Fragments on Optics
Qu. 23. By what means do they bodies act on one another at a distance. The ancient Philosophers who held Atoms & Vacuum attributed gravity to Atoms without telling us the means unless perhaps in figures: as by calling God Harmony & {illeg} \representing/ him & matter by the God Pan & his Pipe, or by calling the Sun the prison of Jupiter because he keeps the Planets in their orbs. Whence it seems to have been an ancient opinion that matter depends upon a Deity for its \laws of/ motion as well as for its existence. The Cartesians make God the author of all motion & its as reasonable to make him the author of {illeg} the laws of motion. Matter is a passive principle & cannot move it self. It continues in its state of moving or resting unless disturbed. It receives motion proportional to the force impressing it. And resists as much as it is resisted. These are passive laws & to affirm that there are no other is to speak against experience. For we find in or selves a power of moving our bodies by or thought |Life & thinking \will/ are active Principles by wch we move our bodies, & thence arise other laws of motion unknown to us.|
And since all matter duly formed is attended with signes of life & all things \natural \{illeg}// |things| are framed wth perfect {&} art & wisdom & Nature does nothing in vain; if there be an universal life & all space be the sensorium of a thinking being & finite things therein {illeg}he \to {his} what/ instead of their pictures formed in or sensorium by motion \are to us,/ as having a perception \perceiving/ of these things \themselves his/ by the actual presence of himself as we have \perceive/ a perception of th{ese} their pictures by {This} \the/ actual presence of what thinks in us \who by immediate presence perceives all things in it as that wch thinks in us perceives | see their pictures in the brain/: the{se} laws of motion \arising from life or will/ may be of universal extent.
— those laws. To some such laws the ancient Philosophers seem to have elluded when they called God Have said that God was \called God/ H{arm}ony, & {illeg} \attributing musick to the spheres/ /represented\ \signified/ his actuating the {illeg} matter {&} harmonicaly proportion{illeg} by the God Pan's playing upon a Pipe & {illeg} \attribute attribute musick to the spheres/ made the distances & motions of the heavenly bodies to be harmonical, & called the Sun the Prison of Jupiter represented the Planets by the seven strings of Apollo's Harp. & attributing musick to the spheres
——— If you think that ye Vis inertia is sufficient for conserving motion, pray tell me the Experiments from whence you gather this conclusion. For Does experim Do you learn by any experiment that the beating of the heart give no new motion to ye blood, that the explosion of Gunpouder gives no new motion to {a} bullet or that a man by his will can give no new motion to his body? Or do you learn do you learn by experimt that the beating of ye heart takes \away/ as much motion from something else as it gives to the blood or that explosion takes \away/ as much motion rom something else as it gives to th a bullet or that a man by his will takes \away/ as much motion from something else as he gives to his body? If so, tell me your experiments {;} if not, your opinion is a dream {ungrounded} {illeg} {ungrounded} without a prejudice. Arguments Reasoning without experience is very slippery. A man may puzzle me by arguents {sic} against \local{ized}/ motion but I'le beleive my ey experience \my eyes./ A man may puzzle not by \may bring plausible/ arguēnts against {doing} {illeg} {doing} what I will \{acting} {illeg} my will voluntary motion \the power of the will// but I'le beleive experience. A man may argue plausibly against for blind fate against final causes but I find by experience that all m I am constantly aiming {illeg} at something. Were it not for experience I should not know that {illeg} matter is \heavy or/ impenetrable or moveable or that matter or that I think o I think or |am or| that there is \matter or/ any thing \else./ in the {illeg} being And therefore to affirm any thing more then I know by {illeg} experience & good reasoning upon it is precarious. An A \Even arguments for a Being if not taken from Phænomena are slippery & serve only for ostentation./ An Atheist will allow that there is a Being absolutely perfect, necessarily existing & the author of all th manking|d| & call it Nature: & if you talk of infinite wisdom \or of any perfection more then \he allows to {say}/ in {natur}/ heel \reccon at a chemæra &/ tell you that you have the notion of \finite or/ limited wisdom from what you find in yor self & are able without ye {illeg} of your self to add \{prefin}/ ye word |no{t}| {&} to understan \or more yt to any verb or adjective &/ without the existence of wisdome not limited \or wisdome more then finite/ to understand the meaning of the sentence phrase words phrase as easily as Mathematicians understand the p what is meant by an infinite line or an infinite area. Arguments not borrowed from And heel \may/ tell you further that ye
