An entire body of philosophy according to the principles of the famous Renate Des Cartes in three books, (I) the institution ... (II) the history of nature ... (III) a dissertation of the want of sense and knowledge in brute animals ... / written originally in Latin by the learned Anthony Le Grand ; now carefully translated from the last corrections, alterations, and large additions of the author, never yet published ... by Richard Blome.

CHAP. XI. Concerning the Heaviness and Lightness of Bodies.

I. What Gra∣vity and Levity is. HEaviness and Lightness are the Qualities of Bodies with respect to their aptness to move upwards and downwards, in the Sphere of their Gravitation. Where by the name of Aptness, we are not to understand any Inclination or Active Principle, but only such a disposition of Parts which is capable of receiving the force of Heavi∣ness or Lightness. And by the Sphere of Gravi∣tation, I understand the whole space comprehend∣ed between the Center, or that which is lookt upon to be the middle, and the uttermost bounds of the cause of depression. Which Sphere is not only to be fixed about the Earth, but also about the other Planets, which being much of the same nature with our Earth, it follows, that the union of their Parts proceeds from the same or a like cause to that which keeps the Parts of the Earth together.

II. The opinion of the Peri∣pateticks rejected. The Peripateticks hold Heaviness and Light∣ness to be innate Qualities, proceeding from the Form of Bodies, for their Conservation. Ac∣cordingly they say that heavy things tend down∣wards, from the foresaid Appetite they have to be preserved in the Center, and so be moved by a cer∣tain Law of Nature, whereby all things are dis∣posed in their proper places, or by a Motion im∣prest by the Author of Nature. But this Opinion is grounded on a false Hypothesis. For, First it supposeth the Earth to be the Center of the VVorld. Secondly, that Bodies that are put in Motion tend to Rest, tho' it be certain that nothing tends to its own destruction. Thirdly, that Heavy Bodies are preserved in the Center. Fourthly, that there is an Appetite or desire of this Preservation in inanimate things, when it is apparent that a desire is only competible to living Creatures.

III. The opinion of Gassen∣dus reject∣ed. Others, amongst whom is GASSENDUS, hold that heavy things tend downwards by the Mag∣netick Virtue▪ of the Earth, which draws them down to it. But this opinion also is built on a false supposition, in that in the First place it takes for granted an attractive Motion. Secondly, in that it supposeth the Loadstone to draw Iron to it, by its out-flowing Particles, which is not so, as will ap∣pear hereafter when we come to speak of Magne∣tical Operations. Thirdly, the Magnetick Virtue is communicated by the Poles, and Lines parallel to the Poles; whence it must follow, that the greatest Gravitation would be under the Poles, or near them, less in the intermediate places, and least or none at all under the Aequator. Fourthly, a common Loadstone has greater force, than the Earth it self, at least with us; whence it must fol∣low, that it would be of greater strength also to the drawing of Heavy Bodies downwards; and then a piece of Iron cast upwards, would not in a right Line descend to the Earth, but towards the Magnet.

IV. Des Cartes his opinion concerning the Heavi∣ness of Bo∣dies ex∣plained. The Third opinion is that of Des Cartes, who holds that Heavy Bodies are driven downwards by the Caelestial Matter. For the better under∣standing of which, we must in a few words explain his Hypothesis concerning the Diurnal Motion of the Earth. He supposeth therefore the Earth to∣gether with the Atmosphere to be pois'd in the midst of a little Vortex, which is whirld round from VVest to East; whence it necessarily follows by the Rules of Motion, that the Earth hanging in this Fluid Body, must be whirld about with the same motion, by the Heavenly matter running against its Pores: yet so as that the Earth in its Motion is not separated from the Fluid Body that compasseth it, but as it were swims in it. To illustrate this, let us suppose a VVooden Bowl in the midst of a Vessel with VVater, if any one make the VVater whirl round, that is, in the Circumference or near the sides of the Vessel, it is notorious that the Bowl will turn round likewise, by the Particles of VVater, that dash against the outside of it; and in like manner, is the Earth with the Atmosphere, Whirld about by the Caelestial circumfluent matter, not by any motion of its own.

