The Project Gutenberg eBook of Micrographia, by Robert Hooke

Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries Thereupon

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and the Project Gutenberg Online Distributed Proofreading Team

By the Council of the ROYAL SOCIETY of London
for Improving of Natural Knowledge.

Ordered, That the Book written by Robert Hooke, M.A. Fellow of this Society, Entituled, Micrographia, or some Physiological Descriptions of Minute Bodies, made by Magnifying Glasses, with Observations and Inquiries thereupon, Be printed by John Martyn, and James Allestry, Printers to the said Society.

MICROGRAPHIA:

Physiological Descriptions

MINUTE BODIES

MAGNIFYING GLASSES

OBSERVATIONS and INQUIRIES thereupon.

Non possis oculo quantum contendere Linceus,

Non tamen idcirco contemnas Lippus inungi. Horat. Ep. lib. 1.

LONDON, Printed by Jo. Martyn, and Ja. Allestry, Printers to the ROYAL SOCIETY, and are to be sold at their Shop at the Bell in S. Paul's Church-yard. M DC LX V.

TO THE

KING.

Do here most humbly lay this small Present at Your Majesties Royal feet. And though it comes accompany'd with two disadvantages, the meanness of the Author, and of the Subject; yet in both I am incouraged by the greatness of your Mercy and your Knowledge. By the one I am taught, that you can forgive the most presumptuous Offendors: And by the other, that you will not esteem the least work of Nature, or Art, unworthy your Observation. Amidst the many felicities that have accompani'd your Majesties happy Restauration and Government, it is none of the least considerable that Philosophy and Experimental Learning have prosper'd under your Royal Patronage. And as the calm prosperity of your Reign has given us the leisure to follow these Studies of quiet and retirement, so it is just, that the Fruits of them should, by way of acknowledgement, be return'd to your Majesty. There are, Sir, several other of your Subjects, of your Royal Society, now busie about Nobler matters: The Improvement of Manufactures and Agriculture, the Increase of Commerce, the Advantage of Navigation: In all which they are assisted by your Majesties Incouragement and Example. Amidst all those greater Designs, I here presume to bring in that which is more proportionable to the smalness of my Abilities, and to offer some of the least of all visible things, to that Mighty King, that has establisht an Empire over the best of all Invisible things of this World, the Minds of Men.

ROBERT HOOKE.

TO THE

ROYAL SOCIETY.

fter my Address to our Great Founder and Patron, I could not but think my self oblig'd, in consideration of those many Ingagements you have laid upon me, to offer these my poor Labours to this MOST ILLUSTRIOUS ASSEMBLY. YOU have been pleas'd formerly to accept of these rude Draughts. I have since added to them some Descriptions, and some Conjectures of my own. And therefore, together with YOUR Acceptance, I must also beg YOUR pardon. The Rules YOU have prescrib'd YOUR selves in YOUR Philosophical Progress do seem the best that have ever yet been practis'd. And particularly that of avoiding Dogmatizing, and the espousal of any Hypothesis not sufficiently grounded and confirm'd by Experiments. This way seems the most excellent, and may preserve both Philosophy and Natural History from its former Corruptions. In saying which, I may seem to condemn my own Course in this Treatise; in which there may perhaps be some Expressions, which may seem more positive then YOUR Prescriptions will permit: And though I desire to have them understood only as Conjectures and Quæries (which YOUR Method does not altogether disallow) yet if even in those I have exceeded, 'tis fit that I should declare, that it was not done by YOUR Directions. For it is most unreasonable, that YOU should undergo the imputation of the faults of my Conjectures, seeing YOU can receive so small advantage of reputation by the sleight Observations of

ROBERT HOOKE.

THE

PREFACE.

t is the great prerogative of Mankind above other Creatures, that we are not only able to behold the works of Nature, or barely to sustein our lives by them, but we have also the power of considering, comparing, altering, assisting, and improving them to various uses. And as this is the peculiar priviledge of humane Nature in general, so is it capable of being so far advanced by the helps of Art, and Experience, as to make some Men excel others in their Observations, and Deductions, almost as much as they do Beasts. By the addition of such artificial Instruments and methods, there may be, in some manner, a reparation made for the mischiefs, and imperfection, mankind has drawn upon it self, by negligence, and intemperance, and a wilful and superstitious deserting the Prescripts and Rules of Nature, whereby every man, both from a deriv'd corruption, innate and born with him, and from his breeding and converse with men, is very subject to slip into all sorts of errors.

The only way which now remains for us to recover some degree of those former perfections, seems to be, by rectifying the operations of the Sense, the Memory, and Reason, since upon the evidence, the strength, the integrity, and the right correspondence of all these, all the light, by which our actions are to be guided is to be renewed, and all our command over things it to be establisht.

It is therefore most worthy of our consideration, to recollect their several defects, that so we may the better understand how to supply them, and by what assistances we may inlarge their power, and secure them in performing their particular duties.

As for the actions of our Senses, we cannot but observe them to be in many particulars much outdone by those of other Creatures, and when at best, to be far short of the perfection they seem capable of: And these infirmities of the Senses arise from a double cause, either from the disproportion of the Object to the Organ, whereby an infinite number of things can never enter into them, or else from error in the Perception, that many things, which come within their reach, are not received in a right manner.

The like frailties are to be found in the Memory; we often let many things slip away from us, which deserve to be retain'd, and of those which we treasure up, a great part is either frivolous or false; and if good, and substantial, either in tract of time obliterated, or at best so overwhelmed and buried under more frothy notions, that when there is need of them, they are in vain sought for.

The two main foundations being so deceivable, it is no wonder, that all the succeeding works which we build upon them, of arguing, concluding, defining, judging, and all the other degrees of Reason, are lyable to the same imperfection, being, at best, either vain, or uncertain: So that the errors of the understanding are answerable to the two other, being defective both in the quantity and goodness of its knowledge; for the limits, to which our thoughts are confin'd, are small in respect of the vast extent of Nature it self; some parts of it are too large to be comprehended, and some too little to be perceived. And from thence it must follow, that not having a full sensation of the Object, we must be very lame and imperfect in our conceptions about it, and in all the proportions which we build upon it; hence, we often take the shadow of things for the substance, small appearances for good similitudes, similitudes for definitions; and even many of those, which we think, to be the most solid definitions, are rather expressions of our own misguided apprehensions then of the true nature of the things themselves.

The effects of these imperfections are manifested in different ways, according to the temper and disposition of the several minds of men, some they incline to gross ignorance and stupidity, and others to a presumptuous imposing on other mens Opinions, and a confident dogmatizing on matters, whereof there it no assurance to be given.

Thus all the uncertainty, and mistakes of humane actions, proceed either from the narrowness and wandring of our Senses, from the slipperiness or delusion of our Memory, from the confinement or rashness of our Understanding, so that 'tis no wonder, that our power over natural causes and effects is so slowly improv'd, seeing we are not only to contend with the obscurity and difficulty of the things whereon we work and think, but even the forces of our own minds conspire to betray us.

These being the dangers in the process of humane Reason, the remedies of them all can only proceed from the real, the mechanical, the experimental Philosophy, which has this advantage over the Philosophy of discourse and disputation, that whereas that chiefly aims at the subtilty of its Deductions and Conclusions, without much regard to the first ground-work, which ought to be well laid on the Sense and Memory; so this intends the right ordering of them all, and the making them serviceable to each other.

The first thing to be undertaken in this weighty work, is a watchfulness over the failings and an inlargement of the dominion, of the Senses.

To which end it is requisite, first, That there should be a scrupulous choice, and a strict examination, of the reality, constancy, and certainty of the Particulars that we admit: This is the first rise whereon truth is to begin, and here the most severe, and most impartial diligence, must be imployed; the storing up of all, without any regard to evidence or use, will only tend to darkness and confusion. We must not therefore esteem the riches of our Philosophical treasure by the number only, but chiefly by the weight; the most vulgar Instances are not to be neglected, but above all, the most instructive are to be entertain'd; the footsteps of Nature are to be trac'd, not only in her ordinary course, but when she seems to be put to her shifts, to make many doublings and turnings, and to use some kind of art in indeavouring to avoid our discovery.

The next care to be taken, in respect of the Senses, is a supplying of their infirmities with Instruments, and, as it were, the adding of artificial Organs to the natural; this in one of them has been of late years accomplisht with prodigious benefit to all sorts of useful knowledge, by the invention of Optical Glasses. By the means of Telescopes, there is nothing so far distant but may be represented to our view; and by the help of Microscopes, there is nothing so small, as to escape our inquiry; hence there is a new visible World discovered to the understanding. By this means the Heavens are open'd, and a vast number of new Stars, and new Motions, and new Productions appear in them, to which all the ancient Astronomers were utterly Strangers. By this the Earth it self, which lyes so neer us, under our feet, shews quite a new thing to us, and in every little particle of its matter; we now behold almost as great a variety of Creatures, as we were able before to reckon up in the whole Universe it self.

It seems not improbable, but that by these helps the subtilty of the composition of Bodies, the structure of their parts, the various texture of their matter, the instruments and manner of their inward motions, and all the other possible appearances of things, may come to be more fully discovered; all which the ancient Peripateticks were content to comprehend in two general and (unless further explain'd) useless words of Matter and Form. From whence there may arise many admirable advantages, towards the increase of the Operative, and the Mechanick Knowledge, to which this Age seems so much inclined, because we may perhaps be inabled to discern all the secret workings of Nature, almost in the same manner as we do those that are the productions of Art, and are manag'd by Wheels, and Engines, and Springs, that were devised by humane Wit.

In this kind I here present to the World my imperfect Indeavours; which though they shall prove no other way considerable, yet, I hope, they may be in some measure useful to the main Design of a reformation in Philosophy, if it be only by shewing, that there it not so much requir'd towards it, any strength of Imagination, or exactness of Method, or depth of Contemplation (though the addition of these, where they can be had, must needs produce a much more perfect composure) as a sincere Hand, and a faithful Eye, to examine, and to record, the things themselves as they appear.

And I beg my Reader, to let me take the boldness to assure him, that in this present condition of knowledge, a man so qualified, as I have indeavoured to be, only with resolution, and integrity, and plain intentions of imploying his Senses aright, may venture to compare the reality and the usefulness of his services, towards the true Philosophy, with those of other men, that are of much stronger, and more acute speculations, that shall not make use of the same method by the Senses.

The truth is, the Science of Nature has been already too long made only a work of the Brain and the Fancy: It is now high time that it should return to the plainness and soundness of Observations on material and obvious things. It is said of great Empires, That the best way to preserve them from decay, is to bring them back to the first Principles, and Arts, on which they did begin. The same is undoubtedly true in Philosophy, that by wandring far away into invisible Notions, has almost quite destroy'd it self, and it can never be recovered, or continued, but by returning into the same sensible paths, in which it did at first proceed.

If therefore the Reader expects from me any infallible Deductions, or certainty of Axioms, I am to say for my self, that those stronger Works of Wit and Imagination are above my weak Abilities; or if they had not been so, I would not have made use of them in this present Subject before me: Whenever he finds that I have ventur'd at any small Conjectures, at the causes of the things that I have observed, I beseech him to look, upon them only as doubtful Problems, and uncertain ghesses, and not as unquestionable Conclusions, or matters of unconfutable Science; I have produced nothing here, with intent to bind his understanding to an implicit consent; I am so far from that, that I desire him, not absolutely to rely upon these Observations of my eyes, if he finds them contradicted by the future Ocular Experiments of other and impartial Discoverers.

As for my part, I have obtained my end, if these my small Labours shall be thought fit to take up some place in the large stock, of natural Observations, which so many hands are busie in providing. If I have contributed the meanest foundations whereon others may raise nobler Superstructures, I am abundantly satisfied; and all my ambition is, that I may serve to the great Philosophers of this Age, as the makers and the grinders of my Glasses did to me; that I may prepare and furnish them with some Materials, which they may afterwards order and manage with better skill, and to far greater advantage.

The next remedies in this universal cure of the Mind are to be applyed to the Memory, and they are to consist of such Directions as may inform us, what things are best to be stor'd up for our purpose, and which is the best way of so disposing them, that they may not only be kept in safety, but ready and convenient, to be at any time produc'd for use, as occasion shall require. But I will not here prevent my self in what I may say in another Discourse, wherein I shall make an attempt to propose some Considerations of the manner of compiling a Natural and Artificial History, and of so ranging and registring its Particulars into Philosophical Tables, as may make them most useful for the raising of Axioms and Theories.

The last indeed is the most hazardous Enterprize, and yet the most necessary; and that is, to take such care that the Judgment and the Reason of Man (which is the third Faculty to be repair'd and improv'd) should receive such assistance, as to avoid the dangers to which it it by nature most subject. The Imperfections, which I have already mention'd, to which it is lyable, do either belong to the extent, or the goodness of its knowledge; and here the difficulty is the greater, least that which may be thought a remedy for the one should prove destructive to the other, least by seeking to inlarge our Knowledge, we should render it weak, and uncertain; and least by being too scrupulous and exact about every Circumstance of it, we should confine and streighten it too much.

In both these the middle wayes are to be taken, nothing it to be omitted, and yet every thing to pass a mature deliberation: No Intelligence from Men of all Professions, and quarters of the World, to be slighted, and yet all to be so severely examin'd, that there remain no room for doubt or instability; much rigour in admitting, much strictness in comparing, and above all, much slowness in debating, and shyness in determining, is to be practised. The Understanding is to order all the inferiour services of the lower Faculties; but yet it is to do this only as a lawful Master, and not at a Tyrant. It must not incroach upon their Offices, nor take upon it self the employments which belong to either of them. It must watch the irregularities of the Senses, but it must not go before them, or prevent their information. It must examine, range, and dispose of the bank which it laid up in the Memory: but it must be sure to make distinction between the sober and well collected heap, and the extravagant Ideas, and mistaken Images, which there it may sometimes light upon. So many are the links, upon which the true Philosophy depends, of which, if any one be loose, or weak, the whole chain is in danger of being dissolv'd; it is to begin with the Hands and Eyes, and to proceed on through the Memory, to be continued by the Reason; nor is it to stop there, but to come about to the Hands and Eyes again, and so, by a continual passage round from one Faculty to another, it is to be maintained in life and strength, as much as the body of man it by the circulation of the blood through the several parts of the body, the Arms, the Feet, the Lungs, the Heart, and the Head.

If once this method were followed with diligence and attention, there is nothing that lyes within the power of human Wit (or which is far more effectual) of human Industry, which we might not compass; we might not only hope for Inventions to equalize those of Copernicus, Galileo, Gilbert, Harvy, and of others, whose Names are almost lost, that were the Inventors of Gun-powder, the Seamans Compass, Printing, Etching, Graving, Microscopes, &c. but multitudes that may far exceed them: for even those discoveries seem to have been the products of some such method, though but imperfect; What may not be therefore expected from it if thoroughly prosecuted? Talking and contention of Arguments would soon be turn'd into labours; all the fine dreams of Opinions, and universal metaphysical natures, which the luxury of subtil Brains has devis'd, would quickly vanish, and give place to solid Histories, Experiments and Works. And as at first, mankind fell by tasting of the forbidden Tree of Knowledge, so we, their Posterity, may be in part restor'd by the same way, not only by beholding and contemplating, but by tasting too those fruits of Natural knowledge, that were never yet forbidden.

From hence the World may be assisted with variety of Inventions, new matter for Sciences may be collected, the old improv'd, and their rust rubb'd away; and as it is by the benefit of Senses that we receive all our Skill in the works of Nature, so they also may be wonderfully benefited by it, and may be guided to an easier and more exact performance of their Offices; 'tis not unlikely, but that we may find out wherein our Senses are deficient, and as easily find wayes of repairing them.

The Indeavours of Skilful men have been most conversant about the assistance of the Eye, and many noble Productions have followed upon it; and from hence we may conclude, that there it a way open'd for advancing the operations, not only of all the other Senses, but even of the Eye it self; that which has been already done ought not to content us, but rather to incourage us to proceed further, and to attempt greater things in the same, and different wayes.

'Tis not unlikely, but that there may be yet invented several other helps for the eye, at much exceeding those already found, as those do the bare eye, such as by which we may perhaps be able to discover living Creatures in the Moon, or other Planets, the figures of the compounding Particles of matter, and the particular Schematisms and Textures of Bodies.

And as Glasses have highly promoted our seeing, so 'tis not improbable, but that there may be found many Mechanical Inventions to improve our other Senses, of hearing, smelling, tasting, touching. 'Tis not impossible to hear a whisper a furlongs distance, it having been already done; and perhaps the nature of the thing would not make it more impossible, though that furlong should be ten times multiply'd. And though some famous Authors have affirm'd it impossible to hear through the thinnest plate of Muscovy-glass; yet I know a way, by which 'tis easie enough to hear one speak through a wall a yard thick. It has not been yet thoroughly examin'd, how far Otocousticons may be improv'd, nor what other wayes there may be of quickning our hearing, or conveying sound through other bodies then the Air: for that that it not the only medium, I can assure the Reader, that I have, by the help of a distended wire, propagated the sound to a very considerable distance in an instant, or with as seemingly quick a motion as that of light, at least, incomparably swifter then that, which at the same time was propagated through the Air; and this not only in a straight line, or direct, but in one bended in many angles.

Nor are the other three so perfect, but that diligence, attention, and many mechanical contrivances, may also highly improve them. For since the sense of smelling seems to be made by the swift passage of the Air (impregnated with the steams and effluvia of several odorous Bodies) through the grisly meanders of the Nose whose surfaces are cover'd with a very sensible nerve, and moistned by a transudation from the processus mamillares of the Brain, and some adjoyning glandules, and by the moist steam of the Lungs, with a Liquor convenient for the reception of those effluvia and by the adhesion and mixing of those steams with that liquor, and thereby affecting the nerve, or perhaps by insinuating themselves into the juices of the brain, after the same manner, as I have in the following Observations intimated, the parts of Salt to pass through the skins of Effs, and Frogs. Since, I say, smelling seems to be made by some such way, 'tis not improbable, but that some contrivance, for making a great quantity of Air pass quick through the Nose, might at much promote the sense of smelling, as the any wayes hindring that passage does dull and destroy it. Several tryals I have made, both of hindring and promoting this sense, and have succeeded in some according to expectation; and indeed to me it seems capable of being improv'd, for the judging of the constitutions of many Bodies. Perhaps we may thereby also judge (as other Creatures seem to do) what is wholsome, what poyson; and in a word, what are the specifick properties of Bodies.

There may be also some other mechanical wayes found out, of sensibly perceiving the effluvia of Bodies; several Instances of which, were it here proper, I could give of Mineral steams and exhalations; and it seems not impossible, but that by some such wayes improved, may be discovered, what Minerals lye buried under the Earth, without the trouble to dig for them; some things to confirm this Conjecture may be found in Agricola, and other Writers of Minerals, speaking of the Vegetables that are apt to thrive, or pine, in those steams.

Whether also those steams, which seem to issue out of the Earth, and mix with the Air (and so to precipitate some aqueous Exhalations, wherewith 'tis impregnated) may not be by some way detected before they produce the effect, seems hard to determine; yet something of this kind I am able to discover, by an Instrument I contriv'd to shew all the minute variations in the pressure of the Air; by which I constantly find, that before, and during the time of rainy weather, the pressure of the Air is less, and in dry weather, but especially when an Eastern Wind (which having past over vast tracts of Land is heavy with Earthy Particles) blows, it is much more, though these changes are varied according to very odd Laws.

But this is but one way of discovering the effluvia of the Earth mixt with the Air; there may be, perhaps many others, witness the Hygroscope, an Instrument whereby the watery steams volatile in the Air are discerned, which the Nose it self is not able to find. This I have describ'd in the following Tract in the Description of the Beard of a wild Oat. Others there, are, may be discovered both by the Nose, and by other wayes also. Thus the smoak of burning Wood is smelt, seen, and sufficiently felt by the eyes: The fumes of burning Brimstone are smelt and discovered also by the destroying the Colours of Bodies, as by the whitening of a red Rose: And who knows, but that the Industry of man, following this method, may find out wayes of improving this sense to as great a degree of perfection at it is in any Animal, and perhaps yet higher.

'Tis not improbable also, but that our taste may be very much improv'd either by preparing our taste for the Body, as, after eating bitter things, Wine, or other Vinous liquors, are more sensibly tasted; or else by preparing Bodies for our tast; as the dissolving of Metals with acid Liquors, make them tastable, which were before altogether insipid; thus Lead becomes sweeter then Sugar, and Silver more bitter then Gall, Copper and Iron of most loathsome tasts. And indeed the business of this sense being to discover the presence of dissolved Bodies in Liquors put on the Tongue, or in general to discover that a fluid body has some solid body dissolv'd in it, and what they are; whatever contrivance makes this discovery improves this sense. In this kind the mixtures of Chymical Liquors afford many Instances; as the sweet Vinegar that is impregnated with Lead may be discovered to be so by the affusion of a little of an Alcalizate solution: The bitter liquor of Aqua fortis and Silver may be discover'd to be charg'd with that Metal, by laying in it some plates of Copper: 'Tis not improbable also, but there may be multitudes of other wayes of discovering the parts dissolv'd, or dissoluble in liquors; and what is this discovery but a kind of secundary tasting.

'Tis not improbable also, but that the sense of feeling may be highly improv'd, for that being a sense that judges of the more gross and robust motions of the Particles of Bodies, seems capable of being improv'd and assisted very many wayes. Thus for the distinguishing of Heat and Cold, the Weather-glass and Thermometer, which I have describ'd in this following Treatise, do exceedingly perfect it; by each of which the least variations of heat or cold, which the most Acute sense is not able to distinguish, are manifested. This is oftentimes further promoted also by the help of Burning-glasses, and the like, which collect and unite the radiating heat. Thus the roughness and smoothness of a Body is made much more sensible by the help of a Microscope, then by the most tender and delicate Hand. Perhaps, a Physitian might, by several other tangible proprieties, discover the constitution of a Body as well as by the Pulse. I do but instance in these, to shew what possibility there may be of many others, and what probability and hopes there were of finding them, if this method were followed; for the Offices of the five Senses being to detect either the subtil and curious Motions propagated through all pellucid or perfectly homogeneous Bodies; Or the more gross and vibrative Pulse communicated through the Air and all other convenient mediums, whether fluid or solid: Or the effluvia of Bodies dissolv'd in the Air; Or the particles of bodies dissolv'd or dissoluble in Liquors, or the more quick and violent shaking motion of heat in all or any of these: whatsoever does any wayes promote any of these kinds of criteria, does afford a way of improving some one sense. And what a multitude of these would a diligent Man meet with in his inquiries? And this for the helping and promoting the sensitive faculty only.

Next, as for the Memory, or retentive faculty, we may be sufficiently instructed from the written Histories of civil actions, what great assistance may be afforded the Memory, in the committing to writing things observable in natural operations. If a Physitian be therefore accounted the more able in his Faculty, because he has had long experience and practice, the remembrance of which, though perhaps very imperfect, does regulate all his after actions: What ought to be thought of that man, that has not only a perfect register of his own experience, but it grown old with the experience of many hundreds of years, and many thousands of men.

And though of late, men, beginning to be sensible of this convenience, have here and there registred and printed some few Centuries, yet for the most part they are set down very lamely and imperfectly, and, I fear, many times not so truly, they seeming, several of them, to be design'd more for Ostentation then publique use: For, not to instance, that they do, for the most part, omit those Experiences they have made, wherein their Patients have miscarried, it is very easie to be perceiv'd, that they do all along hyperbolically extol their own Prescriptions, and vilifie those of others. Notwithstanding all which, these kinds of Histories are generally esteem'd useful, even to the ablest Physitian.

What may not be expected from the rational or deductive Faculty that is furnisht with such Materials, and those so readily adapted, and rang'd for use, that in a moment, at 'twere, thousands of Instances, serving for the illustration, determination, or invention, of almost any inquiry, may be represented even to the sight? How neer the nature of Axioms must all those Propositions be which are examin'd before so many Witnesses? And how difficult will it be for any, though never so subtil an error in Philosophy, to scape from being discover'd, after it has indur'd the touch, and so many other tryals?

What kind of mechanical way, and physical invention also is there requir'd that might not this may be found out? The Invention of a way to find the Longitude of places is easily perform'd, and that to as great perfection as is desir'd, or to at great an accurateness as the Latitude of places can be found at Sea; and perhaps yet also to a greater certainty then that has been hitherto found, as I shall very speedily freely manifest to the world. The way of flying in the Air seems principally unpracticable, by reason of the want of strength in humane muscles; if therefore that could be suppli'd, it were, I think, easie to make twenty contrivances to perform the office of Wings: What Attempts also I have made for the supplying that Defect, and my successes therein, which, I think, are wholly new, and not inconsiderable, I shall in another place relate.

'Tis not unlikely also, but that Chymists, if they followed this method, might find out their so much sought for Alkahest. What an universal Menstruum, which dissolves all sorts of Sulphureous Bodies, I have discover'd (which hat not been before taken notice of as such) I have shewn in the sixteenth Observation.

What a prodigious variety of Inventions in Anatomy has this latter Age afforded, even in our own Bodies in the very Heart, by which we live, and the Brain, which is the seat of our knowledge of other things? witness all the excellent Works of Pecquet, Bartholinus, Billius, and many others; and at home, of Doctor Harvy, Doctor Ent, Doctor Willis, Doctor Glisson. In Celestial Observations we have far exceeded all the Antients, even the Chaldeans and Egyptians themselves, whose vast Plains, high Towers, and clear Air, did not give them so great advantages over us, as have over them by our Glasses. By the help of which, they have been very much outdone by the famous Galileo, Hevelius, Zulichem; and our own Countrymen, Mr. Rook, Doctor Wren, and the great Ornament of our Church and Nation, the Lord Bishop of Exeter. And to say no more in Aerial Discoveries, there has been a wonderful progress made by the Noble Engine of the most Illustrious Mr. Boyle, whom it becomes me to mention with all honour, not only as my particular Patron, but as the Patron of Philosophy it self; which he every day increases by his Labours, and adorns by his Example.

The good success of all these great Men, and many others, and the now seemingly great obviousness of most of their and divers other Inventions, which from the beginning of the world have been, as 'twere, trod on, and yet not minded till these last inquisitive Ages (an Argument that there may be yet behind multitudes of the like) puts me in mind to recommend such Studies, and the prosecution of them by such methods, to the Gentlemen of our Nation, whose leisure makes them fit to undertake, and the plenty of their fortunes to accomplish, extraordinary things in this way. And I do not only propose this kind of Experimental Philosophy as matter of high rapture and delight of the mind, but even as a material and sensible Pleasure. So vast it the variety of Objects which will come under their Inflections, so many different wayes there are of handling them, so great is the satisfaction of finding out new things, that I dare compare the contentment which they will injoy, not only to that of contemplation, but even to that which most men prefer of the very Senses themselves.

And if they will please to take any incouragement from so mean and so imperfect endeavours as mine, upon my own experience, I can assure them, without arrogance, That there has not been any inquiry or Problem in Mechanicks, that I have hitherto propounded to my self, but by a certain method (which I may on some other opportunity explain) I have been able presently to examine the possibility of it; and if so, as easily to excogitate divers wayes of performing it: And indeed it is possible to do as much by this method in Mechanicks, as by Algebra can be perform'd in Geometry. Nor can I at all doubt, but that the same method is as applicable to Physical Enquiries, and as likely to find and reap thence at plentiful a crop of Inventions; and indeed there seems to be no subject so barren, but may with this good husbandry be highly improv'd.

Toward the prosecution of this method in Physical Inquiries, I have here and there gleaned up an handful of Observations, in the collection of most of which I made use of Microscopes, and some other Glasses and Instruments that improve the sense; which way I have herein taken, not that there are not multitudes of useful and pleasant Observables, yet uncollected, obvious enough without the helps of Art, but only to promote the use of Mechanical helps for the Senses, both in the surveying the already visible World, and for the discovery of many others hitherto unknown, and to make us, with the great Conqueror, to be affected that we have not yet overcome one World when there are so many others to be discovered, every considerable improvement of Telescopes or Microscopes producing new Worlds and Terra-Incognita's to our view.

The Glasses I used were of our English make, but though very good of the kind, yet far short of what might be expected, could we once find a way of making Glasses Elliptical, or of some more true shape; for though both Microscopes, and Telescopes, as they now are, will magnifie an Object about a thousand thousand times bigger then it appears to the naked eye; yet the Apertures of the Object-glasses are so very small, that very few Rays are admitted, and even of those few there are so many false, that the Object appears dark and indistinct: And indeed these inconveniences are such, as seem inseparable from Spherical Glasses, even when most exactly made; but the way we have hitherto made use of for that purpose is so imperfect, that there may be perhaps ten wrought before one be made tolerably good, and most of those ten perhaps every one differing in goodness one from another, which is an Argument, that the way hitherto used is, at least, very uncertain. So that these Glasses have a double defect; the one, that very few of them are exactly true wrought; the other, that even of those that are best among them, none will admit a sufficient number of Rayes to magnifie the Object beyond a determinate bigness. Against which Inconveniences the only Remedies I have hitherto met with are these.

As for Telescopes, the only improvement they seem capable of, is the increasing of their length; for the Object being remote, there is no thought of giving it a greater light then it has; and therefore to augment the. Aperture, the Glass must be ground of a very large sphere; for, by that means, the longer the Glass be, the bigger aperture will it bear, if the Glasses be of an equal goodness in their kind. Therefore a six will indure a much larger Aperture then a three foot Glass, and a sixty foot Glass will proportionably bear a greater Aperture then a thirty, and will as much excel it also as a six foot does a three foot, as I have experimentally observ'd in one of that length made by Mr. Richard Reives here at London, which will bear an Aperture above three inches over, and yet make the Object proportionably big and distinct; whereas there are very few thirty foot Glasses that will indure an Aperture of more then two inches over. So that for Telescopes, supposing we had a very ready way of making their Object Glasses of exactly spherical Surfaces, we might, by increasing the length of the Glass, magnifie the Object to any assignable bigness. And for performing both these, I cannot imagine any way more easie, and more exact, then by this following Engine, by means of which, any Glasses, of what length soever, may be speedily made. It seems the most easie, because with one and the same Tool may be with care ground an Object Glass, of any length or breadth requisite, and that with very little or no trouble in fitting the Engine, and without much skill in the Grinder. It seems to be the most exact, for to the very last stroke the Glass does regulate and rectifie the Tool to its exact Figure; and the longer or more the Tool and Glass are wrought together, the more exact will both of them be of the desir'd Figure. Further, the motions of the Glass and Tool do so cross each other, that there is not one point of eithers Surface, but has thousands of cross motions thwarting it, so that there can be no kind of Rings or Gutters made either in the Tool or Glass.

But because we are certain, from the Laws of refraction (which I I have experimentally found to be so, by an Instrument I shall presently describe) that the lines of the angles of Incidence are proportionate to the lines of the angles of Refraction, therefore if Glasses could be made of those kind of Figures, or some other, such as the most incomparable Des Cartes has invented, and demonstrated in his Philosophical and Mathematical Works, we might hope for a much greater perfection of Opticks then can be rationally expected from spherical ones; for though, cæteris paribus, we find, that the larger the Telescope Object Glasses are, and the shorter those of the Microscope, the better they magnify, yet both of them, beside such determinate dimensions, are by certain inconveniences rendred unuseful; for it will be exceeding difficult to make and manage a Tube above an hundred foot long, and it will be as difficult to inlighten an Object less then an hundred part of an inch distant from the Object Glass.

I have not as yet made any attempts of that kind, though I know two or three wayes, which, as far as I have yet considered, seem very probable, and may invite me to make a tryal as soon as I have an opportunity, of which I may hereafter perhaps acquaint the world. In the Interim, I shall describe the Instrument I even now mention'd, by which the refraction of all kinds of Liquors may be most exactly measur'd, thereby to give the curious an opportunity of making what further tryals of that kind they shall think requisite to any of their intended tryals; and to let them see that the laws of Refraction are not only notional.

By means of this Instrument I can with little trouble, and a very small quantity of any Liquor, examine, most accurately, the refraction of it not only for one inclination, but for all; and thereby am inabled to make very accurate Tables; several of which I have also experimentally made, and find, that Oyl of Turpentine has a much greater Refraction then Spirit of Wine, though it be lighter; and that Spirit of Wine has a greater Refraction then Water, though it be lighter also; but that salt Water also has a greater Refraction then fresh, though it be heavier: but Allum water has a less refraction then common Water, though heavier also. So that it seems, as to the refraction made in a Liquor, the specifick gravity is of no efficacy. By this I have also found that look what proportion the Sine of the Angle of one Inclination has to the Sine of the Angle of Refraction, correspondent to it, the same proportion have all the Sines of other Inclinations to the Sines of their appropriate Refractions.

Now though this were the Instrument I made most use of, yet I have made several other Tryals with other kinds of Microscopes, which both for matter and form were very different from common spherical Glasses. I have made a Microscope with one piece of Glass, both whose surfaces were plains. I have made another only with a plano concave, without any kind of reflection, divers also by means of reflection. I have made others of Waters, Gums, Resins, Salts, Arsenick, Oyls, and with divers other mixtures of watery and oyly Liquors. And indeed the subject is capable of a great variety; but I find generally none more useful then that which is made with two Glasses, such as I have already describ'd.

What the things are I observ'd, the following descriptions will manifest; in brief, they were either exceeding small Bodies, or exceeding small Pores, or exceeding small Motions, some of each of which the Reader will find in the following Notes, and such, as I presume, (many of them at least) will be new, and perhaps not less strange: Some specimen of each of which Heads the Reader will find in the subsequent delineations, and indeed of some more then I was willing there should be; which was occasioned by my first Intentions to print a much greater number then I have since found time to compleat. Of such therefore as I had, I selected only some few of every Head, which for some particulars seem'd most observable, rejecting the rest as superfluous to the present Design.

What each of the delineated Subjects are, the following descriptions annext to each will inform, of which I shall here, only once for all, add, That in divers of them the Gravers have pretty well follow'd my directions and draughts; and that in making of them, I indeavoured (as far as I was able) first to discover the true appearance, and next to make a plain representation of it. This I mention the rather, because of these kind of Objects there is much more difficulty to discover the true shape, then of those visible to the naked eye, the same Object seeming quite differing, in one position to the Light, from what it really is, and may be discover'd in another. And therefore I never began to make any draught before by many examinations in several lights, and in several positions to those lights, I had discover'd the true form. For it is exceeding difficult in some Objects, to distinguish between a prominency and a depression, between a shadow and a black stain, or a reflection and a whiteness in the colour. Besides, the transparency of most Objects renders them yet much more difficult then if they were opacous. The Eyes of a Fly in one kind of light appear almost like a Lattice, drill'd through with abundance of small holes; which probably may be the Reason, why the Ingenious Dr. Power seems to suppose them such. In the Sunshine they look like a Surface cover'd with golden Nails; in another posture, like a Surface cover'd with Pyramids; in another with Cones; and in other postures of quite other shapes; but that which exhibits the best, is the Light collected on the Object, by those means I have already describ'd.

And this was undertaken in prosecution of the Design which the ROYAL SOCIETY has propos'd to it self. For the Members of the Assembly having before their eys so many fatal Instances of the errors and falshoods, in which the greatest part of mankind has so long wandred, because they rely'd upon the strength of humane Reason alone, have begun anew to correct all Hypotheses by sense, as Seamen do their dead Reckonings by Cœlestial Observations; and to this purpose it has been their principal indeavour to enlarge & strengthen the Senses by Medicine, and by such outward Instruments as are proper for their particular works. By this means they find some reason to suspect, that those effects of Bodies, which have been commonly attributed to Qualities, and those confess'd to be occult, are perform'd by the small Machines of Nature, which are not to be discern'd without these helps, seeming the meer products of Motion, Figure, and Magnitude; and that the Natural Textures, which some call the Plastick faculty, may be made in Looms, which a greater perfection of Opticks may make discernable by these Glasses; so as now they are no more puzzled about them, then the vulgar are to conceive, how Tapestry or flowred Stuffs are woven. And the ends of all these Inquiries they intend to be the Pleasure of Contemplative minds, but above all, the ease and dispatch of the labours of mens hands. They do indeed neglect no opportunity to bring all the rare things of Remote Countries within the compass of their knowledge and practice. But they still acknowledg their most useful Informations to arise from common things, and from diversifying their most ordinary operations upon them. They do not wholly reject Experiments of meer light and theory; but they principally aim at such, whose Applications will improve and facilitate the present way of Manual Arts. And though some men, who are perhaps taken up about less honourable Employments, are pleas'd to censure their proceedings, yet they can shew more fruits of their first three years, wherein they have assembled, then any other Society in Europe can for a much larger space of time. 'Tis true, such undertakings as theirs do commonly meet with small incouragement, because men are generally rather taken with the plausible and discursive, then the real and the solid part of Philosophy; yet by the good fortune of their institution, in an Age of all others the most inquisitive, they have been assisted by the contribution and presence of very many of the chief Nobility and Gentry, and others who are some of the most considerable in their several Professions. But that that yet farther convinces me of the Real esteem that the more serious part of men have of this Society, is, that several Merchants, men who act in earnest (whose Object is meum & tuum, that great Rudder of humane affairs) have adventur'd considerable sums of Money, to put in practice what some of our Members have contrived, and have continued stedfast in their good opinions of such Indeavours, when not one of a hundred of the vulgar have believed their undertakings feasable. And it it also fit to be added, that they have one advantage peculiar to themselves, that very many of their number are men of Converse and Traffick; which is a good Omen, that their attempts will bring Philosophy from words to action, seeing the men of Business have had so great a share in their first foundation.

And of this kind I ought not to conceal one particular Generosity, which more nearly concerns my self. It is the munificence of Sir John Cutler, in endowing a Lecture for the promotion of Mechanick Arts, to be governed and directed by This Society.This Bounty I mention for the Honourableness of the thing it self, and for the expectation which I have of the efficacy of the Example; for it cannot now be objected to them, that their Designs will be esteemed frivolous and vain, when they have such a real Testimony of the Approbation of a Man that is such an eminent Ornament of this renowned City, and one, who, by the Variety, and the happy Success, of his negotiations, has given evident proofs, that he is not easie to be deceiv'd. This Gentleman has well observ'd, that the Arts of life have been too long imprison'd in the dark shops of Mechanicks themselves, & there hindred from growth, either by ignorance, or self-interest: and he has bravely freed them from these inconveniences: He hath not only obliged Tradesmen, but Trade it self: He has done a work that is worthy of London, and has taught the chief City of Commerce in the world the right way how Commerce is to be improv'd. We have already seen many other great signs of Liberality and a large mind, from the same hand: For by his diligence about the Corporation for the Poor; by his honorable Subscriptions for the rebuilding of St. Paul's; by his chearful Disbursment for the replanting of Ireland, and by many other such publick works, he has shewn by what means he indeavours to establish his Memory; and now by this last gift he has done that, which became one of the wisest Citizens of our Nation to accomplish, seeing one of the wisest of our Statesmen, the Lord Verulam, first propounded it.

But to return to my Subject, from a digression, which, I hope, my Reader will pardon me, seeing the Example is so rare that I can make no more such digressions. If these my first Labours shall be any wayes useful to inquiring men, I must attribute the incouragement and promotion of them to a very Reverend and Learned Person, of whom this ought in justice to be said, That there is scarce any one Invention, which this Nation has produc'd in our Age, but it has some way or other been set forward by his assistance. My Reader, I believe, will quickly ghess, that it is Dr. Wilkins that I mean. He is indeed a man born for the good of mankind, and for the honour of his Country. In the sweetness of whose behaviour, in the calmness of his mind, in the unbounded goodness of his heart, we have an evident Instance, what the true and the primitive unpassionate Religion was, before it was sowred by particular Factions. In a word, his Zeal has been so constant and effectual in advancing all good and profitable Arts, that as one of the Antient Romans said of Scipio, That he thanked God that he was a Roman; because whereever Scipio had been born, there had been the seat of the Empire of the world: So may I thank God, that Dr. Wilkins was an Englishman, for whereever he had lived, there had been the chief Seat of generous Knowledge and true Philosophy. To the truth of this, there are so many worthy men living that will subscribe, that I am confident, what I have here said, will not be looked upon, by any ingenious Reader, as a Panegyrick, but only as a real testimony.

By the Advice of this Excellent man I first set upon this Enterprise, yet still came to it with much Reluctancy, because I was to follow the footsteps of so eminent a Person as Dr. Wren, who was the first that attempted any thing of this nature; whose original draughts do now make one of the Ornaments of that great Collection of Rarities in the Kings Closet. This Honor, which his first beginnings of this kind have receiv'd, to be admitted into the most famous place of the world, did not so much incourage, as the hazard of coming after Dr. Wren did affright me; for of him I must, affirm, that, since the time of Archimedes, there scarce ever met in one man, in so great a perfection, such a Mechanical Hand, and so Philosophical a Mind.

But at last, being assured both by Dr. Wilkins, and Dr. Wren himself, that he had given over his intentions of prosecuting it, and not finding that there was any else design'd the pursuing of it, I set upon this undertaking, and was not a little incourag'd to proceed in it, by the Honour the Royal Society was pleas'd to favour me with, in approving of those draughts (which from time to time as I had an opportunity of describing) I presented to them. And particularly by the Incitements of divers of those Noble and excellent Persons of it, which were my more especial Friends, who were not less urgent with me for the publishing, then for the prosecution of them.

