62(1)
HondHonoured SrSir
I have so long deferred to send you my thoughts about yethe Phy
sicall qualities we spake of, that did I not esteem my self obliged
by promise I think I should be ashamed to send them at all. The truth
is my notions about things of this kind are so indigested ytthat I am
not well satisfied my self in them, & what I am not satisfied in
I can scarce esteem fit to be communicated to others, especially
in natural Philosophy where there is no end of fansying. But
because I am indebted to you & yesterday met wthwith a friend Mr
Maulyverer, who told me he was going to London & intended to
give you yethe trouble of a visit, I could not forbear to take
yethe opportunity of conveying this to you by him.
It being only an explication of qualities wchwhich you desire
of me, I shall set down my apprehensions in yethe form of sup
positions as follows. And first I suppose that there is diffused
through all places an æthereal substance capable of contra
ction & dilatation, strongly elastick, & in a word much like air
in all respects, but far more subtile.
2 I suppose this æther pervades all gross bodies, but yet so
as to stand rarer in their pores then in free spaces, & so much
yethe rarer as their pores are less. And this I suppose (wthwith others)
to be yethe cause why light incident on those bodies is refracted
towards yethe perpendicular; why two well polished metalls cohere
in a Receiver exhausted of air: why ☿Quicksilver stands sometimes up to
yethe top of a glass pipe though much higher ynthan inches: & one of yethe main causes why yethe parts of all bodies cohere. Also yethe cause of philtration & of yethe rising of water in small glass pipes above yethe surface of yethe stagnating water they are dipt into: for I suspect yethe æther may stand rarer not only in yethe insensible pores of bodies, but even in yethe very sensible cavities of those pipes. And yethe same principle may cause Menstruums to pervade with violence yethe pores of yethe bodies they dissolve, the surrounding æther as well as yethe Atmosphere pressing ymthem together.
3 I suppose yethe rarer æther within bodies & yethe denser wthwithout them, not to be terminated in a mathematical superficies but to grow gradually into one another: the external æther beginning to grow rarer, & yethe internal to grow denser at some little distance from yethe body superficies of yethe body, & running through all intermediate degrees of density in yethe intermediate spaces. And this may be yethe cause why light in Grimaldo's experiment passing by yethe edge of a knife or other opake body is turned aside & as it were refracted, & by ytthat refraction makes several colours. Let be a dense body whether opake or transparent, yethe outside of yethe uniform æther wchwhich is within it, the inside of yethe uniform æther wchwhich is without it; & conceive yethe æther wchwhich is between and to run through all intermediate degrees of density between ytthat of yethe two uniform æthers on either side. This being supposed, yethe rays of yethe sun , , wchwhich pass by yethe edge of this body between & , ought in their passage through yethe unequally dense æther there, to receive a ply from yethe denser æther wchwhich is on that side towards , & that yethe more by how much they pass nearer to yethe body, & thereby to be scattered through yethe space , as by experience they are found to be. Now yethe space between yethe limits & I shall call yethe space of yethe æther's graduated rarity.
4 When two bodies moving towards one another come neare together I suppose yethe æther between them to grow rarer then before, & yethe spaces of its graduated rarity to extend further from yethe superficies of yethe bodyies towards one another, & this by reason ytthat yethe æther cannot move & play up & down so freely in yethe strait passage between yethe bodies as it could before they came so neare together. Thus if yethe space of yethe æther's graduated rarity reach from yethe body only to yethe distance when no other body is neare it, yet may it reach farther, as to , when another body approchaches: & as the other body approaches more & more I suppose yethe æther between them will grow rarer & rarer.
These suppositions I have so described as if I thought yethe spaces of graduated æther had precise limits, as is exprest at in yethe first figure & in yethe second: for thus I thought I could better express my self. But really I do not think they have such precise limits but rather decay insensibly, & in so decaying extend to a much greater distance then can easily be beleived or need be supposed.
