first Endeavour of the Movent which Endeavour how weak soever is also Motion For if it have no Effect at all neither will it do any thing though doubled trebled or by what number soever multiplied For Nothing though multiplied is still Nothing Other Axiomes and Definitions we will take in as we need them by the way A. Is this all the preparation I am to make B. No you are to consider also the several kinds and properties of Motion viz. when a Body being moved by one or more Movents at once in what way it is carried straight circular or otherwise crooked and what degree of swiftness as also the action of the Movent whether Trusion Vection Percussion Reflexion or Refraction and further you must furnish your self with as many experiments which they call Phaenomenon as you can And supposing some Motion for the Cause of your Phaenomenon try if by evident Consequence without contradiction to any other manifest truth or experiment you can derive the Cause you seek for from your Supposition If you can 't is all that is expected as to that one Question from Philosophy For there is no Effect in Nature which the Author of Nature cannot bring to pass by more ways than one A. What I want of Experiments you may supply out of your own store or such Natural History as you know to be true though I can be well content with the knowledge of the Causes of those things which every Body sees commonly produced Let us therefore now enquire the Cause of some Effect particular B. We will begin with that which is the most universal the Universe and enquire in the first place if any place be absolutely empty that is to say in the language of Philosophers whether there be any Vacuum in Nature CAP. III. Of Vacuum A. 'T Is hard to suppose and harder to believe that the Infinite and Omnipotent Creator of all things should make a work so vast as is the world we see and leave a few little spaces with nothing at all in them which put altogether in respect of the whole Creature would be insensible B. Why say you that Do you think any Argument can be drawn from it to prove there is Vacuum A. Why not For in so great an Agitation of Natural Bodies may not some small parts of them be cast out and leave the places empty from whence they were thrown B. Because he that created them is not a Fancy but the most real substance that is who being Infinite there can be no place empty where he is nor full where he is not A. 'T is hard to answer this Argument because I do not remember that there is any Argument for the maintenance of Vacuum in the writings of Divines Therefore I will quit that Argument and come to another If you take a Glass Vial with a narrow neck and having suckt it dip it presently at the neck into a bason of water you shall manifestly see the water rise into the Vial. Is not this a certain signe that you had suckt out some of the Air and consequently that some part of the Vial was left empty B. No For when I am about to suck and have Air in my mouth contracting my Cheeks I drive the same against the Air in the Glass and thereby against every part of the sides of the hard Glass And this gives to the Air within an Endeavour outward by which if it be presently dipt into the water it will penetrate and enter into it For Air if it be prest will enter into any Fluid much more into water Therefore there shall rise into the Vial so much water as there was Air forced into the Bason A. This I confess is possible and not improbable B. If sucking would make Vacuum what would become of those women that are Nurses Should they not be in a very few days exhausted were it not that either the Air which is in the Childs mouth penetrateth the Milk as it descends and passeth through it or the Breast is contracted A. From what Experiment can you evidently infer that there is no Vacuum B. From many and such as to almost all men are known and familiar If two hard Bodies flat and smooth be joyned together in a common Superficies parallel to the Horizontal Plain you cannot without great force pull them asunder if you apply your force perpendicularly to the common Superficies But if you place that common Superficies erect to the Horizon they will fall asunder with their own weight From whence I argue thus Since their Contiguity in what posture soever is the same and that they cannot be pull'd asunder by a perpendicular force without letting in the ambient Air in an instant which is impossible or almost in an instant which is difficult and on the other side when the common Superficies is erect the weight of the same hard Bodies are able to break the Contiguity and let in the Air successively it is manifest that the difficulty of Separation proceeds from this that neither Air nor any other Body can be moved to any how small soever distance in an instant but may easily be moved the hardness at the sides once mastered successively So that the Cause of this difficulty of Separation is this that they cannot be parted except the Air or other matter can enter and fill the space made by their diremption And if they were infinitely hard not at all And hence also you may understand the Cause why any hard Body when it is suddenly broken is heard to crack which is the swift Motion of the Air to fill the space between Another Experiment and commonly known is of a Barrel of Liquor whose Tap-hole is very little and the Bung so stopt as to admit no Air for then the Liquor will not run but if the Tap-hole be large it will because the Air prest by a heavier Bodie will pierce through it into the Barrel The like reason holds of a Gardeners Watering-pot when the holes in the bottom are not too great A third Experiment is this Turn a thin Brass kettle the bottom upwards and lay it flat upon the Water It will sink till the water rise within to a certain height but no higher Yet let the bottom be perforated and the Kettle will be full and sink and the Air rise again through the water without But if a Bell were so laid on it would be fill'd and sink though it were not perforated because the weight is greater than the weight of the same bulk of water A. By these Experiments without any more I am convinced that there is not actually in Nature any Vacuum but I am not sure but that there may be made some little place empty and this from two Experiments one whereof is Torricellius his Experiment which is this Take a Cylinder of Glass hollow throughout but close at the end in form of a Sack B. How long A. As long as you will so it be