After I had almost compleated these Pictures and Observations (having had divers of them ingraven, and was ready to send them to the Press) I was inform'd, that the Ingenious Physitian Dr. Henry Power had made several Microscopical Observations, which had I not afterwards, upon our interchangably viewing each others Papers, found that they were for the most part differing from mine, either in the Subject it self, or in the particulars taken notice of; and that his design was only to print Observations without Pictures, I had even then suppressed what I had so far proceeded in. But being further excited by several of my Friends, in complyance with their opinions, that it would not be unacceptable to several inquisitive Men, and hoping also, that I should thereby discover something New to the World, I have at length cast in my Mite, into the vast Treasury of A Philosophical History. And it is my hope, as well as belief, that these my Labours will be no more comparable to the Productions of many other Natural Philosophers, who are now every where busie about greater things; then my little Objects are to be compar'd to the greater and more beautiful Works of Nature, A Flea, a Mite, a Gnat, to an Horse, an Elephant, or a Lyon.

MICROGRAPHIA,

Physiological Descriptions

MINUTE BODIES,

MAGNIFYING GLASSES;

OBSERVATIONS and INQUIRIES thereupon.

Observ. I. Of the Point of a sharp small Needle.

s in Geometry, the most natural way of beginning is from a Mathematical point; so is the same method in Observations and Natural history the most genuine, simple, and instructive. We must first endevour to make letters, and draw single strokes true, before we venture to write whole Sentences, or to draw large Pictures. And in Physical Enquiries, we must endevour to follow Nature in the more plain and easie ways she treads in the most simple and uncompounded bodies, to trace her steps, and be acquainted with her manner of walking there, before we venture our selves into the multitude of meanders she has in bodies of a more complicated nature; lest, being unable to distinguish and judge of our way, we quickly lose both Nature our Guide, and our selves too, and are left to wander in the labyrinth of groundless opinions; wanting both judgment, that light, and experience, that clew, which should direct our proceedings.

We will begin these our Inquiries therefore with the Observations of Bodies of the most simple nature first, and so gradually proceed to those of a more compounded one. In prosecution of which method, we shall begin with a Physical point; of which kind the Point of a Needle is commonly reckon'd for one; and is indeed, for the most part, made so sharp, that the naked eye cannot distinguish any parts of it: It very easily pierces, and makes its way through all kind of bodies softer then it self: But if view'd with a very good Microscope, we may find that the top of a Needle (though as to the sense very sharp) appears a broad, blunt, and very irregular end; not resembling a Cone, as is imagin'd, but onely a piece of a tapering body, with a great part of the top remov'd, or deficient. The Points of Pins are yet more blunt, and the Points of the most curious Mathematical Instruments do very seldome arrive at so great a sharpness; how much therefore can be built upon demonstrations made onely by the productions of the Ruler and Compasses, he will be better able to consider that shall but view those points and lines with a Microscope.

Now though this point be commonly accounted the sharpest (whence when we would express the sharpness of a point the most superlatively, we say, As sharp as a Needle) yet the Microscope can afford us hundreds of Instances of Points many thousand times sharper: such as those of the hairs, and bristles, and claws of multitudes of Insects; the thorns, or crooks, or hairs of leaves, and other small vegetables; nay, the ends of the stiriæ or small parallelipipeds of Amianthus, and alumen plumosum; of many of which, though the Points are so sharp as not to be visible, though view'd with a Microscope (which magnifies the Object, in bulk, above a million of times) yet I doubt not, but were we able practically to make Microscopes according to the theory of them, we might find hills, and dales, and pores, and a sufficient bredth, or expansion, to give all those parts elbow-room, even in the blunt top of the very Point of any of these so very sharp bodies. For certainly the quantity or extension of any body may be Divisible in infinitum, though perhaps not the matter.

But to proceed: The Image we have here exhibited in the first Figure, was the top of a small and very sharp Needle, whose point aa nevertheless appear'd through the Microscope above a quarter of an inch broad, not round nor flat, but irregular and uneven; so that it seem'd to have been big enough to have afforded a hundred armed Mites room enough to be rang'd by each other without endangering the breaking one anothers necks, by being thrust off on either side. The surface of which, though appearing to the naked eye very smooth, could not nevertheless hide a multitude of holes and scratches and ruggednesses from being discover'd by the Microscope to invest it, several of which inequalities (as A, B, C, seem'd holes made by some small specks of Rust; and D some adventitious body, that stuck very close to it) were casual. All the rest that roughen the surface, were onely so many marks of the rudeness and bungling of Art. So unaccurate is it, in all its productions, even in those which seem most neat, that if examin'd with an organ more acute then that by which they were made, the more we see of their shape, the less appearance will there be of their beauty: whereas in the works of Nature, the deepest Discoveries shew us the greatest Excellencies. An evident Argument, that he that was the Author of all these things, was no other then Omnipotent; being able to include as great a variety of parts and contrivances in the yet smallest Discernable Point, as in those vaster bodies (which comparatively are called also Points) such as the Earth, Sun, or Planets. Nor need it seem strange that the Earth it self may be by Analogie call'd a Physical Point: For as its body, though now so near us as to fill our eys and fancies with a sense of the vastness of it, may by a little Distance, and some convenient Diminishing Glasses, be made vanish into a scarce visible Speck, or Point (as I have often try'd on the Moon, and (when not too bright) on the Sun it self.) So, could a Mechanical contrivance succesfully answer our Theory, we might see the least spot as big as the Earth it self; and Discover, as Des Cartes also conjectures (Diop. ch. 10. § 9.), as great a variety of bodies in the Moon, or Planets, as in the Earth.

But leaving these Discoveries to future Industries, we shall proceed to add one Observation more of a point commonly so call'd, that is, the mark of a full stop, or period. And for this purpose I observed many both printed ones and written; and among multitudes I found few of them more round or Schem. 2.
Fig. 3. regular then this which I have delineated in the third figure of the second Scheme, but very many abundantly more disfigur'd; and for the most part if they seem'd equally round to the eye, I found those points that had been made by a Copper-plate, and Roll-press, to be as misshapen as those which had been made with Types, the most curious and smothly engraven strokes and points, looking but as so many furrows and holes, and their printed impressions, but like smutty daubings on a matt or uneven floor with a blunt extinguisht brand or stick's end. And as for points made with a pen they were much more ragged and deformed. Nay, having view'd certain pieces of exceeding curious writing of the kind (one of which in the bredth of a two-pence compris'd the Lords prayer, the Apostles Creed, the ten Commandments, and about half a dozen verses besides of the Bible, whose lines were so small and near together, that I was unable to number them with my naked eye,) a very ordinary Microscope, I had then about me, inabled me to see that what the Writer of it had asserted was true, but withall discover'd of what pitifull bungling scribbles and scrawls it was compos'd, Arabian and China characters being almost as well shap'd, yet thus much I must say for the Man, that it was for the most part legible enough, though in some places there wanted a good fantsy well preposest to help one through. If this manner of small writing were made easie and practicable (and I think I know such a one, but have never yet made tryal of it, whereby one might be inabled to write a great deale with much ease, and accurately enough in a very little roome) it might be of very good use to convey secret Intelligence without any danger of Discovery or mistrusting. But to come again to the point. The Irregularities of it are caused by three or four coadjutors, one of which is, the uneven surface of the paper, which at best appears no smother then a very course piece of shag'd cloth, next the irregularity of the Type or Ingraving, and a third is the rough Daubing of the Printing-Ink that lies upon the instrument that makes the impression, to all which, add the variation made by the Different lights and shadows, and you may have sufficient reason to guess that a point may appear much more ugly then this, which I have here presented, which though it appear'd through the Microscope gray, like a great splatch of London dirt, about three inches over; yet to the naked eye it was black and no bigger then that in the midst of the Circle A. And could I have found Room in this Plate to have inserted an O you should have seen that the letters were not more distinct then the points of Distinction, nor a drawn circle more exactly so, then we have now shown a point to be a point.

Observ. II. Of the Edge of a Razor.

The sharpest Edge hath the same kind of affinity to the sharpest Point in Physicks, as a line hath to a point in Mathematicks; and therefore the Treaty concerning this, may very properly be annexed to the former. A Razor doth appear to be a Body of a very neat and curious aspect, till more closely viewed by the Microscope, and there we may observe its very Edge to be of all kind of shapes, except what it should be. For examining that of a very sharp one, I could not find that any part of it had any thing of sharpness in it; but it appeared a rough surface of a very considerable bredth from side to side, the narrowest part not seeming thinner then the back of a pretty thick Knife. Nor is't likely that it should appear any otherwise, since as we just now shew'd that a point appear'd a circle, 'tis rational a line should be a parallelogram.

Now for the drawing this second Figure (which represents a part of the Edge about half a quarter of an inch long of a Razor well set) I so plac'd it between the Object-glass & the light, that there appear'd a reflection from the very Edge, represented by the white line abcdef. In which you may perceive it to be somewhat sharper then elsewhere about d, to be indented or pitted about b, to be broader and thicker about c, and unequal and rugged about e, and pretty even between ab and ef. Nor was that part of the Edge ghik so smooth as one would imagine so smooth bodies as a Hone and Oyl should leave it; for besides those multitudes of scratches, which appear to have raz'd the surface ghik, and to cross each other every way which are not half of them exprest in the Figure, there were several great and deep scratches, or furrows, such as gh and ik, which made the surface yet more rugged, caus'd perhaps by some small Dust casually falling on the Hone, or some harder or more flinty part of the Hone it self. The other part of the Razor ll, which is polish'd on a grinding-stone, appear'd much rougher then the other, looking almost like a plow'd field, with many parallels, ridges, and furrows, and a cloddy, as 'twere, or an uneven surface: nor shall we wonder at the roughnesses of those surfaces, since even in the most curious wrought Glasses for Microscopes, and other Optical uses, I have, when the Sun has shone well on them, discover'd their surface to be variously raz'd or scratched, and to consist of an infinite of small broken surfaces, which reflect the light of very various and differing colours. And indeed it seems impossible by Art to cut the surface of any hard and brittle body smooth, since Putte, or even the most curious Powder that can be made use of, to polish such a body, must consist of little hard rough particles, and each of them must cut its way, and consequently leave some kind of gutter or furrow behind it. And though Nature does seem to do it very readily in all kinds of fluid bodies, yet perhaps future observators may discover even these also rugged; it being very probable, as I elsewhere shew, that fluid bodies are made up of small solid particles variously and strongly mov'd, and may find reason to think there is scarce a surface in rerum naturâ perfectly smooth. The black spot mn, I ghess to be some small speck of rust, for that I have oft observ'd to be the manner of the working of Corrosive Juyces. To conclude, this Edge and piece of a Razor, if it had been really such as it appear'd through the Microscope, would scarcely have serv'd to cleave wood, much less to have cut off the hair of beards, unless it were after the manner that Lucian merrily relates Charon to have made use of, when with a Carpenters Axe he chop'd off the beard of a sage Philosopher, whose gravity he very cautiously fear'd would indanger the oversetting of his Wherry.

Observ. III. Of fine Lawn, or Linnen Cloth.

This is another product of Art, A piece of the finest Lawn I was able to get, so curious that the threads were scarce discernable by the naked eye, and yet through an ordinary Microscope you may perceive what a goodly piece of coarse Matting it is; what proportionable cords each of its threads are, being not unlike, both in shape and size, the bigger and coarser kind of single Rope-yarn, wherewith they usually make Cables. That which makes the Lawn so transparent, is by the Microscope, nay by the naked eye, if attentively viewed, plainly enough evidenced to be the multitude of square holes which are left between the threads, appearing to have much more hole in respect of the intercurrent parts then is for the most part left in a lattice-window, which it does a little resemble, onely the crossing parts are round and not flat.

These threads that compose this fine contexture, though they are as small as those that constitute the finer sorts of Silks, have notwithstanding nothing of their glossie, pleasant, and lively reflection. Nay, I have been informed both by the Inventor himself, and several other eye-witnesses, that though the flax, out of which it is made, has been (by a singular art, of that excellent Person, and Noble Vertuoso, M. Charls Howard, brother to the Duke of Norfolk) so curiously dress'd and prepar'd, as to appear both to the eye and the touch, full as fine and as glossie, and to receive all kinds of colours, as well as Sleave-Silk; yet when this Silken Flax is twisted into threads, it quite loseth its former luster, and becomes as plain and base a thread to look on, as one of the same bigness, made of common Flax.

The reason of which odd Phenomenon seems no other then this; that though the curiously drest Flax has its parts so exceedingly small, as to equallize, if not to be much smaller then the clew of the Silk-worm, especially in thinness, yet the differences between the figures of the constituting filaments are so great, and their substances so various, that whereas those of the Silk are small, round, hard, transparent, and to their bigness proportionably stiff, so as each filament preserves its proper Figure, and consequently its vivid reflection intire, though twisted into a thread, if not too hard; those of Flax are flat, limber, softer, and less transparent, and in twisting into a thread they joyn, and lie so close together, as to lose their own, and destroy each others particular reflections. There seems therefore three Particulars very requisite to make the so drest Flax appear Silk also when spun into threads. First, that the substance of it should be made more clear and transparent, Flax retaining in it a kind of opacating brown, or yellow; and the parts of the whitest kind I have yet observ'd with the Microscope appearing white, like flaw'd Horn or Glass, rather then clear, like clear Horn or Glass. Next that, the filaments should each of them be rounded, if that could be done, which yet is not so very necessary, if the first be perform'd, and this third, which is, that each of the small filaments be stifned; for though they be square, or flat, provided they be transparent and stiff, much the same appearances must necessarily follow. Now, though I have not yet made trial, yet I doubt not, but that both these proprieties may be also induc'd upon the Flax, and perhaps too by one and the same Expedient, which some trials may quickly inform any ingenious attempter of, who from the use and profit of such an Invention, may find sufficient argument to be prompted to such Inquiries. As for the tenacity of the substance of Flax, out of which the thread is made, it seems much inferiour to that of Silk, the one being a vegetable, the other an animal substance. And whether it proceed from the better concoction, or the more homogeneous constitution of animal substances above those of vegetables, I do not here determine; yet since I generally find, that vegetable substances do not equalize the tenacity of animal, nor these the tenacity of some purified mineral substances; I am very apt to think, that the tenacity of bodies does not proceed from the hamous, or hooked particles, as the Epicureans and some modern Philosophers have imagin'd; but from the more exact congruity of the constituent parts, which are contiguous to each other, and so bulky, as not to be easily separated, or shatter'd, by any small pulls or concussion of heat.

Observ. IV. Of fine waled Silk, or Taffety.

This is the appearance of a piece of very fine Taffety-riband in the bigger magnifying Glass, which you see exhibits it like a very convenient substance to make Bed-matts, or Door-matts of, or to serve for Beehives, Corn-scuttles, Chairs, or Corn-tubs, it being not unlike that kind of work, wherewith in many parts in England, they make such Utensils of Straw, a little wreathed, and bound together with thongs of Brambles. For in this Contexture, each little filament, fiber, or clew of the Silk-worm, seem'd about the bigness of an ordinary Straw, as appears by the little irregular pieces, ab, cd, and ef; The Warp, or the thread that ran crossing the Riband, appear'd like a single Rope of an Inch Diameter; but the Woof, or the thread that ran the length of the Riband, appear'd not half so big. Each Inch of six-peny-broad Riband appearing no less then a piece of Matting Inch and half thick, and twelve foot square, a few yards of this, would be enough to floor the long Gallery of the Loure at Paris. But to return to our piece of Riband: It affords us a not unpleasant object, appearing like a bundle, or wreath, of very clear and transparent Cylinders, if the Silk be white, and curiously ting'd; if it be colour'd, each of those small horney Cylinders affording in some place or other of them, as vivid a reflection, as if it had been sent from a Cylinder of Glass or Horn. In-so-much, that the reflexions of Red, appear'd as if coming from so many Granates, or Rubies. The loveliness of the colours of Silks above those of hairy Stuffs, or Linnen, consisting, as I else-where intimate, chiefly in the transparency, and vivid reflections from the Concave, or inner surface of the transparent Cylinder, as are also the colours of Precious Stones; for most of the reflections from each of these Cylinders, come from the Concave surface of the air, which is as 'twere the foil that incompasses the Cylinder. The colours with which each of these Cylinders are ting'd, seem partly to be superficial, and sticking to the out-sides of them; and partly, to be imbib'd, or sunck into the substance of them: for Silk, seeming to be little else then a dried thread of Glew, may be suppos'd to be very easily relaxt, and softened, by being steeped in warm, nay in cold, if penetrant, juyces or liquors. And thereby those tinctures, though they tinge perhaps but a small part of the substance, yet being so highly impregnated with the colour, as to be almost black with it, may leave an impression strong enough to exhibite the desir'd colour. A pretty kinde of artificial Stuff I have seen, looking almost like transparent Parchment, Horn, or Ising-glass, and perhaps some such thing it may be made of, which being transparent, and of a glutinous nature, and easily mollified by keeping in water, as I found upon trial, had imbib'd, and did remain ting'd with a great variety of very vivid colours, and to the naked eye, it look'd very like the substance of the Silk. And I have often thought, that probably there might be a way found out, to make an artificial glutinous composition, much resembling, if not full as good, nay better, then that Excrement, or whatever other substance it be out of which, the Silk-worm wire-draws his clew. If such a composition were found, it were certainly an easie matter to find very quick ways of drawing it out into small wires for use. I need not mention the use of such an Invention, nor the benefit that is likely to accrue to the finder, they being sufficiently obvious. This hint therefore, may, I hope, give some Ingenious inquisitive Person an occasion of making some trials, which if successfull, I have my aim, and I suppose he will have no occasion to be displeas'd.

Observ. V. Of watered Silks, or Stuffs.

There are but few Artificial things that are worth observing with a Microscope, and therefore I shall speak but briefly concerning them. For the Productions of art are such rude mis-shapen things, that when view'd with a Microscope, is little else observable, but their deformity. The most curious Carvings appearing no better then those rude Russian Images we find mention'd in Purchas, where three notches at the end of a Stick, stood for a face. And the most smooth and burnish'd surfaces appear most rough and unpolisht: So that my first Reason why I shall add but a few observations of them, is, their mis-shapen form; and the next, is their uselessness. For why should we trouble our selves in the examination of that form or shape (which is all we are able to reach with a Microscope) which we know was design'd for no higher a use, then what we were able to view with our naked eye? Why should we endeavour to discover mysteries in that which has no such thing in it? And like Rabbins find out Caballisms, and ænigmâs in the Figure, and placing of Letters, where no such thing lies hid: whereas in natural forms there are some so small, and so curious, and their design'd business so far remov'd beyond the reach of our sight, that the more we magnify the object, the more excellencies and mysteries do appear; And the more we discover the imperfections of our senses; and the Omnipotency and Infinite perfections of the great Creatour. I shall therefore onely add one or two Observations more artificial things, and then come to the Treaty concerning such matters as are the Productions of a more curious Workman. One of these, shall be that of a piece of water'd Silk, Schem. 3.
Fig. 2. represented in the second Figure of the third Scheme, as it appear'd through the least magnifying Glass. AB signifying the long way of the Stuff, and CD the broad way. This Stuff, if the right side of it be looked upon, appears to the naked eye, all over so waved, undulated, or grain'd, with a curious, though irregular variety of brighter and darker parts, that it adds no small gracefulness to the Gloss of it. It is so known a propriety, that it needs but little explication, but it is observable, which perhaps everyone has not considered, that those parts which appear the darker part of the wave, in one position to the light, in another appears the lighter, and the contrary; and by this means the undulations become transient, and in a continual change, according as the position of the parts in respect of the incident beams of light is varied. The reason of which odd phænomena, to one that has but diligently examin'd it even with his naked eye, will be obvious enough. But he that observes it with a Microscope, may more easily perceive what this Proteus is, and how it comes to change its shape. He may very easily perceive, that it proceeds onely from the variety of the Reflections of light, which is caus'd by the various shape of the Particles, or little protuberant parts of the thread that compose the surface; and that those parts of the waves that appear the brighter, throw towards the eye a multitude of small reflections of light, whereas the darker scarce afford any. The reason of which reflection, the Microscope plainly discovers, as appears by the Figure. In which you may perceive, that the brighter parts of the surface consist of an abundance of large and strong reflections, denoted by a, a, a, a, a, &c. for the surfaces of those threads that run the long way, are by the Mechanical process of watering, creas'd or angled in another kind of posture then they were by the weaving: for by the weaving they are onely bent round the warping threads; but by the watering, they are bent with an angle, or elbow, that is in stead of lying, or being bent round the threads, as in the third Figure, a, a, a, a, a, are about b, b, b (b, b, b representing the ends, as 'twere, of the cross threads, they are bent about) they are creas'd on the top of those threads, with an angle, as in the fourth Figure, and that with all imaginable variety; so that, whereas before they reflected the light onely from one point of the round surface, as about c, c, c, they now when water'd, reflect the beams from more then half the whole surface, as de, de, de, and in other postures they return no reflections at all from those surfaces. Hence in one posture they compose the brighter parts of the waves, in another the darker. And these reflections are also varied, according as the particular parts are variously bent. The reason of which creasing we shall next examine; and here we must fetch our information from the Mechanism or manner of proceeding in this operation; which, as I have been inform'd, is no other then this.

They double all the Stuff that is to be water'd, that is, they crease it just through the middle of it, the whole length of the piece, leaving the right side of the Stuff inward, and placing the two edges, or silvages just upon one another, and, as near as they can, place the wale so in the doubling of it, that the wale of the one side may lie very near parallel, or even with the wale of the other; for the nearer that posture they lie, the greater will the watering appear; and the more obliquely, or across to each other they lie, the smaller are the waves. Their way for folding it for a great wale is thus: they take a Pin, and begin at one side of the piece in any wale, and so moving it towards the other side, thereby direct their hands to the opposite ends of the wale, and then, as near as they can, place the two opposite ends of the same wale together, and so double, or fold the whole piece, repeating this enquiry with a Pin at every yard or two's distance through the whole length; then they sprinkle it with water, and fold it the longways, placing between every fold a piece of Pastboard, by which means all the wrong side of the water'd Stuff becomes flat, and with little wales, and the wales on the other side become the more protuberant; whence the creasings or angular bendings of the wales become the more perspicuous. Having folded it in this manner, they place it with an interjacent Pastboard into an hot Press, where it is kept very violently prest, till it be dry and stiff; by which means, the wales of either contiguous sides leave their own impressions upon each other, as is very manifest by the second Figure, where 'tis obvious enough, that the wale of the piece ABCD runs parallel between the pricked lines ef, ef, ef, and as manifest to discern the impressions upon these wales, left by those that were prest upon them, which lying not exactly parallel with them, but a little athwart them, as is denoted by the lines of, oooo, gh, gh, gh, between which the other wales did lie parallel; they are so variously, and irregularly creas'd that being put into that shape when wet, and kept so till they be drie, they so let each others threads, that the Moldings remain almost as long as the Stuff lasts.

Hence it may appear to any one that attentively considers the Figure, why the parts of the wale a, a, a, a, a, a, should appear bright; and why the parts b, b, b, b, b, b, b, should appear shadowed, or dark; why some, as d, d, d, d, d, d, should appear partly light, and partly dark: the varieties of which reflections and shadows are the only cause of the appearance of watering in Silks, or any other kind of Stuffs.

From the variety of reflection, may also be deduc'd the cause why a small breez or gale of wind ruffling the surface of a smooth water, makes it appear black; as also, on the other side, why the smoothing or burnishing the surface of whitened Silver makes it look black; and multitudes of other phænomena might hereby be solv'd, which are too many to be here insisted on.

Observ. VI. Of Small Glass Canes.

That I might be satisfied, whether it were not possible to make an Artificial pore as small as any Natural I had yet found, I made several attemps with small glass pipes, melted in the flame of a Lamp, and then very suddenly drawn out into a great length. And, by that means, without much difficulty, I was able to draw some almost as small as a Cobweb, which yet, with the Schem. 4. Microscope, I could plainly perceive to be perforated, both by looking on the ends of it, and by looking on it against the light which was much the easier way to determine whether it were solid or perforated; for, taking a small pipe of glass, and closing one end of it, then filling it half full of water, and holding it against the light, I could, by this means, very easily find what was the differing aspect of a solid and a perforated piece of glass; and so easily distingish, without seeing either end, whether any Cylinder of glass I look'd on, were a solid stick, or a hollow cane. And by this means, I could also presently judge of any small filament of glass, whether it were hollow or not, which would have been exceeding tedious to examine by looking on the end. And many such like ways I was fain to make use of, in the examining of divers other particulars related in this Book, which would have been no easie task to have determined meerly by the more common way of looking on, or viewing the Object. For, if we consider first, the very faint light wherewith the object is enlightened, whence many particles appear opacous, which when more enlightned, appear very transparent, so that I was fain to determine its transparency by one glass, and its texture by another. Next, the unmanageableness of most Objects, by reason of their smalness, 3. The difficulty of finding the desired point, and of placing it so, as to reflect the light conveniently for the Inquiry. Lastly, ones being able to view it but with one eye at once, they will appear no small obstructions, nor are they easily remov'd without many contrivances. But to proceed, I could not find that water, or some deeply ting'd liquors would in small ones rise so high as one would expect; and the highest I have found it yet rise in any of the pipes I have try'd, was to 21 inches above the level of the water in the vessel: for though I found that in the small pipes it would nimbly enter at first, and run about 6 or 7 inches upwards; yet I found it then to move upwards so slow, that I have not yet had the patience to observe it above that height of 21 inches (and that was in a pretty large Pipe, in comparison of those I formerly mentioned; for I could observe the progress of a very deep ting'd liquor in it with my naked eye, without much trouble; whereas many of the other pipes were so very small, that unless in a convenient posture to the light, I could not perceive them:) But 'tis very probable, that a greater patience and assiduity may discover the liquors to rise, at least to remain suspended, at heights that I should be loath now even to ghess at, if at least there be any proportion kept between the height of the ascending liquor, and the bigness of the holes of the pipes.

My Conjecture, That the unequal height of the surfaces of the water, proceeded from the greater pressure made upon the water by the Air Schem. 4.
Fig. 1. without the Pipes ABC, then by that within them I shall endeavour to confirm from the truth of the two following Propositions:

The first of which is, That an unequal pressure of the incumbent Air, will cause an unequal height in the water's Surfaces.

That the first is true, the following Experiment will evince. For if you take any Vessel so contrived, as that you can at pleasure either increase or diminish the pressure of the Air upon this or that part of the Superficies of the water, the equality of the height of those parts will presently be lost; and that part of the Superficies that sustains the greater pressure, will be inferior to that which undergoes the less. A fit Vessel for this purpose, will be an inverted Glass Syphon, such an one as is described in the Sixth Figure. For if into it you put Water enough to fill it as high as AB, and gently blow in at D, you shall depress the Superficies B, and thereby raise the opposite Superficies A to a considerable height, and by gently sucking you may produce clean contrary effects.

Next, That there is such an unequal pressure, I shall prove from this, That there is a much greater incongruity of Air to Glass, and some other Bodies, then there is of Water to the same.

By Congruity, I mean a property of a fluid Body, whereby any part of it is readily united with any other part, either of itself, or of any other Similar, fluid, or solid body: And by Incongruity a property of a fluid, by which it is hindred from uniting with any dissimilar, fluid, or solid Body.

This last property, any one that hath been observingly conversant about fluid Bodies, cannot be ignorant of. For (not now to mention several Chymical Spirits and Oyls, which will very hardly, if at all, be brought to mix with one another; insomuch that there may be found some 8 or 9, or more, several distinct Liquors, which swimming one upon another, will not presently mix) we need seek no further for Examples of this kind in fluids, then to observe the drops of rain falling through the air and the bubbles of air which are by any means conveyed under the surface of the water; or a drop of common Sallet Oyl swimming upon water. In all which, and many more examples of this kind that might be enumerated, the incongruity of two fluids is easily discernable. And as for the Congruity or Incongruity of Liquids, with several kinds of firm Bodies, they have long since been taken notice of, and called by the Names of Driness and Moisture (though these two names are not comprehensive enough, being commonly used to signifie only the adhering or not adhering of water to some other solid Bodies) of this kind we may observe that water will more readily wet some woods then others; and that water, let fall upon a Feather, the whiter side of a Colwort, and some other leaves, or upon almost any dusty, unctuous, or resinous superficies, will not at all adhere to them, but easily tumble off from them, like a solid Bowl; whereas, if dropt upon Linnen, Paper, Clay, green Wood, &c. it will not be taken off, without leaving some part of it behind adhering to them. So Quick-silver, which will very hardly be brought to stick to any vegetable body, will readily adhere to, and mingle with, several clean metalline bodies.

And that we may the better finde what the cause of Congruity and Incongruity in bodies is, it will be requisite to consider, First, what is the cause of fluidness; And this, I conceive, to be nothing else but a certain pulse or shake of heat; for Heat being nothing else but a very brisk and vehement agitation of the parts of a body (as I have elswhere made probable) the parts of a body are thereby made so loose from one another, that they easily move any way, and become fluid. That I may explain this a little by a gross Similitude, let us suppose a dish of sand set upon some body that is very much agitated, and shaken with some quick and strong vibrating motion, as on a Milstone turn'd round upon the under stone very violently whilst it is empty; or on a very stiff Drum-head, which is vehemently or very nimbly beaten with the Drumsticks. By this means, the sand in the dish, which before lay like a dull and unactive body, becomes a perfect fluid; and ye can no sooner make a hole in it with your finger, but it is immediately filled up again, and the upper surface of it levell'd. Nor can you bury a light body, as a piece of Cork under it, but it presently emerges or swims as 'twere on the top; nor can you lay a heavier on the top of it, as a piece of Lead, but it is immediately buried in Sand, and (as 'twere) sinks to the bottom. Nor can you make a hole in the side of the Dish, but the sand shall run out of it to a level, not an obvious property of a fluid body, as such, but this dos imitate; and all this meerly caused by the vehement agitation of the conteining vessel; for by this means, each sand becomes to have a vibrative or dancing motion, so as no other heavier body can rest on it, unless sustein'd by some other on either side: Nor will it suffer any Body to be beneath it, unless it be a heavier then it self. Another Instance of the strange loosening nature of a violent jarring Motion, or a strong and nimble vibrative one, we may have from a piece of iron grated on very strongly with a file: for if into that a pin screw'd so firm and hard, that though it has a convenient head to it, yet it can by no means be unscrew'd by the fingers; if, I say, you attempt to unscrew this whilst grated on by the file, it will be found to undoe and turn very easily. The first of these Examples manifests, how a body actually divided into small parts, becomes a fluid. And the latter manifests by what means the agitation of heat so easily loosens and unties the parts of solid and firm bodies. Nor need we suppose heat to be any thing else, besides such a motion; for supposing we could Mechanically produce such a one quick and strong enough, we need not spend fuel to melt a body. Now, that I do not speak this altogether groundless, I must refer the Reader to the Observations I have made upon the shining sparks of Steel, for there he shall find that the same effects are produced upon small chips or parcels of Steel by the flame, and by a quick and violent motion; and if the body of steel may be thus melted (as I there shew it may) I think we have little reason to doubt that almost any other may not also. Every Smith can inform one how quickly both his File and the Iron grows hot with filing, and if you rub almost any two hard bodies together, they will do the same: And we know, that a sufficient degree of heat causes fluidity, in some bodies much sooner, and in others later; that is, the parts of the body of some are so loose from one another, and so unapt to cohere, and so minute and little, that a very small degree of agitation keeps them always in the state of fluidity. Of this kind, I suppose, the Æther, that is the medium or fluid body, in which all other bodies do as it were swim and move; and particularly, the Air, which seems nothing else but a kind of tincture or solution of terrestrial and aqueous particles dissolv'd into it, and agitated by it, just as the tincture of Cocheneel is nothing but some finer dissoluble parts of that Concrete lick'd up or dissolv'd by the fluid water. And from this Notion of it, we may easily give a more Intelligible reason how the Air becomes so capable of Rarefaction and Condensation. For, as in tinctures, one grain of some strongly tinging substance may sensibly colour some hundred thousand grains of appropriated Liquors, so as every drop of it has its proportionate share, and be sensibly ting'd, as I have try'd both with Logwood and Cocheneel: And as some few grains of Salt is able to infect as great a quantity, as may be found by præcipitations, though not so easily by the sight or taste; so the Air, which seems to be but as 'twere a tincture or saline substance, dissolv'd and agitated by the fluid and agil Æther, may disperse and expand it self into a vast space, if it have room enough, and infect, as it were, every part of that space. But, as on the other side, if there be but some few grains of the liquor, it may extract all the colour of the tinging substance, and may dissolve all the Salt, and thereby become much more impregnated with those substances, so may all the air that sufficed in a rarfy'd state to fill some hundred thousand spaces of Æther, be compris'd in only one, but in a position proportionable dense. And though we have not yet found out such strainers for Tinctures and Salts as we have for the Air, being yet unable to separate them from their dissolving liquors by any kind of filtre, without præcipitation, as we are able to separate the Air from the Æther by Glass, and several other bodies. And though we are yet unable and ignorant of the ways of præcipitating Air out of the Æther as we can Tinctures, and Salts out of several dissolvents; yet neither of these seeming impossible from the nature of the things, nor so improbable but that some happy future industry may find out ways to effect them; nay, further, since we find that Nature does really perform (though by what means we are not certain) both these actions, namely, by præcipitating the Air in Rain and Dews, and by supplying the Streams and Rivers of the World with fresh water, strain'd through secret subterraneous Caverns: And since, that in very many other proprieties they do so exactly seem of the same nature; till further observations or tryals do inform us of the contrary, we may safely enough conclude them of the same kind. For it seldom happens that any two natures have so many properties coincident or the same, as I have observ'd Solutions and Air to have, and to be different in the rest. And therefore I think it neither impossible, irrational, nay nor difficult to be able to predict what is likely to happen in other particulars also, besides those which Observation or Experiment have declared thus or thus; especially, if the circumstances that do often very much conduce to the variation of the effects be duly weigh'd and consider'd. And indeed, were there not a probability of this, our inquiries would be endless, our tryals vain, and our greatest inventions would be nothing but the meer products of chance, and not of Reason; and, like Mariners in an Ocean, destitute both of a Compass and the sight of the Celestial guids, we might indeed, by chance, Steer directly towards our desired Port, but 'tis a thousand to one but we miss our aim. But to proceed, we may hence also give a plain reason, how the Air comes to be darkned by clouds, &c. which are nothing but a kind of precipitation, and how those precipitations fall down in Showrs. Hence also could I very easily, and I think truly, deduce the cause of the curious sixangular figures of Snow, and the appearances of Haloes, &c. and the sudden thickning of the Sky with Clouds, and the vanishing and disappearing of those Clouds again; for all these things may be very easily imitated in a glass of liquor, with some slight Chymical preparations as I have often try'd, and may somewhere else more largely relate, but have not now time to set them down. But to proceed, there are other bodies that consist of particles more Gross, and of a more apt figure for cohesion, and this requires somewhat greater agitation; such, I suppose

, fermented vinous Spirits, several Chymical Oils, which are much of kin to those Spirits, &c. Others yet require a greater, as water, and so others much greater, for almost infinite degrees: For, I suppose there are very few bodies in the world that may not be made aliquatenus fluid, by some or other degree of agitation or heat.

Having therefore in short set down my Notion of a Fluid body, I come in the next place to consider what Congruity is; and this, as I said before, being a Relative property of a fluid, whereby it may be said to be like or unlike to this or that other body, whereby it does or does not mix with this or that body. We will again have recourse to our former Experiment, though but a rude one; and here if we mix in the dish several kinds of sands, some of bigger, others of less and finer bulks, we shall find that by the agitation the fine sand will eject and throw out of it self all those bigger bulks of small stones and the like, and those will be gathered together all into one place; and if there be other bodies in it of other natures, those also will be separated into a place by themselves, and united or tumbled up together. And though this do not come up to the highest property of Congruity, which is a Cohæsion of the parts of the fluid together, or a kind of attraction and tenacity, yet this does as 'twere shadow it out, and somewhat resemble it; for just after the same manner, I suppose the pulse of heat to agitate the small parcels of matter, and those that are of a like bigness, and figure, and matter, will hold, or dance together, and those which are of a differing kind will be thrust or shov'd out from between them; for particles that are similar, will, like so many equal musical strings equally stretcht, vibrate together in a kind of Harmony or unison; whereas others that are dissimilar, upon what account soever, unless the disproportion be otherwise counter-ballanc'd, will, like so many strings out of tune to those unisons, though they have the same agitating pulse, yet make quite differing kinds of vibrations and repercussions, so that though they may be both mov'd, yet are their vibrations so different, and so untun'd, as 'twere to each other, that they cross and jar against each other, and consequently, cannot agree together, but fly back from each other to their similar particles. Now, to give you an instance how the disproportion of some bodies in one respect, may be counter-ballanc'd by a contrary disproportion of the same body in another respect, whence we find that the subtil vinous spirit is congruous, or does readily mix with water, which in many properties is of a very differing nature, we may consider that a unison may be made either by two strings of the same bigness, length, and tension, or by two strings of the same bigness, but of differing length, and a contrary differing tension, or 3ly. by two strings of unequal length and bigness, and of a differing tension, or of equal length, and differing bigness and tension, and several other such varieties. To which three properties in strings, will correspond three proprieties also in sand, or the particles of bodies, their Matter or Substance, their Figure or Shape, and their Body or Bulk. And from the varieties of these three, may arise infinite varieties in fluid bodies, though all agitated by the same pulse or vibrative motion. And there may be as many ways of making Harmonies and Discords with these, as there may be with musical strings. Having therefore seen what is the cause of Congruity or Incongruity, those relative properties of fluids, we may, from what has been said, very easily collect, what is the reason of those Relative proprieties also between fluid bodies and solid; for since all bodies consist of particles of such a Substance, Figure, and Bulk; but in some they are united together more firmly then to be loosened from each other by every vibrative motion (though I imagine that there is no body in the world, but that some degree of agitation may, as I hinted before, agitate and loosen the particles so as to make them fluid) those cohering particles may vibrate in the same manner almost as those that are loose and become unisons or discords, as I may so speak, to them. Now that the parts of all bodies, though never so solid, do yet vibrate, I think we need go no further for proof, then that all bodies have some degrees of heat in them, and that there has not been yet found any thing perfectly cold: Nor can I believe indeed that there is any such thing in Nature, as a body whose particles are at rest, or lazy and unactive in the great Theatre of the World, it being quite contrary to the grand Oeconomy of the Universe. We see therefore what is the reason of the sympathy or uniting of some bodies together, and of the antipathy or flight of others from each other: For Congruity seems nothing else but a Sympathy, and Incongruity an Antipathy of bodies, hence similar bodies once united will not easily part, and dissimilar bodies once disjoyn'd will not easily unite again; from hence may be very easily deduc'd the reason of the suspension of water and Quick-silver above their usual station, as I shall more at large anon shew.

These properties therefore (alwayes the concomitants of fluid bodies) produce these following visible Effects:

First, They unite the parts of a fluid to its similar Solid, or keep them separate from its dissimilar. Hence Quick-silver will (as we noted before) stick to Gold, Silver, Tin, Lead, &c. and unite with them: but roul off from Wood, Stone, Glass, &c. if never so little scituated out of its horizontal level; and water that will wet salt and dissolve it, will slip off from Tallow, or the like, without at all adhering; as it may likewise be observed to do upon a dusty superficies. And next they cause the parts of homogeneal fluid bodies readily to adhere together and mix, and of heterogeneal, to be exceeding averse thereunto. Hence we find, that two small drops of water, on any superficies they can roul on, will, if they chance to touch each other, readily unite and mix into one 3^d drop: The like may be observed with two small Bowls of Quick-silver upon a Table or Glass, provided their surfaces be not dusty; and with two drops of Oyl upon fair water, &c. And further, water put unto wine, salt water, vinegar, spirit of wine, or the like, does immediately (especially if they be shaken together) disperse it self all over them. Hence, on the contrary, we also find, that Oyl of Tartar poured upon Quick-silver, and Spirit of Wine on that Oyl, and Oyl of Turpentine on that Spirit, and Air upon that Oyl, though they be stopt closely up into a Bottle, and shaken never so much, they will by no means long suffer any of their bigger parts to be united or included within any of the other Liquors (by which recited Liquors, may be plainly enough represented the four Peripatetical Elements, and the more subtil Æther above all.) From this property 'tis, that a drop of water does not mingle with, or vanish into Air, but is driven (by that Fluid equally protruding it on every side) and forc't into as little a space as it can possibly be contained in, namely, into a Round Globule. So likewise a little Air blown under the water, is united or thrust into a Bubble by the ambient water. And a parcel of Quick-silver enclosed with Air, Water, or almost any other Liquor, is formed into a round Ball.

Now the cause why all these included Fluids, newly mentioned, or as many others as are wholly included within a heterogeneous fluid, are not exactly of a Spherical Figure (seeing that if caused by these Principles only, it could be of no other) must proceed from some other kind of pressure against the two opposite flatted sides. This adventitious or accidental pressure may proceed from divers causes, and accordingly must diversifie the Figure of the included heterogeneous fluid: For seeing that a body may be included either with a fluid only, or only with a solid, or partly with a fluid, and partly with a solid, or partly with one fluid, and partly with another; there will be found a very great variety of the terminating surfaces, much differing from a Spherical, according to the various resistance or pressure that belongs to each of these encompassing bodies.

