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-South-Sea run also up into the Northern Seas But I think the Indian and the south-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-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
Aequator B. And so did I once But the reason commonly given for it is so improbable that I do not think so now For the Cause they render of it is onely that the Motion of the Earth is swiftest in the Aequinoctial and slowest about the Poles and consequently since Motion is the Cause of Heat and Cold is but as 't was thought a want of the same they inferr'd that the greatest Cold must be about the Poles of the Aequinoctial Wherein they miscounted For not every Motion causeth Heat but this agitation onely which we call compounded Motion though some have alleadged Experience for that opinion as that a Bullet out of a Gun will with its own swiftness melt Which I never shall believe A. 'T is a common thing with many Philosophers to maintain their Fancies with any rash report and sometimes with a Lye But how is it possible that so soft a Substance as water should be turned into so hard a Substance as Ice B. When the Air shaves the Globe of the Earth with such swiftness as that of Sixty miles in a minute of an hour it cannot where it meets with still water but beat it up into small and undistinguishable bubbles and involve it self in them as in so many bladders or skins of Water And Ice is nothing else but the smallest imaginable parts of Air and Water mixt which is made hard by this compounded Motion that keeps the parts so close together as not to be separated in one place without disordering the Motion of them all For when a Body will not easily yield to the impression of an external Movent in one place without yielding in all we call it Hard And when it does we say 't is Soft A. Why is not Ice as well made in a moved as in a still water Are there not great Seas of Ice in the Northern parts of the Earth B. Yes and perhaps also in the Southern parts But I cannot imagine how Ice can be made in such agitation as is always in the open Sea made by the Tides and by the Winds But how it may be made at the Shoar it is not hard to imagine For in a River or Current though swift the water that adhereth to the banks is quiet and easily by the Motion of the Air driven into small insensible bubbles and so may the water that adhereth to those bubbles and so forwards till it come into a stream that breaks it and then it is no wonder though the fragments be driven into the open Sea and freeze together into greater lumps But when in the open Sea or at the Shoar the Tide or a great Wave shall arise this young and tender Ice will presently be washt away And therefore I think it evident that as in the Thames the Ice is first made at the banks where the Tide is weak or none and broken by the stream comes down to London and part goes to the Sea floating till it dissolve and part being too great to pass the Bridge stoppeth there and sustains that which follows till the River be quite frozen over So also the Ice in the Northern Seas begins first at the banks of the Continent and Islands which are scituated in that Climate and then broken off are carried up and down and one against another till they become great Bodies A. But what if there be Islands and narrow Inlets of the Sea or Rivers also about the Pole of the Aequinoctial B. If there be 't is very likely the Sea may also there be covered all over with Ice But for the truth of this we must stay for some further discovery A. When the Ice is once made and hard what dissolves it B. The Principal Cause of it is the weight of the water it self but not without some abatement in the Stream of the Air that hardned it as when the Sun-beams are less oblique to the Earth or some contrary Wind resisteth the stream of the Air. For when the impediment is removed then the nature of the water only worketh and being a heavie Body downward A. I forgot to ask you Why two pieces of Wood rub'd swiftly one against another will at length set on fire B. Not onely at length but quickly if the Wood be dry And the Cause is evident viz. the compounded Motion which dissipates the external small parts of the Wood. And then the inner parts must of necessity to preserve the Plenitude of the Universe come after first the most Fluid and then those also of greater consistence which are first erected and the Motion continued made to flie swiftly out whereby the Air driven to the Eye of the beholder maketh that fancie which is called Light A. Yes I remember you told me before that upon any strong pressure of the Eye the resistance from within would appear a Light But to return to the enquiry of Heat and Cold there be two things that beyond all other put me into admiration One is the swiftness of kindling in Gunpowder The other is the freezing of Water in a Vessel though not far from the fire set about with other water with Ice and Snow in it When Paper or Flax is flaming the flame creeps gently on and if a house full of Paper were to be burnt with putting a Candle to it it will be long in burning whereas a spark of fire would set on flame a mountain of Gunpowder in almost an instant B. Know you not Gunpowder is made of the powder of Charcole Brimstone and Salt-peter Whereof the first will kindle with a spark the second flame as soon as toucht with fire and the third blows it as being composed of many Orbs of Salt fill'd with Air and as it dissolveth in the flame furiously blowing increaseth it And as