Draft of the 'Hypothesis Concerning Light and Colors'Isaac Newtonc.9,121 wordsNewton ProjectBrighton2011Newton Project, Sussex University
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c. early 1675, c. 9,210 words, 15 pp.15 pp.MS Add. 3970.3, ff. 475r-482v, Cambridge University Library, Cambridge, UKUKCambridgeCambridge University LibraryPortsmouth CollectionMS Add. 3970.3, ff. 475r-482vc. early 1675EnglandEnglishLatinHolographUnknown HandScienceOpticsCorrespondenceTranscribed and tagged by Linda CrossCoding audited and updated to Newton v2.0 DTD by Michael HawkinsUpdated to Newton V3.0 (TEI P5 Schema) by Michael HawkinsInline images embedded and minor code corrections by Michael HawkinsProofread by Margarita Fernandez-ChasProofed by Robert IliffeReviewed by John Young
475
SrSir
I have sent you yethe papers I mentioned, by Iohn Stiles. Vpon reviewing them I find somethingssome things so obscure as to need a further explication by figures, & some other things I guess will not be new to to you though almost all was new to me when I wrote them: but as they are I hope you will accept of them though not worth yethe ample thanks you sent. I remember in some discourse wthwith Mr Hook I happend to say that I thought light was reflected not by yethe parts of glass water air or other sensible bodies, but by that same superficies of yethe æthereal Mediums wchwhich refracts ityethe rays ytthat happen to break through it, yethe rays finding some difficulty to break through it in passing out of denser æther into rarer & a greater difficulty in passing out of yethe rarer into yethe denser, & so being either reflected or refracted by yethe superficies as yethe circumstances they happend to be in at their incidence make 'em unable or able to break through it. And for confirmation of this I addedsaid further that I thought the refractflexion of yethe light at its tending out of glass into air would not be diminisht or weakend at its passingby drawing away yethe air in Mr Boyles an air Pump as it ought to be if they were yethe parts of yethe air ytthat reflected it:ButAndadded that I had not tryed this experiment; but thought he was not unacquainted wthwith notions of this kind. To wchwhich he replied that yethe notion was new & ytthat he would yethe first opportunity try yethe experiment I propounded. But upon reviewing yethe papers I send you, I findound it there set down for tryed; wchwhich madkes me recollect that some years ago I had occasionally observed in an Air Pump here at Christs College ytthat I could not perceive yethe reflexion ofyethe inside of yethe glass diminished by drawing out yethe air. This I thought fit to mention least my former forgetfulness should seem to make me seem to have set down for certain what I had notnever tryed.
SrSir I had formerly determinedpurposed never to write any Hypothesis of light & colours, fearing it might be a means to ingage me in vain disputes: but I hope I need not fear ytthat if it proceed no further then to yethe ears of yethe Society. Considering therefore that such an Hypothesis will much illustrate yethe papers I send you; I shall not longer scruple to describe one so far as it may be done in this cursory letter: not concerning my self whether it shall be thought probable or improbable so it do but render yethe papers I send you more intellegible
First then I supposein this Hypothesis it is to be supposedytthat there is an æthereal Medium much of yethe same constitution wthwith air but only far more rare more subtile & more strongly elastic: And of yethe existence of this Medium yethe motion of a pendulum in Mr Boyles a glass exhasted of air almost as quickly as in yethe open air is no inconsiderable arguments.
.2. I suppose this æther a vibrating mMedium like air, only yethe vibrations far more swift & minute; those of air made by a man's ordinary voice succeeding one another at a foot distance mo more then a foot distance, but those of æther at a less distance then yethe hundred thousandth part of an inch. And as in air yethe vibrations are some larger then others, but yet all equally swift (for in a ring of bells yethesound of every tone is heard at 3 or 4 miles distance, in yethe same order ytthatyethe bells are stroke:) so I suppose yethe æthereal vibrations differ in bignes but not in swiftness.
3 As yethe air can pervade yethe bores of small glass pipes but yet not so easily as if they were wider, & therefore stands at greater degree of rarity then in yethe free aereal spaces, & at so much a greater degree of rarity as yethe pipe is smaller, as is known by yethe rising of water in such pipesto a much greater heighheight then yethe surface of yethe stagnating water into wchwhich they are dipt: so I suppose æther, though it pervades the pores of crystal, glass, water & other natural bodies, yet it stands at a greater degree of rarity in those pores then in the free æthereal spaces & at so much a greater degree of rarity as yethe pores of yethe body are smaller. And this I take toWhence it may be ytthat for instance though a lighter body yet having subtiler ꝑparts & consequently smaller pores then water is the more strongly refracting liquor.This also may be yetheprincipall cause of yethe cohesion of yethe parts of solids & fluids, & of yethe standing of yethe☿ in yethe Torricellian experiment at a much greater height then 29 inches: For yethe denser æther wchwhich surrounds these bodies must croud & press their parts together much after yethe same manner ytthatytethe air surrounding two marbles presses them together if there be little or no air between them.