Which Properties may in general be deduced from two heads, viz. Motion, and Rest. For, either this Globular Figure is altered by a natural Motion, such as is Gravity, or a violent, such as is any accidental motion of the fluids, as we see in the wind ruffling up the water, and the purlings of Streams, and foaming of Catarracts, and the like. Or thirdly, By the Rest, Firmness and Stability of the ambient Solid. For if the including Solid be of an angular or any other irregular Form, the included fluid will be near of the like, as a Pint-Pot full of water, or a Bladder full of Air. And next, if the including or included fluid have a greater gravity one than another, then will the globular Form be deprest into an Elliptico-spherical: As if, for example, we suppose the Circle ABCD, in the fourth Figure, to represent a drop of water, Quick-silver, or the like, included with the Air or the like, which supposing there were no gravity at all in either of the fluids, or that the contained and containing were of the same weight, would be equally comprest into an exactly spherical body (the ambient fluid forcing equally against every side of it.) But supposing either a greater gravity in the included, by reason whereof the parts of it being prest from A towards B, and thereby the whole put into motion, and that motion being hindred by the resistance of the subjacent parts of the ambient, the globular Figure ADBC will be deprest into the Elliptico-spherical, EGFH. For the side A is detruded to E by the Gravity, and B to F by the resistance of the subjacent medium: and therefore C must necessarily be thrust to G; and D to H. Or else, supposing a greater gravity in the ambient, by whose more then ordinary pressure against the under side of the included globule; B will be forced to F, and by its resistance of the motion upwards, the side A will be deprest to E, and therefore C being thrust to G and D to H; the globular Figure by this means also will be made an Elliptico-spherical. Next if a fluid be included partly with one, and partly with another fluid, it will be found to be shaped diversly, according to the proportion of the gravity and incongruity of the 3 fluids one to another: As in the second Figure, let the upper MMM be Air, the middle LMNO be common Oyl, the lower OOO be Water, the Oyl will be form'd, not into a spherical Figure, such as is represented by the pricked Line, but into such a Figure as LMNO, whose side LMN will be of a flatter Elliptical Figure, by reason of the great disproportion between the Gravity of Oyl and Air, and the side LOM of a rounder, because of the smaller difference between the weight of Oyl and Water. Lastly, The globular Figure will be changed, if the ambient be partly fluid and partly solid. And here the termination of the incompassed fluid towards the incompassing is shap'd according to the proportion of the congruity or incongruity of the fluids to the solids, and of the gravity and incongruity of the fluids one to another. As suppose the subjacent medium that hinders an included fluids descent, be a solid, as let KI, in the fourth Figure, represent the smooth superficies of a Table; EGFH, a parcel of running Mercury; the side GFH will be more flatted, according to the proportion of the incongruity of the Mercury and Air to the Wood, and of the gravity of Mercury and Air one to another; The side GEH will likewise be a little more deprest by reason the subjacent parts are now at rest, which were before in motion.

Or further in the third figure, let AILD represent an including solid medium of a cylindrical shape (as suppose a small Glass Jar) Let FGEMM represent a contain'd fluid, as water; this towards the bottom and sides, is figured according to the concavity of the Glass: But its upper Surface, (which by reason of its gravity, (not considering at all the Air above it, and so neither the congruity or incongruity of either of them to the Glass) should be terminated by part of a Sphere whose diameter should be the same with that of the earth, which to our sense would appear a straight Line, as FGE, Or which by reason of its having a greater congruity to Glass than Air has, (not considering its Gravity) would be thrust into a concave Sphere, as CHB, whose diameter would be the same with that of the concavity of the Vessel:) Its upper Surface, I say, by reason of its having a greater gravity then the Air, and having likewise a greater congruity to Glass then the Air has, is terminated, by a concave Elliptico-spherical Figure, as CKB. For by its congruity it easily conforms it self, and adheres to the Glass, and constitutes as it were one containing body with it, and therefore should thrust the contained Air on that side it touches it, into a spherical Figure, as BHC, but the motion of Gravity depressing a little the Corners B and C, reduces it into the aforesaid Figure CKB. Now that it is the greater congruity of one of the two contiguous fluids, then of the other, to the containing solid, that causes the separating surfaces to be thus or thus figured: And that it is not because this or that figurated surface is more proper, natural, or peculiar to one of these fluid bodies, then to the other, will appear from this; that the same fluids will by being put into differing solids, change their surfaces. For the same water, which in a Glass or wooden Vessel will have a concave surface upwards, and will rise higher in a smaller then a greater Pipe, the same water, I say, in the same Pipes greased over or oyled, will produce quite contrary effects; for it will have a protuberant and convex surface upwards, and will not rise so high in small, as in bigger Pipes: Nay, in the very same solid Vessel, you may make the very same two contiguous Liquids to alter their Surfaces; for taking a small Wine-glass, or such like Vessel, and pouring water gently into it, you shall perceive the surface of the water all the way concave, till it rise even with the top, when you shall find it (if you gently and carefully pour in more) to grow very protuberant and convex; the reason of which is plain, for that the solid sides of the containing body are no longer extended, to which the water does more readily adhere then the air; but it is henceforth to be included with air, which would reduce it into a hemisphere, but by reason of its gravity, it is flatted into an Oval. Quicksilver also which to Glass is more incongruous then Air (and thereby being put into a Glass-pipe, will not adhere to it, but by the more congruous air will be forced to have a very protuberant surface, and to rise higher in a greater then a lesser Pipe) this Quicksilver to clean Metal, especially to Gold, Silver, Tin, Lead, &c. Iron excepted, is more congruous then Air, and will not only stick to it, but have a concave Surface like water, and rise higher in a less, then in a greater Pipe.

In all these Examples it is evident, that there is an extraordinary and adventitious force, by which the globular Figure of the contained heterogeneous fluid is altered; neither can it be imagined, how it should otherwise be of any other Figure then Globular: For being by the heterogeneous fluid equally protruded every way, whatsoever part is protuberant, will be thereby deprest. From this cause it is, that in its effects it does very much resemble a round Spring (such as a Hoop.) For as in a round Spring there is required an additional pressure against two opposite sides, to reduce it into an Oval Form, or to force it in between the sides of a Hole, whose Diameter is less then that of the Spring, there must be a considerable force or protusion against the concave or inner side of the Spring; So to alter this spherical constitution of an included fluid body, there is required more pressure against opposite sides to reduce it into an Oval; and, to press it into an Hole less in Diameter then it self, it requires a greater protrusion against all the other sides, What degrees of force are requisite to reduce them into longer and longer Ovals, or to press them into less and less holes, I have not yet experimentally calculated; but thus much by experiment I find in general, that there is alwayes required a greater pressure to close them into longer Ovals, or protude them into smaller holes. The necessity and reason of this, were it requisite, I could easily explain: but being not so necessary, and requiring more room and time then I have for it at present, I shall here omit it; and proceed to shew, that this may be presently found true, if Experiment be made with a round Spring (the way of making which trials is obvious enough.) And with the fluid bodies of Mercury, Air, &c, the way of trying which, will be somewhat more difficult; and therefore I shall in brief describe it. He therefore that would try with Air, must first be provided of a Glass-pipe, made of the shape of that in the fifth Figure, whereof the side AB, represents a straight Tube of about three foot long, C, represents another part of it, which consists of a round Bubble; so ordered, that there is left a passage or hole at the top, into which may be fastened with cement several small Pipes of determinate cylindrical cavities: as let hollow of

There may be added as many more, as the Experimenter shall think fit, with holes continually decreasing by known quantities, so far as his senses are able to help him; I say, so far, because there may be made Pipes so small that it will be impossible to perceive the perforation with ones naked eye, though by the help of a Microscope, it may easily enough be perceived: Nay, I have made a Pipe perforated from end to end, so small, that with my naked eye I could very hardly see the body of it, insomuch that I have been able to knit it up into a knot without breaking: And more accurately examining one with my Microscope, I found it not so big as a sixteenth part of one of the smaller hairs of my head which was of the smaller and finer sort of hair, so that sixteen of these Pipes bound faggot-wise together, would but have equalized one single hair; how small therefore must its perforation be? It appearing to me through the Microscope to be a proportionably thick-sided Pipe.

To proceed then, for the trial of the Experiment, the Experimenter must place the Tube AB, perpendicular, and fill the Pipe F (cemented into the hole E) with water, but leave the bubble C full of Air, and then gently pouring in water into the Pipe AB, he must observe diligently how high the water will rise in it before it protrude the bubble of Air C, through the narrow passage of F, and denote exactly the height of the Cylinder of water, then cementing in a second Pipe as G, and filling it with water; he may proceed as with the former, denoting likewise the height of the Cylinder of water, able to protrude the bubble C through the passage of G, the like may he do with the next Pipe, and the next, &c. as far as he is able: then comparing the several heights of the Cylinders, with the several holes through which each Cylinder did force the air (having due regard to the Cylinders of water in the small Tubes) it will be very easie to determine, what force is requisite to press the Air into such and such a hole, or (to apply it to our present experiment) how much of the pressure of the Air is taken off by its ingress into smaller and smaller holes. From the application of which to the entring of the Air into the bigger hole of the Vessel, and into the smaller hole of the Pipe, we shall clearly find, that there is a greater pressure of the air upon the water in the Vessel or greater pipe, then there is upon that in the lesser pipe: For since the pressure of the air every way is found to be equal, that is, as much as is able to press up and sustain a Cylinder of Quicksilver of two foot and a half high, or thereabouts; And since of this pressure so many more degrees are required to force the Air into a smaller then into a greater hole that is full of a more congruous fluid. And lastly, since those degrees that are requisite to press it in, are thereby taken off from the Air within, and the Air within left with so many degrees of pressure less then the Air without; it will follow, that the Air in the less Tube or pipe, will have less pressure against the superficies of the water therein, then the Air in the bigger: which was the minor Proposition to be proved.

The Conclusion therefore will necessarily follow, viz. That this unequal pressure of the Air caused by its ingress into unequal holes, is a cause sufficient to produce this effect, without the help of any other concurrent; therefore is probably the principal (if not the only) cause of these Phænomena.

This therefore being thus explained, there will be divers Phænomena explicable thereby, as, the rising of Liquors in a Filtre, the rising of Spirit of Wine, Oyl, melted Tallow, &c. in the Week of a Lamp, (though made of small Wire, Threeds of Asbestus, Strings of Glass, or the like) the rising of Liquors in a Spunge, piece of Bread, Sand, &c. perhaps also the ascending of the Sap in Trees and Plants, through their small, and some of them imperceptible pores, (of which I have said more, on another occasion) at least the passing of it out of the earth into their roots. And indeed upon the consideration of this Principle, multitudes of other uses of it occurr'd to me, which I have not yet so well examined and digested as to propound for Axioms, but only as Queries and Conjectures which may serve as hints toward some further discoveries.

As first, Upon the consideration of the congruity and incongruity of Bodies, as to touch, I found also the like congruity and incongruity (if I may so speak) as to the Transmitting of the Rates of Light: For as in this regard, water (not now to mention other Liquors) seems nearer of affinity to Glass then Air, and Air then Quicksilver: whence an oblique Ray out of Glass, will pass into water with very little refraction from the perpendicular, but none out of Glass into Air, excepting a direct, will pass without a very great refraction from the perpendicular, nay any oblique Ray under thirty degrees, will not be admitted into the Air at all. And Quicksilver will neither admit oblique or direct, but reflects all; seeming, as to the transmitting of the Raies of Light, to be of a quite differing constitution, from that of Air, Water, Glass, &c. and to resemble most those opacous and strong reflecting bodies of Metals: So also as to the property of cohesion or congruity, Water seems to keep the same order, being more congruous to Glass then Air, and Air then Quicksilver.

A Second thing (which was hinted to me, by the consideration of the included fluids globular form, caused by the protrusion of the ambient heterogeneous fluid) was, whether the Phænomena of gravity might not by this means be explained, by supposing the Globe of Earth, Water, and Air to be included with a fluid, heterogeneous to all and each of them, so subtil, as not only to be every where interspersed through the Air, (or rather the air through it) but to pervade the bodies of Glass, and even the closest Metals, by which means it may endeavour to detrude all earthly bodies as far from it as it can; and partly thereby, and partly by other of its properties may move them towards the Center of the Earth. Now that there is some such fluid, I could produce many Experiments and Reasons, that do seem to prove it: But because it would ask some time and room to set them down and explain them, and to consider and answer all the Objections (many whereof I foresee) that may be alledged against it; I shall at present proceed to other Queries, contenting my self to have here only given a hint of what I may say more elswhere.

A Third Query then was, Whether the heterogeneity of the ambient fluid may not be accounted a secondary cause of the roundness or globular form of the greater bodies of the world, such as are those of the Sun, Stars, and Planets, the substance of each of which seems altogether heterogeneous to the circum-ambient fluid æther? And of this I shall say more in the Observation of the Moon.

A Fourth was, Whether the globular form of the smaller parcels of matter here upon the Earth, as that of Fruits, Pebbles, or Flints, &c. (which seem to have been a Liquor at first) may not be caused by the heterogeneous ambient fluid. For thus we see that melted Glass will be naturally formed into a round Figure; so likewise any small Parcel of any fusible body, if it be perfectly enclosed by the Air, will be driven into a globular Form; and, when cold, will be found a solid Ball. This is plainly enough manifested to us by their way of making shot with the drops of Lead; which being a very pretty curiosity, and known but to a very few, and having the liberty of publishing it granted me, by that Eminent Virtuoso Sir Robert Moray, who brought in this Account of it to the Royal Society, I have here transcribed and inserted.

To make small shot of different sizes; Communicated by his Highness P.R.

Take Lead out of the Pig what quantity you please, melt it down, stir and clear it with an iron Ladle, gathering together the blackish parts that swim at top like scum, and when you see the colour of the clear Lead to be greenish, but no sooner, strew upon it Auripigmentum powdered according to the quantity of Lead, about as much as will lye upon a half Crown piece will serve for eighteen or twenty pound weight of some sorts of Lead; others will require more, or less. After the Auripigmentum is put in, stir the Lead well, and the Auripigmentum will flame: when the flame is over, take out some of the Lead in a Ladle having a lip or notch in the brim for convenient pouring out of the Lead, and being well warmed amongst the melted Lead, and with a stick make some single drops of Lead trickle out of the Ladle into water in a Glass, which if they fall to be round and without tails, there is Auripigmentum enough put in, and the temper of the heat is right, otherwise put in more. Then lay two bars of Iron (or some more proper Iron-tool made on purpose) upon a Pail of water, and place upon them a round Plate of Copper, of the size and figure of an ordinary large Pewter or Silver Trencher, the hollow whereof is to be about three inches over, the bottom lower then the brims about half an inch, pierced with thirty, forty, or more small holes; the smaller the holes are, the smaller the shot will be; and the brim is to be thicker then the bottom, to conserve the heat the better.

The bottom of the Trencher being some four inches distant from the water in the Pail, lay upon it some burning Coles, to keep the Lead melted upon it. Then with the hot Ladle take Lead off the Pot where it stands melted, and pour it softly upon the burning Coles over the bottom of the Trencher, and it will immediately run through the holes into the water in small round drops. Thus pour on new Lead still as fast as it runs through the Trencher till all be done; blowing now and then the Coles with hand-Bellows, when the Lead in the Trencher cools so as to stop from running.

While one pours on the Lead, another must, with another Ladle, thrusted four or five inches under water in the Pail, catch from time to time some of the shot, as it drops down, to see the size of it, and whether there be any faults in it. The greatest care is to keep the Lead upon the Trencher in the right degree of heat; if it be too cool, it will not run through the Trencher, though it stand melted upon it; and this is to be helped by blowing the Coals a little, or pouring on new Lead that is hotter: but the cooler the Lead, the larger the Shot; and the hotter, the smaller; when it it too hot, the drops will crack and fly; then you must stop pouring on new Lead, and let it cool; and so long as you observe the right temper of the heat, the Lead will constantly drop into very round Shot, without so much as one with a tail in many pounds.

When all is done, take your Shot out of the Pail of water, and put it in a Frying-pan over the fire to dry them, which must be done warily, still shaking them that they melt not; and when they are dry you may separate the small from the great, in Pearl Sives made of Copper or Lattin let into one another, into as many sizes at you please. But if you would have your Shot larger then the Trencher makes them, you may do it with a Stick, making them trickle out of the Ladle, as hath been said.

If the Trencher be but toucht a very little when the Lead stops from going through it, and be not too cool, it will drop again, but it it better not to touch it at all. At the melting of the Lead take care that there be no kind of Oyl, Grease, or the like, upon the Pots, or Ladles, or Trencher.

The Chief cause of this Globular Figure of the Shot, seems to be the Auripigmentum; for, as soon as it is put in among the melted Lead, it loses its shining brightness, contracting instantly a grayish film or skin upon it, when you scum it to make it clean with the Ladle. So that when the Air comes at the falling drop of the melted Lead, that skin constricts them every where equally: but upon what account, and whether this be the true cause, is left to further disquisition.

Much after this same manner, when the Air is exceeding cold through which it passes; do we find the drops of Rain, falling from the Clouds, congealed into round Hail-stones by the freezing Ambient.

To which may be added this other known Experiment, That if you gently let fall a drop of water upon small sand or dust, you shall find, as it were, an artificial round stone quickly generated. I cannot upon this occasion omit the mentioning of the strange kind of Grain, which I have observed in a stone brought from Kettering in Northamptonshire, and therefore called by Masons Kettering-Stone, of which see the Description. Which brings into my mind what I long since observed in the fiery Sparks that are struck out of a Steel. For having a great desire to see what was left behind, after the Spark was gone out, I purposely struck fire over a very white piece of Paper, and observing diligently where some conspicuous sparks went out, I found a very little black spot no bigger then the point of a Pin, which through a Microscope appeared to be a perfectly round Ball, looking much like a polisht ball of Steel, insomuch that I was able to see the Image of the window reflected from it. I cannot here stay (having done it more fully in another place) to examine the particular Reasons of it, but shall only hint, that I imagine it to be some small parcel of the Steel, which by the violence of the motion of the stroke (most of which seems to be imprest upon those small parcels) is made so glowing hot, that it is melted into a Vitrum, which by the ambient Air is thrust into the form of a Ball.

A Fifth thing which I thought worth Examination was, Whether the motion of all kind of Springs, might not be reduced to the Principle whereby the included heterogeneous fluid seems to be moved; or to that whereby two Solids, as Marbles, or the like, are thrust and kept together by the ambient fluid.

A Sixth thing was, Whether the Rising and Ebullition of the Water out of Springs and Fountains (which lie much higher from the Center of the Earth then the Superficies of the Sea, from whence it seems to be derived) may not be explicated by the rising of Water in a smaller Pipe: For the Sea-water being strained through the Pores or Crannies of the Earth, is, as it were, included in little Pipes, where the pressure of the Air has not so great a power to resist its rising: But examining this way, and finding in it several difficulties almost irremovable, I thought upon a way that would much more naturally and conceivably explain it, which was by this following Experiment: I took a Glass-Tube, of the form of that described in the sixth Figure, and chusing two heterogeneous fluids, such as Water and Oyl, I poured in as much Water as filled up the Pipes as high as AB, then putting in some Oyl into the Tube AC, I deprest the superficies A of the Water to F, and B I raised to G, which was not so high perpendicularly as the superficies of the Oyl F, by the space FI, wherefore the proportion of the gravity of these two Liquors was as GH to FE.

This Experiment I tried with several other Liquors, and particularly with fresh Water and Salt (which I made by dissolving Salt in warm Water) which two though they are nothing heterogeneous, yet before they would perfectly mix one with another, I made trial of the Experiment: Nay, letting the Tube wherein I tried the Experiment remain for many dayes, I observed them not to mix; but the superficies of the fresh was rather more then less elevated above that of the Salt. Now the proportion of the gravity of Sea-water, to that of River-water, according to Stevinus and Varenius, and as I have since found pretty true by making trial my self, is as 46. to 45. that is, 46. Ounces of the salt Water will take up no more room then 45. of the fresh. Or reciprocally 45 pints of salt-water weigh as much as 46 of fresh.

But I found the proportion of Brine to fresh Water to be near 13 to 12: Supposing therefore GHM to represent the Sea, and FI the height of the Mountain above the Superficies of the Sea, FM a Cavern in the Earth, beginning at the bottom of the Sea, and terminated at the top of the Mountain, LM the Sand at the bottom, through which the Water is as it were strained, so as that the fresher parts are only permitted to transude, and the saline kept back; if therefore the proportion of G M to FM be as 45 to 46, then may the Cylinder of Salt-water GM make the Cylinder of Fresh-water to rise as high as E, and to run over at N. I cannot here stand to examine or confute their Opinion, who make the depth of the Sea, below its Superficies, to be no more perpendicularly measured then the height of the Mountains above it: 'Tis enough for me to say, there is no one of those that have asserted it, have experimentally known the perpendicular of either; nor shall I here determine, whether there may not be many other causes of the separation of the fresh water from the salt, as perhaps some parts of the Earth through which it is to pass, may contain a Salt, that mixing and uniting with the Sea-salt, may precipitate it; much after the same manner as the Alkalizate and Acid Salts mix and precipitate each other in the preparation of Tartarum Vitriolatum. I know not also whether the exceeding cold (that must necessarily be) at the bottom of the Water, may not help towards this separation, for we find, that warm Water is able to dissolve and contain more Salt, then the same cold; insomuch that Brines strongly impregnated by heat, if let cool, do suffer much of their Salt to subside and crystallize about the bottom and sides. I know not also whether the exceeding pressure of the parts of the Water one against another, may not keep the Salt from descending to the very bottom, as finding little or no room to insert it self between those parts, protruded so violently together, or else squeeze it upwads into the superiour parts of the Sea, where it may more easily obtain room for it self, amongst the parts of the Water, by reason that there is more heat and less pressure. To this Opinion I was somewhat the more induced by the relations I have met with in Geographical Writers, of drawing fresh Water from the bottom of the Sea, which is salt above. I cannot now stand to examine, whether this natural perpetual motion may not artificially be imitated: Nor can I stand to answer the Objections which may be made against this my Supposition: As, First, How it comes to pass, that there are sometimes salt Springs much higher then the Superficies of the Water? And, Secondly, Why Springs do not run faster and slower, according to the varying height made of the Cylinder of Sea-water, by the ebbing and flowing of the Sea?

As to the First, In short, I say, the fresh Water may receive again a saline Tincture near the Superficies of the Earth, by passing through some salt Mines, or else many of the saline parts of the Sea may be kept back, though not all.

And as to the Second, The same Spring may be fed and supplyed by divers Caverns, coming from very far distant parts of the Sea, so as that it may in one place be high, in another low water; and so by that means the Spring may be equally supply'd at all times. Or else the Cavern may be so straight and narrow, that the water not having so ready and free passage through it, cannot upon so short and quick mutations of pressure, be able to produce any sensible effect at such a distance. Besides that, to confirm this hypothesis, there are many Examples found in Natural Historians, of Springs that do ebb and flow like the Sea: As particularly, those recorded by the Learned Camden, and after him by Speed, to be found in this Island: One of which, they relate to be on the Top of a Mountain, by the small Village Kilken in Flintshire, Maris æmulus qui statis temporibus suos evomit & resorbet Aquas; Which at certain times riseth and falleth after the manner of the Sea. A Second in Caermardenshire, near Caermarden, at a place called Cantred Bichan; Qui (ut scribit Giraldus) naturali die bis undis deficiens, & toties exuberans, marinas imitatur instabilitates; That twice in four and twenty hours ebbing and flowing; resembleth the unstable motions of the Sea. The Phænomena of which two may be easily made out, by supposing the Cavern, by which they are fed, to arise from the bottom of the next Sea. A Third, is a Well upon the River Ogmore in Glamorganshire, and near unto Newton, of which Camden relates himself to be certified, by a Letter from a Learned Friend of his that observed it, Fons abest hinc, &c. The Letter is a little too long to be inserted, but the substance is this; That this Well ebbs and flows quite contrary to the flowing and ebbing of the Sea in those parts: for 'tis almost empty at Full Sea, but full at Low water. This may happen from the Channel by which it is supplied, which may come from the bottom of a Sea very remote from those parts, and where the Tides are much differing from those of the approximate shores. A Fourth, lies in Westmorland, near the River Leder; Qui instar Euripi sæpius in die reciprocantibus undis fluit & refluit, which ebbs and flows many times a day. This may proceed from its being supplyed from many Channels, coming from several parts of the Sea, lying sufficiently distant asunder to have the times of High-water differing enough one from the other; so as that whensoever it shall be High water over any of those places, where these Channels begin, it shall likewise be so in the Well; but this is but a supposition.

A Seventh Query was, Whether the dissolution or mixing of several bodies, whether fluid or solid, with saline or other Liquors, might not partly be attributed to this Principle of the congruity of those bodies and their dissolvents? As of Salt in Water, Metals in several Menstruums, Unctuous Gums in Oyls, the mixing of Wine and Water, &c. And whether precipitation be not partly made from the same Principle of Incongruity? I say partly, because there are in some Dissolutions, some other Causes concurrent.

I shall lastly make a much more seemingly strange and unlikely Query; and that is, Whether this Principle, well examined and explained, may not be found a co-efficient in the most considerable Operations of Nature? As in those of Heat, and Light consequently of Rarefaction and Condensation, Hardness, and Fluidness, Perspicuity and Opacousness, Refractions and Colours. &c. Nay, I know not whether there may be many things done in Nature, in which this may not (be said to) have a Finger? This I have in some other passages of this Treatise further enquired into and shewn, that as well Light as Heat may be caused by corrosion, which is applicable to congruity, and consequently all the rest will be but subsequents: In the mean time I would not willingly be guilty of that Error, which the thrice Noble and Learned Verulam justly takes notice of, as such, and calls Philosophiæ Genus Empiricum, quod in paucorum Experimentorum Angustiis & Obscuritate fundatum est. For I neither conclude from one single Experiment, nor are the Experiments I make use of all made upon one Subject: Nor wrest I any Experiment to make it quadrare with any preconceiv'd Notion. But on the contrary, I endeavour to be conversant in divers kinds of Experiments, and all and every one of those Trials, I make the Standards or Touchstones, by which I try all my former Notions, whether they hold out in weight, and measure, and touch, &c. For as that Body is no other then a Counterfeit Gold, which wants any one of the Proprieties of Gold, (such as are the Malleableness, Weight, Colour, Fixtness in the Fire, Indissolubleness in Aqua fortis, and the like) though it has all the other; so will all those Notions be found to be false and deceitful, that will not undergo all the Trials and Tests made of them by Experiments. And therefore such as will not come up to the desired Apex of Perfection, I rather wholly reject and take new, then by piecing and patching, endeavour to retain the old, as knowing such things at best to be but lame and imperfect. And this course I learned from Nature; whom we find neglectful of the old Body, and suffering its Decaies and Infirmities to remain without repair, and altogether sollicitous and careful of perpetuating the Species by new Individuals. And it is certainly the most likely way to erect a glorious Structure and Temple to Nature, such as she will be found (by any zealous Votary) to reside in; to begin to build a new upon a sure Foundation of Experiments.

But to digress no further from the consideration of the Phænomena, more immediately explicable by this Experiment, we shall proceed to shew, That, as to the rising of Water in a Filtre, the reason of it will be manifest to him, that does take notice, that a Filtre is constituted of a great number of small long solid bodies, which lie so close together, that the Air in its getting in between them, doth lose of its pressure that it has against the Fluid without them, by which means the Water or Liquor not finding so strong a resistance between them as is able to counter-ballance the pressure on its superficies without, is raised upward, till it meet with a pressure of the Air which is able to hinder it. And as to the Rising of Oyl, melted Tallow, Spirit of Wine, &c. in the Week of a Candle or Lamp, it is evident, that it differs in nothing from the former, save only in this, that in a Filtre the Liquor descends and runs away by another part; and in the Week the Liquor is dispersed and carried away by the Flame; something there is ascribable to the Heat, for that it may rarifie the more volatil and spirituous parts of those combustible Liquors, and so being made lighter then the Air, it maybe protruded upwards by that more ponderous fluid body in the Form of Vapours; but this can be ascribed to the ascension of but a very little, and most likely of that only which ascends without the Week. As for the Rising of it in a Spunge, Bread, Cotton, &c. above the superficies of the subjacent Liquor, what has been said about the Filtre (if considered) will easily suggest a reason, considering that all these bodies abound with small holes or pores.

From this same Principle also (viz. the unequal pressure of the Air against the unequal superficies of the water) proceeds the cause of the accession or incursion of any floating body against the sides of the containing Vessel; or the appropinquation of two floating bodies, as Bubbles, Corks, Sticks, Straws, &c. one towards another. As for instance, Take a Glass-jar, such as AB in the seventh Figure, and filling it pretty near the top with water, throw into it a small round piece of Cork, as C, and plunge it all over in water, that it be wet, so as that the water may rise up by the sides of it, then placing it any where upon the superficies, about an inch, or one inch and a quarter from any side, and you shall perceive it by degrees to make perpendicularly toward the nearest part of the side, and the nearer it approaches, the faster to be moved, the reason of which Phænomenon will be found no other then this, that the Air has a greater pressure against the middle of the superficies, then it has against those parts that approach nearer, and are contiguous to the sides. Now that the pressure is greater, may (as I shewed before in the explication of the third Figure) be evinced from the flatting of the water in the middle, which arises from the gravity of the under fluid: for since, as I shewed before, if there were no gravity in the under fluid, or that it were equal to that of the upper, the terminating Surface would be Spherical, and since it is the additional pressure of the gravity of water that makes it so flat, it follows, that the pressure upon the middle must be greater then towards the sides. Hence the Ball having a stronger pressure against that side of it which respects the middle of the superficies, then against that which respects the approximate side, must necessarily move towards that part, from whence it finds least resistance, and so be accelerated, as the resistance decrease. Hence the more the water is raised under that part of its way it is passing above the middle, the faster it is moved: And therefore you will find it to move faster in E then in D, and in D then in C. Neither could I find the floating substance to be moved at all, until it were placed upon some part of the Superficies that was sensibly elevated above the height of the middle part. Now that this may be the true cause, you may try with a blown Bladder, and an exactly round Ball upon a very smooth side of some pliable body, as Horn or Quicksilver. For if the Ball be placed under a part of the Bladder which is upon one side of the middle of its pressure, and you press strongly against the Bladder, you shall find the Ball moved from the middle towards the sides.

Having therefore shewn the reason of the motion of any float towards the sides, the reason of the incursion of any two floating bodies will easily appear: For the rising of the water against the sides of either of them, is an Argument sufficient, to shew the pressure of the Air to be there less, then it is further from it, where it is not so much elevated; and therefore the reason of the motion of the other toward it, will be the same as towards the side of the Glass, only here from the same reason, they are mutually moved toward each other, whereas the side of the Glass in the former remains fixt. If also you gently fill the Jar so full with water, that the water is protuberant above the sides, the same piece of Cork that before did hasten towards the sides, does now fly from it as fast towards the middle of the Superficies; the reason of which will be found no other then this, that the pressure of the Air is stronger against the sides of the Superficies G and H, then against the middle I; for since, as I shewed before, the Principle of congruity would make the terminating Surface Spherical, and that the flatting of the Surface in the middle is from the abatement of the waters pressure outwards, by the contrary indeavour of its gravity; it follows that the pressure in the middle must be less then on the sides; and therefore the consecution will be the same as in the former. It is very odd to one that considers not the reason of it, to see two floating bodies of wood to approach each other, as though they were indued with some magnetical vigour; which brings into my mind what I formerly tried with a piece of Cork or such like body, which I so ordered, that by putting a little stick into the same water, one part of the said Cork would approach and make toward the stick, whereas another would discede and fly away, nay it would have a kind of verticity, so as that if the Æquator (as I may so speak) of the Cork were placed towards the stick, if let alone, it would instantly turn its appropriate Pole toward it, and then run a-tilt at it: and this was done only by taking a dry Cork, and wetting one side of it with one small stroak; for by this means gently putting it upon the water, it would depress the superficies on every side of it that was dry, and therefore the greatest pressure of the Air, being near those sides, caused it either to chase away, or else to fly off from any other floating body, whereas that side only, against which the water ascended, was thereby able to attract.

It remains only, that I should determine how high the Water or other Liquor may by this means be raised in a smaller Pipe above the Superficies of that without it, and at what height it may be sustained: But to determine this, will be exceeding difficult, unless I could certainly know how much of the Airs pressure is taken off by the smalness of such and such a Pipe, and whether it may be wholly taken off, that is, whether there can be a hole or pore so small, into which Air could not at all enter, though water might with its whole force, for were there such, 'tis manifest, that the water might rise in it to some five or six and thirty English Foot high. I know not whether the capillary Pipes in the bodies of small Trees, which we call their Microscopical pores, may not be such; and whether the congruity of the sides of the Pore may not yet draw the juyce even higher then the Air was able by its bare pressure to raise it: For, Congruity is a principle that not only unites and holds a body joyned to it, but, which is more, attracts and draws a body that is very near it, and holds it above its usual height.

And this is obvious even in a drop of water suspended under any Similar or Congruous body: For, besides the ambient pressure that helps to keep it sustein'd, there is the Congruity of the bodies that are contiguous. This is yet more evident in Tenacious and Glutinous bodies; such as Gummous Liquors, Syrups, Pitch, and Rosin melted, &c. Tar, Turpentine, Balsom, Bird-lime, &c. for there it is evident, that the Parts of the tenacious body, as I may so call it, do stick and adhere so closely together, that though drawn out into long and very slender Cylinders, yet they will not easily relinquish one another; and this, though the bodies be aliquatenus fluid, and in motion by one another, which, to such as consider a fluid body only as its parts are in a confused irregular motion, without taking in also the congruity of the parts one among another, and incongruity to some other bodies, does appear not a little strange. So that besides the incongruity of the ambient fluid to it, we are to consider also the congruity of the parts of the contein'd fluid one with another.

And this Congruity (that I may here a little further explain it) is both a Tenaceous and an Attractive power; for the Congruity, in the Vibrative motions, may be the cause of all kind of attraction, not only Electrical, but Magnetical also, and therefore it may be also of Tenacity and Glutinousness. For, from a perfect congruity of the motions of two distant bodies, the intermediate fluid particles are separated and droven away from between them, and thereby those congruous bodies are, by the incompassing mediums, compell'd and forced neerer together; wherefore that attractiveness must needs be stronger, when, by an immediate contact, they are forc'd to be exactly the same: As I shew more at large in my Theory of the Magnet. And this hints to me the reason of the suspension of the Mercury many inches, nay many feet, above the usual station of 30 inches. For the parts of Quick-Silver, being so very similar and congruous to each other, if once united, will not easily suffer a divulsion: And the parts of water, that were any wayes heterogeneous, being by exantlation or rarefaction exhausted, the remaining parts being also very similar, will not easily part neither. And the parts of the Glass being solid, are more difficultly disjoyn'd; and the water, being somewhat similar to both, is, as it were, a medium to unite both the Glass and the Mercury together. So that all three being united, and not very dissimilar, by means of this contact, if care be taken that the Tube in erecting be not shogged, the Quicksilver will remain suspended, notwithstanding its contrary indeavour of Gravity, a great height above its ordinary Station; but if this immediate Contact be removed, either by a meer separation of them one from another by the force of a shog, whereby the other becomes imbodied between them, and licks up from the surface some agil parts, and so hurling them makes them air, or else by some small heterogeneous agil part of the Water, or Air, or Quicksilver, which appears like a bubble, and by its jumbling to and fro there is made way for the heterogeneous Æther to obtrude it self between the Glass and either of the other Fluids, the Gravity of Mercury precipitates it downward with very great violence; and if the Vessel that holds the restagnating Mercury be convenient, the Mercury will for a time vibrate to and fro with very large reciprocations, and at last will remain kept up by the pressure of the external Air at the height of neer thirty inches. And whereas it may be objected, that it cannot be, that the meer imbodying of the Æther between these bodies can be the cause, since the Æther having a free passage alwayes, both through the Pores of the Glass, and through those of the Fluids, there is no reason why it should not make a separation at all times whilst it remains suspended, as when it is violently dis-joyned by a shog. To this I answer, That though the Æther passes between the Particles, that is, through the Pores of bodies, so as that any chasme or separation being made, it has infinite passages to admit its entry into it, yet such is the tenacity or attractive virtue of Congruity, that till it be overcome by the meer strength of Gravity, or by a shog assisting that Conatus of Gravity, or by an agil Particle, that is like a leaver agitated by the Æther; and thereby the parts of the congruous substances are separated so far asunder, that the strength of congruity is so far weakened, as not to be able to reunite them, the parts to be taken hold of being removed out of the attractive Sphere, as I may so speak, of the congruity; such, I say, is the tenacity of congruity, that it retains and holds the almost contiguous Particles of the Fluid, and suffers them not to be separated, till by meer force that attractive or retentive faculty be overcome: But the separation being once made beyond the Sphere of the attractive activity of congruity, that virtue becomes of no effect at all, but the Mercury freely falls downwards till it meet with a resistance from the pressure of the ambient Air, able to resist its gravity, and keep it forced up in the Pipe to the height of about thirty inches.

Thus have I gently raised a Steel pendulum by a Loadstone to a great Angle, till by the shaking of my hand I have chanced to make a separation between them, which is no sooner made, but as if the Loadstone had retained no attractive virtue, the Pendulum moves freely from it towards the other side. So vast a difference is there between the attractive virtue of the Magnet when it acts upon a contiguous and upon a disjoyned body: and much more must there be between the attractive virtues of congruity upon a contiguous and disjoyned body; and in truth the attractive virtue is so little upon a body disjoyned, that though I have with a Microscope observed very diligently, whether there were any extraordinary protuberance on the side of a drop of water that was exceeding neer to the end of a green stick, but did not touch it, I could not perceive the least; though I found, that as soon as ever it toucht it the whole drop would presently unite it self with it; so that it seems an absolute contact is requisite to the exercising of the tenacious faculty of congruity.

Observ. VII. Of some Phænomena of Glass drops.

These Glass Drops are small parcels of coarse green Glass taken out of the Pots that contain the Metal (as they call it) in fusion, upon the end of an Iron Pipe; and being exceeding hot, and thereby of a kind of sluggish fluid Confidence, are suffered to drop from thence into a Bucket of cold Water, and in it to lye till they be grown sensibly cold.

Some of these I broke in the open air, by snapping off a little of the small stem with my fingers, others by crushing it with a small pair of Plyers; which I had no sooner done, then the whole bulk of the drop flew violently, with a very brisk noise, into multitudes of small pieces, some of which were as small as dust, though in some there were remaining pieces pretty large, without any flaw at all, and others very much flaw'd, which by rubbing between ones fingers was easily reduced to dust; these dispersed every way so violently, that some of them pierced my skin. I could not find either with my naked Eye, or a Microscope, that any of the broken pieces were of a regular figure, nor any one like another, but for the most part those that flaw'd off in large pieces were prettily branched.

The ends of others of these drops I nipt off whilst all the bodies and ends of them lay buried under the water, which, like the former, flew all to pieces with as brisk a noise, and as strong a motion.

Others of these I tried to break, by grinding away the blunt end, and though I took a seemingly good one, and had ground away neer two thirds of the Ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off the very tip of its slender end.

Another of these drops I began to grind away at the smaller end, but had not worn away on the stone above a quarter of an inch before the whole drop flew with a brisk crack into sand or small dust; nor would it have held so long, had there not been a little flaw in the piece that I ground away, as I afterwards found.

Several others of these drops I covered over with a thin but very tuff skin of Icthyocolla, which being very tough and very transparent, was the most convenient substance for these tryals that I could imagine, having dipt, I say, several of these drops in this transparent Glue whilst hot, and suffering them to hang by a string tied about the end of them till they were cold, and the skin pretty tough; then wrapping all the body of the drop (leaving out only the very tip) in fine supple Kids-leather very closely, I nipped off the small top, and found, as I expected, that notwithstanding this skin of Glue, and the close wrapping up in Leather, upon the breaking of the top, the drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture; and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacous and all over flaw'd, all those flaws lying in the manner of rings, from the bottom or blunt end, to the very top or small point. And by several examinations with a Microscope, of several thus broken, I found the flaws, both within the body of the drop, and on the outward surface, to lye much in this order.

Let AB in the Figure X of the fourth Scheme represent the drop cased over with Icthyocolla or Isinglass, (by being ordered as is before prescribed) crazed or flawed into pieces, but by the skin or case kept in its former figure, and each of its flawed parts preserved exactly in its due posture; the outward appearance of it somewhat plainly to the naked eye, but much more conspicuous if viewed with a small lens appeared much after this shape. That is, the blunt end B for a pretty breadth, namely, as far as the Ring CCC seemed irregularly flawed with divers clefts, which all seemed to tend towards the Center of it, being, as I afterwards found, and shall anon shew in the description of the figure Y, the Basis, as it were, of a Cone, which was terminated a little above the middle of the drop, all the rest of the Surface from CCC to A was flawed with an infinite number of small and parallel Rings, which as they were for the most part very round, so were they very thick and close together, but were not so exactly flaw'd as to make a perfect Ring, but each circular part was by irregular cracks flawed likewise into multitudes of irregular flakes or tiles; and this order was observed likewise the whole length of the neck.

Now though I could not so exactly cut this conical Body through the Axis, as is represented by the figure Y; yet by anatomizing, as it were, of several, and taking notice of divers particular circumstances, I was informed, that could I have artificially divided a flaw'd drop through the Axis or Center, I should with a Microscope have found it to appear much of this form, where A signifies the Apex, and B the blunt end, CC the Cone of the Basis, which is terminated at T the top or end of it, which seems to be the very middle of the blunt end in which, not only the conical body of the Basis CC is terminated, but as many of the parts of the drop as reach as high as DD.

And it seemed to be the head or beginning of a Pith, as it were, or a part of the body which seemed more spungy then the rest, and much more irregularly flawed, which from T ascended by EE, though less visible, into the small neck towards A. The Grain, as it were, of all the flaws, that proceeds from all the outward Surface ADCCDA, was much the same, as is represented by the black strokes that meet in the middle DT, DT, DE, DE, &c.