for making Ice by the fire side It is manifest that whilst the Snow is dissolving in the external vessel the Air must in the like manner break forth and shave the Superficies of the inner vessel and work through the water till it be frozen A. I could easily assent to this if I could conceive how the Air that shaves as you say the outside of the Vessel could work through it I conceive well enough a pail of water with Ice or Snow dissolving in it and how it causeth Wind. But how that Wind should communicate it self through the vessel of wood or metal so as to make it shave the Superficies of the water which is within it I do not so well understand B. I do not say the inner Superficies of the vessel shaves the water within it But 't is manifest that the Wind made in the Pail of water by the melting Snow or Ice presseth the sides of the Vessel that standeth in it and that the pressure worketh clean through how hard soever the Vessel be and that again worketh on the water within by restitution of its parts and so hardeneth the water by degrees A. I understand you now The Ice in the Pail
fall by their weight So also it is forced up in moist ground and with it many small Atomes of the Earth which are either twisted with the rising water into Plants or are carried up and down in the Air incertainly But the greatest Quantity of Water is forced up from the great South and Indian Seas that lie under the Tropique of Capricorn And this Climate is that which makes the Suns Perigaeum to be always on the Winter-Solstice And that is the part of the Terrestrial Globe which Keplerus says is kinde to the Sun whereas the other part of the Globe which is almost all dry land has an Antipathy to the Sun And so you see where this Magnetical vertue of the Earth lies For the Globe of the Earth having no Natural Appetite to any place may be drawn by this Motion of the Sun a little neerer to it together with the water which it raiseth A. Can you guess what may be the Cause of Wind B. I think it manifest that the unconstant Winds proceed from the uncertain Motion of the Clouds ascending and descending or meeting with one another For the Winds after they are generated in any place by the descent of a Cloud they drive other Clouds this way and that way before them the Air seeking to free it self from being pent up in a straight For when a Cloud descendeth it makes no wind sensible directly under it self But the Air between it and the Earth is prest and forced to move violently outward For it is a certain Experiment of Mariners that if the Sea go high when they are becalmed they say they shall have more Wind than they would and take in their Sails all but what is necessary for steering They know it seems that the Sea is moved by the descent of Clouds at some distance off Which presseth the water and makes it come to them in great Waves For a Horizontal Wind does but curl the Water A. From whence come the Rivers B. From the Rain or from the falling of Snow on the higher ground But when it descendeth under ground the place where it again ariseth is called the Spring A. How then can there be a Spring upon the top of a Hill B. There is no Spring upon the very top of a Hill unless some Natural Pipe bring it thither from a higher Hill A. Julius Scaliger says there is a River and in it a Lake upon the top of Mount Cenis in Savoy and will therefore have the Springs to be ingendred in the Caverns of the Earth by Condensation of the Air. B. I wonder he should say that I have pass'd over that Hill twice since the time I read that in Scaliger and found that River as I pass'd and went by the side of it in plain ground almost two miles Where I saw the water from two great Hills one on one side the other on the other in a thousand small Rillets of melting Snow fall down into it Which has made me never to use any Experiment the which I have not my self seen As for the conversion of Air into Water by Condensation and of Water into Air by Rarefaction though it be the doctrine of the Peripatetiques it is a thing incogitable and the words are insignificant For by Densum is signified onely frequencie and closeness of parts and by Rarum the contrary As when we say a Town is thick with houses or a Wood with trees we mean not that one house or tree is thicker than another but that the spaces between are not so great But since there is no Vacuum the spaces between the parts of Air are no larger than between the parts of Water or of any thing else A. What think you of those things which Mariners that have sailed through the Atlantick Sea called Spouts which pour down water enough at once to drown a great Ship B. 'T is a thing I have not seen And therefore can say nothing to it though I doubt not but when two very large and heavie Clouds shall be driven together by two great and contrary winds the thing is possible A. I think your reason good And now will propound to you another Experiment I have seen an exceeding small Tube of Glass with both ends open set upright in a Vessel of Water and that the Superficies of the Water within the Tube was higher a good deal than of that in the Vessel but I see no reason for it B. Was not part of the Glass under Water Must not then the Water in the Vessel rise Must not the Air that lay upon it rise with it Whither should this rising Air go since there is no place empty to receive it It is therefore no wonder if the Water press'd by the Substance of the Glass which is dipt into it do rather rise into a very small Pipe than come about a longer way into the open Air. A. 