5 Now from yethe 4th supposition it follows that when two bodies approaching one another, come so neare together as to make yethe æther between them begin to rarefy, they will begin to have a reluctance from being brought nearer together, & an endeavour to recede from one another: wchwhich reluctance & endeavour will encrease as they come nearer together because thereby they cause the interjacent æther to rarefy more & more. But at length, when they come so neare together that the excess of pressure of yethe external æther wchwhich surrounds yethe bodies, above ytthat of yethe rarefied æther wchwhich is between them, is so great as to overcome yethe reluctance wchwhich yethe bodies have from being brought together: then will that excess of pressure drive them with violence together & make them adhere strongly to one another, as was said in yethe second supposition. For instance in yethe second Figure when yethe bodies & are so neare together, ytthat yethe spaces of yethe æthers graduated rarity begin to reach to one another & meet in yethe line ; the æther between them will have suffered much rarefaction wchwhich rarefaction requires much force ytthat is much pressing of yethe bodies together: & yethe endeavour wchwhich yethe æther between them has to return to its former state natural state of condensation will cause yethe bodies to have an endeavour of receding from one another. But on yethe other hand to counterpoise this endeavour there will not yet be any excess of density of yethe æther wchwhich surrounds yethe bodies above that of yethe æther wchwhich is between them at yethe line . But if yethe bodies come nearer together so as to
63 to make yethe æther in yethe mid-way-line grow rarer then yethe surrounding æther, there will arise from yethe excess of density of yethe surrounding æther a compressure of yethe bodies towards one another: which when by yethe nearer approach of yethe bodies it becomes so great as to overcome yethe afforesaid endeavour yethe bodies have to recede from one another, they will then go towards one another & adhere together. And on yethe contrary if any power force them as under to that distance where yethe endeavour to recede begins to overcome yethe endeavour to accede, they will again leap from one another. Now hence I conceive it is chiefly ytthat a fly walks on water wthwithout wetting her feet, & consequently without touching yethe water; that two polished pieces of glass are not wthwithout pressure brought to contact, no not though yethe one be plain, yethe other a little convex; ytthat yethe particles of dust cannot by pressing be made to cohere, as they would do if they did but fully touch; ytthat yethe particles of tinging substances & salts dissolved in water do not of their own accord concrete & fall to yethe bottom, but diffuse themselves all over yethe liquor, & expand still more if you ad more liquor to them. Also ytthat yethe particles of vapors exhalations & air do stand at a distance from one another, & endeavour to recede as far from one another as yethe pressure of yethe incumbent atmosphere will let them: for I conceive yethe confused mass of vapors air & exhalations wchwhich we call yethe Atmosphere to be nothing els but yethe particles of all sorts of bodies of wchwhich yethe earth consists, separated from one another & kept at a distance by yethe said principle.
From these principles yethe actions of Menstruums upon bodies may be thus explained. Suppose any tinging body as Cochineel or Logwood be put into water, so soon as the water sinks into its pores & wets on all sides any particle, wchwhich adheres to yethe body only by yethe principle in second supposition: it takes of or at least much diminishes yethe efficacy of ytthat principle to hold yethe particle to yethe body because it makes yethe æther on all sides yethe particle to be of a more uniform density then before. And then the particle being shaken of by any little motion, flotes in yethe water, & wthwith many such others makes a tincture; wchwhich tincture will be of some lively colour if yethe particles be all of yethe same size & density, otherwise of a dirty one. For yethe colours of all natural bodies whatever seem to depend on nothing but yethe various sizes & densities of their particles: as I think you have seen described by me more at large in another paper. If yethe particles be very small (as are those of salts Vitriols & gumms) they are transparent, & as they are supposed bigger & bigger they put on these colours in order black, white, yellow, red; violet, blew, pale green, yellow, orange, red; purple, blew, green, yellow, orange, red &c: as is discerned by yethe colours wchwhich appear at yethe several thicknesses of very thin plates of transparent bodies. Whence to know yethe causes of yethe changes of colours wchwhich are often made by yethe mixtures of several liquors, it is to be considered how yethe particles of any tincture may have their size or density altered by the infusion of another liquor.
