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
to b B m the Line n G will be in the Ecliptick of the Earth because G d is in the Aequator of the Earth So that in the Annual Motion of the Earth through the Ecliptick every streight Line drawn in the Earth is perpetually kept parallel to the place from whence it is removed A. 'T is true and 't is the Doctrine of Copernicus But I cannot yet conceive by what one Motion this Circle can be described otherwise than we are taught by Euclid And then I am sure that all the Diameters shall cross one another in the Centre which in this Figure is A. B. I do not say that the Diameters of a Sphere or Circle can be parallel but that if a Circle of a lesser Sphere be moved upon the Circumference of a great Circle of a greater Sphere that the streight Lines that are in the lesser Sphere may be kept parallel perpetually to the places they proceed from A. How And by what Motion B. Take into your hand any streight Line as in this Figure the Line L A M which we suppose to be the diameter of the Suns Body and moving it parallelly with the ends in the Circumference so as that the end M may withal describe a small Circle as M a. It is manifest that all the other points of the same Line L M will by the same Motion at the same time describe equal Circles to it Likewise if you take in your hand any two Diameters fastened together the same Parallel-motion of the line L M shall cause all the points of the other Diameter to make equal Circles to the same M a. A. 'T is evident as also that every point of the Suns body shall do the like And not onely so but also if one end describe any other Figure all the other points of the Body shall describe like and equal Figures to it B. You see by this that this Parallel-motion is compounded of two Motions one Circular upon the Superficies of a Sphere the other a streight Motion from the Centre to every point of the same Superficies and beyond it A. I see it B. It follows hence that the Sun by this Motion must every way repel the Air and since there is no empty place for retiring the Air must turn about in a Circular stream but slower or swifter according as it is more or less remote from the Sun and that according to the nature of Fluids the Particles of the Air must continually change place with one another and also that the stream of the Air shall be the contrary way to that of the Motion for else the Air cannot be repelled A. All this is certain B. Well Then if you suppose the Globe of the Earth to be in this stream which is made by the Motion of the Suns Body from East to West the stream of Air wherein is the Earths Annual Motion will be from West to East A. 'T is certain B. Well Then if you suppose the Globe of the Earth whose Circle is moved Annually to be l m the stream of the Air without the Ecliptick falling upon the Superficies of the Earth l m without the Ecliptick being slower and the stream that falleth within swifter the Earth shall be turned upon its own Centre proportionally to the greatness of the Circles and consequently their Diameters shall be parallel as also are other streight Lines correspondent A. I deny not but the streams are as you say and confess that the proportion of the swiftness without is to the swiftness within as the Suns Ecliptick to the Ecliptick of the Earth that is to say as the Angle HAB to the Angle m B b. And I like your Argument the better because it is drawn from Copernicus his foundation I mean the compounded Motion of Streight and Circular B. I think I shall not offer you many demonstrations of Physical conclusions that are not derived from the Motions supposed or proved by Copernicus For those Conclusions in Natural Philosophy I most suspect of falshood which require most variety of Suppositions for their demonstrations A. The next thing I would know is how great or little you suppose that Circle a M. B. I suppose it less than you can make it For there appears in the Sun no such Motion sensible 'T is the first Endeavour of the Suns Motion But for all that as small as the Circle is the Motion may be as swift and of as great strength as 't is possible to be named 'T is but a kinde of trembling that necessarily happeneth in those Bodies which with great resistance press upon one another A. I understand now from what Cause proceedeth the Annual Motion Is the Sun the Cause also of the Diurnal Motion B. Not the immediate Cause For the Diurnal Motion of the Earth is upon its own Centre and therefore the Suns Motion cannot describe it But it proceedeth as a necessary consequence from the Annual Motion For which I have both experience and demonstration The Experiment is this Into a large Hemisphere of Wood spherically Concave put in a Globe of Lead and with your hands hold it fast by the brim moving your hands circularly but in a very small compass you shall see the Globe circulate about the Concave Vessel just in the same manner as the Earth doth every year in the Air and you shall see withal that as it goes it turns perpetually upon its own Centre and very swiftly A. I have seen it And 't is used in some great Kitchins to grinde Mustard B. Is it so Therefore take a Hemisphere of Gold if you have it the greater the better and a Bullet of Gold and without Mustard you shall see the same Effect A. I doubt it not But the of it Cause is evident For any Spherical Body being in Motion upon the sides of a Concave and hard Sphere is all the way turned upon its own Centre by the resistance of the hard Wood or Metal But the Earth is a Bullet without weight and meeteth onely with Air without any harder body in the way to resist it B. Do you think the Air makes no resistance especially to so swift a Motion as is the Annual Motion of the Earth If it do make any resistance you cannot doubt but that it shall turn the Earth circularly and in a contrary way to its Annual Motion that is to say from East to West because the Annual Motion is from West to East A. I confess it But what deduce you from these Motions of the Sun B. I deduce first that the Air must of necessity be moved both circularly about the Body of the Sun according to the Ecliptick and also every way directly from it For the Motion of the Suns Body is compounded of this Circular Motion upon the Sphere L M and of the streight motion of its Semi-diameters from the Centre A to the Superficies of the Suns Body which is LM And therefore the Air must needs be repelled
