straight line from my Eye to the Sun terminated in the East B. 'T is not due East but partly East partly South For the Earth being but a point compared to the Sun all the parallels to D E the Aequator such as are e a f b e g if they be produced will fall upon the Body of the Sun And therefore A b is North-East A a East North-East And A c North North-East A. Proceed now to the Cause of Attraction B. Suppose now that the Internal parts of the Loadstone had the same Motion with that of the Internal parts of the Sun which make the Annual Motion of the Earth from West to East but in a contrary way for otherwise the Loadstone and the Iron can never be made to meet Then set the Loadstone at a little distance from the Earth marked with z and the Iron marked with x upon the superficies of the Earth Now that which makes x rise to z can be nothing else but Air for nothing touches it but Air. And that which makes the Air to rise can be nothing but those small circles made by the parts of the Earth such as are at a b c for nothing else touches the Air. Seeing then the Motion of each point of the Loadstone is from East to West in Circles and the motion of each point of the Iron from West to East it follows that the Air between the Loadstone and the Iron shall be cast off both East and West and consequently the place left empty if the Iron did not rise up and fill it Thus you see the Cause that maketh the Loadstone and the Iron to meet A. Hitherto I assent But why they should meet when some Heterogeneous Body lyes in the Air between them I cannot imagine And yet I have seen a Knife though within the Sheath attract one end of the Needle of a Mariners Compass and have heard it will do the same though a Stone-wall were between B. Such Iron were indeed a very and vigorous Loadstone But the Cause of it is the same that causeth Fire or hot Water which have the same compounded Motion to work through a Vessel of Brass For though the Motion be altered by restraint within the Heterogeneous Body yet being continued quite through it restores it self A. What is the Cause why the Iron rub'd over by a Loadstone will receive the vertue which the Loadstone hath of drawing Iron to it B. Since the Motion that brings two Bodies to meet must have contrary ways and that the Motions of the Internal parts of the Magnet and of the Iron are contrary the rubbing of them together does not give the Iron the first Edeavour to rise but multiplies it For the Iron untouch'd will rise to a Loadstone but if touch'd it becomes a Loadstone to other Iron For when they touch a piece of Iron they pass the Loadstone over it only one way viz. from Pole to Pole not back again for that would undo what before had been done also they press it in passing to the very end of the Iron and somewhat hard So that by this pressing Motion all the small Circles about the points a b c are turned the contrary way And the halves of those small Circles made on the Arch D B will be taken away and the Poles changed so as that the North-Poles shall point South and the South Poles North as in the Figure A. But how comes it to pass that when a Loadstone hath drawn a piece of Iron you may add to it another as if they begat one another Is there the like Motion in the generation of Animals B. I have told you that Iron of it self will rise to the Loadstone Much more then will it adhere to it when it is armed with Iron and both it and the Iron have a plain Superficies For then not only the points of Contact will be many which make the coherence stronger but also the Iron wherewith it is armed is now another Loadstone differing a little which you perhaps think as Male and Female But whether this compounded Motion and confrication causeth the generation of Animals how should I know that never had so much leasure as to make any observation which might conduce to that A. My next Question is seeing you say the Loadstone or a Needle touch'd with it naturally respecteth the Poles of the Earth but that the variation of it proceedeth from some accidents in the Superficies of the Earth what are those accidents B. Suppose there be a Hill upon the Earth for example at r then the stream of the Air which was between z and x Westward coming to the Hill shall go up the Hills side and so down to the other side according to the crooked Line which I have mark'd about the Hill by points and this infallibly will turn the North-point of the Needle being on the East side more toward the East and that on the other side more towards the West than if there had been no Hill And where upon the Earth are there not Eminencies and depressions except in some wide Sea and a great way from Land A. But if that be true the Variation in the same place should be always the same For the Hills are not removed B. The Variation of the Needle at the same place is still the same but the Variation of the Variation is partly from the Motion of the Pole it self which by the Astronomers is called Motus trepidationis and partly from that that the Variation cannot be truly observ'd for the Horizontal Needle and the Inclinatory Needle incline alike but cannot incline in due quantity For whether set upon a Pin or an Axis their Inclination is hindred in the Horizontal Needle by the Pin it self If upon an Axis if the Axis be just it cannot move if slack the weight