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
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
of states in regard of more and lesse in the same kind These thinges being premised and calling to mind that it is the nature of density to make the partes of a dense thing compact and sticke together and be hardly diuisible and on the contrary side that it is the nature of rarity to diffuse and extend a rare thing and to prepare and approach it to diuision according to the proportion of the degree of rarity which it hath and that weight doth abound where there is excesse of density and is very litle or none in excesse of rarity wee may now begin in our imagination to putt these qualities into the scales one against an other to see what effects they produce in bodies And first lett vs weigh grauity against density or sticking together of partes which sticking or compactednesse being naturall to density requireth some excesse of grauity in proportion to the density or some other outward violence to breake it If then in a dense body the grauity ouercome the density and do make the partes of it breake a sunder it will draw them downewardes towards the center that grauity tendeth vnto and will neuer lett them rest till they come thither vnlesse some impediment meete them by the way and stoppe theire iourney so that such a body will as neere as possibly it can lye in a perfect sphericall figure in respect of the center and the partes of it will be changed and altered and thrust on any side that is the ready way thither so that by the force of grauity working vpon it it will runne as farre as it meeteth with nothing to hinder it from attaining this sphericall superficies Wherefore such bodies for the most part haue noe settled outside of theire owne but do receiue theire figure and limits from such letts as hinder them from attaining to that sphericalnesse they ayme att Now Aristotle whose definitions are in these matters generally receiued as fully expressing the notions of mankind telleth vs and our owne experience confirmeth it that wee vse to call those thinges moist which runne in such sort as wee haue here sett downe and that wee terme those thinges dry which haue a consistence within themselues and which to enioy a determinate figure do not require the stoppe or hinderance of an other body to limit and circle them in which will be the nature of those that haue a greater proportion of density in respect of theire grauity And thus out of the comparison of density with weight wee haue found two more qualities then wee yett had mett withall namely wettenesse and drynesse For although a body be dense which of its owne nature singly considered would preserue the continuity of its partes as making the body hardly diuisible whereby it would be dry yet if the grauity that worketh vpon it be in proportion greater then the density it will seuer the partes of it and make them runne to the center and so become fluide and moist though not in the eminentest degree that may be of fluidity and moisture by reason that if the like ouerproportion of grauity happen in a rare body it will there more powerfully worke its effect then it can in a dense body because a rare body will more easily obey and yield to the grauity that mastereth it then a dense one will and consequently will be more fluide and moist then it Now on the other side in weighing rarity against grauity if it happen that the rarity ouercome the grauity then the grauity will not change the figure of a body so proportioned but what figure it hath from its proper naturall causes the same will still remaine with it and consequently such a body will haue termes of its owne and will not require an ambient body to limit and circle it in which nature wee call dry But if the proportion of the grauity be the greater and do ouercome the rarity then by how much the rarity is greater so much the more will the grauity force it to apply it selfe equally and on all sides to the center and such a body will the more easily receiue its figure from an other and will be lesse able to consist of it selfe which properties wee attribute to wettenesse or moisture So that it appeareth how the qualities of wett and dry which first wee found in thinges that were dense are also common to that nature of bodies which wee terme rare And thus by our first inquiry after what kind of bodies do result out of the compounding of rarity and density with grauity wee discouer foure different sortes some dense ones that are dry and others likewise dense that are moist then againe some rare ones that are likewise moist and other rare ones that are dry But wee must not rest here lett vs proceede a litle further to search what other properties these foure kindes of bodies will haue which wee shall best discouer if wee apply them seuerally to some other compounded body of which nature are all those wee conuerse with or see and then consider the effects which these do worke vpon it To beginne with that which wee said is so excessiuely rare that grauity hath no power ouer it If wee looke vpon the multitude of litle partes it may be diuided into whereof euery one will subsist by it selfe for wee haue already prooued it dry and then suppose them to be mooued with force and strength against the body wee apply them to it must necessarily follow that they will forcibly gett into the porousnesse of it and passe with violence betweene part and part and of necessity seperate the partes of that thing one from an other as a knife or wedge doth a solide substance by hauing theire thinnest partes pressed into it so that if in the compounded thing some partes be more weighty others more light as of necessity there must be the heauiest will all fall lowest the lightest will fly vppermost and those which are of a meane nature betweene the two extremes will remaine in the middle In summe by this action of an extreme rare body vpon a compounded one all the partes of one kind that were in the compounded one will be gathered into one place and those of diuers kindes into diuers places which is the notion whereby Aristotle hath expressed the nature of heate and is an effect which dayly experience in burning and boyling teacheth vs to proceede from heate And therefore wee can not doubt but that such extreme rare bodies are as well hoat as dry On the other side if a dense thing be applyed to a compound it will because it is weighty presse it together and if that application be continued on all sides so that noe part of the body that is pressed be free from the siege of the dense body that presseth it it will forme it into a narrower roome and keepe in the partes of it not permitting any of them to slippe out So that what thinges soeuer
light which two termes passe through all the bodies we haue notice of Therefore proceeding vpon our groundes before layed to witt that no body can be mooued of it selfe wee may determine those motions to be naturall vnto bodies which haue constant causes or percutients to make them alwayse in such bodies and those violent which are contrary to such naturall motions Which being supposed we must search out the causes that so constantly make some bodies descend towardes the center or middle of the earth and others to rise and goe from the center by which the world is subiect to those restlesse motions that keepe all thinges in perpetuall fluxe in this changeing sphere of action and passion Lett vs then begin with considering what effects the sunne which is a constant and perpetuall cause worketh vpon inferior bodies by his being regularly sometimes present and sometimes absent Obserue in a pott of water hanging ouer a fire how the heate maketh some partes of the water to ascend and others to supply the roome by descending so that as long as it boyleth it is in a perpetuall confused motion vp and downe Now hauing formely cōcluded that fire is light and light is fire it can not be doubted but that the sunne doth serue instead of fire to our globe of earth and water which may be fittly compared to the boyling pott and all the day long draweth vapors from those bodies that his beames strike vpon For he shooting his little darts of fire in multitudes and in continued streames from his owne center against the Python the earth we liue on they do there ouertake one an other and cause some degree of heate as farre as they sinke in But not being able by reason of their great expansion in their long iorney to conuert it into their owne nature and sett it on fire which requireth a high degree of condensation of the beames they do but pierce and diuide it very subtilely and cutt some of the outward partes of it into extreme litle atomes Vnto which they sticking very close and being in a manner incorporated with them by reason of the moisture that is in thē they do in their rebound backe from the earth carry them along with them like a ball that struck against a moist wall doth in its returne from it bring backe some of the mortar sticking vpon it For the distance of the earth from the sunne is not the vtmost periode of these nimble bodies flight so that when by this solide body they are stopped in their course forwardes on they leape backe from it and carry some litle partes of it with them some of them a farther some of them a shorter iorney according as their litlenesse and rarity make them fitt to ascend As is manifest by the consent of all authors that write of the regions of the ayre who determine the lower region to reach as farre as the reflexion of the sunne and conclude this region to be very hoat For if we marke how the heate of fire is greatest when it is incorporated in some dense body as in iron or in seacoale we shall easily conceiue that the heate of this region proceedeth mainely out of the incorporation of light with those litle bodies which sticke to it in its reflexion And experience testifyeth the same both in our sultry dayes which we see are of a grosse temper and ordinarily goe before raine as also in the hoat springes of extreme cold countries where the first heates are vnsufferable which proceede out of the resolution of humidity congealed and in hoat windes which the Spaniards call Bochornos from Boca de horno by allusion to the breathing steame of an ouen when it is opened which do manifestly shew that the heate of the sunne is incorporated in the litle bodies which compose the steame of that wind And by the principles we haue already layed the same would be euident though we had no experience to instruct vs for seeing that the body of fire is dry the wett partes which are easilyest resolued by fire must needes sticke vnto them and accompany them in their returne from the earth Now whiles these ascend the ayre must needes cause others that are of a grosser complexion to descend as fast to make roome for the former and to fill the places they left that there may be no vacuity in nature And to find what partes they are and from whence they come that succeede in the roome of light and atomes glewed together that thus ascend we may take a hinte from the maxime of the Optikes that light reflecting maketh equall angles whence supposing the superficies of the earth to be circular it will follow that a perpendicular to the center passeth iust in the middle betweene the two rayes the incident and the reflected Wherefore the ayre betweene these two rayes and such dodies as are in it being equally pressed on both sides those bodies which are iust in the middle are neerest and likelyest to succeede immediately in the roome of the light and atomes which ascend from the superficies of the earth and their motion to that point is vpon the perpendicular Hence it is euident that the ayre and all such bodies as descend to supply the place of light and atomes which ascend from the earth do descend perpendicularly towardes the center of the earth And againe such bodies as by the force of light being cutt from the earth or water do not ascend in forme of light but do incorporate a hidden light and heate within them and thereby are rarer then these descending bodies must of necessity be lifted vp by the descent of those denser bodies that goe downewardes because they by reason of their density are mooued with a greater force And this lifting vp must be in a perpendicular line because the others descending on all sides perpendicularly must needes raise those that are betweene them equally from all sides that is perpendicularly from the center of the earth And thus we see a motion sett on foote of some bodies continually descending and others continually ascending all in perpendicular lines excepting those which follow the course of lights reflexion Againe as soone as the declining sunne groweth weaker or leaueth our horizon and that his beames vanishing do leaue the litle horsemen which rode vpon them to their owne temper and nature from whence they forced them they finding themselues surrounded by a smart descending streame do tumble downe againe in the night as fast as in the day they were carryed vp and crowding into their former habitations they exclude those that they find had vsurped them in their absence And thus all bodies within reach of the sunnes power but especially our ayre are in perpetuall motion the more rarifyed ones ascending and the dense ones descending Now thē because no bodies wheresoeuer they be as we haue already shewed haue any inclination to moue towardes a particular place otherwise thē as they are
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
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