think you must happen to the Sea which resteth on it and is a Fluid Body A. I think it must make the Sea rise and fall And the same happeneth also to the Air from the Motion of the Sun B. Remember also in what manner the Sea is situated in respect of the Dry Land A. Is not there a great Sea that reacheth from the Straight of Magellan Eastward to the Indies and thence to the same Straight again And is not there a great Sea called the Atlantick Sea that runneth Northward to us and does not the great South-Sea run also up into the Northern Seas But I think the Indian and the South-Sea of themselves to be greater than all the rest of the Surface of the Globe B. How lieth the water in those two Seas A. East and West and rises and falls a little as it is forc'd to do by this compounded Motion which is a kind of succussion of the Earth and fills both the Atlantick and Northern Seas B. All this would not make a visible difference between High and Low water because this Motion being so regular the unevenness would not be great enough to be seen For though in a Bason the water would be thrown into the Air yet the Earth cannot throw the Sea into the Air. A. Yes The Bason if gently moved will make the water so move that you shall hardly see it rise B. It may be so But you should never see it rise as it doth if it were not checkt For at the Straight of Magellan the great South-Sea is checkt by the shore of the Continent of Peru and Chily and forced to rise to a great height and made to run up into the Northern Seas on that side by the coast of China and at the return is checkt again and forced through the Atlantick into the British and German Seas And this is done every day For we have supposed that the Earths Motion in the Ecliptique caused by the Sun is Annual and that its Motion in the Aequinoctial is Diurnal It followeth therefore from this compounded Motion of the Earth the Sea must Ebb and Flow twice in the space of Twenty four hours or thereabout A. Has the Moon nothing to do in this business B. Yes For she hath also the like Motion And is though less swift yet much neerer to the Earth And therefore when the Sun and Moon are in Conjunction or Opposition the Earth as from two Agents at once must needs have a greater Succussion And if it chance at the same time the Moon also be in the Ecliptique it will be yet greater because the Moon then worketh on the Earth less obliquely A. But when the Full or New Moon happen to be then when the Earth is in the Aequinoctial points the Tides are greater than ordinary Why is that B. Because then the force by which they move the Sea is at that time to the force by which they move the same at other times as the Aequinoctial Circle to one of its Parallels which is a lesser Circle A. 'T is evident And 't is pleasant to see the Concord of so many and various motions when they proceed from one and the same Hypothesis But what say you to the stupendious Tides which happen on the Coasts of Lincolnshire on the East and in the River of Severn on the West B. The cause of that is their proper Scituation For the Current of the Ocean through the Atlantick Sea and the Current of the South-Sea through the Northern Seas meeting together raise the water in the Irish and British Seas a great deal higher than ordinary Therefore the mouth of the Severn being directly opposite to the Current from the Atlantick Sea and those Sands on the Coast of Lincolnshire directly opposite to the Current of the German Sea those Tides must needs fall furiously into them by this Succussion of the water A. Does when the Tide runs up into a River the water all rise together and fall together when it goes out No One part riseth and another falleth at the same time because the Motion of the Earth rising and falling is that which makes the Tide A. Have you any Experiment that shews it B. Yes You know that in the Thames it is high water at Greenwich before it is high water at London-bridge The water therefore falls at Greenwich whilst it riseth all the way to London But except the top of the water went up and the lower part downward it were impossible A. 'T is certain It is strange that this one Motion should salve so many apparences and so easily But I will produce one Experiment of water not in the Sea but in a Glass If you can shew me that the cause of it is this compounded Motion I shall go neer to think it the Cause of all other Effects of Nature hitherto disputed of The Experiment is common and described by the Lord Chancellour Bacon in the third page of his Natural History Take saith he a Glass of water and draw your finger round about the lip of the Glass pressing it somewhat hard after you have done so a few times it will make the water frisk up into a fine Dew After I had read this I tried the same with all diligence my self and found true not onely the frisking of the water to above an inch high but also the whole Superficies to circulate and withal to make a pleasant sound The Cause of the frisking he attributes to a tumult of the inward parts of the Substance of the Glass striving to free it self from the pressure B. I have tried and found both the Sound and Motion and do not doubt but the pressure of the parts of the Glass was part of the Cause But the Motion of my finger about the Glass was always parallel and when it chanced to be otherwise both Sound and Motion ceased A. I found the same And being satisfied I proceed to other questions How is the water being a heavie Body made to ascend in small particles into the Air and be there for a time sustained in form of a Cloud and then fall down again in Rain B. I have shewn already that this compounded Motion of the Sun in one part of its Circumlation drives the Air one way and in the other part the contrary way and that it cannot draw it back again no more than he that sets a stone a flying can pull it back The Air therefore which is contiguous to the water being thus distracted must either leave a Vacuum or else some part of the water must rise and fill the spaces continually forsaken by the Air. But that there is no Vacuum you have granted Therefore the water riseth into the Air and maketh the Clouds and seeing they are very small and invisible parts of the water are though naturally heavie easily carried up and down with the Wind till meeting with some Mountain or other Clouds they be prest together into greater drops and