4 I suppose light is neither this æther not its vibrating motion, but something of a different kind propagated from lucid bodies, whether it be an aggregate of peripatetic qualities or of unimagiblyunimaginably small & swift corpuscles from luminous bodies at gtgreat distances from one another. or any other corporeal emanation, or some motion of the æther of a differing kind from its vibrations itf any such can be imagind proper for this purpose, or an impuls or motion of some other medium dispersed through yethe æther For yethe air, vapors – For yethe air, vapours, exhalations electric & magnetic effluvia are all instances that there may be other various mediums diffused through yethe æther. a corporeal emanation or an impuls or motion of some other medium dispersed through æther like yethe magnetic or electric effluvia, or some motion of yethe æther of a differing kind from its vibrations if any such can be imagin'd proper for this purpose, or a peripatetic quality. To avoyd dispute & make this HyposesisHypothesis general let every man here take his fancy. Only whatever itlight be I would suppose it consists of successive rays differing from one another in some accidentalcontingent circumstances, as bignes form or vigour; like as yethe sands on yethe shore yethe waves of yethe sea the faces of men & all other natural things of yethe same kind differ, it being almost impossible for any sort of things to be foundwthwithout some contingent variety. And further I would suppose it divers from yethe æthereal vibrations becaus
[5 As there is a certain tenacity in yethe superficies of water more then in yetheinwards parts of either water or air so that dust or even yethe filings of a metalwchwhich readily fall in either water or air will swim upon if thrown upon their common superficies: so I suppose there is a greater tenacity in yethe common superficies of a rarer & denser æther then in other places, so that yethe rays of light find some difficulty in passing through ytthat superficies & are reflected or refracted or reflected accordingly as they can or cannot overcome thate difficulty. Yet this superficies I superficies I suppose to be not a mathematical one like ytthat of water, but of some breadth, the æther therein being of all intermediate degrees of rarity between yethe rarer & denser Mediums.
6 When yethe rays impinge upon this superficies I suppose they cause vibrations in it as stones thrown into water do in its surface, & that these vibrations are propagated every way into both yethe rarer & denser Mediums as yethe vibrations of air wchwhich cause sound, are from a stroke but yet continue strongest where they began, & alternately contract & dilate yethe æther in that physical superficies: ♀wchwhich superficies being thus continually agitated by vibration & the æther therein continually expanded & comprest by turns; if a ray of 476 light impinge upon it while it is much comprest, I suppose it is then too dense & stiffe to let yethe ray pass through & so it reflects it, but attheotherays that impinge on it at other times, go through & are refracted.
To explain this a little further you may consider how fluids when formed into thin shells or plates grow much more tenacious & tough then otherwise. Thus things wchwhich readily fall uponin water if let fall upon a bubble of water they do not so easily break through it as through yethe superficies of stagnating water, but are apt to slide down by yethe sides of it if they be not too bigg & heavy. So if two well polished convex glasses grownd on very large shpheres be laid one upon another, the air between them easily recedes till they almost touch but then begins to resist so much that yethe weight of yethe upper glasse is too little to bring together so as to make yethe black spot mentioned in these papers appeare in yethe middlst of yethe rings of colours; & if yethe glasses be plain though no broader then a two pence, a man wthwith his whole strength is not able to press all yethe air out from between them so as to make 'em fully touch. You may observe also that Insects will walk upon water wthwithout wetting their feet, yethe thin skin or shell between their feet & yethe water bearing them up & so motes falling upon water will often lye long upon it wthwithout being wetted. And in like manner I suppose a ray in passing out of denser æther into rarer, when there remains between yethe ray of yethe rarer æther so little distance to be part through that yethe denser æther between them may be compared to a thin skin or shell, it finds muchsome difficulty to get through this skin: & this skin bein the æther where this skin is being alternately expanded & comprest by yethecontinuall vibrations wherewith 'tis continually agitated, the skin is sometimes weakned by yethe expansion sometimes strengthend & stifned by yethe compression & accordingly reflects or transmits or reflectsyethe ray.
When a ray finds the refracting superficies so much condensed that it cannot get through, so soon as the ray has spent its force upon yethe superficies in endeavouring to pierce it, yethe superficies by its elasticity returns back upon yethe ray as a racket upon a tennis ball, all yethe force it received & so reflects it at an angle equal to that of incidence. But if yethe superficies at yethe arrival of yethe ray be in a state of expansion, or not so much condensed but ytthatyethe ray can pierce it, then I suppose upon yethe rays departing into yethe next Medium the superficies acts upon yethe it & puts inadds more or less celerity to it according to yethe rarity of that Medium; for the rarer yethe medium is wchwhichyethe ray enters, yethe more easily does yethe ray yeild to yetheaction of yethe superficies. To use a gross similitude you may conceive yethe action of yethe superficies upon yethe departing ray, to be something like that of a man's fingers darting a plumb-stone or other slippery body from between them by compressing it; for ]When a ray therefore moves through æther of uneaven density, I suppose it may beis most prest, urged or otherwise acted upon by the ætherby yethe on that side towards yethe denser æther & receives a continual impulsor ply from that side to recede towards yethe rarer, & beso is accelerated if it move that way or is retarded if yethe contrary. On this ground if a ray move obliquely through such an uneavenly dense medium (that is obliquely to those imaginary superficies wchwhich run through yetheequally dens parts of ye medium of equal density& may be called yethe refracting superficies,) it must be incurved, as Mr Hook hasit is found it to be by observation in water when lower parts were gradually made more salt & so more dense then yethe upperSee hisMr Hooks Micrographia where he speaks of yethe inflexion of a ray. And this I take tomay be yethe ground of all refraction & reflexion: for as the rarer air wthwith a small glas pipe & yethe denser air wthwithout are not disterminated by a mathematical superficies but the air between at yethe orifice of yethe pipe runs through all intermediate degrees of density so I suppose yethe refracting superficies of æther between unequally dense Mediums to be not a mathematical one but of some breadth yethe æther therein being of all intermediate degrees of rarity between yetherarer & denser æthereal mediums, & ytthat refraction I conceive to proceed from the continual incurvation of yethe ray all yethe while it is passing this physical superficies. Now if yethe motion of yethe ray be supposed in this passage to be incurved or diminished in a certain proportion according to yethe difference of yethe densities of yethe æthereal mediums, & yethe addition or detraction of yethe motion be reccond in yethe perpendicular frōomyethe refracting superficies, the sines of of incidence & refraction will be proportional according towtwhat Cartes has demonstrated.