our whole scope both in this and in all other occasions where like qualities are vrged is to prooue superfluous and ill grounded in nature and to be but meere termes to confound and leaue in the darke whosoeuer is forced to fly vnto them THE THERTEENTH CHAPTER Of three sortes of violent motion Reflexion Vndulation and Refraction THe motion we haue last spoken of because it is ordinarily either in part or wholy contrary to grauity which is accounted the naturall motion of most bodies vseth to be called violent or forced And thus you haue deliuered vnto you the natures and causes both of naturall and of forced motion yet it remaineth that we aduertise you of some particular kindes of this forced motion which seeme to be different from it but indeed are not As first the motion of reflexion which if we do but consider how forced motion is made we shall find that it is nothing else but a forced motion whose line wherevpon it is made is as it were snapped in two by the encounter of a hard body For euen as we see in a spoute of water that is strongly shott against a wall the water following driueth the precedent partes first to the wall and afterwardes coming themselues to the wall forceth them againe an other way from the wall right so the latter partes of the torrent of ayre which is caused by the force that occasioneth the forced motion driueth the former partes first vpon the resistent body and afterwardes againe from it But this is more eminent in light then in any other body because light doth lesse rissent grauity and so obserueth the pure course of the stroake better then any other body from which others do for the most part decline some way by reason of their weight Now the particular law of reflexion is that the line incident and the line of reflexion must make equall angles with that line of the resistent superficies which is in the same superficies with themselues The demonstration whereof that great witt Renatus Des Cartes hath excellently sett downe in his booke of Dioptrikes by the example of a ball strucken by a rackett against the earth or any resisting body the substance where of is as followeth The motion which we call vndulation needeth no further explication for it is manifest that since a pendant when it is remooued from its perpendicular will restore it selfe therevnto by the naturall force of grauity and that in so doing it gaineth a velocity and therefore can not cease on a suddaine it must needes be carried out of the force of that motion directly the coÌ„trary way vntill the force of grauity ouercoming the velocity it must be brought backe againe to the perpeÌ„dicular which being done likewise with velocity it must send it againe towardes the place from which it fell att the first And in this course of motion it must coÌ„tinue for a while euery vndulation being weaker then other vntill att last it quite ceaseth by the course of nature settling the ayre in its due situatioÌ„ according to the naturall causes that worke vpon it And in this very manner also is performed that vndulation which we see in water when it is stirred from the naturall situation of its sphericall superficies Galileo hath noted that the time in which the vndulations are made which follow one an other of their owne accord is the same in euery one of them and that as much time precisely is take vp in a pendants going a very short arch towardes the end of its vibration as was in its going of the greatest arch att the beginning of its motion The reason whereof seemeth strange to him and he thinketh it to be an accident naturall to the body out of its grauity and that this effect conuinceth it is not the ayre which mooueth such bodies Whereas in truth it is clearely the ayre which causeth this effect Because the ayre striuing att each end where it is furthest from the force of the motion to quiett it selfe getteth att euery bout somewhat vpon the space and so contracteth that into a shorter arch That motion also which we call Refraction and is manifest to sense onely in light though peraduenture hereafter more diligent searchers of nature may likewise find it in such other bodies as are called qualities as in cold or heate c. is but a kind of Reflexion for there being certaine bodies in which the passages are so well ordered with their resistances that all the partes of them seeme to permitt light to passe through them and yet all partes of them seeme to reflect it when light passeth through such bodies it findeth att the very entrance of them such resistances where it passeth as serue it for a reflectent body and yet such a reflectent body as hindereth not the passage through but onely hindereth the passage from being in a straight line with the line incident Wherefore the light must needes take a plye as beaten from those partes towardes a line drawne from the illuminant and falling perpendicularly vpon the resisting superficies and therefore is termed by mathematicians to be refracted or broken towardes the Perpendicular Now at the very going out againe of the light the second superficies if it be parallel to the former must needes vpon a contrary cause strike it the contrary way which is termed from the Perpendicular But before we wade any deeper into this difficulty we can not omitt a word of the manner of explicating refraction which Monsieur Des Cartes vseth so witty a one as I am sorry it wanteth successe He therefore following the demonstration aboue giuen of reflexion supposeth the superficies which a ball lighteth vpon to be a thinne linnen cloth or some other such matter as will breake cleanely by the force of the ball striking smartly vpon it And because that superficies resisteth onely one way therefore he inferreth that the velocity of the ball is lessened onely one way and not the other so that the velocity of its motion that way in which it findeth no resistance must be after the balles passage through the linnen in a greater proportion to the velocity which it hath the other way where it findeth resistance then it was before And therefore the ball will in lesse time arriue to its periode on the one side then on the other and consequently it will leane towardes that side vnto which the course wherein it findeth no opposition doth carry it Which to shâ—w how it is contrary vnto his owne principle lett vs conceiue the cloth CE to be of some thickenesse and so draw the line OP to determine that thicknesse And lett vs make from B vpon AL an other Parallelogramme like the Parallelogramme AL whose diameter shall be BQ And it must necessarilly follow that the motion from B to Q if there were no resistance were in the same proportion as from A to B. But the proportion of the motion from
thriddes of iett or amber do in their streaming abroad meete with a piece of straw or of hay or of a dryed leafe or some such light and spungy body it is no maruayle if they glew themselues vnto it like birdlime and that in their shrinking backe by being condensed againe and repulsed through the coldnesse of the ayre they carry it along with them to their entire body Which they that onely see the effect and can not penetrate into a possibility of a naturall cause thereof are much troubled withall And this seemeth vnto me to beare a fairer semblance of truth then what Cabeus deliuereth for cause of Electricall attractions Whose speculation herein though I can not allow for solide yet I must for ingenious And certainely euen errors are to be commended when they are witty ones and do proceed from a casting further about then the beaten tracke of verball learning or rather termes which explicate not the nature of the thing in question He sayth that the coming of strawes and such other light bodies vnto amber iett and the like proceedeth from a wind raysed by the forcible breaking out of subtile emanations from the Electricall bodies into the ayre which bringeth those light bodies along with it to the Electricall ones But this discourse can not hold for first it is not the nature of vnctuous emanations Generally speaking to cause smart motions singly of themselues Secondly although they should rayse a wind I do not comprehend how this wind should driue bodies directly backe to the source that raysed it but rather any other way and so consequently should driue the light bodies it meeteth with in its way rather from then towardes the Electricall body Thirdly if there should be such a wind raysed and it should bring light bodies to the Electricall ones yet it could not make them sticke therevnto which we see they do turne them which way you will as though they were glewed together Neyther do his experiences conuince any thing for what he sayth that the light bodies are sometimes brought to the Electricall body with such a violence that they rebound backe from it and then returne againe to it maketh rather against him for if wind were the cause of their motion they would not returne againe after they had leaped backe from the Electricall body no more then we can imagine that the wind it selfe doth The like is of his other experience when he obserued that some little graines of sawdust hanging att an Electricall body the furthermost of them not onely fell of but seemed to be driuen away forcibly for they did not fall directly downe but sidewayes and besides did fly away with a violence and smartnesse that argued some strong impulse The reason whereof might be that new emanations might smite them which not sticking and fastening vpon them whereby to draw them neerer must needes push them further or it might be that the emanations vnto which they were glewed shrinking backe vnto their maine body the latter graines were shouldered of by others that already besieged the superficies and then the emanations retiring swiftly the graines must breake of with a force or else we may conceiue it was the force of the ayre that bore them vp a little which made an appearance of their being driuen away as we see feathers and other light thinges descend not straight downe THE TWENTIETH CHAPTER Of the Loadstones generation and its particular motions THere is yet remaining the great mystery of the Loadstone to discourse of Which all Authors both auntient and moderne haue agreed vpon as an vndenyable example and euidence of the shortenesse of mans reach in comprehending and of the impossibility of his reason in penetrating into and explicating such secrets as nature hath a mind to hide from vs. Wherefore our reader I am sure will not in this subiect expect cleare satisfaction or plaine demonstrations att our handes but will iugde we haue fairely acquitted our selues if what we say be any whitt plausible Therefore to vse our best endeauours to content him lett vs reflect vpon the disposition of partes of this habitable globe whereof we are tenants for liues And we shall find that the sunne by his constant course vnder the zodiake heateth a great part of it vnmeasurably more then he doth the rest And consequently that this zodiake being in the middest betweene two as it were endes which we call the Poles these poles must necessarily be extremely cold in respect of the torride zone for so we call that part of the earth which lyeth vnder the zodiake Now looking into the consequence of this we find that the sunne or the sunnes heate which reflecteth from the earth in the torride zone must rarify the ayre extremely and according to the nature of all heate and fire must needes carry away from thence many partes of the ayre and of the earth sticking to that heate in such sort as we haue formerly declared Whence it followeth that other ayre must necessarily come from the regions towardes both the poles to supply what is carryed away from the middle as is the course in other fires and as we haue explicated aboue especially cōsidering that the ayre which cometh from the polewardes is heauyer then the ayre of the torride zone and therefore must naturally presse to be still neerer the earth and so as it were shouldereth vp the ayre of the torride zone towardes the circumference by rouling into its place and this in great quantities and consequently the polar ayre must draw a great trayne after it Which if we consider the great extent of the torride zone we shall easily persuade our selues that it must reach on each side to the very pole for taking from Archimedes that the sphericall superficies of a portion of a spher◠is to the superficies of the whole sphere according as the part of the axis of that sphere comprised within the said portion is to the whole axis and considering that in our case the part of the axis comprised within the torride zone is to the whole axis of the earth in about the proportion of 4. to 10 it must of necessity follow that a fire or great heate raigning in so vast an extent will draw ayre very powerfully from the rest of the world Neyther lett any man apprehend that this course of the sunnes eleuating so great quantities of atomes in the torride zone should hinder the course of grauity there for first the medium is much rarer in the torride zone then in other partes of the earth and therefore the force of the descending atomes needeth not to be so great there as in other places to make bodies descend there as fast as they do else where Secondly there being a perpetuall supply of fresh ayre from the polar partes streaming continually into the torride zone it must of necessity happen that in the ayre there come atomes to the torride zone of that grossenesse that
they are Lett vs then in the next place consider what will follow in the rest of the body out of these varieties of passions once raysed in the hart and sent into the braine It is euidēt that according to the nature and quality of these motions the hart must needes in euery one of them voyde out of it selfe into the arteries a greater or lesser quantity of bloud and that in diuers fashions and the arteries which lye fittest to receiue these suddaine egestions of bloud are those which goe into the braine whose course being directly vpwardes we can not doubt but that it is the hoatest and subtilest part of the bloud and the fullest of spirits that flyeth that way These spirits then running a lōg and perplexed iourney vp and downe in the braine by various meanders and anfractuosities are there mingled with the humide steame of the braine it selfe and are therewith cooled and do come at the last to smoake at liberty in the hollow ventricles of the braine by reeking out of the little arteriall branches that do weaue the plexus choroides or nette we spoke of ere while and they being now growne heauy do fall by their naturall course into that part or processe of the braine which is called medulla spinalis or the marrow of the backe bone which being all besett by the nerues that runne through the body it can not happen otherwise but that these thickened and descending spirits must eyther fall themselues into those nerues or else presse into them other spirits which are before them that without such new force to driue them violently forwardes would haue slided downe more leisurely Now this motion being downewardes and meeting with no obstacle till it arriue vnto its vtmost periode that way the lowest nerues are those which naturally do feele the communication of these spirits first But it is true if the flowing tide of them be great and plentifull all the other nerues will also be so suddainely filled vpon the filling of the lowermost that the succession of their swellings will hardly be perceptible as a suddaine and violent inundation of water seemeth to rise on the sides of the channell as it doth at the milldamme though reason assureth vs it must beginne there because there it is first stopped On the contrary side if the spirits be few they may be in such a proportion as to fill only the lower nerues and to cōmunicate little of thēselues to any of the others And this is the case in the passion of feare which being stored with fewer spirits thē any other passiō that causeth a motiō in the body it moueth the legges most and so carryeth the animal that is affrayd with violence from the obiect that affrighteth him Although in truth it is a faint hope of escaping mingled with feare which begetteth this motion for when feare is single and at its height it stoppeth all motion by contracting the spirits and thence is called stupor as well as griefe for the same reason and accordingly we see extreme cowardes in the extremity of their feare haue not the courage to runne away no more then to defend or helpe themselues by any other motions But if there be more aboundance of spirits then the vpper partes are also moued as well as the legges whose motion contributeth to defense but the braine it selfe and the senses which are in the head being the first in the course of this flood of spirits that is sent from the hart to the head it is impossible but that some part of them should be pressed into the nerues of those senses and so will make the animal vigilant and attentiue to the cause of its feare or griefe But if the feare be so great that it contracteth all the spirits and quite hindereth their motion as in the case we touched aboue then it leaueth also the nerues of the senses destitute of spirits and so by too strong apprehension of a danger the animall neyther seeth nor apprehendeth it but as easily precipitateth it selfe into it as it happeneth to auoyde it being meerely gouerned by chance and may peraduenture seeme valiant through extremity of feare And thus you see in common how all the naturall operations of the body do follow by naturall consequence out of the passions of the mind without needing to attribute discourse or reason eyther to men or beastes to performe them Although at the first sight some of them may appeare vnto those that looke not into their principles and true causes to flow from a source of intelligence whereas it is euident by what wee haue layed open they all proceed from the due ranging and ordering of quantitatiue partes so or so proportioned by rarity and density And there is no doubt but who would follow this search deepely might certainly retriue the reasons of all those externall motions which wee see vse to accompany the seuerall passions in men and Beastes But for our intent wee haue said enough to shew by what kind or order and course of nature they may be effected without confining our selues ouer scrupulously to euery circumstance that we haue touched and to giue a hinte whereby others that will make this inquiry their taske may compile an intire and well grounded and intelligible doctrine of this matter Only we will adde one aduertissement more which is that these externall motions caused by passion are of two kindes for some of them are as it were the beginnings of the actions which nature intendeth to haue follow out of the passions that cause them but others are only bare signes of the passions that produce them and are made by the cōnexion of partes vnnecessary for the maine action that is to follow out of the passion with other partes that by the passion are necessarily moued as for example when an hungry mans mouth watereth at the sight of good meate it is a kind of beginning of eating or of preparation for eating for when we eate nature draweth a moysture into our mouth to humectate our meate and to conuey the tast of it into the nerues of the tongue which are to make report of it vnto the braine but when we laugh the motion of our face aymeth at no further end and followeth only by the connexion of those muscles which draw the face in such a sort vnto some inward partes that are moued by the passion out of which laughing proceedeth But we must not leaue this subiect without some mention of the diaphragma into which the other branch of those nerues that are called of the sixth coniugation doth come for the first branch we haue said goeth into the hart and carryeth thither the obiects that come into the braine and this we shall find carryeth backe to the braine the passion or motion which by the obiect is raysed in the hart Concerning this part of our body you are to note that it is a muscolous membrane which in the middle of it hath a
