which made little parts of bodies naturally heavie descend slowly in regard of the velocity of greater parts of the same bodies descending the Doctrine of which we intend to deliver hereafter Others therfore perceiving this rule to fall short have indeavour'd to piece it out by the mixtion of Vacuitie among bodies believing it is that which makes one rarer then another Which mixtion they do not put always immediate to the main body they consider but if it have other rarer and lighter bodies mingled with it they conceive this mixtion immediate only to the rarest or lightest As for example a Crystal being lighter and consequently rarer then a Diamond they will not say there is more vacuity in a Crystal then in a Diamond but that the pores of a Crystal are greater and consequently there is more aire in a Crystal to fil the pores of it then is in a Diamond and the vacuities are in the aire which abounding in a Crystal more then in a Diamond makes that lighter and rarer then this by the more vacuites that are in the greater Quantity of aire which is mingled with it But against this suppsition a powerful adversary is urged for Aristotle in his 4. Book of Physicks hath demonstrated that there can be no motion in vacuity 'T is true they indeavour to evade his demonstration as not reaching home to their supposition by acknowledging it to be an evident one in such a vacuity as he there speaks of which he supposed so great that a body may swim in it as in an Ocean and not touch or be near any other body whereas this opinion exclude all such vast inanity admit no vacuities but so little ones as no body whatever can come to but wil be biger than they and consequently must on some side orother touch the corporal parts which those vacuities divide for they are the separations of the least parts that are or can be actually divided from one another which parts must of necessity touch one another on some side or else they could not hang together to compose one substance and and therefore the dividing vacuities must be less then the divided parts And thus no body will ever be in danger of floating up and down without touching any thing which is the difficulty that Aristotle chiefly impugns I confess I should be very glad that this supposition might serve our turne and save the Phenomena that appear among bodies through their variety of Rarity and Density Which if it might be then would I straight go on to the inquiring after what follow'd out of this ground as Astronomers to use our former similitude calculate the future appearances of the Celestial bodies out of those motions and orbs they assign to the Heavens For as this apprehension of vacuity in bodies is very easie and intelligible so the other which I conceive to be the truth of the case is exceedingly abstracted and one of the most difficult points in all the Metaphysicks and therefore I would if it were possible avoid touching upon it in this discourse which I desire should be as plain and easie and as much removed from Scholastick terms as may be But indeed the inconveniences that follow out of this supposition of vacuities are so great as it is impossible by any means to slide them over As for example let us borrow of Gallileus the proportion of weight between water and air He shews us how the one is 400 times heavier then the other And Marinus Ghetaldus teaches us that gold is 19 times heavier then water so that gold must be 7600 times heavier then air Now then considering that nothing in a body can weigh but the solid parts of it it follows that the proportion of the parts of gold in a sphere of an inch Diameter is to the parts of the air of a like dimension as 7600 is to one Therfore in air it self the vacuities that are supposed in it will be to the solid parts of it in the same proportion as 7600 to one Indeed the proportion of difference shal be greater for even in gold many vacuities must be admitted as appears by the heating of it which shews that in every least part it is exceeding porous But according to this rate without pressing the inconvenience any further the air will by this reckoning appear to be like a net whose holes distances are to the lines and threds in the proportion of 7600 to one and so would be lyable to have little parts of its body swim in those greater vacuities contrary to what they strive to avoid Which would be excedingly more if we found on the one side any bodies heavier denser then gold that were so solid as to exclude all vacuities on the other side should balance them withsuch bodies as are lighter and rarer then air as fire is and as some say will have the aether to be But already the disproportion is so great and the vacuity so strangely exceeds the body in which it is as were too great an absurdity to be admitted And besides it would destroy all motion of small bodies in the air if it be true as Aristotle hath demonstrated in the fourth Book of his Physicks that motion cannot be made but among bodies and not in vacuo Again if rarity were made by vacuity rare bodies could not be gather'd together without losing their rarity and becoming dense The contrary of which we learn by constant experience as when the Smith and Glassemender drive their white and fury fires as they term them when aire pierces most in the sharp wind and generally we see that more of the same kind of rare bodies in less place works more efficaciously according to the nature that results out of that degree of rarity Which argues that every little part is as rare as it was before for else it would lose the vertue of working according to the nature but that by their being crowded together they exclude all other bodies that before mediated between the little parts of their main body and so more parts being gotten together in the same place then formerly there were they work more forcibly Thirdly if such vacuities were the cause of rarity it would follow that fluid bodies being rarer then solid ones would be of themselvs standing like nets or cobwebs wheras contrariwise we see their natures are to run together and to fill up every little creek and corner which effect following out of the very nature of the things themselves needs must exclude vacuities out of that nature And lastly if it be true as we have shew'd in the last Chapter that there are no actual parts in Quantity it follows of necessity that all Quantity must of it self be one as Metaphysicks teach us and then no distance can be admitted between one Quantity and another And truely if I understand Aristotle right he hath perfectly demonstrated that no vacuity is possible in nature
other things be seen as being accompanied by light is called Fire What admits the illuminative action of fire and is not seen is called Air What admits the same action and is seen in the rank of Elements is called Water And what through the density of it admits not that action but absolutely reflects it is called Earth And out of all we said of these four Elements it is manifest there cannot be a fifth as is to be seen at large in every Aristotelian Philosopher that writes of this matter I am not ignorant that there are sundry objections used to be made both against these notions of the First Qualities and against the division of the Elements but because they and their solotions are to be found in every ordinary Philosopher and not of any great difficulty and that the handling them is too particular for the design of this discourse and would make it too prolix I refer the Reader to seek them for his satisfaction in those Authors that treat Physick professedly and have deliver'd a compleat body of Phylosophy And I will end this Chapter with advertising him lest I should be misunderstood that though my disquisition here has pitch'd on the four bodies of Fire Air Water and Earth yet it is not my intention to affirme that those which we ordinary call so and fall daily within our use are such as I have here express'd them or that these Phlosophicall ones which arise purely out of the combination of the first qualities have their residence or consistence in great bulks in any places of the World be they never so remote as Fire in the hollow of the Moons Orb Water in the bottom of the Sea Air above the Clouds and Earth below the Mines But these notions are onely to serve for certain Idea's of Elements by which the forenamed bodies and the compounds of them may be tryed and receive their doom of more or lesse pure and approaching to the nature from whence they have their denomination And yet I will not deny but that such perfect Elements may be foumd in some very little quantities in mixed bodies and the greatest abundance of them in these four known bodies that we call in ordinary practise by the names of the pure ones for they are least compounded and approach most to the simpleness of the Elements But to determine absolutely their existence or not existence either in bulk or in little parts depends of the manner of action among bodies which as yet we have not medled with CHAP. V. Of the operations of the Elements in general And of their activities compared with one another HAving by our former discourse inquired out what degrees and proportions of rarity and density compounded with gravity are necessary for the production of the Elements and first qualities whose combinations frame the Elements our next consideration in that orderly progress we have proposed to our selves in this Treatise wherein our aim is to follow successively the steps which nature has printed out to us will be to examine the operations of the Elements by which they work upon one another To which end let us propose to our selves a rare and a dense body encountring one another by the impulse of some exterior agent In this case 't is evident that since rarity implyes a greater proportion of quantity and quantity is nothing but divisibility rare bodies must needs be more divisible then dense ones and consequently when two such bodies are press'd one against another the rare body not being able to resist division so strongly as the dense one is and being not permitted to retire back by reason of the extern violence impelling it against the dense body it follows that the parts of the rare body must be sever'd to let the dense one come between them and so the rare body becomes divided and the dense body the divider And by this we see that the notions of divider and divisible immediately follow rare and dense bodies and so much the more properly agree to them as they exceed in the qualities of Rarity and Density Likewise we are to observe in our case that the dense or dividing body must necessarily cut and enter further and further into the rare or divided body and so the sides of it be joyn'd successively to new and new pars of the rare body that gives way to it and forsake others it parts from Now the rare body being in a determinate situation of the Universe which we call being in a place and is a necessary condition belonging to all particular bodies and the dense body comming to be within the rare body whereas formerly it was not so it follows that it loses the place it had and gains another This effect is that which we call local motion And thus we see by explicating the manner of this action that locall motion is nothing else but the change of that respect or relation which the body moved has to the rest of the Universe following out of Division and the name of Locall Motion formerly signifies only the mutation of a respect to other extrinsecall bodies subsequent to that division And this is so evident and agreeable to the notions that all mankind who as we have said is judge and master of language naturally frames of place as I wonder much why any will labour to give other artificall and intricate doctrine of this that in it self is so plain and clear What need is there to introduce an imaginary space or with Johannes Grammaticus a subsistent quantity that must run through all the World and then entail to every body an aiery entity an unconceiveable mood an unintelligible Ubi that by an intrinsecall relation to such a part of the imaginary space must thereto pin and fasten the body it is in It must needs be a ruinous Phylosophy that is grounded upon such a contradiction as is the allotting of parts to that which the Authors themselvs upon the matter acknowledge to be merely nothing and upon so weak a shift to deliver them from the inconveniences that in their course of doctrine other circumstances bring them to as is the voluntary creating of new imaginary Entities in things without any ground in nature for them Learned men should express the advantage and subtilty of their wits by penetrating further into nature then the vulgar not by vexing and wresting it from its own course They should refine and carry higher not contradict and destroy the notions of mankind in those things it is the competent judge of as it undoubtedly is of those primary notions which Aristotle has rank'd under Ten Heads which as we have touched before every one can conceive in gross and the work of Scholars is to explicate them in particular and not to make the Vulgar believe they are mistaken in framing those apprehensions that nature taught them Out of that which hath been hitherto resolvd 't is manifest that Place really and abstracting from
from its nature by suffering the like effect Yet dilated water will in proportion moisten more then dilated fire will burn for the rarefaction of water brings it nearer to the nature of air whose chief propriety is moisture and the fire that accompanies it when it raiseth it into steam gives it more powerful ingression into what body it meets withal whereas fire when 't is very pure and at entire liberty to stretch and spread it self as wide as the nature of it will carry it gets no advantage of burning by its mixture with air and although it gains force by its purity yet by reason of its extreme rarefaction it must needs be extreamly faint But if by the help of Glasses you will gather into less room what is diffused into a great one and so condense it as much as it is for example in the flame of a candle then that fire or compacted light will burn much more forcibly then so much flame for there is as much of it in quantity excepting what is lost in the carriage of it and it is held in together in as little room and it has this advantage besides that 't is clog'd with no grosse body to hinder the activity of it It seems to me now that the very answering this objection doth besides repelling the force of it evidently prove that light is nothing but fire in its own nature and exceedingly dilated for if you suppose fire for example the flame of a candle to be stretch'd out to the utmost expansion that you may well imagine such a gross body is capable of 't is impossible it should appear and work otherwise then it doth in light as I have shewd above And again we see plainly that light gather'd together burns more forcibly then any other fire whatever and therefore must needs be fire Why then shall we not confidently conclude that what is fire before it gets abroad and is fire again when it comes together doth likewise remain fire during all its journey Nay even in the journey it self we have particular testimony that it is fire for light returning back from the earth charg'd with little atomes as it doth in soultry gloomy weather heats much more than before just as fire doth when it is imprisoned in a dense body Philosophers ought not to judge by the same rules that the common people doth Their gross sense is all their guide and therfore they cannot apprehend any thing to be fire that doth not make it self to be known for such by burning them But he that judiciously examines the matter and traces the pedigree and period of it and sees the reason why in some circumstances it burns and in others not is too blame if he suffer himself to be led by others ignorance contrary to his own reason When they that are curious in perfumes will have their chamber fil'd with a good scent in a hot season that agrees not with burning perfumes and therfore make some odoriferous water be blown about it by their servants mouthes that are dexterous in that ministery as is used in Spain in the Summer time every one that sees it done though on a sudden the water be lost to his eyes and touch and is only discernable by his nose yet is well satisfied that the scent which recreates him is the very water he saw in the glass extremely dilated by the forcible sprouting of it out from the servants mouth and will by little and little fall down and become again palpable water as it was before and therefore doubts not but it is still water whiles it hangs in the air divided into little atomes Whereas one that saw not the beginning of this operation by water nor observ'd how in the end it shews it self again in water might the better be excused if he should not think that what he smel'd were water blown about the air nor any substance of it self because he neither sees nor handles it but some adventitious quality he knows not how adhering to the air The like difference is between Philosophers that proceed orderly in their discourses and others that pay themselves with terms which they understand not The one see evidence in what they conclude whiles the others guesse wildly at random I hope the Reader will not deem it time lost from our main drift which we take up thus in examples and digressions for if I be not much deceived they serve exceedingly to illustrate the matter Which I hope I have now rendred so plain as no man that shall have well weighed it will expect that Fire dilated into that rarified substance which mankind who according to the different appearance of things to their sense gives different names to them calls Light should burn like that grosser substance which from doing so they call fire nor doubt but that they may be the same thing more or less attenuated as leaf-gold that flies in the air as light as down is as truly gold as that in an ingot which being heavier then any other substance falls most forcibly to the ground What we have said of the unburning fire which we call light streaming from the flame of a Candle may easily be apply'd to all other lights deprived of sensible heat whereof some appear with flame others without it Of the first sort are the innoxious flames that are often seen on the hair of mens heads and horses manes on the Masts of ships over graves and fat marish grounds and the like and of the latter sort are Glow-worms and the light-conserving stones rotten wood some kinds of fish and of flesh when they begin to putrifie and some other things of the like nature Now to answer the second part of this objection That we daily see great heats without any light as well as much light without any heat and therefore light and fire cannot be the same thing You may call to mind how Dense bodies are capable of great quantities of Rare ones and thereby it comes to pass that bodies which repugn to the dilatation of flame may nevertheless have much fire inclosed in them As in a stove let the fire be never so great yet it appears not outwards to the sight although that stove warm all the rooms near it So when many little parts of heat are imprison'd in as many little cells of gross earthly substance which are like so many little stoves to them that imprisonment will not hinder them from being very hot to the sense of feeling which is most perceptible of dense things But because they are choak'd with the closeness of the gross matter wherein they are closed they cannot break out into a body of flame or light so to discover their nature which as we have said before is the most unfit way for burning for we see that light must be condensed to produce flame and fire as flame must be to burn violently Having thus clear'd the third objection as I
conceive let us go on to the fourth which requires that we satisfie their inquisition who ask what becomes of that vast body of shining light if it be a body that fills all the distance between heaven and earth and vanishes in a moment assoon as a cloud or the Moon interposes it self between the Sun and us or that the Sun quits our Hemisphere No sign at all remains of it after its extinction as doth of all other substances whose destruction is the birth of some new thing Whither then is it flown we may be perswaded that a mist is a corporeal substance because it turns to drops of water upon the twigs that it invirons and so we might believe light to be fire if after the burning of it out we found any ashes remaing but experience assures us that after it is extinguished it leaves not the least vestigium behind it of having been there Now before we answer this objection we will intreat our Adversary to call to mind how we have in our solution of the former declared and proved that the light which for example shines from a candle is no more then the flame is from whence it springs the one being condensed and the other dilated and that the flame is in a perpetual flux of consumption about the circumference and of restauration at the center where it sucks in the fewell and then we will enquire of him what becomes of the bodie of flame which so continually dies and is renewed and leaves no remainder behind it as well as he doth of us what becomes of our body of light which in like manner is alwaies dying and alwaies springing fresh And when he hath well considered it he will find that one answer will serve for both Which is That as the fire streams out from the fountain of it and growes more subtile by its dilatation it sinks the more easily into those bodies it meets withall the first of which and that environs it round about is aire With air then it mingles and incorporates it self and by consequence with the other little bodies that are mingled with the aire and in them it receives the changes which nature works by which it may be turn'd into the other Elements if there be occasion or be still conserv'd in bodies that require heat Upon this occasion I remember a rare experiment that a Noble-Man of much sincerity and a singular friend of mine told me he had seen which was That by meanes of glasses made in a very particular manner and artificially placed one by another he had seen the Sun-beams gather'd together and precipitated down into a brownish or purplish red powder There could be no fallacy in this operation for nothing whatever was in the glasses when they were placed and disposed for this intent and it must be in the hot time of the year else the effect would not follow And of this Magistry he could gather some dayes near two ounces in a day And it was of a strange volative nature and would pierce and imprint his spiritual quality into gold it self the heaviest and most fixed body we converse withall in a very short time If this be plainly so without any mistaking then mens eyes and hands may tell them what becomes of light when it dies if a great deal of it were swept together But from what cause soever this experience had its effect our reason may be satisfied with what we have said above for I confesse for my part I beleeve the appearing body might be something that came along with the Sun-beams and was gather'd by them but not ther pure substance Some peradventure will object those lamps which both ancient and modern writers have reported to have been found in Tombes and Urns long time before closed up from mens repair to them to supply them with new fewel and therefore they believe such fires to feed upon nothing and consequently to be inconsumptible and perpetual Which if they be then our doctrine that will have light to be nothing but the body of fire perpetually flowing from his center and perpetual dying cannot be sound for in time such fires would necessarily spend themselves in light although light be so subtile a substance that an exceeding little quantity of fewel may be dilated into a vast quantity of light However there would be some consumption which how imperceptible soever in a short time yet after a multitude of revolutions of years must needs discover it self To this I answer That for the most part the witnesses who testifie originally the stories of these lights are such as a rational man cannot expect from them that exactness or nicitie of observation which is requisite for our purpose For they are usually gross labouring people who as they dig the ground for other intentions Stumble upon these Lamps by chance before they are aware and commonly they break them in the finding and imagine they see a glimpse of light which vanishes before they can in a manner take notice of it and is peradventure but the glistering of the broken glass or glazed pot which reflects the outward light assoon as by rummaging in the ground and discovering the Glass the light strikes upon it in such manner as sometimes a Diamond by a certain incountring of light in a dusky place may in the first twinkling of the motion seem to sparkle like fire And afterwards when they shew their broken Lamp and tell their tale to some man of a pitch of wit above them who is curious to inform himself of all the circumstances that may concern such lights they strain their memory to answer him satisfactorily unto all his demands and thus for his sake they perswade themselves to remember what they never saw and he again on his side is willing to help out the story a little And so after a while a very formal and particular relation is made of it As happens in like sort in reporting of all strange and unusual things when even those that in their nature abhor from lying are naturally apt to strain a little and fashion up in a handsome mould and almost to perswade themselves they saw more then they did so innate it is to every man to desire the having of some preeminence beyond his neighbours be it but in pretending to have seen something which they have not Therefore before I engage my self in giving any particular answer to this objection of pretended inconsumptible lights I would gladly see the effect certainly averred and undoubtedly proved For the testemonies which Fortunius Licetus produces who has been very diligent in gathering them and very sub 〈◊〉 in discoursing upon them and as the exactest Author that has written upon this subject do not seem to me to make that certainty which is required for the establishing of a ground in Philosophy Nevertheless if there be any certain experience in this particular I should think there might be some Art by circulation