Licensed May 26. 1677. Ro. L'strange Decameron Physiologicum OR TEN DIALOGUES OF NATURAL Philosophy By THOMAS HOBBES of Malmsbury To which is added The Proportion of a straight Line to half the Arc of a Quadrant By the same AUTHOR LONDON Printed by J. C. for W. Crook at the Green Dragon without Temple-Bar 1678. The Contents Dial. 1. OF the Original of Natural Philosophy Pag. 1. 2. Of the Principles and Method of Natural Philosophy p. 14. 3. Of Vacuum p. 23. 4. Of the Systeme of the World p. 31. 5. Of the Motions of Water and Air. p. 46. 6. Of the Causes and Effects of Heat and Cold. p. 58. 7. Of Hard and Soft and of the Atomes that fly in the Air. p. 72. 8. Of Gravity and Gravitation p. 84. 9. Of the Loadstone and its Poles and whether they shew the Longitude of Places on the Earth p. 104. 10. Of Transparence Refraction and of the Power of the Earth to produce living Creatures p. 121. The Proportion of a straight Line to half the Arc of a Quadrant by the same Author p. 133. CAP. I. Of the Original of Natural Philosophy A. I Have heard exceeding highly commended a kinde of thing which I do not well understand though it be much talkt of by such as have not otherwise much to do by the name of Philosophy And the same again by others as much despised and derided So that I cannot tell whether it be good or ill nor what to make of it though I see many other men that thrive by it B. I doubt not but what so many do so highly praise must be very admirable and what is derided and scorn'd by many foolish and ridiculous The honour and scorn falleth finally not upon Philosophy but upon the Professors Philosophy is The knowledge of Natural Causes And there is no Knowledge but of Truth And to know the true Causes of things was never in contempt but in admiration Scorn can never fasten upon Truth But the difference is all in the Writers and Teachers Whereof some have neither studied nor care for it otherwise than as a Trade to maintain themselves or gain Preferment and some for Fashion and to make themselves fit for ingenious Company and their study hath not been meditation but acquiescence in the Authority of those Authors whom they have heard commended And some but few there be that have studied it for Curiosity and the delight which commonly men have in the acquisition of Science and in the mastery of difficult and subtil Doctrines Of this last sort I count Aristotle and a few others of the Ancients and some few Moderns and to these it is that properly belong the Praises which are given to Philosophy A. If I have a minde to study for example Natural Philosophy must I then needs read Aristotle or some of those that now are in request B. There 's no necessity of it But if in your own meditation you light upon a difficulty I think 't is no loss of time to enquire what other men say of it but to rely onely upon Reason For though there be some few Effects of Nature especially concerning the Heavens whereof the Philosophers of old time have assigned very rational Causes such as any man may acquiesce in as of Eclipses of the Sun and Moon by long observation and by the Calculation of their visible Motions yet what is that to the numberless and quotidian Phaenomena of Nature Who is there amongst them or their Successors that has satisfied you with the Causes of Gravity Heat Cold Light Sense Colour Noise Rain Snow Frost Winds Tides of the Sea and a thousand other things which a few mens lives are too short to go through and which you and other curious Spirits admire as quotidian as they are and fain would know the Causes of them but shall not finde them in the Books of Naturalists and when you ask what are the Causes of any of them of a Philosopher now he will put you off with mere words which words examined to the bottom signifie not a jot more than I cannot tell or Because it is Such as are Intrinsecal quality Occult quality Sympathy Antipathy Antiperistasis and the like Which pass well enough with those that care not much for such wisdom though wise enough in their own ways but will not pass with you that ask not simply what 's the Cause but in what manner it comes about that such Effects are produced A. That 's Cozening What need had they of that When began they thus to play the Charletants B. Need had they none But know you not that men from their very birth and naturally scramble for every thing they covet and would have all the world if they could to fear and obey them If by fortune or industry one light upon a Secret in Nature and thereby obtain the credit of an extraordinary Knowing man should he not make use of it to his own benefit There is scarce one of a thousand but would live upon the charges of the people as far as he dares What poor Geometrician is there but takes pride to be thought a Conjurer what Mountebank would not make a living out of a false opinion that he were a great Physician And when many of them are once engaged in the maintenance of an Errour they will joyn together for the saving of their Authority to decry the Truth A. I pray tell me if you can how and where the study of Philosophy first began B. If we may give Credit to old Histories the first that studyed any of the Natural Sciences were the Astronomers of Aethiopia My Author is Diodorus Siculus accounted a very faithful Writer who begins his History as high as is possible and tells us that in Aethiopia were the first Astronomers and that for their Predictions of Eclipses and other Conjunctions and Aspects of the Planets they obtained of their King not onely Towns and Fields to a third part of the whole Land but were also in such veneration with the People that they were thought to have discourse with their Gods which were the Stars and made their Kings thereby to stand in awe of them that they durst not either eat or drink but what and when they prescribed no nor live if they said the Gods commanded them to die And thus they continued in subjection to their false Prophets till by one of their Kings called Ergamenes about the time of the Ptolemies they were put to the Sword But long before the time of Ergamenes the Race of these Astrologers for they had no Disciples but their own Children was so numerous that abundance of them whether sent for or no I cannot tell transplanted themselves into Egypt and there also had their Cities and Lands allowed them and were in request not onely for Astronomy and Astrologie but also for Geometry And Egypt was then as it were an University to all the world and thither went the curious Greeks as Pythagoras