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
shelter of a thicke body doth not hinder the descent of that which is vnder it pag. 91. § 6. The reason why some bodies sinke others swimme pag. 92. § 7. The fifth obiection answered concerning the descending of heauy bodies in streames pag. 93. § 8. The sixt obiection answered and that all heauy elements do weigh in their owne spheres pag. 95. § 9. The seuenth obiection answered and the reason why we do not feele the course of the ayre and atomes that beate continually vpon vs. ibidem § 10. How in the same body grauity may be greater then density and density then grauity though they be the same thing pag. 96. § 11. The opinion of grauities being an intrinsecall inclination of a body to the center refuted by reason pag 97. § 12. The same opinion refuted by seuerall experiences pag. 98. CHAP. XII Of Violent Motion pag. 100. § 1. The state of the question touching the cause of violent motion ibid. § 2. That the medium is the onely cause which continueth violent motion ibidem § 3. A further explication of the former doctrine pag. 101. § 4. That the ayre hath strength enough to continue violent motion in a moueable pag. 102. § 5. An answere to the first obiection that ayre is not apt to conserue motion And how violent motion cometh to cease pag 103. § 6. An answere to the second obiection that the ayre hath no power ouer heauy bodies pag. 104. § 7. An answere to the third obiection that an arrow should fly faster broadwayes then long wayes pag. 105. CHAP. XIII Of three sortes of violent motion Reflexion Vndulation and Refraction pag. 106. § 1. That reflexion is a kind of violent motion ibid. § 2. Reflection is made at equall angles ibid. § 3. The causes and properties of vndulation pag. 107. § 4. Refraction at the entrance into the reflectent body is towardes the perpendicular at the going out it is from it when the second superficies is parallel to the first pag. 108. § 5. A refutation of Monsieur Des Cartes his explication of refraction pag. 109. § 6. An answere to the arguments brought in fauour of Monsieur Des Cartes his opinion pag. 111. § 7. The true cause of refraction of light both at its entrance and at its going out from the reflecting body pag. 112. § 8. A generall rule to know the nature of reflection and refractions in all sortes of surfaces pag. 113. § 9. A body of greater partes and greater pores maketh a greater refraction then one of lesser partes and lesser pores pag. 114. § 10. A confirmation of the former doctrine out of the nature of bodies that refract light pag. 115. CHAP. XIV Of the composition qualities and generation of Mixed bodies pag. 116. § 1. The connexion of this chapter with the rest and the Authors intent in it ibid. § 2. That there is a least cise of bodies and that this least cise is found in fire pag. 117. § 3. The first coniunction of partes is in bodies of least cise and it is made by the force of Quantity ibid. § 4. The second sort of coniunction is compactednesse in simple Elements and it procedeth from density pag. 118. § 5. The third coniunction is of parres of different Elements and it proceedeth from quantity and density together ibid. § 6. The reason why liquide bodies do easily ioyne together and dry ones difficultly pag. 119. § 7. That no two hard bodies can touch one an other immediately ibid. § 8. How mixed bodies are framed in generall pag. 121. § 9. The cause of the seuerall degrees of solidity in mixed bodies ibid. § 10. The rule where vnto are reduced all the seuerall combinations of Elements in compounding of mixed bodies pag. 122. § 11. Earth and water are the basis of all permanent mixed bodies pag. 123. § 12. What kind of bodies those are where water is the basis and earth the predominant Element ouer the other two ibid. § 13. Of those bodies where water being the basis ayre is the predominant Element ibid. § 14. What kind of bodies result where water is the basis and fire the predominant Element pag. 124. § 15. Of those bodies where water is in excesse it alone being both the basis and the predominant Element pag. 125. § 16. Of those bodies where Earth alone is the basis and also the predominant in excesse ouer the other three Elements ibid. § 17. Of those bodies where Earth is the basis and water the predominant Element ouer the other two ibid. § 18. Of those bodies where earth being the basis ayre is the predominant ibid. § 19. Of those bodies where Earth being the basis fire is the predominant pag. 126. § 20. All the secōd qualities of mixed bodies arise from seuerall combinations of the first qualities and are att last resolued into seuerall degrees of rarity and density ibid. § 21. That in the planets and starres there is a like variety of mixed bodies cause by light as here vpon Earth pag. 127. § 22. In what manner the Elements do worke vpon one an other in the composition of mixed bodies and in particular fire which is the most actiue ibid. § 23. A particular declaration touching the generation of mettalls pag. 128. CHAP. XV. Of the dissolution of Mixed bodies pag. 130. § 1. Why some bodies are brittle and others tough or apt to withstand outward violence the first instrument to dissolue mixed bodies ibid. § 2. How outward violence doth worke vpon the most compacted bodies pag. 131. § 3. The seueral effects of fire the second and chiefest instrument to dissolue all compounded bodies ibid. § 4. The reason why some bodies are not dissolued by fire pag. 132. § 5. The reason why fire melteth gold but can not consume it ibid. § 6. Why leade is easily consumed and calcined by fire pag. 133. § 7. Why and how some bodies are diuided by fire into spirits waters oyles saltes and earth And what those partes are ibid. § 8. How water the third instrument to dissolue bodies dissolueth calx into salt and so into Terra damnata pag. 135. § 9. How water mingled with salt becometh a most powerfull Agent to dissolue other bodies pag. 136. § 10. How putrefaction is caused ibid. CHAP. XVI An explication of certaine Maximes touching the operations and qualities of bodies and whether the Elements be found pure in any part of the world pag. 137. § 1. What is the sphere of actiuity in corporeall Agents ibid. § 2. The reason why no body can worke in distance pag. 138. § 3. An obiection answered against the manner of explicating the former axiome pag. 139 § 4. Of reaction and first in pure locall motion that each Agent must suffer in acting and acte in suffering ibid. § 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 pag. 141. § 6. Why some notions do admitt
to performe vitall motion pag. 203. § 1. The connexion of the following Chapters with the precedent ones ibid. § 2. Concerning seuerall compositions of mixed bodies pag. 204. § 3. Two sortes of liuing creatures pag. 205. § 4. An engine to expresse the first sort of liuing creatures ibid. § 5. An other engine by which may be expressed the second sort of liuing creatures pag. 207. § 6. The two former engines and some other comparisons applyed to expresse the two seuerall sortes of liuing creatures ibid. § 7. How plantes are framed pag. 209. § 8. How sensitiue creatures are formed pag. 210. CHAP. XXIV A more particular suruay of the generation of Animals in which is discouered what part of the animal is first generated pag. 213 § 1. The opinion that the seede containeth formally euery part of the parent ibid. § 2. The former opinion reiected pag. 214. § 3. The Authors opinion of this question pag. 215. § 4. Their opinion refuted who hold that euery thing containeth formally all thinges pag. 216. § 5. The Authors opinion concerning the generation of Animals declared and confirmed pag. 217. § 6. That one substance is changed into an other pag. 219. § 7. Concerning the hatching of chickens and the generation of other Animals pag. 220. § 8. From whence it happeneth that the deficiences or excrescences of the parents body are often seene in their children pag. 221 § 9. The difference betweene the Authors opinion and the former one p. 222 § 10. That the hart is imbued with the generall specifike vertues of the whole body whereby is confirmed the doctrine of the two former paragraphes pag. 223. § 11. That the hart is the first part generated in a liuing creature pag. 225. CHAP. XXV How a Plant or Animal cometh to that figure it hath pag. 226. § 1. That the figure of an Animal is produced by ordinarie second causes as well as any other corporeall effect pag. 226. § 2. That the seuerall figures of bodies proceed from a defect in one of â—he three dimensions caused by the concurrance of accidentall causes pag. 227 § 3. The former doctrine is confirmed by seuerall instances pag 228 § 4. The same doctrine applyed to Plantes pag. 229 § 5. The same doctrine declared in leafes of trees ibid. § 6. The same applyed to the bodies of Animals pag. 230 § 7. In what sense the Author doth admitt of Vis formatrix pag. 231 CHAP. XXVI How motion beginneth in liuing creatures And of the motion of the hart circulation of the bloud Nutrition Augmentation and corruption or death pag. 232 § 1. Fromwhence doth proceed the primary motion and growth in Plantes ibid. § 2. Monsieur des Cartes his opinion touching the motion of the hart p. 233 § 3. The former opinion reiected ibid. § 4. The Authors opinion concerning the motion of the hart pag. 234 § 5. The motion of the hart dependeth originally of its fibers irrigated by bloud pag. 236 § 6. An obiection answered against the former doctrine pag. 237 § 7. The circulation of the bloud and other effects that follow the motion of the hart pag. 238 § 8. Of Nutrition pag. 239 § 9. Of Augmentation pag. 240 § 10. Of death and sicknesse pag. 241 CHAP. XXVII Of the motions of sense and of the sensible qualities in generall and in particular of those which belong to Touch Tast and Smelling pag. 242 § 1. The connexion of the subsequent chapters with the precedent ibid. § 2. Of the senses and sensible qualities in generall And of the end for which they serue ibid. § 3. Of the sense of touching and that both it and its qualities are bodies 244 § 4. Of the tast and its qualities that they are bodies pag. 245 § 5. That the smell and its qualities are reall bodies ibid. § 6. Of the conformity betwixt the two senses of smelling and tasting p. 246 § 7. The reason why the sense of smelling is not so perfect in man as in beastes with a wonderfull historie of a man who could wind a sent as well as any beast pag. 247 CHAP. XXVIII Of the sense of hearing and of the sensible quality sound p. 249 § 1. Of the sense of hearing and that sound is purely motion ibid. § 2. Of diuers artes belonging to the sense of hearing all which confirme that sound is nothing but motion pag. 250 § 3. The same is confirmed by the effects caused by great noises pag. 251 § 4. That solide bodies may conueye the motion of the ayre or sound to the organe of hearing pag. 252 § 5. Where the motion is interrupted there is no sound ibid. § 6. That not only the motion of the ayre but all other motions coming to our eares make sounds pag. 253 § 7. How one sense may supply the want of an other ibid. § 8. Of one who could discerne sounds of words with his eyes pag. 254 § 9. Diuers reasons to proue sound to be nothing els but a motion of some reall body pag. 256 CHAP. XXIX Of Sight and Colours pag. 257 § 1. That Colours are nothing but light mingled with darkenesse or the disposition off a bodies superficies apt to reflect light so mingled ibid. § 2. Concerning the disposition of those bodies which produce white or blacke coulours pag. 259 § 3. The former doctrine confirmed by Aristotles authority reason and experience ibid. § 4. How the diuersity of coulours doe follow out of various degrees of rarity and density pag. 260 § 5. Why some bodies are Diaphanous others opacous pag. 261 § 6. The former doctrine of coulours confirmed by the generation of white and Blacke in bodies pag. 262 CHAP. XXX Of luminous or apparente Colours pag. 262 § 1. Apparitions of coulours through a prisme or triangular glasse are of two sortes ibid. § 2. The seuerall parts of the obiect make seuerall angles at their entrance into the prisme pag. 263 § 3. The reason why some times the same obiect appeareth throwgh the prisme in two places and in one place more liuely in the other place more dimme ibid. § 4. The reason of the various colours that appeare in looking throwgh a prisme pag. 264 § 5. The reason why the prisme in one position may make the colours appeare quite contrary to what they did when it was in an other position pag. 265 § 6. The reason of the various colours in generall by pure light passing through a prisme pag 266 § 7. Vpon what side euery colour appeareth that is made by pure light passing through a prisme pag. 267 CHAP. XXXI The causes of certaine appearances in luminous Colours with a conclusion of the discourse touching the senses and the sensible qualities pag. 268 § 1. The reason of each seuerall colour in particular caused by light passing through a prisme pag. 268 § 2. A difficult probleme resolued touching the prisme pag. 270 § 3. Of the rainebow and how by the colour of any body wee may know the composition of
