C O N S I D E R A T I O N S

C O L O U R S.

First occasionally written, among some other Essays, to a Friend;

and now suffered to come abroad as

E x p e r i m e n t a l H i s t o r y of

C O L O U R S.

HAVING, in convenient places of the following treatise, mentioned the motives that induced me to write it, and the scope I proposed to myself in it, I think it superfluous to entertain the reader now with what he will meet with hereafter. And I should judge it needless, to trouble others, or myself, with any thing of preface; were it not, that I can scarce doubt, but this book will fall into the hands of some readers, who being unacquainted with the difficulty of attempts of this nature, will think it strange that I should publish any thing about colours, without a particular theory of them. But I dare expect, that intelligent and equitable readers will consider on my behalf, that the professed design of this treatise is to deliver things rather historical than dogmatical, and consequently, if I have added divers new speculative considerations and hints which perhaps may afford no despicable assistance towards the framing of a solid and comprehensive hypothesis, I have done at least as much as I promised, or as the nature of my undertaking exacted. But another thing there is, which if it should be objected, I fear I should not be able so easily to answer it; and that is, that in the following treatise (especially in the third part of it) the experiments might have been better marshalled, and some of them delivered in fewer words. For I must confess, that this essay was written to a private friend, and that too by snatches, at several times and places, and (after my manner) in loose sheets, of which I oftentimes had not all by me that I had already written, when I was writing more; so that it needs be no wonder if all the experiments be not ranged to the best advantage, and if some connexions and consecutions of them might easily have been mended: especially since, having carelessly laid by the loose papers, or several years after they were written, when I came to put them together to dispatch them to the press, I found some of those I reckoned upon, to be very unseasonably wanting. And to make any great change in the order of the rest was more than the printer's importunity, and that of my own avocations (and perhaps also considerable sollicitations) would permit. But though some few preambles of the particular experiments might have (perchance) been spared, or shortened, if I had had all my papers under my view at once; yet in the most of those introductory passages, the reader will (I hope) find hints, or advertisements, as well as transitions. If I sometimes seem to insist long upon the circumstances of a trial, I hope I shall be easily excused by those, that both know how nice divers experiments of colours are, and consider, that I was not barely to relate them, but so as to teach a young gentleman to make them. And if I was not sollicitous to make a nicer division of the whole treatise, than into three parts, whereof the one contains some considerations about colours in general; the other exhibits a specimen of an account of particular colours, exemplified in whiteness and blackness; and the third, promiscuous experiments about the remaining colours (especially red) in order to a theory of them: if, I say, I contented myself with this easy division of my discourse, it was perhaps, because I did not think it so necessary to be curious about the method or contrivance of a treatise, wherein I do not pretend to present my reader with a compleat fabric, or so much as model; but only to bring in materials proper for the building. And if I did not well know, how ingenious the curiosity and civility of friends makes them, to persuade men by specious allegations, to gratify their desires; I should have been made to believe by persons very well qualified to judge of matters of this nature, that the following experiments will not need the addition of accurate method and speculative notions to procure acceptance for the treatise that contains them. For it hath been represented, that in most of them, as the novelty will make them surprizing, and the quickness of performance keep them from being tedious; so the sensible changes, that are effected by them, are so manifest, so great, and so sudden, that scarce any will be displeased to see them, and those that are any thing curious will scarce be able to see them, without finding themselves excited to make reflections upon them. But though with me, who love to measure physical things by their use, not their strangeness, or prettiness, the partiality of others prevails not to make me over-value these, or look upon them in themselves as other than trifle; yet I confess, that ever since I did divers years ago show some of them to a learned company of Virtuosi, so many persons of differing conditions, and even sexes, have been curious to see them, and pleased not to dislike them, that I cannot despair, but that by complying with those that urge the publication of them, I may both gratify and excite the curious, and lay perhaps a foundation, whereon either others or myself may in time superstruct a substantial theory of colours. And if Aristotle, after his master Plato, have rightly observed admiration to be the parent of philosophy, the wonder, some of these-trifles have been wont to produce in all sorts of beholders, and the access they have sometimes gained even to the closets of ladies, seem to promise, that since the subject is so pleasing, that the speculation appears as delightful as difficult, of such easy and recreative experiments, which require but little time, or charge, or trouble in the making, and when made are sensible and surprizing enough, may contribute more than others (far more important, but as much more difficult) to recommend those parts of learning (chymistry and corpuscular philosophy) by which they have been produced, and to which they give testimony even to such kind of persons, as value a pretty trick more than a true notion, and would scarce admit philosophy, if it approached them in another dress. Without the strangeness or endearments of pleasantness to recommend it, I know, that I do but ill consult my own advantage in the consenting to the publication of the following treatis: for those things, which, whilst men knew not how they were performed, appeared so strange, will, when the way of making them, and the grounds on which I devised them, shall be public, quickly lose all, that their being rarities, and their being thought mysteries, contributed to recommend them. But it is fitter for mountebanks than naturalists to desire to have their discoveries rather admired than understood; and for my part I had much rather deserve the thanks of the ingenious, than enjoy the applause of the ignorant. And if I can so far contribute to the discovery of the nature of colours, as to help the curious to it, I shall have reached my end, and saved myself some labour, which else I may chance to be tempted to undergo in prosecuting that subject, and adding to this treatise, which I therefore call a history, because it chiefly contains matters of fact, and which history the title declares me to look upon but as begun. Because though that above a hundred, not to say a hundred and fifty experiments (some loose, and others interwoven amongst the discourses themselves) may suffice to give a beginning to a history not hitherto, that I know, begun by any; yet the subject is so fruitful and so worthy, that those, who are curious of these matters, will be far more wanting to themselves than I can suspect if what I now publish prove any more than a beginning. For, as I hope my endeavours may afford them some a assistance towards this work, so those endeavours are too much unfinished to give them any discouragement, as if there were little left for others to do towards the history of colours.

