied 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 rarefac- tions in the air may happen near the earth, or much abore it ; and is the reason why clouds fly in contrary directions. This oc- casioned the loss of the great kite, which we were a whole fortnight in making ; for though there was scarcely wind in the park sufficient to raise it, yet when lifted Of the Air ^ Atmosphere^ fcfr. 61 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 rarefaction or disturbance there has been in the atmosphere. A violent wind, in a great storm, flies at 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 at the rate of about 15 miles an hour, and is of great use in cooling the air, and cleansing it from poi- sonous and pestilential exhalations. The winds have various qualities ; they are generally either hot or cold, according to the quarter from whence they blow. In England, some years ago, they had a south- west wind in February, which blew so long from that quarter, that it brought them 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 thick- en : some raise rain, and others disperse it : some winds blow constantly from one quar- ter, and are therefore called the General Trade winds \ these are met with on each e2 Of the Air, Atmosphere, ^c. side of the Equator, in the Atlantic, Ethi- opic, and Pacific Oceans. Some winds, again, blow constantly one way for one half, or one quarier of the year, and then blow the contrary w^ay. These are met with in the East- Indian seas, and are cal- led Monsoons, or Periodical Trade Winds. But as these subjects are abstruse and dif- ficult, and afford little entertainment, I will defer an explanation of them at present, and endeavour to give you some account of the meteors that attend the ain We have already observed, that, besides pure air, the atmosphere contains minute particles of different sorts, which are contin- ually arising in streams from the earth and waters, and are suspended and kept floating in the air. The most considerable of these are the small particles of water; which are so sepa- rated 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 Snov/. When these small particles are, by a rare- fied state of the air, suffered to unite many of them together, and descend so as to ren- Of the Air^ Atmosphere^ ^c. 63 der the hemisphere more opaque, and bf 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 Psalm- ist 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 be- low. That these vapours are raised in the air, in the manner above-mentioned, 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. It is probable, that by uniting first into small drops, then into larger, they become too heavy to be suspended by the air, and fall down in rain. ,G4 Of the Air^ Atmosphere^ £srV. We come now to describe the causes of Thunder and Lightning; but here I must take the Electrical Machine to my aid. On account of the many late improve- ments that have been made in the science of electricity, the instrument-makers have made electrical machines upon various construc- tions. The one I am now going to describe is not the most modern of these; but as the essential parts are exactly the same in all, you will obtain by this a sufficiently com- plete and just information of the curious properties belonging to them. All the phenomena called Electrical, are supposed to be effected by an invisible sub- tile fluid existing in all the bodies of the earth. The Electrical Machine is made to extract this fluid from the earth, in the man- per I will describe to you. Of the Ah\ Atmosphere y ^e. 65- The handle (marked A) behig turned round, by means of some wheelwork in the box (marked B) it turns round the glass ey- Imder (marked C); this cylinder rubs against the cushion of stuffed silk, which is called the Rubber (marked D): by this means the electric fluid is extracted from the rubber, and carried round by the glass to the points (marked E) which it enters, and remains in the tin tube or conductor (marked F), which F 2 66 Of the Air^ Atmosphere, E^V. is fixed upon a glass stem (marked G): as the electric fluid camiot pervade glass, this stem hinders it from returning again to the earth. When the machine is worked, if a person places one of his knuckles about half an inch from the brass knob at the end of the conductor (marked H) the electric fluid will dart like a bright spark of fire from it to the knuckle, and give the person a small degree of pain. If instead of the knuckle, a coated jar is placed to the conductor, the fire will be received by it, and accumulated therein : so that if a person touch the bottom of the jar with one hand, and the ball at the top of it with the other, he will receive the charge of electricity through him, and feel the sensa- tion of a sudden shock. The similarity of lightning and electricity is not to be remarked in a few appearances only, but is observable throughout all their various effects. Lightning destroys edifices animals, trees, &:c. It always goes through the best conductors, such as metal or water; but if it meet with substances which will not conduct it (such as stone or wood) it rends them, and disperses them in every direction. Lightning burns, and often melts metals and other substances. All these effects, as I said Of the Air, Atmosphere, fcf<7. 