demonstrated to be impossible Besides you know when they have sucked out as they think all the Air from the Glass Globe they can nevertheless both see through it what is done and hear a sound from within when there is any made Which if there were no other but there are many other is argument enough that the place is still full of Air. A. What say you to the swelling of a Bladder even to bursting if it be a little blown when it is put into the Receiver for so they call the Globe of Glass B. The stream of Air that from every side meeting together and turning in an infinite number of small points do pierce the Bladder in innumerable places with great violence at once like so many invisible small wimbles especially if the Bladder be a little blown before it be put in that it may make a little resistance And when the Air has once pierced it it is easie to conceive that it must afterward by the same violent motion be extended till it break If before it break you let in fresh Air upon it the violence of the motion will thereby be tempered and the Bladder be less extended For that also they have observed Can you imagine how a Bladder should be extended and broken by being too full of Emptiness A. How come living creatures to be killed in this Receiver in so little a time as 3 or 4 minutes of an hour B. If they suck into their lungs so violent a wind thus made you must needs think it will presently stop the passage of their bloud and that is death though they may recover if taken out before they be too cold And so likewise will it put out fire but the Coals taken out whilst they are hot will revive again 'T is an ordinary thing in many Coal-pits whereof I have seen the experience that a wind proceeding from the sides of the Pit every way will extinguish any fire let down into it and kill the workmen unless they be quickly taken out A. If you put a vessel of water into the Receiver and then suck out the Air the water will boil What say you to that B. It is like enough it will dance in so great a bustling of the Air but I never heard it would be hot Nor can I imagine how Vacuum should make any thing dance I hope you are by this time satisfied that no experiment made with the Engine at Gresham Colledge is sufficient to prove that there is or that there may be Vacuum A. The World you know is finite and consequently all that infinite space without it is empty Why may not some of that Vacuum be brought in and mingled with the Air here B. I know nothing in matters without the World A. What say you to Torricellioes Experiment in Quick-silver which is this There is a Bason at A filled with Quick-silver suppose to B And CD a hollow glass pipe filled with the same Which if you stop with your finger at B and so set it upright and then if you take away your finger the Quick-silver will fall from C downwards but not to the bottom For it will stop by the way suppose at D. Is it not therefore necessary that that space between C and D be left empty Or will you say the Quick silver does not exactly touch the sides of the glass pipe B. I 'le say neither If a man thrust down into a vessel of Quick-silver a blown Bladder will not that Bladder come up to the top A. Yes certanly or a Bladder of Iron or of any thing else but Gold B. You see then that Air can pierce Quick-silver A. Yes with so much force as the weight of Quick-silver comes to B. When the Quick-silver is fallen to D there is so much the more in the bason And that takes up the place which so much Air took up before Whither can this Air go if all the World without that glass pipe B C were full There must needs be the same or as much Air come to that space which only is empty between C and D. By what force By the weight of the Quick-silver between D and B. Which Quick-silver weigheth now upward or else it could never have raised that part higher which was at first in the Bason So you see the weight of Quick-silver can press the Air through Quick-silver up into the pipe till it come to an equality of force as in D. Where the weight of the Quick-silver is equal to the force which is required in Air to go through it A. If a man suck a Vial that has nothing in it but Air and presently dip the mouth of it into water the water will ascend into the Vial. Is not that an argument that part of the Air had been sucked out and part of the room within the Vial left empty B. No. If there were empty space in the World why should not there be also some empty space in the Vial before it was sucked And then why does not the water rise to fill that when a man sucks the Vial he draws nothing out neither into his Belly not into his Lungs nor into his Mouth only he sets the Air within the glass into a circular motion giving it at once an endeavour to go forth by the sucking and an endeavour to go back by not receiving it into his mouth And so with a great deal of labour glues his lips to the neck of the Vial. Then taking it off and dipping the neck of the Vial into the water before the circulation cease the Air with the endeavour it hath now gotten pierces the water and goes out And so much Air as goes out so much matter comes up into the room of it CHAP. IIII. Problems of Heat and Light A. WHat is the cause of Heat B. How know you that any thing is Hot but your self A. Because I perceive by sense it Heats me B. It is no good argument The thing Heats me therefore it is Hot. But what alteration do you find in your body at any time by being Hot A. I find my skin more extended in Summer than in Winter and am sometimes fainter and weaker then ordinary as if my Spirits were exhaled and I sweat B. Then that is it you would know the cause of I have told you before that by the motion I suppose both in the Sun and in the Earth the Air is dissipated and consequently that there would be an infinite number of small empty places but that the World being full there comes from the next parts other Air into the spaces they would else make empty When therefore this motion of the Sun is excercised upon the Superficies of the Earth if there do not come out of the Earth it self some corporal substance to supply that tearing of the Air we must return again to the admission of Vacuum If there do then you see how by this motion fluid bodies are made to exhale out of the