Plato Thales and others to fetch Philosophy into Greece But long before that time abundance of them went into Assyria and had their Towns and Lands assigned them also there and were by the Hebrews called Chaldies A. Why so B. I cannot tell but I finde in Martinius Lexicon they were called Chasdim and Chesdim and as he saith from one Chesed the son of Nachor but I finde no such man as Chesed amongst the issue of Noah in the Scripture Nor do I finde that there was any certain Country called Chaldaea though a Town where any of them inhabited were called A Town of the Chaldies Martinius saith further that the same word Chasdim did signifie also Demons A. By this reckoning I should conjecture they were called Chusdim as being a Race of Ethiopians For the Land of Chus is Aethiopia and so the name degenerated first into Chuldim and then into Chaldim so that they were such another kinde of people as we call Gypsies saving that they were admired and feared for their Knavery and the Gypsies counted Rogues B. Nay pray except Claudius Ptolomaeus Author of that great Work of Astronomy the Almegest A. I grant he was excellent both in Astronomy and Geometry and to be commended for his Almegest but then for his Judiciar Astrologie annexed to it he is again a Gypsie But the Greeks that travelled you say into Egypt what Philosophy did they carry home B. The Mathematiques and Astronomy But for that sublunary Physiques which is commonly called Natural Philosophy I have not read of any Nation that studied it earlier than the Greeks from whom it proceeded to the Romans Yet both Greeks and Romans were more addicted to Moral than to Natural Philosophy in which kinde we have their Writings but loosly and incoherently written upon no other Principles than their own Passions and Presumptions without any respect to the Laws of Common-wealth which are the ground and measure of all true Morality So that their Books tend rather to teach men to censure than to obey the Laws Which has been a great hinderance to the Peace of the Western world ever since But they that seriously applied themselves to Natural Philosophy were but few as Plato and Aristotle whose Works we have and Epicurus whose Doctrine we have in Lucretius The Writings of Philolaus and many other curious Students being by fire or negligence now lost though the Doctrine of Philolaus concerning the Motion of the Earth have been revived by Copernicus and explained and confirmed by Galileo now of late A. But methinks the Natural Philosophy of Plato and Aristotle and the rest should have been cultivated and made to flourish by their Disciples B. Whom do you mean the Successors of Plato Epicurus Aristotle and the other first Philosophers It may be some of them may have been learned and worthy men But not long after and down to the time of our Saviour and his Apostles they were for the most part a sort of needy ignorant impudent cheating fellows who by the profession of the Doctrine of those first Philosophers got their living For at that time the name of Philosophy was so much in fashion and honour amongst great persons that every rich man had a Philosopher of one Sect or another to be a Schoolmaster to his Children And these were they that faining Christianity with their disputing and readiness of talking got themselves into Christian Commons and brought so many Heresies into the Primitive Church every one retaining still a tang of what they had been us'd to teach A. But those Heresies were all condemned in the first Council of Nice B. Yes But the Arrian Heresie for a long time flourished no less than the Roman and was upheld by divers Emperours and never fully extinguished as long as there were Vandals in Christendom Besides there arose daily other Sects opposing their Philosophy to the Doctrine of the Councils concerning the Divinity of our Saviour as how many Persons he was how many Natures he had And thus it continued till the time of Charlemain when he and Pope Leo the third divided the Power of the Empire into Temporal and Spiritual A. A very unequal division B. Why Which of them think you had the greater share A. No doubt the Emperour For he onely had the Sword B. When the Swords are in the hands of men whether had you rather command the Men or the Swords A. I understand you For he that hath the hands of the Men has also the use both of their Swords and strength B. The Empire thus divided into Spiritual and Temporal the freedom of Philosophy was to the power Spiritual very dangerous And for that cause it behoved the Pope to get Schools set up not onely for Divinity but also for other Sciences especially for Natural Philosophy Which when by the power of the Emperour he had effected out of the mixture of Aristotle's Metaphysicks with the Scripture there arose a new Science called School-Divinity which has been the principal Learning of these Western parts from the time of Charlemain till of very late A. But I finde not in any of the Writings of the School-men in what manner from the causes they assigne the Effect is naturally and necessarily produced B. You must not wonder at that For you enquire not so much when you see a change of any thing what may be said to be the cause of it as how the same is generated which generation is the entire progress of Nature from the efficient cause to the Effect produced Which is always a hard Question and for the most part impossible for a man to answer to For the alterations of the things we perceive by our five Senses are made by the motion of Bodies for the most part either for distance smalness or transparence invisible A. But what need had they then to assigne any cause at all seeing they could not shew the Effect was to follow from it B. The Schools as I said were erected by the Pope and Emperour but directed by the Pope onely to answer and confute the Heresies of the Philosophers Would you have them then betray their Profession and Authority that is to say their Livelihood by confessing their ignorance Or rather uphold the same by putting for causes strange and unintelligible words which might serve well enough not onely to satisfie the people whom they relied on but also to trouble the Philosophers themselves to finde a fault in A. Seeing you say that Alteration is wrought by the Motion of Bodies pray tell me first what I am to understand by the word Body B. It is a hard Question though most men think they can easily answer it as that it is whatsoever they can see feel or take notice of by their Senses But if you will know indeed what is body we must enquire first what there is that is not Body You have seen I suppose the Effects of Glasses how they multiply and magnifie the Object of our sight as when