V. The force of the Cae∣lestial mat∣ter drives heavy things down∣wards. And forasmuch as the Caelestial matter being ve∣ry solid and agitated, hath more agitation in it, than is required to the whirling about of the Earth, and is hindred by the Earth from continuing its motion in Right Lines; what will follow hereup∣on? It is evident from the Laws of Motion, that its Motion cannot perish, and therefore will per∣sue its course, what way it can best; that is, it will have a Power of rebounding upwards. Now we know that nothing can move upwards except some∣thing move Downwards at the same time; and accordingly that will move downwards, which hath not so strong a force of Agitation, which is the case of all Earthly Bodies, except something else should intervene and hinder it.

VI. An Exam∣ple taken from a Vessel fill'd with vari∣ous matter. Any one may Experience this by filling some round Vessel with small leaden Bullets, and amongst them, some pieces of VVood, or any other Matter lighter than Lead: If this Vessel be whirld round swiftly about its Center, all the pieces of Wood which have less Agitation will be driven to the Middle by the Leaden Bullets, which with greater force recede from the Center of their Motion.

VII. Heavy things do not tend down∣wards of themselves but are driven down. The same was lately experimentally demon∣strated by a Mathematician at Paris, in a Vessel with VVater agitated, into which if the Powder of Sealing-wax be cast, the little Particles thereof

will be seen driven towards the sides of the Vessel, for that by reason of their roughness they are easily carried that way by the strong agitation of the VVater. But when that agitation begins to cease, and the Particles of the Water are more softly moved, this Dust or Powder is driven to the midst. The Cause whereof is this, because as long as any Agitation is continued in the Water, its parts endea∣vour to recede from the Center, in which recess they force the particles of VVax towards the Center, and as it were appoint their place to them. Whence it appears, that Bodies are not of themselves carri∣ed, but are driven downwards by the Matter that surrounds them.

VIII. A particu∣lar Expli∣cation of the Heavi∣ness of Bodies. But to the end that the Action of the subtil Mat∣ter may be more distinctly perceived, let us imagine all that is included in the Circle ABCD to be a Mass consisting of the Earth, VVater and Air, the Center whereof is E, where the little Circle FGHI represents the Earth. Then let us imagine this whole Mass to be divided into many Pyra∣mids, which with their Extremities reach to the * 1.1Center, one whereof let be AEB. Having sup∣pos'd this, we shall find first, that tho' all the several parts, which make up so many Pyramids, strive to withdraw from the Center E, yet can they not recede all at once, because there is no empty space about that Mass which they constitute, whither they might retire, and the subtil Matter hinders them from moving out of their place. Moreover we shall find that not one of these Pyra∣mids, by Example, AEB, can recede whole and entire, enlarging it self in its extremity AB, and driving away from it the adjoyning matter, and making it to come closer to the Center: Because the Pyramids, which surround the Pyramid AEB, do with a like endeavour recede from the same Center, and for which they have no less force, than the Pyramid AEB. But if we suppose some Ter∣restrial Body, as L. in the Pyramid AEB. without any in the Neighbouring Pyramids; we shall easily conceive, that it will have less force to re∣cede from the Center, than the others, that are about it, by how much the Body L hath less force than the subtil Matter, whose place it takes up. Whence we must conclude that the Matter of some of the Pyramids will recede from the Center, and drive the Body L nearer to it, after the same man∣ner, as they who hold all Bodies to be Heavy, suppose the Water to lift up a piece of Cork, and force it to the Surface of it.