to pass his way without hindring his fellow Wherfore seeing that one single light could not send rayes enough to fil every little space of aire that is capable of light and the less the further it is from the flame 't is obvious enough to conceive how in the space where the air is there is capacity for the rays of many candles Which being well sum'd up will take away the great admiration how the beams of light though they be corporeall can in such great multitudes without hindering one another enter into bodies and come to our eye and will shew that 't is the narrowness of our capacities and not the defect of nature which makes these difficulties seem so great For she hath sufficiently provided for all these subtile operations of fire as also for the entrance of it into glass and into all other solid bodies that are Diaphanous upon which was grounded the last instance the second objection pressed for all such bodies being constituted by the operation of fire which is alwaies in motion there must needs be ways left for it both to enter in and to evaporate out And this is most evident in glass which being wrought by an extreme violent fire and swelling with it as water and other things do by the mixture of fire must necessarily have great store fire in it self whiles it is boyling as we see by its being red hot And hence it is that the workmen are forced to let it cool by degrees in such relentings of fire as they call their nealing heats lest it should shiver in pieces by a violent succeeding of air in the room of the fire for that being of greater parts then the fire would strain the pore of the glass too suddenly and break it all in pieces to get ingressions whereas in those nealing heats the air being rarer lesser parts of it succeed to the fire and leisurely stretch the pores without hurt And therefore we need not wonder that light passes so easily through glass and much less that it gets through other bodies seeing the experience of Alchymists assures us 't is hard to find any other body so impenitrable as glass But now to come to the answer of the first and in appearance most powerful objection against the corporeity of light which urges that its motion is perform'd in an instant and therefore cannot belong to what is material and cloth'd with quantity We will endeavour to shew how unable the sense is to judge of sundry sorts of motions of Bodies and how grosly it is mistaken in them And then when it shall appear that the motion of light must necessarily be harder to be observed then those others I conceive all that is rais'd against our opinion by so incompetent a judge will fall flat to the ground First then let me put the Reader in mind how if ever he mark'd children when they play with firesticks they move and whirle them round so fast that the motion will cosen their eyes and represent an entire circle of Fire to them and were it somewhat distant in a dark night that one play'd so with a lighted Torck it would appear a constant Wheele of fire without any discerning of motion in it And then let him consider how slow a motion that is in respect of what 't is possible a body may participate of and he may safely conclude that 't is no wonder though the motion of light be not descried and that indeed no argument can be made from thence to prove that light is not a body But let us examine this consideration a little further and compare it to the motion of the earth or heavens Let the appearing circle of the fire be some three foot Diameter and the time of one entire circulation of it be the sixtieth part of a minute of which minutes there are 60. in an hour so that in a whole day there will but be 86400. of these parts of time Now the Diameter of the wheel of fire being but of three foot the whole quantity of space that it moves in that atome of time will be at the most ten foot which is three paces and a foot of which parts there are near eleven millions in the compass of the earth so that if the earth be moved round in 24. hours it must go near 130. times as fast as the Boy 's stick which by its swift motion deceives our eye But if we allow the Sun the Moon and the fixed Stars to move how extreme swift must their flight be and how imperceptible would their motion be in such a compass as our sight would reach to And this being certain that whether the earth or they move the appearances to us are the same 't is evident that as now they cannot be perceiv'd to move as peradventure they do not so it would be the very same in shew to us although they did move If the Sun were near us and gallop'd at that rate surely we could not distinguish between the beginning and ending of his race but there would appear one permanent Line of light from East to West without any motion at all as the Torch seems to make with so much a slower motion one permanent immoveable wheel of fire But contrary to this effect we see that the Sun and Stars by onely being removed further from our eyes do cosen our sight so grossely that we cannot discern them to be moved at all One would imagine that so rapid and swift a motion should be perceiv'd in some sort or other which whether it be in the earth or in them is all one to this purpose Either we should see them change their places whiles we look upon them as Arrows and Birds do when they fly in the Aire or else they should make a stream of light bigger then themselvs as the Torch doth But none of all this happens Let us gaze upon them so long and so attentively that our eyes be dazled with looking and all that while they seem to stand immovable and our eyes can give us no account of their journey till it be ended They discern it not while it is in doing So that if we consult with no better counsellour then them we may wonder to see that body at night setting in the West which in the morning we beheld rising in the East But that which seems to be yet more strange is that these bodies move cross us and nevertheless are not perceiv'd to have any motion at all Consider then how much easier it is for a thing that moves towards us to be with us before we are aware A nimble Fencer will put in a thrust so quick that the â—oil will be in your bosome when you thought it a yard off because in the same moment you saw his point so far distant and could not discerne it to move towards you till you felt the rude salutation it gave you If then you will compare the body of light with
continue some time before it can be settled and it being determin'd by the motion of the arrow that way that it slides it follows that all this commotion and undulation of the air serves to continue the arrow in its flight And thus faster then any part behind can be setled new ones before are stir'd till the resistance of the medium grows stronger then the impulse of the movers Besides this the arrow pressing on the air before it with a greater velocity then the air which is a liquid rare body can admit to move all of a piece without breaking it must of necessity happen that the parts of the air immediately before the arrow be driven upon others further off before these can be moved to give place unto them so that in some places the air becomes condens'd and consequently in others rarified Which also the wind we make in walking which will shake a paper pin'd loosly at the wall of a chamber towards which we walk and the cooling air caus'd by faning when we are hot do evidently confirm So that it cannot be doubted but condensation and rarefaction of the air must necessarily follow the motion of any solid body which being admitted 't is evident that a greater disorder and for some remarkable time must necessarily be in the air since it cannot brook to continue in more rarity or density then is natural to it Nor can weighty and light parts agree to rest in an equal height or lowness which the violence of the arrows motion forces them to for the present Therefore it cannot be deni'd but that though the arrow slide away there still remains behind it by this condensation and confusion of parts in the air motion enough to give impulse to the arrow so as to make it continue its motion after the bowstring has left it But here will arise a difficulty which is how this clapping in and undulation of the air should have strength and efficacy enough to cause the continuance of so smart a motion as is an arrow shot from a bow To this I need no other argument for an answer then to produce Galileo's testimony how great a body one single mans breath alone can in due circumstances give a rapid motion to and withal let us consider how the arrow and the air about it are already in a certain degree of velocity that is to say the obstacle that would hinder it from moving that way namely the resistance of the air is taken away and the causes that are to produce it namely the determining of the airs and atomes motion that way are heightned And then we may safely conclude that the arrow which of it self is indifferent to be moved upwards or downwards or forwards must needs obey that motion which is caused in it by the atomes and the air 's pressing upon it either according to the impulse of the string or when the string begins to flag according to the beating that follows the general constitution of nature or in a mixt manner according to the proportions that these two hold to one another Which proportions Galileus in his 4 Dialogue of Motion has attempted to explicate very ingeniously but having miss'd in one of his suppositions to wit that forced motion upon an Horizontal line is throughout uniform his great labours therein have taken little effect towards the advancing the knowledge of nature as he pretended for his conclusions succeed not in experience as Mersenius assures us after very exact trials nor can they in their reasons be fitted to nature So that to conclude this point I find no difficulty in allowing this motion of the air strength enough to force the moveable onwards for sometime after the first mover is sever'd from it and long after we see no motions of this nature endure so that we need seek no further cause for the continuance of it but may rest satisfied upon the whole matter that since the causes and circumstances our reason suggests to us are after mature and particular examination proportionable to the effects we see the doctrine we deliver must be sound and true For the establishing wherof we need not considering what we have already said spend much time in solving Galileo's arguments against it seeing out of what we have set down the answers to them appear plain enough For first we have assign'd causes how the air may continue its motion long enough to give as much impression as is needful to the arrow to make it go on as it does Which motion is not requisite to be near so great in the air behind the arrow that drives it on as what the arrow causes in the air before it for by reason of its density it must needs make a greater impression in the air it cuts then the air causes its motion would do of it self without the mediation of the arrow As when the force of a hand gives motion to a knife to cut a loaf of bread the knife by reason of the density and figure it has makes a greater impression in the loaf then the hand alone would do And this is the same that we declared in the natural motion of a heavy thing downwards to which we assigned two causes namely the beating of the atoms in the air falling down in their natural course to determine it the way it is to go and the density of the body that cutting more powerfully then those atoms can do gives together with their help a greater velocity to the moveable then the atoms of themselves can give Nor imports it that our resolution it aginst the general nature of rare and dense bodies in regard of conserving motion as Galileo objects For the reason why dense bodies conserve motion longer then rare bodies is because in regard of their dividing virtue they get in equal time a greater velocity Wherfore seeing velocity is equal to gravity it follows that resistance works not so much upon them as upon rare bodies and therfore cannot make them cease from motion so easily as it does rare bodies This is the general reason for the conservation of motion in dense bodies But because in our case there is a continual cause which conserves motion in the air the air may continue its motion longer than of it self it would do not in the same part of air which Galileus as it seems aim'd at but in divers parts in which the moveable successively is Which being concluded let us see how the forced motion comes to decrease and be ended To which purpose we may observe that the impression which the arrow receives from the air that drives it forwards being weaker than that which it receiv'd at first from the string by reason that the air is not so dense and therfore cannot strike so great a blow the arrow does not in this second measure of time wherein we consider the impulse given by the air only cut so strongly the air before it nor press so
carried out of the force of that motion directly the contrary way till the force of gravity overcoming the velocity it must be brought back again to the perpendicular which being done likewise with velocity it must send it again towards the place from which it fell at the first And in this course of motion it must continue for a while every Undulation being weaker then other till at last it quite ceases by the course of nature setling the air in its due situation according to the natural causes that work upon it And in this very manner also is performed that Undulation we see in water when it is stir'd from the natural situation of its Spherical superficies Galileo hath noted that the time in which the Undulations are made which follow one another of their own accord is the same in every one of them and that as much time precisely is taken up in a pendants going a very short arch towards the end of its vibration as was in its going the greatest arch at the beginning of its motion The reason wherof seems strange to him and he thinks it an accident natural to the body out of its gravity and that this effect convinces it is not the air which moves such bodies Wheras in truth 't is clearly the air which causes this effect Because the air striving at each end where it is furthest from the force of the motion to quiet it self gets at every bout somwhat upon the space and so contracts that into a shorter arch That motion also which we call Refraction and is manifest to sense only in light though peradventure hereafter more diligent searchers of nature may likewise find in such other bodies as are called qualitie as in cold or heat c. is but a kind of Reflexion For there being certain bodies in which the passages are so well order'd with their resistences that all the parts of them seem to permit light passe through them and yet all seem to reflect it when light passes through such bodies it finds at the very entrance of them such resistences where it passes as serve it for a reflecting body and yet such a reflectent body as hinders not the passage through but only from being a staight line with the line incident Wherfore the light must needs take a ply as beaten from those parts towards a line drawn from the illuminant falling perpendicularly upon the resisting superficies and therfore is term'd by Mathematicians to be refracted or broken towards the perpendicular Now at the very going out again of the light the second superficies if it be parallel to the former must needs upon a contrary cause strike it the contrary way which is which is termed from the perpendicular But before we wade any deeper into this difficulty we cannot omit a word of the manner of explicating Refraction which Monsieur des Cartes uses so witty a one as I am sorry it wants success He therefore following the demonstration above given of Reflection supposes the superficies which a ball lights upon to be a thin linen cloth or some other such matter as will break cleanly by the force of the ball striking smartly upon it And because that superficies resists only one way therfore he infers that the velocity of the ball is lessen'd only one way and not the other so that the velocity of its motion that way in which it finds no resistance must be after the balls passage through the linnen in a greater proportion to the velocity which it has the other way were it finds resistance then it was before And therfore the ball will in less time arrive to its period on the one side then on the other and consequently lean towards that side to which the course wherin it findes no opposition carries it Which to shew how it is contrary to his own principle Let us conceive the cloth CE to be of some thickness and so draw the line OP to determine that thickness And let us make from B upon AL another Parallelogram like the Parallelogram AL whose Diameter shall be BQ And it must necessarily follow that the motion from B to Q if there were no resistance were in the same proportion as from A to B. But the proportion of the motion as from A to B is the proportion of CB to CA that is it goes in the same time faster towards D then towards M in proportion which CB hath to CA. By which account the resistance it has in the way towards D must also be greater then the resistance it has in the towards M in the proportion which CB has to CA and therfore the more tardicy must be in the way to D and not in the way to M and consequently the declination must be from E wards and to M wards For where there is most resistance that way likewise must the tardity be greatest and the declination must be from that way but which way the thickness to be passed in the same time is most that way the resistance is greatest and the thickness is clearly greater towards E then towards M therfore the resistance must be greatest towards E and consequently the declination from the line BL must be towards M and not towards E. But the truth is in his Doctrine the ball would go in a straight line as if there were no resistance unless peradventure towards the contrary side of the cloth at which it goes out into the free air For as the resistance of the cloth is greater in the way towards D then in the way towards M because it passes a longer line in the same time as also it did formerly in the air so likewise is the force that moves it that way greater then the force which moves it the other And therfore the same proportions that were in the motion before it came to the resisting passage will remain also in it at least till coming near the side at which it goes out the resistance be weakned by the thinness of the resistent there which because it must needs happen on the side that has least thickness the ball must consequently turn the other way where it findes greatest yielding and so at its getting out into the free air it will bend from the greater resistance in such manner as we have said above Neither do the examples brought by Monsieur des Cartes and others in the maintenance of this Doctrine any thing avail them for when a Canon Bullet shot into a River hurts the people on the other side 't is not caused by refraction but by reflection as Monsir des Cartes himself acknowledges and therfor has no force to prove any thing in refraction whose Laws are divers from those of pure reflection And the same answer servs against the instance of a Musket bullot shot at a mark under water which perpetually lights higher then the mark though exactly just aim'd at For we knowing that it is the nature of