IfThe ray therefore in passing out of yethe rarer medium into yethe denser inclines continually more & more towards yethe refracting superficies & if yethe differing densities of yethe mediums be not so great nor yethe incidence of yethe ray so oblibut that it as to make it ∥ to ytthat superficies before it gets through, then it goes through & is refractedkeeps its last inclination & is refracted, but if through yethe aforesaid causes yethe ray become ∥ to that superficies before it can get through, then it must turns back & isbe reflected. Thus for instance it may be observed that in atriangular glas prism OEF that ye rays AN that tend out of yethe refr. sup glass into air, do by inclining yenrefracting superficies more & more to them, emerge more & more obliquely as at NL till they be infinitely oblique ytthat is in a manner ∥ to yethe refracting suꝑperficissuperficieswchwhich happens when yethe angle of incidence is about 60 or 61 gr. & then if yethe refracting superficiesthey be a little more inclined yetheraysthey become all reflected, as at Aνλ becoming I suppose ∥ to yethe superficies before they can get through it. For instance let ABCD represent yethe rarer Medium, EFHG yethe denser CDFE yethespacerefracting physical superficies space between them inorwchwhich refracting physicall superficies in wchwhichyethe æther is of all intermediate degrees of density from yethe rarest æther at CD to yethedensest at EF. AIKL a ray, AIN itits incident part IKMN its incurvation by yethe refracting superficies, & KNL its emergent part. Now if the ray AM become so much incurved as to become at its emergence KN, as nearelyas may be ∥ to yethe refrac CD or EF, its plain ytthat if ytthat ray had been incident a little more obliquely as is represented at Aμ it must have become parallel to CD before it had arrived at EF & so could never have got to yethe outside of the refracting superficies EF but must have turnd back & been reflected as it is represented at Aμνλ. And yethe like would have happend if yethe density of yethe æther had further increased from EF to PQ so ytthat PQHG might be a denser medium then EFHG was supposed, for then yethe ray in passing from m to n being so much incurved as at n to become ∥ to CD or PQ, its impossible it should ever get nearer to PQ but must at N begin by further incurvation to turn back & so be reflected. *○
This may be yethe cause & manner of relexion when light passes out oftend fromyethe rarer intotowardyethe denser æther, but to know how it should be reflected when it tends out offromyethedenser into yethe rarer is more difficult to say; yet thus I explain it thus you are to consider how fluids neare their superficies are less pliant & yeilding then in their more inward parts, & if formed into a thin plate or shel they become much more stif & tenacious then otherwise. Thus things let fall –––– And so apply æ I suppose æther in yethe confine of two mediums is less pliant & yeilding then in other places &so much yetheless pliant by how much yethe mediums differ more in density: so that if a ray in passing through this cuticle & so great difficulty where yethe mediums are of very differing density as to be reflected by incurvation after yethe manner described above: yethe parts of yethe æther on that side where they are less pliant & yeilding acting upon yethe ray much after yethe manner that thay would do were they there denser on that sidethere then on yethe other side[whence if yethe superficies be not so unpliant but that yethe ray can get through it, yet the ray must first becom bent from yethe perpendicular incurved till it get to yethe most unpliant part of yethe superficies & in moving further through yethelessmore pliant parts be unbent again & bent yethe contrary way by yethe greater density of yethe Medium yethe ray is moving out of.] And this I suppose may be yethe cause of the reflexion of Quicksilver & other metalline bodies. It must concur to increase yethe reflective virtue of yethe superficies when rays tend out of yethedenserarerinto yethe denser. And in that case therefore thereforeyethe reflexyethe reflexion having a double cause 477much; after the same manner as if all the glass between B & D were broken off at B the obtuse angle of the Diamond cut.
Exempl. 2. In machinis mobilibus.
. . . . . . . . . . . ◻ECG ut . ∠ECG ut ∠ECG ut . ∠ECG×EKq−KDq ut ◻EDG.