FOR, (first) I have been willing to leave unmentioned the most part of those phænomena of colours, that nature presents us of her own accord (that is, without being guided or over-ruled by man;) such as the different colours, that several sorts of fruits pass through before they are perfectly ripe, and those that appear upon the fading of flowers and leaves, and the putrefaction (and its several degrees) of fruits, &c. together with a thousand other obvious instances of the changes of colours. Nor have I much meddled with those familiar phænomena, wherein man is not an idle spectator; such as the greenness produced by salt in beef much powdered, and the redness produced in the shells of lobsters upon the boiling of those fishes: for I was willing to leave the gathering of observations to those, that have not the opportunity to make experiments. And for the same reasons, among others, I did purposely omit the lucriferous practice of tradesmen about colours; as the ways of making pigments, of blanching wax, of dying scarlet, &c. though to divers of them I be not a stranger and of some I have myself made trial.

NEXT I did purposely pass by divers experiments of other writers that I had made trial of (and that not without registering some of their events) unless I could some way or other improve them; because I wanted leisure to insert them, and had thoughts of prosecuting the work once begun, of laying together those I had examined by themselves, in case of my not being prevented by others diligence. So that there remains not a little, among the things that are already published, to employ those, that have a mind to exercise themselves in repeating and examining them. And I will not undertake, that none the things delivered, even in this treatise, though never so faithfully set down, may not prove to be thus far of this sort, as to afford the curious somewhat to add about them. For I remember, that I have somewhere in the book itself acknowledged, that having written it by snatches, partly in the country and partly at unseasonable times of the year, when the want of fit instruments, and of a competent variety of flowers, salts, pigments, and other materials, made me leave some of the following experiments (especially those about emphatical colours) far more unfinished than they should have been, if it had been as easy for me to supply what was wanting to compleat them, as to discern. Thirdly, to avoid discouraging the young gentleman I call Pyrophilus, whom the less familiar and more laborious operations of chymistry would probably have frighted, I purposely declined, in what I writ to him, the setting down any number of such chymical experiments, as by being very elaborate or tedious, would either require much skill, or exercise his patience. And yet that this sort of experiments is exceedingly numerous, and might more than a little enrich the history of colours, those that are versed in chymical processes will, I presume, easily allow me.

AND (lastly) for as much as I have occasion more than once in my several writings to treat either purposely or incidentally of matters relating to colours, I did not, perhaps, conceive myself obliged to deliver in one treatise all that I would say concerning that subject.

BUT to conclude, by summing up what I would say concerning what I have, and what I have not done, in the following papers; I shall not (on the one side) deny, that considering, that I pretended not to write an accurate treatise of colours, but an occasional essay to acquaint a private friend with what then occurred to me of the things I had thought or tried concerning them; I might presume I did enough for once, if I did clearly and faithfully set down, though not all the experiments I could, yet at least such a variety of them, that an attentive reader, that shall consider the grounds on which they have been made, and the hints that are purposely (though dispersedly) couched in them, may easily compound them, and otherwise vary them, so as very much to increase their number. And yet (on the other side) I am so sensible both of how much I have, either out of necessity or choice, lest undone, and of the fruitfulness of the subject I have begun to handle; that though I had performed far more than it is like many readers will judge I have, I should yet be very free to let them apply to my attempts that of Seneca, where having spoken of the study of nature's mysteries, and particularly of the cause of earthquakes, he subjoins; Nulla res consmmata est dum incipit. Nec in hac tantum re omnium maxima ac involutissima, in qua etiam cum multum actum erit, omnis etas, quod agat, inveniet; sed in omni alio negotio, lenge semper a perfecto suere principia.

L. Annaei Senecae Natur. Quaest. 1. 6.c. 5-

HERE is presented to thy view one of the abstrusest as well as the genteelest subjects of natural philosophy, the Experimental History of Colours, which, though the noble author be pleased to think but begun, yet I must take leave to say, that I think it so well begun, that the work is more than half dispatched. Concerning which I cannot but give this advertisement to the reader, that I have heard the author express himself, that it would not surprize him, if it should happen to be objected, that some of these experiments have been already published, partly by chymists, and partly by two or three very fresh writers upon other subjects. And though the number of these experiments be but very small, and though they be none of the considerablest, yet it may on this occasion be further represented, that it is easy for our author to name several men (of whose number I can truly name myself) who remember either their having seen him make, or their having read his accounts of the experiments delivered in the following tract several years since, and long before the publication of the books, wherein they are mentioned. Nay, in divers passages (where he could do it without any great inconvenience) he hath struck out experiments, which he had tried many years ago, because he since found them divulged by persons, from whom he had not the least hint of them. Which yet is not touched, with design to reflect upon any ingenious man, as if he were a plagiary: for, though our generous author were not reserved enough in shewing his experiments to those that expressed a curiosity to see them (amongst whom a very learned man hath been pleased publickly to acknowledge it several years *;) yet the same thing may be well enough lighted on by persons, that know nothing of one another. And especially chymical laboratories may many times afford the same phenomenon, about colours, to several persons, at the same or differing times. And as for the few phænomena mentioned in the same chymical writers, as well as in the following treatise, our author hath given an account, why he did not decline rejecting them in the annotations upon the 47th experiment of the third part. Not here to mention, what lie elsewhere saith, to shew what use may justifiably made of experiments not of his own devising by a writer of natural history, if, what he employs of other men’s, be well examined or verified by himself.