equal B. The cause can be no other The smallest spark of Fire flying up seems a line drawn upward and again by that swift circular Motion which we have supposed for the cause of Light seems also broader then it is And consequently the Flame of every thing must needs seem much greater then it is A. What are those sparks that flie out of the Fire B. They are small pieces of the wood or Coals or other Fuel loosened and carried away with the Air that cometh up with them And being extiguished before their parts be quite dissipated into others are so much Soot and black and may be fired again A. A Spark of Fire may be stricken out of a cold stone It is not therefore Heat that makes this shining B. No 'T is the Motion that makes both the Heat and shining and the stroke makes the Motion For every of those Sparks is a little parcel of the stone which swiftly moved imprinteth the same Motion into the matter prepared or 〈◊〉 receive it A. How comes the Light of the Sun to burn almost any combustible matter by rerefraction through a convex glass and by reflection from a concave B. The Air moved by the Sun presseth the convex glass in such manner as the action continued through it proceedeth not in the same streight line by which it proceeded from the Sun but tendeth more toward the center of the body it enters Also when the action is continued through the convex body it bendeth again the same way By which means the whole action of the Sun-beams are enclosed within a very small compass in which place therefore there must be a very vehement Motion and consequently if there be in that place combustible matter such as is not very hard kindle the parts of it will be dissipated and receive that Motion which worketh on the Eye as other Fire does The same reason is to be given for burning by Reflection For there also the Beams are collected into almost a point A. Why may not the Sun-beams be such a Body as we call Fire and pass through the pores of the glass so disposed as to cary them to a point or very near B. Can there be a glass that is all pores If there cannot then cannot this effect be produced by the passing of Fire through the pores You have seen men llght their Tobacco at the Sun with a burning glass or with a ball of Cristal held which way they will indifferently Which must be impossible unless the ball were all pores Again neither you nor I can conceive any other Fire then we have seen nor then such as water will put out But not only a solid Globe of Glass or Cristal will serve for a burning Glass but also a hollow one filled with water How then does the Fire from the Sun pass through the glass of water without being put out before it come to the matter they would have it burn A. I know not There comes nothing from the Sun If there did there is come so much from it already that at this day we had had no Sun CHAP. V. Problems of Hard and Soft A. WHat call you Hard and what Soft B. That body whereof no one part is easily put out of its place without removing the whole is that which I and all men call Hard and the contrary Soft So that they are but degrees one of another A. What is the cause that makes one body Harder then another or seeing you say they are but degrees of one another what makes one body Softer then another and the same body sometimes Harder sometimes Softer B. The same Motion which we have supposed from the beginning for the cause of so many other effects Which Motion not being upon the center of the part moved but the part it self going in another circle to and again it is not necessary that the Motion be perfectly circular For it is not circulation but the reciprocation I mean the to and again that does cast off and lacerrate the Air and consequently produce the fore-mentioned effects For the cause therefore of Hardness I suppose the reciprocation of Motion in those things which are Hard to be very swift and in very small circles A. This is somewhat hard to believe I would you could supply it with some visible experience B. When you see for example a Cross-bow bent do you think the parts of it stir A. No. I am sure they do not B. How are you sure You have no argument for it but that you do not see the Motion When I see you sitting still must I believe there is no Motion in your parts within when there are so many arguments to convince me there is A. What argument have you to convince me that there is Motion in a Cross-bow when it stands bent B. If you cut the string or any way set the Bow at liberty it will have then a very visible Motion What can be the cause of that A. Why the setting of the Bow at liberty B. If the Bow had been crooked before it was bent and a string tied to both ends and then cut asunder the Bow would not have stir'd Where lies the difference A. The Bow bent has a Spring unbent it has none how crooked soever B. What mean you by Spring A. An endeavour of restitution to it's former posture B. I understand Spring as well as I do endeavour A. I mean a Prnciple or beginning of Motion in a contrary way to that of the force which bent it B. But the beginning of Motion is also Motion how insensible soever it be And you know that nothing can give a beginning of Motion to it self What is it therefore that gives the Bow which you say you are sure was at rest when it stood bent its first endeavour to return to its former posture A. It was he that bent it B. That cannot be For he gave it an endeavour to come forward and the Bow endeavours to go backward A. Well grant that endeavour be Motiou and Motion in the Bow unbent how do you derive from thence that being set at liberty it must return to its former posture B. Thus There being within the Bow a swift though invisible Motion of all the parts and consequently of the whole the bending causeth that Motion which was along the Bow that was beaten out when it was hot into that length to operate a cross the length in every part of it and the more by how much it is more bent and consequently endeavours to unbend it all the while it stands bent And therefore when the force which kept it bent is removed it must of necessity return to the posture it had before A. But has that endeavour no effect at all before the impediment be removed For if endeavour be Motion and every Motion have some effect more or less methinks this endavour should in time produce something B. So it does For in time in a long time the
SEVEN Philosophical Problems AND TWO PROPOSITIONS OF GEOMETRY By Thomas Hobbes of Malmesbury With an Apology for Himself and his WRITINGS Dedicated to the KING in the year 1662. LONDON Printed for William Crook at the Green-Dragon without Temple-Bar 1682. TO THE KING THat which I do here most humbly present to Your Sacred Majesty is the best Part of my Meditations upon the Natural Causes of Events both of such as are commonly known and of such as have been of late artificially exhibited by the Curious They are ranged under seven Heads 1. Problems of Gravity 2. Problems of Tides 3. Problems of Vacuum 4. Problems of Heat 5. Problems of Hard and Soft 6. Problems of Wind and Weather 7. Problems of Motion Perpendicular and Oblique c. To which I have added Two Propositions of Geometry One is The Duplication of the Cube hitherto sought in vain The other A Detection of the absurd Use of Arithmetick as it is now applied to Geometry The Doctrine of Natural Causes hath not infallible and evident Principles For there is no Effect which the Power of God cannot produce by many several ways But seeing all Effects are produced by Motion he that supposing some one or more Motions can derive from them the necessity of that Effect whose Cause is required has done all that is to be expected from Natural Reason And though he prove not that the thing was thus produced yet he proves that thus it may be produced when the Materials and the power of Moving is in our hands which is as useful as if the Causes themselves were known And notwithstanding the absence of rigorous Demonstration this Contemplation of Nature if not rendred obscure by empty terms is the most Noble Imployment of the Mind that can be to such