will hinder it But chiefly because the North Pole of the Earth draws away from it the North Pole of the Needle For two like Poles cannot come together And this is the cause why the Variation in one place is East and another West A. This is indeed the most probable reason why the Variation varies that ever I heard given And I should presently acknowledge that this parallel Motion of the Axis of the Earth in the Ecliptick supposed by Copernicus is the true Annual Motion of the Earth but that there is lately come forth a Book called Longitude found which makes the Magnetical Poles distant from the Poles of the Earth eight Degrees and a half B. I have the Book 'T is far from being demonstrated as you shall find if you have the patience to see it examined For wheresoever his demonstration is true the conclusion if rightly inferred will be this that the Poles of the Loadstone and the Poles of the Earth are the same And where on the contrary his demonstrations are fallacies it is because sometimes he fancieth the Lines he hath drawn not where they are sometimes because he mistakes
by its dissolution transfers its Hardness to the water within B. You are merry But supposing as I do that the Ice in the Pail is more than the water in the Vessel you will finde no absurdity in the Argument Besides the Experiment you know is common A. I confess it is probable The Greeks have the word 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 whence the Latins have their word Frigus to signifie the curling of water by the Wind and use the same also for Horrour which is the passion of one that cometh suddenly into a cold Air or is put into a sudden affright whereby he shrinks and his hair stands upright Which manifestly shews that the Motion which causeth Cold is that which pressing the Superficies of a Body sets the parts of it closer together But to proceed in my Quaeries Monsieur Des Cartes who you know hath written somewhere that the noise we hear in Thunder proceeds from breaking of the Ice in the Clouds What think you of it Can a Cloud be turned into Ice B. Why not A Cloud is but Water in the Air. A. But how For he has not told us that B. You know that 't is onely in Summer and in hot weather that it Thunders or if in Winter it is taken for a Prodigie You know also that of Clouds some are higher some lower and many in number as you cannot but have oftentimes observed with spaces between them Therefore as in all Currents of water the Water is there swiftest where it is streightned with Islands so must the Current of Air made by the Annual Motion be swiftest there where it is checkt with many Clouds through which it must as it were be strained and leave behinde it many small particles of earth always in it and in hot weather more than ordinary A. This I understand and that it may cause Ice But when the Ice is made how is it broken And why falls it not down in shivers B. The particles are inclosed in small Caverns of the Ice and their Natural Motion being the same which we have ascribed to the Globe of the Earth requires a sufficient space to move in But when it is imprisoned in a less room that that then a great part of the Ice breaks And this is the Thunder-clap The Murmur following is from the settling of the Air. The Lightening is the fancie made by the recoiling of the Air against the Eye The fall is in Rain not in Shivers because the prisons which they break are extreme narrow and the shivers being small are dissolved by the Heat But in less Heat they would fall in Drops of Hail that is to say half frozen by the shaving of the Air as they fall and be in a very little time much less than Snow or Ice dissolved A. Will not that Lightning burn B. No. But it hath often kill'd men with Cold. But this extraordinary swiftness of Lightning consisteth not in the Expansion of the Air but in a straight and direct stream from where it breaks forth which is in many places successively according to the Motion of the Cloud A. Experience tells us that I have now done with my Problems concerning the great Bodies of the world the Stars and Element of Air in which they are moved and am therein satisfied and the rather because you have answered me by the Supposition of one onely Motion and commonly known and the same with that of Copernicus whose Opinion is received by all the Learned and because you have not used any of these empty terms Sympathy Antipathy Antiperistasis c. for a natural Cause as the old Philosophers have done to save their credit For though they were many of them wise men as Plato Aristotle Seneca and others and have written excellently of Morals and Politiques yet there is very little Natural Philosophy to be gathered out of their Writings B. Their Ethiques and Politiques are pleasant reading but I finde not any argument in their discourses of Justice or Vertue drawn from the supreme Authority on whose Laws all Justice Vertue and good Politiques depend A. Concerning this Cover or as some have called it the Scurf or Scab of the Terrestrial Star I will begin with you to morrow For it is a large Subject containing Animals Vegetables Metals Stones and many other kinds of Bodies the knowledge whereof is desired by most men and of the greatest and most general profit B. And this is it in which I shall give you the least satisfaction so great is