<620v>And While these powers are of so large extent, I do not see but that they may be numbred among the \general/ laws of motion. The Vis inertiæ is a passive principle by wch bodies persist in their state motion or rest, receive motion in proportion to ye force impressing it & resist in proportion to ye for as much as they are resisted: \By this principle alone there could never have been any motion in the world./ Thinking is an active principle by wch we move or bodies according to or will, & thence arise other laws of motion unknown to us, wch may be of great entent if |if {not} {illeg} be alive & \{all}/| the Universe be the sensorium of a thinking b|B|eing, may be of great|er| entent. Gravity was recconed among the laws of motion & by the ancient Philosphers who attributed gravity to their Atoms in vacuo, & the same the forces by above mentioned by wch smal bodies act on one another seem to \at small distances may/ have a good a title \as gravity/ to be recconed among those laws.
But while I call those forces attraction \& repulse/ I would not be understood to define the \cause or/ manner of ye action. That wch I call attraction may be done by impulse or by some other meane unknown to me. I only use that word to signify a force by wch bodies tend towards one another whatever \perfect {great} Art &/ be the cause duly formed is attended with signes of life: & if since \all things are framed wth wisdome &/ Nature does nothing in vain \all matter/ if there be an universal life & all space be the sensorium of a thinking Being & the \finite/ things {illeg} \{illeg} be {sic}/ be \{illeg}/ instead of \their/ sensible pictures \formed by motion/ in or Brain; such those laws may be of Universal extent.
I have hitherto been arguing from the effects to their causes & fro carried the argument as high as up to the power \certain forces/ by wch \little/ bodies act on one another at small distances. These forces may be recconed among the laws of motion, & referred to an active principle \perhaps/ \but whether they depend on/ \For bodies alone/ Bodies \alone considered only a long broad & thick/ \bodies alone may be a question For/ are passive. They /By their vis inertiæ they\ continue in their state of moving or resting & receive motion proportional to ye force impressing it & \are/ resistes as much as they are \are/ resisted/ed\, but they cannot move themselves; & without some other principle \then the vis inertiæ/ there could be no motion in the world. And what that Principle is & by \means or/ laws it acts on matter is a mystery & how it stands related to matter is a {illeg} difficult to explain And if there be another Principle \of motion/ there must be other laws of motion de{g} depending on that Principle. [And the first thing to be done in Philosophy is to find out all the \general/ laws of motion so far as they can be discover on wch the frame of nature depends.] For the powers of Nature are not {illeg} And in this search metaphysical arguments are very slippery. A man must argue from phenomena. We find in or selves a power of moving our bodies by or thoughts [but the laws of this power were do not know] & see ye same power in other living creatures but the {illeg} of this pow laws of this power \how this is done & by what laws/ we do not know. [|And| By this instance \& that of gravity/ it appears that there are |other| laws of motion unknown to us, & {illeg} by consequence wch is enough to justify \& encourage/ or search after them} \And/ We cannot say that all Nature is not alive. [What bodies are & whence it is that they are hard \& moveable/ & {mo} impenetrable {illeg} \to/ one another & moveable we do not know we have no certain knowledge of any thing without as the metaphysical {con} we cannot see the \Our senses tell us not the essencesof things/ essences of things & Metaphysical arguments \about them/ are very slippery. By such arguments a man may prove that And Tis safest to argue from Phænomena, & stop where Phænomena \& sound reasoning from them/ are wanting to carry us farther] What bodies {are} I do {illeg} \{illeg}/ not \know/ her laws or powers any further then we gather them from Phænomena. And by such arguments
If the parts \body \is compact & yet/ bends or/ yealds \inward/ to pre pression \{or} {illeg} bends/ without sliding any sliding of its parts, the bod it is hard & return to its figure with \elastic/ returning to its figure with an elastick force \arising from the \mutual/ attraction of its parts/. If the parts slide {illeg} |upon| \one another/ the body is \maleable and/ soft. If they slip easily & are of a figure \size/ most apt to be agitated by heat it is fluid but {illeg} is hard whenever \&/ the heat is big enough to keep its parts in agitation \the body is fluid/, & if |it| the fluid be apt to stick to things it is humid; & what \ye drops of/ every fluid when affect a round figure by the mutual attraction of its parts as the globe of the earth & sea affects a round figure by the mutual attraction of its parts & by gravity.