'T is very probable I observed also that the top of the inclosed Water was a concave Superficies which I never saw in other Fluids B. The Water hath some degree of tenacity though not so great but that it will yield a little to the Motion of the Air as is manifest in the Bubbles of water where the concavity is always towards the Air. And this I think the cause why the Air and Water meeting in the Tube make the Superficies towards the Air concave which it cannot do to a Fluid of greater tenacity A. If you put into a Bason of Water a long rag of Cloth first drenched in water and let the longer part of it hang out it is known by Experience that the Water will drop out as long as there is any part of the other end under Water B. The cause of it is that water as I told you hath a degree of tenacity And therefore being continued in the rag till it be lower without than within the weight will make it continue dropping though not onely because it is heavie for if the rag lay higher without than within and were made heavier by the breadth it would not descend but 't is because all heavie Bodies Naturally descend with proportion of swiftness duplicate to that of the time whereof I shall say more when we talk of Gravity A. You see how despicable Experiments I trouble you with But I hope you will pardon me B. As for mean and common Experiments I think them a great deal better Witnesses of Nature than those that are forced by fire and known but to very few CAP. VI. Of the Causes and Effects of Heat and Cold. A. 'T Is a fine day and pleasant walking through the Fields but that the Sun is a little too hot B. How know you that the Sun is hot A. I feel it B. That is to say you know that your self but not that the Sun is hot But when you finde your self hot what Body do you feel A. None B. How then can you infer your heat from the Sense of Feeling Your walking
may have made you hot Is Motion therefore hot No. You are to consider the Concomitants of your heat as that you are more faint or more ruddy or that you sweat or feel some Endeavour of Moisture or Spirits tending outward and when you have found the Causes of those Accidents you have found the Causes of Heat which in a living Creature and specially in a Man is many times the Motion of the parts within him such as happen in sickness anger and other passions of the minde which are not in the Sun nor in Fire A. That which I desire now to know is what Motions and of what Bodies without me are the Efficient Causes of my Heat B. I shewed you yesterday in discoursing of Rain how by this compounded Motion of the Suns Body the Air was every way at once thrust off West and East so that where it was contiguous the small parts of the water were forced to rise for the avoiding of Vacuum Think then that your hand were in the place of water so exposed to the Sun Must not the Sun work upon it as it did upon the Water Though it break not the skin yet it will give to the inner Fluids and looser parts of your hand an Endeavour to get forth which will extend the skin and in some climates fetch up the bloud and in time make the skin black The Fire also will do the same to them that often sit with their naked skins too neer it Nay one may sit so neer without touching it as it shall blister or break the skin and fetch up both spirits and bloud mixt into a putrid oyly matter sooner than in a Furnace Oyl can be extracted out of a Plant. A. But if the Water be above the Fire in a Kettle what then will it do Shall the particles of water go toward the Fire as it did toward the Sun B. No. For it cannot But the Motion of the parts of the Kettle which are caused by the Fire shall dissipate the Water into Vapour till it be all cast out A. What is that you call Fire Is it a hard or Fluid Body B. It is not any other Body but that of the shining coal which coal though extinguished with Water is still the same Body So also in a very hot Furnace the hollow spaces between the shining coals though they burn that you put into them are no other Body than Air moved A. Is it not Flame B. No. For flame is nothing but a multitude of Sparks and Sparks are but the Atomes of the Fewel dissipated by the incredible swift Motion of the Movent which makes every Spark to seem a hundred times greater than it is as appears by this That when a man swings in the Air a small stick fired at one end though the Motion cannot be very swift yet the Fire will appear to the eye to be a long streight or crooked Line Therefore a great many sparks together flying upward must needs appear unto the sight as one continued Flame Nor are the sparks striken out of a Flint any thing else but small particles of the stone which by their swift Motion are made to shine But that Fire is not a substance of it self is evident enough by this that the Sun-beams passing through a Globe of Water will burn as other fire does Which beams if they were indeed Fire would be quenched in the passage A. This is so evident that I wonder so wise men as Aristotle and his followers for so long a time could hold it for an Element and one of the primary parts of the Universe But the Natural heat of a man or other living Creature whence proceedeth it Is there any thing within their Bodies that hath this compounded Motion B. At the breaking up of a Deer I have seen it plainly in his Bowels as long as they were warm And it is called the Peristaltique Motion and in the Heart of a Beast newly taken out of his Body and this Motion is called Systole and Diastole But they are both of them