thinges pag. 359 § 7. Respect or relation hath not really any formall being but only in the apprehension of man ibid. § 8. That Existence or being is the proper affection of man and that mans soule is a comparing power pag. 360 § 9. A thing by coming into the vnderstanding of man looseth nothing of its owne peculiar nature ibid. § 10. A multitude of thinges may be vnited in mans vnderstanding without being mingled or confounded together pag. 361 § 11. Of abstracted and concrete termes pag. 362 § 12. Of vniuersal notions pag. 363 § 13. Of apprehending a multitude vnder one notion pag. 364 § 14. The power of the vnderstanding reacheth as farre as the extent of being pag. 365 CHAP. II. Of Thinking and Knowing pag. 365 § 1. How a iudgement is made by the vnderstanding ibid. § 2. That two or more apprehensions are identifyed in the soule by vniting them in the stocke of being pag. 366 § 3. How the notions of a substantiue and an adiectiue are vnited in the soule by the common stocke of being pag. 367 § 4. That a settled iudgement becometh a part of our soule pag. 368 § 5. How the soule commeth to deeme or settle a iudgement ibid. § 6. How opinion is begotten in the vnderstanding pag. 371 § 7. How faith is begotten in the vnderstanding pag. 372 § 8. Why truth is the perfection of a reasonable soule and why it is not found in simple apprehensions as well as in Enuntiations ibid. § 9. What is a solid iudgement and what a slight one pag. 373 § 10. What is an acute iudgement and what a dull one pag. 375 § 11. In what consisteth quicknesse and Clearenesse of iudgement and there oposite vices ibid. CHAP. III. Of Discoursing pag. 376 § 1. How discourse is made ibid. § 2. Of the figures and moodes of Syllogismes ibid. § 3. That the life of man as man doth consist in discourse and of the vast extent of it pag. 377 § 4. Of humane actions and of those that concerne ourselues pag. 379 § 5. Of humane actions as they concerne our neighbours pag. 380 § 6. Of Logike ibid. § 7. Of Grammar pag. 381 § 8. Of Rhetorike ibid. § 9. Of Poetry pag. 382 § 10. Of the Power of speaking ibid. § 11. Of arts that concerne dumbe and insensible creatures pag. 383 § 13. Of Arithmetike ibid. § 14. Of Prudence ibid. § 15. Obseruations vpon what hath beene said in this Chapter pag. 384 CHAP. IIII. How a man proceedeth to Action pag. 386 § 1. That humane actions proceed from two seuerall principles vnderstanding and sense ibid. § 2. How our generall and inbred maximes doe concurre to humane action pag. 387 § 3. That the rules and maximes of arts doe worke positiuely in vs though we thinke not of them pag. 388 § 4. How the vnderstanding doth cast about when it wanteth sufficient grounds for action pag. 389 § 5. How reason doth rule ouer sense and passion ibid. § 6. How we recall our thoughts from distractions pag 390 § 7. How reason is sometimes ouercome by sense and passion pag. 391 CHAP. V. Containing proofes out of our single apprehensions that our soule is incorporeall pag. 393 § 1. The connection of the subsequent Chapters with the precedent ibid. § 2. The existence of corporeall thinges in the soule by the power of apprehension doth proue her to be immateriall pag. 394 § 3. The notion of being which is innate in the soule doth proue the same ibid. § 4. The same is proued by the notion of respects pag. 396 § 5. That corporeall thinges are spiritualized in the vnderstanding by meanes of the soules working in and by respects ibid. § 6. That thâ— abstracting of notions from all particular and indiuiduall accidents doth proue the immaterialitie of the soule pag. 397 § 7. That the vniuersalitie of abstracted notions doth proue the same ibid. § 8. That collectiue apprehensions do proue the same pag. 398 § 9. The operations of the soule drawing allwayes from multitude to vnitie do proue the same 399 § 10. The difference betwixt the notion of a thing in our vnderstanding and the impression that correspondeth to the same thing in our fansie doth proue the same pag. 400 § 11. The apprehension of negations and priuations do proue the same 401 CHAP. VI. Containing proofes of our soules operations in knowing or deeming any thing that she is of a spirituall nature pag. 400 § 1. The manner of iudging or deeming by apprehending two thinges to be idenâ—ified doth proue the soule to be immateriall ibid. § 2. The same is proued by the manner of apprehending opposition in a negatiue iudgement pag. 403 § 3. That thinges in themselues opposite to one an other hauing no opposition in the soule doth prooue the same pag. 404 § 4. That the first truthes are identified to the soule pag. 405 § 5. That the soule hath an infinite capacitie and consequently is immateriall pag. 406 § 6. That the opposition of contradictory propositions in the Soule doth proue her immaterialitie ibid. § 7. How propositions of eternall truth do proue the immaterialitie of the soule pag. 407 CHAP. VII That our discoursing doth prooue our soule to be incorpore all pag. 408 § 1. That in discoursing the soule containeth more in it at the same time then is in the fantasie which prooueth her to be immateriall ibid. § 2. That the nature of discourse doth prooue the soule to be ordered to infinite knowledge and consequently to be immateriall pag. 409 § 3. That the most naturall obiects of the soule are immateriall and consequently the soule her selfe is such ibid. CHAP. VIII Containing proofes out of our manner of proceeding to action that our soule is incorporeall pag. 410 § 1. That the soules being a power to order thinges proueth her to be immateriall ibid. § 2. That the soules being able to mooue without being mooued doth prooue her to be immateriall pag. 411 § 3. That the soules proceeding to action with an vniuersality and indifferency doth prooue the same pag. 412 § 4. That the quiet proceeding of reason doth prooue the same pag. 414 § 5. A conclusion of what hath beene said hetherto in this second Treatise ibid. CHAP. IX That our soule is a Substance and Immortall pag. 415 § 1. That Mans Soule is a substance ibid. § 2. That man is compounded of some other substance besides his body ibid. § 3. That the soule doth subsist of it selfe independently of the body pag. 416 § 4. Two other arguments to prooue the same one positiue the other negatiue pag. 417 § 5. The same is prooued because the soule can not be obnoxious to the cause of mortality ibid. § 6. The same is prooued because the soule hath no contrary pag. 418 § 7. The same is prooued from the end for which the soule was created ibid. § 8. The same is prooued because she can mooue without being mooued pag. 420 § 9. The same is
prooued from her manner of operation which is grounded in being ibid. § 10. Lastly it is prooued from the science of Morality the principles whereof would be destroied if the soule were mortall pag. 421 CHAP. X. Declaring what the soule of a man separated from his body is and of her knowledge and manner of working pag. 422 § 1. That the soule is one simple knowing act which is a pure substance and nothing but substance ibid. § 2. That a separated soule is in no place and yet is not absent from any place pag. 424 § 3. That a separated soule is not in time nor subiect to it ibid. § 4. That the soule is an actiue substance and all in it is actiuitie pag. 425 § 5. A description of the soule pag. 426 § 6. That a separated soule knoweth all that which she knew whilst she wâ—s in her bodie ibid. § 7. That the least knowledge which the soule acquireth in her bodie of anie one thing doth cause in her when she is separated from her bodie a compleat knowledge of all thinges whatsoeuer pag. 427 § 8. An answere to the obiections of some Peripatetikes who maintaine the soule to perish with the body pag. 429 § 9 The former Peripatetikes refuted out of Aristotle pag. 431 § 10. The operations of a separated soule compared to her operations in her bodie ibid. § 11. That a separated soule is in a state of pure being and consequently immortall pag. 432 CHAP. XI Shewing what effects the diuers manners of liuing in this world do cause in a soule after she is separated from her body p. 433 § 1. That a soule in this life is subiect to mutation and may be perfected in knowledge ibid. § 2. That the knowledges which a soule getteth in this life will make her knowledge in the next life more perfect and firme pag. 434 § 3. That the soules of men addicted to science whilst they liued here are more perfect in the next world then the soules of vnlearned men pag. 435 § 4. That those soules which embrace vertue in this world will be most perfect in the next and those which embrace vice most miserable ibid. § 5. The state of a vitious soule in the next life pag. 437 § 6. The fundamentall reason why as well happinesse as misery is so excessiue in the next life pag. 439 § 7. The reason why mans soule requireth to be in a body and to liue for some space of time ioyned with it pag. 441 § 8. That the misery of the soule in the next world proceedeth out of inequality and not out of falsity of her iudgements pag. 442 CHAP. XII Of the perseuerance of a soule in the state she findeth herselfe in at her first separation from her body pag. 443 § 1. The explication and proofe of that maxime that if the cause be in act the effect must also be ibid. § 2. The effects of all such agents as worke instantaneously are complete in the first instant that the agents are putt ibid. § 3. All pure spirits do worke instantaneously pag. 444 § 4. That a soule separated from her body can not suffer any change after the first instant of her separation ibid. § 5. That temporall sinnes are iustly punished with eternall paines pag. 445 The Conclusion pag. 446 THE PREFACE THIS writing was designed to haue seene the light vnder the name of one treatise But after it was drawne in paper as I cast a view ouer it I found the prooemiall part which is that which treateth of Bodies so ample in respect of the other which was the end of it and for whose sake I meddled with it that I readily apprehended my reader would thinke I had gone much astray from my text when proposing to speake of the immortality of Mans Soule three parts of foure of the whole discourse should not so much as in one word mention that soule whose nature and proprieties I aymed at the discouery of To auoyde this incongruity occasioned mee to change the name and vnity of the worke and to make the suruay of bodies a body by it selfe though subordinate to the treatise of the soule Which notwithstanding it be lesse in bulke then the other yet I dare promise my Reader that if he bestow the paines requisite to perfect him selfe in it he will find as much time well spent in the due reading of it as in the reading of the former treatise though farre more large But I discerne an obiection obuious to be made or rather a question why I should spend so much time in the consideration of bodies whereas none that hath formerly written of this subiect hath in any measure done the like I might answere that they had vpon other occasions first written of the nature of bodies as I may instance in Aristotle and sundry others who either haue themselues professedly treated the science of bodies or haue supposed that part sufficiently performed by other pennes But truly I was by an vnauoydable necessity hereunto obliged which is a current of doctrine that at this day much raigneth in the Christian Schooles where bodies and their operations are explicated after the manner of spirituall thinges For wee hauing very slender knowledge of spirituall substances can reach no further into their nature then to know that they haue certaine powers or qualities but can seldome penetrate so deepe as to descend to the particulars of such Qualities or Powers Now our moderne Philosophers haue introduced such a course of learning into the schooles that vnto all questions concerning the proper natures of bodies and their operations it is held sufficient to answere they haue a quality or a power to doe such a thing And afterwards they dispute whether this Quality or Power be an Entity distinct from its subiect or no and how it is seperable or vnseperable from it and the like Conformable to this who will looke into the bookes which are in vogue in these schooles shall find such answers and such controuersies euery where and few others As of the sensible qualities aske what it is to be white or red what to be sweete or sower what to be odoriferous or stincking what to be cold or hott And you are presently paid with that it is a sensible quality which hath the power to make a wall white or red to make a meate agreeable or disagreeable to the tast to make a gratefull or vngratefull smell to the nose etc Likewise they make the same questions and resolutions of Grauity and Leuity as whether they be qualities that is entities distinct from their subiect and whether they be actiue or passiue which when they haue disputed slightly and in common with logicall arguments they rest there without any further searching into the physicall causes or effects of them The like you shall find of all strange effects of them The loadestone and Electricall bodies are produced for miraculous and not vnderstandable thinges and in which it must be
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
of Physickes hath demonstrated that there can be no motion in vacuity It is true they endeauour to euade his demonstration as not reaching home to theire supposition by acknowledging it to be an euident one in such a vacuity as he there speaketh of which he supposed to be so great a one that a body may swimme in it as in an ocean and not touch or be neere any other body whereas this opinion excludeth all such vast inanity and admitteth no vacuities but so litle ones as no body whatsoeuer can come vnto but will be bigger then they and consequently must on some side or other touch the corporeall partes which those vacuities diuide for they are the seperations of the least partes that are or can be actually diuided from one an other which partes must of necessity touch one an other on some side or else they could not hang together to compose one substance and therefore the diuiding vacuities must be lesse then the diuided partes And thus no body will euer be in danger of floating vp and downe without touching any thing which is the difficulty that Aristotle chiefely impugneth I confesse I should be very glad that this supposition might serue our turne and saue the Phoenomena that appeare among bodies through theire variety of Rarity and Density which if it might be then would I straight go on to the inquiring after what followed out of this ground as Astronomers to vse our former similitude do calculate the future appearances of the celestiall bodies out of those motions and orbes they assigne vnto the heauens For as this apprehension of vacuity in bodies is very easy and intelligibile so the other which I conceiue to be the truth of the case is exceedingly abstracted and one of the most difficult pointes in all the Metaphysickes and therefore I would if it were possible auoyde touching vpon it in this discourse which I desire should be as plaine and easy and as much remooued from scholasticke termes as may be But indeed the inconueniences that follow out of this supposition of vacuities are so great as it is impossible by any meanes to slide them ouer As for example lett vs borrow of Galilaeus the proportion of weight betweene water and ayre He sheweth vs how the one is 400 times heauyer then the other And Marinus Ghetaldus teacheth vs that gold is 19 times heauyer then water so that gold must be 7600 times heauyer then ayre Now then considering that nothing in a body can weigh but the solide partes of it it followeth that the proportion of the partes of gold in a sphere of an inch diameter is to the partes of ayre of a like dimension as 7600 is to one Therefore in ayre it selfe the vacuities that are supposed in it will be to the solide partes of it in the same proportion as 7600 to one Indeed the proportion of difference will be greater for euen in gold many vacuities must be admitted as appeareth by the heating of it which sheweth that in euery the least part it is exceeding porous But according to this rate without pressing the inconuenience any further the ayre will by this reckoning appeare to be like a nett whose holes and distances are to the lines and thriddes in the proportion of 7600 to one and so would be lyable to haue litle partes of its body swimme in those greater vacuities contrary to what they striue to auoyde Which would be exceedingly more if we found on the one