67 before, may be produced by electricity. But beside the great similarity existing be- tween lightning and electricity, what fully jproves them the same is, that the matter of lightningmay be actually brought down from the clouds by means of electrical kites : but as this is a very dangerous experiment in unskilful hands, I will not now describe the method of making it. Clouds have almost always some electrical matter in them ; and the lightning accompanying, which is sup- posed to be collected from the earth with the thunder, is only that matter darting from one or more clouds into another cloud, or else upon the earth ; * in which case it strikes upon the most lofty and pointed places, and by this stroke produces all those dreadful effects that are known to be occasioned by lightning. But, says Miss Caroline, you have not yet mentioned those pointed rods on the tops of many large buildings ; I have been told they protect the buildings from lightning. That they certainly do, Madam, said Master Telescope, for the lightnino- ig * The lightning, in a thunder-stornn, perhaps as fre- quently paises from the earth to the cloud, as in the con- trary direction, yet in both cases, the pointed lightning-rod, is equally advantageous Ed^ 68 Of the Air ^ Atmosphere^ is'e. attracted from the clouds by the pointed rod, and is by it conducted down the side of the building to the nearest water without dama- ging it. These rods were the invention of^ the late ingenious Dr. Franklin of Philadel- phia. People in general, when they happen to be caught in a thunder-storm, run for shel- ter under a tree ; but that is very wrong ; for the lightning is attracted by the tree, and thus accidents often happen. The best way is to get into an open place and lay at a dis- tance all metal which you may have about you : if you do this, you are not in much danger of being hurt by the thunder and lightning. Snow is the small particles of water fro- zen in the air before they had united into drops ; and hail is drops of rain frozen in its fall. The Aurora Borealis^ or northern lights, are occasioned by certain nitrous and sul- phureous vapours, which are thinly spread through the atmosphere, above the clouds^ where they ferment, and, taking fire, the ex- plosion of one portion kindles the next, and the flashes succeed one another, till all the vapour is set on fire, the streams wliereof seem to converge towards the Of the Atr^ Atmosphere y ^e. 69 zenith of the spectator, or that point of the heavens which is immediately over his head.^ \, At this instant, up started Master Long, and said, I should be glad to have an account of this Jack-with-a-Lantcrn, which so haunts Mr. Setstar's park, and t'other day led my friend Tom Wilson into a large pond. Mas- ter Wilson, you are to understand, had been at his uncle's, where he had staid rather too late, and therefore his uncle ordered the foot- man to light him home ; but; Tom, being a very courageous fellow, and a little obstinate, would walk home alone and in the dark : and just as he came into the marshy meadow, who should he almost overtake but this same gentleman, this Jack-with-a- Lantern, whom he mistook for Goody Curtis, the washer- woman, and thought she was lighting herself home from work. Tom ran to overtake Dame Curtis ; but Mr. Jack with his Lan- tern still kept ovit of reach, and led my friend Tom out of the path ; which he did not per- ceive till he had lost himself: on which Tom halloo'd, and Jack would not answer. At * The Aurora Borealis is, most probably, an electrical phenomenon, though the manner in which it is produced is still uncertain. — IlcL Id Of the Air J Atmosphere, &?od} is occasioned by this caloric passing into or out of the body — Ed. and of his Understanding,, 13.3 while the other was kept in a state of rest ; and for no other reason but because the mo- tion of the insensible particles of that hand with which he has been rubbing, will be more brisk than the particles of the other which was at rest. I have mentioned those objects which are peculiar to each of our senses ; as light and colour to the sight ; sound to the hearing ; odours to the smell, &c. but there are two others common to all the