Motion of the Earth For whatsoever having been asunder comes together again must come contrary ways as those that follow one another go the same way though both move upon the same Line A. What Experiment have you seen to this purpose B. I have seen a drop of glass like that of the second Figure newly taken out of the furnace and hanging at the end of an Iron rod and yet Fluid and let fall into the water and hardned The Club-end of it A A coming first to the water the tail B C following it 'T is proved before that the motion that makes it is a compounded Motion and gives an Endeavour outward to every part of it and that the Motion which maketh Cold is such as shaving the Body in every point of contact and turning it gives them all an Endeavour inward Such is this Motion made by the sinking of the hot and fluid glass into the water 'T is therefore manifest that the Motion which hardneth a Soft Body must in every point of contact be in the contrary way to that which makes a hard body Soft And further that slender tail B C shall be made much more hard than common Glass For towards the upper end in C you cannot easily break it as small as it is And when you have broken it the whole Body will fall into dust as it must do seeing the bending is so difficult For all the parts are bent with such force that upon the breaking at D by their sudden restitution to their liberty they will break together And the cause why the tail B C being so slender becomes so hard is that all the Endeavour in the great part A B is propagated to the small part B C in the same manner as the force of the Sun-beams is derived almost to a point by a Burning-glass But the Cause why when it is broken in D it breaks also in so many other places is that the Endeavour in all the other parts which is called the Spring unbends it from whence a Motion is caused the contrary way and that Motion continued bends it more the other way and breaks it as a Bow over-bent is broken into shivers by a sudden breaking of the string A. I conceive now how a Body which having been Hard and softned again may be re-hardned but how a Fluid and meer Homogeneous Body as Air or Water may be so I see not yet For the hardning of water is making a hard Body of two Fluids whereof one which is the water hath some tenacity and so a man may make a Bladder hard with blowing into it B. As for meer Air which hath no Natural Motion of it self but is moved onely by other Bodies of a greater consistence I think it impossible to be hardned For the parts of it so easily change places that they can never be fixt by any Motion No more I think can Water which though somewhat less Fluid is with an insensible force very easily broken A. It is the opinion of many learned men that Ice in long time will be turned into Christal and they alleadge Experience for it For they say that Christal is found hanging on high Rocks in the Alps like Isicles on the Eaves of a house and why may not that have formerly been Ice and in many years have lost the power of being reduced B. If that were so it would still be Ice though also Christal Which cannot be because Christal is heavier than Water and therefore much heavier than Ice A. Is there then no transubstantiation of Bodies but by mixture B. Mixture is no transubstantiation A. Have you never seen a Stone that seemed to have been formerly Wood and some like Shells and some like Serpents and others like other things B. Yes I have seen such things and particularly I saw at Rome in a Stone-cutters work-house a Billet of Wood as I thought it partly covered with bark and partly with the grain bare as long as a mans Arm and as thick as the Calf of a mans Leg which handling I found extreme heavie and saw a small part of it which was polished and had a very fine Gloss and thought it a substance between Stone and Metal but neerest to Stone I have seen also a kind of Slate painted naturally with Forest-work And I have seen in the hands of a Chymist of my acquaintance at Paris a broken Glass part of a Retort in which had been the Rozin of Turpentine wherein though there were left no Rozin yet there appeared in the piece of Glass many Trees and Plants in the ground about them such as grow in Woods and better designed than they could be done by any Painter and continued so for a long time These be great wonders of Nature but I will not undertake to shew their causes But yet this is most certain that nothing can make a hard Body of a Soft but by some Motion of its parts For the parts of the Hardest Body in the world can be no closer together than to touch and so close are the parts of Air and Water and consequently they should be equally Hard if their smallest parts had not different Natural Motions Therefore if you ask me the Causes of these Effects I answer They are different Motions But if you expect from me how and by what Motions I shall fail you For there is no kind of Substance in the World now that was not at the first Creation when the Creator gave to all things what Natural and special Motion he thought good And as he made some Bodies wondrous great so he made others wondrous little For all his works are wondrous Man can but guess nor guess further than he hath knowledge of the variety of Motion I am therefore of opinion that whatsoever perfectly Homogeneous is Hard consisteth of the smallest parts or as some call them Atomes that were made Hard in the beginning and consequently by an Eternal Cause and that the hardness of the whole Body is caused onely by the contact of the parts by pressure A. What Motion is it that maketh a hard Body to melt B. The same compounded Motion that heats namely that of Fire if it be strong enough For all Motion compounded is an Endeavour to dissipate as I have said before the parts of the Body to be moved by it If therefore hardness consist onely in the pressing Contact of the least parts this Motion will make the same parts slide off from one another and the whole to take such a figure as the weight of the parts shall dispose them to as in Lead Iron Gold and other things melted with Heat But if the small parts have such figures as they cannot exactly touch but must leave spaces between them filled with Air or other Fluids then this Motion of the fire will dissipate those parts some one way some another the Hard part still hard as in the burning of Wood or Stone into Ashes or Lime For this Motion
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