<621r>But how two Æthers can be diffused through all space one of wch acts upon the other & by consequence is reacted upon, without retarding slackening \shattering/ & confounding one anothers motions, is inconceivable & in is inconceivable. And against filling the heavens with fluid Medium unless they be exceeding rare a great objection arises from the regular & very lasting motions of the Planets & Comets through the heavens in all — — —
By a vacuum I do not mean a space void of all substances. Glass cannot attract light without a Medium. I mean only such a Vacuum as may be made by drawing Aer out of a vessel of glass.
What I mean \here |in this Question|/ by a Vacuum, & the attractions of the glass {on the} rays of light may by \towards/ the glass or crystall, may be understood by the 18th Quæstion what was said in the 18th Question.
Now in bodies — — — — — forces more easily. And for the like reason Gravity in the surfaces of small globes is greater in proportion to the globes then in the surfaces of great globes of equal density. And therefore since the rays of light are the smallest bodies yet known to us (For I do not here consider the particles of æther) we may expect to find their attractions very strong. And how strong they are may be gatherred by this Rule — — — — — — —; — to be above an hundred million of millions of millions of tines {sic} greater \in proportion to the matter in them/ then th{illeg}|e| gravity of the Earth towards the Sunn in proportion to the matter in it.
As attraction is stronger in small magnets then in great ones in proportion to their \bulk/, & gravity is greater in the surfaces of small Planets the|n| on in those of great ones in proportion to their bulk so the smallness of the rays of light may very much contribute to the force by which they are refracted. And so if any one should suppose that a|E|ther to be of the same nature with Aer but exceedingly more subtile \(like our aer)consists of \may {containe}/ particles which f{illeg} endeavour to recede from one another {illeg} the/ (for I do not know what the Ether is) |& that its particles are exceedingly smaller then those of aer, or even the{ir} those of light, the| the exceeding smalness of it|s| {illeg} particles of Ether may contribute to the greatness of the force by which those particles sh{illeg} \recede from/ one another & thereby compose \make/ that medium exceedingly more \rare &/ elastick then Aer.
