On the Infinite Universe and Worlds
(DE L'INFINITO UNIVERSO ET MONDI)
Philotheo. The infinity of worlds is not then as the imagined complex of this earth surrounded by numerous spheres, some containing one star, some, innumerable stars. For space is such that innumerable stars can wander through it; moreover each one of these stars can by its own inner power and quality move toward communication with convenient things. Each is so large and comprehensive as to be worthy to be considered a world in itself; not one lacketh the efficient principle and power to preserve and maintain perpetual generation and life to innumerable and excellent individuals. As soon as we have recognized that the apparent world-motion is caused by the real diurnal motion of our earth (which happeneth similarly to other similar stars), no argument will constrain us to accept the vulgar opinion that the stars are equidistant from us, that they are as though nailed and fixed in an eighth sphere; and no persuasion will hinder us from knowing that the differences are innumerable in the distances from us  of these innumerable stars. We shall understand that the orbs and spheres of the universe are not disposed one beyond another, each smaller unit being contained within a greater -- as, for example, the infoldings of an onion. But throughout the ethereal field, heat and cold, diffused from the bodies wherein they predominate, gradually mingle and temper one another to varied degree, so as to become the proximate origin of the innumerable forms and species of being.
Elpino. Prithee, come speedily to the refutation of the contrary arguments and especially those of Aristotle, the most famed of all, which are regarded by the foolish crowd as perfect demonstrations. That naught may appear forgotten, I will enumerate all the arguments and phrases of that poor sophist and you shall consider them one by one.
Philotheo. So let it be.
Elpino. It is to be discovered (saith he, in the first book of his De coelo et mondo) whether beyond this world there lieth another. 
Philotheo. Concerning this question, you know that his interpretation of the word world is different from ours. For we join world to world and star to star in this vast ethereal bosom, as is seemly and hath been understood by all those wise men who have believed in innumerable and infinite worlds. But he applieth the name world to an aggregate of all those ranged elements and fantastic spheres reaching to the convex surface of that primum mobile, the perfect sphere which draweth the whole revolving with it at immense speeds around the centre near which we are placed. Therefore it would be a vain and childish entertainment if we were to consider such a conceit, argument by argument. But it will be well and expedient to overthrow his arguments in so far as they conflict with our judgement, and to ignore those Which do not so conflict.
Fracastoro. What then shall we say to those who might upbraid us for equivocal disputation?
Philotheo. We will say two things: firstly, that the fault is on the part of him who hath wrongly understood the world, fashioning for himself an imaginary corporeal universe; secondly, that our arguments are no less valid if we assume the significance of the world to be in accord with the imagination of our adversaries rather than with truth. For the points they suppose to be on the ultimate circumference of the world whose centre is our earth may be conceived as points on innumerable other earths beyond that imagined circumference. Thus they exist indeed, though not in accord with the imagination of those whose conception, whatever it be, doth not support or refute aught suggested concerning the size of the universe and the number of worlds.
Fracastoro. Well said; let Elpino now continue.
Elpino. All bodies, saith he [Aristotle]  either move or are stationary; their motion or stationary condition is either natural or constrained. Moreover in every case, if a body remaineth in a certain position not by constraint but of his own nature, thither also it moveth not by constraint but of his own nature; and in that place whither the body is impelled without constraint, there it naturally resideth. So that everything which is forced upward by constraint, is naturally impelled downward and vice versa. Thence it followeth that there are no more worlds than our own  when we reflect that if earth which is beyond our world moveth to the centre of our world by constraint; then earth within our world will of its own nature move to the centre of another world; and if the motion of earth from the centre of this world to the centre of another is by constraint, then the motion thereof from the centre of another world to our own will be natural. The reason of this is that if there be other earths, the power of one must be similar to the power of another, as also the power of fire will be similar in one and the other world; otherwise the parts of those worlds would be similar to the parts of ours in name only, and not in being; consequently such another world would not be a world like to ours except in name. Moreover, all bodies which have the same nature and belong to but one species, have the same motion -- for every body is endowed with some natural motion. If, then, there exist on the other worlds earths like unto our own, and of the same species as our earth, then they will certainly have the same motion. So also, on the other hand, where the motion is the same, the elements performing it must be the same. This being so, earth in that world will necessarily approach earth in our own, and the fire of that other will approach ours, whence it followeth moreover that earth will move upward no less naturally than downward; and fire will move downward no less naturally than upward. Since these things are impossible, there can be but one earth, one centre, one mid-point, one horizon, one world. 