the variety of Motion and so concealed from humane senses CAP. VII Of Hard and Soft and of the Atomes that flie in the Air. A. COncerning this Cover of the Earth made up of an infinite number of parts of different natures I had much ado to finde any tolerable method of enquiry But I resolved at last to begin with the Questions concerning Hard and Soft and what kinde of Motion it is that makes them so I know that in any pulsion of Air the parts of it go innumerable and inexplicable ways but I ask only if every point of it be moved B. No. If you mean a Mathematical point you know it is impossible For nothing is movable but Body But I suppose it divisible as all other Bodies into parts divisible For no Substance can be divided into Nothings A. Why may not that Substance within our Bodies which are called Animal spirits be another kind of Body and more subtile than the common Air B. I know not why no more than you or any man else knows why it is not very Air though purer perhaps than the common Air as being strained through the blood into the Brain and Nerves But howsoever that be there is no doubt but the least parts of the common Air respectively to the whole will easilier pierce with equal Motion the Body that resisteth them than the least parts of water For it is by Motion onely that any mutation is made in any thing and all things standing as they did will appear as they did And that which changeth Soft into Hard must be such as makes the parts not easily to be moved without being moved all together which cannot be done but by some Motion compounded And we call Hard that whereof no part can be put out of order without disordering all the rest which is not easily done A. How Water and Air beaten into extreme small Bubbles is hardned into Ice you have told me already and I understand it But how a soft Homogeneous Body as Air or Water should be so hardned I cannot imagine B. There is no hard Body that hath not also some degree of Gravity and consequently being loose there must be some Efficient Cause that is some Motion when it is severed from the Earth to bring the same to it again And seeing this compounded Motion gives to the Air and Water an Endeavour from the Earth the Motion which must hinder it must be in a way contrary to the compounded
ask concerning Gravity If Gravity be as some define it an intrinsecal quality whereby a Body descendeth towards the Center of the Earth how is it possible that a piece of Iron that hath this intrinsecal quality should rise from the Earth to go to a Loadstone Hath it also an intrinsecal quality to go from the Earth It cannot be The Cause therefore must be extrinsecal And because when they are come together in the Air if you leave them to their own nature they will fall down together they must also have some like extrinsecal Cause And so this magnetique vertue will be such another vertue as makes all other heavy Bodies to descend in this our World to the Earth If therefore you can from this your Hypothesis of compounded Motion by which you have so probably salved the Problem of Gravity salve also this of the Loadstone I shall acknowledge both your Hypothesis to be true and your Conclusion to be well deduced B. I think it not impossible But I will proceed no further in it now than for the facilitating of the demonstrations to tell you the several proprieties of the Magnet whereof I am to shew the causes As first That Iron and no other Body at some little distance though heavy will rise to it Secondly That if it be laid upon a still Water in a floating Vessel and left to it self it will turn it self till it lye in a Meridian that is to say with one and the same Line still North and South Thirdly If you take a long slender piece of Iron and apply the Loadstone to it and according to the position of the Poles of the Loadstone draw it over to the end of the Iron the Iron will have the same Poles with the Magnet so it be drawn with some pressure but the Poles will lye in a contrary Position and also this long Iron will draw other Iron to it as the Magnet doth Fourthly This long Iron if it be so small as that poiz'd upon a Pin the weight of it have no visible Effect the Navigators use it for the Needle of their Compass because it points North and South saving that in most places by particular accidents it is diverted which diversion is called the variation of the Horizontal Needle Fifthly The same Needle placed in a Plain perpendicular to the Horizon hath another Motion called the Inclination Which that you may the better conceive draw a fourth Figure wherein let there be a Circle to represent the Terrella that is to say a Spherical Magnet A. Let this be it whose Center is A the North Pole B the South Pole C. B. Join B C and cross it at right Angles with the Diameter D E. A. 'T is done B. Upon the point D set the Needle parallel to B C with the cross for the South Pole and the Barb for the North and describe a Square about the Circle B D C E and divide the arch D B into four equal parts in a b c. A. 