IN the mean time, this treatise is such, that there needs no other invitation to peruse it, but that it is composed by one of the deepest and most indefatigable searchers of nature, which, I think the world, as far as I know it, affords. For mine own part, I feel a secret joy within me, to see such beginnings upon such themes, it being demonstratively true, mota facilius moveri; which causeth me to entertain strong hopes, that this illustrious virtuoso and restless inquirer into nature's secrets will not stop here, but go on and prosper in the disquisition of the other principal colours, green, red, and yellow. The reasoning faculty set once afloat will be carried on, and that with ease; especially, when the productions thereof meet, as they do here, with so greedy an entertainment at home and abroad. I am confident, that the ROYAL SOCIETY, lately constituted by his most Excellent Majesty for improving Natural Knowledge will judge it their interest to exhort our author to the prosecution of this argument; considering, how much it is their design and business to accumulate a good stock of such accurate observations and experiments, as may afford them and their offspring genuine matter to raise a masculine philosophy upon, whereby the mind of man may be ennobled with the knowledge of solid truths, and the life of man benefited with ampler accommodations, than it hath been hitherto.

OUR great author, one of the pillars of that illustrious corporation, is constantly furnishing large symbolas to this work; and is now fallen, as you see, upon so comprehensive and important a theme, as will, if insisted on and compleated, prove one of the considerablest pieces of that structure. To which if he shall please to add his treatise of heat and flame, as he is ready to publish his experimental accounts of cold, I esteem, the world will be obliged to him for having shewed them both the right and left-hand of nature, and the operations thereof.

THE considering reader will by this very treatise see abundant cause to sollicit the author for more. Sure I am, that whatever of the productions of his ingeny comes into foreign parts (where I am happy in the acquaintance of many intelligent friends) is highly valued; and to my knowledge, there are those among the French, that have lately begun to learn English, on purpose to enable themselves to read his books, being impatient of their traduction into Latin. If I durst say all I know of the elogies received by me from abroad concerning him, I should perhaps make this preamble too prolix, and certainly offend the modesty of our author.

WHEREFORE I shall leave this, and conclude with desiring the reader, that if he meet with other faults besides those that the Errata take notice of (as I believe he may) he will please to consider both the weakness of the author's eyes for not reviewing, and the manifold avocations of the publisher for not doing his part; who taketh his leave with inviting those, that have also considered this nice subject experimentally, to follow the example of our noble author, and impart such and the like performances to the now very inquisitive world. Farewel.

H. O.

EXPERIMENTAL HISTORY

O F

C O L O U R S

B E G U N.

THE FIRST PART.

C H A P. 1.

1. I HAVE seen you so passionately addicted, Pyrophilus, to the delightful art of limning and painting, that I cannot but think myself obliged to acquaint you with some of those things that have occurred to me concerning the changes of colours. And I may expect that I shall as well serve the Virtuosi in general, as gratify you in particular, by furnishing a person, who, I hope, will both improve my communications, and communicate his improvements, with such experiments and observations as may both invite you to enquire seriously into the nature of colours, and assist you in the investigation of it. This being the principal scope of the following tract, I should do that which might prevent my own design, if I should here attempt to deliver you an accurate and particular theory of colours for that were to present you with what I desire to receive from you; and, as far as in me lay, to make that study needless, to which I would engage you.

2. WHEREFORE my present work shall be but to divert and recreate, as well as excite you by the delivery of matters of fact, such as you may for the most part try with much ease, and possibly not without some delight. And lest you should expect any thing of elaborate or methodical in what you will meet with here, I must confess to you before-hand, that the seasons I was wont to chuse to devise and try experiments about colours, were those days, wherein having taken physic, and finding myself as unfit to speculate, as unwilling to be altogether idle, I chose this diversion as a kind of mean betwixt the one and the other. And I have the less scrupled to set down the following experiments, as some of them came to my mind, and as the notes wherein I had set down the rest, occurred to my hands; that by declining a methodical way of delivering them, I might leave you and myself the greater liberty and convenience to add to them, and transpose them as shall appear expedient.

3. YEA, that you may not think me too reserved, or look upon an inquiry made up of mere narratives, as somewhat jejune, I am content to premise a few considerations, that now offer themselves to my thoughts, which relate in a more general way. either to the nature of colours, or to the study of it. And I shall insert an essay, as well speculative as historical, of the nature of whiteness and blackness, that you may have a specimen of the history of colours, I have sometimes had thoughts of, and if you dislike not the method I have made use of, I hope you, and some of the Virtuosi your friends, may be thereby invited to go thorough with red, blue, yellow, and the rest of the particular colours, as I have done with white and black, but with far more sagacity and success. And if I can invite ingenious men to undertake such tasks, I doubt not but the curious will quickly obtain a better account of colours, than as yet we have, since in our method the theorical part of the inquiry being attended, and as it were interwoven with the historical conjectures, the philosophy of colours will be promoted by the indisputable experiments.

