shew vs that the lesse the atomes should penetrate into a moouing body by reason of the extreme density of it the more efficaciously they would worke and the greater celerity they would cause in its motion And hence we may giue the fullest solution to the obiection aboue which was to this effect that seeing diuision is made onely by the superficies or exteriour part of the dense body and that the vertue whereby a dense body doth worke is onely its resistance to diuision which maketh it apt to diuide it would follow that a hollow boule of brasse or iron should be as heauy as a solide one For we may answere that seeing the atomes must stricke through the body and that a cessible body doth not receiue their stroakes so firmely as a stiffe one nor can conuey them so farre if vnto a stiffe superficies there succeede a yielding inside the stroakes must of necessity loose much of their force and consequently can not mooue a body full of ayre with so much celerity or with so much efficacy as they may a solide one But then you may peraduenture say that if these stroakes of the descending atomes vpon a dense body were the cause of its motion downewardes we must allow the atomes to mooue faster then the dense body that so they may still ouertake it and driue it along and enter into it whereas if they should mooue slower then it none of them could come in their turne to giue it a stroake but it would be past them and out of their reach before they could strike it But it is euident say you out of these pretended causes of this motion that such atomes can not mooue so swiftly downewardes as a great dense body since their litlenesse and their rarity are both of them hindering to their motion and therefore this can not be the cause of that effect which we call grauity To this I reply that to haue the atomes giue these blowes to a descending dense body doth not require that their naturall and ordinary motion should be swifter then the descent of such a dense body but the very descent of it occasioneth their striking it for as it falleth and maketh it selfe a way through them they diuide themselues before it and swell on the sides and a litle aboue it and presently close againe behind it and ouer it as soone as it is past Now that closing to hinder vacuity of space is a suddaine one and thereby attaineth great velocity which would carry the atomes in that degree of velocity further then the descending body if they did not encounter with it in their way to retarde them which encounter and retarding implyeth such stroakes vpon the dense body as we suppose to cause this motion And the like we see in water into which letting a stone fall presently the water that was diuided by the stone and swelleth on the sides higher then it was before closeth vpon the backe of the descending stone and followeth it so violently that for a while after it leaueth a purling hole in the place where the stone went downe till by the repose of the stone the water returneth likewise to its quiet and so its superficies becometh euen In the third place an enquiry occurreth emergent out of this doctrine of the cause of bodies moouing vpwardes and downewardes Which is whether there would be any naturall motion deepe in the earth beyond the actiuity of the sunnes beames For out of these principles it followeth that there would not and consequently there must be a vast orbe in which there would be no motion of grauity or of leuity for suppose that the sunne beames might pierce a thousand miles deepe into the body of the earth yet there would still remaine a masse whose diameter would be neere 5000 miles in which there would be no grauitation nor the contrary motion For my part I shall make no difficulty to grant the inference as farre as concerneth motion caused by our sunne for what inconuenience would follow out of it But I will not offer att determining whether there may not be enclosed within that great sphere of earth some other fire such as the Chymistes talke of an Archeus a Demogorgon seated in the center like the hart in animals which may raise vp vapours and boyle an ayre out of them and diuide grosse bodies into atomes and accordingly giue them motions answerable to ours but in different lines from ours according as that fire or sunne is situated since the farre-searching Author of the Dialogues de Mundo hath left that speculation vndecided after he had touched vpon it in the 12 knott of his first Dialogue Fourthly it may be obiected that if such descending atomes as we haue described were the cause of a bodies grauity and descending towardes the center the same body would att diuers times descend more and lesse swiftly for example after midnight when the atomes begin to descend more slowly then likewise the same body would descend more slowly in a like proportion and not weigh so much as it did in the heate of the day The same may be said of summer and winter for in winter time the atomes seeme to be more grosse and consequently to strike more strongly vpon the bodies they meete with in their way as they descend yet on the other side they seeme in the summer to be more numerous as also to descend from a greater height both which circumstances will be cause of a stronger stroake and more vigourous impulse vpon the body they hitt And the like may be obiected of diuers partes of the world for in the torride zone it will alwayes happen as in summer in places of the temperate zone and in the polar climes as in deepest winter so that no where there would be any standard or certainty in the weight of bodies if it depended vpon so mutable a cause And it maketh to the same effect that a body which lyeth vnder a thicke rocke or any other very dense body that can not be penetrated by any great store of atomes should not be so heauy as it would be in the open and free ayre where the atomes in their complete numbers haue their full stroakes For answere to these and such like instances we are to note first that it is not so much the number or the violence of the percussion of the striking atomes as the density of the thing strucken which giueth the measure to the descending of a weighty body and the chiefe thing which the stroake of the atomes giueth vnto a dense body is a determination of the way which a dense body is to cutt vnto it selfe therefore multiplication or lessening of the atomes will not make any sensible difference betwixt the weight of one dense body where many atomes do strike and an other body of the same density where but few do strike so that the stroake downewardes of the descending atomes be greater then the stroake vpwardes
ibid. § 2. What place is both notionally and really pag. 33. § 3. Locall motion is that diuision whereby a body chāeth its place pag. 34. § 4. The nature of quantity of it selfe is sufficient to vnite a body to its place ibidem § 5. All operations amongst bodies are eyther locall motion or such as follow out of locall motion pag. 35. § 6. Earth compared to water in actiuity pag. 36. § 7. The manner whereby fire getteth in fewel prooueth that it exceedeth earth in actiuity ibid. § 8. The same is prooued by the manner whereby fire cometh ut of fewell and worketh vpon other bodies pag. 37. CHAP. VI. Of Light what it is pag. 39. § 1. In what sense the Author reiecteth qualities ibid. § 2. In what sense the Author doth admitt of qualities pag. 40. § 3. Fiue arguments proposed to proue that light is not a body pag. 41. § 4. The two first reasons to proue light to be a body are the resemblance it hath with fire and because if it were a quality it would alwayes produce an equall to it selfe pag. 42. § 5. The third reason because if we imagine to our selues the substance of fire to be rarifyed it will haue the same appearences which light hath pag. 43. § 6. The fourth reason from the manner of the genertion and corruption of light which agreeth with fire ibid. § 7. The fifth reason because such properies belong to light as agree only vnto bodies pag. 45. CHAP. VII Two objections answered against light being fire a more ample proofe of its being such ibid. § 1. That all light is hoat and apt o heate ibid. § 2. The reason why our bodies for the most part do not feele the heate of pure light pag. 46. § 3. The experience of burningglasses and of soultry gloomy weather proue light to be fire pag. 48. § 4. Philosophers ought not to be iudge ot thinges by the rules of vulgar people ibidem § 5. the different names of light and fire proceede from different notions of the same substance pag. 49. § 6. The reason why many times fire and heate are depriued of light pag. 50. § 7. What becometh of the body of light when it dyeth ibid. § 8. An experiment of some who pretend that light may be precipitated into pouder pag. 51. § 9. The Authors opinion concerning lampes pretended to haue been found in tombes with inconsumptible lights ibid. CHAP. VIII An answere to three other objections formely proposed against light being a substance pag. 53. § 1. Light is not really in euery part of the roome it enlighteneth nor filleth entirely any sensible part of it though it seeme to vs to do so ibid. § 2. Tha least sensible poynt of a diaphanous body hath roome sufficient to containe both ayre and light together with a multitude of beames issuing from seuerall lights without penetrating one another pag. 54. § 3. That light doth not enlighten any roome in an instant and that the great celerity of its motion doth make it inperceptible to our senses pag. 56. § 4. The reason why the motion of light is not discerned comingtowardes vs and that there is some reall tardity in it pag. 58. § 5. The planets are not certainely euer in that place where they appeare to be pag. 59. § 6. The reason why light being a body doth not by its motion shatter other bodies into pieces ibid. § 7. The reason why the body of light is neuer perceiued to be fanned by the wind pag. 61. § 8. The reasons for and against lights being