'T is done B. Then place the middle of the Needle on the points a b c so that they may freely turn and set the Barb which is at D toward the North and that which is at C towards the South You see plainly by this that the Angles of Inclination through the Arch D C taken all together are double to a Right Angle For when the South point of the Needle looking North as at D comes to look South as at C it must make half a Circle A. That is true And if you draw the Sine of the Arch D a which is d a and the Sine of the Arch B a which is a c and the Sine of the Arch D b which is b f and the Sine of the Arch B c which is c g the Needle will lye upon b f with the North-point downwards so that the Needle will be parallel to A D. Then from a draw the line a h making the Angle e a h equal to the Angle D A a. And then the Needle at a shall lye in the line a h with the South point toward h. Finally draw the line c h which with c g will also make a quarter of a right Angle and therefore if the Needle be plac'd on the point c it will lye in c h with the South point toward h. And thus you see by what degrees the Needle inclines or dips under the Horizon more and more from D till it come to the North Pole at B where it will lye parallel to the Needle in D but with their Barbs looking contrary ways And this is certain by experience and by none contradicted B. You see then why the degrees of the Inclinatory Needle in coming from D to B are double to the degrees of a Quadrant It is found also by experience that Iron both of the Mine and of the Furnace put into a Vessel so as to float will lay it self if some accident in the Earth hinder it not exactly North and South And now I am from this compounded Motion supposed by Copernicus to derive the causes why a Loadstone draws Iron why it makes Iron to do the same why naturally it placeth it self in a parallel to the Axis of the Earth why by passing it over the Needle it changes its Poles and what is the cause that it inclines But it is your part to remember what I told you of Motion at our second meeting and what I told you of this compounded Motion supposed by Copernicus at our fourth meeting CAP. IX Of the Loadstone and its Poles and whether they shew the Longitude of places on the Earth A. I Come now to hear what Natural Causes you can assign of the vertues of the Magnet and first why it draws Iron to it and only Iron B. You know I have no other cause to assign but some local Motion and that I never approved of any argument drawn from Sympathy Influence Substantial Forms or Incorporeal Effluvia For I am not nor am accounted by my Antagonists for a Witch But to answer this Question I should describe the Globe of the Earth greater than it is at B in the first Figure but that the Terrella in the fourth Figure will serve our turn For 't is but calling B and C the Poles of the Earth and D E the Diameter of the Aequinoctial Circle and making D the East and E the West And then you must remember that the Annual Motion of the Earth is from West to East and compounded of a straight and circular Motion so as that every point of it shall describe a small Circle from West to East as is done by the whole Globe And let the Circles about a b c be three of those small Circles A. Before you go any further I pray you shew me how I must distinguish East and West in every part of this Figure For wheresoever I am on Earth suppose at London and see the Sun rise suppose in Cancer is not a
Sphere that encompasseth the Earth being a substance that hath not solidity to keep pace with the Earth looseth in its Motion And that may be the Cause of the Motion of the Magnetick Poles from East to West A. This is very fine and unexpected The Magnetick Sphere which I took for a Globe made of a Magnet has not solidity to keep pace with the Earth though it be one of the hardest Stones that are It encompasseth the Earth yet I thought nothing had encompassed the Earth but Air in which I breath and move By this also the whole Earth must be a Loadstone For two Bodies cannot be in one place So that he is yet no further than Dr. Gilbert whom he sleights And if the Sphere be a Magnet then the Earth and Loadstone have the same Poles See the force of Truth which though it could not draw to it his reason hath drawn his words to it B. But perhaps he meant that the Magnetick vertue encompasseth the Earth and not the Magnetick Body A. But that helpeth him not For if the Body of the Magnet be not there the vertue then is the vertue of the Earth and so again the Poles of the Earth are Magnetick Poles B. You see how unsafe it is to boast of Doctrines as of Gods gifts till we are sure that they are true For God giveth and denieth as he pleaseth not as our selves wish as now to him he hath given Confidence enough but hath denied him at least hitherto the finding of the Longitudes In the next place Pag. 8. he seems much pleased that his Doctrine agrees with an opinion of Keplerus That from the Creation to the year of our Lord it is to the year 1657 now 5650 years and with that which he saith some Divines have held in times past That as this World was created in six days so it should continue six thousand years By which account the World will be at an end 350 years hence though the Scripture tell us it shall come as a Thief in the night O what advantage 340 years hence will they have that know this over them that know it not by taking up Money at Interest or selling Lands at 20 years purchase A. But he says he will not meddle with that B. Yes when he had medled with it too much already A. But you have not told me wherein consisteth this Agreement between him