1. To come then in the first place to our more general considerations, I shall begin with saying something as to the importance of examining the colours of bodies. For there are some, especially chymists, who think that a considerable diversity of colours does constantly argue an equal diversity of nature, in the bodies wherein it is conspicuous; but I confess I am not altogether of their mind: for not to mention changeable taffaties, the blue and golden necks of pigeons, and divers water-fowl, rainbows natural and artificial, and other bodies, whose colours the philosophers have been pleased to call not real, but apparent and fantastical; not to insist on these, I say (for fear of needlessly engaging in a controversy) we see in parrots, goldfinches, and divers other birds, not only that the contiguous feathers which are probably as near in properties as place, are some of them red, and others white, some of them blue, and others yellow, &c. but that in the several parts of the self-same feather there may often be seen the greatest disparity of colours. And so in the leaves of tulips, july-flowers, and some other vegetables, the several leaves, and even the several parts of the same leaf, although no difference have been observed in their other properties, are frequently found painted with very different colours. And such a variety we have much more admired in that lovely plant which is commonly, and not unjustly called the Marvel of Peru; for of divers scores of fine flowers, which in its season that gaudy plant does almost daily produce, I have scarce taken notice of any two that were dyed perfectly alike. But though, Pyro, such things as these, among others, keep me from daring to affirm that the diversity and change of colours does always argue any great difference or alteration betwixt, or in the bodies, wherein it is to be discerned; yet that oftentimes the alteration of colours does signify considerable alterations in the disposition of parts of bodies, may appear in the extraction of tinctures, and divers other chymical operations, wherein the change of colours is the chief, and sometimes the only thing, by which the artist regulates his proceeding; and is taught to know when 'tis seasonable for him to leave off. Instances of this sort are more obvious in divers sorts of fruits, as cherries, plums, &c. wherein, according as the vegetable sap is sweetened, or otherwise ripened, by passing from one degree to another of maturation, the external part of the fruit passes likewise from one to another colour. But one of the noblest instances I have met with of this kind, is not so obvious; and that is the way of tempering steel to make gravers, drills, springs, and other mechanical instruments, which we have divers times both made artificers practise in our presence, and tried ourselves after the following manner. First, the slender steel to be tempered is to be hardened by heating as much of it as is requisite among glowing coals, till it be glowing hot, but it must not be quenched as soon as it is taken from the fire (for that would make it too brittle, and spoil it) but must be held over a bason of water, till it descend from a white heat to a red one, which as soon as ever you perceive, you must immediately quench as much as you desire to harden in the cold water. The steel thus hardened will, if it be good, look somewhat white, and must be made bright at the end, that its change of colours may be there conspicuous; and then holding it so in the flame of a candle, that the bright end may be, for about half an inch or more, out of the flame, that the smoak do not stain or fully the brightness of it, you shall after a while see that clean end, which is almost contiguous to the flame, pass very nimbly from one colour to another, as from a brighter yellow, to a deeper and reddish yellow, which artificers call a sanguine; and from that to a fainter first, and then a deeper blue. And to bring home this experiment to our present purpose, it is found by daily experience, that each of these succeeding colours argue such a change made in the texture of the steel, that if it be taken from the flame, and immediately quenched in the tallow (whereby it is settled in whatever temper it had before) when it is yellow, it is of such a hardness as makes it fit for gravers, drills, and such like tools; but if it be kept a few minutes longer in the flame till it grow blue, it becomes much softer, and unfit to make gravers for metals, but fit to make springs for watches, and such like instruments, which are therefore commonly of that colour: and if the steel be kept in the flame, after this deep blue hath disclosed itself, it will grow so soft, as to need to be new hardened again, before it can be brought to a temper fit for drills or penknives. And I confess, Pyro, I have taken much pleasure to see the colours run along from the parts of the steel contiguous to the flame, to the end of the instrument, and succeed one another so fast, that if a man be not vigilant, to thrust the steel into the tallow at the very nick of time, at which it has attained its due colour, he shall miss of giving his tool the right temper. But because the flame of a candle is offensive to my weak eyes, and because it is apt to either black or sully the contiguous part of the steel which is held in it, and thereby hinder the change of colours from being so long and clearly discerned, I have sometimes made this experiment by laying the steel to be tempered upon a heated bar of iron, which we find also, to be employed by some artificers in the tempering of such great instruments, as are too big to be soon heated sufficiently by the flame of a candle. And you may easily satisfy yourself, Pyro, of the differing hardness and toughness, which is ascribed to steel tempered at different colours, if you break but some slender wires of steel so tempered, and observe how they differ in brittleness, and if with a file you also make trial of their various degrees of hardness.