as are at leisure from their necessary Business This that I have done I know is anunworthy Present to be offered to a KING though considered as God considers Offerings together with the Mind and Fortune of the Offerer I hope will not be to Your Majesty unacceptable But that which I chiefly consider in it is that my Writing should be tryed by Your Majesties Excellent Reason untainted with the Language that has been invented or made use of by Men when they were puzzled and who is acquainted with all the Experiments of the time and whose approbation if I have the good Fortune to obtain it will protect my reasoning from the Contempt of my Adversaries I will not break the custom of joyning to my Offering a Prayer And it is That Your Majesty will be pleased to pardon this following short Apology for my Leviathan Not that I rely upon Apologies but upon Your Majesties most Gracious General Pardon That which is in it of Theology contrary to the general Current of Divines is not put there as my Opinion but propounded with submission to those that have the Power Ecclesiastical I did never after either in Writing or Discourse maintain it There is nothing in it against Episcopacy I cannot therefore imagine what reason any Episcopal-man can have to speak of me as I hear some of them do as of an Atheist or man of no Religion unless it be for making the Authority of the Church wholly upon the Regal Power which I hope Your Majesty will think is neither Atheism nor Heresie But what had I to do to meddle with matters of that nature seeing Religion is not Philosophy but Law It was written in a time when the pretence of Christ's Kingdom was made use of for the most horrid Actions that can be imagined And it was in just Indignation of that that I desired to see the bottom of that Doctrine of the Kingdom of Christ which divers Ministers then Preached for a Pretence to their Rebellion which may reasonably extenuate though not excuse the writing of it There is therefore no ground for so great a Calamny in my writing There is no sign of it in my Life and for my Religion when I was at the point of Death at St. Germains the Bishop of Durham can bear witness of it if he be asked Therefore I most humbly beseech Your Sacred Majesty not to believe so ill of me upon reports that proceed often and may do so now from the displeasure which commonly ariseth from difference in Opinion nor to think the worse of me if snatching up all the Weapons to fight against Your Enemies I lighted upon one that had a double edge Your Majesties Poor and most Loyal Subject THOMAS HOBBES PHILOSOPHICAL PROBLEMS CHAP. I. Problems of Gravity A. WHat may be the cause think you that stones and other bodies thrown upward or carried up and left to their liberty fall down again for ought a man can see of their own accord I do not think with the old Philosophers that they have any love to the Earth or are sullen that they will neither go nor stay And yet I cannot imagine what body there is above that should drive them back B. For my part I believe the cause of their descending is not in any natural appetite of the bodies that descend but rather that the Globe of the Earth hath some special motion by the which it more easily casteth off the Air than it doth other bodies And then this descent of those we call heavy bodies must of necessity follow unless there be some empty spaces in the world to receive them For when the Air is thrown off from the Earth somewhat must come into the place of it in case the world be full and it must be those things which are hardliest cast off that is those things which we say are heavy A. But suppose there be no place empty for I will defer the Question till anon how can the Earth cast off either the Air or any thing else B. I shall shew you how and that by a familiar Example If you lay both your hands upon a Basen with water in it how little soever and move it circularly and continue that motion for a while and you shall see the water rise upon the sides and fly over by which you may be assured that there is a kind of circulating motion which would cast off such bodies as are contiguous to the body so moved A. I know very well there is and it is the same motion which Country people use to purge their Corn For the Chaff and Straws by casting the Grain to the side of the Seive will come towards the middle But I would see the Figure B. Here it is There is a Circle pricked out whose Center is A and three less Circles whose Centers are B C D let every one of them represent the Earth as it goeth from B to C and from C to D always touching the uttermost Circle and throwing off the Air as is marked at E and F. And if the world were not full there would follow by this scattering of the Air a great deal of space left empty But supposing the world
full there must be a perpetual shifting of the Air one part into the place of another A. But what makes a stone come down suppose from G B. If the Air be thrown up beyond G it will follow that at the last if the motion be continued all the Air will be above G that is above the stone which cannot be till the stone be at the Earth A. But why comes it down still with encreasing swiftness B. Because as it descends and is already in motion it receiveth a new impression from the same cause which is the Air whereof as part mounteth part also must descend supposing as we have done the plenitude of the world For as you may observe by the Figure the motion of the Earth according to the Diameter of the uttermost Circle is progressive and so the whole motion is compounded of two motions one circular and the other progressive and consequently the Air ascends and circulates at once And because the stone descending receiveth a new pressure in every point of its way the motion thereof must needs be accelerated A. 'T is true For it will be accelerated equally in equal times and the way it makes will encrease in a double proportion to the times as hath heretofore been demonstrated by Galileo I see the solution now of an Experiment which before did not a little puzzle me You know that if two plummets hang by two strings of equal length and you remove them from the perpendicular equally I mean in equal angles and then let them go they will make their turns and returns together and in equal times And though the arches they describe grow continually less and less yet the times they spend in the greater arches will still be equal to the time they spend in the lesser B. 'T is true Do you find any Experiment to the contrary A. Yes For if you remove one of the plummets from the perpendicular so as for example to make an angle with the perpendicular of 80 degrees and the other so as to make an angle of 60 degrees they will not make their turns and returns in equal times B. And what say you is the cause of this A. Because the arches are the spaces which these two motions describe they must be in double proportion to their own times which cannot be unless they be let go from equal altitudes that is from equal angles B. 