side any bodies heauyer and denser then gold and that were so solide as to exclude all vacuities and on the other side should ballance them with such bodies as are lighter and rarer then ayre as fire is and as some will haue the aether to be But already the disproportion is so great and the vacuity so strangely exceedeth the body in which it is as were too great an absurdity to be admitted And besides it would destroy all motion of small bodies in the ayre if it be true as Aristotle hath demonstrated in the 4th booke of his Physickes that motion can not be made but among bodies and not in vacuo Againe if rarity were made by vacuity rare bodies could not be gathered together without loosing theire rarity and becoming dense The contrary of which we learne by constant experience as when the smith and glassemender driue theire white and fury fires as they terme them when ayre pierceth most in the sharpe wind and generally we see that more of the same kind of rare bodies in lesse place worketh most efficaciously according to the nature that resulteth out of that degree of rarity Which argueth that euery litle part is as rare as it was before for else it would loose the vertue of working according to that nature but that by theire being crowded together they exclude all other bodies that before did mediate betweene the litle partes of theire maine body and so more partes being gotten together in the same place then formerly there were they worke more forcibly Thirdly if such vacuities were the cause of rarity it would follow that fluide bodies being rarer then solide ones they would be of themselues standing like nettes or cobbewebbes whereas contrariwise we see theire natures are to runne together and to fill vp euery litle creeke and corner which effect following out of the very nature of the thinges themselues must needes exclude vacuities out of that nature And lastly if it be true as we haue shewed in the last Chapter that there are no actuall partes in Quantity it followeth of necessity that all Quantity must of it selâ—e be one as Metaphysickes teach vs and then no distance can be admitted betweene one Quantity and an other And truly if I vnderstand Aristotle right he hath perfectly demonstrated that no vacuity is possible in nature neither great nor litle and consequently the whole machine raysed vpon that supposition must be ruinous His argument is to this purpose What is nothing can not haue partes but vacuum is nothing because as the aduersaries conceiue it vacuum is the want of a corporeall substance in an enclosing body within whose sides nothing is whereas a certaine body might be contained whithin them as if in a paile or bowle of a gallon there were neither milke nor water nor ayre nor any other body whatsoeuer therefore vacuum can not haue partes Yet those who admitt it do putt it expressely for a space which doth essentially include partes And thus they putt two contradictories nothing and partes that is partes and no partes or something and nothing in the same proposition And this I conceiue to be absolutely vnauoydable For these reasons therefore I must entreate my readers fauour that he will allow me to touch vpon metaphysickes a litle more then I desire or intended but it shall be no otherwise then as is said of the dogges by the riuer Nilus side who being thirsty lappe hastily of the water onely to serue
consider further that as this superficies hath in it selfe so the body enclosed in it gaineth a certaine determinate respect unto the stable and immoouable bodies that enuiron it As for example we vnderstand such a tree to be in such a place by hauing such and such respects to such a hill neere it or to such a house that standeth by it or to such a riuer that runneth vnder it or to such an immoouable point of the heauen that from the sunnes rising in the aequinox is called east and such like To which purpose it importeth not whether these that we call immoouable bodies and pointes be truly so or do but seeme so to mankinde For man talking of thinges according to the notions he frameth of them in his minde speech being nothing else but an expression to an other man of the images he hath within himselfe and his notions being made according to the seeming of the thinges he must needes make the same notions whether the thinges be truly so in themselues or but seeme to be so when that seeming or appearance is alwayes constantly the same Now then when one body diuiding an other getteth a new immediate cloathing and consequently new respects to the stable and immoouable bodies or seeming such that enuiron it we do vary in our selues the notion we first had of that thing conceiuing it now accompanied with other circumstances and other respects then formerly it had Which notion we expresse by saying it hath changed its place and is now no longer where it was att the first And this change of place we call Locall motion to witt the departing of a body from that hollow superficies which inclosed it and its changing vnto an other whereby it gaineth new respects to those partes of the world that haue or in some sort may seeme to haue immobility and fixed stablenesse So as hence it is euident that the substance of locall motion consisteth in diuision and that the alteration of Locality followeth diuision in such sort as becoming like or vnlike of one wall to an other followeth the action whereby one of them becometh white And therefore in nature we are not to seeke for any entity or speciall cause of applying the mooued body to a place as place which is but a respect consequent to the effect of diuision but onely to consider what reall and physicall action vniteth it to that other body which is called its place and truly serueth for that effect And consequently they who thinke they haue discouered a notable subtility by bringing in an Entity to vnite a body to its place haue strained beyond theire strength and haue grasped but a shadow Which will appeare yet more euident if they but marke well how nothing is diuisible but what of it selfe abstracting from diuision is one For the nature of diuision is the making of many which implyeth that what is to be diuided must of necessity be not many before it be diuided Now quantity being the subiect of diuision it is euident that purely of it selfe and without any force or adioyned helpes it must needes be one wheresoeuer some outward agent doth not introduce multiplicity vpon it And whensoeuer other thinges worke vpon quantity as quantity it is not the nature and power of theire operation to produce vnity in it and make it one for it is already one but contrariwise the immediate necessary effect that floweth from them in this case is to make one quantity many according to the circumstances that accompany the diuider and that which is to be diuided And therefore although wee may seeke causes why some one thing sticketh faster together then some other yet to aske absolutely why a body sticketh together were preiudiciall to the nature of quantity whose essence is to haue partes sticking together or rather to haue such vnity as without it all diuisibility must be excluded Out of which discourse it followeth that in locall motion we are to looke only for a cause or power to diuide but not for any to vnite For the very nature of quantity vniteth any two partes that are indistant from one an other without needing any other cement to glew them together as we see the partes of water and all liquide substances do presently vnite themselues to other partes of like bodies when they meete with them and to solide bodies if they chance to be next vnto them And therefore it is vaine to trouble our heades with Vnions and imaginary Moodes to vnite a body to the place it is in when theire owne nature maketh them one as soone as they are immediate to each other And accordingly if when we see a boule mooue we would examine the causes of that motion we must consider the quantity of ayre or water it maketh to breake from the partes next vnto it to giue place vnto it selfe and not speculate vpon an intrinsecall relation from the body to a certaine part of the imaginary space they will haue to runne through all thinges And by ballancing that quantity of ayre or water which it diuideth we may arriue to make an estimate of what force the boule needeth to haue for its motion Thus hauing declared that the locality of motion is but an extrinsecall denomination and no reality in the thing mooued wee may now cast an eye vpon a vast consequence that may be deduced out of what wee haue hitherto said For if we consider the nature of a body that is that a body is a body by quantity and that the formall notion of quantity is nothing else but diuisibility and that the adaequate act of diuisibility is diuision it is euident there can be no other operation vpon quantity nor by consequence among bodies but must eyther be such diuision as we haue here explicated or what must necessarily follow out of such diuision And diuision as we haue euen now explicated being locall motion it is euident that all operations among bodies are either locall motion or such as follow out of locall motion Which conclusion howsoeuer vnexpected and may att the first hearing appeare a Paradoxe will neuerthelesse by the ensuing worke receiue such euidence as it can not be doubted of and that not onely by force of argumentation and by necessity of notions as is already deduced but also by experience and by declaration of particulars as they shall occurre But now to apply what we haue said to our proposed subiect it is obuious to euery man that seeing the diuider is the agent in diuision and in locall motion and that dense bodies are by theire nature diuiders the earth must in that regard be the most actiue among the Elements since it is the most dense of them all But this seemeth to be against the common iudgement of all the searchers of nature who vnanimously agree that fire is the most actiue Element As also it seemeth to impugne what we our selues haue determined when we said there were two
cleared the third obiection as I conceiue lett vs goe on to the fourth which requireth that we satisfy their inquisition who aske what becometh of that vast body of shining light if it be a body that filleth all the distance betweene heauen and earth and vanisheth in a moment as soone as a cloude or the moone interpâ—seth it selfe betweene the sunne and vs or that the sunne quitteth our hemisphere No signe att all remaineth of it after the extinction of it as doth of all other substances whose destruction is the birth of some new thing Whither then is it flowne We may be persuaded that a mist is a corporeall substance because it turneth to droppes of water vpon the twigges that it enuironeth and so we might beleeue light to be fire if after the burning of it out we found any ashes remaining but experience assureth vs that after it is extinguished it leaueth not the least vestigium behind it of hauing beene there Now before we answere this obiection we will entreate our aduersary to call to minde how we haue in our solution of the former declared and proued that the light which for example shineth from à candle is no more then the flame is from whence it springeth the one being condensed and the other dilated and that the flame is in a perpetuall fluxe of consumption about the circumference and of restauration att the center where it sucketh in the fewell and then we will enquire of him what becometh of that body of flame which so continually dyeth and is renewed and leaueth no remainder behind it as well as he doth of vs what becometh of our body of light which in like manner is alwayes dying and alwayes springing fresh And when he hath well considered it he will find that one answere will serue for both Which is that as the fire streameth out from the fountaine of it and groweth more subtile by its dilatation it sinketh the more easily into those bodies it meeteth withall the first of which and that enuironeth it round about is ayre With ayre then it mingleth and incorporateth it selfe and by consequence with the other litle bodies that are mingled with the ayre and in them it receiueth the changes which nature worketh by which it may be turned into the other Elements if there be occasion or be still conserued in bodies that require heate Vpon this occasion I remember a rare experiment that a noble man of much sincerity and a singular frind of mine told me he had seene which was that by meanes of glasses made in a very particular manner and artificially placed one by an other he had seene the sunne beames gathered together and precipitated downe into a brownish or purplish red pouder There could be no fallacy in this operation for nothing whatsoeuer was in the glasses when they were placed and disposed for this intent and it must be in the hoat time of the yeare else the effect would not follow And of this Magistery he could gather some dayes neere two ounces in a day And it was of a strange volatile nature and would pierce and imprint his spirituall quality into gold it selfe the heauiest and most fixed body we conuerse withall in a very short time If this be plainely so without any mistaking then mens eyes and handes may tell them what becometh of light when it dyeth if a great deale of it were swept together But from what cause soeuer this experience had its effect our reason may be satisfyed with what we haue said aboue for I confesse for my part I beleeue the appearing body might be some thing that came along with the sunne beames and was gathered by them but not their pure substance Some peraduenture will obiect those lampes which both auncient and moderne writers haue reported to haue been found in tombes and vrnes long time before closed vp from mens repayre vnto them to supply them with new fewell and therefore they beleeue such fires to feede vpon nothing and consequently to be inconsumptible and perpetuall Which if they be then our doctrine that will haue light to be nothing but the body of fire perpetually flowing from its center and perpetually dying can not be sound for in time such fires would necessarily spend themselues in light although light be so subtile a substance that an exceeding litle quantity of fewell may be dilated into a vast quantity of light Yet still there would be some consumption which how imperceptible soeuer in a short time yet after a multitude of reuolutions of yeares it must needes discouer it selfe To this I answere that for the most part the wittnesses who testify originally the stories of these lights are such as a rationall man can not expect from them that exactnesse or nicety of obseruation which is requisite for our purpose for they are vsually grosse labouring people who as they digge the ground for other intentions do stumble vpon these lampes by chance before they are aware and for the most part they breake them in the finding and they imagine they see a glimpse of light which vanisheth before they can in a manner take notice of it and is peraduanture but the glistering of the broken glasse or glased pott which reflecteth the outward light as soone as by rummaging in the ground and discouering the glasse the light striketh vpon it in such manner as some times a diamond by a certaine encountring of light in a dusky place may in the first twincling of the motion seeme to sparkle like fire and afterwardes when they shew their broken lampe and tell their tale to some man of a pitch of witt aboue them who is curious to informe himselfe of all the circumstances that may concerne such lights they straine their memory to answere him satisfactorily vnto all his demandes and thus for his sake they persuade themselues to remember what they neuer saw And he againe on his side is willing to helpe out the story a litle And so after awhile a very formall and particular relation is made of it As happeneth in like sort in reporting of all strange and vnusuall thinges which euen those that in their nature abhorre from lying are naturally apt to straine a litle and fashion vp in a handsome mould and almost to persuade themselues they saw more then they did so innate it is vnto euery man to desire the hauing of some preeminence beyond his neighbours be it but in pretending to haue seene some thing which they haue not Therefore before I engage my selfe in giuing any particular answere to this obiection of pretended inconsumptible lights I would gladly see the effect certainely auerred and vndoubtedly proued for the testimonies which Fortunius Licetus produceth who hath been very diligent in gathering them and very subtile in discoursing vpon them and is the exactest author that hath written vpon this subiect do not seeme vnto mee to make that certainty which is required for the establishing of a