2. BUT, Pyrophilus, I must not at present any further prosecute the consideration of the importance of experiments about colours, not only because you will in the following papers find some instances, that would here be presented you out of their due place, of the use that may be made of such experiments, in discovering in divers bodies what kind the salt is, that is predominant in them; but also because a speculative Naturalist might justly enough allege, that as light is so pleasing an object, as to be well worth our contemplation, though it discovered to us nothing but itself; so modified light, called colour, were worth our contemplation, though by understanding its nature we should be taught nothing else. And however, I need not make either you or myself excuses for entertaining you on the subject I am now about to treat of; since the pleasure Pyro takes in mixing and laying on of colours, will I presume keep him, and will (I am sure) keep me from thinking it troublesome to set down, especially after the tedious processies (about other matters) wherewith I fear I may have tired him, some easy, and not unpleasant experiments relating to that subject.

3. BUT, before we descend to the more particular considerations we are to present you concerning colours, I presume it will be seasonable to propose at the very entrance a distinction; the ignorance or neglect of which, seems to me to have frequently enough occasioned either mistakes or confusion in the writings of divers modern philosophers. For colour may be considered, either as it is a quality residing in, the body that is said to be coloured, or to modify the light after such or such a manner; or else as the light itself, which so modified, strikes upon the organ of sight, and so cause that sensation which we call colour: and that this latter may be looked upon as the more proper, though not the usual acceptation of the word colour, will be made probable by divers passages in the ensuing part of our discourse. And indeed it is the light itself, which after a certain manner, either mingled with shades or some other ways troubled, strikes our eyes, that does more immediately produce that motion in the organ, upon whose account men say they see such or such a colour in the object: yet, because there is in the body that is said to be coloured, a certain disposition of the superficial particles, whereby it sends the light reflected, or refracted, to our eyes thus and thus altered, and not otherwise, it may also in some sense be said, that colour depends upon the visible body; and therefore we shall not be against that way of speaking of colours, that is most used among the modern Naturalists, provided we be allowed to have recourse, when occasion shall require, to the premised distinction, and to take the more immediate cause of colour to be the modified light itself, as it affects the sensory; though the disposition also of the coloured body, as that modifies the light, may be called by that name metonymically (to borrow a school-term) or efficiently, that is, in regard of its turning the light, that rebounds from it, or passes through it, into this or that particular colour.

4. I KNOW not whether I may not on this occasion add, that colour is so far from being an inherent quality of the object in the sense that is wont to be declared by the schools, or even in the sense of some modern Atomists, that, if we consider the matter more attentively, we shall see cause to suspect, if not to conclude, that though light do more immediately affect the organ of sight, than do the bodies that send it thither, yet light itself produces the sensation of a colour, but as it produces such a determinate kind of local motion in some part of the brain; which, though it happen most commonly from the motion whereinto the slender string of the retina are put, by the appulse of light; yet if the like motion happen to be produced by any other cause, wherein the light concurs not at all, a man shall think he sees the same colour. For proof of this, I might put you in mind, that it is usual for dreaming men to think they see the images that appear to them in their sleep, adorned some with this, and some with that lively colour, whilst yet, both the curtains of their bed, and those of their eyes, are close drawn. And I might add the confidence with which distracted persons do oftentimes, when they are awake, think they see black fiends in places, where there is no black object in sight without them. But I will rather observe, that not only when a man receives a great stroke upon his eye, or a very great one upon some other part of his head, he is wont to see, as it were, flashes of lightning, and little vivid, but vanishing flames, though perhaps his eyes be shut; but the like apparitions may happen, when the motion proceeds not from something without, but from something within the body, provided the unwonted fumes that wander up and down in the head, or the propagated concussion of any internal part in the body, do cause, about the inward extremities of the optic nerve, such a motion as is wont to be there produced, when the stroke of the light upon the retina makes us conclude, that we see either light or such and such a colour. This the most ingenious Des Cartes hath very well observed; but because he seems not to have exemplified it by any unobvious or peculiar observation, I shall endeavour to illustrate this doctrine by a few instances.

5. AND first, I remember, that having, through God's goodness, been free for several years from troublesome coughs, being afterwards, by an accident, suddenly cast into a violent one, I did often when I was awaked in the night by my distempers, observe, that upon coughing strongly, it would seem to me, that I saw very vivid, but immediately disappearing flames; which I took particular notice of, because of the conjecture I am now mentioning.

6. AN excellent and very discreet person, very near allied both to you and me, was relating to me, that some time since, whilst she was talking with some other ladies, upon a sudden, all the objects she looked upon appeared to her dyed with unusual colours, some of one kind, and some of another, but all so bright and vivid, that she should have been as much delighted, as surprized with them; but that finding the apparition to continue, she feared it portended some very great alteration as to her health: and indeed, the day after she was assaulted with such violence by hysterical and hypocondrical distempers, as both made her rave for some days, and gave her, during that time, a bastard palsy.

7. BEING awhile since in a town, where the plague had made great havock, and inquiring of an ingenious man, that was so bold, as without much scruple to visit those that were sick of it, about the odd symptoms of a disease that had swept away so many there; he told me, among other things, that he was able to tell divers patients, to whom he was called, before they took their beds, or had any evident symptoms of the plague, that they were indeed infested, upon peculiar observations, that being asked, they would tell him that the neighbouring objects, and particularly his clothes, appeared to them beautified with most glorious colours, like those of the rainbow, oftentimes succeeding one another: and this he affirmed to be one of the most usual, as well as the most early symptoms, by which this odd pestilence disclosed itself, And when I asked how long the patients were wont to be thus affected, he answered, that it was most commonly for about a day; and when I further inquired whether or no vomits, which in that pestilence were usually given, did not remove this symptom (for some used the taking of a vomit, when they came ashore, to cure themselves of the obstinate and troublesome giddiness caused by the motion of the ship) he replied, that generally, upon the evacuation made by the vomit, that strange apparition of colours ceased, though the other symptoms were not so soon abated; yet he added (to take notice of that upon the by, because the observation may perchance do good) that an excellent physician, in whose company he was wont to visit the sick, did give to almost all those to whom he was called, in the beginning, before nature was much weakened, a pretty odd vomit, consisting of eight or ten drachms of infusion of Crocus Metallorum, and about half a drachm, or much more, of white vitriol, with such success, that scarce one of ten to whom it was seasonably administred, miscarried.