'T is right and the Experiment does not cross but confirm the equality of the times in all the arches they describe even from 90 degrees to the least part of one degree A. But is it not too bold if not extravagant an assertion to say the Earth is moved as a man shakes a Basen or a Seive Does not the Earth move from West to East every day once upon his own Center and in the Ecliptick Circle once a year And now you give it another odd motion How can all these consist in one and the same body B. Well enough If you be a Shipboard under sail do not you go with the Ship Cannot you also walk upon the Deck Cannot every drop of bloud move at the same time in your veins How many motions now do you assign to one and the same drop of bloud Nor is it so extravagant a thing to attribute to the Earth this kind of motion but that I believe if we certainly knew what motion it is that causeth the descent of bodies we should find it either the same or more extravagant But seeing it can be nothing above that worketh this effect it must be the Earth it self that does it and if the Earth then you can imagine no other motion to do it withal but this And you will wonder more when by the same motion I shall give you a probable account of the causes of very many other works of Nature A. But what part of the Heaven do you suppose the Poles of your pricked Circle point to B. I suppose them to be the same with the Poles of the Ecliptick For seeing the Axis of the Earth in this Nation and in the annual motion keeps parallel to it self the Axis must in both motions be parallel as to sense For the Circle which the Earth describes is not of visible magnitude at the distance it is from the Sun A. Though I understand well enough how the Earth may make a stone descend very swiftly under the Ecliptick or not far from it where it throws off the Air perpendicularly yet about the Poles of the Circle methinks it should cast off the Air very weakly I hope you will not say that bodies descend faster in places remote from the Poles than nearer to them B. No but I ascribe it to the like motion in the Sun and Moon For such motions meeting must needs cast the stream of the Air towards the Poles And then there will be the same necessity for the descent there that there is in other places though perhaps a little more slowly For you may have observed that when it snows in the South Parts the flakes of Snow are not so great as in the North which is a probable sign they fall in the South from a greater height and consequently disperse themselves more as water does that falls down from a high and steep Rock A. 'T is not improbable B. In natural causes all you are to expect is but probability which is better yet then making Gravity the cause when the cause of Gravity is that you desire to know and better then saying the Earth draws it when the Question is how it draws A. Why does the Earth cast off Air more easily than it does Water or any other heavy bodies B. It is indeed the Earth that casteth off that Air which is next unto it But it is that Air which casteth off the next Air and so continually Air moveth Air which it can more easily do then any other thing because like bodies are more susceptible of one anothers motions as you may see in two Lute-strings equally strained what motion one string being stricken communicates to the Air the same will the other receive from the Air but strained to a differing note will be less or not at all moved For there is no body but Air that hath not some internal though invisible motion of its parts And it is that internal motion which distinguisheth all natural bodies one from another A. What is the cause why certain Squibs though their substance be either Wood or other heavy matter made hollow and filled with Gunpowder which is also heavy do nevertheless when the Gunpowder is kindled fly upwards B. The same that keeps a man that swims from sinking though he be heavier then so much water He keeps himself up and goes forward by beating back the water with his Feet and so does a Squib by beating down the Air with the stream of the fired Gunpowder that proceeding from its Tail makes it recoil A. Why does any Brass or Iron
Earth The like happens to a mans body or hand which when he perceives he says he is Hot. And so of the Earth when it sendeth forth Water and Earth together in Plants we say it does it by Heat from the Sun A. 'T is very probable and no less probable that the same action of the Sun is that which from the Sea and moist places of the Earth but especially from the Sea fetcheth up the water into the Clouds But there be many ways of Heating besides the action of the Sun or of Fire Two pieces of Wood will take Fire if in Torning they be prest together B. Here again you have a manifest laceration of the Air by the reciprocal and contrary motions of the two pieces of wood which necessarily causeth a coming forth of whatsoever is Aereal or fluid within them and the motion pursued a dissipation also of the other more solid parts into Ashes A. How comes it to pass that a man is warmed even to sweating almost with every extraordinary labour of his body B. It is easie to understand how by that labour all that is liquid in his body is tossed up and down and thereby part of it also cast forth A. There be some things that make a man Hot without sweat or other evaporation as Caustiques Nettles and other things B. No doubt But they touch the part they so Heat and cannot work that effect at any distance A. How does Heat cause light and that partially in some bodies more in some less though the Heat be equal B. Heat does not cause Light at all But in many Bodies the same cause that is to say the same motion causeth both together so that they are not to one another as cause and effect but are concomitant Effects sometimes of one and the same motion A. How B. You know the rubbing or heard pressing of the Eye or a stroke upon it makes an apparition of Light without and before it which way soever you look This can proceed from nothing else but from the restitution of the Organ pressed or stricken unto its former ordinary situation of parts Does not the Sun by his thrusting back the Air upon you eyes press them Or does not those bodies whereon the Sun shines though by reflection do the same though not so strongly And do not the Organs of Sight the Eye the Heart and Brains resist that pressure by an endeavour of restitution outwards Why then should there not be without and before the Eye an apparition of Light in this case as well as in the other A. I grant there must But what is that which appears after the pressing of the eye For there is nothing without that was not there before or if there were methinks another should see it better or as well as he or if in the dark methinks it should enlighten the place B. It is a fancy such as is the appearance of your face in a Looking-glass such as is a Dream such as is a Ghost such as is a spot before the Eye that hath stared upon the Son or Fire For all these are of the Regiment of Fancy without any body concealed under them or behind them by which they are produced A. And when you look towards the Sun or Moon why is not that also which appears before your Eyes at that time a fancy B. So it is Though the Sun it self be a real Body yet that bright Circle of about a foot Diameter cannot be