vnresistable force to pierce and shatter not onely the ayre but euen the hardest bodies that are Peraduenture some may thinke it reasonable to grant the consequence in due circumstances since experience teacheth vs that the congregation of a litle light by a glasse will sett very solide bodies on fire and will melt mettals in a very short space which sheweth a great actiuity and the great actiuity sheweth a great percussion burning being effected by a kind of attrition of the thing burned And the great force which fire sheweth in gunnes and in mines being but a multiplication of the same doth euidently conuince that of its owne nature it maketh a strong percussion when all due circumstances concurre Whereas it hath but litle effect if the due circumstances be wanting as we may obserue in the insensible burning of so rarifyed a body as pure spiritt of wine conuerted into flame But we must examine the matter more particularly and must seeke the cause why a violent effect doth not alwayes appeare wheresoeuer light striketh for the which wee are to note that three thinges do concurre to make a percussion great The bignesse the density and the celerity of the body mooued Of which three there is only one in light to witt celerity for it hath the greatest rarity and the rayes of it are the smallest parcels of all naturall bodies And therefore since only celerity is considerable in the account of lights percussions we must examine what celerity is necessary to make the stroke of a ray sensible first then we see that all the motes of the ayre nay euen feathers and strawes do make no sensible percussion when they fall vpon vs therefore we must in light haue att the least a celerity that may be to the celerity of the straw falling vpon our hand for example as the density of the straw is to the density of light that the percussion of light may be in the least degree sensible But let vs take a corne of gunnepowder insteede of a straw betweene which there can not be much difference and then putting that the density of fire is to the density of gunnepowder as 1. to 125000 and that the density of the light we haue here in the earth is to the density of that part of fire which is in the sunnes body as the body of the sunne is to that body which is called Orbis magnus whose semidiameter is the distance betweene the sunne and the earth which must be in subtriple proportion of the diameter of the sunne to the diameter of the great orbe it followeth that 125000. being multiplyed by the proportion of the great orbe vnto the sunne which Galileo telleth vs is as 106000000. vnto one will giue a scantling of what degree of celerity light must haue more then a corne of gunnepouder to recompence the excesse of weight which is in a corne of gunnepouder aboue that which is in a ray of light as bigge as a corne of gunnepouder Which will amount to be much greater then the proportion of the semidiater of Orbis magnus to the semidiater of the corne of gunnepouder for if you reckon 5. graines of gunnepouder to a barley cornes breadth and 12. of them in an inch and 12. inches in a foote and 3. feete in a pace and 1000. paces in a mile and 3500. miles in the semidiameter of the earth and 1208. semidiameters of the earth in the semidiameter of the Orbis magnus there will be in it but 9132480000000. graines of gunnepouder whereas the other calculation maketh light to be 13250000000000. times raver then gunnepouder which is almost tenne times a greater proportion then the other And yet this celerity supplyeth but one of the two conditions wanting in light to make its percussions sensible namely density Now because the same velocity in a body of a lesser bulke doth not make so great a percussion as it doth in a bigger body and that the littlenesse of the least partes of bodies followeth the proportion of their rarity this vast proportion of celerity must againe be drawne into it selfe to supply for the excesse in bignesse that a corne of gunnepouder hath ouer an atome of light and the product of this multiplication will be the celerity required to supply for both defects Which euidently sheweth it is impossible that a ray of light should make any sensible percussion though it be a body Especially considering that sense neuer taketh notice of what is perpetually done in a moderate degree And therefore after this minute looking into all circumstances we neede not haue difficulty in allowing vnto light the greatest celerity imaginable and a percussion proportionate to such a celerity in so rare a body and yett not feare any violent effect from its blowes vnlesse it be condensed and many partes of it be brought together to worke as if they were but one As concerning the last obiection that if light were a body it would be fanned by the wind wee must first consider what is the cause of a thinges appearing to be mooued and then examine what force that cause hath in light As for the first part we see that when a body is discerned now in one place now in an other then it appeareth te be mooued And this we see happeneth also in light as when the sunne or a candle is carried or mooueth the light thereof in the body of the candle or sunne seemeth to be mooued along with it And the likes is in a shining cloud or comete But to apply this to our purpose wee must note that the intention of the obiection is that the light which goeth from the fire to an opacous body farre distant without interruption of its continuity should seeme to be iogged or putt out of its way by the wind that crosseth it Wherein the first fayling is that the obiectour conceiueth light to send species vnto our eye from the middest of its line whereas with a litle consideration he may perceiue that not light is seene by vs but that which is reflected from an opacous body to our eye so that the light he meaneth in his obiection is neuer seene att all Secondly it is manifest that the light which stricketh our eye doth strike it in a straight line and seemeth to be att the end of that straight line wheresoeur that is and so can neuer appeare to be in an other place but the light which wee see in an other place wee conceiue to be an other light Which maketh it againe euident that the light can neuer appeare to shake though wee should suppose that light may be seene from the middle of its line for no part of wind or ayre can come into any sensible place in that middle of the line with such speede that new light from the source doth not illuminate it sooner then it can be seene by vs wherefore it will appeare to vs illuminated as being in that place and therefore the light can neuer
in the time EF is greater then the force B in so much time the force B will be able to mooue A through CD Which discourse is euident if we take it in the common termes but if it be applyed to action wherein physicall accidents intervene the artificer must haue the iudgement to prouide for them according to the nature of his matter Vpon this last discourse doth hang the principle which gouerneth Mechanikes to witt that the force and the distance of weights counterpoising one an other ought to be reciprocall That is that by how much the one weight is heauyer then the other by so much must the distance of the lighter from the fixed point vpon which they are mooued be greater then the distance of the greater weight from the same point for it is plaine that the weight which is more distant must be mooued a greater space then the neerer weight in the proportion of the two distāces Wherefore the force moouing it must carry it in a velocity of the said proportion to the velocity of the other And consequently the Agent or moouer must be in that proportion more powerfull then the contrary moouer And out of this practise of Geometricians in Mechanikes which is confirmed by experience it is made euident that if other conditions be equall the excesse of so much grauity will make so much velocity And so much velocity in proportion will recompence so much grauity Out of the precedent conclusions an other followeth which is that nothing recedeth frō quiet or rest and attaineth a great degree of celerity but it must passe through all the degrees of celerity that are below the obtained degree And the like is in passing from any lesser degree of velocity vnto a greater because it must passe through all the intermediate degrees of velocity For by the declaration of velocity which we haue euen now made we see that there is as much resistance in the medium to be ouercome with speede as there is for it to be ouercome in regard of the quantity or line of extent of it because as we haue said the force of the Agent in counterpoises ought to be encreased as much as the line of extent of the medium which is to be ouercome by the Agent in equall time doth exceede the line of extent of the medium along which the resistent body is to be mooued Wherefore it being prooued that no line of extent can be ouercome in an instant it followeth that no defect of velocity which requireth as great a superproportion in the cause can be ouercome likewise in an instant And by the same reason by which we prooue that a mooueable can not be drawne in an instant from a lower degree of velocity to a higher it is with no lesse euidence concluded that no degree of velocity can be attained in an instant for diuide that degree of velocity into two halfes and if the Agent had ouercome the one halfe he could not ouercome the other halfe in an instant much lesse therefore is he able to ouercome the whole that is to reduce the mooueable from quiet to the said degree of velocity in an instant An other reason may be because the moouers themselues such moouers as we treate of here are bodies likewise mooued and do consist of partes whereof not euery one part but a competent number of them doth make the moouing body to be a fitt Agent able to mooue the proposed body in a proposed degree of celerity Now this Agent meeting with resistance in the mooueable and not being in the vtmost extremity of density but condensable yet further because it is a body and that euery resistance be it neuer so small doth worke something vpon the moouer though neuer so hard to condense it the partes of the moouer that are to ouercome this resistance in the mooueable must to worke that effect be condensed and brought together as close as is needefull by this resistance of the mooueable to the moouer and so the remote partes of the moouer become neerer to the mooueable which can not be done but successiuely because it includeth locall motion And this application being likewise diuisible and not all the partes flocking together in an instant to the place where they are to exercise their power it followeth that whiles there are fewer moouing partes knitt together they must needes mooue lesse and more weakely then when more or all of them are assembled and applyed to that worke So that the motiue vertue encreasing thus in proportion to the multiplying of the partes applyed to cause the motion of necessity the effect which is obedience to be mooued and quicknesse of motion in the mooueable must do so too that is it must from nothing or from rest passe through all the degrees of celerity vntill it arriue to that which all the partes together are able to cause As for example when with my hand I strike a ball till my hand toucheth it it is in quiet but then it beginneth to mooue yet with such resistance that although it obey in some measure the stroke of my hand neuerthelesse it presseth the yielding flesh of my palme backwardes towardes the vpper and bony part of it That part then ouertaking the other by the continued motion of my hand and both of them ioyning together to force the ball away the impulse becometh stronger then att the first touching of it And the longer it presseth vpon it the more the partes of my hand do condense and vnite themselues to exercise their force and the ball therefore must yield the more and consequently the motion of it groweth quicker and quicker till my hand parteth from it Which condensation of the partes of my hand encreasing successiuely by the partes ioyning closer to one an other the velocity of the balles motion which is an effect of it must also encrease proportionably thereunto And in like manner the motion of my hand and arme must grow quicker and quicker and passe all the degrees of velocity betweene rest and the vtmost degree it attaineth vnto for seeing they are the spirits swelling the nerues that cause the armes motion as we shall hereafter shew vpon its resistance they flocke from other partes of the body to ouercome that resistance And since their iourney thither requireth time to performe it in and that the neerest come first it must needes follow that as they grow more and more in number they must more powerfully ouercome the resistance and consequently encrease the velocity of the motion in the same proportion as they flocke thither vntill it attaine that degree of velocity which is the vtmost periode that the power which the Agent hath to ouercome the resistance of the medium can bring it selfe vnto Betweene which and rest or any inferiour degree of velocity there may be designed infinite intermediate degrees proportionable to the infinite diuisibility of time and space in which the moouer doth moue Which degrees