And that the gravity of the Planets towards the Sun may not be thought too great for \to be produced by/ the cause of gravity here insinuated \suggested/: upon a fair computation it will found that the gravity of our earth towards the Sun in proportion to the quantity of its matter is above ten hundred millions of millions of millions of millions of times less then th{en} the force by wch a ray of light in entring into glass or crystall is drawn \or f{orced} impelled/ towards the refracting body. And therefore the gravity of the earth towards the Sun is effected by a requires a variation of the density of the Ether at the Orb of ye Earth an hundred millions of millions of millions of millions of times slower then the variation of the density of the Ether at the surface of glass or crystal requisite to refract light. For the velocity of light is to the \annual/ velocity of the Earth \reciprocally |in the Orbis magnus|/ as about 70 minutes \the time/ in wch light comes from the sun to {illeg} it to {illeg} 58 days the time in the Earth describes the same space; that is \an earth equal to the {illeg}|radius of| its orb to about 7 minutes, the time in wch light comes fro ☉ to {as}/ as about 12000 to 1. And the curvity of a ray of light {is to} the curvity of l|a| ray of light {illeg} in {illeg} during it refraction at the surface of glass on wch it falls very obliquely, is to the curvity of the earths Orb, as the radius of that Orb to the space radius of the curvity of the ray [which is less then the five \five/ hundred thousandth parat of an inch,] or as above the {2}|1|000000000000000000 to 1. And the force which bends the ray is to the force wch keeps the earch {sic} {on} it or Orb or l any Projectile in its orb \or line of Projection/ in a ratio{illeg} compounded of the \duplicate/ ratio of the velocities & this ratio{illeg} of the curv\i/ties of the lines of projection.
The Atmosphere by its weight presses the Quicksilver into the glass to the height of 29 or 30 inches. And some other Agent raises it higher, not by pressing it into the glass but by making its parts stick to ye glass & to one another. For upon any discontinuation \of parts/ made either by bubbles or by shaking the glass, the whole liquor falls down.
<621v>And if it were not for these Principles the {illeg}|B|odies of the Earth Planets & \Comets/ Sun \& all things in them/ would grow cold, & freeze \& become inactive masses/, & putrefaction generation & vegetation & life would cease, & the Planets & Comets would not remain in their Orbs.
— causes be not yet explained. For these are manifest qualities & their causes only are occult. |[Occult qualities are not manifest qualities but \are/ specific quailites {sic} {illeg} wch do not yet appear to be in the Species but are only supposed to be in the{ir} species for producing manifest effects whose causes are unko] the| To tell — — extent & leave their causes to be enquired into.
of any third thing. The Organs of sense are not for enabling the soul to perceive the species of things {illeg} in its Sensorium, but only for conveying them thither & God has no need of such Organs, the things themselves being present to them. he being every where present to the things themselves.
& in arguing from them by Induction taking the Argument \& admitting of no And tho objections but from expts/ this sort of argumt is not demonstrative \but/ yet it is the best which the nature of things admits off, & may be looked upon as so much the stronger by how much the induction is more general. And if no exception occur from Phenomena, the Conclusion may be pronounced generally. But if \at any time/ afterwards any exception occur from Experiments, it may then begin to be pronounced wth such exceptions as occurr.
— & admitting of no objections fr against exp the conclusions but such as are taken from Experiments. For Hypotheses are not to be regarded in Experimental Philosophy. Nor are we here to regard Metaphysical Principles unless so far as they are founded upon exper{illeg}|ienc|e. For all Metaphysicks not founded upon experience is {illeg}|H|ypothetical: And so far as {illeg} Metaphysical Propositions are founded upon experience they are a part of experimental Philosophy. Even that celebrated Proposition Ego cogito ergo sum is known to us by experience. We know that we think by an inward sensation of or thoughts. And \therefore/ from {illeg} \that Proposition/ we cannot conclude that any thing more is true then what we deduce from experience✝ ✝Metaphysical proofs \of a deity/ not grounded on Phænomena are \no{illeg}/ dreams
✝And even in proving a Deity all aguments \not/ taken from Phænomena are little better then dreams. Now \{altho}/ the arguing from experiments & observations by Induction be no demonstration of general Propositions, yet it is the best way of