the Sun unless there be two Suns a greater and a lesser And because you may see that which you call the Sun both above you in the Skie and before you in the Water and two Suns by distorting your Eye in two places of the Skie one of them must needs be Fancy And if one both All sense is Fancy though the cause be always in a real Body A. I see by this that those things which the Learned call the Accidents of Bodies are indeed nothing else but diversity of Fancy and are inherent in the Sentient and not in the Objects except Motion and Quantity And I perceive by your Doctrine you have been tampering with Leviathan But how comes Wood with a certain degree of Heat to shine and Iron also with a greater degree but no Heat at all to be able to make water shine B. That which shineth hath the same Motion in its parts that I have all this while supposed in the Sun and Earth In which Motion there must needs be a competent degree of swiftness to move the sense that is to make it visible All Bodies that are not fluid will shine with Heat if the Heat be very great Iron will shine and Gold will shine but water will not because the parts are carried away before they attain to that degree of swiftness which is requisite A. There are many fluid Bodies whose parts evaporate and yet they make a flame as Oyl and Wine and other strong drinks B. As for Oyl I never saw any inflamed by it self how much soever Heated therefore I do not think they are the parts of the Oyl but of the combustible body oyled that shine but the parts of Wine and strong Drinks have partly a strong Motion of themselves and may be made to shine but not with boiling but by adding to them as they rise the flame of some other body A. How can it be known that the particles of Wine have such a Motion as you suppose B. Have you ever been so much distempered with drinking Wine as to think the Windows and Table move A. I confess though you be not my Confessor I have but very seldom and I remember the window seemed to go and come in a kind of circling Motion such as you have described But what of that B. Nothing but that it was the Wine that caused it which having a good degree of that Motion before did when it was Heated in the Veins give that concussion which you thought was in the window to the Veins themselves and by the continuation of the parts of mans Body to the Brain and that was it which made the window seem to move A. What is Flame For I have often thought the Flame that comes out of a small heap of Straw to be more before it hath done Flaming then a hundred times the Straw it self B. It was but your Fancy If you take a stick in your hand by one end the other end burning and move it swiftly the burning end if the Motion be circular shall seem a circle if streight a streight line of Fire longer or shorter according to the swiftness of the Motion or to the space it moves in You know the cause of that A. I think it is because the impression of that visible Object which was made at the first instant of the Motion did last till it was ended For then it will follow that it must be visible all the way the impressions in all points of the time being
course of this internal Motion will lie along the Bow not according to the former but to the new acquired posture And then it will be as uneasie to return it to its former posture as it was before to bend it A. That 's true For Bows long bent lose their appetite to restitution long custom becoming nature But from this internal reciprocation of the parts how do you infer the Hardness of the whole Body B. If you apply force to any single part of such a body you must needs disorder the Motion of the next parts to it before it yield and there disordered the Motion of the next again must also be disordered and consequently no one part can yield without force sufficient to disorder all But then the whole body must also yield Now when a body is of such a nature as no single part can be removed without removing the whole men say that body is Hard. A. Why does the Fire melt divers Hard bodies and yet not all B. The hardest bodies are those wherein the Motion of the parts are the most swift and yet in the least circles Wherefore if the Fire the Motion of whose parts are swift and in greater circiles he made so swit as to be strong enough to master the Motion of the parts of the Hard body it will make those parts to move in a greater compass and thereby weaken their resistance that is to say Soften them which is a degree of liquefaction And when the Moton is so weakened as that the parts lose their coherence by the force of their own weight then we count the body melted A. Why are the Hardest things the most brittle insomuch that what force soever is enough to bend them is enough also to break them B. In bending a Hard body as for example a Rod of Iron you do not inlarge the space of the internal Motion of the parts of Iron as the Fire does but you master and interrupt the Motion and that chiefly in one place In which place the Motion that makes the Iron Hard being once overcome the prosecution of that bending must needs suddenly master the Motions of the parts next unto it being almost mastered before A. I have seen a small piece of glass the figure whereof is this A A B C. Which piece of glass if you bend toward to top as in C the whole body will shatter asunder into a Million of pieces and be like to so much dust I would fain see you give a probable reason of that B. I have seen the Experiment The making of the glass is thus They dip an Iron Rod into the molten glass that stands in a Vessel within the Furnace Upon which Iron Rod taken out there will hang a drop of molten but tough Mettal of the figure you have described which they let fall into the water So that the main drop comes first to the water and after it the tail which though streight whilst it hung on the end of the Rod yet by falling into the water becomes crooked Now you know the making of it you may consider what must be the consequence of it Because the main drop A comes first to the water it is therefore first quenched and consequently that the Motion of the parts of that drop which by the Fire were made to be moved in a larger compass is by the water made to shrink into lesser circles towards the other end B but with the same or not much less swiftness A. Why so B. If you take any long piece of Iron Glass or other uniform and continued body and having Heated one end thereof you hold the other end in your hand and so quench it suddenly though before you held it easily enough yet now it will burn your fingers A. It will so B. You see then how the Motion of the parts from A toward C is made more violent and in less compass by quenching the other parts first Besides the whole Motion that was in all the parts of the main drop A is now united in the small end B C. And this I take to be the cause why that small part B C is so exceeding stiff Seeing also this Motion in every small part of the glass is not only circular but proceeds also all along the glass from A to B the whole Motion compounded will be such as the Motion of Spinning any Soft matter unto Thread and will dispose the whole body of the glass in Threads which in other Hard bodies are called the grain Therefore if you bend this body for example in C which to do will require more force then a man would think that has not tryed those threads of Glass must needs be all bent at the same time and stand so till by the breaking of the Glass at C they be all at once set at liberty And then all at once being suddenly unbent like so many brittle and over-bent Bows their Strings breaking be shivered in pieces A. 