a Glass of a certain Figure will make a Counter or a Shilling seem twenty though you be well assured there is but one And if you set a mark upon it you will finde the mark upon them all The Counter is certainly one of those things we call Bodies Are not the others so too A. No without doubt For looking through a Glass cannot make them really more than they are B. What then be they but fancies so many fancies of one and the same thing in several places A. 'T is manifest they are so many Idols mere Nothings B. When you have look'd upon a Star or Candle with both your eyes but one of them a little turn'd awry with your finger has not there appeared two Stars or two Candles And though you call it a deception of the sight you cannot deny but there were two Images of the Object A. 'T is true and observed by all men And the same I say of our faces seen in Looking-glasses and of all Dreams and of all Apparitions of dead mens Ghosts and wonder since 't is so manifest I never thought upon 't before for it is a very happy encounter and such as being by every body well understood would utterly destroy both Idolatry and Superstition and defeat abundance of Knaves that cheat and trouble the world with their devices B. But you must not hence conclude that whosoever tells his Dream or sometimes takes his direction from it is therefore an Idolater or Superstitious or a Cheater For God doth often admonish men by Dreams of what they ought to do yet men must be wary in this case that they trust not Dreams with the conduct of their lives further than by the Laws of their Country is allow'd For you know what God says Deut. 13. If a Prophet or a Dreamer of Dreams give thee a signe or a wonder and the signe come to pass yet if he did thee serve other Gods let him be put to death Here by serving other Gods since they had chosen God for their King we are to understand revolting from their King or disobeying of his Laws Otherwise I see no Idolatry nor Superstition in following a Dream as many of the Patriarches in the Old Testament and of the Saints in the New Testament did A. Yes Their own Dreams But when another man shall dream or say that he has dream'd and require me to follow that he must pardon me if I ask him by what Authority especially if he look I should pay him for it B. But if commanded by the Laws you live under you ought to follow it But when there proceed from one Sound divers Echoes what are those Echoes And when with fingers cross'd you touch a small Bullet and think it two and when the same Herb or Flower smells well to one and ill to another and the same at several times well and ill to your self and the like of Tastes what are those Echoes Feelings Odours and Tastes A. 'T is manifest they are all but Fancies But certainly when the Sun seems to my eye no bigger than a Dish there is behinde it somewhere somewhat else I suppose a real Sun which creates those fancies by working one way or other upon my eyes and other Organs of my Senses to cause that diversity of Fancy B. You say right and that is it I mean by the word Body which briefly I define to be any thing that hath a Being in it self without the help of Sense A. Aristotle I think meaneth by Body Substance or Subjectum wherein Colour Sound and other Fancies are as he says inherent For the word Essence has no affinity with Substance And Seneca says he understands it not And no wonder for Essence is no part of the Language of mankinde but a word devised by Philosophers out of the Copulation of two names as if a man having two Hounds could make a third if 't were need of therâ— Couples B. 'T is just fo For having said in themselves for example A Tree is a Plant and conceiving well enough what is the signification of those Names knew not what to make of the word Is that couples those Names nor daring to call it a Body they called it by a new name derived from the word est Essentia and Substantia deceived by the Idiome of their own Language For in many other Tongues and namely in the Hebrew there is no such Copulative They thought the Names of things sufficiently connected when they are placed in their natural consequence and were therefore never troubled with Essences nor other Fallacy from the Copulative Est. CAP. II. Of the Principles and Method of Natural Philosophy A. THis History of the old Philosophers has not put me out of love but out of hope of Philosophy from any of their Writings I would therefore try if I could attain any knowledge therein by my own meditation But I know neither where to begin nor which way to proceed B. Your desire you say is to know the Causes of the Effects or Phaenomena of Nature and you confess they are Fancies and consequently that they are in your self so that the Causes you seek for onely are without you and now you would know how those external Bodies work upon you to produce those Phaenomena The beginning therefore of your enquiry ought to be at What it is you call a Cause I mean an Efficient Cause For the Philosophers make four kindes of Causes whereof the Efficient is one Another they call the Formal Cause or simply the form or essence of the thing caused as when they say Four equal Angles and four equal Sides are the Cause of a Square Figure or that Heaviness is the Cause that makes heavie Bodies to descend But that 's not the Cause you seek for nor any thing but this It descends because it descends The third is the Material Cause as when they say The Walls and Roof c. of a house are the cause of a House The fourth is the Final Cause and hath place onely in Moral Philosophy A. We will think of Final Causes upon some other occasion of Formal and Material not at all I seek onely the Efficient and how it acteth from the beginning to the production of the Effect B. I say then that in the first place you are to enquire diligently into the nature of Motion For the variations of Fancies or which is the same thing of the Phaenomena of Nature have all of them one Universal Efficient Cause namely the variety of Motion For if all things in the world were absolutely at rest there could be no variety of Fancy but living Creatures would be without sense of all Objects which is little less than to be dead A. What if a Childe new taken from the Womb should with open eyes be exposed to the Azure-Sky do not you think it would have some sense of the Light but that all would seem unto him Darkness B. Truly if he had no memory of any