Let AB, CD represent yethe ∥ planes of a lookinglassBD the plane of the Diamond cut making at B a very obtuse angle with yethe plane AB. And let all the light between yethe rays The preceding diagram has been written over in the manuscript. FBM pass perpendicularly through the parallel planes of the glass & fall upon yethe paper between I & M & all the light between yethe rays GO et HD be refracted by the plane oblique plane of yethe diamond cut BD & fall upon the paper between K & L: and the light wchwhich passes perpendicularly thorough the ∥ planes of yethe glass & falls upon the paper between I and M will be bordered with three or more fringes of colours at M If Plates of Looking glass sloopt off neare the edges with a diamond cut & the be held in the same beam of light, the light wchwhich passes through the parallel planes of the glass, & is bounded at within [& falls upon white paper at some distance from the glass] will be bordered with three fringesbordered at the diamond cut with the like fringes of colours although it be bounded only by the diamond cut if Obs. 1. And hence I seem to gather that yethe rays in passing by the sides of yethe hair at a little distance are bent & those are most bent wchwhich pass by paribus)wchwhich pass by the hair at yethe leats distance. Let H represent yethehair, aei, bfk, cgl, dhm four rays passing by the hair at several distances & bent in e, f, g, h & falling let them fall on yethe paper beyond yethe hair at i, k, l, m. And let nrw, osx, pty, qvz represent four other rays passing by the hair on yethe other side & bent in r, s, t, v & let them fall on yethe paper at w, x, y, z. And let mz be yethe shadow of the hair cast upon the paper. [ By this bending of the rays the shadow will become broader then it would be if they were not bent, [&] Produce the outmost rays dh & qu in right lines to A & B & the if those rays were not bent the hai in passing by the hair the breadth of yethe shadow of yethe hair upon yethe paper would not be greater then AB whereas by experrience its found considerably greater.] And if the rays wchwhich pass by the hair at the least distance be most bent as is represented in the figure the shadow will be broadest in proportion to yethe distance of yethe paper from yethe hair when the paper is nearest to the hair, But as is found true by experience. But if yethe outmost rays dh & qu werebe not bent, produce them in right lines & let them fall on yethe paper at A, B & will be the breadth of the shadow will be AB wchwhich is less then it is found by experience if these rays are therefore bent tho not so much as the as yethe rays wchwhich pass by the hair at a less distance.So then the dark lines above mentioned wchwhich run bealong between the first and second fascias of either knife fringes of yethe shadows of either knife & meet in the middle of yethe light wchwhich passes between the knives at yethedistance of a fift part of an inch from the concourse of yethe edges of yetheknives, are in the passage betwe of yethe light between the knives distant from yethe edges of the knives the 320th part of an inch or there abouts.At another time when the two knives were distant eight feet & five inches from the little hole in the window made with a small pin as above, the dark line or shadow the point i where the dark line is & xip meet & cross one another between the first fringes of yethe shadows of either the two knives, fell upon a paper placed at the following distances from yethe knives when made at the distances between the edges of the knives were also as follows.Distances between the edges of the knives in myillesimal parts of an inchDistances of yethe Paper from the knives in inches & decimals of an inchdeg0'0121'5.1.0'0203'45.3 3 3.0'0348'6.8.0'05732.32.0'08196.96.0'087131'5131.And hence I gather that the light wchwhichpass makes the fringes wthwithyethe shadows between them passes by the edges of the knives at a less distanceupon the paper is not the same light at all distances of yethe paper from yethe knives, but when yethe paper is held neare yethe knives yethe fringes are made by light wchwhich passes by the edges of yethe knives at a less distance & is more bent then when the paper is held at a greater distance.When I made these Observations I designed to repeat most of them with more care & exactiness & to make some othersnew ones for determining the manner how the rays of light are bent in their passage by bodies for making these fa fringes of colourswthwithyethe dark lines between them:Butbut I was then interrupted & cannot now think of taking these things into further consideration. And since I have have not finished this part of my designe &I shall conclude with proposing only some Quæres in order to a further search to be made by others in these matters by others. [who may take these things into consideration]Quære 1. Do not Bodies act upon light at a distance & by their action bend its rays & is not this action strongest at yethe least distance.☉ 1B. Are not &c☉ 1B. Are not the rays of light in passing by the edges & sides of bodies bent several times backwards & forwards with a motion like that of an Eele.2 Are not the rays more or less flexible accordingly as they are more or less refrangible, & are they withDo not the rays wchwhich differ in refrangibility differ also in flexibility& are they not by their different inflexions made at equall distances from yethe bodiesare they not separated from one another so as byafter separation to make the colours in the three fringes of colours above described. And after what manner are they inflected to make those fringes.3 Do not the rays of light wchwhich fall upon bodies & are reflected or refracted begin to bend before they arive at yethe bodies, & are they not reflected refracted & inflected by one & yethe same Principle acting variously in various circumstances.4 Do not light & bodies act mutually upon one another, that is to say bodies upon light in emitting reflecting refracting & inflecting it, & light make ally478ally upon bodies for heating them & pulling their parts into a vibrating motion wherein heat consists. And do not black bodies conceive heat more easily from light then those ‡‡ Ad 4. Ad Do not black bodies conceive heat more easily from light then those of other colours do by reason that yethe light falling on them is not reflected back but enters yethebodies & is often reflected & refracted within them before it is shifted & lost. And is not the greatness or vigour of the action between light & sulphureous