a body compared together pag. 62. § 9. A summary repetition of the reasons which prooue that light is fire ibidem CHAP. IX Of locall Motion in common pag 63. § 1. No locall motion can be performed without succession ibid. § 2. Time is the common measure of all succession pag. 64. § 3. What velocity is and that it can not be infinite ibid. § 4. No force so litle that is not able to moue the greatest weight imaginable pag. 65. § 5. The cheife principle of Mechanikes deduced out of the former discourse pag. 66. § 6. No moueable can passe from rest to any determinate degree of velocity or from a lesser degree to a greater without passing through all the intermediate degrees which are below the obtained degree pag. 67. § 7. The conditions which helpe to motion in the moueable are three in the medium one pag 69. § 8. No body hath any intrinsecall vertue to moue it selfe towardes any determinate part of the vniuerse pag. 70. § 9. The encrease of motion is alwayes made in the proportion of the odde numbers ibid. § 10. No motion can encrease for euer without coming to a periode pag. 72. § 11. Certaine problemes resolued concerning the proportion of some mouing Agents compared to their effects pag 73. § 12. When a moueable cometh to rest the motion doth decrease according to the rules of encrease pag. 75. CHAP. X. Of Grauity and Leuity and of Locall Motion commonly termed Naturall pag. 76. § 1. Those motions are called naturall which haue constant causes and those violent which are contrary to them ibid. § 2. The first and most generall operation of the sunne is the making and raising of atomes ibid. § 3. The light rebounding from the earth with atomes causeth two streames in the ayre the one ascending the other descending and both of them in a perpendicular line pag. 77. § 4. A dense body placed in the ayre betweene the ascending and descending streame must needes descend pag. 78. § 5. A more particular explication of all the former doctrine touching grauity pag. 79. § 6. Grauity and leuity do not signify an intrinsecall inclination to such a motion in the bodies themselues which are termed heauy and light pag. 81. § 7. The more dense a body is the more swiftly it descendeth ibid. § 8. The velocity of bodies descending doth not encrease in proportion to the difference that may be betweene their seuerall densities pag. 82. § 9. More or lesse grauity doth produce a swifter or a slower descending of a heauy body Aristotles argument to disproue motion in vacuo is made good pag. 84. § 10. The reason why att the inferiour quarter of a circle a body doth descend faster by the arch of that quarter then by the chord if it pag. 85. CHAP. XI An answere to objections against the causes of naturall motion auowed in the former chapter and a refutation of the contrary opinion pag. 86. § 1. The first obiection answered why a hollow body descendeth slower then a solide one pag. 86. § 2. The second obiection answered and the reasons shewne why atomes do continually ouertake the descending dense body pag. 88. § 3. A curious question left vndecided pag. 89. § 4. The fourth obiection answered why the descent of the same heauy bodies is equall in so great inequality of the atomes which cause it ibidem § 5. The reason why the
of intension and Remission and others do not ibid. § 7. That in euery part of our habitable world all the foure Elements are found pure in small atomes but not in any great bulke pag. 142. CHAP. XVII Of Rarefaction and Condensation the two first motions of particular bodies pag. 144. § 1. The Authors intent in this and the following chapters ibid. § 2. That bodies may be rarifyed both by outward heat aud how this is performed pag. 145. § 3. Of the great effects fo Rarefaction pag. 147. § 4. The first manner of condensation by heate pag. 148. § 5. The second manner of condensation by cold pag. 149. § 6. That yce is not water rarifyed but condensed pag. 151. § 7. How wind snow and haile are made and wind by raine allayed pag. 152. § 8. How partes of the same or diuers bodies are ioyned more strongly together by condensation pag. 153. § 9. Vacuites can not be the reason why water impregnated to the full with one kind of salt will notwithstanding receiue more of an other pag. 154. § 10. The true reason of the former effect pag. 155. § 11. The reason why bodies of the same nature do ioyne more easily together then others pag. 156. CHAP. XVIII Of an other motion belonging to particular bodies called Attraction and of certaine operations termed Magicall pag. 157. § 1. What Attraction is and from whence it proceedeth ibid. § 2. The true sense of the Maxime that Nature abhorreth from vacuity pag. 158. § 3. The true reason of attraction pag. 159. § 4. Water may be brought by the force of attraction to what height soeuer pag. 160. § 5. The doctrine touching the attraction of water in syphons ibid § 6. That the syphon doth not proue water to weigh in its owne orbe pag. 161. § 7. Concerning attraction caused by fire pag. 162. § 8. Concerning attraction made by vertue of hoat bodies amulets etc. pag. 163. § 9. The naturall reason giuen for diuers operations esteemed by some to be magicall ibid. CHAP. XIX Of three other motions belonging to particular bodies Filtration Restitution and Electricall attraction pag. 166. § 1. What is Filtration and how it is effected ibid. § 2. What causeth the water in filtration to ascend pag. 167. § 3. Why the filter will not droppe vnlesse the labell hang lower then the water ibid. § 4. Of the motion of Restitution and why some bodies stand bent others not pag. 168. § 5. Why some bodies returne onely in part to their natural figure others entirely pag. 170. § 6. Concerning the nature of those bodies which do shrinke and stretch pag. 171. § 7. How great and wonderfull effects proceed from small plaine and simple principles ibid. § 8. Concerning Electricall attraction and the causes of it pag. 172. § 9. Cabeus his opinion refuted concerning the cause of Electricall motions pag. 174. CHAP. XX. Of the Loadestones generation and its particular motions pag. 175. § 1. The extreme heat of the sunne vnder the zodiake draweth a streame of ayre from each Pole into the torride zone ibid. § 2. The atomes of these two streames coming together are apt to incorporate with one an other pag. 176. § 3. By the meeting and mingling together of these streames att the Equator diuers riuolets of atomes of each Pole are continuated from one Pole to te other pag. 177. § 4. Of these atomes incorporated with some fitt matter in the bowels of the earth is made a stone pag. 179. § 5. This stone worketh by emanations ioyned with agreeing streames that meete them in the ayre and in fine it is a loadestone ibid. § 6. A methode for making experiences vpon any subiect pag. 181. § 7. The loadestones generation by atomes flowing from both Poles is confirmed by experiments obserued in the stone it selfe ibid. § 8. Experiments to proue that the loadestone worketh by emanations meeting with agreeing streames pag. 182. CHAP. XXI Positions drawne out of the former doctrine and confirmed by experimentall proofes pag. 185. .1 The operations of the loadestone are wrought by bodies and not by qualities ibid. § 2. Obiections against the former position answered pag. 186. § 3. The loadestone is imbued with his vertue from an other body ibid. § 4. The vertue of the loadestone is a double and not one simple vertue 188. § 5. The vertue of the laodestone worketh more strongly in the Poles of it then in any other part ibid. § 6. The laodestone sendeth forth its emanations spherically Which are of two kindes and each kind is strongest in that hemisphere through whose polary partes they issue out ibid. § 7. Putting two loadestones within the sphere of one an other euery part of one laodestone doth not agree with euery part of the other loadestone pag 189. § 8. Concerning the declination and other respects of a needle towardes the loadestone it toucheth ibid. § 9. The vertue of the laodestone goeth from end to end in lines almost paralelle to the axis pag. 191. § 10. The vertue of loadestone is not perfectly sphericall though the stone be such pag. 192. § 11. The intention of nature in all the operations of the loadestone is to make an vnion betwixt the attractiue and attracted bodies ibid. § 12. The maine globe of the earth is not a loadestone ibid. § 13. The laodestone is generated in all partes or climats of the earth pag. 193. § 14. The conformity betwixt the two motions of magnetike thinges and of heauy thinges ibid. CHAP. XXII A solution of certaine Problemes concerning the loadestone and a short summe of the whole doctrine touching it pag. 194. § 1. Which is the North and which the South Pole of a loadestone ibid. § 2. Whether any bodies besides magnetike ones be attractiue ibid. § 3. Whether an iron placed perpendicularly towardes the earth doth gett a magneticall vertue of pointing towardes the north or towardes the south in that end that lyeth downewardes pag. 195. § 4. Why loadestones affect iron better then one an other ibid. § 5. Gilberts reason refuted touching a capped loadestone that taketh vp more iron then one not capped and an iron impregnated that in some case draweth more strongly then the stone it selfe ibid. § 6. Galileus his opinion touching the former effects refuted pag. 196. § 7. The Authors solution to the former questions pag. 197. § 8. The reason why in the former case a lesser loadestone doth draw the interiacent iron from the greater pag. 198. § 9. Why the variation of a touched needle from the north is greater the neerer you go to the Pole pag. 199. § 10. Whether in the same part of the world a touched needle may att one time vary more from the north and att an other time lesse pag. 200. § 11. The whole doctrine of the loadestone summed vp in short pag. 201. CHAP. XXIII A description of the two sortes of liuing creatures Plantes and Animals and how they are framed in common