8. BUT to return to the consideration of colours: as an apparition of them may be produced by motions from within, without the assistance of an outward object; so I have observed, that it is sometimes possible that the colour that would otherwise be produced by an outward object, may be changed by some motion, or new texture already already produced in the sensory, as long as that unusual motion, or new disposition lasts; for I have divers times tried, that after I have through a telescope looked upon the sun, though thorough a thick, red, or blue glass, to make its splendor supportable to the eye, the impression upon the retina would be not only so vivid, but so permanent, that if afterwards I turned my eye towards a flame, it would appear to me of a colour very differing from its usual one. And if I did divers times successively shut and open the same eye, I should see the adventitious colour (if I may so call it) changed or impaired by degrees, till at length (for this unusual motion of the eye would not presently cease) the flame would appear to me of the same hue that it did to other beholders. A not unlike effect I found by looking upon the moon, when she was near full, thorough an excellent telescope, without coloured glass to screen my eye with: but that which I desire may be taken notice of, because we may elsewhere have occasion to reflect upon it, and because it seems not agreeable to what Anatomists and optical writers deliver, touching the relation of the two eyes to each other, is this circumstance; that though my right eye, with which I looked thorough the telescope, were thus affected by the over-strong impression of the light, yet when the flame of a candle, or some other bright object appeared to me of a very unusual colour, whilst looked upon with the discomposed eye, or (though not so notably) with both eyes at once; yet if I shut that eye, and looked upon the same object with the other, it would appear with no other than its usual colour, though if I again opened, and made us of the dazzled eye, the vivid adventitious colour would again appear. And on this occasion I must not pretermit an observation which may persuade us, that an over-vehement stroke upon the sensory, especially if it be naturally of a weak constitution, may make a more lasting impression than one would imagine; which impression may in some cases, as it were, mingle with, and vitiate the action of vivid objects for a long time after.

FOR I know a lady of unquestionable veracity, who having lately, by a desperate fall, received several hurts, and particularly a considerable one upon a part of her face near her eye, had her sight so troubled and disordered, that, as she hath more than once related to me, not only when the next morning one of her servants came to her bed-side, to ask how she did, his clothes appeared adorned with such variety of dazzling colours, that she was fain presently to command him to withdraw; but the images in her hangings did, for many days after, appear to her, if the room were not extraordinarily darkened, embellished with several offensively vivid colours, which no body else could see in them. And when I enquired whether or no white objects did not appear to her adorned with more luminous colours than others, and whether she saw not some which she could not well describe to any, whose eyes had never been distempered, she answered me, that sometimes she thought she saw colours so new and glorious, that they were of a peculiar kind, and such as she could not describe by their likeness to any she had beheld either before or since; and that white objects did so much disorder her sight, that if, several days after her fall, she looked upon the inside of a book, she fancied she saw there colours like those of the rainbow: and even when she thought herself pretty well recovered, and made bold to leave her chamber, the coming into a place where the walls and ceiling were whited over, made those objects appear to her cloathed with such glorious and dazzling colours, as much offended her sight, and made her repent her venturousness; And she added, that this distemper of her eyes lasted not less than five or six weeks, though since that, she hath been able to read and write much without finding the least inconvenience in doing so. I would gladly have known, whether if she has shut the injured eye the phænomena would have been the same, when she employed only the other; but I heard not of this accident early enough to satisfy that inquiry.

9. WHEREFORE, I shall now add, that some years before, a person exceedingly eminent for his profound skill in almost all kinds of philological learning, coming to advise with me about a distemper in his eyes, told me, among other circumstances of it, that having upon a time looked too fixedly upon the sun, thorough a telescope, without any coloured glass, to take off from the dazzling splendor of the object, the excess of light did so strongly affect his eye, that ever since, when he turns it towards a window, or any white object, he fancies he seeth a globe of light, of about the bigness; the sun then appeared of to him, to pass before his eyes: and having inquired of him, how long he had been troubled with this indisposition, he replied, that it was already nine or ten years since the accident, that occasioned it, first befel him.

10. I COULD here subjoin, Pyrophilus, some memorable relations that I have met with in the account given us by the experienced Epiphanius Ferdinandus, of the symptoms he observed to be incident to those that are bitten with the Tarantula; by which (relations) I could probably shew, that without any change in the object, a change in the instruments of vision may for a great while make some colours appear charming, and make others provoking, and both to a high degree, though neither of them produced any such effect before. These things, I say, I could here subjoin in confirmation of what I have been saying, to shew that the disposition of the organ is of great importance in the dijudications we make of colours, were it not that these strange stories belonging more properly to another discourse, I had rather (contenting myself to have given you an intimation of them here) that you should meet with them fully delivered there.