thing formerly seen or by any other sense perceived which is my supposition I think he would be in the dark For Darkness is Darkness whether it be black or blue to him that cannot distinguish A. Howsoever that be it is evident enough that whatsoever worketh is moved for Action is Motion B. Having well considered the nature of Motion you must thence take your Principles for the foundation and beginning of your Enquiry A. As how B. Explain as fully and as briefly as you can what you constantly mean by Motion which will save your self as well as others from being seduced by Aequivocation A. Then I say Motion is nothing but change of place For all the Effect of a Body upon the Organs of our Senses is nothing but Fancy Therefore we can fancy nothing from seeing it moved but change of place B. 'T is right But you must then tell me also what you understand by Place For all men are not yet agreed on that A. Well then seeing we fancy a Body we cannot but fancy it somewhere And therefore I think Place is the fancy of Here or There B. That is not enough Here and There are not understood by any but your self except you point towards it But pointing is no part of a Definition Besides though it help him to finde the Place it will never bring him to it A. But seeing Sense is Fancy when we fancy a Body we fancy also the Figure of it and the space it fills up And then I may define Place to be The precise space within which the Body is contained For Space is also part of the Image we have of the Object seen B. And how define you Time A. As Place is to a Body so I think is Time to the Motion of it and consequently I take Time to be our fancy or Image of the Motion But is there any necessity of so much niceness B. Yes The want of it is the greatest if not the onely cause of all the discord amongst Philosophers as may easily be perceived by their abusing and confounding the names of things that differ in their nature as you shall see when there is occasion to recite some of the Tenets of divers Philosophers A. I will avoid Aequivocation as much as I can And for the nature of Motion I suppose I understand it by the Definition What is next to be done B. You are to draw from these Definitions and from whatsoever Truth else you know by the light of Nature such general Consequences as may serve for Axiomes or Principles of your Ratiocination A. That is hard to do B. I will draw them my self as many as for our present discourse of Natural Causes we shall have need of so that your part will be no more than to take heed I do not deceive you A. I will look to that B. My first Axiome then shall be this Two Bodies at the same Time cannot be in one Place A. That 's true For we number Bodies as we fancy them distinct and distinguish them by their Places You may therefore adde Nor one Body at the same time in two Places And Philosophers mean the same when they say There is no penetration of Bodies B. But they understand not their own words For penetration signifies it not My second Axiome is That nothing can begin change or put an end to its own Motion For supposing it begin just now or being now in Motion change its Way or Stop I require the Cause why now rather than before or after having all that is necessary to such Motion Change or Rest alike at all times A. I do not doubt but the Argument is good in Bodies inanimate but perhaps in Voluntary Agents it does not hold B. How it holds in Voluntary Agents we will then consider when our Method hath brought us to the Powers and Passions of the minde A third Axiome shall be this Whatsoever Body being at Rest is afterwards moved hath for its Immediate Movent some other Body which is in Motion and toucheth it For since nothing can move it self the Movent must be external And because Motion is change of place the Movent must put it from its place which it cannot do till it touch it A. That is manifest and that it must more than touch it it must also follow it And if more parts of the Body are moved than are by the Movent touched the Movent is not Immediate And by this reason a continued Body though never so great if the first Superficies be prest never so little back the Motion will proceed through it B. Do you think that to be impossible I will prove it from your own words For you say that the Movent does then touch the Body which it moveth Therefore it puts it back But that which is put back puts back the next behinde and that again the next and so onward to any distance the body being continued The same is also manifest by experience seeing one that walks with a Staff can distinguish though blinde between Stone and Glass which were impossible if the parts of his Staff between the ground and his hand made no resistance So also he that in the silence of the night lays his Ear to the ground shall hear the treading of mens feet further than if he stood upright A. This is certainly true of a Staff or other hard Body because it keeps the Motion in a straight Line from diffusion But in such a Fluid Body as the Air which being put back must fill an Orb and the further it is put back the greater Orb the Motion will decrease and in time by the resistance of Air to Air come to an end B. That any Body in the world is absolutely at Rest I think not true But I grant that in a space filled every where with Body though never so Fluid if you give Motion to any part thereof that Motion will by resistance of the parts moved grow less and less and at last cease but if you suppose the space utterly void and nothing in it then whatsoever is once moved shall go on eternally Or else that which you have granted is not true viz. That nothing can put an end to its own Motion A. But what mean you by resistance B. Resistance is the Motion of a Body in a way wholly or partly contrary to the way of its Movent and thereby repelling or retarding it As when a man runs swiftly he shall feel the Motion of the Air in his face But when two hard Bodies meet much more may you see how they abate each others Motion and rebound from one another For in a space already full the Movent cannot in an instant be communicated through the whole depth of the Body that is to be moved A. What other Definitions have I need of B. In all Motion as in all Quantity you must take the beginning of your reckoning from the least supposed Motion And this I call the