the same biggenesse and consequently be conuerted into a greater Quantity of fire and ayre Oyle will make much more flame then spiritt of wine that is farre rarer then it These and such like considerations haue much perplexed Philosophers and haue driuen them into diuerse thoughts to find out the reasons of them Some obseruing that the diuiding of a body into litle partes maketh it lesse apt to descend then when it is in greater haue beleeued the whole cause of litghnesse and rarity to be deriued from diuision As for example they find that lead cutt into litle pieces will not goe downe so fast in water as when it is in bulke and it may be reduced into so small atomes that it will for some space swimme vpon the water like dust of wood Which assumption is prooued by the greate Galileus vnto whose excellent witt and admirable industry the world is beholding not onely for his wonderfull discoueries made in the heauens but also for his accurate and learned declaring of those very thinges that lye vnder our feete He about the 90th page of his first Dialogue of motion doth clearly demonstrate how any reall medium must of necessity resist more the descent of a litle piece of lead or any other weighty matter then it would a greater piece and the resistence will be greater and greater as the pieces are lesser and lesser So that as the pieces are made lesse they will in the same medium sinke the slower and do seeme to haue acquired a new nature of lightnesse by theire diminution not onely of hauing lesse weight in them then they had as halfe an ounce is lesse then a whole ounce but also of hauing in themselues a lesse proportion of weight to theire bulke then they had as a pound of corke is in regard of its magnitude lighter then a pound of lead so as they conclude that the thing whose continued partes are the lesser is in its owne nature the lighter and the rarer and other thinges whose continued partes are greater they be heauier and denser But this discourse reacheth not home for by it the weight of any body being discouered by the proportion it hath to the medium in which it descendeth it must euer suppose a body lighter then it selfe in which it may sinke and goe to the bottome Now of that lighter body I enquire what maketh it be so and you must answere by what you haue concluded that it is lighter then the other because the partes of it are lesse and more seuered from one an other for if they be as close together theire diuision auayleth them nothing since thinges sticking fast together do worke as if they were but one and so a pound of lead though it be filed into small dust if it be compacted hard together will sinke as fast as if it were in one bulke Now then allowing the litle partes to be seperated I aske what other body filleth vp the spaces betweene those litle partes of the medium in which your heauy body descended For if the partes of water are more seuered then the partes of lead there must be some other substance to keepe the partes of it a sunder lett vs suppose this to be ayre and I aske whether an equall part of ayre be as heauy as so much water or whether it be not If you say it is then the compound of water and ayre must be as heauy as lead seeing that theire partes one with an other are as much compacted as the partes of lead are For there is no difference whether those bodies whose litle partes are compacted together be of the same substance or of diuers or whether the one be diuided into smaller partes then the other or no so they be of equall weights in regard of making the whole equally heauy as you may experience if you mingle pinnedust with a sand of equall weight though it be beaten into farre smaller diuisions then the pinnedust and putt them in a bagge together But if you say that ayre is not so heauy as water it must be because euery part of ayre hath againe its partes more seuered by some other body then the partes of water are seuered by ayre And then I make the same instance of that body which seuereth the partes of ayre And so att the last since there can not actually be an infinite processe of bodies one lighter then an other you must come to one whose litle partes filling the pores and spaces between the partes of the others haue no spaces in themselues to be filled vp But as soone as you acknowledge such a body to be lighter and rarer then all the rest you contradict and destroy all you said before For by reason of its hauing no pores it followeth by your rule that the litle partes of it must be as heauy if not heauier then the litle partes of the same bignesse of that body whose pores it filleth and consequently it is proued by the experience we alleadged of pinnedust mingled with sand that the litle partes of it can not by theire mingling with the partes of the body in which it is immediately contained make that lighter then it would be if these litle partes were not mingled with it Nor would both theire partes mingled with the body which immediately containeth them make that body lighter And so proceeding on in the same sort through all the mingled bodies till you come to the last that is immediately mingled with water you will make water nothing the lighter for being mingled with all these and by consequence it should be as heauy and as dense as lead Now that which deceiued the authors of this opiniion was that they had not a right intelligence of the causes which made litle partes of bodies naturally heauy descend slowly in regard of the velocity of greater partes of the same bodies descending the doctrine of which we intend to deliuer hereafter Others therefore perceiuing this rule to fall short haue endeauoured to piece it out by the mixtion of vacuity among bodies belieuing it is that which maketh one rarer then an other Which mixtion they do not putt alwayes immediate to the maine body they consider but if it haue other rarer and lighter bodies mingled with it they conceiue this mixtion immediate onely to the rarest or lightest As for example a crystall being lighter and consequently rarer then a diamond they will not say that there is more vacuity in a crystall then in a diamond but that the pores of a crystall are greater and that consequently there is more ayre in a crystall to fill the pores of it then is in a diamond and the vacuities are in the ayre which abounding in a crystall more then in a diamond maketh that lighter and rarer then this by the more vacuities that are in the greater Quantity of ayre which is migled with it But against this supposition a powerfull aduersary is vrged for Aristotle in his 4th booke
and giue the like motion to any body they find in their way if it be susceptible of such a motion which it is euident that all bodies are vnlesse they be strucken by some contrary impulse For since that a bodies being in a place is nothing else but the continuity of its outside to the inside of the body that containeth it and is its place it can haue no other repugnance to locall motion which is nothing else but a successiue changing of place besides this continuity Now the nature of density being the power of diuiding and euery least power hauing some force and efficacy as we haue shewed aboue it followeth that the stroake of euery atome eyther descending or ascending will worke some thing vpon any body though neuer so bigge it chanceth to encounter with and strike vpon in its way vnlesse there be as strong an impulse the contrary way to oppose it But it being determined that the descending atomes are denser then those that ascend it followeth that the descending ones will preuayle And consequently all dense bodies must necessarily tend downewardes to the center which is to be Heauy 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 as positiue grauity or leuity but that their course vpwardes or downewardes happeneth vnto them by the order of nature which by outward causes giueth them an impulse one of these wayes without which they would rest quietly wheresoeuer they are as being of themselues indifferent to any motion But because our wordes expresse our notions and they are framed according to what appeareth vnto vs when we obserue any body to descend constantly towardes our earth we call it heauy and if it mooue contrarywise we call it light But we must take heed of considering such grauity and leuity as if they were Entities that worke such effects since vpon examination it appeareth that these wordes are but short expressions of the effects themselues the causes whereof the vulgar of mankinde who impose names to thinges do not consider but leaue that worke vnto Philosophers to examine whiles they onely obserue what they see done and agree vpon wordes to expresse that Which wordes neither will in all circumstances alwayes agree to the same thing for as corke doth descend in ayre and ascend in water so also will any other body descend if it lighteth among others more rare then it selfe and will ascend if it lighteth among bodies that are more dense then it And we terme bodies light and heauy onely according to the course which we vsually see them take Now proceeding further on and considering how there are various degrees of density or grauity it were irrationall to conceiue that all bodies should descend att the same rate and keepe equall pace with one an other in their iourney downewardes For as two knifes whereof one hath a keener edge then the other being pressed with equall strength into like yielding matter the sharper will cutt deeper then the other so if of two bodies one be more dense then the other that which is so will cutt the ayre more powerfully and will descend faster then the other for in this case density may be compared to the knifes edge since in it consisteth the power of diuiding as we haue heretofore determined And therefore the pressing them downewardes by the descending atomes being equall in both or peraduenture greater in the more dense body as anone we