1. BUT, Pyrophilus, I would not, by all that I have hitherto discoursed, be thought to have forgotten the distinction (of colour) that I mentioned to you about the beginning of the third session of the former chapter; and therefore, after all I have said of colour, as it is modified light, and immediately affects the sensory, I shall now remind you, that I did not deny, but that colour might, in some sense be considered as a quality residing in the body that is said to be coloured; and indeed the greatest part of the following experiments refer to colour principally under that notion, for there is in the bodies we call coloured, and chiefly in their superficial parts, a certain disposition, whereby they do so trouble the light that comes from them to our eye, as that it there makes that distinct impression, upon whose account we say, that the seen body is either white or black, or red or yellow, or of any one determinate colour. But because we shall (God permitting) by the experiments that are to follow some pages hence, more fully and particularly shew, that the changes, and consequently in divers places the production and the appearance of colours, depends upon the continuing or altered texture of the object we shall in this place intimate (and that too but as by the way) two or three things about this matter.

2. AND first, it is not without some reason, that I ascribe colour (in the sense formerly explained) chiefly to the superficial parts of bodies; for not to question how much opacous corpuscles may abound even in those bodies we call diaphanous, it seems plain that of opacous bodies we do indeed see little else than the superficies. For if we found the beams of light that rebound from the object to the eye, to pierce deep into the coloured body, we should not judge it opacous, but either translucid, or at least semi-diaphanous: and though the schools seem to teach us that colour is a penetrative quality, that reaches to the innermost parts of the object, as if a piece of sealing-wax be broken into never so many pieces, the internal fragments will be as red as the external surface did appear; yet that is but a particular example, that will not overthrow the reason lately offered, especially since I can allege other examples of a contrary import and two or three negative instances are sufficient to overthrow the generality of a positive rule, especially if that be built but upon one or a few examples. Not (then) to mention cherries, plums, and I know not how many other bodies, wherein the skin is of one colour, and what it hides of another, I shall name a couple of instances drawn from the colours of durable bodies that are thought far more homogeneous, and have not parts that are either organical, or of a nature approaching thereunto.

3. To give you the first instance, I shall need but to remind you of what I told you a little after the beginning of this essay, touching the blue and red and yellow, that may be produced upon a piece of tempered steel; for these colours, though they be very vivid, yet if you break the steel they adorn, they will appear to be but superficial; not only the innermost parts of the metal, but those that are within a hair's breadth of the superficies, having not any of these colours, but retaining that of the steel itself. Besides that, we may as well confirm this observation, as some other particulars we elsewhere deliver concerning colours, by the following experiment which we purposely made.

4. WE took a good quantity of clean lead, and melted it with a strong fire, and then immediately pouring it out into a clean vessel of a convenient shape and matter (we used one of iron, that the great and sudden heat might not injure it) and then carefully and nimbly taking off the scum that floated on the top, we perceived, as we expected, the smooth and glossy surface of the melted matter to be adorned with a very glorious colour, which being as transitory as delightful, did almost immediately give place to another vivid colour, and that was as quickly succeeded by a third, and this as it were chased away by a fourth; and so these wonderfully vivid colours successively appeared and vanished (yet the same now and then appearing the second time) till the metal ceasing to be hot enough to afford any longer this pleasing spectacle, the colours that chanced to adorn the surface, when the lead thus began to cool, remained upon it; but were so superficial, that how little soever we scraped off the surface I the lead, we did in such places scrape off all the colour, and discover only that which is natural to the metal itself; which receiving its adventitious colours, only when the heat was very intense, and in that part which was exposed to the comparatively very cold air (which by other experiments seems to abound with subtile saline parts, perhaps not uncapable of working upon lead so disposed:) these things, I say, together with my observing that whatever parts of the so strongly melted lead were exposed a while to the air, turned into a kind of scum or lithargre, how bright and clean soever they appeared before, suggested to me some thoughts or ravings, which I have not now time to acquaint you with. One that did not know me, Pyrophilus, would perchance think I endeavoured to impose upon you by relating this experiment, which I have several times tried; but the reason why the phænomena mentioned have not been taken notice of, may be, that unless lead be brought to a much higher degree of fusion or fluidity than is usual, or than is indeed requisite to make it melt, the phænomena I mentioned will scarce at all disclose themselves; and we have also observed, that this successive appearing and vanishing of vivid colours was wont to be impaired or determined whilst the metal exposed to the air remained yet hotter than one would readily suspect. And one thing I must further note, of which I leave you to search after the reason, namely, that the same colours did not always and regularly succeed one another, as is usual in steel, but in the diversified order mentioned in this following note, which I was scarce able to write down, the succession of the colours was so very quick: whether that proceeded from the differing degrees of heat in the lead exposed to the cool air, or from some other reason, I leave you to examine.

5. THE Atomists of old, and some learned men of late, have attempted to explicate the variety of colours in opacous bodies from the various figures of their superficial parts; the attempt is ingenious, and the doctrine seems partly true: but I confess I think there are divers other things that must be taken in as concurrent to produce those differing forms of asperity, whereon the colours of opacous bodies seem to depend. To declare this a little, we must assume, that the surfaces of all such bodies, how smooth or polite soever they may appear to our dull sight and touch, are exactly smooth only in a popular, or at most in a physical sense, but not in a strict and rigid sense.