Philotheo. To this we reply that in the very manner that our earth revolveth around our region in this infinite universal space and occupieth this part thereof, so also the other stars occupy their parts of space and revolve around their own regions in the immense field. And as our earth is constituted by her own members, undergoeth changes, with flux and reflux of her parts as we have seen happeneth to animals, whose humours and parts suffer continual alteration and motion; so also the other stars are constituted by their members which are similarly affected. Again, even as our earth, moving naturally in accord with the whole universal frame, hath none but circular-like motion, whereby she doth spin around her own centre, and revolveth about the sun, so also must it be with those other bodies of the same nature as hers. And such individual parts of those bodies, not principal parts or members, as have by some accident become removed from their proper position will naturally return thereto of their own impulse; precisely as particles of either the dry or the watery matter which, through the action of the sun and of the earth have receded as exhalations or vapours toward members and regions above our world, having resumed their proper form do return to their places. Thus also the particles of those bodies will no more than ours stray beyond a certain limit outside their own containing body, as will be manifest when we shall observe that the matter of which comets are formed doth not appertain to our globe. Similarly the parts of one animal -- I speak of the principal and distant parts thereof -- will never readily replace even the same parts of another animal, for they belong to separate individuals, just as my hand will never suit thine arm, nor thy head my body. These postulates being accepted, we say that there is indeed likeness between all stars, between all worlds, and that our own and the other earths are similarly organized. Nevertheless it followeth not that where this world is, there too must be all the others; nor that where this earth is situated, there also must be situated all others; but it may well be inferred that even as our earth maintaineth her position, so also do all the others; just as it is not well that our earth should remove from her region of space to that of the other earths, so also is it not well that those others should move into our region; as our earth differeth from those others both as to her matter and in other particular circumstances, so do they differ from her; as particles of our fire tend toward our main fire, and the fiery particles of other worlds tend toward the main fire thereof, and as the [elemental] particles of our earth tend toward our whole earth, so do the particles of another earth tend similarly toward her. So also only by constraint and against their nature could the particles of that earth which we call the moon, with the waters thereof, be brought to move to this earth, or the particles of this earth move toward the moon. For the moon naturally revolveth in her own position in space and attaineth her own region which is there, as our earth appertaineth to her own region here; and as her own particles, whether of water or of fire are in relation to that earth, so are our earth's particles to our earth. The lowest depth of this earth is no point of the ethereal region beyond and outside herself (such as happeneth to parts separated from their own sphere, if this can occur), but is in the centre of her own figure or sphere or weight; just as the lowest depth of that other earth is no place outside herself, but is her own proper middle, indeed her own centre. Similarly the upper portion of this earth is all that lieth on or beyond her circumference. Wherefore the parts either of another earth or of our own are only by constraint diverted beyond their own sphere, but naturally tend toward their own centre. Thus may be understood the veritable similarity between other earths and our own.
Elpino. You say most truly that just as it would be inconvenient and indeed impossible that one of these animate beings should move or dwell in the place occupied by another, or should derive her own individual sustenance from other than her own region and circumstances; so also it would be highly inconvenient that the parts of our own should tend or actually move toward the position occupied by the parts of another.
Philotheo. You understand that we speak of veritable parts; for concerning those prime indivisible bodies from which the whole universe was originally composed, we must believe that they undergo certain vicissitudes through the immensity of space whereby they ebb and flow, now hither, now thither. And if by divine providence they do not form new bodies nor dissolve from the old, they are at least able to do so. For mundane bodies are in fact dissoluble, though through either intrinsic quality or external influence they may persist to eternity, suffering a certain influx and a similar and equal efflux of atoms; so they remain constant in number though their corporeal substance be, like ours, renewed from day to day, from hour to hour, from moment to moment, by the processes of attraction and digestion of all the parts of the body.