shall haue occasion to touch and there being no other cause to determine them that way the effect of diuision must be the greater where the diuider is the more powerfull Which the more dense body is and therefore cutteth more strongly through the resistance of the ayre and consequently passeth more swiftly that way it is determined to mooue I do not meane that the velocities of their descent shall be in the same proportion to one an other as their densities are for besides their density those other considerations which we haue discoursed of aboue when we examined the causes of velocity in motion must likewise be ballanced And out of the comparison of all them not out of the consideration of any one alone resulteth the differences of their velocities and that neither but in as much as concerneth the consideration of the mooueables for to make the calculation exact the medium must likewise be considered as by and by we shall declare for since the motion dependeth of all them together although there should be difference betweene the mooueables in regard of one onely and that the rest were equall yet the proportion of the difference of their motions must not follow the proportion of their difference in that one regard because their difference considered single in that regard will haue one proportion and with the addition of the other considerations though alike in both to their difference in this they will haue an other As for example reckon the density of one mooueable to be double the density of an other mooueable so that in that regard it hath two degrees of power to descend whereas the other hath but one suppose then the other causes of their descent to be alike in both and reckon them all three and then ioyne these three to the one which is caused by the density in one of the mooueables as likewise to the two which is caused by the density in the other mooueable and you will find that thus altogether their difference of power to descend is no longer in a double proportion as it would be if nothing but their density were considered but is in the proportion of fiue to foure But after we haue considered all that concerneth the mooueables we are then to cast an eye vpon the medium they are to mooue in and we shall find the addition of that to decrease the proportion of their difference exceedingly more according to the cessibility of the medium Which if it be ayre the great disproportion of its weight to the weight of those bodies which men vse to take in making experiences of their descent in that yielding medium will cause their difference of velocity in descending to be hardly perceptible Euen as the difference of a sharpe or dull knife which is easily perceiued in cutting of flesh or bread is not to be distinguished in diuiding of water or oyle And likewise in weights a pound and a scruple will beare downe a dramme in no sensible proportion of velocity more then a pound alone would do and yet putt a pound in that scale instead of the dramme and then the difference of the scruple will be very notable So then those bodies whose difference of descending in water is very sensible because of the greater proportion of weight in water to the bodies that descend in it will yield no sensible difference of velocity when they descend in ayre by reason of the great disproportion of weight betweene
ayre and the bodies that descend in it The reason of this will clearely shew it selfe in abstracted proportions Thus suppose ayre to haue one degree of density and water to haue 400 then lett the mooueable A haue 410 degrees of density and the mooueable B haue 500. Now compare their motion to one an other in the seuerall mediums of ayre and water The exuperance of the density of A to water is 10 degrees but the exuperace of B vnto the same water is 100 degrees so that B must mooue in water swifter then A in the proportion of 100 to tenne that is of 10 to one Then lett vs compre the exuperance of the two mooueables ouer ayre A is 409 times more dense then ayre but B is 499 times more dense then it By which account the motion of B must be in that medium swifter then the motion of A in the proportion of 499 to 409 that is about 50 to 41 which to auoyde fractions we may account as 10 to 8. But in water they exceede one an other as 10 to one so that their difference of velocity must be scarce perceptible in ayre in respect of what it is in water Out of all which discourse I onely inferre in common that a greater velocity in motion will follow the greater density of the mooueable without determining here their proportions which I leaue vnto them who make that examination their taske for thus much serueth my present turne wherein I take a suruay of nature but in grosse And my chiefe drift in this particular is onely to open the way for the discouering how bodies that of themselues haue no propension vnto any determinate place do neuerthelesse mooue constantly and perpetually one way the dense ones descending and the rare ones ascending not by any intrinsecall quality that worketh vpon them but by the oeconomy of nature that hath sett on foote due and plaine causes to produce knowne effects Here we must craue patience of the great soule of Galileo whose admirable learning all posterity must reuerence whiles we reprehend in him that which we can not terme lesse then absurd and yet he not onely mainetaineth it in seuerall places but also professeth Dial. P o de motu pag. 8 to make it more cleare then day His position is that more or lesse grauity contributeth nothing att all to the faster or slower descending of a naturall body but that all the effect it giueth vnto a body is to make it descend or not descend in such a medium Which is against the first and most knowne principle that is in bodies to witt that more doth more and lesse doth lesse for he alloweth that grauity causeth a body to descend and yet will not allow that more grauity causeth it to descend more I wonder that he neuer marked how in a paire of scales a superproportion of ouerweight in one ballance lifted vp the other faster then a lesse proportion of ouerweight would do Or that more weight hanged to a iacke made the spitt turne faster or to the lines of a clocke made it goe faster and the like But his argument whereby he endeauoureth to prooue his position is yet more wonderfull for finding in pendants vnequall in grauity that the lighter went in the same time almost as fast as the heauyer he gathereth from thence that the different weights haue each of them the same celerity and that it is the opposition of the ayre which maketh the lighter body not reach so farre at each vndulation as the heauyer doth For reply wherevnto first we must aske him whether experience or reason taught him that the slower going of the lighter pendant proceeded onely from the medium and not from want of grauity And when he shall haue answered as he needes must that experience doth not shew this then we must importune him for a good reason but I do not find that he bringeth any att all Againe if he admitteth which he doth in expresse termes that a lighter body can not resist the medium so much as a heauyer body can we must aske him whether it be not the weight that maketh the heauyer body resist more which when he hath acknowledged that it is he hath therein likewise acknowledged that whensoeuer this happeneth in the descending of a body the more weight must make the heauyer body descend faster But we can not passe this matter without noting how himselfe maketh good those arguments of Aristotle which he seemeth by no meanes to esteeme of for since the grauity doth ouercome the resistance of the medium in some proportion it followeth that the proportions betweene the grauity and the medium may be multiplyed without end so as if he suppose that the grauity of a body do make it goe att a certaine rate in imaginary space which is his manner of putting the force of grauity then there may be giuen such a proportion of a heauy body to the medium as it shall goe in such a medium att the same rate and neuerthelesse there will be an infinite difference betwixt the resistance of the medium compared to that body and the resistance of the imaginary space compared to that other body which he supposeth to be mooued in it at the same rate which no man will sticke att confessing to be very absurd Then turning the scales because the resistance of the medium doth somewhat hinder grauity and that with lesse resistance the heauy body mooueth faster it must follow that since there is no proportion betwixt the medium and imaginary space there must neither be any proportion betwixt the time in which a heauy body shall passe through a certaine quantity of the medium and the time in which it shall passe through as much imaginary space wherefore it must passe ouer so much imaginary space in an instant Which is the argument that Aristotle is so much laughed att for pressing And in a word nothing is more euident then that for this effect which Galileo attributeth to grauity it is vnreasonable to putt a diuisible quality since the effect is indiuisible And therefore as euident it is that in his doctrine such aquality as intrinsecall grauity is conceiued to be ought not to be putt since euery power should be fitted to the effect or end for which it is putt An other argument of Galileo is as bad as this when he endeauoureth to prooue that all bodies goe of a like velocity because it happeneth that a lighter body in some case goeth faster then a heauyer body in an other case as for example in two pendants whereof the lighter is in the beginning of its motion and the heauyer towardes the end of it or if the lighter hangeth att a longer string and the heauyer att a shorter we see that the lighter will goe faster then the heauyer But this concludeth no more then if a man should prooue that a lighter goeth faster then a heauyer because a greater force can make it goe faster for it