ask concerning Gravity If Gravity be as some define it an intrinsecal quality whereby a Body descendeth towards the Center of the Earth how is it possible that a piece of Iron that hath this intrinsecal quality should rise from the Earth to go to a Loadstone Hath it also an intrinsecal quality to go from the Earth It cannot be The Cause therefore must be extrinsecal And because when they are come together in the Air if you leave them to their own nature they will fall down together they must also have some like extrinsecal Cause And so this magnetique vertue will be such another vertue as makes all other heavy Bodies to descend in this our World to the Earth If therefore you can from this your Hypothesis of compounded Motion by which you have so probably salved the Problem of Gravity salve also this of the Loadstone I shall acknowledge both your Hypothesis to be true and your Conclusion to be well deduced B. I think it not impossible But I will proceed no further in it now than for the facilitating of the demonstrations to tell you the several proprieties of the Magnet whereof I am to shew the causes As first That Iron and no other Body at some little distance though heavy will rise to it Secondly That if it be laid upon a still Water in a floating Vessel and left to it self it will turn it self till it lye in a Meridian that is to say with one and the same Line still North and South Thirdly If you take a long slender piece of Iron and apply the Loadstone to it and according to the position of the Poles of the Loadstone draw it over to the end of the Iron the Iron will have the same Poles with the Magnet so it be drawn with some pressure but the Poles will lye in a contrary Position and also this long Iron will draw other Iron to it as the Magnet doth Fourthly This long Iron if it be so small as that poiz'd upon a Pin the weight of it have no visible Effect the Navigators use it for the Needle of their Compass because it points North and South saving that in most places by particular accidents it is diverted which diversion is called the variation of the Horizontal Needle Fifthly The same Needle placed in a Plain perpendicular to the Horizon hath another Motion called the Inclination Which that you may the better conceive draw a fourth Figure wherein let there be a Circle to represent the Terrella that is to say a Spherical Magnet A. Let this be it whose Center is A the North Pole B the South Pole C. B. Join B C and cross it at right Angles with the Diameter D E. A. 'T is done B. Upon the point D set the Needle parallel to B C with the cross for the South Pole and the Barb for the North and describe a Square about the Circle B D C E and divide the arch D B into four equal parts in a b c. A. 'T is done B. Then place the middle of the Needle on the points a b c so that they may freely turn and set the Barb which is at D toward the North and that which is at C towards the South You see plainly by this that the Angles of Inclination through the Arch D C taken all together are double to a Right Angle For when the South point of the Needle looking North as at D comes to look South as at C it must make half a Circle A. That is true And if you draw the Sine of the Arch D a which is d a and the Sine of the Arch B a which is a c and the Sine of the Arch D b which is b f and the Sine of the Arch B c which is c g the Needle will lye upon b f with the North-point downwards so that the Needle will be parallel to A D. Then from a draw the line a h making the Angle e a h equal to the Angle D A a. And then the Needle at a shall lye in the line a h with the South point toward h. Finally draw the line c h which with c g will also make a quarter of a right Angle and therefore if the Needle be plac'd on the point c it will lye in c h with the South point toward h. And thus you see by what degrees the Needle inclines or dips under the Horizon more and more from D till it come to the North Pole at B where it will lye parallel to the Needle in D but with their Barbs looking contrary ways And this is certain by experience and by none contradicted B. You see then why the degrees of the Inclinatory Needle in coming from D to B are double to the degrees of a Quadrant It is found also by experience that Iron both of the Mine and of the Furnace put into a Vessel so as to float will lay it self if some accident in the Earth hinder it not exactly North and South And now I am from this compounded Motion supposed by Copernicus to derive the causes why a Loadstone draws Iron why it makes Iron to do the same why naturally it placeth it self in a parallel to the Axis of the Earth why by passing it over the Needle it changes its Poles and what is the cause that it inclines But it is your part to remember what I told you of Motion at our second meeting and what I told you of this compounded Motion supposed by Copernicus at our fourth meeting CAP. IX Of the Loadstone and its Poles and whether they shew the Longitude of places on the Earth A. I Come now to hear what Natural Causes you can assign of the vertues of the Magnet and first why it draws Iron to it and only Iron B. You know I have no other cause to assign but some local Motion and that I never approved of any argument drawn from Sympathy Influence Substantial Forms or Incorporeal Effluvia For I am not nor am accounted by my Antagonists for a Witch But to answer this Question I should describe the Globe of the Earth greater than it is at B in the first Figure but that the Terrella in the fourth Figure will serve our turn For 't is but calling B and C the Poles of the Earth and D E the Diameter of the Aequinoctial Circle and making D the East and E the West And then you must remember that the Annual Motion of the Earth is from West to East and compounded of a straight and circular Motion so as that every point of it shall describe a small Circle from West to East as is done by the whole Globe And let the Circles about a b c be three of those small Circles A. Before you go any further I pray you shew me how I must distinguish East and West in every part of this Figure For wheresoever I am on Earth suppose at London and see the Sun rise suppose in Cancer is not a
not declared in what that resistance consisteth B. I suppose it proceedeth from the Hardness A. But from thence it will follow that all Transparent Bodies that equally refract are equally Hard. Which I think is not true because the Refraction of Glass is not greater at least in comparison of their Hardnesses than that of Water B. I confess it Therefore I think we must take in Gravity to a Share in the production of this Refraction For I never considered Refraction but in Glass because my business then was only to find the Causes of the Phaenomena of Telescopes and Microscopes Let therefore A B in Fig. 7. be a hard and consequently a heavy Body And from above as from the Sun let C A be the line of Incidence and produced to D. And draw A E perpendicular to A B. It is manifest that the Hardness in A B shall turn the stream of the Light inwards toward A E suppose in the line A e. It is also evident that the Endeavour in B which is being heavy downward shall turn the stream again inward towards A E as in A