Nor is this kind of Grain, as I may call it, peculiar to Glass drops thus quenched; for (not to mention Coperas-stones, and divers other Marchasites and Minerals, which I have often taken notice of to be in the very same manner flaked or grained, with a kind of Pith in the middle) I have observed the same in all manner of cast Iron, especially the coarser sort, such as Stoves, and Furnaces, and Backs, and Pots are made of: For upon the breaking of any of those Substances it is obvious to observe, how from the out-sides towards the middle, there is a kind of Radiation or Grain much resembling this of the Glass-drop; but this Grain is most conspicuous in Iron-bullets, if they be broken: the same Phænomena may be produced by casting regulus of Antimony into a Bullet-mold, as also with Glass of Antimony, or with almost any such kind of Vitrified substance, either cast into a cold Mold or poured into Water.

Others of these Drops I heat red hot in the fire, and then suffered them to cool by degrees. And these I found to have quite lost all their fulminating or flying quality, as also their hard, brittle and springy texture; and to emerge of a much softer temper, and much easier to be broken or snapt with ones finger; but its strong and brittle quality was quite destroyed, and it seemed much of the same consistence with other green Glass well nealed in the Oven.

The Figure and bigness of these for the most part was the same with that of the Figure Z; that is, all the surface of them was very smooth and polisht, and for the most part round, but very rugged or knobbed about D, and all the length of the stem was here and there pitted or flatted. About D, which is at the upper part of the drop under that side of the stem which is concave, there usually was made some one or more little Hillocks or Prominences. The drop it self, before it be broken, appears very transparent, and towards the middle of it, to be very full of small Bubbles, of some kind of aerial substance, which by the refraction of the outward surface appear much bigger then really they are, and this may be in good part removed, by putting the drop under the surface of clear Water, for by that means most part of the refraction of the convex Surface of the drop is destroyed, and the bubbles will appear much smaller. And this, by the by, minds me of the appearing magnitude of the aperture of the iris, or pupil of the eye, which though it appear, and be therefore judged very large, is yet not above a quarter of the bigness it appears of, by the lenticular refraction of the Cornea.

The cause of all which Phænomena I imagine to be no other then this, That the Parts of the Glass being by the excessive heat of the fire kept off and separated one from another, and thereby put into a kind of sluggish fluid consistence, are suffered to drop off with that heat or agitation remaining in them, into cold Water; by which means the outsides of the drop are presently cool'd and crusted, and are thereby made of a loose texture, because the parts of it have not time to settle themselves leisurely together, and so to lie very close together: And the innermost parts of the drop, retaining still much of their former heat and agitations, remain of a loose texture also, and, according as the cold strikes inwards from the bottom and sides, are quenched, as it were, and made rigid in that very posture wherein the cold finds them. For the parts of the crust being already hardened, will not suffer the parts to shrink any more from the outward Surface inward; and though it shrink a little by reason of the small parcels of some Aerial substances dispersed through the matter of the Glass, yet that is not neer so much as it appears (as I just now hinted;) nor if it were, would it be sufficient for to consolidate and condense the body of Glass into a tuff and close texture, after it had been so excessively rarified by the heat of the glass-Furnace.

But that there may be such an expansion of the aerial substance contained in those little blebbs or bubbles in the body of the drop, this following Experiment will make more evident.

Take a small Glass-Cane about a foot long, seal up one end of it hermetically, then put in a very small bubble of Glass, almost of the shape of an Essence-viol with the open mouth towards the sealed end, then draw out the other end of the Pipe very small, and fill the whole Cylinder with water, then set this Tube by the Fire till the Water begin to boyl, and the Air in the bubble be in good part rarified and driven out, then by sucking at the smalling Pipe, more of the Air or vapours in the bubble may be suck'd out, so that it may sink to the bottom; when it is sunk to the bottom, in the flame of a Candle, or Lamp, nip up the slender Pipe and let it cool: whereupon it is obvious to observe, first, that the Water by degrees will subside and shrink into much less room: Next, that the Air or vapours in the Glass will expand themselves so, as to buoy up the little Glass: Thirdly, that all about the inside of the Glass-pipe there will appear an infinite number of small bubbles, which as the Water grows colder and colder will swell bigger and bigger, and many of them buoy themselves up and break at the top.

From this Disceding of the heat in Glass drops, that is, by the quenching or cooling Irradiations propagated from the Surface upwards and inwards, by the lines CT, CT, DT, DE, &c. the bubbles in the drop have room to expand themselves a little, and the parts of the Glass contract themselves; but this operation being too quick for the sluggish parts of the Glass, the contraction is performed very unequally and irregularly, and thereby the Particles of the Glass are bent, some one way, and some another, yet so as that most of them draw towards the Pith or middle TEEE, or rather from that outward: so that they cannot extricate or unbend themselves, till some part of TEEE be broken and loosened, for all the parts about that are placed in the manner of an Arch, and so till their hold at TEEE be loosened they cannot fly asunder, but uphold, and shelter, and fix each other much like the stones in a Vault, where each stone does concurre to the stability of the whole Fabrick, and no one stone can be taken away but the whole Arch falls. And wheresoever any of those radiating wedges DTD, &c. are removed, which are the component parts of this Arch, the whole Fabrick presently falls to pieces; for all the Springs of the several parts are set at liberty, which immediately extricate themselves and fly asunder every way; each part by its spring contributing to the darting of it self and some other contiguous part. But if this drop be heat so hot as that the parts by degrees can unbend themselves, and be settled and annealed in that posture, and be then suffered gently to subside and cool; The parts by this nealing losing their springiness, constitute a drop of a more soft but less brittle texture, and the parts being not at all under a flexure, though any part of the middle or Pith TEEE be broken, yet will not the drop at all fly to pieces as before.

This Conjecture of mine I shall indeavour to make out by explaining each particular Assertion with analogous Experiments: The Assertions are there.

That the first of these is true may be gathered from this, That Heat is a property of a body arising from the motion or agitation of its parts; and therefore whatever body is thereby toucht must necessarily receive some part of that motion, whereby its parts will be shaken and agitated, and so by degrees free and extricate themselves from one another, and each part so moved does by that motion exert a conatus of protruding and displacing all the adjacent Particles. Thus Air included in a vessel, by being heated will burst it to pieces. Thus have I broke a Bladder held over the fire in my hand, with such a violence and noise, that it almost made me deaf for the present, and much surpassed the noise of a Musket: The like have I done by throwing into the fire small glass Bubbles hermetically sealed, with a little drop of Water included in them. Thus Water also, or any other Liquor, included in a convenient vessel, by being warmed, manifestly expands it self with a very great violence, so as to break the strongest vessel, if when heated it be narrowly imprisoned in it. This is very manifest by the Sealed Thermometers, which I have, by several tryals, at last brought to a great certainty and tenderness: for I have made some with stems above four foot long, in which the expanding Liquor would so far vary, as to be very neer the very top in the heat of Summer, and prety neer the bottom at the coldest time of the Winter. The Stems I use for them are very thick, straight, and even Pipes of Glass, with a very small perforation, and both the head and body I have made on purpose at the Glass-house, of the same metal whereof the Pipes are drawn: these I can easily in the flame of a Lamp, urged with the blast of a pair of Bellows, seal and close together, so as to remain very firm, close and even; by this means I joyn on the body first, and then fill both it and a part of the stem, proportionate to the length of the stem and the warmth of the season I fill it in with the best rectified Spirit of Wine highly ting'd with the lovely colour of Cocheneel, which I deepen the more by pouring some drops of common Spirit of Urine, which must not be too well rectified, because it will be apt to make the Liquor to curdle and stick in the small perforation of the stem. This Liquor I have upon tryal found the most tender of any spirituous Liquor, and those are much more sensibly affected with the variations of heat and cold then other more flegmatick and ponderous Liquors, and as capable of receiving a deep tincture, and keeping it, as any Liquor whatsoever; and (which makes it yet more acceptable) is not subject to be frozen by any cold yet known. When I have thus filled it, I can very easily in the forementioned flame of a Lamp seal and joyn on the head of it.

Then, for graduating the stem, I fix that for the beginning of my division where the surface of the liquor in the stem remains when the ball is placed in common distilled water, that is so cold that it just begins to freeze and shoot into flakes; and that mark I fix at a convenient place of the stem, to make it capable of exhibiting very many degrees of cold, below that which is requisite to freeze water: the rest of my divisions, both above and below this (which I mark with a [0] or nought) I place according to the Degrees of Expansion, or Contraction of the Liquor in proportion to the bulk it had when it indur'd the newly mention'd freezing cold. And this may be very easily and accurately enough done by this following way; Prepare a Cylindrical vessel of very thin plate Brass or Silver, ABCD of the figure Z; the Diameter AB of whose cavity let be about two inches, and the depth BC the same; let each end be cover'd with a flat and smooth plate of the same substance, closely soder'd on, and in the midst of the upper cover make a pretty large hole EF, about the bigness of a fifth part of the Diameter of the other; into this fasten very well with cement a straight and even Cylindrical pipe of Glass, EFGH, the Diameter of whose cavity let be exactly one tenth of the Diameter of the greater Cylinder. Let this pipe be mark'd at GH with a Diamant, so that G from E may be distant just two inches, or the same height with that of the cavity of the greater Cylinder, then divide the length EG exactly into 10 parts, so the capacity of the hollow of each of these divisions will be 1/1000 part of the capacity of the greater Cylinder. This vessel being thus prepared, the way of marking and graduating the Thermometers may be very easily thus performed:

Fill this Cylindrical vessel with the same liquor wherewith the Thermometers are fill'd, then place both it and the Thermometer you are to graduate, in water that is ready to be frozen, and bring the surface of the liquor in the Thermometer to the first marke or [0]; then so proportion the liquor in the Cylindrical vessel, that the surface of it may just be at the lower end of the small glass-Cylinder; then very gently and gradually warm the water in which both the Thermometer and this Cylindrical vessel stand, and as you perceive the ting'd liquor to rise in both stems, with the point of a Diamond give several marks on the stem of the Thermometer at those places, which by comparing the expansion in both Stems, are found to correspond to the divisions of the cylindrical vessel, and having by this means marked some few of these divisions on the Stem, it will be very easie by these to mark all the rest of the Stem, and accordingly to assign to every division a proper character.

A Thermometer, thus marked and prepared, will be the fittest Instrument to make a Standard of heat and cold that can be imagined. For being sealed up, it is not at all subject to variation or wasting, nor is it liable to be changed by the varying pressure of the Air, which all other kind of Thermometers that are open to the Air are liable to. But to proceed.

This property of Expansion with Heat, and Contraction with Cold, is not peculiar to Liquors only, but to all kind of solid Bodies also, especially Metals, which will more manifestly appear by this Experiment.

Take the Barrel of a Stopcock of Brass, and let the Key, which is well fitted to it, be riveted into it, so that it may slip, and be easily turned round, then heat this Cock in the fire, and you will find the Key so swollen, that you will not be able to turn it round in the Barrel; but if it be suffered to cool again, as soon as it is cold it will be as movable, and as easie to be turned as before.

This Quality is also very observable in Lead, Tin, Silver, Antimony, Pitch, Rosin, Bees-wax, Butter, and the like; all which, if after they be melted you suffer gently to cool, you shall find the parts of the upper Surface to subside and fall inwards, losing that plumpness and smoothness it had whilst in fusion. The like I have also observed in the cooling of Glass of Antimony, which does very neer approach the nature of Glass,

But because these are all Examples taken from other materials then Glass, and argue only, that possibly there may be the like property also in Glass, not that really there is; we shall by three or four Experiments indeavour to manifest that also.

And the First is an Observation that is very obvious even in these very drops, to wit, that they are all of them terminated with an unequal or irregular Surface, especially about the smaller part of the drop, and the whole length of the stem; as about D, and from thence to A, the whole Surface, which would have been round if the drop had cool'd leisurely, is, by being quenched hastily, very irregularly flatted and pitted; which I suppose proceeds partly from the Waters unequally cooling and pressing the parts of the drop, and partly from the self-contracting or subsiding quality of the substance of the Glass: For the vehemency of the heat of the drop causes such hidden motions and bubbles in the cold Water, that some parts of the Water bear more forcibly against one part then against another, and consequently do more suddenly cool those parts to which they are contiguous.

A Second Argument may be drawn from the Experiment of cutting Glasses with a hot Iron. For in that Experiment the top of the Iron heats, and thereby rarifies the parts of the Glass that lie just before the crack, whence each of those agitated parts indeavouring to expand its self and get elbow-room, thrusts off all the rest of the contiguous parts, and consequently promotes the crack that was before begun.

A Third Argument may be drawn from the way of producing a crack in a sound piece or plate of Glass, which is done two wayes, either First, by suddenly heating a piece of Glass in one place more then in another. And by this means chymists usually cut off the necks of Glass-bodies, by two kinds of Instruments, either by a glowing hot round Iron-Ring, which just incompasses the place that is to be cut, or else by a Sulphur'd Threed, which is often wound about the place where the separation is to be made, and then fired. Or Secondly, A Glass may be cracked by cooling it suddenly in any place with Water, or the like, after it has been all leisurely and gradually heated very hot. Both which Phænomena seem manifestly to proceed from the expansion and contraction of the parts of the Glass, which is also made more probable by this circumstance which I have observed, that a piece of common window-glass being heated in the middle very suddenly with a live Coal or hot Iron, does usually at the first crack fall into pieces, whereas if the Plate has been gradually heated very hot, and a drop of cold Water and the like be put on the middle of it, it only flaws it, but does not break it asunder immediately.

A Fourth Argument may be drawn from this Experiment; Take a Glass-pipe, and fit into a solid stick of Glass, so as it will but just be moved in it. Then by degrees heat them whilst they are one within another, and they will grow stiffer, but when they are again cold, they will be as easie to be turned as before. This Expansion of Glass is more manifest in this Experiment.

Take a stick of Glass of a considerable length, and fit it so between the two ends or screws of a Lath, that it may but just easily turn, and that the very ends of it may be just toucht and susteined thereby; then applying the flame of the Candle to the middle of it, and heating it hot, you will presently find the Glass to stick very fast on those points, and not without much difficulty to be convertible on them, before that by removing the flame for a while from it, it be suffered to cool, and when you will find it as easie to be turned round as at the first.

From all which Experiments it is very evident, that all those Bodies, and particularly Glass, suffers an Expansion by Heat, and that a very considerable one, whilst they are in a state of Fusion. For Fluidity, as I elsewhere mention, being nothing but an effect of very strong and quick shaking motion, whereby the parts are, as it were, loosened from each other, and consequently leave an interjacent space or vacuity; it follows, that all those shaken Particles must necessarily take up much more room then when they were at rest, and lay quietly upon each other. And this is further confirmed by a Pot of boyling Alabaster, which will manifestly rise a sixth or eighth part higher in the Pot, whilst it is boyling, then it will remain at, both before and after it be boyled. The reason of which odd Phænomenon (to hint it here only by the way) is this, that there is in the curious powder of Alabaster, and other calcining Stones, a certain watery substance, which is so fixt and included with the solid Particles, that till the heat be very considerable they will not fly away; but after the heat is increased to such a degree, they break out every way in vapours, and thereby so shake and loosen the small corpusles of the Powder from each other, that they become perfectly of the nature of a fluid body, and one may move a stick to and fro through it, and stir it as easily as water, and the vapours burst and break out in bubbles just as in boyling water, and the like; whereas, both before those watery parts are flying away, and after they are quite gone; that is, before and after it have done boyling, all those effects cease, and a stick is as difficultly moved to and fro in it as in sand, or the like. Which Explication I could easily prove, had I time; but this is not a fit place for it.

To proceed therefore, I say, that the dropping of this expanded Body into cold Water, does make the parts of the Glass suffer a double contraction: The first is, of those parts which are neer the Surface of the Drop. For Cold, as I said before, contracting Bodies, that is, by the abatement of the agitating faculty the parts falling neerer together; the parts next adjoyning to the Water must needs lose much of their motion, and impart it to the Ambient-water (which the Ebullition and commotion of it manifests) and thereby become a solid and hard crust, whilst the innermost parts remain yet fluid and expanded; whence, as they grow cold also by degrees, their parts must necessarily be left at liberty to be condensed, but because of the hardness of the outward crust, the contraction cannot be admitted that way; but there being many very small, and before inconspicuous, bubbles in the substance of the Glass, upon the subsiding of the parts of the Glass, the agil substance contained in them has liberty of expanding it self a little, and thereby those bubbles grow much bigger, which is the second Contraction. And both these are confirmed from the appearance of the Drop it self: for as for the outward parts, we see, first, that it is irregular and shrunk, as it were, which is caused by the yielding a little of the hardened Skin to a Contraction, after the very outmost Surface is settled; and as for the internal parts, one may with ones naked Eye perceive abundance of very conspicuous bubbles, and with the Microscope many more.

The Consideration of which Particulars will easily make the Third Position probable, that is, that the parts of the drop will be of a very hard, though of a rarified Texture; for if the outward parts of the Drop, by reason of its hard crust, will indure very little Contraction, and the agil Particles, included in those bubbles, by the losing of their agitation, by the decrease of the Heat, lose also most part of their Spring and Expansive power; it follows (the withdrawing of the heat being very sudden) that the parts must be left in a very loose Texture, and by reason of the implication of the parts one about another, which from their sluggishnes and glutinousness I suppose to be much after the manner of the sticks in a Thorn-bush, or a Lock of Wool; it will follow, I say, that the parts will hold each other very strongly together, and indeavour to draw each other neerer together, and consequently their Texture must be very hard and stiff, but very much rarified.

And this will make probable my next Position, That the parts of the Glass are under a kind of tension or flexure, out of which they indeavour to extricate and free themselves, and thereby all the parts draw towards the Center or middle, and would, if the outward parts would give way, as they do when the outward parts cool leisurely (as in baking of Glasses) contract the bulk of the drop into a much less compass. For since, as I proved before, the Internal parts of the drop, when fluid, were of a very rarified Texture, and, as it were, tos'd open like a Lock of Wool, and if they were suffered leisurely to cool, would be again prest, as it were, close together: And since that the heat, which kept them bended and open, is removed, and yet the parts not suffered to get as neer together as they naturally would; It follows, that the Particles remain under a kind of tension and flexure, and consequently have an indeavour to free themselves from that bending and distension, which they do, as soon as either the tip be broken, or as soon as by a leisurely heating and cooling, the parts are nealed into another posture.

And this will make my next Position probable, that the parts of the Glass drops are contignated together in the form of an Arch, cannot any where yield or be drawn inwards, till by the removing of some one part of it (as it happens in the removing one of the stones of an Arch) the whole Fabrick is shatter'd, and falls to pieces, and each of the Springs is left at liberty, suddenly to extricate it self: for since I have made it probable, that the internal parts of the Glass have a contractive power inwards, and the external parts are incapable of such a Contraction, and the figure of it being spherical; it follows, that the superficial parts must bear against each other, and keep one another from being condens'd into a less room, in the same manner as the stones of an Arch conduce to the upholding each other in that Figure. And this is made more probable by another Experiment which was communicated to me by an excellent Person, whose extraordinary Abilities in all kind of Knowledg, especially in that of Natural things, and his generous Disposition in communicating, incouraged me to have recourse to him on many occasions. The Experiment was this: Small Glass-balls (about the bigness of that represented in the Figure &.) would, upon rubbing or scratching the inward Surface, fly all insunder, with a pretty brisk noise; whereas neither before nor after the inner Surface had been thus scratcht, did there appear any flaw or crack. And putting the pieces of one of those broken ones together again, the flaws appeared much after the manner of the black lines on the Figure, &. These Balls were small, but exceeding thick bubbles of Glass, which being crack'd off from the Puntilion whilst very hot, and so suffered to cool without nealing them in the Oven over the Furnace, do thereby (being made of white Glass, which cools much quicker then green Glass, and is thereby made much brittler) acquire a very porous and very brittle texture: so that if with the point of a Needle or Bodkin, the inside of any of them be rubbed prety hard, and then laid on a Table, it will, within a very little while, break into many pieces with a brisk noise, and throw the parts above a span asunder on the Table: Now though the pieces are not so small as those of a fulminating drop, yet they as plainly shew, that the outward parts of the Glass have a great Conatus to fly asunder, were they not held together by the tenacity of the parts of the inward Surface: for we see as soon as those parts are crazed by hard rubbing, and thereby their tenacity spoiled, the springiness of the more outward parts quickly makes a divulsion, and the broken pieces will, if the concave Surface of them be further scratcht with a Diamond, fly again into smaller pieces.

From which preceding considerations it will follow Sixthly, That the sudden flying asunder of the parts as soon as this Arch is any where disordered or broken, proceeds from the springing of the parts; which, indeavouring to extricate themselves as soon as they get the liberty, they perform it with such a quickness, that they throw one another away with very great violence: for the Particles that compose the Crust have a Conatus to lye further from one another, and therefore as soon as the external parts are loosened they dart themselves outward with great violence, just as so many Springs would do, if they were detained and fastened to the body, as soon as they should be suddenly loosened; and the internal parts drawing inward, they contract so violently; that they rebound back again and fly into multitude of small shivers or sands. Now though they appear not, either to the naked Eye, or the Microscope, yet I am very apt to think there may be abundance of small flaws or cracks, which, by reason the strong reflecting Air is not got between the contiguous parts, appear not. And that this may be so, I argue from this, that I have very often been able to make a crack or flaw, in some convenient pieces of Glass, to appear and disappear at pleasure, according as by pressing together, or pulling asunder the contiguous parts, I excluded or admitted the strong reflecting Air between the parts: And it is very probable, that there may be some Body, that is either very rarified Air, or something analogous to it, which fills the bubbles of these drops; which I argue, first, from the roundness of them, and next, from the vivid reflection of Light which they exhibite: Now though I doubt not, but that the Air in them is very much rarified, yet that there is some in them, to such as well consider this Experiment of the disappearing of a crack upon the extruding of the Air, I suppose it will seem more then probable.

The Seventh and last therefore that I shall prove, is, That the gradual heating and cooling of these so extended bodies does reduce the parts of the Glass to a looser and softer temper. And this I found by heating them, and keeping them for a prety while very red hot in a fire; for thereby I found them to grow a little lighter, and the small Stems to be very easily broken and snapt any where, without at all making the drop fly; whereas before they were so exceeding hard, that they could not be broken without much difficulty; and upon their breaking the whole drop would fly in pieces with very great violence. The Reason of which last seems to be, that the leisurely heating and cooling of the parts does not only wast some part of the Glass it self, but ranges all the parts into a better order, and gives each Particle an opportunity of relaxing its self, and consequently neither will the parts hold so strongly together as before, nor be so difficult to be broken: The parts now more easily yielding, nor will the other parts fly in pieces, because the parts have no bended Springs. The relaxation also in the temper of hardned Steel, and hammered Metals, by nealing them in the fire, seems to proceed from much the same cause. For both by quenching suddenly such Metals as have vitrifed parts interspers'd, as Steel has, and by hammering of other kinds that do not so much abound with them, as Silver Brass, &c. the parts are put into and detained in a bended posture, which by the agitation of Heat are shaken, and loosened, and suffered to unbend themselves.

Observ. VIII. Of the fiery Sparks struck from a Flint or Steel.

It is a very common Experiment, by striking with a Flint against a Steel, to make certain fiery and shining Sparks to fly out from between those two compressing Bodies. About eight years since, upon casually reading the Explication of this odd Phænomenon, by the most Ingenious Des Cartes, I had a great desire to be satisfied, what that Substance was that gave such a shining and bright Light: And to that end I spread a sheet of white Paper, and on it, observing the place where several of these Sparks seemed to vanish, I found certain very small, black, but glittering Spots of a movable Substance, each of which Schem. 5.
Fig. 1. examining with my Microscope, I found to be a small round Globule; some of which, as they looked prety small, so did they from their Surface yield a very bright and strong reflection on that side which was next the Light; and each look'd almost like a prety bright Iron-Ball, whose Surface was prety regular, such as is represented by the Figure A. In this I could perceive the Image of the Window prety well, or of a Stick, which I moved up and down between the Light and it. Others I found, which were, as to the bulk of the Ball, prety regularly round, but the Surface of them, as it was not very smooth, but rough, and more irregular, so was the reflection from it more faint and confused. Such were the Surfaces of B. C. D. and E. Some of these I found cleft or cracked, as C, others quite broken in two and hollow, as D. which seemed to be half the hollow shell of a Granado, broken irregularly in pieces. Several others I found of other shapes; but that which is represented by E, I observed to be a very big Spark of fire, which went out upon one side of the Flint that I struck fire withall, to which it stuck by the root F, at the end of which small Stem was fastened-on a Hemisphere, or half a hollow Ball, with the mouth of it open from the stemwards, so that it looked much like a Funnel, or an old fashioned Bowl without a foot. This night, making many tryals and observations of this Experiment, I met, among a multitude of the Globular ones which I had observed, a couple of Instances, which are very remarkable to the confirmation of my Hypothesis.

And the First was of a pretty big Ball fastened on to the end of a small sliver of Iron, which Compositum seemed to be nothing else but a long thin chip of Iron, one of whose ends was melted into a small round Globul; the other end remaining unmelted and irregular, and perfectly Iron.

The Second Instance was not less remarkable then the First; for I found, when a Spark went out, nothing but a very small thin long sliver of Iron or Steel, unmelted at either end. So that it seems, that some of these Sparks are the slivers or chips of the Iron vitrified, Others are only the slivers melted into Balls without vitrification, And the third kind are only small slivers of the Iron, made red-hot with the violence of the stroke given on the Steel by the Flint.

He that shall diligently examine the Phænomena of this Experiment, will, I doubt not, find cause to believe, that the reason I have heretofore given of it, is the true and genuine cause of it, namely, That the Spark, appearing so bright in the falling, is nothing else but a small piece of the Steel or Flint, but most commonly of the Steel, which by the violence of the stroke is at the same time sever'd and heat red-hot, and that sometimes to such a degree, as to make it melt together into a small Globule of Steel; and sometimes also is that heat so very intense, as further to melt it and vitrifie it; but many times the heat is so gentle, as to be able to make the sliver only red hot, which notwithstanding falling upon the tinder (that is only a very curious small Coal made of the small threads of Linnen burnt to coals and char'd) it easily sets it on fire. Nor will any part of this Hypothesis seem strange to him that considers, First, that either hammering, or filing or otherwise violently rubbing of Steel, will presently make it so hot as to be able to burn ones fingers. Next, that the whole force of the stroke is exerted upon that small part where the Flint and Steel first touch: For the Bodies being each of them so very hard, the puls cannot be far communicated, that is, the parts of each can yield but very little, and therefore the violence of the concussion will be exerted on that piece of Steel which is cut off by the Flint. Thirdly, that the filings or small parts of Steel are very apt, as it were, to take fire, and are presently red hot, that is, there seems to be a very combustible sulphureous Body in Iron or Steel, which the Air very readily preys upon, as soon as the body is a little violently heated.

And this is obvious in the filings of Steel or Iron cast through the flame of a Candle; for even by that sudden transitus of the small chips of Iron, they are heat red hot, and that combustible sulphureous Body is presently prey'd upon and devoured by the aereal incompassing Menstruum, whose office in this Particular I have shewn in the Explication of Charcole.

And in prosecution of this Experiment, having taken the filings of Iron and Steel, and with the point of a Knife cast them through the flame of a Candle, I observed where some conspicuous shining Particles fell, and looking on them with my Microscope, I found them to be nothing else but such round Globules, as I formerly found the Sparks struck from the Steel by a stroke to be, only a little bigger; and shaking together all the filings that had fallen upon the sheet of Paper underneath and observing them with the Microscope, I found a great number of small Globules, such as the former, though there were also many of the parts that had remained untoucht and rough filings or chips of Iron. So that, it seems, Iron does contain a very combustible sulphureous Body, which is, in all likelihood, one of the causes of this Phænomenon, and which may be perhaps very much concerned in the business of its hardening and tempering: of which somewhat it said in the Description of Muscovy-glass.

So that, these things considered, we need not trouble our selves to find out what kind of Pores they are, both in the Flint and Steel, that contain the Atoms of fire, nor how those Atoms come to be hindred from running all out, when a dore or passage in their Pores is made by the concussion: nor need we trouble our selves to examine by what Prometheus the Element of Fire comes to be fetcht down from above the Regions of the Air, in what Cells or Boxes it is kept, and what Epimetheus lets it go: Nor to consider what it is that causes so great a conflux of the atomical Particles of Fire, which are said to fly to a flaming Body, like Vultures or Eagles to a putrifying Carcass, and there to make a very great pudder. Since we have nothing more difficult in this Hypothesis to conceive, first, as to the kindling of Tinder, then how a large Iron-bullet, let fall red or glowing hot upon a heap of Small-coal, should set fire to those that are next to it first: Nor secondly, is this last more difficult to be explicated, then that a Body, as Silver for Instance, put into a weak Menstruum, as unrectified Aqua fortis should, when it is put in a great heat, be there dissolved by it, and not before; which Hypothesis is more largely explicated in the Description of Charcoal. To conclude, we see by this Instance, how much Experiments may conduce to the regulating of Philosophical notions. For if the most Acute Des Cartes had applied himself experimentally to have examined what substance it was that caused that shining of the falling Sparks struck from a Flint and a Steel, he would certainly have a little altered his Hypothesis, and we should have found, that his Ingenious Principles would have admitted a very plausible Explication of this Phænomenon; whereas by not examining so far as he might, he has set down an Explication which Experiment do's contradict.

But before I leave this Description, I must not forget to take notice of the Globular form into which each of these is most curiously formed. And this Phænomenon, as I have elsewhere more largely shewn, proceeds from a propriety which belongs to all kinds of fluid Bodies more or less, and is caused by the Incongruity of the Ambient and included Fluid, which so acts and modulates each other, that they acquire, as neer as is possible, a spherical or globular form, which propriety and several of the Phænomena that proceed from it, I have more fully explicated in the sixth Observation.

One Experiment, which does very much illustrate my present Explication, and is in it self exceeding pretty, I must not pass by: And that is a way of making small Globules or Balls of Lead, or Tin, as small almost as these of Iron or Steel, and that exceeding easily and quickly, by turning the filings or chips of those Metals also into perfectly round Globules. The way, in short, as I received it from the Learned Physitian Doctor I.G. is this;

Reduce the Metal you would thus shape, into exceeding fine filings, the finer the filings are, the finer will the Balls be: Stratifie these filings with the fine and well dryed powder of quick Lime in a Crucible proportioned to the quantity you intend to make: When you have thus filled your Crucible, by continual stratifications of the filings and powder, so that, as neer as may be, no one of the filings may touch another, place the Crucible in a gradual fire, and by degrees let it be brought to a heat big enough to make all the filings, that are mixt with the quick Lime, to melt, and no more; for if the fire be too hot, many of these filings will joyn and run together; whereas if the heat be proportioned, upon washing the Lime-dust in fair Water, all those small filings of the Metal will subside to the bottom in a most curious powder, consisting all of exactly round Globules, which, if it be very fine, is very excellent to make Hour-glasses of.

Now though quick Lime be the powder that this direction makes choice of, yet I doubt not, but that there may be much more convenient ones found out, one of which I have made tryal of, and found very effectual; and were it not for discovering, by the mentioning of it, another Secret, which I am not free to impart, I should have here inserted it.

Observ. IX. Of the Colours observable in Muscovy Glass, and other thin Bodies.

Moscovy-glass, or Lapis specularis, is a Body that seems to have as many Curiosities in its Fabrick as any common Mineral I have met with: for first, It is transparent to a great thickness: Next, it is compounded of an infinite number of thin flakes joyned or generated one upon another so close & smooth, as with many hundreds of them to make one smooth and thin Plate of a transparent flexible substance, which with care and diligence may be flit into pieces so exceedingly thin as to be hardly perceivable by the eye, and yet even those, which I have thought the thinnest, I have with a good Microscope found to be made up of many other Plates, yet thinner; and it is probable, that, were our Microscopes much better, we might much further discover its divisibility. Nor are these flakes only regular as to the smoothness of their Surfaces, but thirdly, In many Plates they may be perceived to be terminated naturally with edges of the figure of a Rhomboeid. This Figure is much more conspicuous in our English talk, much whereof is found in the Lead Mines, and is commonly called Spar, and Kauck, which is of the same kind of substance with the Selenitis, but is seldom found in so large flakes as that is, nor is it altogether so tuff, but is much more clear and transparent, and much more curiously shaped, and yet may be cleft and flak'd like the other Selenitis. But fourthly, this stone has a property, which in respect of the Microscope, is more notable, and that is, that it exhibits several appearances of Colours, both to the naked Eye, but much more conspicuously to the Microscope; for the exhibiting of which, I took a piece of Muscovy-glass, and splitting or cleaving it into thin Plates, I found that up and down in several parts of them I could plainly perceive several white specks or flaws, and others diversly coloured with all the Colours of the Rainbow; and with the Microscope I could perceive, that these Colours were ranged in rings that incompassed the white speck or flaw, and were round or irregular, according to the shape of the spot which they terminated; and the position of Colours, in respect of one another, was the very same as in the Rainbow. The consecution of those Colours from the middle of the spot outward being Blew, Purple, Scarlet, Yellow, Green; Blew, Purple, Scarlet, and so onwards, sometimes half a score times repeated, that is, there appeared six, seven, eight, nine or ten several coloured rings or lines, each incircling the other, in the same manner as I have often seen a very vivid Rainbow to have four or five several Rings of Colours, that is, accounting all the Gradations between Red and Blew for one: But the order of the Colours in these Rings was quite contrary to the primary or innermost Rainbow, and the same with those of the secondary or outermost Rainbow; these coloured Lines or Irises, as I may so call them, were some of them much brighter then others, and some of them also very much broader, they being some of them ten, twenty, nay, I believe, neer a hundred times broader then others; and those usually were broadest which were neerest the center or middle of the flaw. And oftentimes I found, that these Colours reacht to the very middle of the flaw, and then there appeared in the middle a very large spot, for the most part, all of one colour, which was very vivid, and all the other Colours incompassing it, gradually ascending, and growing narrower towards the edges, keeping the same order, as in the secundary Rainbow, that is, if the middle were Blew, the next incompassing it would be a Purple, the third a Red, the fourth a Yellow, &c. as above; if the middle were a Red, the next without it would be a Yellow, the third a Green, the fourth a Blew, and so onward. And this order it alwayes kept whatsoever were the middle Colour.

There was further observable in several other parts of this Body, many Lines or Threads, each of them of some one peculiar Colour, and those so exceedingly bright and vivid, that it afforded a very pleasant object through the Microscope. Some of these threads I have observed also to be pieced or made up of several short lengths of differently coloured ends (as I may so call them) as a line appearing about two inches long through the Microscope, has been compounded of about half an inch of a Peach colour, 1/8 of a lovely Grass-green, 3/4 of an inch more of a bright Scarlet, and the rest of the line of a Watchet blew. Others of them were much otherwise coloured; the variety being almost infinite. Another thing which is very observable, is, that if you find any place where the colours are very broad and conspicuous to the naked eye, you may, by pressing that place with your finger, make the colours change places, and go from one part to another.

There is one Phænomenon more, which may, if care be used, exhibit to the beholder, as it has divers times to me, an exceeding pleasant, and not less instructive Spectacle; And that is, if curiosity and diligence be used, you may so split this admirable Substance, that you may have pretty large Plates (in companion of those smaller ones which you may observe in the Rings) that are perhaps an 1/8 or a 1/6 part of an inch over, each of them appearing through the Microscope most curiously, intirely, and uniformly adorned with some one vivid colour: this, if examined with the Microscope, may be plainly perceived to be in all parts of it equally thick. Two, three, or more of these lying one upon another, exhibit oftentimes curious compounded colours, which produce such a Compositum, as one would scarce imagine should be the result of such ingredients: As perhaps a faint yellow and a blew may produce a very deep purple. But when anon we come to the more strict examination of these Phænomena, and to inquire into the causes and reasons of these productions, we shall, I hope, make it more conceivable how they are produced, and shew them to be no other then the natural and necessary effects arising from the peculiar union of concurrent causes.

These Phænomena, being so various, and so truly admirable, it will certainly be very well worth our inquiry, to examine the causes and reasons of them, and to consider, whether from these causes demonstratively evidenced, may not be deduced the true causes of the production of all kind of Colours. And I the rather now do it, instead of an Appendix or Digression to this History, then upon the occasion of examining the Colours in Peacocks, or other Feathers, because this Subject, as it does afford more variety of particular Colours, so does it afford much better wayes of examining each circumstance. And this will be made manifest to him that considers, first, that this laminated body is more simple and regular then the parts of Peacocks feathers, this consisting only of an indefinite number of plain and smooth Plates, heaped up, or incumbent on each other. Next, that the parts of this body are much more manageable, to be divided or joyned, then the parts of a Peacocks feather, or any other substance that I know. And thirdly, because that in this we are able from a colourless body to produce several coloured bodies, affording all the variety of Colours imaginable: And several others, which the subsequent Inquiry will make manifest.

To begin therefore, it is manifest from several circumstances, that the material cause of the apparition of these several Colours, is some Lamina or Plate of a transparent or pellucid body of a thickness very determinate and proportioned according to the greater or less refractive power of the pellucid body. And that this is so, abundance of Instances and particular Circumstances will make manifest.

As first, if you take any small piece of the Muscovy-glass, and with a Needle, or some other convenient Instrument, cleave it oftentimes into thinner and thinner Laminæ, you shall find, that till you come to a determinate thinness of them, they shall all appear transparent and colourless, but if you continue to split and divide them further, you shall find at last, that each Plate, after it comes to such a determinate thickness, shall appear most lovely ting'd or imbued with a determinate colour. If further, by any means you so flaw a pretty thick piece, that one part does begin to cleave a little from the other, and between those two there be by any means gotten some pellucid medium, those laminated pellucid bodies that fill that space, shall exhibit several Rainbows or coloured Lines, the colours of which will be disposed and ranged according to the various thicknesses of the several parts of that Plate. That this is so, is yet further confirmed by this Experiment.

Take two small pieces of ground and polisht Looking-glass-plate, each about the bigness of a shilling, take these two dry, and with your fore-fingers and thumbs press them very hard and close together, and you shall find, that when they approach each other very near, there will appear several Irises or coloured Lines, in the same manner almost as in the Muscovy-glass; and you may very easily change any of the Colours of any part of the interposed body, by pressing the Plates closer and harder together, or leaving them more lax; that is, a part which appeared coloured with a red, may be presently ting'd with a yellow, blew, green, purple, or the like, by altering the appropinquation of the terminating Plates. Now that air is not necessary to be the interposed body, but that any other transparent fluid will do much the same, may be tryed by wetting those approximated Surfaces with Water, or any other transparent Liquor, and proceeding with it in the same manner as you did with the Air; and you will find much the like effect, only with this difference, that those comprest bodies, which differ most, in their refractive quality, from the compressing bodies, exhibit the most strong and vivid tinctures. Nor is it necessary, that this laminated and ting'd body should be of a fluid substance, any other substance, provided it be thin enough and transparent, doing the same thing: this the Laminæ of our Muscovy-glass hint; but it may be confirm'd by multitudes of other Instances.

And first, we shall find, that even Glass it self may, by the help of a Lamp, be blown thin enough to produce these Phænomena of Colours: which Phænomena accidentally happening, as I have been attempting to frame small Glasses with a Lamp, did not a little surprize me at first, having never heard or seen any thing of it before; though afterwards comparing it with the Phænomena, I had often observed in those Bubbles which Children use to make with Soap-water, I did the less wonder; especially when upon Experiment I found, I was able to produce the same Phænomena in thin Bubbles made with any other transparent Substance. Thus have I produced them with Bubbles of Pitch, Rosin, Colophony, Turpentine, Solutions of several Gums, as Gum-Arabick in water; any glutinous Liquor, as Wort, Wine, Spirit of Wine, Oyl of Turpentine, Glare of Snails, &c.

It would be needless to enumerate the several Instances, these being enough to shew the generality or universality of this propriety. Only I must not omit, that we have instances also of this kind even in metalline Bodies and animal; for those several Colours which are observed to follow each other upon the polisht surface of hardned Steel, when it is by a sufficient degree of heat gradually tempered or softened, are produced, from nothing else but a certain thin Lamina of a vitrum or vitrified part of the Metal, which by that degree of heat, and the concurring action of the ambient Air, is driven out and fixed on the surface of the Steel.

And this hints to me a very probable (at least, if not the true) cause of the hardning and tempering of Steel, which has not, I think, been yet given, nor, that I know of been so much as thought of by any. And that is this, that the hardness of it arises from a greater proportion of a vitrified Substance interspersed through the pores of the Steel. And that the tempering or softning of it arises from the proportionate or smaller parcels of it left within those pores. This will seem the more probable, if we consider these Particulars.

First, That the pure parts of Metals are of themselves very flexible and tuff; that is, will indure bending and hammering, and yet retain their continuity.

Next, That the Parts of all vitrified Substances, as all kinds of Glass, the Scoria of Metals, &c. are very hard, and also very brittle, being neither flexible nor malleable, but may by hammering or beating be broken into small parts or powders.

Thirdly, That all Metals (excepting Gold and Silver, which do not so much with the bare fire, unless assisted by other saline Bodies) do more or less vitrifie by the strength of fire, that is, are corroded by a saline Substance, which I elsewhere shew to be the true cause of fire; and are thereby, as by several other Menstruums converted into Scoria; And this is called, calcining of them, by Chimists. Thus Iron and Copper by heating and quenching do turn all of them by degrees into Scoria, which are evidently vitrified Substances, and unite with Glass, and are easily fusible; and when cold, very hard, and very brittle.

Fourthly, That most kind of Vitrifications or Calcinations are made by Salts, uniting and incorporating with the metalline Particles. Nor do I know any one calcination wherein a Saline body may not, with very great probability, be said to be an agent or coadjutor.

Fifthly, That Iron is converted into Steel by means of the incorporation of certain salts, with which it is kept a certain time in the fire.