Eve Even in Metaphy. Now the ar Now \altho/ the arguing from experiments & obsvations {sic} by Induction be|is| not fully demonstrative yet it is the best way of arguing which the nature of things admits of, & may be looked — — — as ocean. By this way of arguing we may proceed from compositions to ingredients & from motions to \the/ forces producing them & in general from effects — — — the most general. This is the Analysis & the Synthesis consists in assuming
<622r>If two plane polished plates of glass three or four inches broad & \about/ twenty long be laid togeth one of \them/ parallel to the horizon the other upon the first so as to \touch it &/ make an angle with it. at our end \{illeg}/ of about 10 or 15 minutes \at one of their ends/ & the same be first moistened \on their inward sides/ with a cleane cloth dipt into oyle of Oranges, \& rubbed upon it/ & a drop or two of the oyle be let fall upon he lower glass at the other end: so soon as the upper glass is laid down upon the lower so as to touch it at one end & to touch the drop at the other end the making with the lower glass an angle of about 10 or 15 as above; the drop will begin to move towards the concourse of the glasses {illeg} & will continue to move with an accelerated motion till it arrives at that concourse \of the glasses/. {illeg} [And if while it while it is in motion you then open the glasses where they met & touched & make them \touch/ meet \& touch/ at their other end in the same acute angle as before; the g{illeg} dop {sic} will run back {th} to that end of the glasses where they now touch, & where it was at first.] And if For the two glasses attract the drop, & make it by the attraction make it run that way towards which the attractions conspire \incline/. And if when the drop is in motion you lift up that end of the glasses where they meet {illeg}|&| towards which the drop is in motion moves: the drop will ascend between the glasses, & therefore is attracted. And if \as/ you lift up the glasses, \more & more/ the drop will ascend slower & slower & at length rest. And when it rests the drop being \And when you see it rest you may reccon that it/ then carried downward by its weight as much as upwards by the attraction. And thereby you may know the force by wch the drop is attracted at all distances from the plane contact of the glasses. And it has been by some experiments, the attraction is almost reciprocally as the square \in a duplicate proportion/ of the distance of the center \{middle}/ of the drop from the concours of the glasses. And by some experim [And when the drop is four inches distant from the concourse of the glasses, the it will \contein an angle of about 18′ &/ rest if the glasses be lifted up at that end where they touch so that the lower end {illeg} glass be inclined to ye horizon in an angle of about 7 or 8 degrees. And from] And by this recconin And by this progression, the attractive force will become exceeding great where the distance between the glasses is exceeding little] viz in a {som} \viz/ reciprocally in a simple proportion of the distance between the glass by reason of the spreading of the drop & its touching the glasses in alarger surface; & again reciprocally in a duplicate \simple/ proportion by reason of the attractions growing stronger within the same quantity of surface attracting surface. The attraction therefore |wth|in the same quantity of surface is reciprocally as the distance between the glasses. And therefore where the distance is very small, suppose the ten-thousand-thousandth part of an inch, the attraction must be exceeding great; so as to hold up the perhap great perhaps as \within in a circle of an inch in diameter/ to hold suffice to hold up a cylinder of water a mile or two long weight equal to a{n} cylinder of water of an \inch/ in diameter, & one {illeg} \above a/ mile{s} in length. There are therefore Agents in nature sufficient to make strong enough \Attractive/ \Agents in Nature able to/ to make the particles of bodies attract one another very strongly & \to/ stick together \strongly those/ by such attractions. One of those causes \Agents/ may be the Æther above mentioned whereby light is refracted. Another may be the Agent or Spirit which causes electrical attraction. For tho this Agent acts \not/ at great distances only \except/ when it is excited by the friction of electrick bodies: yet it may act perpetually at \very/ small distances not only when it is excited by fr eve without friction, \& that/ not only in electrick \these/ bodies \accounted electric,/ but also in some others. And as there are still other mediums wch may cause attractions, (such as are the Magnetick effluvia); & it is the business of experimental Philosophy to cause find out all these Mediums with their properties.