bodies observed above one reason why sulphureous bodies conceive heat & burntake fire more readily & burn more vehemently then other bodies do?5 Do not all fixt bodies when heated beyond a certain degree emit light by the vibrating motion of their parts.6 Is not fire a body heated so hot as to emit light copiously. For what else is a red hot iron or a red hot stone then fire & what else is a burning coale then red hot wood [whose heat is preserved by the actions of an acid spirit in the air acting upon & dissolving the wood.7 Is not the flame a vapour fume or exhalation heated red hot that is so hot as to shine For bodies do notdo not flame wchwhich do not emit a copious fume.8 Are not the sun & fixt stars great earths vehemently hot whose heat is conserved by the mutuall action & reaction between them & the light wchwhich they emit & whose parts are kept from fuming away by the vast weight of the Atmospheres incumbent upon them.9 Do not the rays of light in falling upon the Tunica retina bottom of the eye, excite vibrations in yethe Tunica retina wchwhich vibrations being propagated along the solid fibres of yethe Optick Nerves into the brain cause the sense of seeing. And are not the vibrations made by several sorts of rays** For since dense bodies conserve their heat a long time & the densest bodies conserve their heat the longest, the vibrations of their parts are of a lasting nature & therefore may be propagated along solid fibres of uniform dense matter to a great distance for conveying into the brain the impressions made upon all the Organs of sense. For that motion wchwhich can continue long in & yethe same part of a body can be propagated a long way from one part to another supposing the body homogeneal so that yethe motion may not be reflected refracted & interrupted or disordered by theany uneavenness of the body. 10 Do And not several sorts of rays make vibrations of several bignesses, wchwhich according to their bigseveral bignesses excite sensations of several colours much after the manner that several the vibrations of yethe air according to their several bignesses exite sensation of several sounds? And particularly do not the most refrangible rays excite the shortest vibrations for making a sensation of deep violet, the least refrangible the largest for making a sensation of deep red & the several intermediate sorts of rays vibrations of several intermediate bignesses to make sensations of the several intermediate colours?11 May not the harmony & discord of colours arise from the proportions of the vibrations as the likepropagated through the optic nerves into the brainandas the harmony & discord of sounds arises from the proportions of yethe vibrations of yethe air. For some colours are agreable as those colours of gold & Indigo & others disagree.12May Are not the species of objects seen wthwith both eyes united when the Optick nerves meet before they come into the brain: For the fibres on the right side of both Nerves uniting there & after unison going thence into yethe brain in the nerve wchwhich is on the right side of the head & the fibres on the left side of both nerves uniting in the same place & after union going into the brain in the nerve wchwhich is on yethe left side of the head into yethe brain & these two nerves meeting again in the brain in such a manner thet their fibres make but one intire species half of wchwhichis on yethe right side of yethe sensorium & comes from yetheright side of both eyes & the other half of wchwhich on yethe left side of yethe sensorium comes from the left side of both eyes? For the optic nerves of such animals as look the same way with both eyes (as of Men, Doggs, Sheep, Oxen) meet before they go into the brain, but the Optic nerves of such animals as do not look the same way wthwith both eyes (as of Fishes & the Chameleon) do not meet if I am rightly informed.7B.Is not the7B. Is not the greatness of the action between light & sulphureous bodies observed above, one reason why sulphureous bodies conceive heat & burn more readily & more vehemently then other bodies do. Obs.1. | Let X represent one end of the Hair, cut cross theadg, beh, cfirepresent three rays passing by one side of yethe hair atseveral distances, & let d e & fkng, lor, mps three other rays passing by the hair at other side of yethehair at yethe like distances; d, e, f & n, o, pthe places where these">these hairsrays are bent in their passage by the hair; g, h, i, q, r, s the places where these rays fall on paper si the breadth of the shadow where these rays of yethe hair cast on the paper And if the rays wchwhich pass by the hair at the least distances be most bent as represented in yethe figure By the bending of yethe rays the shadow becomes broader then it would otherwise be & if the rays which pass by the hair at the least distance be most bent the rays will as is represented in the figure the breadth of the shadow will be broadestincrease most in proportion to yethe distance of yethe paper from yethehair when the paper is nearest to yethe hair as is found by experiensce& Ai & Bs two rays passing to yethe points i & s without bending when the paper& not hair is taken away. Andit is manifest that since all the light between the lines Ai & Bs is bent & turned asid in passing by the hair & turned aside from yethe shadow: for if any rayspart of this light were not bent theyit would fall on the paper within the spaceshadowsi & destroy ththere illuminate it & take away that part of the shadow where it falls wchwhich is contrary to experience. Bodies therefore act upon the light at a gre considerable distance in its passing by them; but the action is strongest on the rays wchwhich pass by at yethe leeast distances & grows weaker & weaker as light the rays on wchwhich they ataccordingly as the rays pass by them at distances greater & greater, as is represented in the scheme For thence it comes to pass that the shadow of the hair is much broaderis much broader in proportion to yethe distance of the paper from the hair is much broader when when yethepaper is at a dis neare the hair then when it is at a great distance from it. Ad Obs. 6. And hence the light of yethe inwchwhich is least bent & goes to the inward ends of the streams passes by the edges of the knives at yethegreatest distance, & this distance when the shadow begins to appear between the streams is is about yethe eight hundredth part of an inch. And the light wchwhich passes by the edges of yethe knives at a distancedistances still less & less distances