and Keplerus B. I forgot it 'T is in the Motion of the Magnetick Poles For precedently Pag. 7. he had said that their Period or Revolution was 600 years their yearly Motion 36 min. and Pag. 8. that their Motion is by sixes Six tenths of a degree in one year six degrees in ten year sixty degrees in a hundred year and six times sixty degrees in 600 year A. But what Natural Cause doth he assign of this revolution of 600 years B. None at all For the Magnet lying upon the Earth can have no Motion at all but what the Earth and the Air give it And because it is always at 8 deg 30 min. distance from the Pole of the Earth the Earth can give it no other Motion than what it gives to its own Poles by the precession of the Aequinoctial points Nor can the Air give it any Motion but by its Stream which must needs vary when the Stream varieth But what a vast difference does he make between the period of the Motion of the Aequinoctial points which are about or near 36000 years according to Copernicus Lib. 3. Cap. 6. which makes the Annual precession to be 36 seconds and the period of the Magnetical Poles Motion which is but 600 years A. Go on B. He comes now Pag. 15. to the Inclinatory Needle upon a Spherical Loadstone Where he shews by Diagram that the Needle and the Instrument together moved toward the Magnetical Pole make the sum of the Inclinations equal to two Quadrants setting the North-point of the Needle Southward Which I confess is true But in the same Page he ascribeth the same Motion to the Earth in these words As the Horizontal Needle hath a double Motion about the Round Loadstone or Terrulla so also the Inclinatory Needle hath a double Motion about the Earth What is this but a confession that the Poles of the Magnet and of the Earth are the same A. 'T is plain enough B. Besides seeing he placeth the Magnetical Pole at M in the Meridian of Vaygates the Needle being touch'd shall Incline to the Pole of the Earth which is P as well there as at London and make the North-Pole of the Earth point South A. 'T is certain because he puts both the Magnetical Pole and the Pole of the Earth in the same Meridian of the Earth Nor see I any Cause why the Needle being the same it should not be as subject to Variation and to Variation of Variation and to all Accidents of the Earth there as in any other part B. He putteth Pag. 16. a Question At what distance from the Earth are the Magnetick Poles and answers to it They are very near the Earth because the nearer the Earth the greater the strength What think you of this A. I think they are in the Superficies of the Magnet as the Pole of the Earth is in the Superficies of the Earth And consequently that then the Earth must be a part of the Magnet and their Poles the same For the Body of the Magnet and the Body of the Earth if they be two cannot be in one place B. His next words are Some things are to be considered concerning those Variations of the Horizontal Needle which are not according to the scituation of the place from the Magnetick Poles but are contrary as all the West-Indies according to the Poles should be Easterly and they are Westerly Which is by some Accidental Cause in the Earth and their Motion as I formerly said is a forced Motion and not Natural A. He has clearly overthrown his main Doctrine For to say the Motion of the Needle is forced and unnatural is a most pityful shift and manifestly false no Motion being more constant or less accidental notwithstanding the Variation to which the Inclinatory Needle is no less subject than the Horizontal Needle B. That which deceived him was that he thought them two sorts of Needles forgetting what he had said of Normans Invention of the Inclinatory Needle by the inclining of the Horizontal Needle Pag. 11. For I will shew you that what he says is Easterly and should be Westerly should be Easterly as it is Consider the fourth Figure in which B is the North-Pole and B c 11 deg 15 min. Easterly which was the Variation at London in 1576 Easterly Suppose A c to be the Needle shall it not incline as well here as at D a and the Variation B c be Easterly Again D a is 11 deg 15 min. and the Needle in D parallel to A B and at a inclining also 11 deg 15 min. Westerly
And is not the Variation there D a Westerly with the North-point of the Needle in the Line a h A. But the West-Indies are not in this Hemisphere B C D E. The Variation therefore will proceed in an Arc of the opposite Hemisphere which is Westerly B. I believe he might think so forgetting that he and his Compass were on the Superficies of the Earth and fancying them in the Center at A. A. 