is manifest that in a violent motion the force which mooueth a body in the end of its course is weaker then that which mooueth it in the beginning and the like is of the two stringes But here it is not amisse to solue a Probleme he putteth which belongeth to our present subiect He findeth by experience that if two bodies descend att the same time from the same point and do goe to the same point the one by the inferiour quarter of the cercle the other by the chord to that arch or by any other lines which are chordes to partes of that arch he findeth I say that the mooueable goeth faster by the arch then by any of the chordes And the reason is euident if we consider that the neerer any motion doth come vnto a perpendicular one downewardes the greater velocity it must haue and that in the arch of such a quadrant euery particular part of it inclineth to the perpendicular of the place where it is more then the part of the chord answerable vnto it doth THE ELEVENTH CHAPTER An answere to obiections against the causes of naturall motion auowed in the former chapter and a refutation of the contrary opinion BVt to returne to the thridde of our doctrine there may peraduenture be obiected against it that if the violence of a bodies descent towardes the center did proceede onely from the density of it which giueth it an aptitude the better to cutt the medium and from the multitude of litle atomes descending that strike vpon it and presse it the way they goe which is downewardes then it would not import whether the inner part of that body were as solide as the outward partes for it cutteth with onely the outward and is smitten onely vpon the outward And yet experience sheweth vs the contrary for a great bullet of lead that is solide and lead throughout descendeth faster then if three quarters of the diameter were hollow within and such a one falling vpon any resisting substance worketh a greater effect then a hollow one And a ball of brasse that hath but a thinne outside of mettall will swimme vpon the water when a massie one sinketh presently Whereby it appeareth that it is rather some other quality belonging to the very bulke of the metall in it selfe and not these outward causes that occasion grauity But this difficulty is easily ouercome if you consider how subtile those atomes are which descending downewardes and striking vpon a body in their way do cause its motion likewise downewardes for you may remember how we haue shewed them to be the subtilest and the minutest diuisions that light the subtilest and sharpest diuider in nature can make It is then easye to conceiue that these extreme subtile bodies do penetrate all others as light doth glasse and do runne through them as sand doth through a small sieue or as water through a spunge so that they strike not onely vpon the superficies but aswell in euery most interiour part of the whole body running quite through it all by the pores of it And then it must needes follow that the solider it is and the more partes it hath within as well as without to be strucken vpon the faster it must goe and the greater effect it must worke in what it falleth vpon whereas if three quarters of the diameter of it within should be filled with nothing but with ayre the atomes would fly without any considerable effect through all that space by reason of the rarity and cessibility of it And that these atomes are thus subtile is manifest by seuerall effects which we see in nature Diuers Authors that write of Egypt do assure vs that though their houses be built of strong stone neuerthelesse a clodde of earth layed in the inmost roomes and shutt vp from all appearing communication with ayre will encrease its weight so notably as thereby they can iudge the change of weather which will shortly ensue Which can proceede from no other cause but from a multitude of litle atomes of saltpeter which floating in the ayre do penetrate through the strongest walls and all the massie defences in their way and do settle in the clodde of earth as soone as they meete with it because it is of a temper fitt to entertaine and to conserue and to embody them Delights haue shewed vs the way how to make the spirits or atomes of snow and saltpeter passe through a glasse vessell which Alchimists hold to be the most impenetrable of all they can find to worke with In our owne bodies the aches which feeble partes do feele before change of weather and the heauynesse of our heades and shoulders if we remaine in the open ayre presently after sunnesett do aboundantly testify that euen the grosser of these atomes which are the first that fall do vehemently penetrate our bodies so as sense will make vs beleeue what reason peraduenture could not But besides all this there is yet a more conuincing reason why the descending atomes should mooue the whole density of a body euen though it were so dense that they could not penetrate it and gett into the bowels of it but must be content to strike barely vpon the outside of it For nature hath so ordered the matter that when dense partes sticke close together and make the length composed of them to be very stiffe one can not be mooued but that all the rest which are in that line must likewise be thereby mooued so that if all the world wery composed of atomes close sticking together the least motion imaginable must driue on all that were in a straight line to the very end of the world This you see is euident in reason And experience confirmeth it when by a litle knocke giuen att the end of a long beame the shaking which maketh sound reacheth sensibly to the other end The blind man that gouerneth his steppes by feeling in defect of eyes receiueth aduertisements of remote thinges through a staffe which he holdeth in his handes peraduenture more particularly then his eyes could haue directed him And the like is of a deafe man that heareth the sound of an instrument by holding one end of a sticke in his mouth whiles the other end resteth vpō the instrumēt And some are of opiniō and they not of the ranke of vulgar Philosophers that if a staffe were as long as to reach from the sunne to vs it would haue the same effect in a moment of time Although for my part I am hard to beleeue that we could receiue an aduertisement so farre vnlesse the staffe were of such a thicknesse as being proportionable to the length might keepe it from facile bending for if it should be very plyant it would do vs no seruice as we experience in a thridde which reaching from our hand to the ground if it knocke against any thing maketh no sensible impression in our hand So that in fine reason sense and authority do all of them
of the ascending atomes and thereby determineth it to weigh to the centerwardes and not rise floating vpwardes which is all the sensible effect we can perceiue Next we may obserue that the first particulars of the obiection do not reach home to enfeeble our doctrine in this particular although we admitt them to be in such sort as they are proposed for they do withall implye such a perpetuall variation of causes euer fauourable to our position that nothing can be inferred out of them to repugne against it As thus when there are many atomes descending in the ayre the same generall cause which maketh them be many maketh them also be light in proportion to their multitude And so when they are few they are heauy likewise when the atomes are light the ayre is rarifyed and thinne and when they are heauy the ayre is thicke and so vpon the whole matter it is euident that we can not make such a precise and exact iudgement of the variety of circumstances as to be able to determine when there is absolutely more cause of weight and when lesse And as we find not weight enough in either side of these opposite circumstances to turne the scales in our discourse so likewise we find the same indifference in experience it selfe for the weights we vse do weigh equally in mysty weather and in cleare and yet in rigour of discourse we can not doubt but that in truth they do not grauitate or weigh so much though the difference be imperceptible to sense when the ayre is thicke and foggy as when it is pure and rarifyed which thickenesse of the medium when it arriueth to a very notable degree as for example to water maketh then a great difference of a heauy bobies grauitation in it and accordingly we see a great difference betweene heauy bodies descending in water and in ayre though betweene two kindes of ayre none is to be obserued their difference is so small in respect of the density of the body that descendeth in thē And therefore seeing that an assured and certaine difference in circumstances maketh no sensible inequality in the effect we can not expect any from such circumstances as we may reasonably doubt whether there be any inequality among thē or no. Besides that if in any of the proposed cases a heauy body should grauitate more and be heauyer one time then an other yet by weighing it we could not discerne it since that the counterpoise which is to determine its weight must likewise be in the same proportion heauyer then it was And besides weighing no other meanes remaineth to discouer its greater grauitation but to compare it to time in its descent and I beleeue that in all such distances as we can try it in its inequalities will be no whitt lesse difficult to be obserued that way then any other Lastly to bend our discourse particularly to that instance of the obiection where it is conceiued that if grauity or descending downewardes of bodies proceeded from atomes striking vpon them as they mooue downewardes it would follow that a stone or other dense body lying vnder shelter of a thicke hard and impenetrable adamantine rocke would haue no impulse downewardes and consequently would not weigh there We may note that no body whatsoeuer compacted by physicall causes and agents can be so dense and imporous but that such atomes as these we speake of must