Elpino. We will speak of this on other occasions. For the moment, you have given me much satisfaction since you have remarked that just as we should consider any other earth to have suffered constraint if she were to rise toward this region, so also would it be regarded if our earth were to rise in motion toward any of those others; for even as motion from any part of our earth toward the circumference or limiting surface thereof, or toward the hemispherical horizon of the ether, appeareth to be in upward direction, so also doth the direction seem upward from every part of the surface of other earths toward our own, since this earth is circumferential to those as they to her. I agree also that although those earths are of the same nature as ours, it followeth not that they are referred to the same centre; for as the centre of another earth is not the centre of ours, and the circumference of our earth is not theirs, and just as my soul is not yours, similarly my weight and that of my inward parts constituteth not your body nor your weight, even though these bodies, weights and souls, be considered and indeed are of one and the same species.
Philotheo. Just so. But I should not therefore have you imagine that if the parts of that earth were to approach our earth, they could not be attracted thereto, even as would happen to the parts of this earth if they were to approach that other: although we do not ordinarily see such events occur among animals or among the diverse individuals of any species of these bodies, except in so far as one deriveth nourishment and increase from another, and one is transmuted into another.
Elpino. Very true. But what wouldst thou say if that whole sphere were no further from ours than the distance by which the parts thereof have become removed from her, though they tend to return to their own containing body?
Philotheo. I readily concede that if perceptible portions of our earth were beyond the circumference thereof, where is said to be pure and limpid air, they could of their own nature return from that region to their own position. But a whole other sphere would not thus remove, nor would her parts of their own nature descend; rather would they be raised by constraint, just as the particles of our earth would not spontaneously sink to another, but would be raised by constraint. For to every world, the part beyond his own circumference is on high, and his own inward centre below; and the centre to which their parts naturally tend is referred inward rather than to any region beyond them; and this hath not been known to those who, feigning a certain limit and vainly defining [a certain boundary of] the universe, have regarded the centre of our earth and the centre of the world as identical. But the mathematicians of our own time have inferred, published and agreed the contrary view, for they have discovered that the imagined circumference of the world is by no means equidistant from the centre of our earth. Moreover others, yet wiser, having comprehended the motion of our earth, have therefore discovered not only by arguments from their own art, but also by a certain natural reason based on observation of this world and of the universe perceptible to our eyes, that we may more reasonably and without inconvenience formulate a theory more logical and just, which fits the more regular motion of the aforesaid wanderers around the centre, whereby we should understand that earth is as far from the centre of the universe as from the sun. From these same principles, they have easily been enabled to discover gradually the vanity of what hath been alleged concerning the weight of our earth, the difference between our own and other regions, the equidistance from ourselves of the innumerable worlds that we see from here beyond the aforesaid planets, and of the exceedingly rapid motion of all these bodies around us rather than of ourselves around them. And they may become at least doubtful about other grave inconveniences which follow from the suppositions of the current philosophy. To return now to the subject from which we started, I must repeat that neither a whole star nor a part thereof could move spontaneously toward the centre of another, even though the first were so very close to our star that the surface or a point of the circumference thereof were to touch point or surface of the circumference of our own.
Elpino. Provident Nature hath provided differently, for otherwise contrary bodies would destroy one another; the cold and moist would annihilate the hot and dry and be annihilated thereby; whereas, placed a certain convenient distance apart, the one liveth and groweth by aid of the other. Moreover, similar bodies, [if placed close together], would hinder one another from convenient intercourse and from the give and take of exchange with the dissimilar, as is occasionally shewn us when our frailty suffereth considerable damage through the interposition between ourselves and the sun of that other earth that we name the moon. What would happen if she were placed yet nearer to the earth and especially if she could thus deprive us for long periods of heat and of vital light?
Philotheo. Well said. Continue now the proposition of Aristotle.
Elpino. He replieth to an imagined objection  that one body cannot spontaneously move toward another, for the further the one is distant from the other, the more diverse will be their natures; against this proposition he maintaineth that greater or less distance doth not cause a difference of nature between one and the other.
Philotheo. And this, properly understood, is indeed most true. But we reply to it in another way, and we give another reason why one earth moveth not toward another whether near or distant.
Elpino. This I have understood. Yet appeareth to me also true that view attributed to the ancients that the further off a body the less is his aptness (by this name they frequently describe quality or nature) to approach another, because the particles which much air underlieth have less power to pass through the [supporting] medium and to move downward.