Now the smallest particles of matter may cohere
By the Table in the second part of the second b|B|ook of Opticks \wherein/ the thicknesses of water between two glasses coloured plates of water are set do between two glasses are set down, the thickness of the plate where it {illeg} appears very black is three eighths of the thousand-thousandth part of an inch. And where the Oyle of Oranges between the glasses is of this thickness, the attraction seems to be so strong as within a circle of an inch in diameter to suffice to hold up \a weight equal to yt of/ a cylinder of \water of/ an inch in diameter & two or three furlongs in lenghth And where it is of a less thickness the attraction seems to \{illeg} may/ be proportionally greater. & increase untill the thickness be no bigger then that of a single particle of water.
<622v>For the Velocitys of the pulses of Elastick mediums are a subduplicate ratio of the elasticityes directly & of the densities inversely. For the squares of the velocities of the pulses of Elastick Mediums are \in to {com}/ as the elasticities & \the/ rarities together of the Mediums taken together
The parts — — — — any sensible effect. All bodies — — — — difficult to conceive The same thing — — — — cohesion of its parts. It is not therefore by the motion pressure of the Æther upon the outside of the Marbles or Mercury (tho such a pressure may contribute to the effect) but by the action of either that or some other Medium or Mediums upon the inward parts of those bodies by wch the contiguous parts of the Marbles stick to one another & those of the glass & Mercury stick to one another. The like \Expt/ hath been tried wth water — — — — amongst themselves.
And of the same kind with these Experiments is this Experiment are those that follow. If two \plane/ polished plates of glass (suppose two pieces of a broken looking-glass) bee laid together so that their parall sides be plane parallel & at a very small distance from one another; & then their lower edges be dipped into water; the water will rise up between them. And the less the distance of the glasses is from the greater will be the height to wch the water will rise. {illeg} If the distance be about the two &thirtith \four & twentith hundreth/ part of an inch, the water will rise to the light of about an inch & if the distance be greater or less in any proportion, the h{l}|e|ight will be {illeg} reciprocally proportial {sic} to the distance very nearly. [And the experiment succeeds in vacuo as well as in {pleno} the open air, & therefore is not influenced by the weight or pressure of the Atmosphere]. |For the attractive force of the glasses is the same whether the distance between them be greater or or {sic} less & the weight of the water of the water {sic} drawn up is the same if the height of it be reciprocally proportional to the distance between the glasses. [And in like manner water ascends between two Marbles polished plane, when their polished sides are parallel to one another, & at a very little distance from one another.]| And if slender pipes of glass be dipt at one end into stagnating water the water will rise in the \up/ within the pipe [& the hight to wch it rises will be reciprocally proportional to the diameter of the {illeg} cavity of the pipe] to hight which & will equall the height to wch it rises between two {planes} glass planes \of glass/ if the semidiameter of the cavity of the Pipe be equal to the distance of \between/ the planes, {illeg} or thereabouts. And these experiments suceed after the same manner in vacuo as in the open air, & therefore are not influenced by the weight or pressure of the Atmosphere.
And if a wi{illeg}|d|e pipe of glass be filled with sifted ashes well pressed together \in the glass/ & one end of the pipe be dipped into stagnating water; the water will rise up slowly in the glass so as in the space of a week or afortnight to reach {illeg} up \to/ 30 or 40 inches above the surface of the stagnating water. And by the {sensin} this case the water is raised to this he\i/ght by the attraction of those parts|i||cles| of the ashes \only/ wch are upon the surface of the elevated water; {illeg} the particles {fet} wch are dipt into \within/ the water, attracting it as much downwards as upwards. And therefore the attraction is very strong & \but it/ would be much stronger were if the ashes were one upon the surface of the attracted water were one continued body, as the glass is wch keeps quicksilver suspended in a pipe of glass to the hight of above \60 or/ 70 inches, as above & therefore attracts with a force wch would keep water suspended to the height of above fifty feet. |And the particles of glass, wch lie closer to one another then they they {sic} do or \the/ quicksilver {mor} attracts one another with a force much stronger.|
By the same principle a sponge sucks in water, & the glands in the bodies of animals {suck} according their several natures & dispositions suck in various juices from the blood