be in them and in euery part of them and euery where passe through and through them as water doth through a seeue or through a spunge and this vniuersall maxime must extend as farre as the sunne or as any other heate communicating with the sunne doth reach and is found The reason whereof is because these atomes are no other thing but such extreme litle bodies as are resolued by heate out of the maine stocke of those massy bodies vpon which the sunne and heate do worke Now then it being certaine out of what we haue heretofore said that all mixt bodies haue their temper and consistence and generation from the mingling of fire with the rest of the Elements that compose them and from the concoction or digestion which fire maketh in those bodies it is euident that no mixt body whatsoeuer nor any sensible part of a mixt body can be voyde of pores capable of such atomes nor can be without such atomes passing through those pores which atomes by mediation of the ayre that likewise hath its share in such pores must haue communication with the rest of the great sea of ayre and with the motions that passe in it And consequently in all and in euery sensible part of any such extreme dense and pretended impenetrable body to the notice whereof we can arriue this percussion of atomes must be found and they will haue no difficulty in running through nor by meanes of it in striking any other body lying vnder the shelter of it and thus both in and from that hard body there must be still an vninterrupted continuation of grauity or of descending towardes the center Vnto which we may adde that the stone or dense body can not lye so close to the rocke that couereth it but that some ayre must be betweene for if nothing were betweene they would be vnited and become one continued body and in that ayre which is a creeke of the great ocean of ayre spread ouer the world that is euery where bestrewed with moouing atomes and which is continually fed like a running streame with new ayre that driueth on the ayre it ouertaketh there is no doubt but there are descending atomes as well as in all the rest of its maine body and these descending atomes meeting with the stone must needes giue some stroake vpon it and that stroake be it neuer so litle can not choose but worke some effect in making the stone remooue a litle that way they goe and that motion whereby the space is enlarged betweene the stone and the sheltering rocke must draw in a greater quantity of ayre and atomes to strike vpon it And thus by litle and litle the stone passeth through all the degrees of tardity by which a descending body parteth from rest which is by so much the more speedily done by how much the body is more eminent in density But this difference of time in regard of the atomes stroakes onely and abstracting from the bodies density will be insensible to vs seeing as we haue said no more is required of them but to giue a determination downewardes And out of this we clearely see the reason why the same atomes striking vpon one body lying vpon the water do make it sinke and vpon an other they do not As for example if you lay vpon the superficies of some water a piece of iron and a piece of corke of equall biggenesse and of the same figure the iron will be beaten downe to the bottome and the corke will floate att the toppe The reason whereof is the different
proportions of the comparison of their densities with the density of water for as we haue said the efficacy and force of desceÌ„ding is to be measured by that So then the stroakes of the atomes being more efficacious vpon water then vpon corke because the density of water is greater then the density of corke considering the aboundance of ayre that is harboured in the large pores of it it followeth that the atomes will make the water goe downe more forcibly then they will corke But the density of iron exceeding the density of water the same stroakes will make the iron descend faster then the water and consequently the iron must sinke in the water and the corke will swimme vpon it And this same is the cause why if a piece of corke be held by force att the bottome of the water it will rise vp to the toppe of the water as soone as the violence is taken away that kept it downe for the atomes stroakes hauing more force vpon the water then vpon the corke they make the water sinke and slide vnder it first a litle thinne plate of water and then an other a litle thicker and so by degrees more and more till it hath lifted the corke quite vp to the toppe Fiâ—thly it may be obiected that these atomes do not descend alwayse perpendicularly be sometimes sloapingly and in that case if their stroakes be the cause of dense bodies mouing they should moue sloaping and not downeward Now that these atomes descend sometimes sloapingly is euident as when for example they meete with a streame of water or with a strong wind or euen with any other litle motion of the ayre such as carryeth feathers vp and downe hither and thither which must needes waft the atomes in some measure along with them their way seeing then that such a gentle motion of the ayre is able to putt a feather out of its way notwithstanding the percussions of the atomes vpon it why shall it not likewise putt a piece of iron out of its way downewardes since the iron hath nothing from the atomes but a determination to its way But much more why should not a strong wind or a current of water do it since the atomes themselues that giue the iron its determination must needes be hurryed along with them To this we answere that we must consider how any wind or water which runneth in that sort is it selfe originally full of such atomes which continually and euery where presse into it and cutt through it in pursuing their constant perpetuall course of descending in such sort as we haue shewed in their running through any hard rocke or other densest body And these atomes do make the wind or the water primarily tend downewardes though other accidentall causes impell them secondarily to a sloaping motion And still their primary naturall motion will be in truth strongest though their not hauing scope to obey that but their hauing enough to obey the violent motion maketh this become the more obseruable Which appeareth euidently out of this that if there be a hole in the bottome of the pipe that conueyeth water sloapingly be the pipe neuer so long and consequently the sloaping motion neuer so forcible yet the water will runne out att that hole to obey its more powerfull impulse to the centerwardes rather then continue the violent motion in which it had arriued to a great degree of celerity Which being so it is easy to conceiue that the atomes in the wind or water which mooue perpendicularly downewardes will still continue the irons motion downewardes notwithstanding the mediums sloaping motion since the preuailing force determineth both the iron and the medium downewardes and the iron hath a superproportion of density to cutt its way according as the preualent motion determineth it But if the descending atomes be in part carryed along downe the streame by the current of wind or water yet still the current bringeth with it new atomes into the place of those that are carryed away and these atomes in euery point of place wheresoeuer they are do of themselues tend perpendicularly downewardes howbeit they are forced from the complete effect of their tendance by the violence of the current so that in this case they are mooued by a declining motion compounded of their owne naturall motion and of the forced motion with which the streame carryeth them Now then if a dense body do fall into such a current where these different motions giue their seuerall impulses it will be carryed in such sort as we say of the atomes but in an other proportion not in a perpendicular but in a mixt declining line compounded of the seuerall impulses which the atomes and the current do giue it in which also it is to be remembred how the current giueth an impulse downewardes as well as sloaping and peraduenture the strongest downewardes and the declination will be more or lesse according as the violent impulse preuayleth more or lesse against the naturall motion But this is not all that is to be considered in estimating the declination of a dense bodies motion when it is sinking in a current of wind or water you must remember that the dense body it selfe hath a particular vertue of its owne namely its density by which it receiueth and prosecuteth more fully its determination downewardes and therefore the force of that body in cutting its way through the medium is also to be considered in this case as well as aboue in calculating its declining from the perpendicular and out of all these causes will result a middle declination coÌ„pounded of the motioÌ„ of the water or wind both wayse and of its owne motion by the perpendicular line And since of these three causes of a dense bodies motion it s owne vertue in prosecuting by its density the determination it requireth is the most efficacious by much after it hath once receiued a determination from without its declination will be but litle if it be very dense and heauy But if it recede much from density so as to haue some neere proportion to the density of the medium the declination will be great And in a word according as the body is heauyer or lighter the declination will be more or lesse in the same current though not exactly according to the proportion of the diminishing of its density as long as there is a superproportion of its density to the medium since that such a superproportion as we haue declared heretofore maketh the mediums operation vpon the dense body scarce considerable And hence you see why a stone or piece of iron is not carried out of its way as well as feather because the stones motion downewardes is greater and stronger then the motion of a feather downewardes And by consequence the force that can deturne a feather from its course downewardes is not able to deturne a stone And if it be replyed that it may be so ordered that the stone shall haue no motion before