this compounded Motion whereof the former causeth the food to Winde up and down through the guts and the later makes the Circulation of the Blood A. What kind of Motion is the Cause of Cold Methinks it should be contrary to that which causeth Heat B. So it is in some respect For seeing the Motion that begets Heat tendeth to the separation of the parts of the Body whereon it acteth it stands with reason that the Motion which maketh Cold should be such as sets them closer together But contrary Motions are to speak properly when upon two ends of a Line two Bodies move towards each other the Effect whereof is to make them meet But each of them as to this Question is the same A. Do you think as many Philosophers have held and now hold that Cold is nothing but a privation of Heat B. No. Have you never heard the Fable of the Satyre that dwelling with a Husbandman and seeing him blow his fingers to warm them and his Pottage to cool it was so scandalized that he ran from him saying he would no longer dwell with one that could blow both Hot and Cold with one breath Yet the Cause is evident enough For the Air which had gotten a Calefactive power from his vital parts was from his mouth and throat gently diffused on his fingers and retained still that power But to cool his Pottage he streightened the passage at his lips which extinguished the Calefactive Motion A. Do you think Wind the general Cause of Cold If that were true in the greatest Winds we should have the greatest Frosts B. I mean not any of those uncertain Winds which I said were made by the Clouds but such as a Body moved in the Air makes to and against it self For it is all one Motion of the Air whether it be carried against the Body or the Body against it Such a Wind as is constant if no other be stirring from East to West made by the Earth turning dayly upon its own Centre Which is so swift as except it be kept off by some hill to kill a man as by Experience hath been found by those who have passed over great Mountains and specially over the Andies which are opposed to the East And such is the Wind which the Earth maketh in the Air by her Annual Motion which is so swift as that by the Calculation of Astronomers to go Sixty miles in a minute of an hour And therefore this must be the Motion which makes it so cold about the Poles of the Ecliptique A. Does not the Earth make the Wind as great in one part of the Ecliptique as in another B. Yes But when the Sun is in Cancer it tempers the Cold and still less and less but least of all in the Winter-Solstice where his beams are most oblique to the Superficies of the Earth A. I thought the greatest Cold had been about the Poles of the
by its dissolution transfers its Hardness to the water within B. You are merry But supposing as I do that the Ice in the Pail is more than the water in the Vessel you will finde no absurdity in the Argument Besides the Experiment you know is common A. I confess it is probable The Greeks have the word 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 whence the Latins have their word Frigus to signifie the curling of water by the Wind and use the same also for Horrour which is the passion of one that cometh suddenly into a cold Air or is put into a sudden affright whereby he shrinks and his hair stands upright Which manifestly shews that the Motion which causeth Cold is that which pressing the Superficies of a Body sets the parts of it closer together But to proceed in my Quaeries Monsieur Des Cartes who you know hath written somewhere that the noise we hear in Thunder proceeds from breaking of the Ice in the Clouds What think you of it Can a Cloud be turned into Ice B. Why not A Cloud is but Water in the Air. A. But how For he has not told us that B. You know that 't is onely in Summer and in hot weather that it Thunders or if in Winter it is taken for a Prodigie You know also that of Clouds some are higher some lower and many in number as you cannot but have oftentimes observed with spaces between them Therefore as in all Currents of water the Water is there swiftest where it is streightned with Islands so must the Current of Air made by the Annual Motion be swiftest there where it is checkt with many Clouds through which it must as it were be strained and leave behinde it many small particles of earth always in it and in hot weather more than ordinary A. This I understand and that it may cause Ice But when the Ice is made how is it broken And why falls it not down in shivers B. The particles are inclosed in small Caverns of the Ice and their Natural Motion being the same which we have ascribed to the Globe of the Earth requires a sufficient space to move in But when it is imprisoned in a less room that that then a great part of the Ice breaks And this is the Thunder-clap The Murmur following is from the settling of the Air. The Lightening is the fancie made by the recoiling of the Air against the Eye The fall is in Rain not in Shivers because the prisons which they break are extreme narrow and the shivers being small are dissolved by the Heat But in less Heat they would fall in Drops of Hail that is to say half frozen by the shaving of the Air as they fall and be in a very little time much less than Snow or Ice dissolved A. Will not that Lightning burn B. No. But it hath often kill'd men with Cold. But this extraordinary swiftness of Lightning consisteth not in the Expansion of the Air but in a straight and direct stream from where it breaks forth which is in many places successively according to the