in bulk but the small ones very hardly Next the smalness and well-working of the parts by means of the airs penetrating every dense one and sticking close to every one of them and consequently joyning them without any unevenness causes that there can be no ruggedness in it and therfore 't is glibb in like manner as we see plaister or starch become smooth when they are well wrought Then the humidity of it causes it to be catching and the shortness of every part makes that where it sticks it is not easily parted thence Now the rarity of air next to fire admits it to be of all the other Elements most easily brought to the height of fire by the operation of fire upon it And therfore oyls are the proper food of that Element And accordingly we see if a drop of oyl be spill'd upon a sheet of paper and the paper set on fire at a corner as the fire comes near the oyl the oyl will disperse and spread it self upon the paper to a broader compass then it had because the heat rarifies it and so in Oyl it self the fire rarifying the air makes it penetrate the earthy parts adjoynd to it more then it did and so subtilizes them till they be reduced to such a height as they are within the power of fire to communicate its own nature to them and thus it turns them into fire and carries them up in its flame But if fire be predominant over earth and air in a watry compound it makes the body so proportion'd to be subtile rare penetrative hot in operation light in weight and subject to burn Of this kind are all sorts of wines and distil'd Spirits commonly called strong waters or Aquavites in Latine Aquaeardentes These will lose their virtues meerly by remaining uncover'd in the air for fire doth not incorporate strongly with water but if it find means raises it self into the air As we see in the smoke of boyling water which is nothing else but little bodies of fire that entring into the water rarifie some parts of it but have no inclination to stay there and therefore as fast as they can get out fly away but the humide parts of the water which they have rarified being of a sticking nature joyn themselves to them and ascend in the air as high as the fiery atomes have strength to carry them which when it fails them that smoke falls down in a dew and so becomes water again as it was All which one may easily discern in a glasse-vessel of water set over the fire in which one may observe the fire come in at the bottome and presently swim up to the top like a little bubble and immediately rise from thence in smoke and that will at last convert it self into drops and settle upon some solid substance thereabouts Of these fiery spirits some are so subtile as of themselves they will vanish and leave no residue of a body behind them and Alchymists profess to make them so etherial and volatile that being pour'd out of a glass from some reasonable height they shall never reach the ground but before they come thither be so rarified by that little motion as they shall grow invisible like the air and dispersing themselves all about in it fill the chamber with the smell of that body which can no longer be seen The last excess in watery bodies must be of water it self which is when so little a proportion of any of the other is mingled with it as is hardly perceptible Out of this composition arise all those several sorts of juices or liquors we commonly call Waters which by their mixture with the other three Elements have peculiar properties beyond simple Elemental water The general quality whereof we shall not need any further to express because by what we have already said of water in common they are sufficiently known In our next survey we will take Earth for our ground to work upon as hitherto we have done water which if in any body it be in the utmost excess beyond all the other three then rocks and stones will grow out of it whose driness and hardness may assure us that Earth sways in their composition with the least allay that may be Nor doth their lightness in respect of some other earthy compositions impeach this resolution for that proceeds from the greatness and multiplicity of pores wherwith their driness causes them to aboundâ— and hinders not but that their real solid parts may be very heavy Now if we mingle a considerable proportion of water with earth so as to exceed the fire and air but still inferiour to the earth we shall poduce metals whose great weight with their ductility and malleability plainly tells us that the smallest of waters gross parts are the glew that holds the earthy dense ones together such weight belonging to earth and that easie changing of parts being most proper to water Quick-silver that is the general matter wherof all the metals are immediately composed gives us evidence hereof for fire works upon it with the same effect as upon water And the calcination of most of the metals proves that fire can easily part and consume the glew by which they were closed and held together which therfore must be rather of a watry then of an aiery substance Likewise the glibness of Mercury and of melted metals without catching or sticking to other substances gives us to understand that this great temper of a moist Element with earth is water and not air and that the watry parts are comprised and as it were shut up within the earthy ones for air catches and sticks notably to all things it touches and will not be imprisoned the divisibility of it being excceeding great though in never so short parts Now if air mingles it self with earth and be prodominant over water and fire it makes such an oily and fat soil as Husbandmen account their best mould which receiving a betterment from the Sun temperate heat assures us of the concourse of the aire for wherever such heat is air cannot fail of accompanying or being effected by it and the richest of such earth as pot-earth and marl will with much fire grow more compacted and stick closer together then it did as we see in baking them into pots or fine bricks Whereas if water were the glew between the dense parts fire would consume it and crumble them asunder as it doth in those bodies it calcines And excesse of fire will bring them to vitrification which still confirms that air abounds in them for it is the nature of air to stick so close where once it is kneaded in as it cannot be separated without extreme difficulty And to this purpose the viscuous holding together of the parts of glass when it is melted shews evidently that air abounds in vitrified bodies The last mixture we are to meddle with is of fire with earth in an over-ruling
a strong bituminous smel in them All which circumstances shew that this electrical virtue consists in a certain degree of rarity or density of the bodies unctuous emanations Now if these refined and viscuous thrids of Jet or Amber in their streaming abroad meet with a piece of straw or hay or dried leaf or some such light and spungy body 't is no marvel if they glew themselvs to it like birdlime and that in their shrinking back by being condens'd again and repuls'd through the coldness of the air they carry it along with them to their entire body Which they that only see the effect and cannot penetrate into a possibility of a natural cause therof are much troubled withal And this seems to me to bear a fairer semblance of truth then what Cabeus delivers for the cause of Electrical attractions whose speculation herein though I cannot allow for solid yet I must for ingenious And certainly even errours are to be commended when they are witty ones and proceed from a casting-further-about then the beaten Tract of verbal learning or rather terms which explicate not the nature of the thing in question He sayes that the coming of straws and such other light bodies to Amber Jet and the like proceeds from a wind raised by the forcible breaking out of subtile emanations from the Electrical bodies into the air which brings those light bodies along with it to the Electrical ones But this discourse cannot hold For First 't is not the nature of unctuous emanation generally speaking to cause smart motions singly of themselvs Secondly although they should raise a wind I do not comprehend how this wind should drive bodies directly back to the source that raised it but rather any other way and so consequently should drive the light bodies it meets with in its way rather from then towards the Electrical body Thirdly if there should be such a wind raised and it should bring light bodies to the Electrical ones yet it could not make them stick therto which we see they do turn them which way you will as though they were glew'd together Neither do his experiences convince any thing For what he saies that the light bodies are somtimes brought to the Electrical body with such a violence that they rebound back from it and then return again to it makes rather against him for if wind were the cause of their motion they would not return again after they had leaped back from the Electrical body no more then we can imagine that the wind it self doth The like is of his other experience when he observ'd that some little grains of Saw-dust hanging at an Electrical body the furthermost of them not only fell off but seem'd to be driven away forcibly for they did not fall directly down but side-wayes and besides flew away with a violence and smartness that argued some strong impulse The reason wherof might be that new emanations might smite them which not sticking and fast'ning upon them wherby to draw them nearer must needs push them further or it might be that the emanations to which they were glew'd shrinking back to their main body the later grains were shoulder'd off by others that already besieg'd the Superficies and then the emanations retiring swiftly the grains must break off with a force or else we may conceive it was the force of the air that bore them up a little which made an appearance of their being driven away as we see feathers and other light things descend not straight down CHAP. XX. Of the Loadstones generation and its particular motions THere is yet remaining the great Mystery of the Loadstone to discourse of Which all Authors both ancient and modern have agreed upon as an undeniable example and evidence of the shortness of mans reach in comprehending and of the impossibility of his reason in penetrating into and explicating such secrets as nature hath a mind to hide from us Wherfore our Reader I am sure will not in this subject expect clear satisfaction or plain demonstrations at our hands but will judg we have fairly acquitted our selves if what we say be any whit plausible Therefore to use our best indeavours to content him let us reflect upon the disposition of parts of this habitable Globe wherof we are Tenants for life And we shall find that the Sun by his constant course under the Zodiack heats a great part of it unmeasurably more then he doth the rest And consequently that this Zodiack being in the mid'st between two as it were ends which we call the Poles these Poles must necessarily be extremely cold in respect of the Torrid Zone for so we call that part of the earth which lies under the Zodiack Now looking into the consequence of this we find that the Sun or the Suns heat which reflects from the earth in the Torrid Zone must rarifie the air extremely and according to the nature of all heat and fire must needs carry away from thence many parts of the air and earth sticking to that heat in such sort as we have formerly declared Whence it follows that other air must necessarily come from the Regions towards both the Poles to supply what is carried away from the middle as is the course in other fires and as we have explicated above Especially considering that the air which comes from the Polewards is heavier then the air of the Torrid Zone and therfore must naturally press to be still nearer the earth and so as it were shoulders on the air of the Torrid Zone towards the circumference by rolling into its place and this in great quantities and consequently the polar air must draw a great train after it Which if we consider the great extent of the Torrid Zone we shall easily perswade our selvs must reach on each side to the very Pole For taking from Archimedes that the Spherical Superficies of a portion of a Sphere is to the Superficies of the whole Sphere according as the parts of the axis of that Sphere comprised within the said portion is to the whole axis and considering that in our case the part of the axis comprised within the Torrid Zone is to the whole axis of the earth in about the proportion of 4. to 10 it must of necessity follow that a fire or great heat reigning in so vast an extent will draw air very powerfully from the rest of the world Neither let any man apprehend that this course of the Sun 's elevating so great quantities of Atoms in the Torrid Zone should hinder the course of gravity there For first the medium is much rarer in thâ— Torrid Zone then in other parts of the earth and therfore the force of the descending Atoms needs not be so great there as in other places to make bodies descend there as fast as they do elsewhere Secondly there being a perpetual supply of fresh air from the Polar parts streaming continually into the Torrid Zone it must of
the touched part Again the longer an iron is in touching the greater vertue it gets and the more constant And both an iron and a loadstone may lose their vertue by long lying out of their due order and situation either to the earth or to another loadstone Besides if a loadstone touch a long iron in the middle of it he diffuses his vertue equally towards both ends and if it be a round plate he diffuses his vertue equally to all sides And lastly the vertue of a loadstone as also of an iron touched is lost by burning it in the fire All which symptoms agreeing exactly with the rules of bodies make it undeniable that the vertue of the loadstone is a real and solid body Against this position Cabeus objects that little atomes would not be able to penetrate all sorts of bodies as we see the vertue of the loadstone doth And argues that although they should be allow'd to do so yet they could not be imagin'd to penetrate thick and solid bodies so suddenly as they would do thin ones and would certainly shew then some sign of facility or difficulty of passing in the interposition and taking away of bodies put between the loadstone and the body it works upon Secondly he objects that atomes being little bodies cannot move in an instant as the working of the loadstone seems to do And lastly that the loadstone by such abundance of continual evaporations would quickly be consumed To the first we answer That atomes whose nature 't is to pierce iron cannot reasonbly be suspected of inability to penetrate any other body and that atomes can penetrate iron is evident in the melting of it by fire And indeed this objection comes now too late after we have so largely declared the divisibility of quantity and the subtility of nature in reducing all things into extreme small parts for this difficulty has no other avow then the tardity of our imaginations in subtilizing sufficiently the quantitative parts that issue out of the loadstone As for any tardity that may be expected by the interposition of a thick or dense body there is no appearance of such since we see light pass through thick glasses without giving any sign of meeting with the least opposition in its passage as we have above declared at large and magnetical emanations have the advantage of light in this that they are not obliged to straight lines as light is Lastly as for Loadstones spending themselves by still venting their emanations odoriferous bodies furnish us with a full answer to that objection for they continue many years palpably spending themselvs and yet keep their odour in vigour wheras a loadstone if it be laid in a wrong position will not continue half so long The reason of the duration of both which makes the matter manifest and takes away all difficulty which is that as in the root of a vegeâ—able there is a power to change the advenient juyce into its nature so is there in such like things as these a power to change the ambient air into their own substance as evident experience shews in the Hermetike Salt as some modern writers call it which is found to be repair'd and encreas'd in its weight by lying in the air and the like happens to Saltpeter And in our present subject experience informs us that a Loadstone will grow stronger by lying in due position either to the earth or to astronger Loadstone whereby it may be better impregnated and as it were feed it self with the emanations issuing out of them into it Our next position is that This virtue comes to a magnetick body from another body as the nature of bodies is to require a being moved that they may move And this is evident in iron which by the touch orby standing in due position near the loadstone gains the power of the Loadstone Again if a Smith in beating his iron into a rod observe to lay it North South it gets a direction to the North by the very beating of it Likewise if an iron rod be made red hot in the fire and kept there a good while together and when it is taken out be laid to cool just North and South it will acquire the same direction towards the North. And this is true not only of iron but also of all other sorts of bodies whatever that endure such ignition particularly of pot-earths which if they be moulded in a long form and when they are taken out of the Kiln be laid as we said of the iron to cool North and South will have the same effect wrought in them And iron though it has not been heated but only continued long unmoved in the some situation of North and South in a building yet it will have the same effect So as it cannot be denied but this virtue comes to iron from other bodies wherof one must be a secret influence from the North. And this is confirmd by a Loadstones losing its virtue as we said before by lying a long time unduly disposed either towards the earth or towards a stronger Loadstone wherby in stead of the former it gains a new virtue according to that situation And this happens not only in the virtue which is resident and permanent in a Loadstone or a touch'd iron but likewise in the actual motion or operation of them As may be experienc'd First in this that the same loadstone or touch'd iron in the South hemisphere of the world hath its operation strongest at that end of it which tends to the North and in the North Hemisphere at the end which tends to the South each pole communicating a vigour proportionable to its own strength in the climate where it is receiv'd Secondly in this that an iron joyn'd to a Loadstone or within the Sphere of the Loadstones working will take up another piece of iron greater then the Loadstone of it self can hold and as soon as the holding iron is removed out of the sphere of the Loadstones activity it presently lets fall the iron it formerly held up And this is so true that a lesser loadstone may be placed so within the sphere of a greater loadstones operation as to take away a piece of iron from the greater Loadstone and this in virtue of the same greater Loadstone from which it plucks it for but remove the lesser out of the sphere of the greater and then it can no longer do it So that 't is evident in these cases the very actual operation of the lesser Loadstone or of the iron proceeds from the actual influence of the greater Loadstone upon and into them And hence we may understand that whenever a magnetick body works it has an excitation from without which makes it issue out and send its streams abroad so as 't is the nature of all bodies to do and as we have given examples of the like done by heat when we discours'd of Rarefaction But to explicate this point more clearly by
parts then another whose parts are less Neither doth it import that the pores be supposed as great as the parts for be they never so large the corners of the thick parts they belong to must needs break the course of what will not bow but goes all in straight lines more then if the parts and pores were both less since for so subtile a piercer as light no pores can be too little to give it entrance 'T is true such great ones would better admit a liquid body into them such a one as water or air but the reason of that is because they will bow and take any ply to creep into those cavities if they be large enough which light will not do Therefore 't is clear That freedom of passage can happen to light only there where there is an extreme great multitude of pores and parts in a very little quantity or bulk of body which pores and parts must consequently be extreme little ones for by reason of their multitude there must be great variety in their situation from whence it will happen that many lines must be all of pores quite through and many others all of parts although the most will be mixed of both pores and parts And so we see that although the light pass quite through in many places yet it reflects from more not onely in the superficies but in the very body it self of the Diaphanous substance But in another substance of great parts and pores there can be but few whole lines of pores by which the light may pass from the object to make it be seen and consequently it must be Opacous which is the contrary of Diaphanous that admits many Rays of Light to passe through it from the Object to the Eye wherby It is seen though the Diaphanous hard body intervene between them Now if we consider the generation of these two Colours White and black in bodies we shall find that likewise to justifie and second our doctrine For white things are generally cold and dry and therfore are by nature ordain'd to be receptacles and conservers of heat and of moisture as Physitians note Contrariwise Black as also green which is near of kin to black are growing colours and are the die of heat incorporated in abundance of wet as we see in smoak in pit-coal in garden ground and in Chymical putrefactions all which are black as also in young herbs which are generally green as long as they are young and growing The other colours keeping their standing betwixt these are generated by the mixture of them and according as they partake more or less of either of them are nearer or further off from it So that after all this discourse we may conclude in short that The colour of a body is nothing else but the power which that body hath of reflecting light to the eye in a certain order and position and consequently is nothing else but the very superficies of it with its asperity or smoothness with its pores or inequalities with its hardness or softness and such like The Rules and limits wherof if they were duly observ'd and order'd the whole nature and science of colours would easily be known and described But out of this little we have deliver'd of this subject it may be rightly inser'd that Real Colours proceed from Rarity and Density as even now we touch'd and have their head spring there and are not strange qualities in the air but tractable bodies on the earth as all are which as yet we have found and medled withal and are indeed the very bodies themselves causing such effects upon our eye by reflecting of light which we express by the names of Colours CHAP. XXX Of Luminous or apparent Colours AS for the Luminous Colours whose natures Art hath made more maniable by us than those which are called real Colours and are permanent in bodies their generation is clearly to be seen in the Prism or Triangular glass we formerly mention'd The considering of which will confirm our doctrine That even the colours of bodies are but various mixtures of light and shadows diversly reflected to our eyes For the right understanding of them we are to note That this glass makes apparitions of colours in two sorts one when looking through it there appear various colours in the objects you look on different from their real ones according to the position you hold the glass in when you look on them The other sort is when the beams of light that pass through the Glass are as it were tincted in their passage and are cast by the Glass upon some solid object and appear there in such and such colours which continue still the same in what position soever you stand to look upon them either before or behind or on any side of the Glass Secondly we are to note that these colours are generally made by refraction though somtimes it may happen otherwise as above we have mention'd To discover the reason of the first sort of colours that appear by refraction when one looks through the glass let us suppose two several bodies one black the other white lying close by one another and in the same horisontal parallel but so that that the black be further from us then the white then if we hold the Prism through which we are to see these two oppositely coloured bodies somwhat above them and that side of it at which the coloured bodies must enter into the glass to come to our eye parallel to those bodies 't is evident That the black will come into the Prism by lesser angles then the white I mean that in the line of distance from that face of the glass at which the colours come in a longer line or part of black will subtend an angle no bigger then a lesser line or part of white doth subtend Thirdly we are to note That from the same point of the object there come various beams of light to that whole superficies of the glass so that it may and somtimes doth happen that from the some part of the object beams are reflected to the eye from several parts of that superficies of the glass at which they enter And whenever this happens the object must necessarily be seen in divers parts that is the picture of it will at the same time appear to the eye in divers places And particularly we may plainly observe two pictures one a lively and strong one the other a faint and dim one Of which the dim one will appear nearer us then the lively one and is caus'd by a secondary ray or rather I should say by a longer ray that striking nearer to the hither edge of the glasses superficies which is the furthest from the object makes a more acute angle then a shorter ray doth that strikes upon a part of the glass further from our eye but nearer the object and therfore the image made by this secondary or longer ray must appear