is more & more bent & goes to those parts of yethe streams which are further & further from the direct light, [because as the knives approach one another till they touch, the light at yethe inward ends of the streams vanishes more and more untill the who & the streams grow shorter & shorter at those ends untill they wholy disappear.]Ad Obs. 7. And hence the light of the first fringe passed by the edge of yethe knife at a distance greater then the eight hundreth part of an inch & the light of yethe second fringe passed by the edge of the knife at a greater distance then yethe light of yethe first fringe did, & that of yethe third at a greater distance479 Could all the phænomena of nature be [evidently] deduced from only thre or four general suppositions there might be great reason to allow the the reasonables ofadmit ofallow the truth of those suppositions to be true:but if you where those forfor explaining every new Phænomena you make a new Hypothesis if you suppose ytthatyethe particles of waterAir are of such a figure size & frame, those of water of such another figurethose of Vinegre of somesuch another figure, those of sea salt of such another figure, those of nitre of such another, those of Vinegre Vitriol of such another, those of Quicksilver of such another, those of fire of flame of such another, those of Magnetick effluvia of such another, If you suppose that yetherays of light consists in such a motion pression or force, those & that those of several colours differ from oneits various colours are made by such & such variations of the motion & so of other things: your Philosophy will systeme of Philosophy wi Philosophy will be nothing else then a systeme of a great number of uncertain Hypotheses. And what certainty can there be in a Philosophy wchwhich consists in as many Hypotheses as there are Phænomena & & explications of Phæ nomena to be explained. What everTo do To explain all nature is too difficult a task for any one man or even for any one age. Tis much better to do a little with certainty then to & leave the rest for others that come after, then to explain all things by conjecture & leave without making sure of any thing. And there is no other way of doing any thing with certainty then by drawing conclusio drawing conclusions from experiments & phænomena untill you come at such general Principles as are & then from those Principles giving an account of Nature. This is yethe only Whatever is certain in Philosophy is owing to this method & nothing can be done without it. I will instance in some particulars.One principle in Philosophy is yethe being of a God or spirit infinite eternal omniscient, omnipotent, & the best argument for such a being is the frame of nature & chiefly the contrivance of yethe bodies of living creatures. All the great land animals have two eyes, in the forehead a nose between them a mouth under the nose, two ears on yethe sides of yethe head, two arms or t or two fore leggs or two wings on the sholders ,& two leggs behind & this symmetry in yethe several species could not proceed For from chance there being an equal chance for one eye or for three or four eyes as for two, & so of the other membersNothing is For Nothing is more curious & difficult then yethe frame of yethe eyes for seeing the& of the ears for hearing of wings for flying & & yet notan animal th a s a species no sort of creatures has these members withoto no purpose. What more difficult then to fly? & ye had flying creatures their wings by chance? or has any creature wings without being able to fly? & yet was it by chance ytthat all creatures can fly wchwhich have wings? Certainly he that framed yethe eyes of all creatures understood the nature of light & vision he that framed their ears understood yethe nature of sounds & hearing, he ytthat framed their noses understood yethe nature of odours & smelling, he that framed the wings of flying creatures & yethe fins of fishes understood the force of air & water & what members were requisite to enable creatures to fly & swim: & therefore yethe first formation of every species of creatures must be ascribed to an intelligent being such a being as we call God These & such like considerations are the most convincing arguments for such a being & have convinced mankind in all ages that yethe world & all yethe species of things therein were originally framed by his power & wisdom. And to lay aside this argumtment is very unphilosophical.Another Principle is that matter is impenitrable by other matter. This is usually looked upon as a maxim known to us by yethe light of nature, altho we know nothing of bodies but by sense. We find by dayly experience that bodies resist one another as often as they come together & cannot by any force be made toto penetrate one anothers dimensions. And this holding true wthwithout exception in all bodies here below in wchwhich we can come to make observations we conclude it to be the property of all bodies whatsoever. And such observations occurring every day to every man this property of bodies is acknowledged by all mankin men without any dispute & looked upon as an Axiom.A third property of bodiesprinciple is is that all the great bodies in yethe Vniverse have a tendency towards one another proportional to yethe quantity of matter conteined in them & that this tendency in receding from the body decreases & is reciprocally proportional to yethe square of yethe distance from yethe body: [And all small bodies have the like tendency towards the great ones & this tendenc This tendency towards yethe earth we find in all bodies here below & call it gravity]ThisSuch a tendency towards the earth we find in all bodies here below & call it gravity. & by experiments of the Pendulum & of falling bodies we find it exactly proportional to the quantity of matter in the several bodies We find it also in the Moon, the force wchwhich keeps her in her Orb being exactlyreciprocallyequal to yethe force of gravity.