Sixthly, That any Iron may, in a very little time, be case hardned, as the Trades-men call it, by casing the iron to be hardned with clay, and putting between the clay and iron a good quantity of a mixture of Urine, Soot, Sea-salt, and Horses hoofs (all which contein great quantities of Saline bodies) and then putting the case into a good strong fire, and keeping it in a considerable degree of heat for a good while, and afterwards heating, and quenching or cooling it suddenly in cold water.

Seventhly, That all kind of vitrify'd substances, by being suddenly cool'd, become very hard and brittle. And thence arises the pretty Phænomena of the Glass Drops, which I have already further explained in its own place.

Eighthly, That those metals which are not so apt to vitrifie, do not acquire any hardness by quenching in water, as Silver, Gold, &c.

These considerations premis'd, will, I suppose, make way for the more easie reception of this following Explication of the Phænomena of hardned and temper'd Steel. That Steel is a substance made out of Iron, by means of a certain proportionate Vitrification of several parts, which are so curiously and proportionately mixt with the more tough and unalter'd parts of the Iron, that when by the great heat of the fire this vitrify'd substance is melted, and consequently rarify'd, and thereby the pores of the Iron are more open, if then by means of dipping it in cold water it be suddenly cold, and the parts hardned, that is, stay'd in that same degree of Expansion they were in when hot, the parts become very hard and brittle, and that upon the same account almost as small parcels of glass quenched in water grow brittle, which we have already explicated. If after this the piece of Steel be held in some convenient heat, till by degrees certain colours appear upon the surface of the brightned metal, the very hard and brittle tone of the metal, by degrees relaxes and becomes much more tough and soft; namely, the action of the heat does by degrees loosen the parts of the Steel that were before streached or set atilt as it were, and stayed open by each other, whereby they become relaxed and set at liberty, whence some of the more brittle interjacent parts are thrust out and melted into a thin skin on the surface of the Steel, which from no colour increases to a deep Purple, and so onward by these gradations or consecutions, White, Yellow, Orange, Minium, Scarlet, Purple, Blew, Watchet, &c. and the parts within are more conveniently, and proportionately mixt; and so they gradually subside into a texture which is much better proportion'd and closer joyn'd, whence that rigidnesse of parts ceases, and the parts begin to acquire their former ductilness.

Now, that 'tis nothing but the vitrify'd metal that sticks upon the surface of the colour'd body, is evident from this, that if by any means it be scraped and rubb'd off, the metal underneath it is white and clear; and if it be kept longer in the fire, so as to increase to a considerable thickness, it may, by blows, be beaten off in flakes. This is further confirm'd by this observable, that that Iron or Steel will keep longer from rusting which is covered with this vitrify'd case: Thus also Lead will, by degrees, be all turn'd into a litharge; for that colour which covers the top being scum'd or shov'd aside, appears to be nothing else but a litharge or vitrify'd Lead.

This is observable also in some sort, on Brass, Copper, Silver, Gold, Tin, but is most conspicuous in Lead: all those Colours that cover the surface of the Metal being nothing else, but a very thin vitrifi'd part of the heated Metal.

The other Instance we have, is in Animal bodies, as in Pearls, Mother of Pearl-shels, Oyster-shels, and almost all other kinds of stony shels whatsoever. This have I also sometimes with pleasure observ'd even in Muscles and Tendons. Further, if you take any glutinous substance and run it exceedingly thin upon the surface of a smooth glass or a polisht metaline body, you shall find the like effects produced: and in general, wheresoever you meet with a transparent body thin enough, that is terminated by reflecting bodies of differing refractions from it, there will be a production of these pleasing and lovely colours.

Nor is it necessary, that the two terminating Bodies should be both of the same kind, as may appear by the vitrified Laminæ on Steel, Lead, and other Metals, one surface of which Laminæ is contiguous to the surface of the Metal, the other to that of the Air.

Nor is it necessary, that these colour'd Laminæ should be of an even thickness, that is, should have their edges and middles of equal thickness, as in a Looking-glass-plate, which circumstance is only requisite to make the Plate appear all of the same colour; but they may resemble a Lens, that is, have their middles thicker then their edges; or else a double concave, that is, be thinner in the middle then at the edges; in both which cases there will be various coloured rings or lines, with differing consecutions or orders of Colours; the order of the first from the middle outwards being Red, Yellow, Green, Blew, &c. And the latter quite contrary.

But further, it is altogether necessary, that the Plate, in the places where the Colours appear, should be of a determinate thickness: First, It must not be more then such a thickness, for when the Plate is increased to such a thickness, the Colours cease; and besides, I have seen in a thin piece of Muscovy-glass, where the two ends of two Plates, which appearing both single, exhibited two distinct and differing Colours; but in that place where they were united, and constituted one double Plate (as I may call it) they appeared transparent and colourless. Nor, Secondly, may the Plates be thinner then such a determinate cize; for we alwayes find, that the very outmost Rim of these flaws is terminated in a white and colourless Ring.

Further, in this Production of Colours there is no need of a determinate Light of such a bigness and no more, nor of a determinate position of that Light, that it should be on this side, and not on that side; nor of a terminating shadow, as in the Prisme, and Rainbow, or Water-ball: for we find, that the Light in the open Air, either in or out of the Sun-beams, and within a Room, either from one or many Windows, produces much the same effect: only where the Light is brightest, there the Colours are most vivid. So does the light of a Candle, collected by a Glass-ball. And further, it is all one whatever side of the coloured Rings be towards the light; for the whole Ring keeps its proper Colours from the middle outwards in the same order as I before related, without varying at all, upon changing the position of the light.

But above all it is most observable, that here are all kind of Colours generated in a pellucid body, where there is properly no such refraction as Des Cartes supposes his Globules to acquire a vertuity by: For in the plain and even Plates it is manifest, that the second refraction (according to Des Cartes his Principles in the fifth section of the eighth Chapter of his Meteors) does regulate and restore the supposed turbinated Globules unto their former uniform motion. This Experiment therefore will prove such a one as our thrice excellent Verulam calls Experimentum Crucis, serving as a Guide or Land-mark, by which to direct our course in the search after the true cause of Colours. Affording us this particular negative Information, that for the production of Colours there is not necessary either a great refraction, as in the Prisme; nor Secondly, a determination of Light and shadow, such as is both in the Prisme and Glass-ball. Now that we may see likewise what affirmative and positive Instruction it yields, it will be necessary, to examine it a little more particularly and strictly; which that we may the better do, it will be requisite to premise somewhat in general concerning the nature of Light and Refraction.

And first for Light it seems very manifest, that there is no luminous Body but has the parts of it in motion more or less.

First, That all kind of fiery burning Bodies have their parts in motion, I think, will be very easily granted me. That the spark struck from a Flint and Steel is in a rapid agitation, I have elsewhere made probable. And that the Parts of rotten Wood, rotten Fish and the like, are also in motion, I think, will as easily be conceded by those, who consider, that those parts never begin to shine till the Bodies be in a state of putrefaction; and that is now generally granted by all, to be caused by the motion of the parts of putrifying bodies. That the Bononian stone shines no longer then it is either warmed by the Sun-beams, or by the flame of a Fire or of a Candle, is the general report of those that write of it, and of others that have seen it. And that heat argues a motion of the internal parts is (as I said before) generally granted.

But there is one Instance more, which was first shewn to the Royal Society by Mr. Clayton a worthy Member thereof, which does make this Assertion more evident then all the rest: And that is, That a Diamond being rub'd, struck or heated in the dark, shines for a pretty while after, so long as that motion, which is imparted by any of those Agents, remains (in the same manner as a Glass, rubb'd, struck, or (by a means which I shall elsewhere mention) heated, yields a sound which lasts as long as the vibrating motion of that sonorous body) several Experiments made on which Stone, are since published in a Discourse of Colours, by the truly honourable Mr. Boyle. What may be said of those Ignes fatui that appear in the night, I cannot so well affirm, having never had the opportunity to examine them my self, nor to be inform'd by any others that had observ'd them: And the relations of them in Authors are so imperfect, that nothing can be built on them. But I hope I shall be able in another place to make it at least very probable, that there is even in those also a Motion which causes this effect. That the shining of Sea-water proceeds from the same cause, may be argued from this, That it shines not till either it be beaten against a Rock, or be some other wayes broken or agitated by Storms, or Oars, or other percussing bodies. And that the Animal Energyes or Spirituous agil parts are very active in Cats eyes when they shine, seems evident enough, because their eyes never shine but when they look very intensly either to find their prey, or being hunted in a dark room, when they seek after their adversary, or to find a way to escape. And the like may be said of the shining Bellies of Gloworms; since 'tis evident they can at pleasure either increase or extinguish that Radiation.

It would be somewhat too long a work for this place Zetetically to examine, and positively to prove, what particular kind of motion it is that must be the efficient of Light; for though it be a motion, yet 'tis not every motion that produces it, since we find there are many bodies very violently mov'd, which yet afford not such an effect; and there are other bodies, which to our other senses, seem not mov'd so much, which yet shine. Thus Water and quick-silver, and most other liquors heated, shine not; and several hard bodies, as Iron, Silver, Brass, Copper, Wood, &c. though very often struck with a hammer, shine not presently, though they will all of them grow exceeding hot; whereas rotten Wood, rotten Fish, Sea water, Gloworms, &c. have nothing of tangible heat in them, and yet (where there is no stronger light to affect the Sensory) they shine some of them so Vividly, that one may make a shift to read by them.

It would be too long, I say, here to insert the discursive progress by which I inquir'd after the proprieties of the motion of Light, and therefore I shall only add the result.

And, First, I found it ought to be exceeding quick, such as those motions of fermentation and putrefaction, whereby, certainly, the parts are exceeding nimbly and violently mov'd; and that, because we find those motions are able more minutely to shatter and divide the body, then the most violent heats menstruums we yet know. And that fire is nothing else but such a dissolution of the Burning body, made by the most universal menstruum of all sulphureous bodies, namely, the Air, we shall in an other place of this Tractate endeavour to make probable. And that, in all extreamly hot shining bodies, there is a very quick motion that causes Light, as well as a more robust that causes Heat, may be argued from the celerity wherewith the bodyes are dissolv'd.

Next, it must be a Vibrative motion. And for this the newly mention'd Diamond affords us a good argument; since if the motion of the parts did not return, the Diamond must after many rubbings decay and be wasted: but we have no reason to suspect the latter, especially if we consider the exceeding difficulty that is found in cutting or wearing away a Diamond. And a Circular motion of the parts is much more improbable, since, if that were granted, and they be suppos'd irregular and Angular parts, I see not how the parts of the Diamond should hold so firmly together, or remain in the same sensible dimensions, which yet they do. Next, if they be Globular, and mov'd only with a turbinated motion, I know not any cause that can impress that motion upon the pellucid medium, which yet is done. Thirdly, any other irregular motion of the parts one amongst another, must necessarily make the body of a fluid consistence, from which it is far enough. It must therefore be a Vibrating motion.

And Thirdly, That it is a very short-vibrating motion, I think the instances drawn from the shining of Diamonds will also make probable. For a Diamond being the hardest body we yet know in the World, and consequently the least apt to yield or bend, must consequently also have its vibrations exceeding short.

And these, I think, are the three principal proprieties of a motion, requisite to produce the effect call'd Light in the Object.

The next thing we are to consider, is the way or manner of the trajection of this motion through the interpos'd pellucid body to the eye: And here it will be easily granted,

First, That it must be a body susceptible and impartible of this motion that will deserve the name of a Transparent. And next, that the parts of such a body must be Homogeneous, or of the same kind. Thirdly, that the constitution and motion of the parts must be such, that the appulse of the luminous body may be communicated or propagated through it to the greatest imaginable distance in the least imaginable time, though I see no reason to affirm, that it must be in an instant: For I know not any one Experiment or observation that does prove it. And, whereas it may be objected, That we see the Sun risen at the very instant when it is above the sensible Horizon, and that we see a Star hidden by the body of the Moon at the same instant, when the Star, the Moon, and our Eye are all in the same line; and the like Observations, or rather suppositions, may be urg'd. I have this to answer, That I can as easily deny as they affirm; for I would fain know by what means any one can be assured any more of the Affirmative, then I of the Negative. If indeed the propagation were very slow, 'tis possible something might be discovered by Eclypses of the Moon; but though we should grant the progress of the light from the Earth to the Moon, and from the Moon back to the Earth again to be full two Minutes in performing, I know not any possible means to discover it; nay, there may be some instances perhaps of Horizontal Eclypses that may seem very much to favour this supposition of the slower progression of Light then most imagine. And the like may be said of the Eclypses of the Sun, &c. But of this only by the by. Fourthly, That the motion is propagated every way through an Homogeneous medium by direct or straight lines extended every way like Rays from the center of a Sphere. Fifthly, in an Homogeneous medium this motion is propagated every way with equal velocity, whence necessarily every pulse or vitration of the luminous body will generate a Sphere, which will continually increase, and grow bigger, just after the same manner (though indefinitely swifter) as the waves or rings on the surface of the water do swell into bigger and bigger circles about a point of it, where, by the sinking of a Stone the motion was begun, whence it necessarily follows, that all the parts of these Spheres undulated through an Homogeneous medium cut the Rays at right angles.

But because all transparent mediums are not Homogeneous to one another, therefore we will next examine how this pulse or motion will be propagated through differingly transparent mediums. And here, according to the most acute and excellent Philosopher Des Cartes, I suppose the sign of the angle of inclination in the first medium to be to the sign of refraction in the second, As the density of the first, to the density of the second. By density, I mean not the density in respect of gravity (with which the refractions or transparency of mediums hold no proportion) but in respect onely to the trajection of the Rays of light, in which respect they only differ in this; that the one propagates the pulse more easily and weakly, the other more slowly, but more strongly. But as for the pulses themselves, they will by the refraction acquire another propriety, which we shall now endeavour to explicate.

We will suppose therefore in the first Figure ACFD to be a physical Ray, or ABC and DEF to be two Mathematical Rays, trajected from a very remote point of a luminous body through an Homogeneous transparent medium LLL, and DA, EB, FC, to be small portions of the orbicular impulses which must therefore cut the Rays at right angles; these Rays meeting with the plain surface NO of a medium that yields an easier transitus to the propagation of light, and falling obliquely on it, they will in the medium MMM be refracted towards the perpendicular of the surface. And because this medium is more easily trajected then the former by a third, therefore the point C of the orbicular pulse FC will be mov'd to H four spaces in the same time that F the other end of it is mov'd to G three spaces, therefore the whole refracted pulse GH shall be oblique to the refracted Rays CHK and GI; and the angle GHC shall be an acute, and so much the more acute by how much the greater the refraction be, then which nothing is more evident, for the sign of the inclination is to the sign of refraction as GF to TC the distance between the point C and the perpendicular from G on CK, which being as four to three, HC being longer then GF is longer also then TC, therefore the angle GHC is less than GTC. So that henceforth the parts of the pulses GH and IK are mov'd ascew, or cut the Rays at oblique angles.

It is not my business in this place to set down the reasons why this or that body should impede the Rays more, others less: as why Water should transmit the Rays more easily, though more weakly than air. Onely thus much in general I shall hint, that I suppose the medium MMM to have less of the transparent undulating subtile matter, and that matter to be less implicated by it, whereas LLL I suppose to contain a greater quantity of the fluid undulating substance, and this to be more implicated with the particles of that medium.

But to proceed, the same kind of obliquity of the Pulses and Rays will happen also when the refraction is made out of a more easie into a more difficult mediū; as by the calculations of GQ & CSR which are refracted from the perpendicular. In both which calculations 'tis obvious to observe, that always that part of the Ray towards which the refraction is made has the end of the orbicular pulse precedent to that of the other side. And always, the oftner the refraction is made the same way, Or the greater the single refraction is, the more is this unequal progress. So that having found this odd propriety to be an inseparable concomitant of a refracted Ray, not streightned by a contrary refraction, we will next examine the refractions of the Sun-beams, as they are suffer'd onely to pass through a small passage, obliquely out of a more difficult, into a more easie medium.

Let us suppose therefore ABC in the second Figure to represent a large Chimical Glass-body about two foot long, filled with very fair Water as high as AB, and inclin'd in a convenient posture with B towards the Sun: Let us further suppose the top of it to be cover'd with an opacous body, all but the hole ab, through which the Sun-beams are suffer'd to pass into the Water, and are thereby refracted to cdef, against which part, if a Paper be expanded on the outside, there will appear all the colours of the Rain-bow, that is, there will be generated the two principal colours, Scarlet and Blue, and all the intermediate ones which arise from the composition and dilutings of these two, that is, cd shall exhibit a Scarlet, which toward d is diluted into a Yellow; this is the refraction of the Ray, ik, which comes from the underside of the Sun; and the Ray ef shall appear of a deep Blue, which is gradually towards e diluted into a pale Watchet-blue. Between d and e the two diluted colours. Blue and Yellow are mixt and compounded into a Green; and this I imagine to be the reason why Green is so acceptable a colour to the eye, and that either of the two extremes are, if intense, rather a little offensive, namely, the being plac'd in the middle between the two extremes, and compounded out of both those, diluted also, or somewhat qualifi'd, for the composition, arising from the mixture of the two extremes undiluted, makes a Purple, which though it be a lovely colour, and pretty acceptable to the eye, yet is it nothing comparable to the ravishing pleasure with which a curious and well tempered Green affects the eye. If removing the Paper, the eye be plac'd against cd, it will perceive the lower side of the Sun (or a Candle at night which is much better, because it offends not the eye, and is more easily manageable) to be of a deep Red, and if against ef it will perceive the upper part of the luminous body to be of a deep Blue; and these colours will appear deeper and deeper, according as the Rays from the luminous body fall more obliquely on the surface of the Water, and thereby suffer a greater refraction, and the more distinct, the further cdef is removed from the trajecting hole.

So that upon the whole, we shall find that the reason of the Phænomena seems to depend upon the obliquity of the orbicular pulse, to the Lines of Radiation, and in particular, that the Ray cd which constitutes the Scarlet has its inner parts, namely those which are next to the middle of the luminous body, precedent to the outermost which are contiguous to the dark and unradiating skie. And that the Ray ef which gives a Blue, has its outward part, namely, that which is contiguous to the dark side precedent to the pulse from the innermost, which borders on the bright area of the luminous body.

We may observe further, that the cause of the diluting of the colours towards the middle, proceeds partly from the wideness of the hole through which the Rays pass, whereby the Rays from several parts of the luminous body, fall upon many of the same parts between c and f as is more manifest by the Figure: And partly also from the nature of the refraction it self, for the vividness or strength of the two terminating colours, arising chiefly as we have seen, from the very great difference that is betwixt the outsides of those oblique undulations & the dark Rays circumambient, and that disparity betwixt the approximate Rays, decaying gradually: the further inward toward the middle of the luminous body they are remov'd, the more must the colour approach to a white or an undisturbed light.

Upon the calculation of the refraction and reflection from a Ball of Water or Glass, we have much the same Phænomena, namely, an obliquity of the undulation in the same manner as we have found it here. Which, because it is very much to our present purpose, and affords such an Instancia crucis, as no one that I know has hitherto taken notice of, I shall further examine. For it does very plainly and positively distinguish, and shew, which of the two Hypotheses, either the Cartesian or this is to be followed, by affording a generation of all the colors in the Rainbow, where according to the Cartesian Principles there should be none at all generated. And secondly, by affording an instance that does more closely confine the cause of these Phænomena of colours to this present Hypothesis.

And first, for the Cartesian, we have this to object against it, That whereas he says (Meteorum Cap. 8. Sect. 5.) Sed judicabam unicam (refractione scilicet) ad minimū requiri, & quidem talem ut ejus effectus aliâ contrariâ (refractione) non destruatur: Nam experientia docet si superficies NM & NP (nempe refringentes) Parallelæ forent, radios tantundem per alteram iterum erectos quantum per unam frangerentur, nullos colores depicturos; This Principle of his holds true indeed in a prisme where the refracting surfaces are plain, but is contradicted by the Ball or Cylinder, whether of Water Or Glass, where the refracting surfaces are Orbicular or Cylindrical. For if we examine the passage of any Globule or Ray of the primary Iris, we shall find it to pass out of the Ball or Cylinder again, with the same inclination and refraction that it enter'd in withall, and that that last refraction by means of the intermediate reflection shall be the same as if without any reflection at all the Ray had been twice refracted by two Parallel surfaces.

And that this is true, not onely in one, but in every Ray that goes to the constitution of the Primary Iris; nay, in every Ray, that suffers only two refractions, and one reflection, by the surface of the round body, we shall presently see most evident, if we repeat the Cartesian Scheme, mentioned in the tenth Section of the eighth Schem. 6.
Fig. 3. Chapter of his Meteors, where EFKNP in the third Figure is one of the Rays of the Primary Iris, twice refracted at F and N, and once reflected at K by the surface of the Water-ball. For, first it is evident, that KF and KN are equal, because KN being the reflected part of KF they have both the same inclination on the surface K that is the angles FKT, and NKV made by the two Rays and the Tangent of K are equal, which is evident by the Laws of reflection; whence it will follow also, that KN has the same inclination on the surface N, or the Tangent of it XN that the Ray KF has to the surface F, or the Tangent of it FY, whence it must necessarily follow, that the refractions at F and N are equal, that is, KFE and KNP are equal. Now, that the surface N is by the reflection at K made parallel to the surface at F, is evident from the principles of reflection; for reflection being nothing but an inverting of the Rays, if we re-invert the Ray KNP, and make the same inclinations below the line TKV that it has above, it will be most evident, that KH the inverse of KN will be the continuation of the line FK, and that LHI the inverse of OX is parallel to FY. And HM the inverse of NP is Parallel to EF for the angle KHI is equal to KNO which is equal to KFY, and the angle KHM is equal to KNP which is equal to KFE which was to be prov'd.

So that according to the above mentioned Cartesian principles there should be generated no colour at all in a Ball of Water or Glass by two refractions and one reflection, which does hold most true indeed, if the surfaces be plain, as may be experimented with any kind of prisme where the two refracting surfaces are equally inclin'd to the reflecting; but in this the Phænomena are quite otherwise.

The cause therefore of the generation of colour must not be what Des Cartes assigns, namely, a certain rotation of the Globuli ætherei, which are the particles which he supposes to constitute the Pellucid medium, But somewhat else, perhaps what we have lately supposed, and shall by and by further prosecute and explain.

But, First I shall crave leave to propound some other difficulties of his, notwithstanding exceedingly ingenious Hypothesis, which I plainly confess to me seem such; and those are,

First, if that light be (as is affirmed, Diopt. cap. 1. §. 8.) not so properly a motion, as an action or propension to motion, I cannot conceive how the eye can come to be sensible of the verticity of a Globule, which is generated in a drop of Rain, perhaps a mile off from it. For that Globule is not carry'd to the eye according to his formerly recited Principle; and if not so, I cannot conceive how it can communicate its rotation, or circular motion to the line of the Globules between the drop and the eye. It cannot be by means of every ones turning the next before him; for if so, then onely all the Globules that are in the odd places must be turned the same way with the first, namely, the 3. 5. 7. 9. 11, &c. but all the Globules interposited between them in the even places; namely, the 2. 4. 6. 8. 10. &c. must be the quite contrary, whence, according to the Cartesian Hypothesis, there must be no distinct colour generated, but a confusion. Next, since the Cartesian Globuli are suppos'd (Principiorum Philosoph. Part. 3. §. 86.) to be each of them continually in motion about their centers, I cannot conceive how the eye is able to distinguish this new generated motion from their former inherent one, if I may so call that other wherewith they are mov'd or turbinated, from some other cause than refraction. And thirdly, I cannot conceive how these motions should not happen sometimes to oppose each other, and then, in stead of a rotation, there would be nothing but a direct motion generated, and consequently no colour. And fourthly, I cannot conceive, how by the Cartesian Hypothesis it is possible to give any plausible reason of the nature of the Colours generated in the thin laminæ of these our Microscopical Observations; for in many of these, the refracting and reflecting surfaces are parallel to each other, and consequently no rotation can be generated, nor is there any necessity of a shadow or termination of the bright Rays, such as is suppos'd (Chap. 8. §. 5. Et præterea observavi umbram quoque, aut limitationem luminis requiri: and Chap. 8. §. 9.) to be necessary to the generation of any distinct colours; Besides that, here is oftentimes one colour generated without any of the other appendant ones, which cannot be by the Cartesian Hypothesis.

There must be therefore some other propriety of refraction that causes colour. And upon the examination of the thing, I cannot conceive any one more general, inseparable, and sufficient, than that which I have before assign'd. That we may therefore see how exactly our Hypothesis agrees also with the Phænomena of the refracting round body, whether Globe or Cylinder, we shall next subjoyn our Calculation or Examen of it.

And to this end, we will calculate any two Rays: as for instance; let EF be a Ray cutting the Radius CD (divided into 20. parts) in G 16. parts distant from C, and ef another Ray, which cuts the same Radius in g 17. parts distant, these will be refracted to K and k, and from thence reflected to N and n, and from thence refracted toward P and p; therefore the Arch Ff will be 5.^d 5'. The Arch FK 106.^d 30'. the Arch fk 101.^d 2'. The line FG 6000. and fg 5267. therefore hf. 733. therefore Fc 980, almost. The line FK 16024. and fk 15436. therefore Nd 196. and no 147 almost, the line Nn 1019 the Arch Nn 5.^d 51'. therefore the Angle Nno is 34.^d 43'. therefore the Angle Non is 139.^d 56'. which is almost 50.^d more than a right Angle.

It is evident therefore by this Hypothesis, that at the same time that ef touches f. EF is arrived at c. And by that time efkn is got to n, EFKN is got to d and when it touches N, the pulse of the other Ray is got to o. and no farther, which is very short of the place it should have arriv'd to, to make the Ray np to cut the orbicular pulse No at right Angles: therefore the Angle Nop is an acute Angle, but the quite contrary of this will happen, if 17. and 18. be calculated in stead of 16. and 17. both which does most exactly agree with the Phænomena: For if the Sun, or a Candle (which is better) be placed about Ee, and the eye about Pp, the Rays EFef at 16. and 17. will paint the side of the luminous object toward np Blue, and towards NP Red. But the quite contrary will happen when EF is 17. and ef 18. for then towards NP shall be a Blue, and towards np a Red, exactly according to the calculation. And there appears the Blue of the Rainbow, where the two Blue sides of the two Images unite, and there the Red where the two Red sides unite, that is, where the two Images are just disappearing; which is, when the Rays EF and NP produc'd till they meet, make an Angle of about 41. and an half; the like union is there of the two Images in the Production of the Secundary Iris, and the same causes, as upon calculation may appear; onely with this difference, that it is somewhat more faint, by reason of the duplicate reflection, which does always weaken the impulse the oftner it is repeated.

Now, though the second refraction made at Nn be convenient, that is, do make the Rays glance the more, yet is it not altogether requisite; for it is plain from the calculation, that the pulse dn is sufficiently oblique to the Rays KN and kn, as wel as the pulse fc is oblique to the Rays FK & fk. And therefore if a piece of very fine Paper be held close against Nn and the eye look on it either through the Ball as from D, or from the other side, as from B. there shall appear a Rainbow, or colour'd line painted on it with the part toward X appearing Red, towards O, Blue; the same also shall happen, if the Paper be placed about Kk, for towards T shall appear a Red, and towards V a Blue, which does exactly agree with this my Hypothesis, as upon the calculation of the progress of the pulse will most easily appear.

Nor do these two observations of the colours appearing to the eye about p differing from what they appear on the Paper at N contradict each other; but rather confirm and exactly agree with one another, as will be evident to him that examines the reasons set down by the ingenious. Des Cartes in the 12. Sect. of the 8. Chapter of his Meteors, where he gives the true reason why the colours appear of a quite contrary order to the eye, to what they appear'd on the Paper if the eye be plac'd in steed of the Paper: And as in the Prisme, so also in the Water-drop, or Globe the Phænomena, and reason are much the same.

Having therefore shewn that there is such a propriety in the prisme and water Globule whereby the pulse is made oblique to the progressive, and that so much the more, by how much greater the refraction is, I shall in the next place consider, how this conduces to the production of colours, and what kind of impression it makes upon the bottom of the eye; and to this end it will be requisite to examine this Hypothesis a little more particularly.

First therefore, if we consider the manner of the progress of the pulse, it will seem rational to conclude, that that part or end of the pulse which precedes the other, must necessarily be somwhat more obtunded, or impeded by the resistance of the transparent medium, than the other part or end of it which is subsequent, whose way is, as it were, prepared by the other; especially if the adjacent medium be not in the same manner Schem. 6.
Fig. 4. enlightned or agitated. And therefore (in the fourth Figure of the sixth Iconism) the Ray AAAHB will have its side HH more deadned by the resistance of the dark or quiet medium PPP, Whence there will be a kind of deadness superinduc'd on the side HHH, which will continually increase from B, and strike deeper and deeper into the Ray by the line BR; Whence all the parts of the triangle, RBHO will be of a dead Blue colour, and so much the deeper, by how much the nearer they lie to the line BHH, which is most deaded or impeded, and so much the more dilute, by how much the nearer it approaches the line BR. Next on the other side of the Ray AAN, the end A of the pulse AH will be promoted, or made stronger, having its passage already prepar'd as 'twere by the other parts preceding, and so its impression wil be stronger; And because of its obliquity to the Ray, there will be propagated a kind of faint motion into QQ the adjacent dark or quiet medium, which faint motion will spread further and further into QQ as the Ray is propagated further and further from A, namely, as far as the line MA, whence all the triangle MAN will be ting'd with a Red, and that Red will be the deeper the nearer it approaches the line MA, and the paler or yellower the nearer it is the line NA. And if the Ray be continued, so that the lines AN and BR (which are the bounds of the Red and Blue diluted) do meet and cross each other, there will be beyond that intersection generated all kinds of Greens.

Now, these being the proprieties of every single refracted Ray of light, it will be easie enough to consider what must be the result of very many such Rays collateral: As if we suppose infinite such Rays interjacent between AKSB and ANOB, which arc the terminating: For in this case the Ray AKSB will have its Red triangle intire, as lying next to the dark or quiet medium, but the other side of it BS will have no Blue, because the medium adjacent to it SBO, is mov'd or enlightned, and consequently that light does destroy the colour. So likewise will the Ray ANOB lose its Red, because the adjacent medium is mov'd or enlightned, but the other side of the Ray that is adjacent to the dark, namely, AHO will preserve its Blue entire, and these Rays must be so far produc'd as till AN and BR cut each other, before there will be any Green produc'd. From these Proprieties well consider'd, may be deduc'd the reasons of all the Phænomena of the prisme, and of the Globules or drops of Water which conduce to the production of the Rainbow.

Next for the impression they make on the Retina, we will further examine this Hypothesis: Suppose therefore ABCDEF, in the fifth Figure, to represent the Ball of the eye: on the Cornea of which ABC two Rays GACH and KCAI (which are the terminating Rays of a luminous body) falling, are by the refraction thereof collected or converg'd into two points at the bottom of the eye. Now, because these terminating Rays, and all the intermediate ones which come from any part of the luminous body, are suppos'd by some sufficient refraction before they enter the eye, to have their pulses made oblique to their progression, and consequently each Ray to have potentially superinduc'd two proprieties, or colours, viz., a Red on the one side, and a Blue on the other, which notwithstanding are never actually manifest, but when this or that Ray has the one or the other side of it bordering on a dark or unmov'd medium, therefore as soon as these Rays are entred into the eye and so have one side of each of them bordering on a dark part of the humours of the eye, they will each of them actually exhibit some colour; therefore ADC the production of GACH will exhibit a Blue, because the side CD is adjacent to the dark medium CQDC, but nothing of a Red, because its side AD is adjacent to the enlightned medium ADFA: And all the Rays that from the points of the luminous body are collected on the parts of the Retina between D and F shall have their Blue so much the more diluted by how much the farther these points of collection are distant from D towards F; and the Ray AFC the production of KCAI, will exhibit a Red, because the side AF is adjacent to the dark or quiet medium of the eye APFA, but nothing of a Blue, because its side CF is adjacent to the enlightned medium CFDC, and all the Rays from the intermediate parts of the luminous body that are collected between F and D shall have their Red so much the more diluted, by how much the farther they are distant from F towards D.

Now, because by the refraction in the Cornea, and some other parts of the eye, the sides of each Ray, which before were almost parallel, are made to converge and meet in a point at the bottom of the eye, therefore that side of the pulse which preceded before these refractions, shall first touch the Retina, and the other side last. And therefore according as this or that side, or end of the pulse shall be impeded, accordingly will the impressions on the Retina be varied; therefore by the Ray GACH refracted by the Cornea to D there shall be on that point a stroke or impression confus'd, whose weakest end, namely, that by the line CD shall precede, and the stronger, namely, that by the line AD shall follow. And by the Ray KCAI refracted to F, there shall be on that part a confus'd stroke or impression, whose strongest part, namely, that by the line CF shal precede, and whose weakest or impeded, namely, that by the line AF shall follow, and all the intermediate points between F and D will receive impressions from the converg'd Rays so much the more like the impressions on F and D by how much the nearer they approach that or this.

From the consideration of the proprieties of which impressions, we may collect these short definitions of Colours: That Blue is an impression on the Retina of an oblique and confus'd pulse of light, whose weakest part precedes, and whose strongest follows. And, that Red is an impression on the Retina of an oblique and confus'd pulse of light, whose strongest part precedes, and whose weakest follows.

Which proprieties, as they have been already manifested, in the Prisme and falling drops of Rain, to be the causes of the colours there generated, may be easily found to be the efficients also of the colours appearing in thin laminated transparent bodies; for the explication of which, all this has been premised.

And that this is so, a little closer examination of the Phænomena and the Figure of the body, by this Hypothesis will make evident.

For first (as we have already observed) the laminated body must be of a determinate thickness, that is, it must not be thinner then such a determinate quantity; for I have always observ'd, that neer the edges of those which are exceeding thin, the colours disappear, and the part grows white; nor must it be thicker then another determinate quantity; for I have likewise observ'd, that beyond such a thickness, no colours appear'd, but the Plate looked white, between which two determinate thicknesses were all the colour'd Rings; of which in some substances I have found ten or twelve, in others not half so many, which I suppose depends much upon the transparency of the laminated body. Thus though the consecutions are the same in the scumm or the skin on the top of metals; yet in those consecutions in the same colour is not so often repeated as in the consecutions in thin Glass, or in Sope-water, or any other more transparent and glutinous liquor; for in these I have observ'd, Red, Yellow, Green, Blue, Purple; Red, Yellow, Green, Blue, Purple; Red, Yellow, Green, Blue, Purple; Red, Yellow, &c. to succeed each other, ten or twelve times, but in the other more opacous bodies the consecutions will not be half so many.

And therefore secondly, the laminated body must be transparent, and this I argue from this, that I have not been able to produce any colour at all with an opacous body, though never so thin. And this I have often try'd, by pressing small Globule of Mercury between two smooth Plates of Glass, whereby I have reduc'd that body to a much greater thinness then was requisite to exhibit the colours with a transparent body.

Thirdly, there must be a considerable reflecting body adjacent to the under or further side of the lamina or plate: for this I always found, that the greater that reflection was, the more vivid were the appearing colours.

From which Observations, is most evident, that the reflection from the under or further side of the body is the principal cause of the production of these colours; which, that it is so, and how it conduces to that effect, I shall further explain in the following Figure, which is here described of a very great thickness, as if it had been view'd through the Microscope; and 'tis indeed much thicker than any Microscope (I have yet us'd) has been able to shew me those colour'd plates of Glass, or Muscovie-glass, which I have not without much trouble view'd with it, for though I have endeavoured to magnifie them as much as the Glasses were capable of, yet are they so exceeding thin, that I have not hitherto been able positively to determine their thickness. This Figure therefore I here represent, is wholy Hypothetical.

Let ABCDHFE in the sixth Figure be a frustum of Muscovy-glass, thinner toward the end AE, and thicker towards DF. Let us first suppose the Ray aghb coming from the Sun, of some remote luminous object to fall obliquely on the thinner plate BAE, part therefore is reflected back by cghd, the first Superficies; whereby the perpendicular pulse ab is after reflexion propagated by cd, cd, equally remote from each other with ab, ab, so that ag + gc, or bh + hd are either of them equal to aa, as is also cc, but the body BAE being transparent, a part of the light of this Ray is refracted in the surface AB, and propagated by gikh to the surface EF, whence it is reflected and refracted again by the surface AB. So that after two refractions and one reflection, there is propagated a kind of fainter Ray emnf, whose pulse is not only weaker by reason of the two refractions in the surface AB, but by reason of the time spent in passing and repassing between the two surfaces AB and EF, ef which is this fainter or weaker pulse comes behind the pulse cd; so that hereby (the surfaces AB, and EF being so neer together, that the eye cannot discriminate them from one) this confus'd or duplicated pulse, whose strongest part precedes, and whose weakest follows, does produce on the Retina, (or the optick nerve that covers the bottom of the eye) the sensation of a Yellow.

And secondly, this Yellow will appear so much the deeper, by how much the further back towards the middle between cd and cd the spurious pulse ef is remov'd, as in 2 where the surface BC being further remov'd from EF, the weaker pulse ef will be nearer to the middle, and will make an impression on the eye of a Red.

But thirdly, if the two reflecting surfaces be yet further remov'd asunder (as in 3 CD and EF are) then will the weaker pulse be so farr behind, that it will be more then half the distance between cd and cd. And in this case it will rather seem to precede the following stronger pulse, then to follow the preceding one, and consequently a Blue will be generated. And when the weaker pulse is just in the middle between two strong ones, then is a deep and lovely Purple generated; but when the weaker pulse ef is very neer to cd, then is there generated a Green, which will be bluer, or yellower, according as the approximate weak pulse does precede or follow the stronger.

Now fourthly, if the thicker Plate chance to be cleft into two thinner Plates, as CDFE is divided into two Plates by the surface GH then from the composition arising from the three reflections in the surfaces CD, GH, and EF, there will be generated several compounded or mixt colours, which will be very differing, according as the proportion between the thicknesses of those two divided Plates CDHG, and GHFE are varied.

And fifthly, if these surfaces CD and FE are further remov'd asunder, the weaker pulse will yet lagg behind much further, and not onely be coincident with the second, cd, but lagg behind that also, and that so much the more, by how much the thicker the Plate be; so that by degrees it will be coincident with the third cd backward also, and by degrees, as the Plate grows thicker with a fourth, and so onward to a fifth, sixth, seventh, or eighth; so that if there be a thin transparent body, that from the greatest thinness requisite to produce colours, does, in the manner of a Wedge, by degrees grow to the greatest thickness that a Plate can be of, to exhibit a colour by the reflection of Light from such a body, there shall be generated several consecutions of colours, whose order from the thin end towards the thick, shall be Yellow, Red, Purple, Blue, Green; Yellow, Red, Purple, Blue, Green; Yellow, Red, Purple, Blue, Green; Yellow, &c. and these so often repeated, as the weaker pulse does lose paces with its Primary, or first pulse, and is coincident with a second, third, fourth, fifth, sixth, &c. pulse behind the first. And this, as it is coincident, or follows from the first Hypothesis I took of colours, so upon experiment have I found it in multitudes of instances that seem to prove it. One thing which seems of the greatest concern in this Hypothesis, is to determine the greatest or least thickness requisite for these effects, which, though I have not been wanting in attempting, yet so exceeding thin are these coloured Plates, and so imperfect our Microscope, that I have not been hitherto successfull, though if my endeavours shall answer my expectations, I shall hope to gratifie the curious Reader with some things more remov'd beyond our reach hitherto.

Thus have I, with as much brevity as I was able, endeavoured to explicate (Hypothetically at least) the causes of the Phænomena I formerly recited, on the consideration of which I have been the more particular.

First, because I think these I have newly given are capable of explicating all the Phænomena of colours, not onely of those appearing in the Prisme, Water-drop, or Rainbow, and in laminated or plated bodies, but of all that are in the world, whether they be fluid or solid bodies, whether in thick or thin, whether transparent, or seemingly opacous, as I shall in the next Observation further endeavour to shew. And secondly, because this being one of the two ornaments of all bodies discoverable by the sight, whether looked on with, or without a Microscope, it seem'd to deserve (somewhere in this Tract, which contains a description of the Figure and Colour of some minute bodies) to be somewhat the more intimately enquir'd into.

Observ. X. Of Metalline, and other real Colours.

Having in the former Discourse, from the Fundamental cause of Colour, made it probable, that there are but two Colours, and shewn, that the Phantasm of Colour is caus'd by the sensation of the oblique or uneven pulse of Light which is capable of no more varieties than two that arise from the two sides of the oblique pulse, though each of those be capable of infinite gradations or degrees (each of them beginning from White, and ending the one in the deepest Scarlet or Yellow, the other in the deepest Blue) I shall in this Section set down some Observations which I have made of other colours, such as Metalline powders tinging or colour'd bodies and several kinds of tinctures or ting'd liquors, all which, together with those I treated of in the former Observation will, I suppose, comprise the several subjects in which colour is observ'd to be inherent, and the several manners by which it inheres, or is apparent in them. And here I shall endeavour to shew by what composition all kind of compound colours are made, and how there is no colour in the world but may be made from the various degrees of these two colours, together with the intermixtures of Black and White.

And this being so, as I shall anon shew, it seems an evident argument to me, that all colours whatsoever, whether in fluid or solid, whether in very transparent or seemingly opacous, have the same efficient cause, to wit, some kind of refraction whereby the Rays that proceed from such bodies, have their pulse obliquated or confus'd in the manner I explicated in the former Section; that is, a Red is caus'd by a duplicated or confus'd pulse, whose strongest pulse precedes, and a weaker follows: and a Blue is caus'd by a confus'd pulse, where the weaker pulse precedes, and the stronger follows. And according as these are, more or less, or variously mixt and compounded, so are the sensations, and consequently the phantasms of colours diversified.