occur other arguments of no less importance to prove this verity than these we have already proposed CHAP. VII Two objections answer'd against light being fire with a more ample proof of its being such HAving then said thus much to perswade us of the corporeity of this subtile thing that so queintly plays with our eyes we will in the next place examine those objections that at the beginning we set down against its being a body and if after a through discussion of them we find they do in truth conclude nothing of what at the first sight they bear so great a shew of but that we shall be able perfectly to solve and enerve their force no body will think it rashness in us to crave leave of Aristotle that we may dissent from him in a matter that he has not look'd to the bottom of and whose opinion therin cannot be defended from plain contradictions and impossibilities 'T is true never any one man looked fo far as he into the bowels of nature he may be rightly termed the Genius of it and whoever follows his principles in the main cannot be led into errour but we must not believe that he or any man else who relies upon the strength and negotiation of his own reason ever had a priviledge of infallibility entail'd to all he said Let us then admire him for what he has deliver'd us and where he falls short or is weary in his search and suffers himself to be born down by popular opinions against his own principles which happens very seldom to him let us seek to supply and relieve him But to pursue our intent We will begin with answerin the third objection which is that if light were fire it must heat as well as enlighten where it shines There 's no doubt but it doth so as is evident by the weather-glasses and other artificiall musical instruments as Organs and Virginals that played by themselvs wâ—ch Cornelius Drebbel That admirable master of Mechanicks made to shew the King All which depends upon the rarefaction and condensation of some subtile body conserv'd in a cavity within the bulk of the whole instrument for assoon as the Sun shined they would have motion and play their parts And questionless that grew out of the rarefaction of the subtile liquor he made use of which was dilated assoon as the air was warmd by the Sun-beams Of whose operation it was so sensible that they no sooner left the Horizon but its motion ceased And if but a cloud came between the instrument and them the musick would presently go slower time And the ancient miracle of Memnons statue seems to be a juggling of the Ethiopian priests made by the like invention But though he and they found some spirituall and refined natter that would receive such notable impressions from so small alterations of temper yet it is no wonder that our gross bodies are not sensible of them for we cannot feel heat unless it be greater then that which is in our sense And the heat there must be in proportion to the heat of our bloud which is an high degree of warmth and therfore 't is very possible that an exceeding rarified fire may cause a far lesse impression of heat then we are able to feel Consider how if you set pure spirit of wine on fire and so convert it into actual flame yet it will not burn nor scarce warm your hand and then can you expect that the light of a candle which fills a great room should burn or warm you as far as it shines If you would exactly know what degree of heat and power of burning that light has which for example shines upon the wall in a great chamber in the midst wherof there stands a candle do but calculate what overproportion of quantitie all the light in the whole room bears to the quantity of the little flame at the top of the candle and that is the overproportion of the force of burning which is in the candle to the force of burning which is in so much light at the wall as in extension is equall to the flame of the candle Which when you have considered you will not quarrel at its not warming you at that distance although you grant it to be fire streaming out from â—e flame as from the spring that feeds it and extreamly dilated according to the nature of fire when it is at liberty by going so far without any other grosse body to imprison or clog it 'T is manifest that this rule of examining the proportion of burning in so much of the light as the flame is by calculating the proportion of the quantity or extension of all the light in the room to the extension of the flame of the candle and then comparing the flame of the candle to a part of light equall in extension unto it is a good and infallible one if we abstract from accidental inequalities since both the light and the flame are in a perpetual flux and all the light was first in the flame which is the spring from whence it continually flows As in a river where every part runs with a settled stream though one place be straighter and another broader yet of necessity since all the water that is in the broad place came out of the narrow it must follow that in equal portions of time there is no more water where it has the liberty of a larg channel then where the banks press it into a narrow bed so that there be no inequalities in the bottome In like manner if in a large stove a basin of water be converted into steam that rarified water which then fills the whole Stove is no more then what the Basin contain'd before and consequently the power of moistening which is in a foot 's extension for example of the stove wherein that steam is must be in proportion to the vertue of wetting in the foot extension of water as the quantity of that great room which the steam fills is to the quantity of the water contain'd in the basin For although the rarified water be not in every least part of that great place it seems to take up by reason that there is Air in which it must swim yet the power of wetting that was in the Basin of water is dilated through the whole room by the conjunction of the Myst or Dew to all the sensible parts of the Air that is in the room and consequently the power of wetting which is in any foot of that room is in a manner as much less then the power of wetting which was in the foot of water as if the water were rarified to the quantity of the whole room and no air were left with it And in the same manner it fares with dilated fire as it doth with dilated water with only this difference peradventure that Fire grows purer and more towards its own nature by dilatation whereas water becomes more mix'd and is carried
of fewel to maintain the same light for a great company of years But I should not easily be perswaded that either flame or light could be made without any manner of consuming the body which serves them for fewel CHAP. VIII An Answer to three other Objectious formerly proposed against Light being a Substance HAving thus defended our selves from their Objections who would not allow light to be fire and having satisfied their inquisition who would know what becomes of it when it dyes if it be a body we will now apply our selves to answer their difficulties who will not let it pass for a body because it is in the same place with another body as when the Sun-beams enlighten all the air and when the several lights of two distinct Candles are both of them every where in the same room Which is the substance of the second main objection This of the justling of the aire is easily answered thus that the aire being a very divisible body doth without resistance yield as much place as is requisite for light And that light though our eyes judge it diffused every where yet is not truly in every point or atome of air but to make us see it every where it suffices that it be in every part of the air which is as big as the black or sight of our eye so that we cannot set our eye in any position where it receives not impressions of light In the same manner as Perfumes which though they be so gross bodies that they may be sensibly wasted by the wind yet â—o fill the air that we can put our nose in no part of the room where a perfume is burned but we shall smell it And the like is of mists as also of the sprouted water to make a perfume which we mention'd above But because pure discourses in such small thrids as these 〈◊〉 but weakly bind such Readers as are not accustom'd to them and I would if possible render this Treatise intelligible to every rational man how ever little vers'd in Scholastick learning among whom I expect it will have a fairer passage then among those that are already deeply imbued with other principles let us try if we can herein inform our selves by our sense and bring our eyes for witness of what we say He then that is desirous to satisfie himself in this particular may put himself in a dark room through which the Sun sends his beams by a cranie or little hole in the wall and he will discover a multitude of little atomes flying about in that little stream of light which his eye cannot discern when he is environ'd on all sides with a full light Then let him examine whether or no there be light in the midst of those little bodies and his own reason will easily till him that if those bodies were as perspicuous as the air they would not reflect upon our eyes the beams by which we see them And therefore he will boldly conclude that at the least such parts of them as reflect light to us do not admit it nor let it sink into them Then let him consider the multitude of them and the little distance betwixt one another and how nevertheless they hinder not our sight but we have it free to discover all objects beyond them in what position soever we place our eye And when he thus perceives that these opacous bodies which are every where do not hinder the eye from judging light to have an equal plenary diffusion through the whole place that it irradiates he can have no difficulty to allow air that is diaphanous and more subtile far then they and consequently divisible into lesser atomes and having lesser pores gives less scope to our eyes to miss light then they do to be every where mingled with light though we see nothing but light and cannot discern any breach of it Especially when he shall adde to this consideration that the subtile body which thus fills the air is the most visible thing in the world and that whereby all other things are seen and that the air it mingles it self with is not at all visible by reason of the extreme diaphaneity of it and easie reception of the light in every pore of it without any resistance or reflection and that such is the nature of light as it easily drowns an obscure body if it be not too big and not onely such but even other light bodies for so we know as well the fixed Stars as the Planets are conceal'd from our sight by the nearness to the Sun neither the lightness of the one nor the bigness of the other prevailing against the darkning of an exuperant light and we have daily experience of the same in very pure chrystal glasses and in very clear water which though we cannot discern by our sight if they be certain positions nevertheless by experience we find that they reflect much light and consequently have great store of opacous parts And then he cannot choose but conclude that it is impossible but light should appear as it doth to be every where and to be one continued thing though his discourse withal assure him it is every where mingled with air And this very answer I think will draw with it by consequence the solution of the other part of the same objection which is of many lights joyning in the same place and the same is likewise concerning the images of colours every where crossing one another without hindrance But to raise this contemplation a strain higher let us consider how light being the most rare of all known bodies is of its own nature by reason of the divisibility that followeth rarity divisible into lesser parts then any other and particularly then flame which being mixed with smoke and other corpulency falls very short of light And this to the proportion in which it is more rare then the body 't is compared to Now a great Mathematician having devised how to measure the rarefaction of Gun-powder into flame found the Diameter fifty times increased and so concluded that the body of the flame was in proportion to the body of the Gun-powder it was made of as 125000. is to one Wherfore by the immediately proceeding consequence we find that 125000 parts of flame may be couched in the room of one least part of gunpowder and peradventure many more considering how porous a body Gun-powder is Which being admitted 't is evident that although light were as gross as the flame of Gun-powder and Gun-powder were as solid as gold yet there might pass 125000. rayes of light in the space wherin one least part of Gun-powder might be contained which space would be absolutely invisible to us and be contained many times in the bigness of the sight of a mans eye Out of which we may gather what an infinity of objects may seem to us to cross themselvs in the same indivisible place and yet may have room sufficient for every one
to which much more might be added but that we have already trespassed in length and I conceive enough is said to decide the matter an equal judge will find the ballance of the question to hang upon these termes that to prove the nature of light to be material corporeal are brought a company of accidents well known to be the proprieties of quantitie or bodies and as well known to be in light Even so far as that 't is manifest light in its beginning before it be dispersed is fire and if again it be gathered together it shews it self again to be fire And the receptacles of it are the receptacles of a body being a multitude of pores as the hardness and coldness of transparent things do give us to understand of which we shall hereafter have occasion to discourse On the contrary side whatever arguments are brought against lights being a body are only negative As that we see not any motion of light that we do not discern where the confines are between light and air that we see not room for both of them or for more lights to be together and the like which is to oppose negative proofs against affirmative ones and to build a doctrine upon the defect of our senses or upon the likeness of bodies which are extremely unlike expecting the same effects from the most subtile as from the most gross ones All which together with the authority of Aristotle his followers have turned light into darkness and made us almost deny the light of our own eyes Now then to take our leave of this important question let us return to the principles from whence we began and consider that Seeing Fire is the most rare of the Elements and very dry and that out of the former it hath that it may be cut into very small pieces and out of the later that it conserves its own figure and so is apt to divide what ever fluid body and joyning to these two principles that it multiplies extremely in its source It must of necessity follow that it sends out in great multitudes little small parts into the air and other bodies circumfused with great dilatation in a spherical manner And likewise that these little parts are easily broken and new ones still following the former are still multiplyed in straight lines from the place where they break Out of which 't is evident that of necessity it must in a manner fill all places and that no sensible place is so little but that fire wil be found in it if the medium be capacious As also that its extreme least parts will be very easily swallow'd up in the parts of the air which are humid and by their enfolding be as it were quite lost so as to lose the appearance of fire Again that in its reflections it will follow the nature of grosser bodies and have glidings like them which is that we call refractions That little streamings from it will cross one another in excessive great numbers in an unsensible part of space without hindering one another That its motion will be quicker then sense can judge of and therefore will seem to move in an instant or to stand still as in a stagnation That if there be any bodies so porous with little and thick pores as that the pores arrive near to equalling the substance of the body then such a body will be so fill'd with these little particles of fire that it will appear as if there were no stop in its passage but were all filled with fire and yet many of these little parts will be reflected And whatever qualities else we find in light we shall be able to derive them out of these principles and shew that fire must of necessity do what experience teaches us that light doth That is to say in one word it will shew us that fire is light But if fire be light then light must needs be fire And so we leave this matter CHAP. IX Of Local motion in common THough in the fifth Chapter we made only earth the pretender in the controversie aginst fire for superiority in activity and in very truth the greatest force of gravity appears in those bodies which are eminently earthy nevertheless both water and air as appears out of the 4. Chapter of the Elements do agree with earth in having gravity and gravity is the chief virtue to make them efficients So that upon the matter this plea is common to all the three Elements Wherfore to explicate this virtue wherby these three weighty Elements work let us call to mind what we said in the beginning of the last Chapter concerning local motion to wit that according as the body moved or the divider did more and more enter into the divided body so it joyn'd it self to some new parts of the Medium or divided body and did in like manner forsake others Whence it happens that in every part of motion it possesses a greater part of the Medium then it self can fill at once And because by the limitation and confinedness of every magnitude to just what it is and no more 't is impossible that a lesser body should at once equalize a greater it followes that this division or motion whereby a body attains to fill a place bigger then it self must be done successively that is it must first fill one part of the place it moves in then another and so proceed on till it have measur'd it self with every part of the place from the first beginning of the line of motion to the last period of it where the body rests By which discourse it is evident that there cannot in nature be a strength so great as to make the least or quickest moveable that is to pass in an instant or all together over the least place that can be imagin'd for that would make the moved body remaining what it is in regard of its bigness to equallize and fit a thing bigger then it is Therfore it is manifest that motion must consist of such parts as have this nature that whiles one of them is in being the others are not yet and as by degrees every new one comes to be all the others that were before do vanish and cease to be Which circumstance accompanying motion we call Succession And whatever is so done is said to be done in time which is the common measure of all succession For the change of situation of the Stars but especally of the Sun and Moon is observ'd more or less by all mankind and appears alike to every man and being the most known constant and uniform succession that men are used to is as it were by nature it self set in their way and offer'd them as fittest to estimate and judge all other particular successions by comparing them both to it and among themselves by it And accordingly we see all men naturally measure all other successions and express their quantities by comparing them to the