Philotheo. It is a certain and proved fact that particles of our earth are accustomed to return from certain distant recesses to their own containing body, and that the nearer they reach to it, the more they hasten. But we are now discussing the particles of another earth.
Elpino. But since earth resembleth earth, and the parts are also alike, what thinkest thou would occur if they were in close neighbourhood? Would not the parts of any one earth be equally apt to join their own or any other earth, and consequently to rise or to fall?
Philotheo. From a postulated inconvenience, if inconvenience it be, what can hinder an inconvenient result? But leaving this aside, I declare that as the parts [of any one earth] are in equal relation to and at equal distance from various other earths, either they will remain in position, or they will tend to a certain region with respect to which they will be said to fall, while they will be said to rise with respect to the other, from which they are moving away.
Elpino. But indeed who knoweth that the particles of a principal body remove to another principal body even of similar species? For it appeareth that the parts and members of one man do not fit or suit another man.
Philotheo. This is true in principle and primarily; in detail and secondarily the contrary occurreth. For we have ourselves seen a nose from a man's flesh become attached to another man in the position previously occupied by his own nose; and we are confident that we could easily implant the ear of a man on to the site of another man's ear.
Elpino. This can be no usual surgery.
Philotheo. That is it not. 
Elpino. I return to the point that I wish to elucidate. If a rock were in mid-air, equidistant from two earths, how may we believe that it would remain fixed, and how would it determine to approach one rather than another of the containing bodies?
Philotheo. I maintain that since the form of the rock is such that it is no more turned toward the one than to the other, so that each is equally affected thereby, it followeth from the doubtful upshot and the equal cause for motion toward either of the opposite limits that the rock would remain unmoved, being unable to resolve on motion toward the one rather than toward the other, neither one attracting it more than the other, and it being no more impelled toward the one than toward the other. But if one is more kindred, congenial, or similar, or more calculated to preserve it, the rock will determine to take the shortest and direct way to join that. Since the chief principle of motion is not the desire to gain a body's own sphere and containing region, but the appetite to maintain itself; even as we see flame creep along the ground, bending and turning downward in order to reach the nearest place where it can feed and nourish itself, not troubling to proceed toward the sun to which it could not rise without growing cold on the way.
Elpino. What sayest thou to Aristotle's further supposition that kindred particles and bodies, however distant from one another, move always toward their own related main body? 
Philotheo. Who doth not see that this is contrary to all reason and sense, in view of what we have just said? Certainly a particle outside his own globe will proceed toward a kindred neighbouring globe even though this may not be his original and primary containing body. Sometimes, too, it will approach a body which conserveth and nourisheth it, though of a different species from itself. For the spontaneous impulse proceedeth not from a relation to any one region, point or sphere, but from the natural impulse to seek that position where it may best and most easily find means to maintain itself and to preserve his present state of being, since this, however ignoble, is the natural desire of all things; even as those men most desire life and most fear death who lack the light of true philosophy and can conceive no manner of being other than this life; nor can they believe that there may follow aught other than now appertaineth to them. For they have not arrived at understanding that the vital principle consisteth not in the accidents resulting from material composition, but in that individual and indissoluble substance to which, if indeed there be no perturbation, there beseemeth neither passion for perpetuity nor fear of dissolution; but these appertain to compounds as such, that is according to the law of symmetry and of the accidental, depending on complexion. For neither spiritual substance, which is understood as uniting, nor material substance, which is understood as united, can be subject to any change or passion. Therefore, they seek not perpetuity, nor doth any motion beseem such substance, for it appertaineth to compounds. Such doctrine will be understood when it is known that to be heavy or light appertaineth not to worlds, nor to their parts; for these differences are not absolute in nature but positive and relative. Moreover we have already on other occasions reflected that the universe hath no edge, nor bound, but is immense and infinite. It followeth that the principal bodies cannot determine on action in a straight line with reference either to some centre or bound, for they have the same identical relationship to every point beyond their own circumference; wherefore they know no motion in a straight line except of their own parts; and that not in relation to any centre or mid-point save that of their own complete, containing and perfect body. This, however, we will consider further in the appropriate place. Coming now to the point: I maintain that this philosopher, according to his own principles, cannot demonstrate that a body, though distant, is disposed to return to his own or to a similar containing body. For let him consider the comets, which are composed of terrestrial matter, that hath risen in the form of exhalation to the enkindling region, and the parts thereof are not apt to descend, but, being seized by the power of the primum mobile, they circle around the earth. Yet the comets are not composed of Quintessence, but are very heavy terrestrial bodies, thick and dense, as may be clearly inferred from the long interval between their appearances and the prolonged resistance which they offer to the fierce, vigorous, burning flame: for sometimes they continue burning more than a month; indeed one hath been seen in our own times to burn continuously for 45 days.  If then the argument of weight is not destroyed by distance of the bodies, what is the cause that this body doth not descend nor even remain in place, but on the contrary revolveth around the earth? If thou sayest that it revolveth not of his own impulse but because it is drawn by constraint, I in reply emphasize that according to Aristotle each one of the heavens and stars is similarly drawn around, and these he asserteth to be neither heavy nor light  nor of similar [earthy] matter. Moreover the motion of these comets appeareth to be peculiar to themselves, for it never conformeth to day and night nor to the motions of the other stars.