To proceed therefore; I suppose, that all transparent colour'd bodies, whether fluid or solid, do consist at least of two parts, or two kinds of substances, the one of a substance of a somewhat differing refraction from the other. That one of these substances which may be call'd the tinging substance, does consist of distinct parts, or particles of a determinate bigness which are disseminated, or dispers'd all over the other: That these particles, if the body be equally and uniformly colour'd, are evenly rang'd and dispers'd over the other contiguous body; That where the body is deepest ting'd, there these particles are rang'd thickest, and where 'tis but faintly ting'd, they are rang'd much thinner, but uniformly. That by the mixture of another body that unites with either of these, which has a differing refraction from either of the other, quite differing effects will be produc'd, that is, the consecutions of the confus'd pulses will be much of another kind, and consequently produce other sensations and phantasms of colours, and from a Red may turn to a Blue, or from a Blue to a Red, &c.

Now, that this may be the better understood, I shall endeavour to Schem. 6.
Fig. 7. explain my meaning a little more sensible by a Scheme: Suppose we therefore in the seventh Figure of the sixth Scheme, that ABCD represents a Vessel holding a ting'd liquor, let IIIII, &c. be the clear liquor, and let the tinging body that is mixt with it be EE, &c. FF, &c. GG, &c. HH, &c. whose particles (whether round, or some other determinate Figure is little to our purpose) are first of a determinate and equal bulk. Next, they are rang'd into the form of Quincunx, or Equilaterotriangular order, which that probably they are so, and why they are so, I shall elsewhere endeavour to shew. Thirdly, they are of such a nature, as does either more easily or more difficultly transmit the Rays of light then the liquor; if more easily, a Blue is generated, and if more difficultly, a Red or Scarlet.

And first, let us suppose the tinging particles to be of a substance that does more impede the Rays of light, we shall find that the pulse or wave of light mov'd from AD to BC, will proceed on, through the containing medium by the pulses or waves KK, LL, MM, NN, OO; but because several of these Rays that go to the constitution of these pulses will be slugged or stopped by the tinging particles E, F, G, H; therefore there shall be secundary and weak pulse that shall follow the Ray, namely PP which will be the weaker: first, because it has suffer'd many refractions in the impeding body; next, for that the Rays will be a little dispers'd or confus'd by reason of the refraction in each of the particles, whether round or angular; and this will be more evident, if we a little more closely examine any one particular tinging Globule.

Suppose we therefore AB in the eighth Figure of the sixth Scheme, to represent a tinging Globule or particle which has a greater refraction than the liquor in which it is contain'd: Let CD be a part of the pulse of light which is propagated through the containing medium; this pulse will be a little stopt or impeded by the Globule, and so by that time the pulse is past to EF that part of it which has been impeded by passing through the Globule, will get but to LM, and so that pulse which has been propagated through the Globule, to wit, LM, NO, PQ, will always come behind the pulses EF, GH, IK, &c.

Next, by reason of the greater impediment in AB, and its Globular Figure, the Rays that pass through it will be dispers'd, and very much scatter'd. Whence CA and DB which before went direct and parallel, will after the refraction in AB, diverge and spread by AP, and BQ; so that as the Rays do meet with more and more of these tinging particles in their way, by so much the more will the pulse of light further lagg behind the clearer pulse, or that which has fewer refractions, and thence the deeper will the colour be, and the fainter the light that is trajected through it; for not onely many Rays are reflected from the surfaces of AB, but those Rays that get through it are very much disordered.

By this Hypothesis there is no one experiment of colour that I have yet met with, but may be, I conceive, very rationably solv'd, and perhaps, had I time to examine several particulars requisite to the demonstration of it, I might prove it more than probable, for all the experiments about the changes and mixings of colours related in the Treatise of Colours, published by the Incomparable Mr. Boyle, and multitudes of others which I have observ'd, do so easily and naturally flow from those principles, that I am very apt to think it probable, that they own their production to no other secundary cause: As to instance in two or three experiments. In the twentieth Experiment, this Noble Authour has shewn that the deep bluish purple-colour of Violets, may be turn'd into a Green, by Alcalizate Salts, and to a Red by acid; that is, a Purple consists of two colours, a deep Red, and a deep Blue; when the Blue is diluted, or altered, or destroy'd by acid Salts, the Red becomes predominant, but when the Red is diluted by Alcalizate, and the Blue heightned, there is generated a Green; for of a Red diluted, is made a Yellow, and Yellow and Blue make a Green.

Now, because the spurious pulses which cause a Red and a Blue, do the one follow the clear pulse, and the other precede it, it usually follows, that those Saline refracting bodies which do dilute the colour of the one, do deepen that of the other. And this will be made manifest by almost all kinds of Purples, and many sorts of Greens, both these colours consisting of mixt colours; for if we suppose A and A in the ninth Figure, to represent two pulses of clear light, which follow each other at a convenient distance, AA, each of which has a spurious pulse preceding it, as BB, which makes a Blue, and another following it, as CC, which makes a Red, the one caus'd by tinging particles that have a greater refraction, the other by others that have a less refracting quality then the liquor or Menstruum in which these are dissolv'd, whatsoever liquor does so alter the refraction of the one, without altering that of the other part of the ting'd liquor, must needs very much alter the colour of the liquor; for if the refraction of the dissolvent be increas'd, and the refraction of the tinging particles not altered, then will the preceding spurious pulse be shortned or stopt, and not out-run the clear pulse so much; so that BB will become EE, and the Blue be diluted, whereas the other spurious pulse which follows will be made to lagg much more, and be further behind AA than before, and CC will become ff, and so the Yellow or Red will be heightned.

A Saline liquor therefore, mixt with another ting'd liquor, may alter the colour of it several ways, either by altering the refraction of the liquor in which the colour swims: or secondly by varying the refraction of the coloured particles, by uniting more intimately either with some particular corpuscles of the tinging body, or with all of them, according as it has a congruity to some more especially, or to all alike: or thirdly, by uniting and interweaving it self with some other body that is already joyn'd with the tinging particles, with which substance it may have a congruity, though it have very little with the particles themselves: or fourthly, it may alter the colour of a ting'd liquor by dis-joyning certain particles which were before united with the tinging particles, which though they were somewhat congruous to these particles, have yet a greater congruity with the newly infus'd Saline menstruum. It may likewise alter the colour by further dissolving the tinging substance into smaller and smaller particles, and so diluting the colour; or by uniting several particles together as in precipitations, and so deepning it, and some such other ways, which many experiments and comparisons of differing trials together, might easily inform one of.

From these Principles applied, may be made out all the varieties of colours observable, either in liquors, or any other ting'd bodies, with great ease, and I hope intelligible enough, there being nothing in the notion of colour, or in the suppos'd production, but is very conceivable, and may be possible.

The greatest difficulty that I find against this Hypothesis, is, that there seem to be more distinct colours then two, that is, then Yellow and Blue. This Objection is grounded on this reason, that there are several Reds, which diluted, make not a Saffron or pale Yellow, and therefore Red, or Scarlet seems to be a third colour distinct from a deep degree of Yellow.

To which I answer, that Saffron affords us a deep Scarlet tincture, which may be diluted into as pale a Yellow as any, either by making a weak solution of the Saffron, by infusing a small parcel of it into a great quantity of liquor, as in spirit of Wine, or else by looking through a very thin quantity of the tincture, and which may be heightn'd into the loveliest Scarlet, by looking through a very thick body of this tincture, or through a thinner parcel of it, which is highly impregnated with the tinging body, by having had a greater quantity of the Saffron dissolv'd in a smaller parcel of the liquor.

Now, though there may be some particles of other tinging bodies that give a lovely Scarlet also, which though diluted never so much with liquor, or looked on through never so thin a parcel of ting'd liquor, will not yet afford a pale Yellow, but onely a kind of faint Red; yet this is no argument but that those ting'd particles may have in them the faintest degree of Yellow, though we may be unable to make them exhibit it; For that power of being diluted depending upon the divisibility of the ting'd body, if I am unable to make the tinging particles so thin as to exhibit that colour, it does not therefore follow, that the thing is impossible to be done; now, the tinging particles of some bodies are of such a nature, that unless there be found some way of comminuting them into less bulks then the liquor does dissolve them into, all the Rays that pass through them must necessarily receive a tincture so deep, as their appropriate refractions and bulks compar'd with the proprieties of the dissolving liquor must necessarily dispose them to empress, which may perhaps be a pretty deep Yellow, or pale Red.

And that this is not gratis dictum, I shall add one instance of this kind, wherein the thing is most manifest.

If you take Blue Smalt, you shall find, that to afford the deepest Blue, which cæteris paribus has the greatest particles or sands; and if you further divide, or grind those particles on a Grindstone, or porphyry stone, you may by comminuting the sands of it, dilute the Blue into as pale a one as you please, which you cannot do by laying the colour thin; for wheresoever any single particle is, it exhibits as deep a Blue as the whole mass. Now, there are other Blues, which though never so much ground, will not be diluted by grinding, because consisting of very small particles, very deeply ting'd, they cannot by grinding be actually separated into smaller particles then the operation of the fire, or some other dissolving menstruum, reduc'd them to already.

Thus all kind of Metalline colours, whether precipitated, sublim'd, calcin'd, or otherwise prepar'd, are hardly chang'd by grinding, as ultra marine is not more diluted; nor is Vermilion or Red-lead made of a more faint colour by grinding; for the smallest particles of these which I have view'd with my greatest Magnifying-Glass, if they be well enlightned, appear very deeply ting'd with their peculiar colours; nor, though I have magnified and enlightned the particles exceedingly, could I in many of them, perceive them to be transparent, or to be whole particles, but the smallest specks that I could find among well ground Vermilion and Red-lead, seem'd to be a Red mass, compounded of a multitude of less and less motes, which sticking together, compos'd a bulk, not one thousand thousandth part of the smallest visible sand or mote.

And this I find generally in most Metalline colours, that though they consist of parts so exceedingly small, yet are they very deeply ting'd, they being so ponderous, and having such a multitude of terrestrial particles throng'd into a little room; so that 'tis difficult to find any particle transparent or resembling a pretious stone, though not impossible; for I have observ'd divers such shining and resplendent colours intermixt with the particles of Cinnaber, both natural and artificial, before it hath been ground and broken or flaw'd into Vermilion: As I have also in Orpiment, Red-lead, and Bise, which makes me suppose, that those metalline colours are by grinding, not onely broken and separated actually into smaller pieces, but that they are also flaw'd and brused, whence they, for the most part, become opacous, like flaw'd Crystal or Glass, &c. But for Smalts and verditures, I have been able with a Microscope to perceive their particles very many of them transparent.

Now, that the others also may be transparent, though they do not appear so to the Microscope, may be made probable by this Experiment: that if you take ammel that is almost opacous, and grind it very well on a Porphyry, or Serpentine, the small particles will by reason of their flaws, appear perfectly opacous; and that 'tis the flaws that produce this opacousness, may be argued from this, that particles of the same Ammel much thicker if unflaw'd will appear somewhat transparent even to the eye; and from this also, that the most transparent and clear Crystal, if heated in the fire, and then suddenly quenched, so that it be all over flaw'd, will appear opacous and white.

And that the particles of Metalline colours are transparent, may be argued yet further from this, that the Crystals, or Vitriols of all Metals, are transparent, which since they consist of metalline as well as saline particles, those metalline ones must be transparent, which is yet further confirm'd from this, that they have for the most part, appropriate colours; so the vitriol of Gold is Yellow; of Copper, Blue, and sometimes Green; of Iron, green; of Tinn and Lead, a pale White; of Silver, a pale Blue, &.

And next, the Solution of all Metals into menstruums are much the same with the Vitriols, or Crystals. It seems therefore very probable, that those colours which are made by the precipitation of those particles out of the menstruums by transparent precipitating liquors should be transparent also. Thus Gold precipitates with oyl of Tartar, or spirit of Urine into a brown Yellow, Copper with spirit of Urine into a Mucous blue, which retains its transparency. A solution of sublimate (as the same Illustrious Authour I lately mention'd shews in his 40. Experiment) precipitates with oyl of Tartar per deliquium, into an Orange colour'd precipitate; nor is it less probable, that the calcination of those Vitriols by the fire, should have their particles transparent: Thus Saccarum Saturni, or the Vitriol of Lead by calcination becomes a deep Orange-colour'd minium, which is a kind of precipitation by some Salt which proceeds from the fire; common Vitriol calcin'd, yields a deep Brown Red, etc.

A third Argument, that the particles of Metals are transparent, is, that being calcin'd, and melted with Glass, they tinge the Glass with transparent colours. Thus the Calx of Silver tinges the Glass on which it is anneal'd with a lovely Yellow, or Gold colour, &c.

And that the parts of Metals are transparent, may be farther argued from the transparency of Leaf-gold, which held against the light, both to the naked eye, and the Microscope, exhibits a deep Green. And though I have never seen the other Metals laminated so thin, that I was able to perceive them transparent, yet, for Copper and Brass, if we had the same conveniency for laminating them, as we have for Gold, we might, perhaps, through such plates or leaves, find very differing degrees of Blue, or Green; for it seems very probable, that those Rays that rebound from them ting'd, with a deep Yellow, or pale Red, as from Copper, or with a pale Yellow, as from Brass, have past through them; for I cannot conceive how by reflection alone those Rays can receive a tincture, taking any Hypothesis extant.

So that we see there may a sufficient reason be drawn from these instances, why those colours which we are unable to dilute to the palest Yellow, or Blue, or Green, are not therefore to be concluded not to be a deeper degree of them; for supposing we had a great company of small Globular essence Bottles, or round Glass bubbles, about the bigness of a Walnut, fill'd each of them with a very deep mixture of Saffron, and that every one of them did appear of a deep Scarlet colour, and all of them together did exhibit at a distance, a deep dy'd Scarlet body. It does not follow, because after we have come nearer to this congeries, or mass, and divided it into its parts, and examining each of its parts severally or apart, we find them to have much the same colour with the whole mats; it does not, I say, therefore follow, that if we could break those Globules smaller, or any other ways come to see a smaller or thinner parcel of the ting'd liquor that fill'd those bubbles, that that ting'd liquor must always appear Red, or of a Scarlet hue, since if Experiment be made, the quite contrary will ensue; for it is capable of being diluted into the palest Yellow.

Now, that I might avoid all the Objections of this kind, by exhibiting an Experiment that might by ocular proof convince those whom other reasons would not prevail with, I provided me a Prismatical Glass, Schem. 6.
Fig. 10. made hollow, just in the form of a Wedge, such as is represented in the tenth Figure of the sixth Scheme. The two parallelogram sides ABCD, ABEF, which met at a point, were made of the clearest Looking-glass plates well ground and polish'd that I could get; these were joyn'd with hard cement to the triangular sides, BCE, ADF, which were of Wood; the Parallelogram base BCEF, likewise was of Wood joyn'd on to the rest with hard cement, and the whole Prismatical Box was exactly stopt every where, but onely a little hole near the base was left, whereby the Vessel could be fill'd with any liquor, or emptied again at pleasure.

One of these Boxes (for I had two of them) I fill'd with a pretty deep tincture of Aloes, drawn onely with fair Water, and then stopt the hole with a piece of Wax, then, by holding this Wedge against the Light, and looking through it, it was obvious enough to see the tincture of the liquor near the edge of the Wedge where it was but very thin, to be a pale but well colour'd Yellow, and further and further from the edge, as the liquor grew thicker and thicker, this tincture appear'd deeper and deeper, so that near the blunt end, which was seven Inches from the edge and three Inches and an half thick; it was of a deep and well colour'd Red. Now, the clearer and purer this tincture be, the more lovely will the deep Scarlet be, and the fouler the tincture be, the more dirty will the Red appear; so that some dirty tinctures have afforded their deepest Red much of the colour of burnt Oker or Spanish brown; others as lovely a colour as Vermilion, and some much brighter; but several others, according as the tinctures were worse or more foul, exhibited various kinds of Reds, of very differing degrees.

The other of these Wedges, I fill'd with a most lovely tincture of Copper, drawn from the filings of it, with spirit of Urine, and this Wedge held as the former against the Light, afforded all manner of Blues, from the faintest to the deepest, so that I was in good hope by these two, to have produc'd all the varieties of colours imaginable; for I thought by this means to have been able by placing the two Parallelogram sides together, and the edges contrary ways, to have so mov'd them to and fro one by another, as by looking through them in several places, and through several thicknesses, I should have compounded, and consequently have seen all those colours, which by other like compositions of colours would have ensued.

But insteed of meeting with what I look'd for, I met with somewhat more admirable; and that was, that I found my self utterly unable to see through them when placed both together, though they were transparent enough when asunder; and though I could see through twice the thickness, when both of them were fill'd with the same colour'd liquors, whether both with the Yellow, or both with the Blue, yet when one was fill'd with the Yellow, the other with the Blue, and both looked through, they both appear'd dark, onely when the parts near the tops were look'd through, they exhibited Greens, and those of very great variety, as I expected, but the Purples and other colours, I could not by any means make, whether I endeavour'd to look through them both against the Sun, or whether I plac'd them against the hole of a darkned room.

But notwithstanding this mis-ghessing, I proceeded on with my trial in a dark room, and having two holes near one another, I was able, by placing my Wedges against them, to mix the ting'd Rays that past through them, and fell on a sheet of white Paper held at a convenient distance from them as I pleas'd; so that I could make the Paper appear of what colour I would, by varying the thicknesses of the Wedges, and consequently the tincture of the Rays that past through the two holes, and sometimes also by varying the Paper, that is, insteed of a white Paper, holding a gray, or a black piece of Paper.

Whence I experimentally found what I had before imagin'd, that all the varieties of colours imaginable are produc'd from several degrees of these two colours, namely, Yellow and Blue, or the mixture of them with light and darkness, that is, white and black. And all those almost infinite varieties which Limners and Painters are able to make by compounding those several colours they lay on their Shels or Palads, are nothing else, but some compositum, made up of some one or more, or all of these four.

Now, whereas it may here again be objected, that neither can the Reds be made out of the Yellows, added together, or laid on in greater or less quantity, nor can the Yellows be made out of the Reds though laid never so thin; and as for the addition of White or Black, they do nothing but either whiten or darken the colours to which they are added, and not at all make them of any other kind of colour: as for instance, Vermilion, by being temper'd with White Lead, does not at all grow more Yellow, but onely there is made a whiter kind of Red. Nor does Yellow Oker, though laid never so thick, produce the colour of Vermilion, nor though it be temper'd with Black, does it at all make a Red; nay, though it be temper'd with White, it will not afford a fainter kind of Yellow, such as masticut, but onely a whiten'd Yellow; nor will the Blues be diluted or deepned after the manner I speak of, as Indico will never afford so fine a Blue as Ultramarine or Bise; nor will it, temper'd with Vermilion, ever afford a Green, though each of them be never so much temper'd with white.

To which I answer, that there is a great difference between diluting a colour and whitening of it; for diluting a colour, is to make the colour'd parts more thin, so that the ting'd light, which is made by trajecting those ting'd bodies, does not receive so deep a tincture; but whitening a colour is onely an intermixing of many clear reflections of light among the same ting'd parts; deepning also, and darkning or blacking a colour, are very different; for deepning a colour, is to make the light pass through a greater quantity of the same tinging body; and darkning or blacking a colour, is onely interposing a multitude of dark or black spots among the same ting'd parts, or placing the colour in a more faint light.

First therefore, as to the former of these operations, that is, diluting and deepning, most of the colours us'd by the Limners and Painters are incapable of, to wit, Vermilion and Red-lead, and Oker, because the ting'd parts are so exceeding small, that the most curious Grindstones we have, are not able to separate them into parts actually divided so small as the ting'd particles are; for looking on the most curiously ground Vermilion, and Oker, and Red-lead, I could perceive that even those small corpuscles of the bodies they left were compounded of many pieces, that is, they seem'd to be small pieces compounded of a multitude of lesser ting'd parts: each piece seeming almost like a piece of Red Glass, or ting'd Crystal all flaw'd; so that unless the Grindstone could actually divide them into smaller pieces then those flaw'd particles were, which compounded that ting'd mote I could see with my Microscope, it would be impossible to dilute the colour by grinding, which, because the finest we have will not reach to do in Vermilion or Oker, therefore they cannot at all, or very hardly be diluted.

Other colours indeed, whose ting'd particles are such as may be made smaller, by grinding their colour, may be diluted. Thus several of the Blues may be diluted, as Smalt and Bise; and Masticut, which is Yellow, may be made more faint: And even Vermilion it self may, by too much grinding, be brought to the colour of Red-lead, which is but an Orange colour, which is confest by all to be very much upon the Yellow. Now, though perhaps somewhat of this diluting of Vermilion by overmuch grinding may be attributed to the Grindstone, or muller, for that some of their parts may be worn off and mixt with the colour, yet there seems not very much, for I have done it on a Serpentine-stone with a muller made of a Pebble, and yet observ'd the same effect follow.

And secondly, as to the other of these operations on colours, that is, the deepning of them, Limners and Painters colours are for the most part also uncapable. For they being for the most part opacous; and that opacousness, as I said before, proceeding from the particles, being very much flaw'd, unless we were able to joyn and re-unite those flaw'd particles again into one piece, we shall not be able to deepen the colour, which since we are unable to do with most of the colours which are by Painters accounted opacous, we are therefore unable to deepen them by adding more of the same kind.

But because all those opacous colours have two kinds of beams or Rays reflected from them, that is, Rays unting'd, which are onely reflected from the outward surface, without at all penetrating of the body, and ting'd Rays which are reflected from the inward surfaces or flaws after they have suffer'd a two-fold refraction; and because that transparent liquors mixt with such corpuscles, do, for the most part, take off the former kind of reflection; therefore these colours mixt with Water or Oyl, appear much deeper than when dry, for most part of that white reflection from the outward surface is remov'd. Nay, some of these colours are very much deepned by the mixture with some transparent liquor, and that because they may perhaps get between those two flaws, and so consequently joyn two or more of those flaw'd pieces together; but this happens but in a very few.

Now, to shew that all this is not gratis dictum, I shall set down some Experiments which do manifest these things to be probable and likely, which I have here deliver'd.

For, first, if you take any ting'd liquor whatsoever, especially if it be pretty deeply ting'd, and by any means work it into a froth, the congeries of that froth shall seem an opacous body, and appear of the same colour, but much whiter than that of the liquor out of which it is made. For the abundance of reflections of the Rays against those surfaces of the bubbles of which the froth consists, does so often rebound the Rays backwards, that little or no light can pass through, and consequently the froth appears opacous.

Again, if to any of these ting'd liquors that will endure the boiling there be added a small quantity of fine flower (the parts of which through the Microscope are plainly enough to be perceiv'd to consist of transparent corpuscles) and suffer'd to boyl till it thicken the liquor, the mass of the liquor will appear opacous, and ting'd with the same colour, but very much whiten'd.

Thus, if you take a piece of transparent Glass that is well colour'd, and by heating it, and then quenching it in Water, you flaw it all over, it will become opacous, and will exhibit the same colour with which the piece is ting'd, but fainter and whiter.

Or, if you take a Pipe of this transparent Glass, and in the flame of a Lamp melt it, and then blow it into very thin bubbles, then break those bubbles, and collect a good parcel of those laminæ together in a Paper, you shall find that a small thickness of those Plates will constitute an opacous body, and that you may see through the mass of Glass before it be thus laminated, above four times the thickness: And besides, they will now afford a colour by reflection as other opacous (as they are call'd) colours will, but much fainter and whiter than that of the Lump or Pipe out of which they were made.

Thus also, if you take Putty, and melt it with any transparent colour'd Glass, it will make it become an opacous colour'd lump, and to yield a paler and whiter colour than the lump by reflection.

The same thing may be done by a preparation of Antimony, as has been shewn by the Learned Physician, D^r. C.M. in his Excellent Observations and Notes on Nery's Art of Glass; and by this means all transparent colours become opacous, or ammels. And though by being ground they lose very much of their colour, growing much whiter by reason of the multitude of single reflections from their outward surface, as I shew'd afore, yet the fire that in the nealing or melting re-unites them, and so renews those spurious reflections, removes also those whitenings of the colour that proceed from them.

As for the other colours which Painters use, which are transparent, and us'd to varnish over all other paintings, 'tis well enough known that the laying on of them thinner or thicker, does very much dilute or deepen their colour.

Painters Colours therefore consisting most of them of solid particles, so small that they cannot be either re-united into thicker particles by any Art yet known, and consequently cannot be deepned; or divided into particles so small as the flaw'd particles that exhibit that colour, much less into smaller, and consequently cannot be diluted; It is necessary that they which are to imitate all kinds of colours, should have as many degrees of each colour as can be procur'd.

And to this purpose, both Limners and Painters have a very great variety both of Yellows and Blues, besides several other colour'd bodies that exhibit very compounded colours, such as Greens and Purples; and others that are compounded of several degrees of Yellow, or several degrees of Blue, sometimes unmixt, and sometimes compounded with several other colour'd bodies.

The Yellows, from the palest to the deepest Red or Scarlet, which has no intermixture of Blue, are pale and deep Masticut, Orpament, English Oker, brown Oker, Red Lead, and Vermilion, burnt English Oker, and burnt brown Oker, which last have a mixture of dark or dirty parts with them, &c.

Their Blues are several kinds of Smalts, and Verditures, and Bise, and Ultramarine, and Indico, which last has many dirty or dark parts intermixt with it.

Their compounded colour'd bodies, as Pink, and Verdigrese, which are Greens, the one a Popingay, the other a Sea-green; then Lac, which is a very lovely Purple.

To which may be added their Black and White, which they also usually call Colours, of each of which they have several kinds, such as Bone Black, made of Ivory burnt in a close Vessel, and Blue Black, made of the small coal of Willow, or some other Wood; and Cullens earth, which is a kind of brown Black, &c. Their usual Whites are either artificial or natural White Lead, the last of which is the best they yet have, and with the mixing and tempering these colours together, are they able to make an imitation of any colour whatsoever: Their Reds or deep Yellows, they can dilute by mixing pale Yellows with them, and deepen their pale by mixing deeper with them; for it is not with Opacous colours as it is with transparent, where by adding more Yellow to yellow, it is deepned, but in opacous diluted. They can whiten any colour by mixing White with it, and darken any colour by mixing Black, or some dark and dirty colour. And in a word, most of the colours, or colour'd bodies they use in Limning and Painting, are such, as though mixt with any other of their colours, they preserve their own hue, and by being in such very smal parts dispers'd through the other colour'd bodies, they both, or altogether represent to the eye a compositum of all; the eye being unable, by reason of their smalness, to distinguish the peculiarly colour'd particles, but receives them as one intire compositum: whereas in many of these, the Microscope very easily distinguishes each of the compounding colours distinct, and exhibiting its own colour.

Thus have I by gently mixing Vermilion and Bise dry, produc'd a very fine Purple, or mixt colour, but looking on it with the Microscope, I could easily distinguish both the Red and the Blue particles, which did not at all produce the Phantasm of Purple.

To summ up all therefore in a word, I have not yet found any solid colour'd body, that I have yet examin'd, perfectly opacous; but those that are least transparent are Metalline and Mineral bodies, whose particles generally, seeming either to be very small, or very much flaw'd, appear for the most part opacous, though there are very few of them that I have look'd on with a Microscope, that have not very plainly or circumstantially manifested themselves transparent.

And indeed, there seem to be so few bodies in the world that are in minimis opacous, that I think one may make it a rational Query, Whether there be any body absolutely thus opacous? For I doubt not at all (and I have taken notice of very many circumstances that make me of this mind) that could we very much improve the Microscope, we might be able to see all those bodies very plainly transparent, which we now are fain onely to ghess at by circumstances. Nay, the Object Glasses we yet make use of are such, that they make many transparent bodies to the eye, seem opacous through them, which if we widen the Aperture a little, and cast more light on the objects, and not charge the Glasses so deep, will again disclose their transparency.

Now, as for all kinds of colours that are dissolvable in Water, or other liquors, there is nothing so manifest, as that all those ting'd liquors are transparent; and many of them are capable of being diluted and compounded or mixt with other colours, and divers of them are capable of being very much chang'd and heightned, and fixt with several kinds of Saline menstruums. Others of them upon compounding, destroy or vitiate each others colours, and precipitate, or otherwise very much alter each others tincture. In the true ordering and diluting, and deepning, and mixing, and fixing of each of which, consists one of the greatest mysteries of the Dyers; of which particulars, because our Microscope affords us very little information, I shall add nothing more at present; but onely that with a very few tinctures order'd and mixt after certain ways, too long to be here set down, I have been able to make an appearance of all the various colours imaginable, without at all using the help of Salts, or Saline menstruums to vary them.

As for the mutation of Colours by Saline menstruums, they have already been so fully and excellently handled by the lately mention'd Incomparable Authour, that I can add nothing, but that of a multitude of trials that I made, I have found them exactly to agree with his Rules and Theories; and though there may be infinite instances, yet may they be reduc'd under a few Heads, and compris'd within a very few Rules. And generally I find, that Saline menstruums are most operative upon those colours that are Purple, or have some degree of Purple in them, and upon the other colours much less. The spurious pulses that compose which, being (as I formerly noted) so very neer the middle between the true ones, that a small variation throws them both to one side, or both to the other, and so consequently must make a vast mutation in the formerly appearing Colour.

Observ. XI. Of Figures observ'd in small Sand.

Sand generally seems to be nothing else but exceeding small Pebbles, or at least some very small parcels of a bigger stone; the whiter kind seems through the Microscope to consist of small transparent pieces of some pellucid body, each of them looking much like a piece of Alum, or Salt Gem; and this kind of Sand is angled for the most part irregularly, without any certain shape, and the granules of it are for the most part flaw'd, through amongst many of them it is not difficult to find some that are perfectly pellucid, like a piece of clear Crystal, and divers likewise most curiously shap'd, much after the manner of the bigger Stiriæ of Crystal, or like the small Diamants I observ'd in certain Flints, of which I shall by and by relate; which last particular seems to argue, that this kind of Sand is not made by the comminution of greater transparent Crystaline bodies, but by the concretion or coagulation of Water, or some other fluid body.

There are other kinds of courser Sands, which are browner, and have their particles much bigger; these, view'd with a Microscope, seem much courser and more opacous substances, and most of them are of some irregularly rounded Figures; and though they seem not so opacous as to the naked eye, yet they seem very foul and cloudy, but neither do these want curiously transparent, no more than they do regularly figur'd and well colour'd particles, as I have often found.

There are multitudes of other kinds of Sands, which in many particulars, plainly enough discoverable by the Microscope, differ both from these last mention'd kinds of Sands, and from one another: there seeming to be as great variety of Sands, as there is of Stones. And as amongst Stones some are call'd precious from their excellency, so also are there Sands which deserve the same Epithite for their beauty; for viewing a small parcel of East-India Sand (which was given me by my highly honoured friend, Mr. Daniel Colwall) and, since that, another parcel, much of the same kind, I found several of them, both very transparent like precious Stones, and regularly figur'd like Crystal, Cornish Diamants, some Rubies, &c. and also ting'd with very lively and deep colours, like Rubys, Saphyrs, Emeralds, &c. These kinds of granuls I have often found also in English Sand. And 'tis easie to make such a counterfeit Sand with deeply ting'd Glass, Enamels and Painters colours.

It were endless to describe the multitudes of Figures I have met with in these kind of minute bodies, such as Spherical, Oval, Pyramidal, Conical, Prismatical, of each of which kinds I have taken notice.

But amongst many others, I met with none more observable than this Schem. 5.
Fig. X. pretty Shell (described in the Figure X. of the fifth Scheme) which, though as it was light on by chance, deserv'd to have been omitted (I being unable to direct any one to find the like) yet for its rarity was it not inconsiderable, especially upon the account of the information it may afford us. For by it we have a very good instance of the curiosity of Nature in another kind of Animals which are remov'd, by reason of their minuteness, beyond the reach of our eyes, so that as there are several sorts of Insects, as Mites, and others, so small as not yet to have had any names; (some of which I shall afterwards describe) and small Fishes, as Leeches in Vineger; and smal vegetables, as Moss, and Rose-Leave-plants; and small Mushroms, as mould: so are there, it seems, small Shel-fish likewise, Nature shewing her curiosity in every Tribe of Animals, Vegetables, and Minerals.

I was trying several small and single Magnifying Glasses, and casually viewing a parcel of white Sand, when I perceiv'd one of the grains exactly shap'd and wreath'd like a Shell, but endeavouring to distinguish it with my naked eye, it was so very small, that I was fain again to make use of the Glass to find it; then, whilest I thus look'd on it, with a Pin I separated all the rest of the granules of Sand, and found it afterwards to appear to the naked eye an exceeding small white spot, no bigger than the point of a Pin. Afterwards I view'd it every way with a better Microscope and found it on both sides, and edge-ways, to resemble the Shell of a small Water-Snail with a flat spiral Shell: it had twelve wreathings, a, b, c, d, e, &c. all very proportionably growing one less than another toward the middle or center of the Shell, where there was a very small round white spot. I could not certainly discover whether the Shell were hollow or not, but it seem'd fill'd with somewhat, and 'tis probable that it might be petrify'd as other larger Shels often are, such as are mention'd in the seventeenth Observation.

Observ. XII. Of Gravel in Urine.

I Have often observ'd the Sand or Gravel of Urine, which seems to be a tartareous substance, generated out of a saline and a terrestrial substance crystalliz'd together, in the form of Tartar, sometimes sticking to the sides of the Urinal, but for the most part sinking to the bottom, and there lying in the form of coorse common Sand; these, through the Microscope, appear to be a company of small bodies, partly transparent and partly opacous, some White, some Yellow, some Red, others of more brown and duskie colours.

The Figure of them is for the most part flat, in the manner of Slats or such like plated Stones, that is, each of them seem to be made up of several other thinner Plates, much like Muscovie Glass, or Englsh Sparr to the last of which, the white plated Gravel seems most likely; for they seem not onely plated like that, but their sides shap'd also into Rhombs, Rhomboeids, and sometimes into Rectangles and Squares. Their bigness and Figure may be Schem. 7.
Fig. 2. seen in the second Figure of the seventh Plate, which represents about a dozen of them lying upon a plate ABCD, some of which, as a, b, c, d seem'd more regular than the rest, and e, which was a small one, sticking on the top of another, was a perfet Rhomboeid on the top, and had four Rectangular sides.

The line E which was the the measure of the Microscope, is 1/32 part of an English Inch, so that the greatest bredth of any of them, exceeded not 1/128 part of an Inch.

Putting these into several liquors, I found oyl of Vitriol, Spirit of Urine, and several other Saline menstruums to dissolve them; and the first of these in less than a minute without Ebullition, Water, and several other liquors, had no sudden operation upon them. This I mention, because those liquors that dissolve them, first make them very white, not vitiating, but rather rectifying their Figure, and thereby make them afford a very pretty object for the Microscope.

How great an advantage it would be to such as are troubled with the Stone, to find some menstruum might dissolve them without hurting the Bladder, is easily imagin'd, since some injections made of such bodies might likewise dissolve the stone, which seems much of the same nature.

It may therefore, perhaps, be worthy some Physicians enquiry, whether there may not be something mixt with the Urine in which the Gravel or Stone lies, which may again make it dissolve it, the first of which seems by it's regular Figures to have been sometimes Crystalliz'd out of it. For whether this Crystallization be made in the manner as Alum, Peter, &c. are crystallized out of a cooling liquor, in which, by boyling they have been dissolv'd; or whether it be made in the manner of Tartarum Vitriolatum, that is, by the Coalition of an acid and a Sulphureous substance, it seems not impossible, but that the liquor it lies in, may be again made a dissolvent of it. But leaving these inquiries to Physicians or Chymists, to whom it does more properly belong, I shall proceed.

Observ. XIII. Of the small Diamants, or Sparks in Flints.

Chancing to break a Flint stone in pieces, I found within it a certain cavity all crusted over with a very pretty candied substance, some of the parts of which, upon changing the posture of the Stone, in respect of the Incident light, exhibited a number of small, but very vivid reflections; and having made use of my Microscope, I could perceive the whole surface of that cavity to be all beset with a multitude of little Crystaline or Adamantine bodies, so curiously shap'd, that it afforded a not unpleasing object.

Having considered those vivid repercussions of light, I found them to be made partly from the plain external surface of these regularly figured bodies (which afforded the vivid reflexions) and partly to be made from within the somewhat pellucid body, that is, from some surface of the body, opposite to that superficies of it which was next the eye.

And because these bodies were so small, that I could not well come to make Experiments and Examinations of them, I provided me several small stiriæ of Crystals or Diamants, found in great quantities in Cornwall and are therefore commonly called Cornish Diamants: these being very pellucid, and growing in a hollow cavity of a Rock (as I have been several times informed by those that have observ'd them) much after the same manner as these do in the Flint, and having besides their outward surface very regularly shap'd, retaining very near the same Figures with some of those I observ'd in the other, became a convenient help to me for the Examination of the proprieties of those kinds of bodies.

And first for the Reflections, in these I found it very observable, That the brightest reflections of light proceeded from within the pellucid body; that is, that the Rays admitted through the pellucid substance in their getting out on the opposite side, were by the contiguous and strong reflecting surface of the Air very vividly reflected, so that more Rays were reflected to the eye by this surface, though the Ray in entring and getting out of the Crystal had suffer'd a double refraction, than there were from the outward surface of the Glass where the Ray had suffer'd no reflection at all.

And that this was the surface of the Air that gave so vivid a re-percussion I try'd by this means I sunk half of a stiria in Water, so that only Water was contiguous to the under surface, and then the internal reflection was so exceedingly faint, that it was scarce discernable. Again, I try'd to alter this vivid reflection by keeping off the Air, with a body not fluid, and that was by rubbing and holding my finger very hard against the under surface, so as in many places the pulp of my finger did touch the Glass, without any interjacent air between, then observing the reflection, I found, that wheresoever my finger or skin toucht the surface, from that part there was no reflection, but in the little furrows or creases of my skin, where there remain'd little small lines of air, from them was return'd a very vivid reflection as before. I try'd further, by making the surface of very pure Quicksilver to be contiguous to the under surface of this pellucid body, and then the reflection from that was so exceedingly more vivid than from the air, as the reflection from air was than the reflection from the Water; from all which trials I plainly saw, that the strong reflecting air was the cause of this Phænomenon.

And this agrees very well with the Hypothesis of light and Pellucid bodies which I have mention'd in the description of Muscovy-glass; for we there suppose Glass to be a medium, which does less resist the pulse of light, and consequently, that most of the Rays incident on it enter into it, and are refracted towards the perpendicular; whereas the air I suppose to be a body that does more resist it, and consequently more are re-percuss'd then do enter it: the same kind of trials have I made, with Crystalline Glass, with drops of fluid bodies, and several other ways, which do all seem to agree very exactly with this Theory. So that from this Principle well establish'd, we may deduce severall Corollaries not unworthy observation.

And the first is; that it plainly appears by this, that the production of the Rainbow is as much to be ascribed to the reflection of the concave surface of the air, as to the refraction of the Globular drops: this will be evidently manifest by these Experiments, if you foliate that part of a Glass-ball that is to reflect an Iris, as in the Cartesian Experiment, above mention'd, the reflections will be abundantly more strong, and the colours more vivid: and if that part of the surface be touch'd with Water, scarce affords any sensible colour at all.

Next we learn, that the great reason why pellucid bodies beaten small are white, is from the multitude of reflections, not from the particles of the body, but from the contiguous surface of the air. And this is evidently manifested, by filling the Interstitia of those powder'd bodies with Water, whereby their whiteness presently disappears. From the same reason proceeds the whiteness of many kinds of Sands, which in the Microscope appear to be made up of a multitude of little pellucid bodies, whose brightest reflections may by the Microscope be plainly perceiv'd to come from their internal surfaces; and much of the whiteness of it may be destroy'd by the affusion of fair Water to be contiguous to those surfaces.

The whiteness also of froth, is for the most part to be ascribed to the reflection of the light from the surface of the air within the Bubbles, and very little to the reflection from the surface of the Water it self: for this last reflection does not return a quarter so many Rays, as that which is made from the surface of the air, as I have certainly found by a multitude of Observations and Experiments.

The whiteness of Linnen, Paper, Silk, &c. proceeds much from the same reason, as the Microscope will easily discover; for the Paper is made up of an abundance of pellucid bodies, which afford a very plentifull reflection from within, that is, from the concave surface of the air contiguous to its component particles; wherefore by the affusion of Water, Oyl, Tallow, Turpentine, &c. all those reflections are made more faint, and the beams of light are suffer'd to traject & run through the Paper more freely.

Hence further we may learn the reason of the whiteness of many bodies, and by what means they maybe in part made pellucid: As white Marble for instance, for this body is composed of a pellucid body exceedingly flaw'd, that is, there are abundance of thin, and very fine cracks or chinks amongst the multitude of particles of the body, that contain in them small parcels of air, which do so re-percuss and drive back the penetrating beams, that they cannot enter very deep within that body; which the Microscope does plainly inform us to be made up of a Congeries of pellucid particles. And I further found it somewhat more evidently by some attempts I made towards the making transparent Marble, for by heating the Stone a little, and baking it in Oyl, Turpentine, Oyl of Turpentine, &c., I found that I was able to see much deeper into the body of Marble then before; and one trial, which was not with an unctuous substance, succeeded better than the rest, of which, when I have a better opportunity, I shall make further trial.