Motion of the Cloud A. Experience tells us that I have now done with my Problems concerning the great Bodies of the world the Stars and Element of Air in which they are moved and am therein satisfied and the rather because you have answered me by the Supposition of one onely Motion and commonly known and the same with that of Copernicus whose Opinion is received by all the Learned and because you have not used any of these empty terms Sympathy Antipathy Antiperistasis c. for a natural Cause as the old Philosophers have done to save their credit For though they were many of them wise men as Plato Aristotle Seneca and others and have written excellently of Morals and Politiques yet there is very little Natural Philosophy to be gathered out of their Writings B. Their Ethiques and Politiques are pleasant reading but I finde not any argument in their discourses of Justice or Vertue drawn from the supreme Authority on whose Laws all Justice Vertue and good Politiques depend A. Concerning this Cover or as some have called it the Scurf or Scab of the Terrestrial Star I will begin with you to morrow For it is a large Subject containing Animals Vegetables Metals Stones and many other kinds of Bodies the knowledge whereof is desired by most men and of the greatest and most general profit B. And this is it in which I shall give you the least satisfaction so great is the variety of Motion and so concealed from humane senses CAP. VII Of Hard and Soft and of the Atomes that flie in the Air. A. COncerning this Cover of the Earth made up of an infinite number of parts of different natures I had much ado to finde any tolerable method of enquiry But I resolved at last to begin with the Questions concerning Hard and Soft and what kinde of Motion it is that makes them so I know that in any pulsion of Air the parts of it go innumerable and inexplicable ways but I ask only if every point of it be moved B. No. If you mean a Mathematical point you know it is impossible For nothing is movable but Body But I suppose it divisible as all other Bodies into parts divisible For no Substance can be divided into Nothings A. Why may not that Substance within our Bodies which are called Animal spirits be another kind of Body and more subtile than the common Air B. I know not why no more than you or any man else knows why it is not very Air though purer perhaps than the common Air as being strained through the blood into the Brain and Nerves But howsoever that be there is no doubt but the least parts of the common Air respectively to the whole will easilier pierce with equal Motion the Body that resisteth them than the least parts of water For it is by Motion onely that any mutation is made in any thing and all things standing as they did will appear as they did And that which changeth Soft into Hard must be such as makes the parts not easily to be moved without being moved all together which cannot be done but by some Motion compounded And we call Hard that whereof no part can be put out of order without disordering all the rest which is not easily done A. How Water and Air beaten into extreme small Bubbles is hardned into Ice you have told me already and I understand it But how a soft Homogeneous Body as Air or Water should be so hardned I cannot imagine B. There is no hard Body that hath not also some degree of Gravity and consequently being loose there must be some Efficient Cause that is some Motion when it is severed from the Earth to bring the same to it again And seeing this compounded Motion gives to the Air and Water an Endeavour from the Earth the Motion which must hinder it must be in a way contrary to the compounded
that they might have called it an intrinsecal Motion rather than an intrinsecal quality A. Yes But not how Motion should be intrinsecal to the special individual Body moved For how should they when you are the first that ever sought the differences of Qualities in local Motion except your authority in Philosophy were greater with them than it is For 't is hard for a man to conceive except he see it how there should be Motion within a Body otherwise than as it is in living creatures B. But it may be they never sought or despaired of finding what natural Motion could make any inanimate thing tend one way rather than another A. So it seems But the first of them enquires no further than Why so much water being a heavie Body as lies perpendicularly on a Fishes back in the bottom of the Sea should not kill it The other whereof the Author is Dr. Wallis treateth universally of Gravity B. Well But what are the Questions which from these Books you intend to ask me A. The Author of the first Book tells me that Water and other Fluids are Bodies continued and act as to Gravity as a piece of Ice would do of the same Figure and quantity Is that true B. That the Universe supposing there is no place empty is one entire Body and also as he saith it is a continual Body is very true And yet the parts thereof may be contiguous without any other cohesion but Touch. And it is also true that a Vessel of Water will descend in a medium less heavie but Fluid as Ice would do A. But he means that water in a Tub would have the same Effect upon a Fish in the bottom of the Tub as so much Ice would have B. That also would be true if the water were frozen to the sides of it Otherwise the Ice if there be enough will crush the Fish to death But how applies he this to prove that the water cannot hurt a Fish in the Sea by its weight A. It plainly appears that Water does not