by descending so that as long as it boyls 't is in a perpetual confused motion up and down Now having formerly concluded that fire is light and light is fire it cannot be doubted but that the Sun serves instead of fire to our Globe of Earth and water which may be fitly compared to the boyling pot and all the day long draws vapours from those bodies that his beams strike upon For he shooting his little darts of fire in multitudes and in continued streams from his own center against the Python the earth we live on they there overtake one another and cause some degrees of heat as far as they sink in But not being able by reason of their great expansion in their long journey to convert it into their own nature and set it on fire which requires a high degree of condensation of the beams they but pierce and divide it very subtilly and cut some of the outwardparts of it into extreme little atomes To which sticking very close and being in a manner incorporated with them by reason of the moisture that is in them they in their rebound back from the earth carry them along with them like a ball that struck against a moist wall in its return from it brings back some of the mortar sticking upon it For the distance of the Earth from the Sun is not the utmost period of these nimble bodie 's flight so that when by this solid body they are stop'd in their course forwards on they leap back from it and carry some little parts of it with them som of them a farther some of them a shorter journey according to their littleness and rarity make them fit to ascend As is manifest by the consent of all Authors that write of the Regions of the Air who determine the Lower Region to reach as far as the reflection of the Sun and conclude this Region to be very hot For if we mark how the heat of fire is greatest when it is incorporated in some dense body as in Iron or in Sea-coal we shall easily conceive that the heat of this Region proceeds mainly out of the incorporation of light with those little bodies which stick to it in its reflection And experience testifies the same both in our soultry days which we see are of a gross temper and ordinarily go before rain as also in the hot Springs of extreme cold countrys where the first heats are unsufferable which proceed out of the resolution of humidity congeal'd in hot winds which the Spaniards call Bochornos from Boca de horno by allusion to the breathing stream of an Oven when it is open'd which manifestly shew that the heat of the Sun is incorporated in the little bodies which compose the steam of that wind And by the principles we have already laid the same would be evident though we had no experience to instruct us for seeing that the body of fire is dry the wet parts which are easiest resolved by fire must needs stick to them and accompany them in their return from the earth Now whiles these ascend the air must needs cause others that are of a grosser complexion to descend as fast to make room for the former and to fill the places they left that there may be no vacuity in nature And to find what parts they are and from whence they come that succeed in the room of light and atomes glew'd together that thus ascend we may take a hint from the Maxime of the Opticks that Light reflecting makes equal angles whence supposing the Superficies of the earth to be circular it will follow that a Perpendicular to the center passes just in the middle between the two rayes the incident and the reflected Wherefore the air between these two rayes and such bodies as are in it being equally pressed on both sides those bodies which are just in the middle are nearest and likeliest to succeed immediately in the room of the light and atomes which ascend from the Superficies of the earth and their motion to that point is upon the Perpendicular Hence 't is evident that the Air and all such bodies as descend to supply the place of light and atomes which ascend from the Earth descend perpendicularly towards the center of the earth And again such bodies as by the force of light being cut from the earth or water do not ascend in form of light but incorporate a hidden light and heat within them and thereby are rarer then these descending bodies must of necessity be lifted up by the descent of those denser bodies that go downwards because they by reason of their density are moved with a greater force And this lifting up must be in a perpendicular line because the others descending on all sides perpendicularly must needs raise those that are between them equally from all sides that is perpendicularly from the center of the earth And thus we see a motion set on foot of some bodies continually descending and others continually ascending all in perpendicular lines excepting those which follow the course of lights reflexion Again as soon as the declining Sun grows weaker or leaves our Horizon and his beams vanishing leave the little hors-men which rode upon them to their own temper and nature from whence they forced them they finding themselvs surrounded by a smart descending stream tumble down again in the night as fast as in the day they were carried up and crowding into their former habitations exclude those they find had usurped them in their absence And thus all bodies within reach of the Suns power but especially our air are in perpetual motion the more rarified ones ascending and the dense ones descending Now then because no bodies wherever they be as we have already shew'd have any inclination to move towards a particular place otherwise then as they are directed and impel'd by extrinsecal Agents let us suppose that a body were placed at liberty in the open air And then casting whether it would be moved from the place we suppose it in and which way it would be moved we shall find it must of necessity happen that it shall descend and fall down till it meet with some other gross body to stay and support it For though of it self it would move no way yet if we find that any other body strikes efficaciously enough upon it we cannot doubt but it will move that way which the striking body impels it Now it is strucken upon on both sides above and below by the ascending and the descending atoms the rare ones striking upon the bottome of it and driving it upwards and the denser ones pressing upon the top of it and bearing it downwards But if you compare the the impressions the denser atoms make with those that proceed from the rare ones 't is evident the dense ones must be the more powerful and therfore will assuredly determine the motion of the body in the air that way they go which is
downwards Nor need we fear lest the littlenessof the agents or the feebleness of their stroaks should not be sufficient to work this effect since there is no resistance in the body it self and the air is continually cut in pieces by the Sun-beams and by the motions of little bodies so that the adhesion to air of the body to be moved will be no hind'rance to this motion especially considering the perpetual new percussions and the multitude of them and how no force is so little but that with time and multiplication it will overcome any resistance But if any man desires to look on as it were at one view the whole chain of this doctrine of Gravity let him turn the first cast of his eyes on what we have said of fire when we explicated the nature of it To wit that it begins from a little source and by extreme multiplication and rarefaction extends it self into a great sphere And then hee 's perceive the reason why light is darted from the body of the Sun with that incredible celerity wherewith its beams fly to visit the remotest parts of the world and how of necessity it gives motion to all circumstant bodies since it is violently thrust forward by so extreme rarefaction and the further it goes is still the more rarified and dilated Next let him reflect how infinitely the quickness of lights motion prevents the motion of a moist body such an one as air is and then he wil plainly see that the first motion which light is able to give the air must needs be a swelling of that moist element perpendicularly round about the earth For the ray descendent and the ray reflectent flying with so great a speed that the air between them cannot take a formal pley any way before the beams of light be on both sides of it it followes that according to the nature of humide things it must first only swell for that is the beginning of motion in them when heat enters into and works on them And thus he may confidently resolve himself that the first motion which light causes in the air will be a swelling of it between the two rays towards the middle of them That is perpendicularly from the surface of the earth And out of this he will likewise plainly see that if there be any other little dense bodies floating in the air they must likewise mount a little through this swelling and rising of the air But that mounting will be no more then the immediate parts of the air themselvs move Because this motion is not by way of impulse or stroke that the air gives those denser bodies but by way of containing them in it and carrying them with it so that it gives them no more celerity then to make them go with it self and as parts of it self Then let him consider that light or fire by much beating upon the earth divides some little parts of it from others wherof if any become so small and tractable as not to exceed the strength which the rays have to manage them the returning rays will at their going back carry away with or drive before them such little atomes as they made or met with and so fill the air with little bodies cut out of the earth After this let him consider that when light caries up an atome with it the light and the atome stick together and make one ascending body in such sort as when an empty dish lies upon the water the air in the dish makes one descendent body together with the dish it self so that the density of the whole body of air and dish which in this case are but as one body is to be esteem'd according to the density of the two parts one of them being allay'd by the other as if the whole where thrughout of such a proportion of density as would arise out of the composition and kneading together the several densities of those two parts Now then when these little compounded bodies of light and earth are carryed up to a determinate height the parts of fire or light by little and little break away from them and therby the bulk of the part which is left becoms of a different degree of density quantity for quantity from the bulk of the entire atome when light was part of it and consequently it is denser then it was Besides let him consider that when these bodies ascend they go from a narrow room to a large one that is from the centrewards to the circumference but when they come down again they go from a larger part to a narrower Whence it followes that as they descend they draw closer and closer together and by consequence are subject to meet and fall in one with another and therby to increase their bulk and become more powerful in density not only by the loss of their fire but also by the encrease of their quantity And so 't is evident that they are denser coming down then going up Lastly let him consider that those atoms which went up first and are parted from their volative companions of fire or light must begin to come down apace when other new atoms which still have their light incorporated with them ascend to where they are and go beyond them by reason of their greater levity And as the latter atoms come up with a violence and great celerity so must the first go down with a smart impulse and by consequence being more dense then the air in which they are carryed must of necessity cut their way through that liquid and rare Medium and go the next way to supply the defect and room of the atoms which ascend that is perpendicularly to the earth and give the like motion to any body they find in their way if it be susceptible of such a motion Which 't is evident that all bodies are unless they be strucken by some contrary impulse For since a bodies being in a place is nothing else but the continuity of its outside to the inside of the body that contains it and is its place it can have no other repugnance to local motion which is nothing else but a successive changing of place besides this continuity Now the nature of density being the power of dividing and every least power having some force efficacy as we have shew'd above it follows that the stroke of every atome either descending or ascending will work somthing upon any body though never so big it chances to incounter with and strike upon in its way unless there be as strong an impulse the contrary way to oppose it But it being determin'd that the descending atoms are denser then those that ascend it follows that the descending ones will prevail And consequently all dense bodies must necessarily tend downwards to the center which is to be heavy if some other more dense body do not hinder them Out of this discourse we may conclude that there is no such thing among bodies
an aptitude the better to cut the medium and from the mltitude of little atomes descending that strike upon it and press it the way they go which is downwards then it would not import whether the inner part of that body were as solid as the outward parts for it cuts with only the outward and is smitten only upon the outward And yet experience shews us the contrary for a great bullet of lead that is solid and lead throughout descends faster then if three quarters of the Diameiter were hollow within and such a one falling upon any resisting substance works a greater effect then a hollow one And a ball of brass that hath but a thin outside of metal will swim upon the water when a massie one sinks presently Whereby it appears that it is rather some other quality belonging to the very bulk of the metal in it self and not these outward causes that occasion gravity But this difficulty is easily overcome if you consider how subtile those atomes are which descending downwards striking upon a body in their way cause its motion likewise downwards for you may remember how we have shew'd them to be the subtilest and the minutest divisions that Light the subtilest and sharpest divider in nature can make It is then easie to conceive that these extreme subtile bodies penetrate all others as light doth glass and run through them as sand through a small sieve or as water through a spunge so that they strike not only upon the Superficies but as well in every most interiour part of the whole body running quite through it all by the pores of it And then it must needs follow that the solider it is and the more parts it has within as well as without to be strucken upon the faster it go and the greater effect it must work in what falls upon whereas if three quarters of the Diameter of it within should be fill'd with nothing but air the atoms would fly without any considerable effect through all that space by reason of the rarity cessibility of it And that these atoms are thus subtile is manifest by several effects which we see in nature Divers Authors that write of Egypt assure us that though their houses be built of strong stone nevertheless a clod of earth laid in the inmost rooms and shut up from all appearing communication with air will encrease its weight so notably as therby they can judge the change of weather which will shortly ensue Which can proceed from no other cause but a multitde of little atoms of Saltpeter which floating in the air penetrate through the strongest wals and all the massie defences in their way and settle in the cold of earth as soon as they meet with it because it is of a temper fit to entertain and conserve embody them Delights have shewed us the way how to make the spirits or atoms of Snow and Saltpeter pass through a glass vessel which Alchimists hold to be the most impenetrable of all they can find to work with In our own bodies the aches which feeble parts feel before change of weather and the heaviness of our heads and shoulders if we remain in the open air presently after sunset abundantly testifie that even the grosser of these atoms which are the first that fall do vehemently penetrate our bodies so as sense will make us believe what reason peradventure could not But besides all this there is yet a more convincing reason why the descending atomes should move the whole density of a body even though it were so dense that they could not penetrate it and get into the bowels of it but must be content to strike barely upon the outside of it For nature has so order'd the matter that when dense parts stick close together and make the length composed of them to be very stiff one cannot be moved but that all the rest which are in that line must likewise be thereby moved so that if all the world were composed of atoms closse sticking together the least motion imaginable must drive on all that were in a straight line to the very end of the world This you see is evident in reason and experience confirms it when by a little knock given at the end of a long beam the shaking which makes sound reaches sensibly to the other end The blind man that governs his steps by feeling in defect of eyes receives advertisements of remote things through a staff which he holdeth in his hands peradventure more particularly then his eyes could have directed him And the like is of a deaf man that hears the sound of an Instrument by holding one end of a stick in his mouth whiles the other end rests upon the Instrument And some are of opinion and they not of the rank of vulgar Philosophers that if a staff were as long as to reach from the Sun to us it would have the same effect in a moment of time Although for my part I am hard to believe we could receive an advertisement so far unless the staff were of such a thickness as being proportionable to the length might keep it from facile bending for if it should be very plyant it would do us no service as we experience in a thrid which reaching from our hand to the ground if it knock against any thing makes no sensible impression in our hand So that in fine reason sense and authority all of them shew us that the less the atomes should penetrate into a moving body by reason of the extreme density of it the more efficaciously they would work and the greater celerity they would cause in its motion And hence we may give the fullest solution to the objection above Which was to this effect that seeing division is made only by the superficies or exteriour part of the dense body and the virtue whereby a dense body works is onely its resistance to division which makes it apt to divide it would follow that a hollow bowl of brass or iron should be as heavy as a solid one For we may answer that seeing the atoms must strike through the body and a cessible body doth not receive their strokes so firmly as a stiffe one nor can convey them so far if to a stiff superficies there succeed a yielding inside the strokes must of necessity lose much of their force and consequently cannot move a body full of air with so much celerity or with so much efficacy as they may a solid one But then you may peradventure say that if these strokes of the descending atomes upon a dense body were the cause of its motion downwards we must allow the atomes to move faster then the dense body that so they may still overtake it and drive it along and enter into it whereas if they should move slower then it none of them could come in their turn to give it a stroke but it would be past them and out of their reach before they
coms as easily as the very air So that in this example as wll as in the other nature teaches us that gravity is no quality And all or most of the arguments which we have urg'd against the quality of gravity in that explication we have consider'd it in have force likewise against it although it be said to be an Inclination of its subject to move it self to unity with the main stock of its own nature as divers witty men put it For this supposition doth but change the intention or end of gravity and is but to make it another kind of intellectual or knowing Entity that determines it self to an other end which is as impossible for a natural quality to do as to determine it self to the former ends And thus much the arguments we have proposed do convince evidently if they be apply'd against this opinion CHAP. XII Of Violent Motion ANd thus we have given a shortscantling wherby to understand in some measure the causes of that motion we call natural by reason it has its birth from the universal Oeconomy of nature here among us that is from the general working of the Sun wherby all natural things have their course and by reason that the cause of it is at all times and in all places constantly the same Next which the order of discourse leads us to take a survey of those forced motions whose first causes the more apparent they are the more obscurity they leave us in to determine by what means they are continued When a Tennis-ball is stroken by a Racket or an Arrow shot from a Bow we plainly see the causes of their motion namely the strings which first yielding and then returning with a greater celerity cause the missives to speed so fast towards their appointed homes Experience informs us what qualities the missives must be endued with to move fast and stedily They must be so heavy that the air may not break their course and yet so light that they may be within the command of the stroke which gives them motion the striker must be dense and in its best velocity the angle which the missive is to mount by if we will have it go to its furthest randome must be the half of a right one and lastly the figure of the missive must be such as may give scope to the air to bear it up and yet not hinder its course by taking too much hold of it All this we see But when with all we see that the mover deserts the moveable assoon as he has given the blow we are at a stand and know not where to seek for that which afterwards makes it flie For motion being a transient not a permanent thing assoon as the cause ceases that begot it in that very point it must be at an end and as long as the motion continues there must be some permanent cause to make it do so so that as soon as the Racket or bow string go back and leave the ball or arrow why should not they presently fall straight down to the ground Aristotle and hs followers have attributed the cause hereof to the air but Galileo relishes not this conception His arguments against it are as I remember to this tenor Frst air by reason of its rarity and divisibility seems not apt to conserve motion next we see that light things are best carried by the air and it has no power over weighty ones lastly it is evident that air takes most hold of the broadest superficies and therfore an arrow would fly faster broad waies then long waies if this were true Nevertheless since every effect must have a proportionable cause from whence it immediately flows and a body must have another body to thrust it on as long as it moves let us examin what bodies touch a moveable whilst it is in motion as the only means to find an issue out of this difficulty for to have recourse to a quality or impressed force for deliverance out of this straight is a shift that will not serve the turn in this way of discourse we use In this Philosophy no knot admits such a solution If then we enquire what body 't is that immediately touches the ball or arrow while it flies we shall find none others does so but the air and the atoms in it after the strings have given their stroke and are parted from the missive And though we have Galileo's authority and arguments to discourage us from believing the air can work this effect yet since there is no other body besides it left for us to consider in this case let us at the least examin how the air behaves it self after the stroke is given by the strings First then t is evident that as soon as the rocket or bow-string shrinks back from the missive and leavs a space between the missive and it as 't is clear it does assoon as it has strucken the resisting body the air must needs clap in with as much velocity as they retire and with somwhat more because the missive goes forward at the same time and therefore the air must hasten to overtake it least any vacuity should be left between the string and the arrow 'T is certain likewise that the air on the sides also upon the division of it slides back and helps to fill that space which the departed arrow leaves void Now this forcible closing of the air at the nock of the arrow must needs give an impulse or blow upon it If it seem to be but a little one you may consider 't is yet much greater then what the air and the bodies swiming in it at the first give to a stone falling from high and how at the last those little atoms that drive a stone in its natural motion with their little blows force it peradventure more violently and swiftly than any impelling agent we are acquainted with can do So that the impulse which they make on the arrow pressing violently upon it after such a vehement concussion and with a great velocity must needs cause a powerful effect in that which of it self is indifferent to any motion any way But unless this motion of the air continue to beat still upon the arrow it will soon fall to the ground for want of a cause to drive it forward and because the natural motion of the air being then the only one will determine it downwards Let us consider then how this violent rending of the air by the blow the bow-string gives to the Arrow must needs disorder the little atones that swim to and fro in it and that being heavier then the air are continually descending downwards This disorder makes some of the heavier parts of them get above others that are lighter then they which they not abiding presse upon those that are next them and they upon their fellows so that there is great commotion and undulation caused in the whole masse of air round about the arrow which must