'T is like enough If we had a straight Line exactly equal to the Arc of a Quadrant I think it would very much facilitate the Doctrine of Spherical Triangles B. When you have done with your Questions of Natural Philosophy I will give you a clear Demonstration of the equality of a straight Line to the Arc of a Quadrant which if it satisfie you you may carry with you and try thereby if you can find the Angle of a Spherical Triangle given A. It is time now to give over And at our next meeting I desire your opinion concerning the Causes of Diaphaniety and Refraction This Copernicus has done much more than he thought of For he has not only restored to us Astronomy but also made the way open to Physiology CAP. X. Of Transparence Refraction and of the Power of the Earth to produce living Creatures A. THinking upon what you said yesterday it lookt like a generation of living Creatures I saw the love between the Loadstone and the Iron in their mutual attraction their engendring in their close and contrary Motion and their issue in the Iron which being touch'd hath the same attractive vertue Now seeing they have the same internal motion of parts with that of the Earth why should not their substance be the same or very near a kin B. The most of them if not all that have written of this Subject when they call the Loadstone a Terrella seem to think as you do But I except I could find proof for it will not affirm it For the Earth attracteth all kind of Bodies but Air and the Loadstone none but Iron The Earth is a Star and it were too bold to pronounce any sentence of its substance especially of the Planets that are so lapt up in their several Coats as that they cannot work on our Eyes or any Organ of our other Senses A. I come therefore now to the business of the day Seeing all Generation Augmentation and Alteration is local Motion how can a Body not Transparent be made Transparent B. I think it can never be done by the Art of Man For as I said of Hard and Heavy Bodies in the Creation so I think of Diaphanous that the very same Individual Body which was not Transparent then shall never be made Transparent by Humane Art A. Do not you see that every day Men make Glass and other Diaphanous Bodies not much inferior in beauty to the fairest Gems B. It is one thing to make one Transparent of many by mixture and another to make Transparent of not Transparent Any very hard Stone if it be beaten into small Sands such as is used for Hour-Glasses every one of those Sands if you look upon it with a Microscope you will find to be Transparent and the harder and whiter the Sone is so much the more Transparent as I have seen in the Stone of which are made Milstones which Stone is here called Greet And I doubt not but the Sands of white Marble must be more Transparent But there are no Sands so Transparent that they have not a scurf upon them as hard perhaps as the Stone it self which they whose profession it is to make Glass have the Art to scour and wash away And therefore I think it no great wonder to bring those Sands into one Lump though I know not how they do it A. I know they do it with Lie made with a Salt extracted from the Ashes of an Herb of which Salt they make a strong Lie and mingle it with the Sand and then bake it B. Like enough But still it is a Compound of two Transparent Bodies whereof one is the Natural Stone the other is the Morter This therefore doth not prove that one and the same Body of not Transparent can be made Transparent A. Since they can make one Transparent Body of many why do they not of a great many small sparks of natural Diamant compound one great one It would bear the charges of all the Materials and beside enrich them B. 'T is probable it would But it may be they know no Salt that howsoever prepared which with how great a Fire soever can make them melt And it may be the true Chrystal of the Mountain which is found in great pieces in the Alps is but a compound of many small ones and made by the Earths Annual Motion For it is a very swift Motion Suppose now that within a very small Cavern of those Rocks whose smallest Atomes are Chrystal and the Cavity fill'd with Air and consider what a tumult would be made by the swift reciprocation of that Air whether it would not in time separate those Atomes from the Rock and jumbling them together make them rub off their scruf from one another and by little and little to touch one another in polish'd plains and consequently stick together till in length of time they become one lump of clean Chrystal A. I believe that the least parts of created substances lay mingled together at first till it pleased God to separate all dissimilar natures and congregate the similar to which this Annual Motion is proper But they say that Chrystal is found in the open Air hanging like Icicles upon the Rocks Which if true defeats this supposition of a narrow Cavern And therefore I must have some further experience of it before I make it my opinion But howsoever it still holds true that Diaphanous Bodies of all sorts in their least parts were made by God in the beginning of the World But it may be true notwithstanding those Icicles For the force of the Air that could break off those Diaphanous Atomes in a Cavern can do the same in the open Air. And I know that a less force of Air can break some Bodies into small pieces not much less hard than Chystal by corrupting them B. That which you now have said is somewhat But I deny not the possibility but only doubt of the Operation You may therefore pass to some other Question A. Well I will ask you then a Question about Refraction I know already that for the Cause of Refraction when the Light falleth through a thinner Medium upon a thicker you assign the resistance of the thicker Body but you do not mean there by Rarum and Densum two Bodies whereof in equal spaces one has more substance in it than the other B. No. For equal spaces contain equal Bodies But I mean by Densum any Body which more resisteth the Motion of the Air and by Rarum that which resisteth less A. But you have