it be in the streame of a riuer and notwithstanding it will still mooue downewardes we may answere that considering the litle decliuity of the bed of such a streame the strongest motion of the partes of the streame must necessarily be downewardes and consequently they will beate the stone downewardes And if they do not the like to a feather or other light body it is because other partes of the streame do gett vnder the light body and beate it vpwardes which they haue not power enough to do to the stone Sixthly it may be obiected that if Elements do not weigh in their owne spheres then their grauity and descending must proceede from some other cause and not from this percussion of the atomes we attribute it to which percussion we haue determined goeth through all bodies whatsoeuer and beateth vpon euery sensible part of them But that Elements weigh not in their owne spheres appeareth out of the experience of a syphon for though one legge of the syphon be suncke neuer so much deeper into the body of the water then the other legge reacheth below the superficies of the water neuerthelesse if once the outward legge become full of water it will draw it out of the other longer legge which it should not do if the partes of water that are comprised within their whole bulke did weigh seeing that the bulke of water is much greater in the sunke legge then in the other and therefore these should rather draw backe the other water into the cisterne then be themselues drawne out of it into the ayre To this we answere that it is euident the Elements do weigh in their owne spheres att least as farre as we can reach to their spheres for we see that a ballone stuffed hard with ayre is heauyer then an empty one Againe more water would not be heauyer then lesse if the inward partes of it did not weigh and if a hole were digged in the bottome of the sea the water would not runne into it and fill it if it did not grauitate ouer it Lastly there are those who vndertake to distinguish in a deepe water the diuers weights which seuerall partes of it haue as they grow still heauyer and heauyer towardes the bottome and they are so cunning in this art that they professe to make instruments which by their equality of their weight to a determinate part of the water shall stand iust in that part and neyther rise nor fall higher or lower but if it be putt lower it shall ascend to its exact equally weighing orbe of the water and if it be putt higher it shall descend vntill it cometh to rest precisely in that place Whence it is euident that partes of water do weigh within the bulke of their maine body and of the like we haue no reason to doubt in the other two weighty Elements As for the opposition of the syphon we referre that point to where we shall haue occasion to declare the nature of that engine of sett purpose And there we shall shew that it could not succeede in its operation vnlesse the partes of water did grauitate in their maine bulke into which one legge of the syphon is sunke Lastly it may be obiected that if there were such a course of atomes as we say and that their stroakes were the cause of so notable an effect as the grauity of heauy bodies we should feele it palpably in our owne bodies which experience sheweth vs we do not To this we answere first that their is no necessity we should feele this course of atomes since by their subtility they penetrate all bodies and consequently do not giue such stroakes as are sensible Secondly if we consider that dustes and strawes and feathers do light vpon vs without causing any sense in vs much more we may cōceiue that atomes which are infinitely more subtile and light can not cause in vs any feeling of them Thirdly we see that what is continuall with vs and mingled in all thinges doth not make vs take any especiall notice of it and this is the case of the smiting of atomes Neuerthelesse peraduenture we feele them in truth as often as we feele hoat and cold weather and in all catarres or other such changes which do as it were sinke into our body without our perceiuing any sensible cause of them for no question but these atomes are the immediate causes of all good and bad qualities in the ayre Lastly when we consider that we can not long together hold out our arme att length or our foote from the ground and reflect vpon such like impotencies of our resisting the grauity of our owne body we can not doubt but that in these cases we feele the effect of these atomes working vpon those partes although we can not by our sense discerne immediately that these are the causes of it But now it is time to draw our Reader out of a difficulty which may peraduenture haue perplexed him in the greatest part of what he hath hitherto gone ouer In our inuestigation of the Elements we tooke for a principle therevnto that grauity is sometimes more sometimes lesse then the density of the body in which it is But in our explication of rarity and density and againe in our explication of grauity we seeme to putt that grauity and density is all one This thorne I apprehend may in all this distance haue putt some to paine but it was impossible for mee to remedy it because I had not yet deliuered the manner of grauitation Here then I will do my best to asswage their greefe by reconciling these appearing repugnancies We are therefore to consider that density in it selfe doth signify a difficultie to haue the partes of its subiect in which it is seperated one from an other and that grauity likewise in it selfe doth signify a quality by which a heauy body doth descend towardes the center or which is consequent therevnto a force to make an other body descend Now this power we haue shewed doth belong vnto density so farre forth as a dense body being strucken by an other doth not yield by suffering its partes to be diuided but with its whole bulke striketh the next before it and diuideth it if it be more diuisible then it selfe is So that you see density hath the name of density in consideration of a passiue quality or rather of an impassibility which it hath and the same density is called grauity in respect of an actiue quality it hath which followeth this impassibility And both of them are estimated by the different respects which the same body or subiect in which they are haue vnto different bodies that are the termes whereunto it is compared for the actiue quality or grauity of a dense body is esteemed by its respect to the body it striketh vpon whereas its density includeth a respect singly to the body that striketh it Now it is no wonder that this change of comparison worketh a disparity
in the denominations and that thereby the same body may be conceiued to be more or lesse impartible then it is actiue or heauy As for example lett vs of a dense Element take any one least part which must of necessity be in its owne nature and kind absolutely impartible and yet it is euident that the grauity of this part must be exceeding litle by reason of the litlenesse of its quantity so that thus you see an extremity of the effect of density ioyned together in one body by the accident of the litlenesse of it with a contrary extremity of the effect of grauity or rather with the want of it each of them within the limits of the same species In like manner it happeneth that the same body in one circumstance is more weighty in an other or rather in the contrary is more partible so water when it is in a payle because it is thereby hindered froÌ„ spreading abroad hath the effect of grauity predominating in it but if it be poured out it hath the effect of partibility more And thus it happeneth that meerely by the gradation of rarity and density one dense body may be apt out of the generall course of naturall causes to be more diuisible theÌ„ to be a diuider though according to the nature of the degrees considered absolutely in theÌ„selues what is more powerfull to diuide is also more resisteÌ„t and harder to be diuided And this arriueth in that degree which maketh water for the falling and beating of the atomes vpon water hath the power both to diuide it and to makâ— it descend but so that by making it descend it diuideth it And therefore we say that it hath more grautty then density though it be the very density of it which is the cause that maketh it partible by the working of one part vpon an other for if the atomes did not find the body so dense as it is they could not by their beating vpon one part make an other be diuided So that a dense body to be more heauy then dense signifyeth nothing else but that it is in such a degree of density â—hat some of its owne partes by their being assisted and sett on worke by a generall cause which is the fall of the atomes are powerfull enough to diuide other adioyning partes of the same density with them one from an other in such sort as we see that water poured out of an eawer into a basen where there is already other water hath the power to diuide the water in the basen by the assistance of the celerity which it getteth in descending And now I hope the reader is fully satisfyed that there is no contradiction in putting Density and Grauity to be the same thing materially and that neuerthelesse the same thing may be more heauy then dense or more dense then heauy as we tooke it to our seuerall purposes in the inuestigation of the Elements Hauing thus layed an intelligible ground to discouer how these motions that are generall to all bodies and are naturall in chiefe are contriued by nature we will now endeauour to shew that the contrary position is not onely voluntary but also impossible Lett vs therefore suppose that a body hath a quality to mooue it downewardes And first wee shall aske what downewardes signifyeth for eyther it signifyeth towardes a fixed point of imaginary space or