violently upon it as in the first measure when the string parting from it did beat it forwards for till then the velocity encreases in the arrow as it does in the string that carries it along which proceeds from rest at the fingers loose from it to its highest degree of velocity which is when it arrives to the utmost extent of its jerk where it quits the arrow And therfore the air now doth not so swiftly nor so much of it rebound back from before and clap it self behind the arrow to fill the space that else would be left void by the arrows moving forward and consequently the blow it gives in the third measure to drive the arrow on cannot be so great as the blow was immediately after the strings parting from it which was in the second measure of time and therefore the arrow must needs move slower in the third measure than it did in the second as formerly it moved slower in the second which was the airs first stroke than it did in the first when the string drove it forwards And thus successively in every moment of time as the causes grow weaker weaker by the encrease of resistance in the air before and by the decrease of force in the subsequent air so the motion must be slower and slower till it come to pure cessation As for Galileu's second argument that the air has little power over heavy things and therfore he will not allow it to be the cause of continuing forced motions in dense bodies I wish he could as well have made experience what velocity of motion a mans breath might produce in an heavy bullet lying upon an even hard and slippery plain for a table would be too short as he did how admirable great a one it produced in pendants hanging in the air and I doubt not but he would have granted it as powerful in causing horizontal motions as he found it in the undulations of his pendants Which nevertheless sufficiently convince how great a power air has over heay bodies As likewise the experience of wind-guns assures us that air duly applyed is able to give greater motion to heavy bodies than to light ones For how can a straw or feather be imagin'd possibly to fly with half the violence as a bullet of lead doth out of one of those Engines And when a man sucks a bullet upwards in a perfectly bored barrel of a Gun which the bullet fits exactly as we have mention'd before with what a violence doth it follow the breath and ascend to the mouth of the barrel I remember to have seen a man that was uncautious and sucked strongly that had his foreteeth beaten out by the blow of the bullet ascending This experiment if well look'd into may peradventure make good a great part of this Doctrine we now deliver For the air pressing in behind the bullet at the touch-hole gives it its impulse upwards to which the density of the bullet being added you have the cause of its swiftness and violence for a bullet of wood or cork would not ascend so fast and so strongly and the sucking away of the air before it takes away that resistance which otherwise it would encounter with by the air lying in its way and its following the breath with so great ease shews as we touch'd before that of it self 't is indifferent to any motion when nothing presses upon it to determine it a certain way Now to Galileo's last argument that an arrow should fly faster broad-ways than long-ways if the air were cause of its motion there needs no more to be said but that the resistance of the air before hinders it as much as the impulse of the air behind helps it on So that nothing is gain'd in that regard but much is lost in respect of the figure which makes the arrow unapt to cut the air so well when it flyes broad-ways as when 't is shot long-ways and therfore the air being weakly cut so much of it cannot clap in behind the arrow and drive it on against the resistance before which is much greater Thus far with due respect and with acknowledging remembrance of the many admirable mysteries of nature which that great man hath taught the world we have taken liberty to dipute against him because this difficulty seems to have driven him against his Genius to believe that in such motions there must be allow'd a quality imprinted into the moved body to cause them which our whole scope both in this and all other occasions where like qualities are urged is to prove superfluous and ill grounded in nature and to be but meer terms to confound and leave in the dark whoever is forced to fly to them CHAP. XIII Of three sorts of violent motion Reflection Undulation and Refraction THe motion we have last spoken of because 't is ordinarily either in part or wholy contrary to gravity which is accounted the natural motion of most bodies uses to be call'd violent or forced And thus you have deliver'd you the natures and causes both of Natural and of Forced Motion yet it remains that we advertise you of some particular kinds of this forced motion which seem to be different from it but indeed are not As first the motion of Reflection which if we but consider how forced motion is made we shall find it is nothing else but a forced motion whose line whereon 't is made is as it were snapp'd in two by the encounter of a hard body For even as we see in a spout of water strongly shot against a wall the water following drives the precedent parts first to the wall and afterwards coming themselves to the wall forces them again another way from the wall so the latter parts of the torrent of air which is caused by the force that occasion'd the forced motion drives the former parts first upon the resistant body and afterwards again from it But this is more eminent in light than in any other body because light doth less rissent gravity and so observes the pure course of the stroke better than any other body from which others for the most part decline some way by reason of their weight Now the particular law of reflection is that the line incident the line of reflection must make equal angles with that line of the resistent superficies wch is in the same superficies with themselvs The demonstration wherof that great wit Renatus des Cartes hath excellently set down in his book of Dioptricks by the example of a ball strucken by a Racket against the earth or any resisting body the substance wherof is as follows The motion which we call Undulation needs no further explication for 't is manifest that since a Pendent when 't is removed from its perpendicular will restore it self therto by the natural force of gravity and that in so doing it gains a velocity and therefore cannot cease on a suddain it must needs be
proportion over air and water And this I conceive produces those substāces which we may term co-agulated juyces and which the Latines call succi concreti whos 's first origine seems to have been liquours that have been afterwards dried by the force either of heat or cold Of this nature are all kind of Salts Niters Sulfurs and divers sorts of Bitumens All which easily bewray the relicks and effects of fire left in them some more some less according to their degrees And thus we have in general deduced from their causes the complexions of those bodies whereof the bulk of the world subjected to our use consists and which serve for the production and nourishment of living creatures both animal and vegetable Not so exactly I confess nor so particularly as the matter in it self or as a Treatise confined to that subject would require yet sufficiently for our intent In the performance whereof if more accurate searchers of nature shall find that we have peradventure been mistaken in the minute delivering of some particular bodies complexion their very correction I dare boldly say will justifie our principal scope which is to shew that all the great variety we see among bodies arises out of the commixion of the First Qualities and of the Elements for they will not be able to correct us upon any other grounds then those we have laid As may easily be perceiv'd if we cast a summary view upon the qualities of compounded bodies All which we shall find to spring out of rarity and density and to savour of their origine for the most manifest qualities of bodies may be reduced to certain pairs opposite to one another As namely some are liquid and flowing others are consistent some are soft others hard some are fatty viscuous and smooth others lean gritty and rough some gross others subtile some tough others brittle and the like Of which the liquid the soft the fat and the viscuous are so manifestly derived from rarity that we need not take any further pains to trace out their origine and the like is of their contraries from the contrary cause to wit of those bodies that are consistent hard lean and gritty all which evidently spring from density As for smoothness we have already shew'd how that proceeds from an airy or oily nature and by consequence from a certain degree of rarity And therefore roughness the contrary of it must proceed from a proportionable degree of density Toughness is also a kind of ductility which we have reduced to watriness that is to another degree of rarity and consequently brittleness must arise from the contrary degree of density Lastly grossness and subtilness consist in a difficulty or facility to be divided into small parts which appears to be nothing else but a certain determination of rarity and density And thus we see how the several complexions of bodies are reduced to the four Elements that compound them and the qualities of those bodies to the two primary differences of quantitative things by which the elements are diversified And out of this discourse it will be evident that these complexions and qualities though in diverse degrees must of necessity be found wherever there is any variation in bodies For seeing there can be no variation in bodies but by rarity and density and that the pure degrees of rarity and density make heat cold moisture and driness and in a word the four Elements 't is evident that wherever there is variety of bodies there must be the four Elements though peradventure far unlike these miked bodies which we call Elements And again because these Elements cannot consist without motion and by motion they of necessity produce Mixed bodies and forge out those Qualities which we come from explicating it must by like necessity follow that wherever there is any variety of active and passive bodies there mixed bodies likewise must reside of the same kinds and be indued with qualities of the like natures as those we have treated of though peradventure such as are in other places of the world remote from us may be in a degree far different from ours Since then it cannot be denied but that there must be notable variety of active and passive bodies wherever there is light neither can it be denied but that in all those Great Bodies from which light is reflected to us there must be a like variety of complexions and qualities and of bodies temper'd by them as we find here in the Orb we live in Which Systeme how different it is from that which Aristotle and the most of the School have deliver'd us as well in the evidencies of the proofs for its being so as in the position and model of it I leave to the prudent Readers to consider and judge Out of what has been already said 't is not hard to discover in what manner the composition of bodies is made In effecting which the main hinge wheron that motion depends is fire or heat as it likewise is in all other motions whatever Now because the composition of a mixed body proceeds from the action of one simple body or element upon the others it will not be amiss to declare by some example how this work passes for that purpose let us examine how fire or heat works upon his fellows By what we have formerly deliver'd 't is clear that fire streaming out from its centre and diffusing it self abroad so as to fill the circumference of a larger circle it must needs follow that the beams of it are most condens'd and compacted together near the centre and the further they stream from the centre the more thin and rarified they must grow yet this is with such moderation as we cannot any where discern that one beam doth not touch another and therfore the distances must be very smal Now let us suppose that fire happens to be in a viscuous and tenacious body and then consider what will happen in this case of one side the fire spreads it self abroad on the other side the parts of the tenacious body being moist as I have formerly determin'd their edges on all hands will stick fast to the dry beams of the fire that pass between them Then they stretching wider and wider from one another must needs draw with them the parts of that tenacious body which stick to them and stretch them into a greater widness or largness then they enjoy'd before from whence it follows that seeing there is no other body near therabouts but they two either there must be a vacuity left or else the tenacious body must hold and fill a greater space then it did before and consequently be more rare Contrariwise of any of the other elements be stronger then fire the denser Elements break off from their continu'd stream the little parts of fire which were gotten into their greater parts and sticking on all sides about them so enclose them that they have no more semblance of fire and
change of place we must call to mind how two dense bodies moving one against the other each of them bear before them some little quantity of a rarer body immediately joyn'd to them and consequently these more rare bodies must be the first to feel the power of the dense bodies and receive impressions from their motions each of them by the opposite rare body which like an Huissier goes before to make way for his following Master that obliges him to this service Now when these rare Ushers have strugled a while like the first lightly armed Ranks of two Armies in the interjacent Field between their main Battails that follow them close at the heels they must at the length yield when they are overborn by a greater weight then they can sustain and then they recoil back as it were to save themselves by getting in among the files of the dense bodies that drove them on Which not opening to admit them and yet they still flying violently from the mastering force that pursues them they presse so hard upon what at the first pressed them on as notwithstanding their density and strength they force them to retire back for unless they do so they are not of the number of those that work upon one another And this retiring is either on both sides or but of one side If both then 't is evident how each of them is an Agent and each of them a sufferer each of them overcoming his opposite in such sort as himself likewise receives blows and loss But if only one of the dense bodies be so shocked as to recoil back then that only suffers in its body and the other suffers only in its vertue that is in the air or other rare body it sends before it which it drives with such a violence that it masters and quells the opposition of the other body before it can reach to shake the dense body before which it runs Yet that rare body must be pressed and broken into in some measure by the incounter of the other which though never so weak yet makes some resistance but much more when it comes to grapple with the dense body it self and so between them it is wounded and infeebled like those souldiers that first enter a Breach in a Town from whence when they have driven the enemy they pursue him to the Cittadel and force him from thence too and so how maimed so ever they prove they make a free and easie way without resistance for the whole body of their army to follow them and take quiet possession of that which cost them so much to win And thus we see how it may happen that one of these moving bodies doth not suffer so much as to be stay'd in its journey much less to be driven back And yet the other body at the same time work in some measure upon it by working upon what is next to it which recoiling against it must needs make some impression upon it since there can be no opposition but must have some effect Now this impression or effect though it be not perceptible by causing a contrary motion yet it must needs infeeble the virtue of the conquering Agent and deaden the celerity of its motion And thus it is evident that in all pure local motions of corporeal Agents every one of them must in some proportion suffer in acting and in suffering must act And what we have said of this kind of action may easily be apply'd to the other where the effect of local motion is design'd by a particular name as it is in the examples we gave of heating and cooling And in that the proceeding will appear to be the very same as in this For if fire heats water the water reacts again either upon the fire and cools it if it be immediate to it or else upon the interjacent air if it be at a distance from the fire And so the air is in some measure cooled by the cold atomes that issue from the water whose compass or sphere of activity being lesser then the fire 's they cannot cool so far off as others can heat but where they a rrive they give their proportion of cold in the very midst of the others army of fiery atomes notwithstanding their multitude and violence According to which doctrine our Countryman Suisseth's argument that in the Schools is held insoluble hath not so much as any semblance of the least difficult For 't is evident that such atomes of fire and water as we determine heat and cold to be may pass and croud by one another into the subjects they are sent to by divers little streams without hindring one another as we have declared of air and light and each of them be receiv'd in their own nature temper by the same subject though sense can judge only according to which of them is predominant and according to the proportion of its superiority Upon which occasion we cannot chuse but note how the doctrine of qualities is not only unable to give account of the ordinary and plain effects of nature but also uses to end in clear impossibilities and contradictions if it be driven far as this argument of Suisseth shews and many others of the like nature A fourth position among Philosophers is that Some Notions admit the denominations of Intention and remission but that others do not The reason of which we shall clearly see if we but consider how these terms of intention and remission do but express more or less of the thing that is said to be intended or remitted for the nature of more and less implyes a latitude and divisibility and therefore cannot agree with the nature of such things as consist in an indivisible being As for example to be a whole or an equal cannot be sometimes more sometimes less for they consist in such a rigorous indivisible being that if the least part imaginable be wanting it is no longer a whole if there be the least excess between two things they are no longer equal but in some other proportion then of equality in regard of one another And hence it is that Aristotle teaches us that Substance and the species of Quantity do not admit of intention and remission but that Quality doth For first in Substance we know that the signification of this word is that which makes a thing be what it is as is evident by our giving it for an answer to the question what a thing is And therfore if there were any divisibility in Substance it would be in what the thing is and consequently every division following that divisibility would make the thing another what that is another thing and so the Substance that 's pretended to be changed by intension or remission would not be divided as is supposed but would cease to be and another substance would succeed in the room of it Wherby you see that every mutation in Substance makes a new thing and that more and
is drawn the more must needs follow Now if there be floating in this air any other atoms subject to the current which the air takes they must also come with it to the fire and by it be rarified and exported out of that little orb Hence it is that men with very good reason hold that fire airs a chamber as we term it that is purifies it both because it purifies it as wind doth by drawing a current of air into it that sweeps through it or by making it purifie it self by motion as a stream of water doth by running as also because those vapours which approach the fire are burned dissolv'd So that the air being noisome and unwholesome by reason of its grossness proceeding from its standing unmoved like a stagnation of dead water in a marish place the fire takes away that cause of annoyance By this very rule we learn that other hot things which participate the nature of fire must likewise in other respects have a resemblance in this quality And accordingly we see that hot loaves in a Bakers shop newly drawn out of the Oven are accounted to draw to them any infection which is in the air The like we say of onyons and other strong breathing substances which by their smel shew much heat in them In like manner 't is conceiv'd that Pigeons and Rabbets and Cats easily take infection by reason of their extraordinary warmth which they have in themselvs And this is confirm'd by the practise of Physitians who use to lay warm Pigeons newly killed to the feet wrists or heads of sick persons and young Puppies to their stomacks and somtimes certain hot gums to their navels to draw out such vapours or humours as infest the body for the same reason they hang amulets of arsenick sublimate dryed Toads or Spiders about their patients necks to draw to them venimous qualities from their bodie Hence also it is that if a man be strucken by a Viper or a Scorpion they use to break the body of the beast it self that stung him if they can get it upon the wound but if the beast be crawl'd out of their finding they do the like by some other venimous creature as I have seen a bruised Toad laid to the biting of a Viper And they manifestly perceive the apply'd body to swel with the Poyson suck'd out from the wound the patient to be reliev'd have less poyson in the same manner as by cupping-glasses the poyson is likewise drawn out from the wound so that you may see the reason of both is the very same or at least very like one another Only we are to note that the proper body of the beast out of which the venome was driven into the wound is more efficacious than any other to suck it out And the like is to be observ'd in all other kinds that such vapours as are to be drawn come better and incorporate faster in bodies of like nature then in those which have only the common conditions of heat and dryness the one of which serves to attract the other to fasten and incorporate into itself the moisture which the first draws to it So we see that water soaks into a dry body whence it was extracted almost inseparably and is hidden in it as when it rains first after hot weather the ground is presently dried after the shower Likewise we see that in most cements you must mingle a dust of the nature of the things which are to be cemented if you will have them bind strongly Out of this discourse we may yield a reason for those Magical operations which some attribute to the Devils assistance peradventure because mans wickedness hath bin more ingenious then his good will and so has found more means to hurt then to help nay when he hath arrived some way to help those very helps have undergone the same calumny because of the likeness which their operations have to the others Without doubt very unjustly if there be truth in the effects For where have we any such good suggestions of the enemy of mankind proposed to us that we may with reason believe he would duly settledly and constantly concur to the help and service of all those he so much hates as he must needs do if he be the Author of such effects Or is it not a wrong to Almighty God and to his careful instruments rather to impute to the Devil the aids which to some may seem supernatural then to them of whom we may justly believe and expect such good Offices and assistances I mean those operations both good and bad which ordinarily are called Magnetical though peradventure wrongfully as not having that property whcih denominates the loadstone One thing I may assure that if the reports be true they have the perfect imitation of nature in them As for example that the Weapons-Salve or the Sympathetick-Powder requires in the using it to be conserved in an equal moderate temper and that the weapon which made the wound or the cloth upon which the blood remains that issued from it be orderly and frequently dressed or else the wounded person will not be cured Likewise the steam or spirits which at the giving of the wound enter'd into the pores of the weapon must not be driven out of it which will be done by fire and so when it is heated by holding over coals you may see a moisture sweat out of the blade at the opposite side to the fire as far as it entred into the wounded persons body which being once all sweated out you shall see no more the like steam upon the sword neither must the blood be washed out of the bloudy cloth for in these cases the powder or salve will work nothing Likewise if there be any excess either of heat or cold in keeping the medicated weapon or cloth the patient feels that as he would do if the like excess where in any remedy that were applyed to the wound it self Likewise if the medicated weapon or bloudy cloth be kept too close no effect follows Likewise the natures of the things used in these cures are of themselves soveraign for healing the like griefs though peradventure too violent if they were apply'd in body without much attenuation And truly if we will deny all effects of this kind we must in a manner renounce all humane faith men of all sorts and qualities and many of them such in my own knowledge as I cannot question their prudence in observing or their sincerity in relating having very frequently made experience of such medicines and all affirming after one fashion to have found the same effects Adde to these the multitude of other like effects appearing or conceited to appear in other things In some Countries 't is a familiar disease with Kine to have a swelling in the soles of their feet and the ordinary cure is to cut a turf upon which they have troden with their sore foot and to hang