Gravitate on any part of it self beneath it B. It appears by Experience but not by this Argument though instead of Water the Tub were fill'd with Quicksilver A. I thought so But how it comes to pass that the Fish remains uncrush'd I cannot tell B. The Endeavour of the Quicksilver downward is stopt by the resistance of the hard bottom But all Resistance is a contrary Endeavour that is an Endeavour upwards which gives the like Endeavour to the Quicksilver which is also heavie and thereby the Endeavour of the Quicksilver is diverted to the sides round-about where stopt again by the resistance of the sides it receives an Endeavour upwards which carries the Fish to the top lying all the way upon a soft bed of Quicksilver This is the true manner how the Fish is saved harmless But your Author I believe either wanted age or had too much business to study the doctrine of Motion and never considered that Resistance is not an impediment onely or privation but a contrary Motion and that when a man claps two pieces of Wax together their contrary Endeavour will turn both the pieces into one Cake of Wax A. I know not the Author but it seems he has deeplier considered this Question than other men For in the Introduction to his Book he saith That men have pre-engaged themselves to maintain certain Principles of their own invention and are therefore unwilling to receive any thing that may render their labour fruitless and That they have not strictly enough considered the several interventions that abate impede advance or direct the Gravitation of Bodies B. This is true enough and he himself is one of those men in that he considered not that Resistance is one of those interventions which abate impede and direct Gravitation But what are his Suppositions for the Question he handles A. His first is That as in a Pyramide of Brick wherein the Bricks are so joyned that the uppermost lies every where over the joynt or Cement of the two next below it you may break down a part and leave a Cavity and yet the Bricks above will stand firm and sustain one another by their cross posture So also it is in Wheat Hail-shot Sand or Water and so they arch themselves and thereby the Fish is every way secured by an arch of water over it B. That the cause why Fishes are not crusht nor hurt in the bottom of the Sea by the weight of the water is the waters arching it self is very manifest For if the uppermost Orb of the water should descend by its Gravity it would tend toward the Centre of the Earth and place it self all the way in a less and lesser Orb which is impossible For the places of the same Body are always equal But that Wheat Sand Hail-shot or loose Stones should make a firm arch is not credible A. The Author therefore it seems quits it And taketh a second Hypothesis for the true Cause though the former he saith be not useless but contributes its part to it B. I see though he depart from his Hypothesis he looks back upon it with some kindness What is his second Hypothesis A. It is That Air and Water have an Endeavour to Motion upward downward directly obliquely and every way For Air he saith will come down his chimney and in at his door and up his stairs B. Yes and mine too and so would Water if I dwelt under water rather than admit of Vacuum But what of that A. Why then it would follow that those several tendencies or Endeavours would so abate impede and correct one another as none of them should Gravitate Which being granted the Fish can take no harm Wherein I finde one difficulty Which is this The Water having an Endeavour to Motion every way at once methinks it should go no way but lie at rest which he saith was the opinion of Stevinus and rejecteth it saying it would crush the Fish into pieces B. I think the Water in this case would neither rest nor crush For the Endeavour being as he saith intrinsecal and every way must needs drive the water perpetually outward that is to say as to this Question upwards and seeing the same Endeavour in one individual Body cannot be more ways at once than one it will carry it on perpetually without limit beyond the fixed Stars and so we shall never more have rain A. As ridiculous as it is it necessarily follows B. What are Dr. Wallis his Suppositions A. He goes upon Experiments And first he alleadgeth this That Water left to it self without disturbance does naturally settle it self into a Horizontal Plain B. He does not then as your Author and all other men take Gravity for that Quality whereby a Body tendeth to the Centre of the Earth A. Yes he defines Gravity to be a Natural propension towards the Centre of the Earth B. Then he contradicteth himself For if all heavie
Bodies tend naturally to one Centre they shall never settle in a Plain but in a Spherical Superficies But against this That such an Horizontal Plain is found in water by Experience I say it is impossible For the Experiment cannot be made in a Bason but in half a mile at Sea Experience visibly shews the contrary According to this he should think also that a pair of Scales should hang parallel A. He thinks that too B. Let us then leave this Experiment What saies he further concerning Gravity A. He takes for granted not as an Experiment but an Axiome that Nature worketh not by election but ad ultimum virium with all the power it can B. I think he means for 't is a very obscure passage that every inanimate Body by nature worketh all it can without election which may be true But 't is certain that men and beasts work often by election and often without election as when