& recipro The like tendency towards yethe sun we find in all the Planets who are thereby keptproportiallproportionall to yethe square of her distance from yethe earth Iupiter we find in yethehis four satellites proportial which are thereby kept in their Orbs about him & this tendency by comparing the Orbs & Revolutions of yetheSatellites together is proportional to the matter in the Satellites reciprocally as their squares of their distances from Iupiter. The like tendency to Saturn we find in this Sa five Satellites, proportional directly to their matter & in reciprocally to the squares of their distances. And all the Planets both primary & secondary &appear to have & some so many cComets as have been well observed appear to have yethe same tendency towards the Sun directly proportional directly to the matter in each of them & reciprocally to their distances from the sun. And by yetherest or very small motion of the Aphelia of the the Planets it appears by that this tendency of allthe Planets towards Iupiter Saturn &yethe Sun & of the Moon towards yethe earth decreases in recedingThe following mathematical fragment is written upside down.. . .A fourth Principle is that all sensible bodies are aggregated of particles laid together wthwith many interstices or pores between them For water soaks into yethe pores of all animal & vegetable substances & some minerals & quicksilver into yethe pores of Metall & acid liquors into yethe pores of all minerals & metals in dissolving them, & light passes through yethe pores ofaire, water oyles glasalt spars sand glass crystal gemms & all other pellucid substances & through the particles of all metals salts & minerals dissolved in pellucid menstruums or vitrified & through thin pieces of wood, flesh, bone horn stone & vitrified earth. As to the former Principle is As by the formerthirdPrinciple we gave an account heretofore of yethe motions of all the Planets & of yethe flux & reflux of yethe sea, so by this Principle we shall give an acct in yethe following treatise give an acct of yethe permanent colours of natural bodies, nothing further being requisite for yethe production of those colours then that yethe coloured bodies abound with pelludcid particles of a certain size & density. This is to be understood of the largest particles or particles of yethe last composition. For as bodies are composed of these larger particles with larger pores between them so it is to be conceived that these larger particles are composed of smaller particles with smaller pores between them. And when water dissolves salts & acid menstruumsor quicksilver dissolves metals it is to be conceived that yethe liquor enters only the larger pores & separates onlyyethelarger particles of yethe salt or metal from one another without soaking into yethe smaller particles480The text on this and the following page is written upside down.. . | . . // . / , . / Between the sines of incidence & refraction counted from yethe sine of incidence when the refraction is made of of out of the thePlate of any substance into yethesurrounding Medium of any other substance, that is out of in this case out of Glass into Air. Now if the thickness of the gGlass be increased by degrees so as to bear to its first thickness (vizt that of an a quarter of an inch) the proportions of 34386 to 34385, 34384, 34383, 34382 &c, the secants analogous to these& the first thickness be divided into 100000000 equal parts the increased thicknesses will be 100002908, 100005816, 1000078725, 1000011633 &c and the Angles of wchwhich these incumber thicknesses are secants will be 26' 13'', 37' 5'', 45' 6'', 52' 26'' the radius being 100000000,and the sines of these Angles are 762, 1079, 1321, 1525 and the proportional sines of refraction 1172, 1659, 2031, 2345 the Radius being 100000. ForAs Mathematicians have two Methods of doing things wchwhich they call cComposition and Resolution & in all difficulties have recourse to their method of resolution before they compound so in explaining the Phænomena of nature the like methods are to be used & he that expects success must resolve before he compounds. For the explications of Phænomena are Problems much harder then those in abstractioMathematicks. The method of Resolution consists in trying experiments & considering all the Phænomena of nature from whence any thing can of nature relating to the subject in hand & drawing conclusions from them & examining the truth of those conclusions by new experiments & so proceeding drawing new conclusions (if it may be) from those experiments & so proceeding alternately from experiments to conclusions & from conclusions to experiments untill you have come to the general properties of things, And when you [& by experiments & phænomena have established the truth of those properties] Then assuming those properties as Principles of Philosophy you may proceed from by them explain the causes of such Phænomena as depend upon them & follow from them: wchwhichis the method of Composition. But, if youwthwithout deriving the properties of things from Phænomena you explain feign Hypotheses & think by them to explain all nature you may make a plausible systeme of Philosophy for getting your self a name, but your systeme being will be little better then a Philosophical Romance Romance. ‡ To explain all nature is too difficult a task for any one man or even for any one age. Tis much better to do a little with certainty then to seem to no & leave the rest for others that come after you then to then to explain all things by conjecture without making sure of any thing.Thus in Mathematical Principles of Philosophy I first shewed from Phænomena that the all bodies endeavoured by a certain force proportional to their matter to approach ane another, that this force in receding from yethebody grows less & less in reciprocal proportion to yethe square of the distance from it & that it wasis equal to gravity & therefore wasis one & the same force with gravity. Then using this force as a Principle of gravity I shewed howPhilosophy I derived from it all the Phænomena of naturemotions of the heavenly bodies & the flux & reflux of yethe sea, shewing by mathematical demonstrations that this force alone was sufficient to produce all those Phænomena, & deriving from it (a priori) some new motions wchwhich Astronomers had not then observed but since appeare to be true, as that Saturn & Iupiter draw one another, that yethe Variation of yethe Moon is bigger in winter then in suppmmer, that there is an equation of yethe Moons meane motion amounting to almost 5 minutes .wchwhichdepends upon the position of her Aphelium Apoge of yethe Sun.Seignr Rizzetti in the beginning of his paper writes thus. Newtonus cum lumini Solis in refraction objecisset Prisma triangulare, agravit spectrum Solis magis produce quam par lex vulgata refractionis postulasset: ideo lumen solis dispergi in refractione dispergi, ita ut unicus simplex radius in plures discindatur. Vnde apinatus est, id ipsum fore si lumenBut Newton affirms no such thing. He affirmsrepresents that every ray emitted from the Sun or other lucid body, continues