'T is like enough to be so And if nature have betrayed her self in any thing I think it is in this and in that other experience of the Cross-bow which strongly and evidently demonstrates the internal reciprocation of the Motion which you suppose to be in the internal parts of every Hard body And I have observed somewhat in Looking-glasses which much confirms that there is some such Motion in the internal parts of Glass as you have supposed for the cause of Hardness For let the Glass be A B and let the Object at C be a Candle and the Eye at D. Now by divers Reflections and Refractions in the two superficies of the Glass if the Lines of Vision be very oblique you shall see many images of the Candle as E F G in such order and position as is here described But if you remove your Eye to C and the Candle to D they will appear in a situation manifestly different from this Which you will yet more plainly perceive if the Looking-Glass be coloured as I have obseved in Red and Blew Glasses and could never conceive any probable cause of it till now you tell me of this secret Motion of the parts across the grain of the Glass acquired by cooling it this or that way B. There be very many kinds of Hard bodies Metals Stones and other kinds in the bowels of the Earth that have been there ever sence the beginning of the World and I believe also many different sorts of Juices that may be made Hard. But for one general cause of Hardness it can be no other then such an internal Motion of parts as I have already described whatsoever may be the cause of the several concomitant qualities of their Hardness in particular A. We see water Hardened every Frosty day It 's likely therefore you may give a pribable cause of Ice What is the cause of Freezing of the Ocean towards the Poles of the Earth B. You know the Sun being always between the Tropicks and
Vessel if it be hollow flote upon the water being so very heavy B. Because the Vessel and the Air in it taken as one body is more easily cast off than a body of water equal to it A. How comes it to pass that a Fish especially such a broad Fish as a Turbut or a Plaice which are broad and thin in the bottom of the Sea perhaps a mile deep is not press'd to death with the weight of water that lies upon the back of it B. Because all heavy bodies descend towards one point which is the Center of the Earth and consequently the whole Sea descending at once does arch it self so as that the upper parts cannot press the parts next below them A. It is evident Nor can there be possibly any weight as some suppose there is of a Cylinder of Air or Water or of any other liquid thing while it remains in its own Element or is sustained and inclosed in a Vessel by which one part cannot press the other CHAP. II. Problems of Tides A. WHat makes the Flux and Reflux of the Sea twice in a natural day B. We must come again to our Basen of water wherein you have seen whilst it was moved how the water mounteth up by the sides and withal goes circling round about Now if you should fasten to the inside of the Basen some bar from the bottom to the top you would see the water instead of going on go back again from that bar ebbing and the water on the other side of the bar to do the same but in counter-time and consequently to be highest where the contrary streams meet together and then return again marking out four quarters of the Vessel two by their meeting which are the high waters and two by their retiring which are the low waters A. What bar is that you find in the Ocean that stops the current of the water like that you make in the Basen B. You know that the main Ocean lies East and West between India and the Coast of America and again on the other side between America and India If therefore the Earth have such a motion as I have supposed it must needs carry the current of the Sea East and West In which course the bar that stoppeth it is the South part of America which leaves no passage for the water but the narrow Streight of Magellan The Tide rises therefore upon the Coast of America And the rising of the same in this part of the world proceedeth from the swelling chiefly of the water there and partly also from the North Sea which lieth also East and West and has a passage out of the South Sea by the Streight of Anian between America and Asia A. Does not the Mediterranean-Sea lie also East and West why are there not the like Tides there B. So there are proportionable to their lengths and quantity of water A. At Genoa at Ancona there are none at all or not sensible B. At Venice there are and in the bottom of the Streights and a current all along both the Mediterranean-Sea and the Gulf of Venice And it is the current that makes the Tides unsensible at the sides but the check makes them visible at the bottom A. How comes it about that the Moon hath such a stroke in the business as so sensibly to encrease the Tides at Full and Change B. The motion I have hitherto supposed but in the Earth I suppose also in the Moon and in all those great Bodies that hang in the Air constantly I mean the Stars both fixed and errant And for the Sun and Moon I suppose the Poles of their motion to be the Poles of the Aequinoctial which supposed it will follow because the Sun the Earth and the Moon at every Full and Change are almost in one streight line that this motion of the Earth will be made swifter than in the Quarters For this motion of the Sun and Moon being communicated to the Earth that hath already the like motion maketh the same greater and much greater when they are all three in one streight line which is only at the Full and Change whose Tides are therefore called Spring Tides A. But what then is the cause that the Spring-Tides themselves are twice a year namely when the Sun is in the Equinoctial greater than at any other times B. At other times of the year the Earth being out of the Aequinoctial the motion thereof by which the Tides are made will be less augmented by so much as a motion in the obliquity of 23 degrees or thereabout which is the distance between the Aequinoctial and Ecliptick Circles is weaker then the motion which is without obliquity A. All this is reasonable enough if it be possible that such motions as you suppose in these bodies be really there But that is a thing I have some reason to doubt of For the throwing off of Air consequent to these motions is the cause you say that other things come to the Earth And therefore the like motions in the Sun and Moon and Stars casting off the Air should also cause all other things to come to every one of them From whence it will follow that the Sun Moon and Earth and all other bodies but Air should presently come together into one heap B. That does not follow For if two bodies cast off the Air the motion of that Air will be repress'd both ways and diverted into a course towards the Poles on both sides and then the two bodies cannot possibly come together A. 