Philotheo.  This is excellent argument by means of which the Aristotelians can be convinced from their own principles. We will therefore discuss the true nature of comets, giving special consideration thereto. And we shall shew that such burning bodies come not from the fiery sphere, for if so, they would become aflame throughout, since their whole circumference or surface would be enveloped in air attenuated by heat, as those would say, or indeed by the fiery sphere. But we always see them burning on one side, so we shall conclude these comets to be a species of star, as the ancients have well said and understood. And such a star, approaching and receding of her own motion toward and from our own, appeareth owing to this advance and retirement first to grow in size as though enkindled, and then to shrink as though dying down; and she moveth not around the earth; her motion is independent of the proper daily motion of the earth which, spinning around herself, giveth the impression that all those luminaries which are beyond her circumference rise and set. Nor is it possible that a terrestrial body of such great size, should be forcibly drawn by so subtle and liquid a body as the air which resisteth naught, or that it should be held suspended thereby contrary to his nature. Moreover if the alleged motion really occurred, it would be solely a motion like to that of the primum mobile by which the comet were drawn around, and it would not imitate the motion of the planets; yet, through such imitation, it is believed to be of the nature sometimes of Mercury, sometimes of the Moon, sometimes of Saturn, sometimes of the others. But of this matter also we will discourse in due season. Suffice it now that we have said enough to disprove this fellow's belief that propinquity or distance doth not imply greater or less power of that which he wrongly nameth individual and natural motion. For truth permitteth not that we apply the terms individual and natural to any subject disposed in a fashion that could never be convenient to it. Wherefore since the parts from beyond a certain distance never move toward their containing body, such motion should not be called natural to them.
Elpino. Whoever considereth the matter will discern clearly that this fellow [Aristotle] holdeth principles totally contrary to the true principles of nature. He further replieth that if the motion of simple bodies be natural to them, then the simple bodies which exist in many worlds and are of the same kind move either toward the same centre or toward the same extremity. 
Philotheo. Yet that is what he can never prove, that these bodies must proceed to the same distinct and individual position; for, since the bodies are of the same kind, it may be inferred that the same kind of position is suitable to them, and a similar centre, which is their own centre; but we may not and cannot infer that they require a numerically identical space.
Elpino. He had some presage of this reply, wherefore with all his vain power he thrusteth out [the idea] that a numerical difference causeth not a difference in position. 
Philotheo. In general we see quite the contrary. But tell us, what is his proof?
Elpino. He saith that if a numerical difference in bodies were in fact a cause of difference of position, it would follow that the parts of our earth, being diverse in number and in weight, would have each his own different centre of gravity in a single world, which would be impossible as well as inconvenient, since the number of different centres would be no less than the number of individual parts of the earth.