b. Thus it is in Refraction from the Sun downwards In like manner if the light come from below as from a Candle in the point D the line of Incidence will be D A and produced will pass to C. And the resistance of the Hardness in A will turn the stream A C inward suppose into B l and make C l equal to D e. For passing into a thinner Medium it will depart from the perpendicular in an Angle equal to the Angle D A e by which it came nearer to it in A e. So also the resistance of the Gravity in the point A shall turn the stream of the Light into the line A i and make the Angle l A i equal to the Angle e A b. And thus you see in what manner though not in what proportion Hardness and Gravity conjoyn their resistance in the Causing of Refraction A. But you proved yesterday that a heavy Body does not Gravitate upon a Body equally heavy Now this A B has upper parts and lower parts and if the upper parts do not Gravitate upon the lower parts how can there be any Endeavour at all downward to contribute to the Refraction B. I told you yesterday that when a heavy Body was set upon another Body heavier or harder than it self the Endeavour of it downward was diverted another way but not that it was extinguished But in this case where it lyeth upon Air the first endeavour of the lowest part worketh downward For neither Motion nor Body can be utterly extinguished by a less than an Omnipotent power All Bodies as long as they are Bodies are in Motion one way or other though the farther it be communicated so much the less A. But since you hold that Motion is propagated through all Bodies how hard or heavy soever they be I see no Cause but that all Bodies should be Transparent B. There are divers Causes that take away Transparency First if the Body be not perfectly Homogeneous that is to say if the smallest parts of it be not all precisely of the same nature or do not so touch one another as to leave no Vacuum within it or though they touch if they be not as hard in the contact as in any other line For then the Refractions will be so changed both in their direction and in their strength as that no Light shall come through it to the Eye as in Wood and ordinary Stone and Metal Secondly The Gravity and hardness may be so great as to make the Angle refracted so great as the second Refraction shall not direct the beam of light to the Eye as if the Angle of Refraction were D A E the Refracted line would be perpendicular to A B and never come to the line A D in which is the Eye A. To know how much of the Refraction is due to the Hardness and how much to the Gravity I believe it is impossible though the Quantity of the whole be easily measured in a Diaphanous Body given And both you and Mr. Warner have demonstrated that as the Sine of the Angle Refracted in one Inclination is to the Sine of the Angle Refracted in another Inclination so is the Sine of one Inclination to the Sine of the Angle of the other Inclination Which Demonstrations are both published by Mersennus in the end of the first Volume of his Cogitata Physico-Mathematica But since there be many Bodies through which though there pass Light enough yet no Object appears through them to the Eye what is the reason of that B. You mean Paper For Paper-Windows will enlighten a Room and yet not show the Image of an Object without the Room But 't is because there are in Paper abundance of pores through which the Air passing moveth the Air within by the Reflections whereof any thing within may be seen And in the same Paper there are again as many parts not Transparent through which the Air cannot pass but must be reflected first to all parts of the Object and from them again to the Paper and at the Paper either reflected again or transmitted according as it falls upon Pores or not Pores so that the Light from the Object can never come together at the Eye A. There belongs yet to this Subject the Causes of the diversity of Colours But I am so well satisfied with that which you have written of it in the 24th Chapter of your Book de Corpore that I need not trouble you further in it And now I have but one Question more to ask you which I thought upon last night I have read in an antient Historian that Living Creatures after a great deluge were produced by the Earth which being then very soft there were bred in it it may be by the rapid Motion of the Sun many Blisters which in time breaking brought forth like so many Eggs all manner of living Creatures great and small which since it is grown hard it cannot do What think you of it B. It is true that the Earth produced the first living Creatures of all sorts but Man For God said Gen. 1. vers 24. Let the Earth produce every living Creature Cattle and creeping thing c. But then again ver 25. it is said that God made the Beast of the Earth c. So that it is evident that God gave unto the Earth that vertue Which vertue must needs consist in Motion because all Generation is Motion But Man though the same day was made afterward A. Why hath not the Earth the same vertue now Is not the Sun the same it was Or is there no Earth now soft enough B. Yes And it may be the Earth may yet produce some very small Living Creatures And perhaps Male and Female For the smallest Creatures which we take notice of do engender though they do not all by conjunction therefore if the Earth produce living Creatures at this day God did not absolutely rest from all his Works on the seventh day but as it is Cap. 2. ver 2. he rested from all the work he had made And therefore it is no harm to think that God worketh still and when and where and what he pleaseth Beside 't is very hard to believe that to produce Male and Female and all that belongs thereto as also the several and curious Organs of Sense and Memory could be the work of any thing that had not understanding From whence I think we may conclude that whatsoever was made after the Creation was a new Creature made by God no therwise than the first Creatures were excepting only Man A. They are then in an Errour that think there are no more different kinds of Animals in the World now than there were in the Ark of Noah B. Yes doubtless For they have no Text of Scripture from which it can be proved A. The Questions of Nature which I could yet propound are innumerable And since I cannot go through them I must give over somewhere and why not here For I have troubled you enough though I hope you will forgive me B. So God forgive us both as we do one another But forget not to take with you the Demonstration of a straight Line equal to an Arc of a Circle FINIS Fig. 1. Fig. 3. Fig. 4.