This also gives us a probable reason of the so much admired Phænomena, of the Oculus Mundi, an Oval stone, which commonly looks like white Alabaster, but being laid a certain time in Water, it grows pellucid, and transparent, and being suffer'd to lie again dry, it by degrees loses that transparency, and becomes white as before. For the Stone being of a hollow spongie nature, has in the first and last of these appearances, all those pores fill'd with the obtunding and reflecting air; whereas in the second, all those pores are fill'd with a medium that has much the same refraction with the particles of the Stone, and therefore those two being contiguous, make, as 'twere, one continued medium, of which more is said in the 15. Observation.

There are a multitude of other Phænomena, that are produc'd from this same Principle, which as it has not been taken notice of by any yet that I know, so I think, upon more diligent observation, will it not be found the least considerable. But I have here onely time to hint Hypotheses, and not to prosecute them so fully as I could wish; many of them having a vast extent in the production of a multitude of Phænomena, which have been by others, either not attempted to be explain'd, or else attributed to some other cause than what I have assign'd, and perhaps than the right; and therefore I shall leave this to the prosecution of such as have more leisure: onely before I leave it, I must not pretermit to hint, that by this Principle, multitudes of the Phænomena of the air, as about Mists, Clouds, Meteors, Haloes, &c. are most plainly and (perhaps) truly explicable; multitudes also of the Phænomena in colour'd bodies, as liquors, &c. are deducible from it.

And from this I shall proceed to a second considerable Phænomenon which these Diamants exhibit, and that is the regularity of their Figure, which is a propriety not less general than the former, It comprising within its extent, all kinds of Metals, all kinds of Minerals, most Precious stones, all kinds of Salts, multitudes of Earths, and almost all kinds of fluid bodies. And this is another propiety, which, though a little superficially taken notice of by some, has not, that I know, been so much as attempted to be explicated by any.

This propriety of bodies, as I think it the most worthy, and next in order to be consider'd after the contemplation of the Globular Figure, so have I long had a desire as wel as a determination to have prosecuted it if I had had an opportunity, having long since propos'd to my self the method of my enquiry therein, it containing all the allurements that I think any enquiry is capable of: For, first I take it to proceed from the most simple principle that any kind of form can come from, next the Globular, which was therefore the first I set upon, and what I have therein perform'd, I leave the Judicious Reader to determine. For as that form proceeded from a propiety of fluid bodies, which I have call'd Congruity, or Incongruity; so I think, had I time and opportunity, I could make probable, that all these regular Figures that are so conspicuously various and curious, and do so adorn and beautifie such multitudes of bodies, as I have above hinted, arise onely from three or four several positions or postures of Globular particles, and those the most plain, obvious, and necessary conjunctions of such figur'd particles that are possible, so that supposing such and such plain and obvious causes concurring the coagulating particles must necessarily compose a body of such a determinate regular Figure, and no other, and this with as much necessity and obviousness as a fluid body encompast with a Heterogeneous fluid must be protruded into a Spherule or Globe. And this I have ad oculum demonstrated with a company of bullets, and some few other very simple bodies; so that there was not any regular Figure, which I have hitherto met withall, of any of those bodies that I have above named, that I could not with the composition of bullets or globules, and one or two other bodies, imitate, even almost by shaking them together. And thus for instance may we find that the Globular bullets will of themselves, if put on an inclining plain, so that they may run together, naturally run into a triangular order, composing all the variety of figures that can be imagin'd to be made out of æquilateral triangles; and such will you find, upon trial, all the Surfaces of Alum to be compos'd of: For three bullets lying on a plain, as close to one another as they can compose an Schem. 7.
Fig. A. &c. æquilatero-triangular form, as in A in the 7. Scheme. If a fourth be joyn'd to them on either side as closely as it can, they four compose the most regular Rhombus consisting of two æquilateral triangles, as B. If a fifth be joyn'd to them on either side in as close a position as it can, which is the propriety of the Texture, it makes a Trapezium, or four-sided Figure, two of whole angles are 120. and two 60. degrees, as C. If a sixth be added, as before, either it makes an æquilateral triangle, as D, or a Rhomboeid, as E, or an Hex-angular Figure, as F, which is compos'd of two primary Rhombes. If a seventh be added, it makes either an æquilatero-hexagonal Figure, as G, or some kind of six-sided Figure, as H, or I. And though there be never so many placed together, they may be rang'd into some of these lately mentioned Figures, all the angles of which will be either 60. degrees, or 120. as the figure K. which is an æquiangular hexagonal Figure is compounded of 12. Globules, or may be of 25, or 27, or 36, or 42, &c. and by these kinds of texture, or position of globular bodies, may you find out all the variety of regular shapes, into which the smooth surfaces of Alum are form'd, as upon examination any one may easily find; nor does it hold only in superficies, but in solidity also, for it's obvious that a fourth Globule laid upon the third in this texture, composes a regular Tetrahedron, which is a very usual Figure of the Crystals of Alum. And (to hasten) there is no one Figure into which Alum is observ'd to be crystallized, but may by this texture of Globules be imitated, and by no other.

I could instance also in the Figure of Sea-salt, and Sal-gem, that it is compos'd of a texture of Globules, placed in a cubical form, as L, and that all the Figures of those Salts may be imitated by this texture of Globules and by no other whatsoever. And that the forms of Vitriol and of Salt-Peter, as also of Crystal, Hore-frost, &c. are compounded of these two textures, but modulated by certain proprieties: But I have not here time to insist upon, as I have not neither to shew by what means Globules come to be thus context, and what those Globules are, and many other particulars requisite to a full and intelligible explication of this propriety of bodies. Nor have I hitherto found indeed an opportunity of prosecuting the inquiry so farr as I design'd; nor do I know when I may, it requiring abundance of time, and a great deal of assistance to go through with what I design'd; the model of which was this:

First, to get as exact and full a collection as I could, of all the differing kinds of Geometrical figur'd bodies, some three or four several bodies of each kind.

Secondly, with them to get as exact a History as possibly I could learn of their places of Generation or finding, and to enquire after as many circumstances that tended to the Illustrating of this Enquiry, as possibly I could observe.

Thirdly, to make as many trials as upon experience I could find requisite, in Dissolutions and Coagulations of several crystallizing Salts; for the needfull instruction and information in this Enquiry.

Fourthly, to make several trials on divers other bodies, as Metals, Minerals, and Stones, by dissolving them in several Menstruums, and crystalizing them, to see what Figures would arise from those several Compositums.

Fifthly, to make Compositions and Coagulations of several Salts together into the same mass, to observe of what Figure the product of them would be; and in all, to note as many circumstances as I should judge conducive to my Enquiry.

Sixthly, to enquire the closeness or rarity of the texture of these bodies, by examining their gravity, and their refraction, &c.

Seventhly, to enquire particularly what operations the fire has upon several kinds of Salts, what changes it causes in their Figures, Textures, or Energies.

Eighthly, to examine their manner of dissolution, or acting upon those bodies dissoluble in them; The texture of those bodies before and after the process. And this for the History.

Next for the Solution, To have examin'd by what, and how many means, such and such Figures, actions and effects could be produc'd possibly.

And lastly, from all circumstances well weigh'd, I should have endeavoured to have shewn which of them was most likely, and (if the informations by these Enquiries would have born it) to have demonstrated which of them it must be, and was.

But to proceed, As I believe it next to the Globular the most simple; so do I, in the second place, judge it not less pleasant; for that which makes an Enquiry pleasant, are, first a noble Inventum that promises to crown the successfull endeavour; and such must certainly the knowledge of the efficient and concurrent causes of all these curious Geometrical Figures be, which has made the Philosophers hitherto to conclude nature in these things to play the Geometrician, according to that saying of Plato, ‛Ο Θεος γεομετρει. Or next, a great variety of matter in the Enquiry; and here we meet with nothing less than the Mathematicks of nature, having every day a new Figure to contemplate, or a variation of the same in another body,

Which do afford us a third thing, which will yet more sweeten the Enquiry, and that is, a multitude of information; we are not so much to grope in the dark, as in most other Enquiries, where the Inventum is great; for having such a multitude of instances to compare, and such easie ways of generating, or compounding and of destroying the form, as in the Solution and Crystallization of Salts, we cannot but learn plentifull information to proceed by. And this will further appear from the universality of the Principle which Nature has made use of almost in all inanimate bodies. And therefore, as the contemplation of them all conduces to the knowledg of any one; so from a Scientifical knowledge of any one does follow the fame of all, and every one.

And fourthly, for the usefulness of this knowledge, when acquir'd; certainly none can doubt, that considers that it caries us a step forward into the Labirinth of Nature, in the right way towards the end we propose our selves in all Philosophical Enquiries. So that knowing what is the form of Inanimate or Mineral bodies, we shall be the better able to proceed in our next Enquiry after the forms of Vegetative bodies; and last of all, of Animate ones, that seeming to be the highest step of natural knowledge that the mind of man is capable of.

Observ. XIV. Of several kindes of frozen Figures.

I have very often in a Morning, when there has been a great hoar-frost, with an indifferently magnifying Microscope, observ'd the small Stiriæ, or Crystalline beard, which then usually covers the face of most bodies that lie open to the cold air, and found them to be generally Hexangular prismatical bodies, much like the long Crystals of Salt-peter, save onely that the ends of them were differing: for whereas those of Nitre are for the most part pyramidal, being terminated either in a point or edge; these of Frost were hollow, and the cavity in some seem'd pretty deep, and this cavity was the more plainly to be seen, because usually one or other of the six parallelogram sides was wanting, or at least much shorter then the rest.

But this was onely the Figure of the Bearded hoar-frost; and as for the particles of other kinds of hoar-frosts, they seem'd for the most part irregular, or of no certain Figure. Nay, the parts of those curious branchings, or vortices, that usually in cold weather tarnish the surface of Glass, appear through the Microscope very rude and unshapen, as do most other kinds of frozen Figures, which to the naked eye seem exceeding neat and curious, such as the Figures of Snow, frozen Urine, Hail, several Figures frozen in common Water, &c. Some Observations of each of which I shall hereunto annex, because if well consider'd and examin'd, they may, perhaps, prove very instructive for the finding out of what I have endeavoured in the preceding Observation to shew, to be (next the Globular Figure which is caus'd by congruity, as I hope I have made probable in the sixth Observation) the most simple and plain operation of Nature, of which, notwithstanding we are yet ignorant.

Several Observables in the six-branched Figures form'd on the surface of Urine by freezing.

1 The Figures were all frozen almost even with the surface of the Urine in the Vessel; but the bigger stems were a little prominent above that surface, and the parts of those stems which were nearest the center (a) were biggest above the surface.

2 I have observ'd several kinds of these Figures, some smaller, no bigger then a Two-pence, others so bigg, that I have by measure found one of its stems or branches above four foot long; and of these, some were pretty round, having all their branches pretty neer alike; other of them were more extended towards one side, as usually those very large ones were, which I have observ'd in Ditches which have been full of foul water.

3 None of all these Figures I have yet taken notice of, had any regular position in respect of one another, or of the sides of the Vessel; nor did I find any of them equally to exactness extended every way from the center a.

4 Where ever there was a center, the branchings from it, ab, ac, ad, ae, af, ag, were never fewer, or more then six, which usually concurr'd, or met one another very neer in the same point or center, a; though oftentimes not exactly; and were enclin'd to each other by an angle, of very near sixty degrees, I say, very neer, because, though having endeavoured to measure them the most acurately I was able, with the largest Compasses I had, I could not find any sensible variation from that measure, yet the whole six-branched Figure seeming to compose a solid angle, they must necessarily be somewhat less.

5 The middle lines or stems of these branches, ab, ac, ad, ae, af, ag, seem'd somewhat whiter, and a little higher then any of the intermediate branchings of these Figures; and the center a, was the most prominent part of the whole Figure, seeming the apex of a solid angle or pyramid, each of the six plains being a little enclin'd below the surface of the Urin.

6 The lateral branchings issuing out of the great ones, such as op, mq, &c. were each of them inclin'd to the great ones, by the same angle of about sixty degrees, as the great ones were one to another, and always the bigger branchings were prominent above the less, and the less above the least, by proportionate gradations.

7 The lateral branches shooting out of the great ones, went all of them from the center, and each of them was parallel to that great branch, next to which it lay; so that as all the branches on one side were parallel to one another, so were they all of them to the approximate great branch, as po, qr, as they were parallel to each other, and shot from the center, so were they parallel also to the great branch ab.

8 Some of the stems of the six branches proceeded straight, and of a thickness that gradually grew sharper towards the end, as ag.

9 Others of the stems of those branches grew bigger and knotty towards the middle, and the branches also as well as stems, from Cylinders grew into Plates, in a most admirable and curious order, so exceeding regular and delicate, as nothing could be more, as is visible in ab, ac, ad, ae, af, but towards the end of some of these stems, they began again to grow smaller and to recover their former branchings, as about k and n.

10 Many of the lateral branches had collateral branches (if I may so call them) as qm had many such as st, and most of those again subcollateral, as vw, and these again had others less, which one may call laterosubcollateral, and these again others, and they others, &c. in greater Figures.

11 The branchings of the main Stems joyn'd not together by any regular line, nor did one side of the one lie over the other side of the other, but the small collateral and subcollateral branches did lie at top of one another according to a certain order or method, which I always observ'd to be this.

12 That side of a collateral or subcollateral, &c. branch, lay over the side of the approximate (as the feathers in the wing of a Bird) whose branchings proceeded parallel to the last biggest stem from which it sprung, and not to the biggest stem of all, unless that were a second stem backwards.

13 This rule that held in the branchings of the Sexangular Figure held also in the branchings of any other great or small stem, though it did not proceed from a center.

14 The exactness and curiosity of the figuration of these branches, was in every particular so transcendent, that I judge it almost impossible for humane art to imitate.

15 Tasting several cleer pieces of this Ice, I could not find any Urinous taste in them, but those few I tasted, seem'd as insipid as water.

16 A figuration somewhat like this, though indeed in some particulars much more curious, I have several times observ'd in regulus martis stellatus, but with this difference, that all the stems and branchings are bended in a most excellent and regular order, whereas in Ice the stems and branchings are streight, but in all other particulars it agrees with this, and seems indeed nothing but one of these stars, or branched Figures frozen on Urine, distorted, or wreathed a little, with a certain proportion: Lead also that has Arsenick and some other things mixt with it, I have found to have its surface, when suffer'd to cool, figured somewhat like the branchings of Urine, but much smaller.

17 But there is a Vegetable which does exceedingly imitate these branches, and that is, Fearn, where the main stem may be observ'd to shoot out branches, and the stems of each of these lateral branches, to send forth collateral, and those subcollateral and those laterosubcollateral, &c. and all those much after the same order with the branchings, divisions, and subdivisions in the branchings of these Figures in frozen Urine; so that if the Figures of both be well consider'd, one would ghess that there were not much greater need of a seminal principle for the production of Fearn, then for the production of the branches of Urine, or the Stella martis, there seeming to be as much form and beauty in the one as in the other.

And indeed, this Plant of Fearn, if all particulars be well consider'd, will seem of as simple, and uncompounded a form as any Vegetable, next to Mould or Mushromes, and would next after the invention of the forms of those, deserve to be enquir'd into; for notwithstanding several have affirm'd it to have seed, and to be propagated thereby; yet, though I have made very diligent enquiry after that particular, I cannot find that there is any part of it that can be imagin'd to be more seminal then another: But this onely here by the by:

First, that the Superficies be not disturbed with any wind, or other commotion of the air, or the like.

Secondly, that it be not too long exposed, so as that the whole bulk be frozen, for oftentimes, in such cases, by reason of the swelling the of Ice, or from some other cause, the curious branched Figures disappear.

Thirdly, an artificial freezing with Snow and Salt, apply'd to the outside of the containing Vessel, succeeds not well, unless there be a very little quantity in the Vessel.

Fourthly, If you take any cleer and smooth Glass, and wetting all the inside of it with Urine, you expose it to a very sharp freezing, you will find it cover'd with a very regular and curious Figure.

Observables in figur'd Snow.

Exposing a piece of black Cloth, or a black Hatt to the falling Snow, I have often with great pleasure, observ'd such an infinite variety of curiously figur'd Snow, that it would be as impossible to draw the Figure and shape of every one of them, as to imitate exactly the curious and Geometrical Mechanisme of Nature in any one. Some coorse draughts, such as the coldness of the weather, and the ill provisions, I had by me for such a purpose, would permit me to make, I Schem. 8.
Fig. 2. have here added in the Second Figure of the Eighth Scheme.

In all which I observ'd, that if they were of any regular Figures, they were always branched out with six principal branches, all of equal length, shape and make, from the center, being each of them inclin'd to either of the next branches on either side of it, by an angle of sixty degrees.

Now, as all these stems were for the most part in one flake exactly of the same make, so were they in differing Figures of very differing ones; so that in a very little time I have observ'd above an hundred several cizes and shapes of these starry flakes.

The branches also out of each stem of any one of these flakes, were exactly alike in the same flake; so that of whatever Figure one of the branches were, the other five were sure to be of the same, very exactly, that is, if the branchings of the one were small Perallelipipeds or Plates, the branchings of the other five were of the same; and generally, the branchings were very conformable to the rules and method observ'd before, in the Figures on Urine, that is, the branchings from each side of the stems were parallel to the next stem on that side, and if the stems were plated, the branches also were the same; if the stems were very long, the branches also were so, &c.

Observing some of these figur'd flakes with a Microscope, I found them not to appear so curious and exactly figur'd as one would have imagin'd, but like Artificial Figures, the bigger they were magnify'd, the more irregularites appear'd in them; but this irregularity seem'd ascribable to the thawing and breaking of the flake by the fall, and not at all to the defect of the plastick virtue of Nature, whose curiosity in the formation of most of these kind of regular Figures, such as those of Salt, Minerals, &c. appears by the help of the Microscope, to be very many degrees smaller then the most acute eye is able to perceive without it. And though one of these six-branched Stars appear'd here below much of the shape described Schem. 8.
Fig. 3. in the Third Figure of the Eighth Scheme; yet I am very apt to think, that could we have a sight of one of them through a Microscope as they are generated in the Clouds before their Figures are vitiated by external accidents, they would exhibit abundance of curiosity and neatness there also, though never so much magnify'd: For since I have observ'd the Figures of Salts and Minerals to be some of them so exceeding small, that I have scarcely been able to perceive them with the Microscope, and yet have they been regular, and since (as far as I have yet examin'd it) there seems to be but one and the same cause that produces both these effects, I think it not irrational to suppose that these pretty figur'd Stars of Snow, when at first generated might be also very regular and exact.

III.

Several kinds of Figures in Water frozen.

Putting fair Water into a large capacious Vessel of Glass, and exposing it to the cold, I observ'd after a little time, several broad, flat, and thin laminæ, or plates of Ice, crossing the bulk of the water and one another very irregularly, onely most of them seem'd to turn one of their edges towards that side of the Glass which was next it, and seem'd to grow, as 'twere from the inside of the Vessel inwards towards the middle, almost like so many blades of Fern. Having taken several of these plates out of water on the blade of a Knife, I observ'd them figur'd much after the manner of Herring bones, or Fern blades, that is, there was one bigger stem in the middle like the back-bone, and out of it, on either side, were a multitude of small stiriæ, or icicles, like the smaller bones, or the smaller branches in Fern, each of these branches on the one side, were parallel to all the rest on the same side, and all of them seem'd to make an angle with the stem, towards the top, of sixty degrees, and towards the bottom or root of this stem, of 120. See the fourth Figure of the 8. Plate.

I observ'd likewise several very pretty Varieties of Figures in Water, frozen on the top of a broad flat Marble-stone, expos'd to the cold with a little Water on it, some like feathers, some of other shapes, many of Schem. 8.
Fig. 5. them were very much of the shape exprest in the fifth Figure of the 8. Scheme, which is extremely differing from any of the other Figures.

I observ'd likewise, that the shootings of Ice on the top of Water, beginning to freez, were in streight prismatical bodies much like those of roch-peter, that they crost each other usually without any kind of order or rule, that they were always a little higher then the surface of the Water that lay between them; that by degrees those interjacent spaces would be fill'd with Ice also, which usually would be as high as the surface of the rest.

In flakes of Ice that had been frozen on the top of Water to any considerable thickness, I observ'd that both the upper and the under sides of it were curiously quill'd, furrow'd, or grain'd, as it were, which when the Sun shone on the Plate, was exceeding easily to be Schem. 8.
Fig. 6. perceiv'd to be much after the shape of the lines in the 6. Figure of the 8. Scheme, that is, they consisted of several streight ends of parallel Plates, which were of divers lengths and angles to one another without any certain order.

The cause of all which regular Figures (and of hundreds of others, namely of Salts, Minerals, Metals, &c. which I could have here inserted, would it not have been too long) seems to be deducible from the same Principles, which I have (in the 13. Observation) hinted only, having not yet had time to compleat a Theory of them. But indeed (which I there also hinted) I judge it the second step by which the Pyramid of natural knowledge (which is the knowledge of the form of bodies) is to be ascended: And whosoever will climb it, must be well furnish'd with that which the Noble Verulam calls Scalam Intellectus; he must have scaling Ladders, otherwise the steps are so large and high, there will be no getting up them, and consequently little hopes of attaining any higher station, such as to the knowledge of the most simple principle of Vegetation manifested in Mould and Mushromes, which, as I elsewhere endeavoured to shew, seems to be the third step; for it seems to me, that the Intellect of man is like his body, destitute of wings, and cannot move from a lower to a higher and more sublime station of knowledg, otherwise then step by step, nay even there where the way is prepar'd and already made passible; as in the Elements of Geometry, or the like, where it is fain to climb a whole series of Propositions by degrees, before it attains the knowledge of one Probleme. But if the ascent be high, difficult and above its reach, it must have recourse to a novum organum, some new engine and contrivance, some new kind of Algebra, or Analytick Art before it can surmount it.

Observ. XV. Of Kettering-stone, and of the pores of Inanimate bodies.

This Stone which is brought from Kettering in Northampton-Shire, and digg'd out of a Quarry, as I am inform'd, has a grain altogether admirable, nor have I ever seen or heard of any other stone that has the like. It is made up of an innumerable company of small bodies, not all of the same cize or shape, but for the most part, not much differing from a Globular form, nor exceed they one another in Diameter above three or four times; they appear to the eye, like the Cobb or Ovary of a Herring, or some smaller fishes, but for the most part, the particles seem somewhat less, and not so uniform; but their variation from a perfect globular ball, seems to be only by the pressure of the contiguous bals which have a little deprest and protruded those toucht sides inward, and forc'd the other sides as much outwards beyond the limits of a Globe; just as it would happen, if a heap of exactly round Balls of soft Clay were heaped upon one another; or, as I have often seen a heap of small Globules of Quicksilver, reduc'd to that form by rubbing it much in a glaz'd Vessel, with some slimy or sluggish liquor, such as Spittle, when though the top of the upper Globules be very neer spherical, yet those that are prest upon by others, exactly imitate the forms of these lately mention'd grains.

Where these grains touch each other, they are so firmly united or settled together, that they seldom part without breaking a hole in one or th'other of them, such as a, a, a, b, c, c, &c. Some of which fractions, as a, a, a, a, where the touch has been but light, break no more then the outward crust, or first shell of the stone, which is of a white colour, a little dash'd with a brownish Yellow, and is very thin, like the shell of an Egg: and I have seen some of those grains perfectly resemble some kind of Eggs, both in colour and shape: But where the union of the contiguous granules has been more firm, there the divulsion has made a greater Chasm, as at b, b, b, in so much that I have observ'd some of them quite broken in two, as at c, c, c, which has discovered to me a further resemblance they have to Eggs, they having an appearance of a white and yelk, by two differing substances that envelope and encompass each other.

That which we may call the white was pretty whitish neer the yelk, but more duskie towards the shell; some of them I could plainly perceive to be shot or radiated like a Pyrites or fire-stone; the yelk in some I saw hollow, in others fill'd with a duskie brown and porous substance like a kind of pith.

The small pores, or interstitia eeee betwixt the Globules, I plainly saw, and found by other trials to be every way pervious to air and water, for I could blow through a piece of this stone of a considerable thickness, as easily as I have blown through a Cane, which minded me of the pores which Des Cartes allow his materia subtilis between the æthereal globules.

The object, through the Microscope, appears like a Congeries or heap of Pibbles, such as I have often seen cast up on the shore, by the working of the Sea after a great storm, or like (in shape, though not colour) a company of small Globules of Quicksilver, look'd on with a Microscope, when reduc'd into that form by the way lately mentioned. And perhaps, this last may give some hint at the manner of the formation of the former: For supposing some Lapidescent substance to be generated, or some way brought (either by some commixture of bodies in the Sea it self, or protruded in, perhaps, out of some subterraneous caverns) to the bottom of the Sea, and there remaining in the form of a liquor like Quicksilver, heterogeneous to the ambient Saline fluid, it may by the working and tumblings of the Sea to and fro be jumbled and comminuted into such Globules as may afterwards be hardned into Flints, the lying of which one upon another, when in the Sea, being not very hard, by reason of the weight of the incompassing fluid, may cause the undermost to be a little, though not much, varied from a globular Figure. But this only by the by.

After what manner this Kettering-stone should be generated I cannot learn, having never been there to view the place, and observe the circumstances; but it seems to me from the structure of it to be generated from some substance once more fluid, and afterwards by degrees growing harder, almost after the same manner as I supposed the generation of Flints to be made.

But whatever were the cause of its curious texture, we may learn this information from it; that even in those things which we account vile, rude, and coorse, Nature has not been wanting to shew abundance of curiosity and excellent Mechanisme.

We may here find a Stone by help of a Microscope, to be made up of abundance of small Balls, which do but just touch each other, and yet there being so many contacts, they make a firm hard mass, or a Stone much harder then Free-stone.

Next, though we can by a Microscope discern so curious a shape in the particles, yet to the naked eye there scarce appears any such thing; which may afford us a good argument to think, that even in those bodies also, whose texture we are not able to discern, though help'd with Microscopes, there may be yet latent so curious a Schematisme, that it may abundantly satisfie the curious searcher, who shall be so happy as to find some way to discover it.

Next, we here find a Stone, though to the naked eye a very close one, yet every way perforated with innumerable pores, which are nothing else but the interstitia, between those multitudes of minute globular particles, that compose the bulk it self, and these pores are not only discover'd by the Microscope, but by this contrivance.

I took a pretty large piece of this stone, and covering it all over with cement, save only at two opposite parts, I found my self able, by blowing in at one end that was left open, to blow my spittle, with which I had wet the other end, into abundance of bubbles, which argued these pores to be open and pervious through the whole stone, which affords us a very pretty instance of the porousness of some seemingly close bodies, of which kind I shall anon have occasion to subjoyn many more, tending to prove the same thing.

I must not here omit to take notice, that in this body there is not a vegetative faculty that should so contrive this structure for any peculiar use of vegetation or growth, whereas in the other instances of vegetable porous bodies, there is an anima or forma informans, that does contrive all the Structures and Mechanismes of the constituting body, to make them subservient and usefull to the great Work or Function they are to perform. And so I ghess the pores in Wood, and other vegetables, in bones, and other Animal substances, to be as so many channels, provided by the Great and Alwise Creator, for the conveyance of appropriated juyces to particular parts. And therefore, that this may tend, or be pervious all towards one part, and may have impediments, as valves or the like, to any other; but in this body we have very little reason so suspect there should be any such design, for it is equally pervious every way, not onely forward, but backwards, and side-ways, and seems indeed much rather to be Homogeneous or similar to those pores, which we may with great probability believe to be the channels of pellucid bodies, not directed, or more open any one way, then any other, being equally pervious every way. And, according as these pores are more or greater in respect of the interstitial bodies, the more transparent are the so constituted concretes; and the smaller those pores are, the weaker is the Impulse of light communicated through them, though the more quick be the progress.

Upon this Occasion, I hope it will not be altogether unseasonable, if I propound my conjectures and Hypothesis about the medium and conveyance of light.

I suppose then, that the greatest part of the Interstitia of the world, that lies between the bodies of the Sun and Starrs, and the Planets, and the Earth, to be an exceeding fluid body, very apt and ready to be mov'd, and to communicate the motion of any one part to any other part, though never so far distant: Nor do I much concern my self, to determine what the Figure of the particles of this exceedingly subtile fluid medium must be, nor whether it have any interstitiated pores or vacuities, it being sufficient to solve all the Phænomena to suppose it an exceedingly fluid, or the most fluid body in the world, and as yet impossible to determine the other difficulties.

That being so exceeding fluid a body, it easily gives passage to all other bodies to move to and fro in it.

That it neither receives from any of its parts, or from other bodies; nor communicates to any of its parts, or to any other body, any impulse, or motion in a direct line, that is not of a determinate quickness. And that when the motion is of such determinate swiftness, it both receives, and communicates, or propagates an impulse or motion to any imaginable distance in streight lines, with an unimaginable celerity and vigour.

That all kind of solid bodies consist of pretty massie particles in respect of the particles of this fluid medium, which in many places do so touch each other, that none of this fluid medium interposes much after the same mannner (to use a gross similitude) as a heap of great stones compose one great congeries or mass in the midst of the water.

That all fluid bodies which we may call tangible, are nothing but some more subtile parts of those particles, that serve to constitute all tangible bodies.

That the water, and such other fluid bodies, are nothing but a congeries of particles agitated or made fluid by it in the same manner as the particles of Salt are agitated or made fluid by a parcel of water, in which they are dissolv'd, and subsiding to the bottom of it, constitute a fluid body, much more massie and dense, and less fluid then the pure water it self.

That the air on the other side is a certain company of particles of quite another kind, that is, such as are very much smaller, and more easiely moveable by the motion of this fluid medium; much like those very subtile parts of Cochenel, other very deep tinging bodies, where by a very small parcel of matter is able to tinge and diffuse it self over a very great quantity of the fluid dissolvent; or somewhat after that manner, as smoak, and such like minute bodies, or steams, are observ'd to tinge a very great quantity of air; onely this last similitude is deficient in one propriety, and that is a perpetuity or continuance in that state of commixture with the air, but the former does more neerly approach to the nature and manner of the air's being dissolv'd by this fluid or Æther. And this Similitude will further hold in these proprieties; that as those tinctures may be increased by certain bodies, so may they be precipitated by others, as I shall afterwards shew it to be very probable, that the like accidents happen even to the Air it self.

Further, as these solutions and tinctures do alter the nature of these fluid bodies, as to their aptness to propagate a motion or impulse through them, even so does the particles of the Air, Water, and other fluid bodies, and of Glass, Crystal, &c. which are commixt with this bulk of the Æther alter the motion of the propagated pulse of light; that is, where these more bulkie particles are more plentifull, and consequently a lesser quantity of the Æther between them to be mov'd, there the motion must necessarily be the swifter, though not so robust, which will produce those effects, which I have (I hope) with some probability, ascribed to it in the digression about Colours, at the end of the Observations on Muscovy-glass.

Now, that other Stones, and those which have the closest and hardest textures, and seem (as far as we are able to discover with our eyes, though help'd with the best Microscopes) freest from pores, are yet notwithstanding replenish'd with them, an Instance or two will, I suppose, make more probable.

A very solid and unflaw'd piece of cleer white Marble, if it be well polish'd and glaz'd, has so curiously smooth a surface, that the best and most polish'd surface of any wrought-glass, seems not to the naked eye, nor through a Microscope, to be more smooth, and less porous. And yet, that this hard close body is replenish'd with abundance of pores, I think these following Experiments will sufficiently prove.

The first is, That if you take such a piece, and for a pretty while boyl it in Turpentine and Oyl of Turpentine, you shall find that the stone will be all imbu'd with it; and whereas before it look'd more white, but more opacous, now it will look more greasie, but be much more transparent, and if you let it lie but a little while, and then break off a part of it, you shall find the unctuous body to have penetrated it to such a determinate depth every way within the surface. This may be yet easier try'd with a piece of the same Marble, a little warm'd in the fire, and then a little Pitch or Tarr melted on the top of it; for these black bodies, by their insinuating themselves into the invisible pores of the stone, ting it with so black a hue, that there can be no further doubt of the truth of this assertion, that it abounds with small imperceptible pores.

Now, that other bodies will also sink into the pores of Marble, besides unctuous, I have try'd, and found, that a very Blue tincture made in spirit of Urine would very readily and easily sink into it, as would also several tinctures drawn with spirit of Wine.

Nor is Marble the only seemingly close stone, which by other kinds of Experiments may be found porous; for I have by this kind of Experiment on divers other stones found much the same effect, and in some, indeed much more notable. Other stones I have found so porous, that with the Microscope I could perceive several small winding holes, much like Worm-holes, as I have noted in some kind of Purbeck-stone, by looking on the surface of a piece newly flaw'd off, for if otherwise, the surface has been long expos'd to the Air, or has been scraped with any tool, those small caverns are fill'd with dust, and disappear.

And to confirm this Conjecture, yet further, I shall here insert an excellent account, given into the Royal Society by that Eminently Learned Physician, Doctor Goddard, of an Experiment, not less instructive then curious and accurate, made by himself on a very hard and seemingly close stone call'd Oculus Mundi, as I find it preserv'd in the Records of that Honourable Society.

In which Experiment, there are three Observables that seem very manifestly to prove the porousness of these seemingly close bodies: the first is their acquiring a transparency, and losing their whiteness after steeping in water, which will seem the more strongly to argue it, if what I have already said about the making transparent, or clarifying of some bodies, as the white powder of beaten Glass, and the froth of some glutinous transparent liquor be well consider'd; for thereby it will seem rational to think that this transparency arises from the insinuation of the water (which has much the same refraction with such stony particles, as may be discover'd by Sand view'd with a Microscope) into those pores which were formerly repleat with air (that has a very differing refraction, and consequently is very reflective) which seems to be confirm'd by the second Observable, namely, the increase of weight after keeping, and decrease upon drying. And thirdly, seem'd yet more sensibly confirm'd by the multitude of bubbles in the last Experiment.

We find also most Acid Salts very readily to dissolve and separate the parts of this body one from another; which is yet a further Argument to confirm the porousness of bodies, and will serve as such, to shew that even Glass also has an abundance of pores in it, since there are several liquors, that with long staying in a Glass, will so Corrode and eat into it, as at last, to make it pervious to the liquor it contain'd, of which I have seen very many Instances.

Since therefore we find by other proofs, that many of those bodies which we think the most solid ones, and appear so to our sight, have notwithstanding abundance of those grosser kind of pores, which will admit several kinds of liquors into them, why should we not believe that Glass, and all other transparent bodies abound with them, since we have many other arguments, besides the propagation of light, which seem to argue for it?

And whereas it may be objected, that the propagation of light is no argument that there are those atomical pores in glass, since there are Hypotheses plausible enough to solve those Phænomena, by supposing the pulse onely to be communicated through the transparent body.

To this I answer, that that Hypothesis which the industrious Mersennus has publish'd about the slower motion of the end of a Ray in a denser medium, then in a more rare and thin, seems altogether unsufficient to solve abundance of Phænomena, of which this is not the least considerable, that it is impossible from that supposition, that any colours should be generated from the refraction of the Rays; for since by that Hypothesis the undulating pulse is always carried perpendicular, or at right angles with the Ray or Line of direction, it follows, that the stroke of the pulse of light, after it has been once or twice refracted (through a Prisme, for example) must affect the eye with the same kind of stroke as if it had not been refracted at all. Nor will it be enough for a Defendant of that Hypothesis, to say, that perhaps it is because the refractions have made the Rays more weak, for if so, then two refractions in the two parallel sides of a Quadrangular Prisme would produce colours, but we have no such Phænomena produc'd.

There are several Arguments that I could bring to evince that there are in all transparent bodies such atomical pores. And that there is such a fluid body as I am arguing for, which is the medium, or Instrument, by which the pulse of Light is convey'd from the lucid body to the enlightn'd. But that it being a digression from the Observations I was recording, about the Pores of Kettering Stone, it would be too much such, if I should protract it too long; and therefore I shall proceed to the next Observation.

Observ. XVI. Of Charcoal, or burnt Vegetables.

Charcoal, or a Vegetable burnt black, affords an object no less pleasant than instructive, for if you take a small round Charcoal, and break it short with your fingers, you may perceive it to break with a very smooth and sleek surface, almost like the surface of black sealing Wax; this surface, if it be look'd on with an ordinary Microscope, does manifest abundance of those pores which are also visible to the eye in many kinds of Wood, rang'd round the pith, both a in kind of circular order, and a radiant one. Of these there are a multitude in the substance of the Coal, every where almost perforating and drilling it from end to end; by means of which, be the Coal never so long, you may easily blow through it; and this you may presently find, by wetting one end of it with Spittle, and blowing at the other.

But this is not all, for besides those many great and conspicuous irregular spots or pores, if a better Microscope be made use of, there will appear an infinite company of exceedingly small, and very regular pores, so thick and so orderly set, and so close to one another, that they leave very little room or space between them to be fill'd with a solid body, for the apparent interstitia or separating sides of these pores seem so thin in some places, that the texture of a Honey-comb cannot be more porous. Though this be not every where so, the intercurrent partitions in some places being very much thicker in proportion to the holes.

Most of these small pores seem'd to be pretty round, and were rang'd in rows that radiated from the pith to the bark; they all of them seem'd to be continued open pores, running the whole length of the Stick; and that they were all perforated, I try'd by breaking off a very thin sliver of the Coal cross-ways, and then with my Microscope, diligently surveying them against the light, for by that means I was able to see quite through them.

These pores were so exceeding small and thick, that in a line of them, 1/18 part of an Inch long, I found by numbring them no less then 150. small pores; and therefore in a line of them an Inch long, must be no less then 2700. pores, and in a circular area of an Inch diameter, must be about 5725350. of the like pores; so that a Stick of an Inch Diameter, may containe no less then seven hundred and twenty five thousand, besides 5 Millions of pores, which would, I doubt not, seem even incredible, were not every one left to believe his own eyes. Nay, having since examin'd Cocus, black and green Ebony, Lignum Vitæ, &c. I found, that all these Woods have their pores, abundantly smaller then those of soft light Wood; in so much, that those of Guajacum seem'd not above an eighth part of the bigness of the pores of Beech, but then the Interstitia were thicker; so prodigiously curious are the contrivances, pipes, or sluces by which the Succus nutritius, or Juyce of a Vegetable is convey'd from place to place.

This Observation seems to afford us the true reason of several Phænomena of Coals; as

First, why they look black; and for this we need go no further then the Scheme, for certainly, a body that has so many pores in it as this is discover'd to have, from each of which no light is reflected, must necessarily look black, especially, when the pores are somewhat bigger in proportion to the intervals then they are cut in the Scheme, black being nothing else but a privation of Light, or a want of reflection; and wheresover this reflecting quality is deficient, there does that part look black, whether it be from a porousness of the body, as in this Instance, or in a deadning and dulling quality, such as I have observ'd in the Scoria of Lead, Tin, Silver, Copper, &c.

Next, we may also as plainly see the reason of its shining quality, and that is from the even breaking off of the stick, the solid interstitia having a regular termination or surface, and having a pretty strong reflecting quality, the many small reflections become united to the naked eye, and make a very pretty shining surface.

Thirdly, the reason of its hardness and brittleness seems evident, for since all the watery or liquid substance that moistn'd and toughn'd those Interstitia of the more solid parts, are evaporated and remov'd, that which is left behind becomes of the nature almost of a stone, which will not at all, or very little, bend without a divulsion or solution of its continuity.

It is not my design at present, to examine the use and Mechanisme of these parts of Wood, that being more proper to another Enquiry; but rather to hint, that from this Experiment we may learn,

First, what is the cause of the blackness of many burnt bodies, which we may find to be nothing else but this; that the heat of the fire agitating and rarifying the waterish, transparent, and volatile water that is contain'd in them, by the continuation of that action, does so totally expel and drive away all that which before fill'd the pores, and was dispers'd also through the solid mass of it, and thereby caus'd an universal kind of transparency, that it not onely leaves all the pores empty, but all the Interstitia also so dry and opacous, and perhaps also yet further perforated, that that light onely is reflected back which falls upon the very outward edges of the pores, all they that enter into the pores of the body, never returning, but being lost in it.

Now, that the Charring or coaling of a body is nothing else, may be easily believ'd by one that shall consider the means of its production, which may be done after this, or any such manner. The body to be charr'd or coal'd, may be put into a Crucible, Pot, or any other Vessel that will endure to be made red-hot in the fire without breaking, and then cover'd over with Sand, so as no part of it be suffer'd to be open to the Air, then set into a good fire, and there kept till the Sand has continu'd red hot for a quarter, half, an hour or two, or more, according to the nature and bigness of the body to be coal'd or charr'd, then taking it out of the fire, and letting it stand till it be quite cold, the body may be taken out of the Sand well charr'd and cleans'd of its waterish parts; but in the taking of it out, care must be had that the Sand be very neer cold, for else, when it comes into the free air, it will take fire, and readily burn away.

This maybe done also in any close Vessel of Glass, as a Retort, or the like, and the several fluid substances that come over may be receiv'd in a fit Recipient, which will yet further countenance this Hypothesis: And their manner of charring Wood in great quantity comes much to the same thing, namely, an application of a great heat to the body, and preserving it from the free access of the devouring air; this may be easily learn'd from the History of Charring of Coal, most excellently describ'd and publish'd by that most accomplish'd Gentleman, Mr. John Evelin, in the 100, 101, 103, pages of his Sylva, to which I shall therefore refer the curious Reader that desires a full information of it.

Next, we may learn what part of the Wood it is that is the combustible matter, for since we shall find that none, or very little of those fluid substances that are driven over into the Receiver are combustible, and that most of that which is left behind is so, it follows, that the solid interstitia of the Wood are the combustible matter. Further, the reason why uncharr'd Wood burns with a greater flame then that which is charr'd, is as evident, because those waterish or volatil parts issuing out of the fired Wood, every way, not onely shatter and open the body, the better for the fire to enter, but issuing out in vapours or wind, they become like so many little æolipiles, or Bellows, whereby they blow and agitate the fir'd part, and conduce to the more speedy and violent consumption or dissolution of the body.