Philotheo. But see what a beggarly persuasion is this. Consider then whether you can thereby be moved a whir from the contrary opinion, or whether it doth not rather confirm you therein. Who doubteth that it would be in no way inconvenient to postulate for the whole mass, for the body and for the entire animal, a single centre to which every part would be related? Each would tend toward it, and thereby they would all be united and have a common basis. And at the same time there can be positively innumerable centres since we may seek, place or suppose a separate centre in each of the innumerable multitude of parts? In man there is but one centre, called the heart; and then there are forsooth many other centres, even as the multitude of parts, so that the heart hath his own centre, the lungs, the liver, the head, the arm, the hand, the foot, this bone, this vein, this joint, each hath his own centre as hath also each of the particles which constitute these members; and they have every one their own distinct and determined situation, both in the primary and general, that is to say in the whole individual, and also in the proximate and particular, that is to say in the special member appertaining to the individual.
Elpino. But consider that he may perhaps have meant not that each part hath his own centre, but that each hath the centre toward which it tendeth.
Philotheo. Ultimately, all tend toward one: for it is not required that all parts of the animal move toward the middle part and centre; this would be impossible and inconvenient; but each is related to the centre by the union of the parts and by the constitution of the whole; for the life and consistence of complex objects is manifested in no other fashion than by the due union of the parts; these must be understood always to have in common that goal which is reckoned for each as their midpoint and centre. Therefore, as regards the constitution of the complete whole, the parts are related to a single centre; while as regards the constitution of each member, the particles thereof are related to the particular centre of that member, in order that the liver may exist through the union of his parts, and similarly the lungs, the head, the ear, the eye, and the other members. Behold then, this is not only not inconvenient, but it is most natural; and there are many centres according to the nature of the many parts and the particles of parts, if he pleaseth; since each one of these parts is constituted, sustained and indeed formed by the constitution, maintenance and the consistency of the others. In truth, the intellect is revolted by the consideration of such idle trifles as are put forward by this philosopher.
Elpino. This must be suffered owing to the reputation which he hath gained rather through not being understood than otherwise. But consider a moment, I pray you, how this honest man taketh pleasure in this bad argumentation. You will observe that he addeth these words almost in triumph: "If then, contradiction cannot confute these arguments, there must necessarily be but one centre and one horizon."
Philotheo. You speak most truly. Proceed.
Elpino. Also he proveth that simple motions are finite and determined, for his assertion that the world is one and that simple motions have each their own proper seat was based on this notion. He argueth thus: Every moving body travelleth from a certain term to a certain term; and, since every change is finite, there is always a specific difference between the terminus a quo and the terminus ad quem. Such are the changes between disease and health, between smallness and large size, between here and there; for that which recovereth health moveth not at haphazard, but toward health. The motions then of earth and of fire are not in the infinite, but are toward certain terms different from those whence they are moving, for motion toward the summit is not motion downward, and these two regions are the horizons of motion. Behold then, how motion in a straight line is determined. Nor is circular motion less determined, for it, too, is from one definite term to another, from contrary to contrary, as we shall see if we consider the diversity of motion on the circle's diameter. For there is no contrary to the motion of the complete circle, for the circle endeth in no point save that where also it began; yet there is diversity in the parts of the revolution when this is measured from one end of the diameter to the other. 
Philotheo. As to such argument shewing that motion is determined and finite, none hath denied or doubted this. But it is false to describe it as simply determined upward or determined downward, and this we have proved on several occasions. For everything moveth indifferently hither or thither, wherever may be his place of conservation, and we maintain that, even if we accept the principles of Aristotle and other principles like unto his -- nevertheless if there were another body within our earth, the parts of our earth would remain within that body only if held by constraint, for they would naturally rise. Nor would Aristotle deny that if the particles of fire were above the fiery sphere -- as for example if they were where these philosophers believe is the cupola or heaven of Mercury  -- they would then naturally descend. You will see then how far in conformity with nature these people determine upward and downward, heavy and light, when you have considered that all bodies, wherever they be and whithersoever they move, as far as possible seek and remain in the place of their conservation. Nevertheless, however true it may be that every object moveth through his own centre to and from his own bounds, and that every motion whether circular or in a straight line is determined between two opposite positions, yet it followeth not that the universe is finite in size, nor that there is but one world. Nor is the infinity disproved of the simple motion of any distinct action whereby as we say that spirit which worketh the composition, unity and quickening of our earth may be and will ever be similarly manifested in innumerable other worlds. We may then believe that all motion is finite (speaking of motion in a given present time, not of absolute simple motion comprehending each individual and the whole) and also that there is an infinity of worlds; since even as each of infinitely numerous worlds is itself finite and is in finite space, so there appertain prescribed terms to the motion of each and of their parts.