When any metal is put into common water, yethe water cannot enter into its pores to act on it & dissolve it. Not ytthat water consists of too gross parts for this purpose, but because it is unsociable to metal. For there is a certain secret principle in nature by wchwhich liquors are sociable to some things & unsociable to others. Thus water will not mix with oyle but readily wthwith sptspirit of wine or wthwith salts. It sinks also into wood wchwhich Quicksilver will not, but Quicksilvers sinks into metals, wchwhich, as I said, water will not. So Aqua fortis dissolves ☽silver not ☉gold; Aqua regis ☉gold & not ☽silver, &c. But a liquor wchwhich is of it self unsociable to a body may by yethe mixture of a convenient mediator be made sociable. So molten Lead wchwhich alone will not mix wthwith copper or wthwith Regulus of Mars, by yethe addition of Tin is made to mix wthwith either. And water by yethe addition of mediation of saline spirits will mix with metal. Now when any metal is put in water impregnated wthwith such spirits, as into Aqua fortis, Aqua Regis, spirit of Vitriol or yethe like, the particles of yethe spirits as they in floting in yethe water, strike on yethe metal, will by their sociableness enter into its pores & gather round its outside particles, & by advantage of yethe continual tremor the particles of yethe metal are in, hitch themselves in by degrees between those particles & yethe body & loosen them from it, & yethe water entring into yethe pores together wthwith yethe saline spirits, yethe particles of yethe metal will be thereby still more loosed, so as by that motion yethe solution puts ymthem into, to be easily shaken of & made to Rote in yethe water: the saline still particles still encompassing yethe metallick ones as a coat or shell does a kernell, after yethe manner expressed in yethe annexed figure. In wchwhich figure I have made yethe particles round, though they may be cubical or of any other shape.
If into a solution of metal thus made, be poured a liquor abounding with particles, suppose of salt to wchwhich yethe former saline particles are more sociable then to yethe particles of yethe metal, (suppose with particles of salt of Tartar:) then so soon as they strike on one another in yethe liquor, yethe saline particles will adhere to those more firmly then to yethe metalline ones, & by degrees be wrought of from those to enclose these. Suppose a metalline particle enclosed wthwith saline ones of spirit of Nitre, & a particle of salt of Tartar contiguous to two of yethe particles of spirtspirit of nitre & , & suppose yethe particle is impelled by any motion towards so as to roll about yethe particle till it touch yethe particle : the particle adhering more firmly to then to , will be forced off from . And by yethe same means yethe particle as it rolls about will tear of yethe rest of yethe saline particles from , one after another, till it has got them all or almost all about it self. And when yethe metallic particles are thus divested of yethe nitrous ones which as a mediator between them & yethe water held them floting in it: the Alcalizate ones crouding for yethe room yethe metallic ones took up before, will press these towards one another & make them come more easily together: so ytthat by the motion they continually have in yethe water they shall be made to strike on one another, & then by means of the principle in yethe second supposition they will cohere & grow into clusters, & fall down by their weight to yethe bottom, wchwhich is called precipitation.
In yethe solution of metals, when a particle is loosing from yethe body, so soon as it gets to that distance from it where yethe principle of receding described in yethe 4th & 5t suppositions begins to overcome yethe principle of acceding described in yethe second conclusion supposition: the receding of yethe particle will be thereby accelerated, so ytthat yethe particle shall as were wthwith violence leap from yethe body, & putting yethe liquor into a brisk agitation, beget & promote ytthat heat we often find to be caused in solutions of Metals. And if any particle happen to leap of thus from yethe body before it be surrounded with water, or to leap of wthwith that smartness as to get loos from yethe water: the water by the principle in yethe 4th & 5t suppositions, will be kept of from yethe particle & stand round about it like a spherically hollow arch, not being able to come to a full contact with it any more. And severall of these particles afterwards gathering into
64(2) into a cluster, so as by yethe same principle to stand at a distance from one another without any water between them, will compose a buble. Whence I suppose it is ytthat in brisk solutions there usually happens an ebullition.
This is one way of transmuting gross compact substances into aereal ones. Another way is by heat. For as fast as yethe motion of heat can shake off yethe particles of water from yethe surface of it: those particles by yethe said principle will Rote up & down in yethe air at a distance both from one another & from yethe particles of air, & make ytthat substance we call vapor. Thus I suppose it is when yethe particles of a body are very small (as I suppose those of water are) so ytthat yethe action of heat alone may be sufficient to shake them asunder. But if yethe particles be much larger, they then require the greater force of dissolving Menstruums to separate them, unless by any means the particles can be first broken into smaller ones. For yethe most fixed bodies, even Gold it self, some have said will become volatile only by breaking their parts smaller. Thus may yethe volatility & fixedness of bodies depend on yethe diffetrent sizes of their parts.