one & the same without any dispersion or splitting by refraction or change in repect of refrangibility or colour. For in his first Definition, he calls the Rays of light its least parts, whether successive in the same lines or contemporary in several lines. And in his second Proposition he brings his 5t, 6t, 7th, 8th, 9th & 10th Experiments to prove that that one & the same ray is not split by refraction disturbed shattered, dilated split or spread into many rays. And his first Proposition is that homogeneal light is refracted regularly without any dilatation splitting or shattering of the Rays.He saith further that if the breadth of the of the image of a lucid point cast upon the bottom of the eye were about the 55th part of the bread of the pupill of the eye the hair of a mans head could not appear so distinct as it really doth; & then he adds. Cum dixerim in visione capilli locum minima esse aberratio ni Newtonianæ quia minime cernitur, adversus hujusmodi argumentum rationabilior mihi videretur objectio ducta a Propositione VII Autoris: nimirum adeo extenuari lumen aberrans in distantia a suo centro, Iut (loquar Newtoni verbis) non sit sensibile nisi in eodem centro aut prope illud. Vt objectioni respondeam, divisa semidiametro luminis aberrantis in undecim partes equales; ejus densitas juxta Newtonianam sententiam, decresit in talam Arithmeticam proportionem, ut cum expressa sit in prima parte a numero 21, exprimatur in secunda a numero 19, & sic deinceps, adeo ut in parte ultima exteriori exprimatur per unitatem.And yet Mr Newton affirms no such Arithmetical proportion. His Rule is that the density of the light at any distance from the center ais as thedistance from the of that point from the circumference applied to its distance from the center. Let the semidiameter of the erring light be divided into eleven equal parts, & the density of the light in the midle of the part next the center will be to its density in the middle of the part next the circumference not as 221 to 1 but as to or as 441 to 1He saith further. Vidit sapientissimus Anglus speciem solarem magis in longum porrectam quam lex vulgaris refractionis postulasset cum illam cerneret diversicolorem, scilicet rubram, mox flavam, deinde viridem, postea cæruleam, & tandem supra violaceam, hoc experimento fretus suum confecit systema luminis at colorum. Omnia experimenta, quibus illud innixum est, renovare curari, & ea (prologuid licet?) partim falsa, & omnia reliqua inveni propter omissionem ––– aliquam alicujus circumstantiæ æquivoca ac minime concludentia. Vt unicum [experimentum] allendas obsecro. Then he describes the experiment of the red & blue colours above recited with & tried before the Royal Society with success & of the red & blue colours as of the chart painted with red & blue coloursof painting a chart wthwith red & blue colours & casting the species thereof through a Lens upon which paper as is described aboveand denies as is described above which was lately shewed to the R. S. as is with success as is described above & denies the success. If it did not succeed with him it was because he did not know perfectly well as is described above. He should have told the world that Newton ground founded his Theory of light & colours upon the experiment wchwhich for its demonstrative evidence he calls experimentum crucis. This experiment he could not deny because it hath been tried again & again with full success both in France & in Italy with fo as well as in England: & therefore he passes it by in silence & denies the conclusion drawn from it, & contrary to the Rules481 Rules of Logic disputes against the conclusion without taking note of the Premisses.Pag. 2. L. 38 & p. 6 l 16 Theoriam meam non intelligit Radius unus simplex non dispergitur in plures.Pag. 2. lin. 15. Vult observationem posse corrigi.Ib. l. 16. Telescopia magis perficientur per reflexionem et p. 10. l. 13.P. 4. l. 21. Ergo Newtonus Objectionem prævidit.P 5. l. 12. Imo ducenties densius et amplius, sed Rizzellus Objectionemcalculum ignorat. Sed et Millies densius intra dimidtiam clatitudinem capillæ & decies millies densius intra septiman partem latitudines capillæ &c.P. 6. l. 14. Falsum est.P. 7. l 6 Hinc patet authorem stuidio partium sesibere.Ib. l. 8 Verum est experimentum, sed Rizellus calculum ignoratnescit vere tentare.P. 6. l. 1 Lux dispergitur quidem transiens per Prisma et non dispergitur transiens per Lentem! Ita Rizzellus, qui et promittit se hoc in libro edendo ostensurum esse.Titus MSti est: Christino Martinella Patricio Veneto Iohannes Rizzellus S. D.The Objector doth not understand the Theory against which he is writing. For he supposes that I make one single principal ray to be by refraction dispersed & spread into many. Pag. 2. lin. 3, 8 & pag. 6 lin 162 His Emanuensis knows not how to try the Experiments For the experiment wchwhich he denyes the success of (pag. 7. lin. 8) doth succeed if tried with intense colours & with a Lens well made, free from veins & of a sufficient breadth.3 If he had reasoned right he would have found the light upon yethehair not only twenty times denser but above 200 times denser then at the extremity pag. 5 lin. 12.4 Whence is it that Telescopes by reflexion out do those by refraction, For yethe Telescope by reflexion made by Mr Hadley which is but five feet & a quarter long discovered the four innermost satellites of ♃ when the Moon was up & by reason of the Moonshine the Telescope of Hugenius wchwhich is 124 feet long & a very good one discovered only three of them. See Pag. 2 lin 16 & pag. 10. lin. 13.5 The Objector denies the cConclusion without shewing the flaw of the Premisses, & brings an objection against it. pag. 4. l. 21. Which way of proceeding being once allowed brings every thing to a squabble. & puts an end to experimental Philosophy & even to Mathematicks it self. And the objection is old & sufficiently answered by Mr N. in Prop. VII lib. 1. Optices, if Mr Rizzell had understood the answer. He should either have showed the flaw in the Premisses, or have granted the Conclusion & enquired how, notwithstanding it, vision can be so distinct as it is.6 He tells us that light is dispersed in passing through a Prism but not in passing through a Lens, & that he hath written a book to prove this (pag. 6. lin. 1, 3 & pag. 10 l. 2 & pag. 1. lin. 6, 11) & whereas Mr Newton had shewn how to mend Object Glasses by putting water between two Glasses he proposes to use instead of water a denser Medium then glass. His Paper is a banter like that of Gorden.