'T is true And besides this driving off the Air on both sides North and South makes the like motion of Air there also And this may answer to the Question How a stone could fall to the Earth under the Poles of the Ecliptick by the only casting off of Air B. It follows from hence that there is a certain and determinate distance of one of these bodies the Stars from another without any very sensible variation A. All this is probable enough if it be true that there is no Vacuum no place empty in all the World And supposing this motion of the Sun and Moon to be in the plain of the Aequinoctial methinks that this should be the cause of the Diurnal motion of the Earth And because this motion of the Earth is you say in the plain of the Aequinoctial the same should cause also a motion in the Moon on her own Center answerable to the Diurnal motion of the Earth B. Why not what else can you think makes the Diurnal motion of the Earth but the Sun And for the Moon if it did not turn upon its own Center we should see sometimes one sometimes another face of the Moon which we do not CHAP. III. Problems of Vacuum WHat convincing Argument is there to prove that in all the world there is no empty place B. Many but I will name but one and that is the difficulty of separating two bodies hard and flat laid
one upon another I say the difficulty not the impossibility It is possible without introducing Vacuum to pull assunder any two bodies how hard and flat soever they be if the force used be greater than the resistance of the hardness And in case there be any greater difficulty to part them besides what proceeds from their hardness then there is to pull them further assunder when they are parted that difficulty is Argument enough to prove there is no Vacuum A. These Assertions need demonstration And first how does the difficulty of separation argue the Plenitude of all the rest of the world B. If two flat polish'd Marbles lie one upon another you see they are hardly separated in all points at one and the same instant and yet the weight of either of them it is enough to make them slide off one from the other Is not the cause of this that the Air succeeds the Marble that so slides and fills up the place it leaves A. Yes certainly What then B. But when you pull the whole Superficies assunder not without great difficulty what is the cause of that difficulty A. I think as most men do that the Air cannot fill up the space between in an instant For the parting is in an instant B. Suppose there be Vacuum in that Air into which the Marble you pull off is to succeed shall there be no Vacuum in the Air that was round about the two Marbles when they touched Why cannot that Vacuum come into the place between Air cannot succeed in an instant because a body and consequently cannot be moved through the least space in an instant But emptiness is not a body nor is moved but made by the act it self of separation There is therefore if you admit Vacuum no necessity at all for the Air to fill the space left in an instant And therefore with what ease the Marble coming off presseth out the Vacuum of the Air behind it with the same ease will the Marbles be pulled assunder Seeing then if there were Vacuum there would be no difficulty of Separation it follows because there is difficulty of separation that there is no Vacuum A. Well now supposing the world full how do you prove it possible to pull those Marbles assunder B. Take a piece of soft wax Do not you think the one half touches the other half as close as the smoothest Marbles yet you can pull them assunder But how still as you pull the wax grows continually more and more slender there being a perpetual parting or discession of the outermost part of the wax one from another which the Air presently fills and so there is a continual lessening of the wax till it be no bigger than a hair and at last separation If you can do the same to a Pillar of Marble till the outside give way the effect will be the same but much quicker after it once begins to break in the Superficies because the force that can master the first resistance of the hardness will quickly dispatch the rest A. It seems so by the brittleness of some hard bodies But I shall afterward put some Questions to you touching the nature of hardness But now to return to our subject What reason can you render without supposing Vacuum of the effects produced in the Engine they use at Gresham Colledge B. That Engine produceth the same effects that a strong wind would produce in a narrow room A. How comes the wind in You know the Engine is a hollow round pipe of brass into which is thrust a Cylinder of wood covered with Leather and fitted to the Cylinder so exactly as no Air can possibly pass between the leather and the brass B. I know it and that they may thrust it up there is a hole left in the Cylinder to let the Air out before it which they can stop when they please There is also in the bottom of the Cylinder a passage into a hollow Globe of Glass which passage they can also open and shut at pleasure And at the top of that Globe there is a wide mouth to put in what they please to try conclusions on and that also to be opened and shut as shall be needful 'T is of the nature of a Pop-gun which Children use but great costly and more ingenious They thrust forward and pull back the wooden Cylinder because it requires much strength with an Iron screw What is there in all this to prove the possibility of Vacuum A. Whan this wooden Cylinder covered with leather fit and close is thrust home to the bottom and the holes in the hollow Cylinder of Brass close stopped how can it be drawn back as with the screw they draw it but that the space it leaves must needs be empty For it is impossible that any Air can pass into the place to fill it B. Truly I think it close enough to keep out Straw and Feathers but not to keep out Air nor yet matter For suppose they were not so exactly close but that there were round about a distance for a small hair to lye between Then will the pulling back of the Cylinder of wood force so much Air in as in retiring it forces back and that without any sensible difficulty And the Air will so much more swiftly enter as the passage is left more narrow Or if they touch and the contract be in some points and not in all the Air will enter as before in case the force be augmented accordingly Lastly though they touch exactly if either the Leather yield or the Brass which it may do to the force of a strong screw the Air will again enter Do you think it possible to make two superficies so exquisitly touch in all points as you suppose or Leather so hard as not to yield to the force of a screw The Body of Leather will give passage both to Air and Water as you will confess when you ride in Rainy and Windy weather You may therefore be assured that in drawing out their wooden-leather Cylinder they force in as much Air as will fill the place it leaves and that with as much swiftness as is answerable to the strength that drives it in The effect therefore of their pumping is nothing else but a vehement Wind a very vehement Wind coming in on all sides of the Cylinder at once into the hollow of the Brass Pipe and into the hollow of the Glass Globe joyned to it A. I see the reason already of one of their wonders which is that the Cylinder they pump with if it be left to it self after it is pulled back will swiftly go up again You will say the Air comes out again with the same violence by reflection and I believe it B. This is argument enough that the place was not empty For what can fetch or drive up the Sucker as they call it if the place within were empty for that there is any weight in the Air to do it I have already