to the iron though the other steam be never so great yet it cannot draw more then according to the proportion of its Antagonists coming from the iron Wherfore seeing the two steams betwixt the iron and the little Loadstone are more proportionable to one another and the steam coming out of the little loadstone is notably greater then the steam going from the iron to the greater Loadstone the conjunction must be made for the most part to the little loadstone And if this discourse doth not hold in the former part of the Probleme betwixt a second iron and Loadstone it is supplyed by the former reason which we gave for that particular purpose The third case depends also of this solution for the bigger an iron is so many more parts it hath to suck up the influence of the Loadstone and consequently doth it therby the more greedily and therfore the Loadstone must be carried to it more violently and when they aâ—e joyn'd stick more strongly The sixth question is Why the variations of the Needle from the true North in the Northern Hemisphere are greater the nearer you go to the Pole and lesser the nearer you approach to the Equator The reason wherof is plain in our doctrine For considering that the magnetick virtue of the earth streams from the North towards the Equator it follows of necessity that if there be two streams of magnetick flowrs issuing from the North one of them precisely from the pole the other from a part of the earth near the pole that the stream coming from the point by side the Pole be but a little the stronger of the two there will appear very little differences in their several operations after they have had a long space to mingle their emanations together which therby join and grow as it were into one stream wheras the nearer you come to the Pole the more you will find them severed and each of them working by its own virtue And very near the point which causes the variation each stream works singly by it self and therfore here the point of variation must be master and will carry the needle strongly to his course from the due North if his stream be never so little more efficacious then the other Again a line drawn from a point of the Earth wide of the Pole to a point of the Meridian near the Equator makes a less angle then a line drawn from the same point of the Earth to a point of the same Meridian nearer the Pole wherfore the variation being esteem'd by the quantities of the said angles it must needs be greater near the Pole then near the Equator though the cause be the same But because it may happen that in the parts near the Equator the variation may proceed from some piece of land not much more northerly then where the needle is but that it bears rather Easterly or Westerly from it and yet Gilbert's assertion goes universally when he says the variations in Southern regions are less then in Northern ones we must examine what may be the reason therof And presently the generation of the Loadstone shews it plainly For seeing the nature of the Loadstone proceeds out of this that the Sun works more upon the Torrid Zone then upon the poles and that his too strong operation is contrary to the Loadstone as being of the nature of fire it follows evidently that the lands of the Torrid Zone cannot be so magnetical generally speaking as the polar lands are and by consequence that a lesser land near the Pole will have a greater effect then a larger continent near the Equator and likewise a land further off towards the Pole will work more strongly then a nearer land which lyes towards the Equator The seventh question is Whether in the same part of the world a touched needle may at one time vary more from the true North point and at another time less In which Gilbert was resolute for the negative part but our latter Mathematicians are of another mind Three experiences were made neer London in three divers years The two first 42 years distant from one another and the third 12 years distant from the second And by them it is found that in the space of 54 years the Loadstone hath at London diminsh'd his variation from the North the quantity of 7 degrees and more But so that in the latter years the diminution hath sensibly gone faster then in the former These observations peradventure are but little credited by Strangers but we who know the worth of the men that made them cannot mistrust any notable errour in them for they were very able Mathematicians and made their observations with very great exactness and there were several judicious witnesses at the making of them as may be seen in Mr. Gillebrand's print concerning this subject And divers other particular persons confirm the same whose credit though each single might peradventure be slighted yet all in body make a great accession We must therfore cast about to find what may be the cause of an effect so paradox to the rest of the doctrine of the Loadstone for seeing that no one place can stand otherwise to the North of the earth at one time then at another how it is possible the needle should receive any new variation since all variation proceeds out of the inequality of the earth But when we consider that this effect proceeds not out of the main body of the earth but only out of the bark of it and that its bark may have divers tempers not as yet discover'd to us out of whose variety the influence of the earthy parts may be divers in respect of one certain place 't is not impossible but that such variation may be especially in England which Island lying open to the North by a great and vast Ocean may receive more particularly then other places the special influences and variation of the weather that happen in those Northeastern countreys from whence this influence comes to us If therfore there should be any cours of weather whose period were a hundred years for example or more or lesse and so might easily pass unmarked this variation might grow out of such a cours But in so obscure a thing we have already hazarded to guess too much And upon the whole matter of the Loadstone it serves our turn if we have proved as we conceive we have done fully that its motions which appear so admirable do not proceed from an occult quality but that the causes of them may be reduced to local motion and all perform'd by such corporeal instruments and means though peradventure more intricately disposed as all other effects are among bodies Whose ordering and disposing and particular progress there is no reason to despair of finding ouâ— would men but carefully apply themselvs to that work upon solid principles and with diligent experiences But because this matter has been very long and scatteringly
of necessity be more humid and figurable then that of an ordinary plant and the Artificer which works and moulds it must be more active Wherfore we must suppose that the mass of which an Animal is to be made must be actually liquid and the fire that works upon it must be so powerful that of its own nature it may be able to convert this liquid matter into such breaths and steams as we see use to rise from water when the Sun or fire works upon it Yet if the mass were altogether as liquid as water it would vanish away by heat boyling it and be dried up therfore it must be of such a convenient temper that although in some of its parts it be fluid and apt to run yet by others it must be held together as we see that unctuous things for the most part are which will swell by heat but not fly away So then if we imagine a great heat to be imprison'd in such a liquor and that it seeks by boyling to break out but that the solidness and viscousness of the substance will not permit it to evaporate it cannot chuse but comport it self in some such sort as we see butter or oyl in a frying-pan over the fire when it rises in bubbles but much more efficaciously For their body is not strong enough to keep in the heat and therfore those bubbles fall again wheras if it were those bubbles would rise higher and higher and stretch themselvs longer and longer as when the Soap-boylers boyl a strong unctuous lye into Soap and every one of them would be as it were a little brook wherof the channel would be the enclosing substance and the inward smoak that extends it might be compared to the water of it as when a glass is blown out by fire and air into a long figure Now we may remember how we have said where we treated of the Production and Resolution of Mixed bodies that there are two sorts of liquid substantial parts which by the operation of fire are sent out of the body it works upon the watery and the oyly parts For thouh there appear somtimes some very subtile and Ethereal parts of a third kind wich are the Aquae Ardentes or borning spirits yet in such a close distilling of circulation as this is they are not sever'd by themselvs but accompany the rest and especially the watery parts which are of a nature that the rising Ethereal spirits easily mingle with and extend themselves in it wherby the water becomes more efficacious and the spiritt less fugitive Of these liquid parts which the fire sends away the watry ones are the first as being the easiest to be raised the oyly parts rise more difficultly and therfore come last And in the same manner it happens in this emission of brooks the watry and oyly steams will each of them fly into different reservs and if there arrive to them abundance of their own quality each of them must make a substance of its own nature by by setling in a convenient place and by due concoction Which substance after it is made and confirm'd if more humidity and heat press it will again break forth into other little channels But when the watry and oyly parts are boyl'd away there remain yet behind other more solid and fixed parts and more strongly incorporated with fire then either of these which yet cannot drie up into a fiery salt because a continual accession of humour keeps them always flowing and so they become like a cauldron of boyling fire Which must propagate it self as wide as either of the other since the activity of it must needs be greater then theirs as being the source of motion to them and that there wants not humidity for it to extend it self by And thus you see three roots of three divers plants all in the same plant proceeding by natural resolution from one primitive source Wherof that which is most watry is fittest to fabricate the body and common outside of the triformed plant since water is the most figurable principle in nature and most susceptible of multiplication and by its cold is easiest to be hardned and therfore fittest to resist the injuries of enemy-bodies that may infest it The oily parts are fittest for the continuance and solidity of the plant for we see that viscuosity and oyliness hold together the parts where they abound and they are slowly wasted by fire but conserve and are an aliment to the fire that consumes them The parts of the third kind are fittest for the conservation of heat which though in them it be too violent yet is necessary for working upon other parts and maintaining a due temper in them And thus we have armed our plant with three sorts of rivers or brooks to run through him with as many different streams the one of a gentle balsamike oyle another of streaming fire and the third of a con-natural and cooler water to irrigate and temper him The streams of water as we have said must run through the whole fabrick of this triformed plant and because it is not a simple water but warm in a good degree and as it were a middle substance betwixt water and air by reason of the ardent volatile spirit that is with it 't is of a fit nature to swell as air doth and yet withall to resist violence in a convenient degree as water doth Therfore if from its source nature sends abundance into any one part that part must swell and grow thicker and shorter and so must be contracted that way which nature has order'd it Whence we perceive a means by which nature may draw any part of the outward fabrick which way soever she is pleased by set instruments for such an effect But when there is no motion or but little in these pipes the standing stream that is in a very little though long channel must needs be troubled in its whole body if any one part of it be press'd upon so as to receive therby any impression and therfore whatever is done upon it though at the very furthest end of it makes a commotion and sends an impression up to its very source Which appearing by our former d scourse to be the origine of particular and accasional motion 't is obvious to conceive how it is apt to be moved and wrought by such an impression to set on foot the begining of any motion which by natures providence is convenient for the plant when such an impression is made upon it And thus you see this plant hath the virtue both of sense or feeling that is of being moved and effected by extern objects lightly striking upon it as also of moving it self to or from such an object according as nature shall have ordain'd Which in sum is that This Plant is a Sensitive Creature composed of three sources the Heart the Brain and the Liver whose off-springs are the Arteries the Nervs and the Veins which are fil'd with Vital
out into an extasie of admiration and hymns of praise as great Galen did upon the like occasion when we reverently consider the infinite Wisedome and deep far-looking Providence of the all-seeing Creatour and Orderer of the World in so punctually adopting such a multitude and swarm of causes to produce by so long a progress so wonderful an effect in the whole course of which if any one the very least of them all went never so little awry the whole fabrick would be discomposed and changed from the nature it is design'd to Out of our short survey of which answerable to our weak talents and slender experience I perswade mv self it appears evident enough that to effect this work of generation there needs not be supposed a forming virtue or Vis formatrix of an anknown power and operation as those that consider things suddenly and but in gross use to put Yet in discourse for conveniency and shortness of expression we shall not quite banish that term from all commerce with us so that what we mean by it be rightly understood which is the complex assemblement or chain of all the causes that concur to produce this effect as they are set on foot to this end by the great Architect and Moderatour of them God Almighty whose instrument Nature is that is the same thing or rather the same things so order'd as we have declared but express'd and compriz'd under another name CHAP. XXVI How motion begins in Living Creatures And of the motion of the Heart circulation of the Bloud Nutrition Augmentation and Corruption or Death BUt we must not take our leave of this subject til we have examin'd how motion begins in living things as well Plants as Sensative creatures We can readily pitch upon the part we are to make our observations in for retriving the origine of this primary motion for having concluded that the roots of Plants and the hearts of Animals are the parts of them which are first made and from which the forming virtue is derived to all the rest it were unreasonable to seek for their first motion any where else But in what manner and by what means doth it begin there For roots the difficulty is not great for the moysture of the earth pressing upon the seed and soaking into it the hot parts of it which were imprison'd in cold and dry ones are therby stir'd up and set on work then they mingling themselves with that moysture ferment and distend the whole seed til making it open and break the skin more juice comes in which imcorporating it self with the heat those hot and now moyst parts will not be contain'd in so narrow a room as at the first but strugling to get out on all sides and striving to enlarge themselvs they thrust forth little parts Which if they stay in the earth grow white and make the root but those which ascend and make their way into the air being less compressed and more full of heat and moysture turn green and as fast as they grow up new moysture coming to the root is sent up through the pores of it and this fails not till the heat of the root it self fails For it being the nature of heat to rarifie and elevate there must of necessity be caus'd in the earth a kind of sucking in of moysture into the root from the next parts to it to fill those capacities which the dilating heat hath made that else would be empty and to supply the rooms of those which the heat continually sends upwards for the moysture of the root hath a continuity with that in the earth and therfore they adhere together as in a Pump or rather as in filtration and follow one another when any of them are in motion and still the next must needs come in and fill the room where it finds an empty space immediate to it The like of which happens to the Air when we breath for our lungs being like a Bladder when we open them the air must needs come in to fill that capacity which else would be empty and when we shut them again as in a pair of Bellows we put it out This may suffice concerning the primary motion of roots but in that of the heart we shall find the matter not altogether so plain Monsieur des Cartes following herein the steps of the learned and ingenuous Dr. Harvey who hath invented and teaches that curious and excellent Doctrine of the Cerculation of the Bloud as indeed what secret of nature can be hidden from so sharp a wit when he applyes himself to penetrate into the bottome of it explicates the matter much after this sort That the heart within the substance of it is like a hollow Cavern in whose bottome were an hot stone on which should drop as much liquor as the fiery stone could blow into smoke and this smoke or steam should be more then the Cave could contain wherfore it must break out which to do it presses on all sides to get an issue or door to let it out It finds of two sorts but only one kind of them will serve it for this purpose for the one sort of these doors opens inwards the other outwards which is the cause that the more it strives to get out the faster it shuts the doors of the first kind but by the same means it beats back the other doors and so gets out Now when it is gone quite out of this Cavern and consequently leaves it to its natural disposition whereas before it violently stretched it out and by doing so kept close the doors that open inwards then all the parts of it begin to slacken and those Doors give way to new liquor to drop in anew which the heat in the bottome of the heart rarifies again in-into smoke as before And thus he conceives the motion of the heart to be made taking the substance of it to be as I may say like to limber Leather which upon the feeling of it with bloud and steam opens and dilates it self and at the going of it out it shrinks together like a bladder But I doubt this Explication will not go through the difficulty For first both Galen and Dr. Harvey shew that as soon as the bloud is come into the heart it contracts it self which agrees not with Monsir des Cartes his supposition for in his doctrine there appears no cause why it should contract it self when it is full but contrariwise it should go on dilating it self till enough of the bloud which drops into the heart were converted into steam to force the doors open that so it may gain an issue thence and a passage into the body Next Monsir des Cartes supposes that the substance of the heart is like a bladder which hath no motion of it self but opens and shuts according as what is within it stretches it out or permits it to shrink and fall together again Wheras Dr. Harvey proves