IX. Wherein the Heavi∣ness of Earthly Bodies doth consist. The Heaviness therefore of Earthly Bodies con∣sists in this, that the Globuli of the Coelestial Mat∣ter, being whirld about in their Vortices, endeavour continually to recede from their Centers, about which they are turn'd; but forasmuch as they cannot exert this their strife and Propension, except in their mounting upwards, they thrust down other Bodies into whose place they may succeed: Wherefore they must needs at the same time depress the Particles of Earthly Bodies that are in the Air, as well because of their Resistance, as be∣cause of the want of Coelestial matter in their Pores; both which hinder the Earthly Particles from having so great a Propension of receding from the Center of the Earth, as the Heavenly matter that every way surrounds them, hath. Wherefore the Lightness of the Coelestial Matter is nothing else but the force or strife it hath to recede from the Earth; as the Heaviness of the parts of the Earth consists in their being such, that this highly agitated Matter exerts its power upon them in thrusting of them downwards,

X. By the name of Heavenly matter we are also to understand the First Element. When it is said, that the Heaviness of Bodies is caused by the Heavenly matter, we do not only understand the Globuli of the Second Element, but also the Matter of the First mixed with it: For this being extreamly agitated, exceeds the Matter of the second Element in the force it has to drive Bodies downwards. Neither are the Particles of the Air to be rejected from having any share in this perfor∣mance, seeing that they accompany them in their Course, and being joyn'd with the Globuli of the second Element, exert their force, and do not a little conduce to the driving down of Bodies.

XI. The Cause of the Des∣cent of Heavy Bodies is Twofold. We may therefore alledge a double Cause of the Descent of Heavy Bodies; the one Primary, viz. the Heavenly Matter, by its strife upward, not from any innate Appetite, but to continue its Motions according to the Laws of Nature. The other Secundary, viz. any Earthly Body carried upwards, whether it be obsequent to the Motion of the Heavenly Matter, as Air, Vapours, Exha∣lations, and any other lesser Particles; or whether it be driven upwards by any other Cause: So Smoak agitated by the Fire, hath a Power of de∣pressing the Air: Thus when any one casts a Stone upwards, he at the same time thrusts down as much Air in its place; which Air because of the Hea∣venly Matter intermix'd with its Particles, and its Agitation thereby caused, as likewise its Elastick force, will first resist the Motion of the Stone, next hinder its Ascent, and at last depress or thrust it downwards.

XII. Whence the various Heaviness and Light∣ness of Bo∣dies doth arise, You will object, if the Heaviness of Bodies depend on both these Causes, it will follow that all Bodies would be of the same Weight or Heaviness, since both the Heavenly Matter, and the small Bodies carried upwards, do press them after the same manner.

I answer, that the Nature of Heaviness and Light∣ness in Bodies, consists herein, that as much Heavenly Matter as there is in any Body, so much cause of Lightness they have, which being substracted, all the rest will come under the notion of Gravity or Heaviness. As for Example, Water is Heavier than the Air, because if you substract the Aethereal interspersed Matter from them both, there remains more Earthly Matter in the Water, than in the Air. So that this may be laid down as a General Rule, That the more Heavenly Matter there is in any Body, by so much the Lighter it is, that is, the more apt it is to be carried upwards; and the less there is of it, the Heavier that Body is, that is, the apter to be thrust downward.

XIII Solid Bodies are more Heavy than soft Bodies. Thus solid Bodies are more Heavy than soft, be∣cause they have more Matter of their own, and therefore are called close Bodies, having less Pores, which can only admit the Subtil Matter, or the Globuli of the second Element, such as are Gold, Silver, Quicksilver and Steel. But soft or less Solid Bodies, contain more Heavenly Matter; and have greater Pores, and are therefore Looser Bodies, such as Wood, &c. Wherefore tho' all the Heavenly Matter, with all its force strives to re∣cede from the Center; yet the more close and com∣pact Bodies have a greater Power to resist, and do more difficulty recede from the Center of their

Motion; whereas Bodies of a more loose Texture, have more of the Heavenly Matter than of their own, and a greater Propension of receding, and therefore do less resist the Agitation of the Heaven∣ly Globuli, or little round Bodies.