do arise out of the reciprocall yielding of the medium And that is likewise diuisible in the same infinite proportion Since then the power of all naturall Agents is limited the moouer be it neuer so powerfull must be confined to obserue these proportions and can not passe ouer all these infinite designable degrees in an instant but must allott some time which hath a like infinity of designable partes to ballance this infinity of degrees of velocity and so consequently it requireth time to attaine vnto any determinate degree And therefore can not recede immediately from rest vnto any degree of celerity but must necessarily passe through all the intermediate ones Thus it is euident that all motion which hath a beginning must of necessity encrease for some time And since the workes of nature are in proportion to their causes it followeth that this encrease is in a determinate proportion Which Galileus vnto whom we owe the greatest part of what is knowne concerning motion teacheth vs how to find out and to discouer what degree of celerity any mooueable that is moued by nature hath in any determinate part of the space it moueth in Hauing settled these conditions of motion we shall do well in the next place to enquire after the causes of it as well in the body moued as also in the mouer that occasioneth the motion And because we haue already shewed that locall motion is nothing in substance but diuision we may determine that those causes which contribute to diuision or resist it are the causes which make or resist locall motion It hath also beene said that Density hath in it a power of diuiding and that Rarity is the cause of being diuided likewise we haue said that fire by reason of its small partes into which it may be cutt which maketh them sharpe hath also an eminence in diuiding so that we haue two qualites density and tenuity or sharpnesse which concurre actiuely to diuision We haue told you also how Galileus hath demonstrated that a greater quantity of the same figure and density hath a priuiledge of descending faster then a lesser And that priuiledge consisteth in this that the proportion of the superficies to the body it limiteth which proportion the greater it is the more it retardeth is lesse in a greater bulke then in a smaller We haue therefore three conditions concurring to make the motion more efficacious namely the density the sharpenesse and the bulke of the mooueable And more then these three we can not expect to find in a moued body for quantity hath but three determinations one by density and rarity of which density is one of the three conditions an other by its partes as by a foote a spanne and in this way wee haue found that the greater excelleth the lesser the third and last is by its figure and in this we find that subtile or edged quantities do preuayle ouer blunt ones Seeing therefore that these three determinations be all that are in quantity there can be no more conditions in the body moued which of necessity is a finite quantity but the three named And as for the medium which is to be diuided there is onely rarity and density the one to helpe the other to hinder that require consideration on its side For neither figure nor littlenesse and greatnesse do make any variation in it And as for the Agent it is not as yet time before we haue looked further intâ— the nature of motion to determine his qualities Now then lett vs reflect how these three conditions do all agree in this circumstance that they helpe nothing to diuision vnlesse the body in which they are be moued and pressed against the body that is to be diuided so that we see no principle to persuade vs that any body can mooue it selfe towards any determinate part or place of the vniuerse of its owne intrinsecall inclination For besides that the learned Author of the Dialogues de Mundo in his third Dialogue and the second knott hath demonstrated that a body can not mooue vnlesse it be mooued by some extrinsecall Agent we may easily frame vnto our selues a conceite of how absurd it is to thinke that a body by a quality in it can worke vpon it selfe as if wee should say that rarity which is but more quantity could worke vpon quantity or that figure which is but that the body reacheth no further could worke vpon the body and in generall that the manner of any thing can worke vpon that thing whose manner it is For Aristotle and St. Thomas and their intelligent commentatours declaring the notion of Quality tell vs that to be a Quality is nothing else but to be the determination or modification of the thing whose quality it is Besides that the naturall manner of operation is to worke according to the capacity of the subiect but when a body is in the middest of an vniforme medium or space the subiect is equally prepared on all sides to receiue the action of that body Wherefore though we should allow it a force to mooue if it be a naturall Agent and haue no vnderstanding it must worke indifferently on all sides and by consequence can not mooue on any side For if you say that the Agent in this case where the medium is vniforme worketh rather vpon one side then vpon an other it must be because this determination is within the Agent it selfe and not out of the circumstant dispositions which is the manner of working of those substances that worke for an end of their owne that is of vnderstanding creatures and not of naturall bodies Now he that would exactly determine what motion a body hath or is apt to haue determining by supposition the force of the Agent must calculate the proportions of all these three conditions of the mooueable and the quality of the medium which is a proceeding too particular for the intention of our discourse But to speake in common it will not be amisse to examine in what proportion motion doth encrease since we haue concluded that all motion proceedeth from quiet by a continuall encrease Galileus that miracle of our age and whose witt was able to discouer whatsoeuer he had a mind to employ it about hath told vs that naturall motion encreaseth in the proportion of the odde numbers Which to expresse by example is thus suppose that in the going of the first yard it hath one degree of velocity then in the going of the second yard it will haue three degrees and in going the third it will haue fiue and so onwardes still adding two to the degrees of the velocity for euery one of the space Or to expresse it more plainely if in the first minute of time it goeth one yard of space then in the next minute it will goe three yardes in the third it will goe fiue in the fourth seauen and so forth But we must enlarge this proposition vnto all motions as we haue
done the former of the encrease it selfe in velocity because the reason of it is common to all motions Which is that all motion as may appeare out of what we haue formerly said proceedeth from two causes namely the Agent or the force that mooueth and the disposition of the body mooued as it is composed of the three qualities we lately explicated In which is to be noted that the Agent doth not mooue simply by its owne vertue but it applyeth also the vertue of the body mooued which it hath to diuide the medium when it is putt on As when we cutt with a knife the effect proceedeth from the knife pressed on by the hand or from the hand as applying and putting in action the edge and cutting power of the knife Now this in Physickes and nature is cleerely parallel to what in Geometry and Arithmetike the Mathematicians call drawing one number or one side into an other for as in Mathematikes to draw one number into an other is to apply the number drawne vnto euery part of the number into which it is drawne as if we draw three into seuen we make twenty one by making euery vnity or part of the number seuen to be three and the like is of lines in Geometry So in the present case to euery part of the handes motion we adde the whole vertue of the cutting faculty which is in the knife and to euery part of the motion of the knife we adde the whole pressing vertue of the hand Therefore the encrease of the effect proceeding from two causes so working must also be parallel to the encrease of the quantities arising out of the like drawing in Mathematikes But in those it is euident that the encrease is according to the order of the odde numbers and therefore it must in our case be the like that is the encrease must be in the said proportion of odde numbers Now that in those the encrease proceedeth so will be euident if you consider the encrease of an Equicrure triangle which because it goeth vpon a certaine proportion of length and breadth if you compare the encreases of the whole triangle that gaineth on each side with the encreases of the perpendicular which gaineth onely in length you will see that they still proceede in the foresaid proportion of odde numbers But we must not imagine that the velocity of motion will alwayse encrease thus for as long as we can fancy any motion but when it is arriued vnto the vtmost periode that such a mooueable with such causes is capable of then it keepeth constantly the same pace and goeth equally and vniformely att the same rate For since the density of the mooueable and the force of the Agent mouing it which two do cause the motion haue a limited proportion to the resistance of the medium how yielding soeuer it be it must needes follow that when the motion is arriued vnto that height which ariseth out of this proportion it can not exceede it but must continue at that rate vnlesse some other cause giue yet a greater impulse to the moueable For velocity consisting in this that the moueable cutteth through more of the medium in an equall time it is euident that in the encrease of velocity the resistance of the medium which is ouercome by it groweth greater and greater and by litle and litle gaineth vpon the foree of the Agent so that the superproportion of the Agent groweth still lesser and lesser as the velocity encreaseth and therefore att the length they must come to be ballanced And then the velocity can encrease no more And the reason of the encrease of it for a while att the beginning is because that coming from rest it must passe through all the intermediate degrees of velocity before it can attaine to the height of it which requireth time to performe and therefore falleth vnder the power of our sense to obserue But because we see it do so for some time we must not therefore conclude that the nature of such motion is still to encrease without any periode or limit like those lines that perpetually grow neerer and yet can neuer meete for we see that our reason examining the causes of this velocity assureth vs that in continuance of time and space it may come to its height which it can not exceede And there would be the pitch att which distance weights being lett fall would giue the greatest stroakes and make greatest impressions It is true that Galileus and Mersenius two exact experimenters do thinke they find this verity by their experiences But surely that is impossible to be done for the encrease of velocity being in a proportion euer diminishing it must of necessity come to an insensible encrease in proportion before it endeth for the space which the moueable goeth through is still encreased and the time wherein it passeth through that space remaineth still the same litle one as was taken vp in passing a lesse space immediately before and such litle differences of great spaces passed ouer in a litle time come soone to be vndiscernable by sense But reason which sheweth vs that if velocity neuer ceased from encreasing it would in time arriue to exceede any particular velocity and by consequence the proportion which the moouer hath to the medium because of the adding still a determinate part to its velocity concludeth plainely that it is impossible motion should encrease for euer without coming to a periode Now the impression which falling weights do make is of two kindes for the body into which impression is made either can yield backward or it can not If it can yield backward then the impression made is a motion as we see a stroak with a rackett vpon a ball or with a pailemaile beetle vpon a boule maketh it fly from it But if the strucken body can not yield backwardes then it maketh it yield on the sides And this in diuerse manners for if the smitten body be dry and brittle it is subiect to breake it and make the pieces fly round about but if it be a tough body it squeeseth it into a larger forme But because the effect in any of these wayse is eminently greater then the force of the Agēt seemeth to be it is worth our labour to looke into the causes of it To which end we may remember how we haue already declared that the force of the velocity is equall to a reciprocall force of weight in the vertue mouent wherefore the effect of a blow that a man giueth with a hammer dependeth vpon the weight of the hammer vpon the velocity of the motion and vpon the hand in case the hand accompanieth the blow But if the motion of the hand ceaseth before as when we throw a thing then onely the velocity and the weight of the hammer remaine to be considered Howsoeuer lett vs putt the hand and weight in one summe which we may equalise by some other vertue or weight Then lett vs
consider the way or space which a weight lying vpon the thing is to goe forwardes to do the same effect in the same time as the percussion doeth And what excesse the line of the blow hath ouer the line of that way or space such an excesse we must adde of equall weight or force to the weight we had already taken And the weight composed of both will be a fitt Agent to make the like impression This Probleme was proposed vnto me by that worthy religious man Father Mersenius who is not content with aduancing learning by his owne industry and labours but besides is alwayse out of his generous affection to verity inciting others to contribute to the publike stocke of it He proposed to me likewise this following question to witt why there is required a weight of water in double Geometricall proportion to make a pipe runne twice as fast as it did or to haue twice as much water runne out in the same time Vnto which I answere out of the same ground as before That because in running twice as fast there goeth out double water in euery part of time and againe euery part of water goeth a double space in the same part of time that is to say because double the celerity is drawne into double the water and double the water into double the celerity therefore the present effect is to the former effect as the effect or quadrate of a double line drawne into it selfe is to the effect or quadrate of halfe the said line drawne into it selfe And consequently the cause of the latter effect which is the weight then must be to the cause of the former effect that is to the former weight in the same proportion namely as the quadrate of a double line is to the quadrate of halfe that line And so you see the reason of what he by experience findeth to be true Though I doubt not but when he shall sett out the treatise which he hath made of this subiect the reader will haue better satisfaction In the meane while an experience which Galileo deliuereth will confirme this doctrine He sayth that to make the same pendant goe twice as fast as it did or to make euery vndulation of it in halfe the time it did you must make the line att which it hangeth double in Geometricall proportion to the line att which it hanged before Whence it followeth that the circle by which it goeth is likewise in double Geometricall proportion And this being certaine that celerity to celerity hath the proportion of force which weight hath to weight it is euident that as in one case there must be weight in Geometricall proportion so in the other case where onely celerity maketh the variance the celerity must be in double Geometricall proportion according as Galileo findeth it by experience But to returne to our maine intent there is to be further noted that if the subiect strucken be of a proportionate cessibility it seemeth to dull and deaden the stroake whereas if the thing strucken be hard the stroake seemeth to loose no force but to worke a greater effect Though indeed the truth be that in both cases the effects are equall but diuerse according to the natures of the thinges that are strucken for no force that once is in nature can be lost but must haue its adequate effect one way or other Lett vs then first suppose the body strucken to be a hard body of no exceeding biggnesse in which case if the stroake light perpendiculary vpon it it will carry such a body before it But if the body be too great and haue its partes so conioyned as that they are weaker thē the stroake in this case the stroake driueth one part before it and so breaketh it from the rest But lastly if the partes of the strucken body be so easily cessible as without difficulty the stroake can diuide them then it entereth into such a body vntill it hath spent its force So that now making vp our account we see that an equall effect proceedeth from an equall force in all the three cases though in themselues they be farre different But we are apt to account that effect greater which is more considerable vnto vs by the profitt or damage it bringeth vs. And therefore we vsually say that the blow which shaketh a wall or beateth it downe and killeth men with the stones it scattereth abroad hath a greater effect then that which penetrateth farre into a mudde wall and doth litle harme