Elpino. You are right. And thereupon, though he can shew no inconvenience against our view, and naught in favour of what he would prove, there is brought forward his final proof that "motion is not infinite; because the nearer either earth or fire approach to their own sphere the more rapid is their motion; wherefore if motion were infinite it would follow that speed, lightness and weight would also be infinite." 
Philotheo. I wish him much joy of it.
Fracastoro. Certainly; but this appeareth to me a juggler's game. For if the atoms are endowed with infinite motion by endless change of position from moment to moment, now leaving this body, now entering into that, now joining in this composition, now that, traversing now in this formation, now in that, the immense space of the universe: they will then truly attain infinite positional motion, they will traverse infinite space, and contribute to infinite changes. But it doth not follow that they will be endowed with infinite weight, lightness, or speed.
Philotheo. Let us leave aside the motion of the primal particles and elements; and let us consider only the proximate parts pertaining to certain kinds of being, that is of substance, such as those parts of the earth which are indeed earth. Of these it is truly said that in those worlds wherein they exist, in those regions which they traverse, and in that form which they attain, they move only from and toward certain bounds; and from this fact there no more followeth the conclusion that the universe is finite and the world unique than, for example, that therefore monkeys are born tailless, that owls see at night without eyes, that bats make wool. Moreover it is never possible to make concerning these parts an inference such as: the universe is infinite, these are infinite worlds; therefore a single part of the world is endowed with infinite motion, and must be infinitely attracted by an infinitely distant earth, and moreover hath infinite weight. This impossibility ariseth from two reasons. On the one hand, such a transition is impossible; for, since the universe consisteth of opposed bodies and principles, such a single particle could not traverse far through the ethereal region without being overcome by his opposite; so that this part of earth would no longer move, because the substance thereof would no longer be earth, having through the victory of the contrary thereof, changed his complexion and aspect. In the second place, we observe in general that far from there being ever an impulse of weight or lightness from an infinite distance as is alleged, such attraction of the parts cannot take place save within the region of their own containing space; for if they were beyond it, they would no longer move there; for the fluid humours (which within the animal move from the outer to the internal parts, both above and below, rising, falling, moving hither and thither according to all their differences), if placed outside their own proper containing region, even though near to it, would lose their natural force and impulse. For this relation is valid within the measured space of the radius from the centre of a given region to the circumference thereof; for around the circumference is the region of least weight, and around the centre that of most; and in the intervening region, according to the degree of propinquity of centre or of circumference, is more or less weight. This appeareth in the following diagram [Diagram VII, wherein at A, the centre of the region, a stone is, to use common parlance, neither heavy nor light. B denoteth the circumference of the region, where similarly the stone is neither heavy nor light, but remaineth passive, whereby is shown once again the coincidence of maximum and minimum, as is demonstrated at the end of the work On Origin, Cause and Unity. The figures 1 2 3 4 5 6 7 8 9 denote the different intermediate spaces.
[Diagram VI] 
Now you see, moreover, that so far from one earth being impelled to approach another, even the parts, if placed beyond their own proper circumference, have no such impulse.
Elpino. You regard this circumference as determined?
Philotheo. Certainly, in so far as concerneth the greatest weight possible in the greatest part; or, if thou wilt, in the whole earth -- since the whole globe is neither heavy nor light. But so far as concerneth the various intervening grades of heavy and light, I say that their diversities must be as numerous as are the diversities of weight of the several parts from the most to the least heavy.
Elpino. But this scale must be interpreted with discretion.
Philotheo. Every man of wit will be able to interpret for himself. As to the arguments of Aristotle, enough hath been said. We will now see whether he bringeth forward aught further on.
Elpino. Pray be content that we speak of this next day. For I am expected by Albertino, who is disposed to join us here to-morrow. From him I think you may hear all most weighty arguments which can be brought to support the contrary opinion, for he is very adept in the current philosophy.
Philotheo. Be it as you wish.
End of the Fourth Dialogue.