senses, w^hich de- serve our notice, and these are Pleasure and Pain, w^hich the senses may receive by their Own peculiar objects : for we know that a proper portion of light is pleasing, but that too much offends the eye ; some sounds de- light, while others are disagreeable and grate the ear; so heat, in a moderate degreee, is very pleasant, yet that heat may be so in- creased as to give the most intolerable pain. But these things are too well known to be longer insisted on. Now, from the ideas or conceptions form- ed in the mind by means of our senses, and the operations of the mind itself, are laid the foundation of the human understanding, the lowest degree of which is perception : and to conceive a right notion of this, we M 134 Of the Five Senses of Man ^ must distinguish the first objects of it, which are simple ideas, such as are represented by the words Red, Bhie, Bitter, Sweet, Sec. from the other objects of our senses ; to which we may add the internal operations of our own minds, or the objects of reflection ; such as are thinking, willing. Sec. for all our ideas are first obtained by sensation and re- flection. The mind, having gained a variety of simple ideas, by putting them together, forms what are called compounded or com- plex ideas ; as those signified by the words, Man, Horse, Marygold, Windmill, &c. The next operation of the mind (or of the understanding) in its progress to knowledge, is that of abstracting its ideas ; for by ab- straction they are made general ; and a ge- neral idea is to be considered as separated from time and place, and lodged in the mind to represent any particular thing that is con- formable to it. Knowledge, which is the highest degree of the speculative faculties consists in the perception of the truth of affirmative or ne- gative propositions ; and this perception is either immediate or mediate. When, by comparing two ideas together in the mind, we peixeive their agreement or disagree- and of his Understandhig, 135 ment, as that black is not white ; that the whole is bigger than a part; and that two and two are equal to four, &c. it is called Immedi- ate Perception, or Intuitive Knowledge ; and as the truth of these and the like propositi- ons is so evident as to be known by a simple intuition of the ideas themselves, they are also called Self-evident Propositions. Mediate perception is when the agree- ment or disagreement of the two ideas is made known by the intervention of some other ideas. Thus : If it be affirmed that Tom Wilson's bay horse is as high as my father's, the agreement or disagreement may be seen by applying the measure to both : And this is called Demonstration, Or Rational Knowledge. The dimensions of any two bodies which cannot be brought together may be thus known, by the same measure being applied to them both. But the understanding is not confined to certain truth ; it also judges of probability, which consists in the likely agreement or disagreement of ideas ; and assenting to any proposition as probable is called Opinion or Belief. — We have now finished this course of Lectures. — I hope not, says Lady Caro^ line, with some emotion. Why, returned the Philosoper, we have taken acursory view of natural bodies, and their causes and ef- 136 Of the Five Senses of Man, fects ; which I have endeavoured to explain in sucli a manner as to be intelligible at least, if not entertaining; and pray, what inore did you expect ? Sir, replied the Lady, I am greatly pleased with the account you have given us ; and I thank you for the pains you have taken to answer the many questions I have troubled you with. What I had further to hope, was that you would liave given us, when you were on the subject of Animals, some strictures on the cruelty with which they are too often treated ; and have thrown in reflections and observations tend- ing to enforce on mankind a different con- duct. This I wished for, and should have been glad to have Mr. Thomas and his La- dy here at the same time, who are both ex- tremely fond of their little domestic crea- tures ; and I admire them for their tender- ness and compassion. — These feelings and sentiments of the human heart. Madam, says the Philosopher, add much to the digni- ty of our nature ; and I am greatly delighted with such behaviour ; but 1 am afraid, La- dy Caroline, that we often mistake charac- ters of this kind, and take that for humanity and tenderness which is only the effect of fancy or self-love. That Mr. Thomas has compassion, I grant you ; but I am afraid and qf his Uiider standing, 137 it is only for himself. He loves his dogs and horses, because his dogs and horses give him pleasure, but to other creatures that afford him none, he is absolutely insen- sible. I have seen him, even