towardes a fixed point of the vniuerse or towardes some mooueable point As for the first who would maintaine it must haue more imagination then iudgment to thinke that a naturall quality could haue an essence determined by a nothing because we can frame a conceit of that nothing As for the second it is very vncertaine whether any such point be in nature for as for the center of the earth it is cleare that if the earth be carryed about the center of it can not be a fixed point Againe if the center signifyeth a determinate point in the earth that is the medium of grauity or of quantity it is changed as often as any dust lighteth vnequally vpon any one side of the earth which would make that side bigger then it was and I doubt a quality can not haue morall considerations to thinke that so litle doth no harme As for the third position likewise it is not intelligible how a quality should change its inclination or essence according to the change that should light to make now one point now an other be the center vnto which it should tend Againe lett vs consider that a quality hath a determinate essence Then seeing its power is to mooue and to moue signifyeth to cutt the mediuÌ„ it is mooued in it belongeth vnto it of its nature to cutt so much of such a medium in such a time So that if no other cause be added but that you take precisely and 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 it is cleare that the being able to cutt so much of such a medium in such a time is not the essence of this quality as it was supposed to be Diuiding then the time and the medium halfe the motion should de made in halfe the time a quarter of the motion in a quarter of the time and so without end as farre as you can diuide But this is demonstratiuely impossible sithhence it is demonstrated that a mooueable coming from rest must of necessity passe through all degrees of tardity and therefore by the demonstration cited out of Galileus we may take a part in which this grauity can not mooue its body in a proportionate part of time through a proportionate part of the mediuÌ„ But because in naturall Theorems experiences are naturally required lett vs see whether nature giueth vs any testimony of this verity To that purpose we may consider a plummet hanged in a small string from a beame which being lifted vp gentlely on the one side att the extent of the string and permitted to fall meerely by the power of grauity it will ascend very neere as high on the contrary side as the place it was held in from whence it fell In this experiment we may note two thinges the first that if grauity be a quality it worketh against its owne nature in lifting vp the plumett seing its nature is onely to carry it downe For though it may be answered that it is not the grauity but an other quality called vis impressa which carrieth it vp neuerthelesse it can not be denyed but that grauity is either the immediate or at least the mediate cause which maketh this vis impressa the effect whereof being contrary to the nature of grauity it is absurd to make grauity the cause of it that is the cause of an essence whose nature is contrary to its owne And the same argument will proceede though you putt not vis impressa but suppose some other thing to be
surfaces 9 A body of greater partes and greater pores maketh a greater refraction then one of lesser partes and lesser pores 10 A coÌ„firmation of the former doctrine out of the nature of bodies that refract light 1 The coÌ„nexion of this chapter with the rest and the Authors intent in it 2 That there is a least cise of bodies and that this least cise is found in fire 3 The first coniunction of partes is in bodies of least cise and it is made by the force of Quantity 4 The second sort of coniunction is coÌ„pactednesse in simple Elements and it proceedeth from density 5 The third coniunction is of partes of different Elements and it proceedeth from quantity and density together 6 The reason why liquide bodies do easily ioyne together and dry ones difficultly 7 That no two hard bodies can touch one an other immediately 8 How mixed bodies arâ— framed in generall 9 The cause of the seuerall degrees of solidity in mixed bodies 10 The rule wherevnto are reduced all the seuerall combinations of Elements in compounding of mixed bodies 11 Earth and water are the basis of all permanent mixed bodies 12 What kind of bodies those are where water is the basis and earth the predominant Element ouer the other two 13 Of those bodies where water being the basis ayre is the predominant Element 14 What kind of bodies result where water is the basis and fire the predominant Element 15 Of those bodies where water is in excesse it alone being both the basis and the predominant Element 16 Of those bodies where Earth alone is the basis and also the predominant in excesse ouer the other threâ— Elements 17 Of those bodies where Earth is the basis and water the predominâ—t Element ouer the other two 18 Of those bodies where earth being the basis ayre is the predominant 19 Of those bodies where Earth being the basis fire is the predominant 20 All the second qualities of mixed bodies arise from seuerall combinations of the first qualities and are att last resolued into seuerall degrees of rarity and density 21 That in the planets and starres there is a like varietâ— of mixed bodies caused by light as here vpon Earth 22 In what maÌ„ner the Elements do worke vpon one an other in the compositioÌ„ of mixed bodies and in particular fire which is the most actiue 23 A particular declaration touching the generation of mettalls 1 Why some bodies are brittle and others tough or apt to withstand outward violence the first instrument to dissolue mixed bodies 2 How outward violence doth worke vpon the most compacted bodies 3 The seuerall effects of fire the second and chiefest instrumeÌ„t to dissolue all coÌ„pounded bodies 4 The reason why some bodies are not dissolued by fire 5 The reason why fire molteth gold but can not consume it 6 Why leade is easily consumed and calcined by fire 7 Why and how some bodies are diuided by fire into spirits waters oyles saltes and earth And what those partes are 8 How water the third iâ—strumeÌ„t to dissolue bodies dissolueth calx into salt and so into Terra damnata 9 How water mingled with salt becometh a most powerfull Agent to dissolue other bodies 10 How putrefactioÌ„ is caused 1 What is the sphere of actiuity in corporeall Agents 2 The reason why no body can worke in distance 3 An obiection answered against the manner of explicating the former axiomâ— 4 Of reaction and first in pure locall motion that each AgeÌ„t must suffer in acting and actâ— in suffering 5 The former doctrine applyed to other locall motions designed by particular names And that Suisseths argument is of no force against this way of doctrine 6 Why some notions do admitt of intension and Remission and others do not 7 That in euery part of our habitable world all the foure ElemeÌ„ts are found pure in small atomes but not in any great bulke 1 The Authors intent in this and the following chapters Mr. Thomas White 2 That bodies may be rarifyed both by outward and inward heat and how this is performed 3 Of the great effects of Rarefaction 4 The first manner of condensation by heate 5 The second manner of condensation by cold 6 That yce is not water rarifyed but condensed 7 How wind snow and haile are made and wind by raine allayed 8 How partes of the same or diuers bodies are ioyned more strongly together by condensation 9 Vacuites can not be the reason why water impregnated to the full with one kind of salt will notwithstaÌ„ding receiue more of an other 10 The true reason of the former effect 11 The reason why bodies of the same nature do ioyne more easily together then others 1 What AttractioÌ„ is and from whence it proceedeth 2 The true sense of the Maxime that Nature abhorreth from vacuity 3 The true reasâ— of attraction 4 Water may be brought by the force of attraction to what height soeuer 5 The doctrine touching the attraction of water in syphons 6 That the syphon doth not proue water to weigh in its owne orbe 7 Concerning attraction caused by fire 8 Concerning attractioÌ„ made by vertue of hoat bodies amulets etc. 9 The naturall reason giuen for diuers operations esteemed by some to be magicall 1 What is Filtration and how it is effected 2 What causeth the water in filtration to ascend 3 Why the filter will not droppe vnlesse the labell hang lower then the water 4 Of the motion of Restitution and why some bodies stand bent others not 5 Why some bodies returne onely in part to their natural figure others entirely 6 Concerning the nature of those bodies which do shrinke and stretch 7 How great and wonderfull effects proceed from small plaine and simple principles 8 Concerning Electricall attraction and the causes of it 9 Cabeus his opinion refuted concerning the cause of Electricall motâ—ons 1 The extreme heat of the sunne vnder the zodiacke draweth a streame of ayre from each Pole into the torride zone Chap. 18. §. 7. 2 The atomes of these two streames coming together are apt to incorporate with one an other 3 By the meeting and mingling together of these streames att the Equator diuers riuolets of atomes of each Pole are continuatâ—d from one Pole to the other 4 Of these atomes incorporated with some fitt matter in the bowels of the earth is made a stone 5 This stone worketh by emanations ioyned with agreeing streames that meete them in the ayre and in fine it is a loadestone 6 A methode for making experiences vpon any subiect 7 The Loadestones generatioÌ„ by atomes flowing from both Poles is confirmed by experiments obserued in the stone it selfe 8 Experiments to proue that the loadestone worketh by emanations meeting with agreeing streames 1 The operations of the loadestone are wrought by bodies and not by qualities 2 Obiections against the former positioÌ„ answered 3 The loadestone is imbued