little parts of the substance which we chew in our Teeth and which passes over it You may observe how if we take any herb or fruit and having chop'd or beaten it small put it into a wooden dish of water and squeeze it a little the juice communicating and mingling it self with the water infects it with the tast of it self and remaining a while in the bowl sinks by little and little into the very pores of the wood as is manifest by its retaining a long time after the tast and smell of that herb In like manner nature hath taught us by chewing our meat and by turning it in our mouths and pressing it a little that we may the more easily swallow it to imbue our Spittle with such little parts as easily diffuse themselvs in water And then our Spittle being continuate to the moysture within our tongue in such sort as we declared of the moisture of the earth that soaks into the root of a plant and particularly in the sinews of it must of necessity affect those little sensible strings with the qualities which these petty bodies mixed every where with the moisture are themselves imbued withal And if thou ask what motions or qualities these be Physitians to whom it belongs most particularly to look into them will tell you that some dilate the tongue more and some less as if some of these little bodies had an aereal and others a watry disposition and these two they express by the names of sweet and fatty That some contract and draw the tongue together as choaky and rough things do most and next to them crabby and immature sharpness That some corrode and pierce the Tongue as Salt and sowre things That bitter things search the outside of it as if they swept it and that other things as it were prick it as spices and hot drinks Now all these are sensible material things which admit to be explicated clearly by the varieties of rarity and density concurring to their compositions and are so proportionable to such material instruments as we cannot doubt but they may be throughly declared by our former principles The next Element above Water is Air which our Nostrils being our Instrument to suck in we cannot doubt but what affects a man by his Nose must come to him in Breath or Air. And as humidity receives grosser and weightier parts so those which are more subtile and light rise up into the Air and these we know attain to this lightness by the commixtion of fire which is hot and dry And therfore we cannot doubt but that the nature of Smells is more or less tending to heat and drought which is the cause that their commixtion with the brain proves comfortable to it because of its own disposition it is usually subject to be too moist and too cold Whether there be any immediate instrument of this sense to receive the passion or effect which by it other bodies make upon us or whether the sense it self be nothing but a passage of these exhalations and little bodies to the brain fitly accommodated to discern what is good or hurtful for it and accordingly to move the body to admit or reject them it imports not us at present to determine let Physicians and Anatomists resolve that question Whiles it suffices us to understand that the operations of bodies by Odours upon our sense are perform'd by real and solid parts of the whole substance which are truly material though very little bodies and not by imaginary qualities And those bodies when they proceed out of the same things that yield also tastive particles although without such material violence and in a more subtile manner must of necessity have in them the same nature which those have that affect the tast and they must both of them affect a man much alike by his tast by his smell and so are very proportionate to one another excepting in those properties which require more cold or liquidity then can well stand with the nature of a smell And accordingly the very names which men have imposed to express the affections of both many times agree as savour and sweet which are common both to the smell and tast the strongest of which we see oftentimes make themselves known as well by the one as by the other sense and either of them in excess will turn a mans stomack And the Physicians that write of these senses find them very conformable whence it happens that the losing of one of them is the losse also of the other And experience teaches us in all Beasts that the Smell is given to living creatures to know what meats are good for them and what are not And accordingly we see them still smell for the most part at any unknown meat before they touch it which seldom fails of informing them rightly nature having provided this remedy against the gluttony which could not choose but follow the convenient disposition and temper of their parts and humours through which they often swallow their meat greedily and suddenly without expecting to try it first by their tast Besides that many meats are so strong that their very tasting them after their usual manner would poison or at least greatly annoy them and therfore nature hath provided this sense to prevent their tast which being far more subtile then their tast the final atoms by which it is perform'd are not so very noxious to the health of the Animal as the other grosser atoms are And doubtlesly the like use men would make of this sense had they not on the one side better means then it to know the qualities of meats and therfore this is not much reflected on And on the other side were they not continually stuff'd and clogg'd with gross vapours of streamy meats which are daily reeking from the Table and their stomacks and permit not purer Atomes of bodies to be discerned which require clear and uninfected organs to take notice of them As we see it fare with doggs who have not so true and sensible noses when they are high fed and lie in the kitchin amidst the steams of meat as when they are kept in their kennel with a more spare diet fit for hunting One full example this age affords us in this kind of a man whose extremity of fear wrought upon him to give us this experiment He was born in some Village of the Countrey of Liege and therfore among strangers he is known by the name of John of Liege I have been informed of this story by several whom I dare confidently believe that have had it from his own mouth and have question'd him with great curiosity particularly about it When he was a little boy there being wars in the Countrey as that State is seldom without molestations from abroad when they have no distempers at home which is an inseparable effect of a Countries situation upon the Frontiers of powerful neighbouring Princes that are at variance the
red The reason hereof is that The colours which appear in the glasse are of the nature of those luminous colours we first explicated that arise from looking upon white and black bordering together For a candle standing in the air is as it were a white situated between two blacks the circumstant dusky air having the nature of a black so then that side of the candle which is seen through the thicker part of the glass appears red and that which is seen through the thinner appears blew in the same manner as when we look through the glass Whereas the colours shine contrariwise upon a paper or reflecting object as we have already declared together with the reasons of both these appearances each fitted to its proper case of looking through the glass upon the luminous object surrounded with darkness in the one and of observing the effect wrought by the same luminous object in some medium or upon some reflectent superficies in the other And to confirm this if a white paper be set standing hollow before the glass like half a hollow pillar whose flats stands edgeways towards the glass so as both the edges may be seen through it the further edge will seem blew and the nearer will be red and the like will happen if the paper be held in the free air parallel to the lower superficies of the glass without any black carpet to limit both ends of it which serves to make the colours the smarter So that in both cases the air serves manifestly for a black in the first between the two white edges and in the second limiting the two white ends and by consequence the air about the candle must likewise serve for two blacks including the light candle between them Several other delightful experiments of luminous colour I might produce to confirm the grounds I have laid for the nature and making of them But I conceive these I have mention'd are abundantly enough for the end I propose to my self Therfore I will take my leave of this subtle and nice subject referring my Reader if he be curious to entertain himself with a full variety of such shining wonders to our ingenious Countreyman and my worthy friend Mr. Hall who at my last being at Liege shew'd me there most of the experiences I have mention'd together with several other very fine and remarkable curiosities concerning light which he promised me he would shortly publish in a work that he had already cast and almost finished upon that svbject And in it I doubt not but He will give entire satisfaction to all the doubts and Problems that may occur in this subject wheras my little exercise formerly in making experiments of this kind and my less conveniency of attempting any now makes me content my self with thus spining a course thred from wooll carded me by others that may run through the whole doctrine of colours whose causes have hitherto been so much admired and that it will do so I am strongly perswaded both because if I look upon the causes which I have assigned à prirori me thinks they appear very agreeable to nature and to reason and if I apply them to the several Phenomens which Mr. Hall shew'd me and to as many others as I have otherwise met with I find they agree exactly with them and render a full account of them And thus you have the whole nature of luminous colours resolv'd into the mixion of light and darkness by the due ordering of which who have skil therin may produce any middle colour he please as I my self have seen the experience of infinite changes in such sort made so that it seems to me nothing can be more manifest then that luminous colours are generated in the way here deliver'd Of which how that gentle and obedient Philosophy of Qualities readily obedient to what hard task soever you assign it will render a rational account and what discreet vertue it will give the same things to produce different colours and maked different appearances meerly by such nice changes of situation I do not well understand But peradventure the Patrones of it may say that every such circumstance is a Conditio sine qua non and therwith no doubt their Auditors will be much the wiser in comprehending the particular nature of light and of the colours that have their origine from it The Rainbow for whose sake most men handle this matter of luminous colours is generated in the first of the two ways we have deliver'd for the production of such colours and hath its origine from refraction when the eye being at a convenient distance from the refracting body looks upon it to discern what apears in it The speculation of which may be found in that excellent discourse of Mounsir des Cartes which is the sixth of his Meteors where he hath with great accurateness deliver'd a most ingenious doctrine of this mystery had not his bad chance of missing in a former principle as I conceive somwhat obscured it For he there gives the cause so neat and so justly calculated to the apearances as no man can doubt but that he hath found out the true reason of this wonder of nature which hath perplex'd so many great wits as may almost be seen with our very eyes when looking upon the fresh dew in a Sunshiny morning we may in due positions perceive the Rainbow colours not three yards distant from us in which we may distinguish even single drops with their effects But he having deterned the nature of light to consist in motion and proceeding consequently concludes colours to be but certain kinds of motion by which I fear it is impossible that any good account should be given of the experiences we see But what we have already said in that point I conceive is sufficient to give the Reader satisfaction therin and to secure him that the generation of the colours in the Rain-bow as well as all other colours is reduced to the mingling of light and darkness which is our principal intent to prove Adding therto by way of advertisement for others whose leisure may permit them to make use thereof that who shall ballance the proportions of luminous colours may peradventure make himself a step to judg of the natures of those bodes which really and constantly wear like dyes for the figures of the least parts of such bodies joyntly with the connexion or mingling of them with pores must of necessity be that which makes them reflect light to our eyes in such proportions as the luminous colours of their tincture and semblance do For two things are to be consider'd in bodies in order to reflecting of light either the extancies and cavities of them or their hardness and softness As for the first the proportions of light mingled with darkness will be varied according as the extancies or the cavities exceed and as each of them is great or small since cavities have the nature of darkness in respect
in the utmost extremity without sending any due proportion of spirits to the brain till they settle a little and grow more moderate Now when these motions are moderate they immediately send up some abundance of spirits to the brain which if they be in a convenient proportion are by the brain thrust into such nervs as are fit to receive them and swelling them they give motion to the muscles and tendons that are fastned to them and they move the whole body or what part of it is under command of those nervs that are thus fill'd and swell'd with spirits by the brain If the object was conformable to the living creature then the brain sends spirits into such nervs as carry the body to it but if otherwise it causes a motion of aversion or flight from it To the cause of this latter we give the name of Fear and the other that carries one to the pursuit of the object we call Hope Anger or Audacity is mixt of both these for it seeks to avoid an evil by embracing and overcoming it and proceeds out of abundance of spirits Now if the proportion of spirits sent from the heart be too great for the brain it hinders or perverts the due operation both in man and beast All which it will not be amiss to open a little more particularly and first why painful or displeasing objects contract the spirits and grateful ones contrariwise dilate them It is because the good of the heart consists in use that is in heat and moisture and 't is the nature of heat to dilate it self in moisture whereas cold and dry things contract the bodies they work on and such are enemies to the nature of men and beasts And accordingly experience as well as reason teaches us that all objects which be naturally good are hot and moist in due proportion to the creature that is affected and pleas'd with them Now the living creature being composed of the same principles as the world round about him is and the heart being an abridgment of the whole sensible creature and besides full of blood and that very hot it comes to pass that if any of these little extracts of the outward world arrive to the hot blood about the heart it works in this blood such like an effect as we see a drop of water falling into a glass of wine which is presently dispersed into a competent compass of the wine so that any little object must needs make a notable motion in the blood about the heart This motion according to the nature of the object will be either conformable or contrary unless it be so little a one as no effect will follow of it and then 't is of that kind which above we call'd indifferent If the ensuing effect be connatural to the heart there rises a motion of a certain fume about the heart which motion we call Pleasure and it never fails of accompanying all those motions which are good as Joy Love Hope and the like but if the motion be displeasing there is likewise a common sense of a heaviness about the heart which we call Grief and it is common to Sorrow Fear Hate and the like Now 't is manifest by experience that these motions are all different ones and strike against divers of those parts of of our body which encompass the heart out of which striking follows that the spirits sent from the heart affect the brain diversly and are by it convey'd into divers nerves and so set divers members in action Whence follows that certain Members are generally moved upon the motion of such a passion in the heart especially in beasts who have a more determinate course of working than man hath and if somtimes we see variety even in beasts upon knowledge of the circumstances we may easily guess at the causes of that variety The particularities of all which motions we remit Physicians and Anatomists advertising only that the fume of pleasure and the heaviness of grief plainly shew that the first motions participate of Dilatation and the latter of Compression Thus you see how by the senses a living creature becomes judg of what is good what bad for him which operation is perform'd more perfectly in Beasts and especially in those that live in the free air remote from humane conversation for their senses are fresh and untainted as nature made them than in Men. Yet without doubt nature has been as favourable in this particular to men as them were it not that with disorder and excess we corrupt and oppress our senses as appears evidently by the Story we have recorded of John of Leige as also by the ordinary practice of some Hermites in the Deserts who by their taste or smell would presently be inform'd whether the herbs and roots and fruits they met with were good or hurtful for them though they never before had had trial of them Of which excellency of the Senses there remains in us only some dim sparks in those qualities which we call sympathies and antipathies wherof the reasonss are plain out of our late discourse and are nothing else but a conformity or opposition of a living creature by some individual property of it to some body without it in such sort as its conformity or opposition to things by its specifical qualities is term'd natubal or against nature But of this we shall discourse more at large hereafter Thus it appears how the senses are seated in us principally for the end of moving us to or from objects that are good for or hurtful to us But though our Reader be content to allow this intent of nature in our three inferiour senses yet he may peradventure not be satisfied how the two more noble ones the Hearing and the Seeing cause such motions to or from objects as are requisite to be in living creatures for the preservation of them for may he say how can a man by only seeing an object or by hearing the sound of it tell what qualities it is imbued with or what motion of liking or disliking can be caus'd in his heart by his meer receiving the visible species of an object at his eyes or by his ears hearing some noise it makes And if there be no such motion there what should occasion him to prosecute or avoid that object When he tasts or smells or touches a thing he finds it sweet or bitter or stinking or hot or cold and is therwith either pleased or displeased but when he only sees or hears it what liking or disliking can he have of it in order to the preservation of his nature The solution of this difficulty may in part appear out of what we have already said But for the most part the objects of these two nobler senses move us by being joyn'd in the Memory with some other thing that either pleas'd or displeas'd some of the other three senses And from thence it is that the motion of going to imbrace the object or
dense signifies nothing else but that it is in such a degree of density that some of its own parts by their being assisted and set on work by a general cause which is the fall of the atomes are powerful enough to divide other adjoyning parts of the same density with them one from another as we see water pour'd out of an Ewer into a Basin where there is already other water has the power to divide the water in the Basin by the assistance of the celerity which it gets in descending And now I hope the Reader is fully satisfied that there is no contradiction in puting Density and Gravity to be the same thing materially and that nevertheless the same thing may be more heavy then dense or more dense then heavy as we took it to our several purposes in the investigation of the Elements Having thus laid an intelligible ground to discover how these motions that are general to all bodies and are natural in chief are contrived by nature we will now endeavour to shew that the contrary position is not only voluntary but also impossible Let us therfore suppose that a body has a quality to move it downwards And first we shall ask what downwards signifies For either it signifies towards a fix'd point of Imaginary Space or towards a fix'd point of the Universe or towards some Moveable point As for the first who would maintain it must have more imagnation then judgment to think that a natural quality could have an essence determin'd by a nothing because we can frame a conceit of that nothing As for the second 't is very uncertain whether any such point be in nature for as for the centre of the earthy 't is clear that if the earth be carried about the centre of it cannot be a fixed point Again if the centre signifies a determinate point in the earth that is the Medium of gravity or of quantity 't is chang'd as often as any dust lights unequally upon any one side of the earth which would make that side bigger then it was and I doubt a quality cannot have moral considerations to think that so little does no harm As for the third position likewise 't is not intelligible how a quality should change its inclination or essence according to the change that should light now to make one point now another be the centre to which it should tend Again let us consider that a quality has a determinate essence Then seeing its power is to move to move signifies to cut the Medium 't is moved in it belongs to it of its nature to cut so much of such a Medium in such a time So that if no other cause be added but that you take precisely in abstracto that quality that Medium and that time this effect will follow that so much motion is made And if this effect should not follow 't is clear that The being able to cut so much of such a Medium in such a time is not the essence of this quality as it was supposed to be Dividing then the time and the Medium half the motion should be made in half the time a quarter of the motion in a quarter of the time and so without end as far as you can divide But this is demonstratively impossibly since 't is demonstrated that a moveable coming from rest must of necessity pass through all degrees of tardity and therefore by the demonstration cited out of Galileus we may take a part in which this gravity cannot move its body in a proportionate part of time through a proportionate part of the medium But because in natural Theorems experiences are naturally required let us see whether nature gives us any testimony of this verity To that purpose we may consider a Plummet hang'd in a small string from a beam which being lifted up gently on the one side at the extent of the string and permitted to fall meerly by the power of gravity will ascend very near as high on the contrary side as the place it was held in from whence it fell In this experiment we may note two things First that if gravity be a quality it works against its own nature in lifting up the plummet seeing its nature is only to carry it down For though it may be answer'd that 't is not the gravity but another quality called vis impressa which carries it up nevertheless it cannot be denied but that gravity is either the immediate or at least the mediate cause which makes this vis impressa the effect whereof being contrary to the nature of gravity 't is absurd to make gravity the cause of it that is the cause of an essence whose nature is contrary to its own And the same argument will proceed though you put not vis impressa but suppose some other thing to be the cause of the plummets remounting as long as gravity is said to be a quality for still gravity must be the cause of an effect contrary to its own inclination by setting on foot the immediate cause to produce it The second thing we are to note in this experiment of the plummets ascent is that if gravity be a quality there must be as much resistance to its going up as there was force to its coming down Therefore there must be twice as much force to make it ascend as there was to make it descend that is to say there must be twice as much force as the natural force of the gravity is for there must be once as much to equallize the resistance of the gravity and then another time as much to carry it as far through the same Medium in the same time But 't is impossible that any cause should produce an effect greater then it self Again the gravity must needs be in a determinate degree and the vertue that makes the plummet remount whatever it be may be put as little as we please and consequently not able to oversway the gravity alone if it be an intrinsecal quality and yet the plummet will remount in which case you put an effect withot a cause Another experience we may take from the force of sucking For take the barrel of a long Gun perfectly bored and set it upright with the breech upon the ground and take a bullet that is exactly fit for it but so as it stick not any where both the barrel and it being perfectly polished and then if you suck at the mouth of the barrel though never so gently the bullet will come up so forcibly that it will hazard the striking out your teeth Now let us consider what force were necessary to suck the bullet up and how very Slowly it would ascend if in the barrel it had as much resistance to ascend as in the free air it has inclination to go down But if it had a quality of gravity natural to it it must of necessity have such resistance wheras in our experiment we see it