And on yethe same difference of size may depend the more or less permanency of aereal substances in their state of rarefaction. To understand this let us suppose to be a large piece of any metal, yethe limit of yethe interior uniform æther, & a part of yethe metal neare at yethe edge superficies of yethe metal . If this part or particle be so little ytthat it reaches not to yethe limit , its plain that yethe æther at its center must be less rare then if yethe particle were greater, for were it greater, its center would be further from the superficies , that is, in a place where yethe æther (by supposition) is rarer. The less yethe particle therefore, yethe denser yethe æther at its center, because its center comes nearer to yethe edge where yethe æther is denser then within yethe limit . And if yethe particle were divided from yethe body & removed to a distance from it where yethe æther is still denser, the æther within it must proportionally grow denser. If you consider this you may apprehend how by diminishing the particle, yethe rarity of yethe æther within it will be diminished, till between the density of yethe æther wthwithout & yethe density of yethe æther within it there be little difference, that is till yethe cause be almost taken away wchwhich should keep this & other such particles at a distance from one another. For that cause, explained in yethe 4th & 5t suppositions, was yethe excess of of density of yethe external æther above ytthat of yethe internal. This may be yethe reason then why the small particles of vapors easily come together & are reduced back into water unless yethe heat wchwhich keeps them in agitation be so great as to dissipate them as faster their as they come together: but yethe grosser particles of exhalations raised by fermentation keep their aerial form more obstinately, because the æther within them is rarer.
Nor does yethe size only but yethe density of yethe particles also conduce to to yethe permanency of aereal substances. For yethe excess of density of yethe æther wthwithout such particles above ytthat of yethe æther wthwithin them is still greater. Which has made me sometimes think that yethe true permanent Air may be of a metallic metallic original: the particles of no substances being more dense then those of metals. This I think is also favoured by experience for I remember I once read in yethe P.Philosophical Transactions how M. Hugens at Paris found that yethe air made by dissolving salt of Tartar would in two or three days dtime condense & fall down again, but yethe air made by dissolving a metal continued permanent wthwithout condensing or relenting in yethe least. If you consider then how by the continual fermentations made in yethe bowels of yethe earth there are aereal substances raised out of all kinds of bodies, all wchwhich together make yethe Atmosphere & that of all these yethe metallic are yethe most permanent, you will not perhaps think it absurd that yethe most permanent part of yethe Atmosphere, wchwhich is yethe true air, should be constituted of these: especially since they are yethe heaviest of all other & so must subside to yethe lower parts of yethe Atmosphere & float upon yethe surface of yethe earth, & buoy up yethe lighter exhalation & vapours to float in greatest plenty above them. Thus I say it ought to be wthwith yethe metallic exhalations raised in yethe bowels of yethe earth by yethe action of acid menstruums, & thus it is wthwith yethe true permanent air. For this as in reason it ought to be esteemed yethe most ponderous part of yethe Atmosphere because yethe lowest: so it betrays its ponderosity by making vapors ascend readily in it, by susteining mists & clouds of snow, & by buoying up gross & ponderous smoke. The air also is yethe most gross unactive part of yethe Atmosphere affording living things no nourishment if deprived of yethe more tender exhalations & spirits ytthat flote in it: & what more unactive & remote from nourishment then metallick bodies.
I shal set down one conjecture more which came into my mind now as I was writing this letter. It is about yethe cause of gravity. For this end I will suppose æther to consist of parts differing from one another in subtilty by indefinite degrees: That in yethe pores of bodies there is less of yethe finer grosser æther in proportion to yethe finer then in open spaces, & consequently that in yethe great body of yethe earth there is much less of yethe grosser æther in proportion to yethe finer then in yethe regions of yethe air: & that yet yethe grosser æther in yethe Air affects yethe upper regions of yethe earth & yethe finer æther in yethe earth yethe lower regions of yethe air, in such a manner ytthat from yethe top of yethe air to yethe surface of yethe earth & again from yethe surface of yethe earth to yethe center thereof the æther is insensibly finer & finer. Imagin now any body suspended in yethe air or lying on yethe earth: & yethe æther being by the Hypothesis grosser in yethe pores wchwhich are in yethe upper parts of yethe body then in those wchwhich are in its lower parts, & that grosser æther being less apt to be lg lodged in those pores then yethe finer æther below, it will endeavour to get out & give way to yethe finer æther below, wchwhich cannot be wthwithout yethe bodies descending to make room above for it to go out into.
From this supposed gradual subtilty of yethe parts of æther some things above might be further illustrated & made more intelligible, but by what has been said you will easily discern whether in these conjectures there be any degree of probability, wchwhich is all I aim at
65 at. For my own part I have so little fansy to things of this nature that had not yoryour encouragement moved me to it, I should never I think have thus far set pen to paper about them. What's amiss therefore I hope you will yethe more easily pardon in
YorYour most humble Servant & honourer
Is. Newton.
Cambridge Feb 28. 167