at Christmas, feed his pretty pups, as he calls them, with delicacies ; but rave at the same time in a merciless manner, at poor children who were shivering at his gate, and send them away empty-handed. Our neighbour, Mr. Williams, is also of the same disposition : he will not sell a horse that is declining, for fear he should fall into the hands of a mas- ter who might treat him with cruelty ; but he is largely concerned in the slave-trade (which I think is carried on by none but us good christains, to the dishonour of our ce- lestial Master) and makes no difficulty of separating the husband from the wife, the parents fi'om the children, and all of them from their native country, to be sold in a foreign market, like so many horses, and often to the most merciless of the human race. Is this humanity. Madam? Is this morality ? But above all, is this Christianity ? And are these the blessed effects of the li- berty we boast of ? But do not let us be misled by specious pretences. We cannot judge of any man, Madam, by one single 138 Of the Five Senses of Man, action, but by the tenor and result of all his actions ; and this requires deep penetration, and an intimate knowledge of human life. Benevolence, Lady Caroline, should be universal, for it is an emanation of the Su* preme Being, whose mercy and goodness are extended to all his creatures, as ours also should be ; for they are fellow-tenants with us of the globe we inhabit. I have often thought that most of the mis- chiefs which embarrass society, and render one contemptible to another, are owing to inordinate ambition, or extreme love of power and wealth ; for all the gold a man pos- sesses, beyond that portion which is requi- site for himself and family, only serves to inflame his ambition ; as all the wine we drink, more than is necessary to recruit the drooping spirits, answers no other purpose but to intoxicate the mind. I have seen a book in my papa's library, which gives some account of one Lycurgus, an old Grecian lawgiver ; with whose cha- racter you ought to be acquainted. This man was of opinion, that religion, virtue, and good manners, were the only natural cements, and preservation of liberty, peace, and friendship ; which he found had been destroyed and extirpated by means of wealth and of his Understanding. 139 and self-interest : he therefore prohibited the use of gold and silver, and all kinds of lux- ury in the state, and established such a plan for the education of youth of ^yery deno- mhiation, as was most likely to confirm and liabituate them in the practice of religion and virtue, and secure to the Spartans and their posterity the blessings of liberty and peace. The event proved that his institutions were founded on sound policy, and a per- fect knowledge of human nature ; for in the space of five hundred years, that is to say, from the time of Lycurgus to the introduc- tion of wealth into the state of Lysander in the reign of the first Agis, there was no mutiny among the people; every man submitted cheerfully to the laws of Ly- curgus, and all were so united and power' ful m consequence of their virtue, sobriety and the martial discipline he had established (which was that of a national militia) that bparta, a very small and inconsiderable state not only gave laws to the rest of Greece but made even the Persian monarchs tremble, though masters of the richest and most ex tensive empire in the world. But ivhen this great and virtuous people of Sparta had conquered Athens, and from thence intro! duced wealth and luxury into their ow. liO Of the Five Senses of Man, Wc. country, they lost their virtue, dwindled to nothing, and were themselves enslaved. Nor is this a matter of wonder ; for where religion and virtue are set at a distance, and wealth leads the waj to posts of honour -and trust, some people will stick at nothing to obtain gold ; but were dignities of this kind conferred on the most deserving, and none but men of virtue and superior abilities pro- moted to places of trust and power, there would be no frauds in the state, or violence Umong the people ; and we might then hope to enjoy the felicities of the Golden Age. Man in that age no rule but reason knew, And with a native bent did good pursue ; Unaw'd by punishment, and void of fear. His words were simple, and his soul sincere. By no forc'd laws his passions were confin'd, . For Conscience kept his heart, and calm'd his mind ; Peace o'er the world her blessed sway maintained) And e'en in desarts smiling Plenty reign'd. FINIS. DIRECTIONS TO THE BINDER. Sronthp'icce '^ f^^e tic Titl* Lecture on Matter and Motion p^g^ 6 Solar System 5* Mount f^esuvius *^^ tafriage f red by Miction '3^ ai63 1 Jr ab*-**^*" iJ^ft^ v*Wb. y^ m "- ^1 -^ ^^H ki \' ^vl \ -%