the two ends of a Staff though they did not remove one another yet they would find in themselves a great disposition to press backward upon whatsoever is behind them though not a total going out of their places Such is the way of Reflecting Light Now when the falling on of the Sun-beams is Oblique the action of them is nevertheless Perpendicular to the Superficies it falls on And therefore the Reflecting Body by resisting turneth back that Motion Perpendicularly as from F to E but taketh nothing from the force that goes on parallel in the line of E H because the Motion never presses And thus of the two Motions from F to E and from E to H is a compounded Motion in the line F H which maketh an Angle in B G equal to the Angle F G E. But in Percussion which is the Motion of the Bullet against a wall the Bullet no sooner goeth off then it loseth of its swiftness and inclineth to the Earth by its weight So that the Angles made in falling on and going off cannot be equal unless they be measured close to the point where the stroke is made A. If a man set a Board upright upon its edge though it may very easily be cast down with a little Pressure of ones finger yet a Bullet from a Musquet shall not throw it down but go through it What is the cause of that B. In pressing with your finger you spend time to throw it down For the Motion you give to the part you touch is communicated to every other part before it fall For the whole cannot fall till every part be moved But the stroke of a Bullet is so swift as it breaks through before the Motion of the part it hits can be communicated to all the other parts that must fall with it A. The stroke of a Hammer will drive a Nail a great way into a piece of Wood on a sudden What weight laid upon the head of a Nail and in how much time will do the same It is a question I have heard propounded amonst Naturalists B. The different manner of the operation of weight from the operation of a stroke makes it uncalculable The suddenness of the stroke upon one point of the wood takes away the time of resistance from the rest Therefore the Nail enters so far as it does But the weight not only gives them time but also augments the resistance but how much and in how much time is I think impossible to determine A. What is tbe difference between Reflection and Recoiling B. Any Reflection may and not unproperly be called recoiling but not contrariwise every Recoiling Reflection Reflection is always made by the Re-action of a Body prest or stricken but Recoiling not always The Recoiling of a Gun is not caused by its own pressing upon the Gun-powder but by the force of the Powder it self inflamed and moved every way alike A. I had thought it had been by the sudden re-entring of the Air after the flame and Bullet were gone out For it is impossible that so much room as is left empty by the discharging of the Gun should be so suddenly filled with the Air that entereth at the Touch-hole B. The flame is nothing but the Powder it self which scattered into its smallest parts seems of greater bulk by much then in truth it is because they shine And as the parts scatter more and more so still more Air gets between them entring not only at the Touch-hole but also at the mouh of the Gun which two ways being opposite it will be much too weak to make the Gun Recoil A. I have heard that a great Gun charged too much or too little will Shoot not above nor below but besides the mark and charged with one certain charge between both will hit it B. How that should be I cannot imagine For when all things in the cause are equal the effects cannot be unnequal As soon as Fire is given and before the Bullet be out the Gun begins to Recoil If then there be any unevenness or rub in the ground more on one side then on the other it shall shoot besides the mark whether too much or too little or justly charged because if the line wherein the Gun Recoileth decline the way of the Bullet will also decline to the contrary side of the mark Therefore I can imagine no cause of this event but either in the ground it Recoils on or in the unequal weight of the parts of the Breech A. How comes Refractin B. When the action is in a line Perpendicular to the superficies of the Body wrought upon there will be no Refraction at all The action will proceed still in the same straight Line whether it be Pression as in Light or in Percussion as in the shooting of a Bullet But when the Pression is Oblique then will the Refraction be that way which the Nature of the Bodies through which the Action proceeds shall determin H. How is light Refracted B. If is pass through a Body of less into a Body of greater resistance and to the Point of the Superficies it falleth on you draw a Line Perpendicular to the same superficies the Action will proceed not in the same Line by which it fell on but in another Line bending toward that Perpendiculare A. What is the reason of that B. I told you before that the falling on worketh only in the Perpendicular But as soon as the Action proceedeth further inward then a meer touch it worketh partly in the Perpendicular and partly forward and would proceed in the same line in which it fell on but for for the greater resistance which now weakneth the Motion forward and makes it to incline towards the Perpendicular A. In transparent Bodies it may be so but there be Bodies through which the Light cannot pass at all B. But the Action by which Light is made passeth through all Bodies For this Action is Pression and whatsoever is prest presseth that which is next behind and so continually But the cause why there is no Light seen through it is the uneveness of the parts within whereby the Action is by an infinite number of Reflections so diverted and weakned that before it hath proceeded through it hath not strength left towork upon the Eye strongly enough to produce sight A. If the Body being transparent the Action proceed quite through into a Body again of less resistance as out of Glass into the Air which way shall it then proceed in the Air B. From the Point where it goeth forth draw a Perpendicular to the superficies of the Glass the Action now freed from the resistance it suffered will go from that Perpendicular as much as it did before come towards it A. When a Bullet from out of the Air entreth into a Wall of Earth will that also be Refracted towards the Perpendicular B. If the Earth be all of one kind it will For the parallel Motion will there also at