Thirdly, from the Experiment of charring of Coals (whereby we see that notwithstanding the great heat, and the duration of it, the solid parts of the Wood remain, whilest they are preserv'd from the free access of the air undissipated) we may learn, that which has not, that I know of, been publish'd or hinted, nay, not so much as thought of, by any; and that in short is this.

First, that the Air in which we live, move, and breath, and which encompasses very many, and cherishes most bodies it encompasses, that this Air is the menstruum, or universal dissolvent of all Sulphureous bodies.

Secondly, that this action it performs not, till the body be first sufficiently heated, as we find requisite also to the dissolution of many other bodies by several other menstruums.

Thirdly, that this action of dissolution, produces or generates a very great heat, and that which we call Fire; and this is common also to many dissolutions of other bodies, made by menstruums, of which I could give multitudes of Instances.

Fourthly, that this action is perform'd with so great a violence, and does so minutely act, and rapidly agitate the smallest parts of the combustible matter, that it produces in the diaphanous medium of the Air, the action or pulse of light, which what it is, I have else-where already shewn.

Fifthly, that the dissolution of sulphureous bodies is made by a substance inherent, and mixt with the Air, that is like, if not the very same, with that which is fixt in Salt-peter, which by multitudes of Experiments that may be made with Saltpeter, will, I think, most evidently be demonstrated.

Sixthly, that in this dissolution of bodies by the Air, a certain part is united and mixt, or dissolv'd and turn'd into the Air, and made to fly up and down with it in the same manner as a metalline or other body dissolved into any menstruums, does follow the motions and progresses of that menstruum till it be precipitated.

Seventhly, That as there is one part that is dissoluble by the Air, so are there other parts with which the parts of the Air mixing and uniting, do make a Coagulum, or precipitation, as one may call it, which causes it to be separated from the Air, but this precipitate is so light, and in so small and rarify'd or porous clusters, that it is very volatil, and is easily carry'd up by the motion of the Air, though afterwards, when the heat and agitation that kept it rarify'd ceases, it easily condenses, and commixt with other indissoluble parts, it sticks and adheres to the next bodies it meets withall; and this is a certain Salt that may be extracted out of Soot.

Eighthly, that many indissoluble parts being very apt and prompt to be rarify'd, and so, whilest they continue in that heat and agitation, are lighter then the Ambient Air, are thereby thrust and carry'd upwards with great violence, and by that means carry along with them, not onely that Saline concrete I mention'd before, but many terrestrial, or indissoluble and irrarefiable parts, nay, many parts also which are dissoluble, but are not suffer'd to stay long enough in a sufficient heat to make them prompt and apt for that action. And therefore we find in Soot, not onely a part, that being continued longer in a competent heat, will be dissolv'd by the Air, or take fire and burn; but a part also which is fixt, terrestrial, and irrarefiable.

Ninthly, that as there are these several parts that will rarifie and fly, or be driven up by the heat, so are there many others, that as they are indissoluble by the aerial menstruum, so are they of such sluggish and gross parts, that they are not easily rarify'd by heat, and therefore cannot be rais'd by it; the volatility or fixtness of a body seeming to consist only in this, that the one is of a texture, or has component parts that will be easily rarify'd into the form of Air, and the other, that it has such as will not, without much ado, be brought to such a constitution; and this is that part which remains behind in a white body call'd Ashes, which contains a substance, or Salt, which Chymists call Alkali: what the particular natures of each of these bodies are, I shall not here examine, intending it in another place, but shall rather add that this Hypothesis does so exactly agree with all Phænomena, of Fire, and so genuinely explicate each particular circumstance that I have hitherto observ'd, that it is more then probable, that this cause which I have assign'd is the true adequate, real, and onely cause of those Phænomena; And therefore I shall proceed a little further, to shew the nature and use of the Air.

Tenthly, therefore the dissolving parts of the Air are but few, that is, it seems of the nature of those Saline menstruums, or spirits, that have very much flegme mixt with the spirits, and therefore a small parcel of it is quickly glutted, and will dissolve no more; and therefore unless some fresh part of this menstruum be apply'd to the body to be dissolv'd, the action ceases, and the body leaves to be dissolv'd and to shine, which is the Indication of it, though plac'd or kept in the greatest heat; whereas Salt-peter is a menstruum, when melted and red-hot, that abounds more with those Dissolvent particles, and therefore as a small quantity of it will dissolve a great sulphureous body, so will the dissolution be very quick and violent.

Therefore in the Eleventh place, it is observable, that, as in other solutions, if a copious and quick supply of fresh menstruum, though but weak, be poured on, or applied to the dissoluble body, it quickly consumes it: So this menstruum of the Air, if by Bellows, or any other such contrivance, it be copiously apply'd to the shining body, is found to dissolve it as soon, and as violently as the more strong menstruum of melted Nitre.

Therefore twelfthly, it seems reasonable to think that there is no such thing as an Element of Fire that should attract or draw up the flame, or towards which the flame should endeavour to ascend out of a desire or appetite of uniting with that as its Homogeneal primitive and generating Element; but that that shining transient body which we call Flame, is nothing else but a mixture of Air, and volatil sulphureous parts of dissoluble or combustible bodies, which are acting upon each other whilst they ascend, that is, flame seems to be a mixture of Air, and the combustible volatil parts of any body, which parts the encompassing Air does dissolve or work upon, which action, as it does intend the heat of the aerial parts of the dissolvent, so does it thereby further rarifie those parts that are acting, or that are very neer them, whereby they growing much lighter then the heavie parts of that menstruum that are more remote, are thereby protruded and driven upward; and this may be easily observ'd also in dissolution made by any other menstruum, especially such as either create heat or bubbles. Now, this action of the menstruum, or Air, on the dissoluble parts, is made with such violence, or is such, that it imparts such a motion or pulse to the diaphanous parts of the Air, as I have elsewhere shewn is requisite to produce light.

This Hypothesis I have endeavoured to raise from an Infinite of Observations and Experiments, the process of which would be much too long to be here inserted, and will perhaps another time afford matter copious enough for a much larger Discourse, the Air being a Subject which (though all the world has hitherto liv'd and breath'd in, and been unconversant about) has yet been so little truly examin'd or explain'd, that a diligent enquirer will be able to find but very little information from what has been (till of late) written of it: But being once well understood, it will, I doubt not, inable a man to render an intelligible, nay probable, if not the true reason of all the Phænomena of Fire, which, as it has been found by Writers and Philosophers of all Ages a matter of no small difficulty, as may be sufficiently understood by their strange Hypotheses, and unintelligible Solutions of some few Phænomena of it; so will it prove a matter of no small concern and use in humane affairs, as I shall elsewhere endeavour to manifest when I come to shew the use of the Air in respiration, and for the preservation of the life, nay, for the conservation and restauration of the health and natural constitution of mankind as well as all other aereal animals, as also the uses of this principle or propriety of the Air in chymical, mechanical, and other operations. In this place I have onely time to hint an Hypothesis, which, if God permit me life and opportunity, I may elsewhere prosecute, improve and publish. In the mean time, before I finish this Discourse, I must not forget to acquaint the Reader, that having had the liberty granted me of making some trials on a piece of Lignum fossile shewn to the Royal Society, by the eminently Ingenious and Learned Physician, Doctor Ent, who receiv'd it for a Present from the famous Ingenioso Cavalliero de Pozzi, it being one of the fairest and best pieces of Lignum fossile he had seen; Having (I say) taken a small piece of this Wood, and examin'd it, I found it to burn in the open Air almost like other Wood, and insteed of a resinous smoak or fume, it yielded a very bituminous one, smelling much of that kind of sent: But that which I chiefly took notice of, was, that cutting off a small piece of it, about the bigness of my Thumb, and charring it in a Crucible with Sand, after the manner I above prescrib'd, I found it infinitely to abound with the smaller sort of pores, so extreamly thick, and so regularly perforating the substance of it long-ways, that breaking it off a-cross, I found it to look very like an Honey-comb; but as for any of the second, or bigger kind of pores, I could not find that it had any; so that it seems, whatever were the cause of its production, it was not without those small kind of pores which we have onely hitherto found in Vegetable bodies: and comparing them with the pores which I have found in the Charcoals that I by this means made of several other kinds of Wood, I find it resemble none so much as those of Fire, to which it is not much unlike in grain also, and several other proprieties.

And therefore, what ever is by some, who have written of it, and particularly by Francisco Stelluto, wrote a Treatise in Italian of that Subject, which was Printed at Rome, 1637, affirm'd that it is a certain kind of Clay or Earth, which in tract of time is turn'd into Wood; I rather suspect the quite contrary, that it was at first certain great Trees of Fir or Pine, which by some Earthquake, or other casualty, came to be buried under the Earth, and was there, after a long time's residence (according to the several natures of the encompassing adjacent parts) either rotted and turn'd into a kind of Clay, or petrify'd and turn'd into a kind of Stone, or else had its pores fill'd with certain Mineral juices, which being stay'd in them, and in tract of time coagulated, appear'd, upon cleaving out, like small Metaline Wires, or else from some flames or scorching forms that are the occasion oftentimes, and usually accompany Earthquakes, might be blasted and turn'd into Coal, or else from certain subterraneous fires which are affirm'd by that Authour to abound much about those parts (namely, in a Province of Italy, call'd Umbria, now the Dutchie of Spoletto, in the Territory of Todi, anciently call'd Tudor; and between the two Villages of Collesecco and Rosaro not far distant from the high-way leading to Rome, where it is found in greater quantity then elsewhere) are by reason of their being encompassed with Earth, and so kept close from the dissolving Air, charr'd and converted into Coal. It would be too long a work to describe the several kinds of pores which I met withall, and by this means discovered in several other Vegetable bodies; nor is it my present design to expatiate upon Instances of the same kind, but rather to give a Specimen of as many kinds as I have had opportunity as yet of observing, reserving the prosecution and enlarging on particulars till a more fit opportunity; and in prosecution of this design, I shall here add:

Observ. XVII. Of Petrify'd wood, and other Petrify'd bodies.

Of this sort of substance, I observ'd several pieces of very differing kinds, both for their outward shape, colour, grain, texture, hardness, &c. some being brown and redish; others gray, like a Hone; others black, and Flint-like: some soft, like a Slate or Whetstone, others as hard as a Flint, and as brittle. That which I more particular examin'd, was a piece about the bigness of a mans hand, which seem'd to have been a part of some large tree, that by rottenness had been broken off from it before it began to be petrify'd.

And indeed, all that I have yet seen, seem to have been rotten Wood before the petrifaction was begun; and not long since, examining and viewing a huge great Oak, that seem'd with meer age to be rotten as it stood, I was very much confirm'd in this opinion; for I found, that the grain, colour, and shape of the Wood, was exactly like this petrify'd substance; and with a Microscope, I found, that all those Microscopical pores, which in sappy or firm and sound Wood are fill'd with the natural or innate juices of those Vegetables, in this they were all empty, like those of Vegetables charr'd; but with this difference, that they seem'd much larger then I have seen any in Char-coals; nay, even then those of Coals made of great blocks of Timber, which are commonly call'd Old-coals.

The reason of which difference may probably be, that the charring of Vegetables, being an operation quickly perform'd, and whilest the Wood is sappy, the more solid parts may more easily shrink together, and contract the pores or interstitia between them, then in the rotten Wood, where that natural juice seems onely to be wash'd away by adventitious or unnatural moisture; and so though the natural juice be wasted from between the firm parts, yet those parts are kept asunder by the adventitious moystures, and so by degrees settled in those postures.

And this I likewise found in the petrify'd Wood, that the pores were somewat bigger then those of Charcoal, each pore being neer upon half as bigg again, but they did not bear that disproportion which Schem. 10.
Fig. 1, 2. is exprest in the tenth Scheme, between the small specks or pores in the first Figure (which representeth the pores of Coal or Wood charr'd) and the black spots of the second Figure (which represent the like Microscopical pores in the petrify'd Wood) for these last were drawn by a Microscope that magnify'd the object above six times more in Diameter then the Microscope by which those pores of Coal were observ'd.

Now, though they were a little bigger, yet did they keep the exact figure and order of the pores of Coals and of rotten Wood, which last also were much of the same cize.

The other Observations on this petrify'd substance, that a while since, by the appointment of the Royal Society, I made, and presented to them an account of, were these that follow, which had the honour done them by the most accomplish'd Mr. Evelin, my highly honoured friend, to be inserted and published among those excellent Observations wherewith his Sylva is replenish'd, and would therefore have been here omitted, had not the Figure of them, as they appear'd through the Microscope been before that engraven.

First, all the parts of it seem'd not at all dislocated, or alter'd from their natural Position, whil'st they were Wood, but the whole piece retain'd the exact shape of Wood, having many of the conspicuous pores of wood still remaining pores, and shewing a manifest difference visible enough between the grain of the Wood and that of the bark, especially when any side of it was cut smooth and polite; for then it appear'd to have a very lovely grain, like that of some curious close Wood.

Next (it resembled Wood) in that all the smaller and (if I may so call those which are onely visible with a good magnifying Glass) Microscopical pores of it appear (both when the substance is cut and polish'd transversly and parallel to the pores of it) perfectly like the Microscopical pores of several kinds of Wood, especially like and equal to those of several sorts of rotten Wood which I have since observ'd, retaining both the shape, position and magnitude of such pores. It was differing from Wood:

First; in weight, being to common water as 3¼ to 1. whereas there are few of our English Woods, that when very dry are found to be full as heavie as water.

Secondly, in hardness, being very neer as hard as a Flint; and in some places of it also resembling the grain of a Flint: and, like it, it would very readily cut Glass, and would not without difficulty, especially in some parts of it, be scratch'd by a black hard Flint: It would also as readily strike fire against a Steel, or against a Flint, as any common Flint.

Thirdly, in the closeness of it, for though all the Microscopical pores of this petrify'd substance were very conspicuous in one position, yet by altering that position of the polish'd surface to the light, it was also manifest, that those pores appear'd darker then the rest of the body, onely because they were fill'd up with a more duskie substance, and not because they were hollow.

Fourthly, in its incombustibleness, in that it would not burn in the fire; nay, though I kept it a good while red-hot in the flame of a Lamp, made very intense by the blast of a small Pipe, and a large Charcoal, yet it seem'd not at all to have diminish'd its extension; but only I found it to have chang'd its colour, and to appear of a more dark and duskie brown colour; nor could I perceive that those parts which seem'd to have been Wood at first, were any thing wasted, but the parts appear'd as solid and close as before. It was further observable also, that as it did not consume like Wood, so neither did it crack and flie like a Flint, or such like hard Stone, nor was it long before it appear'd red-hot.

Fifthly, in its dissolubleness; for putting some drops of distill'd Vinegar upon the Stone, I found it presently to yield very many Bubbles, just like those which may be observ'd in spirit of Vinegar when it corrodes corals, though perhaps many of those small Bubbles might proceed from some small parcels of Air which were driven out of the pores of this petrify'd substance by the insinuating liquid menstruum.

Sixthly, in its rigidness, and friability, being not at all flexible but brittle like a Flint, insomuch that I could with one knock of a Hammer break off a piece of it, and with a few more, reduce that into a pretty fine powder.

Seventhly, it seem'd also very differing from Wood to the touch, feeling more cold then Wood usually does, and much like other close stones and Minerals.

That petrify'd Wood having lain in some place where it was well soak'd with petrifying water (that is, such a water as is well impregnated with stony and earthy particles) did by degrees separate, either by straining and filtration, or perhaps, by precipitation, cohesion or coagulation, abundance of stony particles from the permeating water, which stony particles, being by means of the fluid vehicle convey'd, not onely into the Microscopical pores, and so perfectly stoping them up, but also into the pores or interstitia, which may, perhaps, be even in the texture or Schematisme of that part of the Wood, which, through the Microscope, appears most solid, do thereby so augment the weight of the Wood, as to make it above three times heavier then water, and perhaps, six times as heavie as it was when Wood.

Next, they thereby so lock up and fetter the parts of the Wood, that the fire cannot easily make them flie away, but the action of the fire upon them is onely able to Char those parts, as it were, like a piece of Wood, if it be clos'd very fast up in Clay, and kept a good while red-hot in the fire, will by the heat of the fire be charr'd and not consum'd, which may, perhaps, also be somewhat of the cause, why the petrify'd substance appear'd of a dark brown colour after it had been burnt.

By this intrusion of the petrifying particles, this substance also becomes hard and friable; for the smaller pores of the Wood being perfectly wedg'd, and stuft up with those stony particles, the small parts of the Wood have no places or pores into which they may slide upon bending, and consequently little or no flexion or yielding at all can be caus'd in such a substance.

The remaining particles likewise of the Wood among the stony particles, may keep them from cracking and flying when put into the fire, as they are very apt to do in a Flint.

Nor is Wood the onely substance that may by this kind of transmutation be chang'd into stone; for I my self have seen and examin'd very many kinds of substances, and among very credible Authours, we may meet with Histories of such Metamorphoses wrought almost on all kind of substances, both Vegetable and Animal, which Histories, it is not my business at present, either to relate, or epitomise, but only to set down some Observation I lately made on several kind of petrify'd Shels, found about Keinsham, which lies within four or five miles of Bristol, which are commonly call'd Serpentine-stones.

Examining several of these very curiously figur'd bodies (which are commonly thought to be Stones form'd by some extraordinary Plastick virtue latent in the Earth itself) I took notice of these particulars:

First, that these figured bodies, or stones, were of very differing substances, as to hardness: some of Clay, some Marle, some soft Stone, almost of the hardness of those soft stones which Masons call Fire-stone, others as hard as Portland stone, others as hard as Marble, and some as hard as a Flint or Crystal.

Next, they were of very differing substances as to transparency and colour; some white, some almost black, some brown, some Metalline, or like Marchasites; some transparent like white Marble, others like flaw'd Crystal, some gray, some of divers colours; some radiated like those long petrify'd drops, which are commonly found at the Peak, and in other subterraneous caverns, which have a kind of pith in the middle.

Thirdly, that they were very different as to the manner of their outward figuration; for some of them seem'd to have been the substance that had fill'd the Shell of some kind of Shel-fish; others, to have been the substance that had contain'd or enwrapp'd one of those Shels, on both which, the perfect impression either of the inside or outside of such Shells seem'd to be left, but for the most part, those impressions seem'd to be made by an imperfect or broken Shell, the great end or mouth of the Shell being always wanting, and often times the little end, and sometimes half, and in some there were impressions, just as if there had been holes broken in the figurating, imprinting or moulding Shell; some of them seem'd to be made by such a Shell very much brused or flaw'd, insomuch that one would verily have thought that very figur'd stone had been broken or brused whilst a gelly, as 'twere, and so hardned, but within in the grain of the stone, there appear'd not the least sign of any such bruse or breaking, but onely on the very uttermost superficies.

Fourthly, they were very different, as to their outward covering, some having the perfect Shell, both in figure, colour, and substance, sticking on upon its surface, and adhering to it, but might very easily be separated from it, and like other common Cockle or Scolop-shels, which some of them most accurately resembled, were very dissoluble in common Vinegar, others of them, especially those Serpentine, or Helical stones were cover'd or retained the shining or Pearl-colour'd substance of the inside of a Shel, which substance, on some parts of them, was exceeding thin, and might very easily be rubbed off; on other parts it was pretty thick, and retained a white coat, or flaky substance on the top, just like the outsides of such Shells; some of them had very large pieces of the Shell very plainly sticking on to them, which were easily to be broken or flaked off by degrees: they likewise, some of them retain'd all along the surface of them very pretty kind of sutures, such as are observ'd in the skulls of several kinds of living creatures, which sutures were most curiously shap'd in the manner of leaves, and every one of them in the same Shell, exactly one like another, which I was able to discover plainly enough with my naked eye, but more perfectly and distinctly with my Microscope; all these sutures, by breaking some of these stones, I found to be the termini, or boundings of certain diaphragms, or partitions, which seem'd to divide the cavity of the Shell into a multitude of very proportionate and regular cells or caverns, these Diaphragms, in many of them, I found very perfect and compleat, of a very distinct substance from that which fill'd the cavities, and exactly of the same kind with that which covered the outside, being for the most part whitish, or mother-of-pearl colour'd.

As for the cavities between those Diaphragms, I found some of them fill'd with Marle, and others with several kinds of stones, others, for the most part hollow, onely the whole cavity was usually covered over with a kind of tartareous petrify'd substance, which stuck about the sides, and was there shot into very curious regular Figures, just as Tartar, or other dissolv'd Salts are observ'd to stick and crystallize about the sides of the containing Vessels; or like those little Diamants which I before observed to have covered the vaulted cavity of a Flint; others had these cavities all lin'd with a kind of metalline or marchasite-like substance, which with a Microscope I could as plainly see most curiously and regularly figured, as I had done those in a Flint.

From all which, and several other particulars which I observ'd, I cannot but think, that all these, and most other kinds of stony bodies which are found thus strangely figured, do owe their formation and figuration, not to any kind of Plastick virtue inherent in the earth, but to the Shells of certain Shel-fishes, which, either by some Deluge, Inundation, Earthquake, or some such other means, came to be thrown to that place, and there to be fill'd with some kind of Mudd or Clay, or petrifying Water, or some other substance, which in tract of time has been settled together and hardned in those shelly moulds into those shaped substances we now find them; that the great and thin end of these Shells by that Earthquake, or what ever other extraordinary cause it was that brought them thither, was broken off; and that many others were otherwise broken, bruised and disfigured; that these Shells which are thus spirallied and separated with Diaphragmes, were some kind of Nautili or Porcelane shells; and that others were shells of Cockles, Muscles, Periwincles, Scolops, &c. of various sorts; that these Shells in many, from the particular nature of the containing or enclos'd Earth, or some other cause, have in tract of time rotted and mouldred away, and onely left their impressions, both on the containing and contained substances; and so left them pretty loose one within another, so that they may be easily separated by a knock or two of a Hammer. That others of these Shells, according to the nature of the substances adjacent to them, have, by a long continuance in that posture, been petrify'd and turn'd into the nature of stone, just as I even now observ'd several sorts of Wood to be. That oftentimes the Shell may be found with one kind of substance within, and quite another without; having, perhaps, been fill'd in one place, and afterwards translated to another, which I have very frequently observ'd in Cockle, Muscle, Periwincle, and other shells, which I have found by the Sea side. Nay, further, that some parts of the same Shell may be fill'd in one place, and some other caverns in another, and others in a third, or a fourth, or a fifth place, for so many differing substances have I found in one of these petrify'd Shells, and perhaps all these differing from the encompassing earth or stone; the means how all which varieties may be caus'd, I think, will not be difficult to conceive, to any one that has taken notice of those Shells, which are commonly found on the Sea shore: And he that shall throughly examine several kinds of such curiously form'd stones, will (I am very apt to think) find reason to suppose their generation or formation to be ascribable to some such accidents as I have mention'd, and not to any Plastick virtue: For it seems to me quite contrary to the infinite prudence of Nature, which is observable in all its works and productions, to design every thing to a determinate end, and for the attaining of that end, makes use of such ways as are (as farr as the knowledge of man has yet been able to reach) altogether consonant, and most agreeable to man's reason, and of no way or means that does contradict, or is contrary to humane Ratiocination; whence it has a long time been a general observation and maxime, that Nature does nothing in vain; It seems, I say, contrary to that great Wisdom of Nature, that these prettily shap'd bodies should have all those curious Figures and contrivances (which many of them are adorn'd and contriv'd with) generated or wrought by a Plastick virtue, for no higher end, then onely to exhibite such a form; which he that shall throughly consider all the circumstances of such kind of Figur'd bodies, will, I think, have great reason to believe, though, I confess, one cannot presently be able to find out what Nature's designs are. It were therefore very desirable, that a good collection of such kind of figur'd stones were collected; and as many particulars, circumstances, and informations collected with them as could be obtained, that from such a History of Observations well rang'd, examin'd and digested, the true original or production of all those kinds of stones might be perfectly and surely known; such as are Thunder-stones, Lapides Stellares, Lapides Judaici, and multitudes of other, whereof mention is made in Aldonandus, Wormius, and other Writers of Minerals.

Observ. XVIII. Of the Schematisme or Texture of Cork, and of the Cells and Pores of some other such frothy Bodies.

I took a good clear piece of Cork, and with a Pen-knife sharpen'd as keen as a Razor, I cut a piece of it off, and thereby left the surface of it exceeding smooth, then examining it very diligently with a Microscope, me thought I could perceive it to appear a little porous; but I could not so plainly distinguish them, as to be sure that they were pores, much less what Figure they were of: But judging from the lightness and yielding quality of the Cork, that certainly the texture could not be so curious, but that possibly, if I could use some further diligence, I might find it to be discernable with a Microscope, I with the same sharp Penknife, cut off from the former smooth surface an exceeding thin piece of it, and placing it on a black object Plate, because it was it self a white body, and casting the light on it with a deep plano-convex Glass, I could exceeding plainly perceive it to be all perforated and porous, much like a Honey-comb, but that the pores of it were not regular; yet it was not unlike a Honey-comb in these particulars.

First, in that it had a very little solid substance, in comparison of the empty cavity that was contain'd between, as does more manifestly Schem. 11.
Fig. 1. appear by the Figure A and B of the XI. Scheme, for the Interstitia, or walls (as I may so call them) or partitions of those pores were neer as thin in proportion to their pores, as those thin films of Wax in a Honey-comb (which enclose and constitute the sexangular celts) are to theirs.

Next, in that these pores, or cells, were not very deep, but consisted of a great many little Boxes, separated out of one continued long pore, by certain Diaphragms, as is visible by the Figure B, which represents a sight of those pores split the long-ways.

I no sooner discern'd these (which were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any Writer or Person, that had made any mention of them before this) but me thought I had with the discovery of them, presently hinted to me the true and intelligible reason of all the Phænomena of Cork; As,

First, if I enquir'd why it was so exceeding light a body? my Microscope could presently inform me that here was the same reason evident that there is found for the lightness of froth, an empty Honey-comb, Wool, a Spunge, a Pumice-stone, or the like; namely, a very small quantity of a solid body, extended into exceeding large dimensions.

Next, it seem'd nothing more difficult to give an intelligible reason, why Cork is a body so very unapt to suck and drink in Water, and consequently preserves it self, floating on the top of Water, though left on it never so long: and why it is able to stop and hold air in a Bottle, though it be there very much condens'd and consequently presses very strongly to get a passage out, without suffering the least bubble to pass through its substance. For, as to the first, since our Microscope informs us that the substance of Cork is altogether fill'd with Air, and that that Air is perfectly enclosed in little Boxes or Cells distinct from one another. It seems very plain, why neither the Water, nor any other Air can easily insinuate it self into them, since there is already within them an intus existens, and consequently, why the pieces of Cork become so good floats for Nets, and stopples for Viols, or other close Vessels.

And thirdly, if we enquire why Cork has such a springiness and swelling nature when compress'd? and how it comes to suffer so great a compression, or seeming penetration of dimensions, so as to be made a substance as heavie again and more, bulk for bulk, as it was before compression, and yet suffer'd to return, is found to extend it self again into the same space? Our Microscope will easily inform us, that the whole mass consists of an infinite company of small Boxes or Bladders of Air, which is a substance of a springy nature, and that will suffer a considerable condensation (as I have several times found by divers trials, by which I have most evidently condens'd it into less then a twentieth part of its usual dimensions neer the Earth, and that with no other strength then that of my hands without any kind of forcing Engine, such as Racks, Leavers, Wheels, Pullies, or the like, but this onely by and by) and besides, it seems very probable that those very films or sides of the pores, have in them a springing quality, as almost all other kind of Vegetable substances have, so as to help to restore themselves to their former position.

And could we so easily and certainly discover the Schematisme and Texture even of these films, and of several other bodies, as we can these of Cork; there seems no probable reason to the contrary, but that we might as readily render the true reason of all their Phænomena; as namely, what were the cause of the springingess, and toughness of some, both as to their flexibility and restitution. What, of the friability or brittleness of some others, and the like; but till such time as our Microscope, or some other means, enable us to discover the true Schematism and Texture of all kinds of bodies, we must grope, as it were, in the dark, and onely ghess at the true reasons of things by similitudes and comparisons.

But, to return to our Observation. I told several lines of these pores, and found that there were usually about threescore of these small Cells placed end-ways in the eighteenth part of an Inch in length, whence I concluded there must be neer eleven hundred of them, or somewhat more then a thousand in the length of an Inch, and therefore in a square Inch above a Million, or 1166400. and in a Cubick Inch, above twelve hundred Millions, or 1259712000. a thing almost incredible, did not our Microscope assure us of it by ocular demonstration; nay, did it not discover to us the pores of a body, which were they diaphragm'd, like those of Cork, would afford us in one Cubick Inch, more then ten times as many little Cells, as is evident in several charr'd Vegetables; so prodigiously curious are the works of Nature, that even these conspicuous pores of bodies, which seem to be the channels or pipes through which the Succus nutritius, or natural juices of Vegetables are convey'd, and seem to correspond to the veins, arteries and other Vessels in sensible creatures, that these pores I say, which seem to be the Vessels of nutrition to the vastest body in the World, are yet so exceeding small, that the Atoms which Epicurus fancy'd would go neer to prove too bigg to enter them, much more to constitute a fluid body in them. And how infinitely smaller then must be the Vessels of a Mite, or the pores of one of those little Vegetables I have discovered to grow on the back-side of a Rose-leaf, and shall anon more fully describe, whose bulk is many millions of times less then the bulk of the small shrub it grows on; and even that shrub, many millions of times less in bulk then several trees (that have heretofore grown in England, and are this day flourishing in other hotter Climates, as we are very credibly inform'd) if at least the pores of this small Vegetable should keep any such proportion to the body of it, as we have found these pores of other Vegetables to do to their bulk. But of these pores I have said more elsewhere.

To proceed then, Cork seems to be by the transverse constitution of the pores, a kind of Fungus or Mushrome, for the pores lie like so many Rays tending from the center, or pith of the tree, outwards; so that if you cut off a piece from a board of Cork transversly, to the flat of it, you will, as it were, split the pores, and they will appear just as they are express'd in the Figure B of the XI. Scheme. But if you shave off a very thin piece from this board, parallel to the plain of it, you will cut all the pores transversly, and they will appear almost as they are express'd in the Figure A, save onely the solid Interstitia will not appear so thick as they are there represented.

So that Cork seems to suck its nourishment from the subjacent bark of the Tree immediately, and to be a kind of excrescence, or a substance distinct from the substances of the entire Tree, something analogus to the Mushrome, or Moss on other Trees, or to the hairs on Animals. And having enquir'd into the History of Cork, I find it reckoned as an excrescency of the bark of a certain Tree, which is distinct from the two barks that lie within it, which are common also to other trees; That 'tis some time before the Cork that covers the young and tender sprouts comes to be discernable; That it cracks, flaws, and cleaves into many great chaps, the bark underneath remaining entire; That it may be separated and remov'd from the Tree, and yet the two under-barks (such as are also common to that with other Trees) not at all injur'd, but rather helped and freed from an external injury. Thus Jonstonus in Dendrologia, speaking de Subere, says, Arbor est procera, Lignum est robustum, dempto cortice in aquis non fluitat, Cortice in orbem detracto juvatur, crascescens enim præstringit & strangulat, intra triennium iterum repletur: Caudex ubi adolescit crassus, cortex superior densus carnosus, duos digitos crassus, scaber, rimosus, & qui nisi detrahatur dehiscit, alioque subnascente expellitur, interior qui subest novellus ita rubet ut arbor minio picta videatur. Which Histories, if well consider'd, and the tree, substance, and manner of growing, if well examin'd, would, I am very apt to believe, much confirm this my conjecture about the origination of Cork.

Nor is this kind of Texture peculiar to Cork onely; for upon examination with my Microscope, I have found that the pith of an Elder, or almost any other Tree, the inner pulp or pith of the Cany hollow stalks of several other Vegetables: as of Fennel, Carrets, Daucus, Bur-docks, Teasels, Fearn, some kinds of Reeds, &c. have much such a kind of Schematisme, as I have lately shewn that of Cork, save onely that here the pores are rang'd the long-ways, or the same ways with the length of the Cane, whereas in Cork they are transverse.

The pith also that fills that part of the stalk of a Feather that is above the Quil, has much such a kind of texture, save onely that which way soever I set this light substance, the pores seem'd to be cut transversly; so that I ghess this pith which fills the Feather, not to consist of abundance of long pores separated with Diaphragms, as Cork does, but to be a kind of solid or hardned froth, or a congeries of very small bubbles consolidated in that form, into a pretty stiff as well as tough concrete, and that each Cavern, Bubble, or Cell, is distinctly separate from any of the rest, without any kind of hole in the encompassing films, so that I could no more blow through a piece of this kinde of substance, then I could through a piece of Cork, or the sound pith of an Elder.

But though I could not with my Microscope, nor with my breath, nor any other way I have yet try'd, discover a passage out of one of those cavities into another, yet I cannot thence conclude, that therefore there are none such, by which the Succus nutritius, or appropriate juices of Vegetables, may pass through them; for, in several of those Vegetables, whil'st green, I have with my Microscope, plainly enough discover'd these Cells or Poles fill'd with juices, and by degrees sweating them out; as I have also observed in green Wood all those long Microscopical pores which appear in Charcoal perfectly empty of any thing but Air.

Now, though I have with great diligence endeavoured to find whether there be any such thing in those Microscopical pores of Wood or Piths, as the Valves in the heart, veins, and other passages of Animals, that open and give passage to the contain'd fluid juices one way, and shut themselves, and impede the passage of such liquors back again, yet have I not hitherto been able to say any thing positive in it; though, me thinks, it seems very probable, that Nature has in these passages, as well as in those of Animal bodies, very many appropriated Instruments and contrivances, whereby to bring her designs and end to pass, which 'tis not improbable, but that some diligent Observer, if help'd with better Microscopes, may in time detect.

And that this may be so, seems with great probability to be argued from the strange Phænomena of sensitive Plants, wherein Nature seems to perform several Animal actions with the same Schematism or Orginization that is common to all Vegetables, as may appear by some no less instructive then curious Observations that were made by divers Eminent Members of the Royal Society on some of these kind of Plants, whereof an account was delivered in to them by the most Ingenious and Excellent Physician, Doctor Clark, which, having that liberty granted me by that most Illustrious Society, I have hereunto adjoyn'd.

Observations on the Humble and Sensible Plants in M Chiffin's Garden in Saint James's Park, made August the 9^th, 1661. Present, the Lord Brouncker, Sr. Robert Moray, Dr. Wilkins, Mr. Evelin, Dr. Henshaw, and Dr. Clark.

I have not yet made so full and satisfactory Observations as I desire on this Plant, which seems to be a Subject that will afford abundance of information. But as farr as I have had opportunity to examine it, I have discovered with my Microscope very curious structures and contrivances; but designing much more accurate examinations and trials, both with my Microscope, and otherwise, as soon as the season will permit, I shall not till then add any thing of what I have already taken notice of; but as farr as I have yet observ'd, I judge the motion of it to proceed from causes very differing from those by which Gut-strings, or Lute-strings, the beard of a wilde Oat, or the beard of the Seeds of Geranium, Mosscatum, or Musk-grass and other kinds of Cranes-bill, move themselves. Of which I shall add more in the subsequent Observations on those bodies.

Observ. XIX. Of a Plant growing in the blighted or yellow specks of Damask-rose-leaves, Bramble-leaves, and some other kind of leaves.

I have for several years together, in the Moneths of June, July, August, and September (when any of the green leaves of Roses begin to dry and grow yellow) observ'd many of them, especially the leaves of the old shrubs of Damask Roses, all bespecked with yellow stains; and the undersides just against them, to have little yellow hillocks of a gummous substance, and several of them to have small black spots in the midst of those yellow ones, which, to the naked eye, appear'd no bigger then the point of a Pin, or the smallest black spot or tittle of Ink one is able to make with a very sharp pointed Pen.

Examining these with a Microscope, I was able plainly to distinguish, up and down the surface, several small yellow knobs, of a kind of yellowish red gummy substance, out of which I perceiv'd there sprung multitudes of little cases or black bodies like Seed-cods, and those of them that were quite without the hillock of Gumm, disclos'd themselves to grow out of it with a small Straw-colour'd and transparent stem, the which seed and stem appear'd very like those of common Moss (which I elsewhere describe) but that they were abundantly less, many hundreds of them being not able to equalize one single seed Cod of Moss.

I have often doubted whether they were the seed Cods of some little Plant, or some kind of small Buds, or the Eggs of some very small Insect, they appear'd of a dark brownish red, some almost quite black, and of a Figure much resembling the seed-cod of Moss, but their stalks on which they grew were of a very fine transparent substance, almost like the stalk of mould, but that they seem'd somewhat more yellow.

That which makes me to suppose them to be Vegetables, is for that I perceiv'd many of those hillocks bare or destitute, as if those bodies lay yet conceal'd, as G. In others of them, they were just springing out of their gummy hillocks, which all seem'd to shoot directly outwards, as at A. In others, as at B, I found them just gotten out, with very little or no stalk, and the Cods of an indifferent cize; but in others, as C, I found them begin to have little short stalks, or stems; in others, as D, those stems were grown bigger, and larger; and in others, as at E, F, H, I, K, L, &c. those stems and Cods were grown a great deal bigger, and the stalks were more bulky about the root, and very much taper'd towards the top, as at F and L is most visible.

I did not find that any of them had any seed in them, or that any of them were hollow, but as they grew bigger and bigger, I found those heads or Cods begin to turn their tops towards their roots, in the same manner as I had observ'd that of Moss to do; so that in all likelihood, Nature did intend in that posture, what she does in the like seed-cods of greater bulk, that is, that the seed, when ripe, should be shaken out and dispersed at the end of it, as we find in Columbine Cods, and the like.

The whole Oval OOOO in the second Figure of the 12. Scheme represents a small part of a Rose leaf, about the bigness of the little Oval in the hillock, C, marked with the Figure X. in which I have not particularly observ'd all the other forms of the surface of the Rose-leaf, as being little to my present purpose.

Now, if these Cods have a seed in them so proportion'd to the Cod, as thole of Pinks, and Carnations, and Columbines, and the like, how unimaginably small must each of those seeds necessarily be, for the whole length of one of the largest of those Cods was not 1/500 part of an Inch; some not above 1/1000, and therefore certainly, very many thousand of them would be unable to make a bulk that should be visible to the naked eye; and if each of these contain the Rudiments of a young Plant of the same kind, what must we say of the pores and constituent parts of that?

The generation of this Plant seems in part, ascribable to a kind of Mildew or Blight, whereby the parts of the leaves grow scabby, or putrify'd, as it were, so as that the moisture breaks ou

The Project Gutenberg eBook, Micrographia, by Robert Hooke

E-text prepared by Robert Shimmin, Keith Edkins, and the Project Gutenberg Online Distributed Proofreading Team

By the Council of the ROYAL SOCIETY of London for Improving of Natural Knowledge.

MICROGRAPHIA:

Physiological Descriptions

MINUTE BODIES

MAGNIFYING GLASSES

OBSERVATIONS and INQUIRIES thereupon.

TO THE

KING.

ROBERT HOOKE.

TO THE

ROYAL SOCIETY.

ROBERT HOOKE.

THE

PREFACE.

MICROGRAPHIA,

Physiological Descriptions

MINUTE BODIES,

MAGNIFYING GLASSES;

OBSERVATIONS and INQUIRIES thereupon.

Observ. I. Of the Point of a sharp small Needle.

Observ. II. Of the Edge of a Razor.

Observ. III. Of fine Lawn, or Linnen Cloth.

Observ. IV. Of fine waled Silk, or Taffety.

Observ. V. Of watered Silks, or Stuffs.

Observ. VI. Of Small Glass Canes.

To make small shot of different sizes; Communicated by his Highness P.R.

Observ. VII. Of some Phænomena of Glass drops.

Observ. VIII. Of the fiery Sparks struck from a Flint or Steel.

Observ. IX. Of the Colours observable in Muscovy Glass, and other thin Bodies.

Observ. X. Of Metalline, and other real Colours.

Observ. XI. Of Figures observ'd in small Sand.

Observ. XII. Of Gravel in Urine.

Observ. XIII. Of the small Diamants, or Sparks in Flints.

Observ. XIV. Of several kindes of frozen Figures.

I.

Several Observables in the six-branched Figures form'd on the surface of Urine by freezing.

II

Observables in figur'd Snow.

III.

Several kinds of Figures in Water frozen.

Observ. XV. Of Kettering-stone, and of the pores of Inanimate bodies.

Observ. XVI. Of Charcoal, or burnt Vegetables.

Observ. XVII. Of Petrify'd wood, and other Petrify'd bodies.

Observ. XVIII. Of the Schematisme or Texture of Cork, and of the Cells and Pores of some other such frothy Bodies.

Observations on the Humble and Sensible Plants in M Chiffin's Garden in Saint James's Park, made August the 9th, 1661. Present, the Lord Brouncker, Sr. Robert Moray, Dr. Wilkins, Mr. Evelin, Dr. Henshaw, and Dr. Clark.

Observ. XIX. Of a Plant growing in the blighted or yellow specks of Damask-rose-leaves, Bramble-leaves, and some other kind of leaves.

E-text prepared by Robert Shimmin, Keith Edkins,
and the Project Gutenberg Online Distributed Proofreading Team

By the Council of the ROYAL SOCIETY of London
for Improving of Natural Knowledge.

Observations on the Humble and Sensible Plants in M Chiffin's Garden in Saint James's Park, made August the 9^th, 1661. Present, the Lord Brouncker, Sr. Robert Moray, Dr. Wilkins, Mr. Evelin, Dr. Henshaw, and Dr. Clark.