for that innocuousnesse of the effect maketh that although in it selfe it be as great as the other yet it is litle obserued or considered This discourse draweth on an other which is to declare how motion ceaseth And to summe that vp in short we say that when motion cometh vnto rest it decreaseth and passeth through all the degrees of celerity and tardity that are betweene rest and the height of that motion which so declineth And that in the proportion of the odde numbers as we declared aboue that it did encrease The reason is cleare because that which maketh a motion cease is the resistance it findeth which resistance is an action of a moouer that mooueth some thing against the body which is mooued or some thing equiualent to such an action wherefore it must follow the lawes that are common to all motions of which kind those two are that we haue expressed in this conclusion Now that resistance is a countermotion or equiualent to one is plaine by this that any body which is pressed must needes presse againe vpon the body that presseth it wherefore the cause that hindereth such a body from yielding is a force mouing that body against the body which presseth it The particulars of all which we shall more att large declare where we speake of the action and reaction of particular bodies THE TENTH CHAPTER Of Grauity and Leuity and of Locall Motion commonly termed Naturall IT is now time to consider that distinction of motions which is so famous in Aristotle to witt that some motions are naturall others violent and to determine what may be signifyed by these termes For seeing we haue said that no body hath a naturall intrinsecall inclination vnto any place to which it is able to moue it selfe we must needes conclude that the motion of euery body followeth the percussion of extrinsecall Agents It seemeth therefore impossible that any body should haue any motion naturall to it selfe And if there be none naturall there can be none violent And so this distinction will vainsh to nothing But on the other side liuing creatures do manifesty shew naturall motions hauing naturall instruments to performe certaine motions wherefore such motions must of necessity be naturall to them But these are not the motions which we are to speake of for Aristotles diuision is common to all bodies or att the least to all those we conuerse withall and particulary to those which are called heauy and
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
behind the arrow that driueth it on as what the arrow causeth in the ayre before it for by reason of the density of it it must needes make a greater impression in the ayre it cutteth then the ayre that causeth its motion would do of it selfe without the mediation of the arrow As when the force of a hand giueth motion vnto a knife to cutt a loafe of bread the knife by reason of the density and of the figure it hath mâ—kâ—th a greater impression in the loafe thâ—n the hand alone would do And this is the same that we declared in the naturall motion of a heauy thing downewardes vnto which we assigned two causes namely the beating of the atomes in the ayre falling downe in their naturall coursâ— to determine it the way it is to goe and the density of the body that cutting more powerfully then those atomes can do giueth together with their helpe a greater velocity vnto the mooueable then the atomes of themselues can giue Nor doth it import that our resolution is against the generall nature of rare and dense bodies in regard of conseruing motion as Galileo obiecteth for the reason why dense bodies do conserue motion longer then rare bodies is because in regard of their diuiding vertue they gett in equall times a greater velocity Wherefore seeing that velocity is equall vnto grauity it followeth thâ—t resistance worketh not so much vpon them as vpon rare bodies and therefore can not make them cease from motion so easily as it doth rare bodies This is the generall reason for the conseruation of motion in dense bodies But because in our case there is a continuall cause which conserueth motion in the ayre the ayre may continue its motion longer then of it selfe it would do not in the same part of ayre which Galileus as it seemeth did ayme att but in diuers partes in which the mooueable successiuely is Which being concluded lett vs see how the forced motion cometh to decrease and to be ended To which purpose we may obserue that the impression which the arrow receiueth from the ayre that driueth it forwardes being weaker then that which it receiued att the first from the string by reasoÌ„ that the ayre is not so deÌ„se and therefore caÌ„ not strike so great a blow the arrow doth not in this second measure of time wherein we coÌ„sider the impulse giuen by the ayre onely cutt so strongly the ayre before it nor presse so violently vpon it as in the first measure when the string parting from it did beate it forwardes for till then the velocity encreaseth in the arrow as it doth in the string that carryeth it along which proceedeth from rest att the singers loose from it to its highest degree of velocity which is when it arriueth to the vtmost extent of its ierke where it quitteth the arrow And therefore the ayre now doth not so swiftly nor so much of it rebound backe from before and clappe it selfe behind the arrow to fill the space that else would be left voyde by the arrowes moouing forward and consequently the blow it giueth in the third measure to driue the arrow on can not be so great as the blow was immediately after the stringes parting from it which was in the second measure of time and therefore the arrow must needes mooue slower in the third measure then it did in the second as formerly it mooued slower in the second which was the ayres first stroake then it did in the first when the string droue it forwardes And thus successiuely in euery moment of time as the causes grow weaker and weaker by the encrease of resistance in the ayre before and by the decrease of force in the subsequent ayre so the motion must be slower and slower till it come to pure cessation As for Galileus second argument that the ayre hath litle power ouer heauy thinges and therefore he will not allow it to be the cause of continuing forced motions in dense bodies I wish he could as well haue made experience what velocity of motion a mans breath might produce in a heauy bullett lying vpon an euen hard and slippery plaine for a table would be too short as he did how admirable great a one it produced in pendants hanging in the ayre and I doubt not but he would haue granted it as powerfull in causing horizontall motions as he found it in the vndulations of his pendantes Which neuerthelesse do sufficiently conuince how great a power ayre hath ouer heauy bodies As likewise the experience of windgunnes assureth vs that ayre duly applyed is able to giue greater motion vnto heauy bodies then vnto light ones For how can a straw or feather be imagined possibly to fly with halfe the violence as a bullett of lead doth out of one of those engines And when a man sucketh a bullett vpwardes in a perfectly bored barrell of a gunne which the bullett fitteth exactly as we haue mentioned before with what a violence doth it follow the breath and ascend to the mouth of the barrell I remember to haue seene a man that was vncautious and sucked strongly that had his foreteeth beaten out by the blow of the bullett ascending This experiment if well looked into may peraduenture make good a greate part of this doctrine we now deliuer For the ayre pressing in behind the bullett att the touch hole giueth it its impulse vpwardes vnto which the density of the bullett being added you haue the cause of its swiftnesse and violence for a bullett of wood or corke would not ascend so fast and so strongly and the sucking away of the ayre before it taketh away that resistance which otherwise it would encounter with by the ayre lying in the way of it and its following the breath with so great ease sheweth as we touched before that of it selfe it is indifferent to any motion when nothing presseth vpon it to determine it a certaine way Now to Galileos last argument that an arrow should fly faster broadwayes then longwayes if the ayre were cause of its motion there needeth no more to be saide but that the resistance of the ayre before hindereth it as much as the impulse of the ayre behind helpeth it on so that nothing is gained in that regard but much is lost in respect of the figure which maketh the arrow vnapt to cutt the ayre so well when it flyeth broadwayes as when it is shott longwayes and therefore the ayre being weakely cutt so much of it can not clappe in behind the arrow and driue it on against the resistance before which is much greater Thus farre with due respect and with acknowledging remembrance of the many admirable mysteries of natute which that great man hath taught the world we haue taken liberty to dispute against him because this difficulty seemeth to haue driuen him against his Genius to beleeue that in such motions there must be allowed a quality imprinted into the mooued body to cause them which
A to B is the proportion of CB to CA that is it goeth in the same time faster towardes D then it doth towardes M in the proportion which CB hath to CA. By which account the resistance it hath in the way towardes D must also be greater then the resistance it hath in the way towardes M in the proportion which CB hath to CA and therefore the more tardity must be in the way to D and not in the way to M and consequently the declination must be from Ewardes and to Mwardes For where there is most resistance that way likewise must the tardity be greatest and the declination must be from that way but which way the thickenesse to be passed in the same time is most that way the resistance is greatest and the thickenesse is clearely greater towardes E then towardes M therefore the resistance must be greatest towardes E and consequently the declination from the line BL must be towardes M and not towardes E. But the truth is that in his doctrine the ball would goe in a straight line as if there were no resistance vnlesse peraduenture towardes the contrary side of the cloth att which it goeth out into the free ayre for as the resistance of the cloth is greater in the way towardes D then in the way towardes M because it passeth a longer line in the same time as also it did formerly in the ayre so likewise is the force that mooueth it that way greater then the force which mooueth it the other And therefore the same proportions that were in the motion before it came to the resisting passage will remaine also in it att the least vntill coming neere the side att which it goeth out the resistance be weakned by the thinnenesse of the resistent there which because it must needes happen on the side that hath least thicknesse the ball must consequently turne the other way where it findeth greatest yielding and so att its getting out into the free ayre it will bend from the greater resistance in such manner as we haue said aboue Neither do the examples brought by Monsieur Des Cartes and others in maintenance of this doctrine any thing auayle them for when a canon bullett shott into a riuer hurteth the people on the other side it is not caused by refraction but by reflexion as Monsieur Des Cartes himselfe acknowledgeth and therefore hath no force to prooue any thing in refraction whose lawes are diuers from those of pure reflexion And the same answere serueth against the instance of a muskett bullett shott att a marke vnder water which perpetually lighteth higher then the marke though it be exactly iust aymed att For we knowing that it is the nature of water by sinking in one place to rise round about it must of necessity follow that the bullett which in entring hath pressed downe the first partes of the water hath withall thereby putt others further off in a motion of rising and therefore the bullet in its goeing on must meete with some water swelling vpwardes and must from it receiue a ply that way which can not faile of carrying it aboue the marke it was leuelled att And so we see this effect proceedeth from reflection or the bounding of the water and not from refraction Besides that it may iustly be suspected the shooter tooke his ayme too high by reason of the markes appearing in the water higher then in truth it is vnlesse such false ayming were duly preuented Neither is Monsieur Des Cartes his excuse to be admitted when he sayth that light goeth otherwise then a ball would do because that in a glasse or in water the etheriall substance which he supposeth to runne through all bodies is more efficaciously mooued then in ayre and that therefore light must go faster in the glasse then in the ayre and so turne on that side of the straight line which is contrary to the side that the ball taketh because the ball goeth not so swiftly For not to dispute of the verity of this proposition the effect he pretendeth is impossible for if the etheriall substance in the ayre before the glasse be slowly mooued the motion of which he calleth light it is impossible that the etheriall substance in the glasse or in the water should be more smartly mooued then it Well it may be lesse but without all doubt the impulse of the etheriall substance in the glasse can not be greater then its adequate cause which is the motion of the other partes that are in the ayre precedent to the glasse Againe after it is passed the glasse it should returne to be a straight line with the line that it made in the ayre precedent to the glasse seeing that the subsequent ayre must take off iust as much and no more as the glasse did adde the contrary whereof experience sheweth vs. Thirdly in this explication it would alwayes go one way in the ayre and an other way in the glasse whereas all experience testifyeth that in a glasse conuexe on both sides it still goeth in the ayre after its going out to the same side as it did in the glasse but more And the like happeneth in glasses on both sides concaue Wherefore it is euident that it is the superficies of the glasse that is the worker on both sides and not the substance of the ayre on the one side and of the glasse on the other And lastly his answere doth no wayes solue our obiection which prooueth that the resistance both wayes is proportionate to the force that mooueth and by consequence that the thing moued must go straight As we may imagine would happen if a bullett were shott sloaping through a greene mudde wall in which there were many round stickes so thinne sett that the bullett mighr passe with ease through them for as long as the bullett touched none of them which expresseth his case it would go straight but if it touched any of them which resembleth ours as by and by will appeare it would glance according to the quality of the touch and mooue from the sticke in an other line Some peraduenture may answere for Monsieur Des Cartes that this subtile body which he supposeth to runne through all thinges is stiffe and no wayes plyable But that is so repugnant to the nature of rarity and so many insuperable inconueniencies do follow out of it as I can not imagine he will owne it and therefore I will not spend any time in replying therevnto We must therefore seeke some other cause of the refraction of light which is made att the entrance of it into a diaphanous body Which is plainely as we said before because the ray striking against the inside of a body it can not penetrate turneth by reflexion towardes that side on which the illuminant standeth and if it findeth cleare passage through the whole resistent it followeth the course it first taketh if not then it is lost by many reflexions too and
fro And taking a body of concaue surfaces we shall according to this doctrine of ours find the causes of refraction iust contrary and accordingly experience