XIV. Whence proceeds the variety of Heaviness. This is the reason why the Water is placed on or above the Earth, and the Air above the Water; because the parts of the Earth being more solid than those of the Water, and the parts of the Water, than those of the Air, they are more strongly driven down to the Earth, by the Aethereal Matter; much after the same manner, as Corn, that is mixt with Chaff, is by the Agitation of a Fan cast off further, leaving the Chaff behind it.

XV. How it comes to pass that a Stone to∣wards the end of its▪ motion comes down faster than at the Be∣ginning. It may be objected against this, that the Globuli of the second Element, do strike with a greater force against Bodies, before they begin to descend, than in their falling down; and therefore they ought to thrust them down more swiftly at the Beginning of their Motion, than towards the end of it; which not withstanding is contrary to expe∣rience; for a Stone moves swifter towards the end of its Motion, than at the Beginning; and there∣fore the Descent of Earthly Bodies is not to be ascribed to the Subtil matter.

XVI. Answer. I answer, that the reason of the Difference of the Stones Motion is this, because the Stone in its Descent, retains the Force of the foregoing Mo∣tion, and besides receives an encrease from the Im∣pulse of the Subtil Matter that follows it; for the Subtil Matter is swifter than it. Now the cause why Descending Bodies are less forceably driven down by the Subtil Matter, towards the End, than at the Beginning of their Motion, is this, because there is not so great a difference of swiftness be∣tween their Motion, and that of the Subtil Mat∣ter.

XVII. How Bodies can move in the Air seeing they are prest on all sides by the Fluid Matter. But you will say, seeing that the Bodies that are surrounded with Fluid Matter, are equally prest upon on all sides, they are not like to move at all, but will remain hanging in the Air. I an∣swer, that this indeed would follow, in case the Fluid Body be simply consider'd as Fluid: But since the case is otherwise here, and that the whole Fluid Matter, because of the Resistance of the Earth, strives to get free from its Neighbour∣hood, this is sufficient to determine the Motion of Gross Bodies downwards, as being much more un∣fit for Motion, than the Heavenly Matter, and Fluid Bodies, in which they are carried, are.

XVIII. This opinion doth most appositly explain all the Phaeno∣mena of Gravity. How Appositely this opinion solves all the Phoe∣nomena of Heaviness will appear from the follow∣ing particulars.

First, This force will exert it self every where throughout the Earth, because the Celestial Mat∣ter will find resistance every where, that is, it will be determined upwards as well towards the Poles, as about the Aequator and Lines Parallel to it.

Secondly, All things fall down perpendicularly to the Horizon; because the Coelestial Matter hit∣ting against the Earthly Particles, will rebound back with infinite variety, because of their different meeting, Figure and Situation of their Parts, that is on every side equally, at least to Sense; and con∣sequently will make all those things Fluid, which are fit to follow its motion; and whatsoever is impulst by the Fluid Mass, will fall perpen∣dicularly, because it is with equal force prest on all sides.

Thirdly, The Sphere of Gravity becomes ter∣minated, where this force of receding, because of the too great distance, is not strong enough.

Fourthly, Here we find the reason, why every Planet hath its Sphere of Gravity, because nothing else is required to this, but its swimming in the midst of Fluid Matter.

XIX. Heaviness is either absolute or Respective▪ From all that hath been said it is obvious, that Heaviness is nothing else, but the strife or effort wherewith a Body is pusht towards the Axis of the Earth by other Bodies, which strive to recede from it. That Absolute Heaviness is that by which eve∣ry Body is pusht downwards by a Column of the second Element equal to its own; and that Re∣spective Heaviness is that which belongs to a Body, only with respect to other Bodies.

Notes

• * 1.1

  Figure 11.