he goes by election and falls without it In this sence I grant him that Nature does all it can But what infers he from it A. That naturally every Body has every way if the ways oppose not one another an Endeavour to Motion And consequently that if a Vessel have two holes one at the side another at the bottom the water will run out at both B. Does he think the Body of water that runs out at the side and that which runs out at the bottom is but one and the same Body of water A. No sure He cannot think but that they are two several parts of the whole Water in the Vessel B. What wonder is it then if two parts of water run two ways at once or a thousand parts a thousand ways Does it follow thence that one Body can go more than one way at once Why is he still medling with things of such difficulty He will finde at last that he has not a Genius either for Natural Philosophy or for Geometry What other Suppositions has he A. My first Author had affirmed that a lighter Body does not Gravitate on a heavier against this Dr. Wallis thus argueth Let there be a Siphon A B C D filled with Quicksilver to the level A D. If then you pour Oyl upon A as high as to E he asketh if the Oyl in A E as being heavie shall not press down the Quicksilver a little at A and make it rise a little at D suppose to F. And answers himself that certainly it will So that it is neither an Experiment nor an Hypothesis but onely his opinion B. Whatsoever it be it is not true though the Doctor may be pardoned because the contrary was never proved A. Can you prove the contrary B. Yes For the Endeavour of the Quicksilver both from A and D downward is stronger than that of the Oyl downward If therefore the Endeavour of the Quicksilver were not resisted by the bottom B C it would fall so by reason of the acceleration of heavie Bodies in their descending as to leave the Oyl so that it should not onely not press but also not touch the Quicksilver It is true in a pair of Scales equally charged with Quicksilver that the addition of a little Oyl to either Scale will make it praeponderate And that was it deceiv'd him A. 'T is evident The last Experiment he cites is the weighing of Air in a pair of Scales where 't is found manifestly that it has some little weight For if you weigh a Bladder and put the weight into one Scale and then blow the Bladder full of Air and put it into the other Scale the full Bladder will outweigh the empty Must not then the Air Gravitate B. It does not follow I have seen the Experiment just as you describe it but it can never be thence demonstrated that Air has any weight For as much Air as is prest downward by the weight of the blown Bladder so much will rise from below and lay it self Spherically at the altitude of the Center of gravity of the Bladder so blown So that all the Air within the Bladder above that Centre is carried thither imprisoned and by violence And the force that carries it up is equal to that which presseth it down There must therefore be allowed some little counterpoise in the other Scale to ballance it Therefore the Experiment proves nothing to his purpose And whereas they say there be small heavie Bodies in the Air which make it Gravitate do they think the force which brought them thither cannot hold them there A. I leave this Question of the Fish as cleerly resolved because the water tending every way to one point which is the Centre of the Earth must of necessity arch it self And now tell me your own opinion concerning the Cause of Gravity and why all Bodies descend or ascend not all alike For there can be no more Matter in one place than another if the places be equal B. I have already shewed you in general that the difference of Motion in the parts of several Bodies makes the difference of their Natures And all the difference of Motions consisteth either in swiftness or in the way or in the duration But to tell you in Special why Gold is heaviest and then Quicksilver and then perhaps Lead is more than I hope to know or mean to enquire for I doubt not but that the Species of heavie hard Opaque and Diaphanous were all made so at their creation and at the same time separated from different Species So that I cannot guess at any particular Motions that should constitute their natures further than I am guided by the Experiments made by fire or mixture A. You hope not then to make Gold by Art B. No unless I could make one and the same thing heavier than it was God hath from the beginning made all the Kindes of Hard and Heavie and Diaphanous Bodies that are and of such Figure and magnitude as he thought fit but how small soever they may by accretion become greater in the Mine or perhaps by generation though we know not how But that Gold by the art of man should be made of not Gold I cannot understand nor can they that pretend to shew how For the heaviest of all Bodies by what mixture soever of other Bodies will be made lighter and not to be received for Gold A. Why when the Cause of Gravity consisteth in Motion should you despair of finding it B. It is certain that when any two Bodies meet as the Earth and any heavie Body will the Motion that brings them to or towards one another must be upon two contrary ways and so also it is when two Bodies press each other in order to make them Hard. So that one contrariety of Motion might cause both Hard and Heavie But it doth not For the hardest Bodies are not always the heaviest Therefore I finde no access that way to compare the Causes of different Endeavours of heavie Bodies to descend A. But shew