6. THIS excellent microscopes shew us in many bodies, that seem smooth to our naked eyes; and this not only as to the little hillocks or protuberances that swell above that which may be conceived to be the plane or level of the considered surface; for it is obvious enough to those that are any thing conversant with such glasses: but as to numerous depressions beneath that level, of which sort of cavities, by the help of a microscope, which the greatest artificer that makes them, judges to be the greatest magnifying glass in Europe, except one that equals it, we have on the surface of a thin piece of cork that appeared smooth to the eye, observed about sixty in a row, within the length of less than a 31 and 32d part of an inch (for the glass takes in no longer a space at one view;) and these cavities (which made that little piece of cork almost like an empty honey-comb) were not only very distinct and figured like one another, but of a considerable bigness, and a scarce credible depth; insomuch that their distinct shadows as well as sides were plainly discerned and easy to be reckoned, and might have been well distinguished, though they had been ten times lesser than they were. Which I thought it not amiss to mention to you, Pyrophilus, upon the by, that you may thence make some estimate, what a strange inequality, and what a multitude of little shades there may really be, in a scarce sensible part of the physical superficies, though the naked eye sees no such matter. And as excellent microscopes shew us this ruggedness in many bodies that pass for smooth, so there are divers experiments, though we must not now stay to urge them, which seem to persuade us of the same thing, as to the rest of such bodies as we are now treating of; so that there is no sensible part of an opacous body, that may not be conceived to be made up of a multitude of singly insensible corpuscles. But in the giving these surfaces that disposition, which makes them alter the light that reflects thence to the eye after the manner requisite to make the object appear green, blue, &c the figures of these particles have a great, but not the only stroke. It is true indeed, that the protuberant particles may be of very great variety of figures, spherical, elliptical, polyedrical, and some very irregular; and that according to the nature of these, and the situation of the lucid body, the light must be variously affected, after one manner from surfaces (I now speak of physical surfaces) consisting of spherical, and in and other from those that are made up of conical or cylindrical corpuscles, some being fitted to reflect more of the incident beams of light, others less, and some towards one part, others towards another. But besides this difference of shape, there may be divers other things that may eminently concur to vary the forms of asperity that colours so much depend on. For, willingly allowing the figure of the particles in the first place, I confider secondly, that the superficial corpuscles, if I may so call them, may be bigger in one body, and less in another, and consequently fitted to allay the light falling on them with greater shades. Next, the protuberant particles may be set more or less close together, that is, there may be a greater or a smaller number of them within the compass of one, than within the compass of another small part of the surface of the same extent; and how much these qualities may serve to produce colour, may be somewhat guessed at, by that which happens in the agitation of water: for if the bubbles that are thereby made be great, and but few, the water will scarce acquire a sensible colour; but if it be reduced to a froth, consisting of bubbles, which being very minute and contiguous to each other, are a multitude of them crowded into a narrow room, the water (turned to froth) does then exhibit a very manifest white colour, to which these last named conditions of the bubbles do, well as their convex figure, contribute; and that for reasons to be mentioned anon. See the Discourse of the nature of whiteness and blackness Besides, it is not necessary that the superficial particles that exhibit one colour should be all of them round, or all conical, or all of any one shape; but corpuscles of differing figures may be mingled on the surface of the opacous body, as when the corpuscles that make a blue colour, and those, that make a yellow, come to be accurately and skillfully mixed, they make up a green; which, though it seem one simple colour, yet, in this case, appears to be made by corpuscles of very differing kinds, duly commixed. Moreover, the figure and bigness of the little depressions, cavities, furrows, or pores intercepted betwixt these protuberant corpuscles, are as well to be considered as the sizes and shapes of the corpuscles themselves: for we may conceive the physical superficies of a body, where (as we said) its colour does, as it were, reside, to be cut transversely by a mathematical plane, which you know is conceived to be without any depth or thickness at all; and then, as some parts of the physical superficies will be protuberant, or swell above this last plane, so others may be depressed beneath it, as (to explain myself by a gross comparison) in divers places of the surface of the earth, there are not only neighboring hills, trees, &c. that are raised above the horizontal level of the valley, but rivers, wells, pits and other cavities that are depressed beneath it. And that such protuberant and concave parts of a surface may remit the light so differingly, as much to vary a colour, some examples, and other things that we shall hereafter have occasion to take notice of in this tract, will sufficiently declare; till when, it may suffice to put you in mind, that of two flat sides of the same piece of, for example, red marble, the one being diligently polished, and the other left to its former roughness, the differing degrees or sorts of asperity, for the side that is shiooth to the touch wants not its roughness, will so diversify the light reflected from the several planes to the eye, that a painter would employ two differing colours to represent them.

7. AND I hope, Pyrophilus, you will not think it strange or impertinent, that I employ, in divers passages of these papers, examples drawn from bodies and shadows far more gross than those minute protuberances and shady pores on which, in most cases, the colour of a body, as it is an inherent quality or disposition of its surface, seems to depend, For sometimes I employ such examples, rather to declare my meaning, than prove any conjecture; things, whom their smallness makes insensible, being better represented to the imagination by such familiar objects, as being like them enough in other respects, are of a visible bulk. And next, though the beams of light are such subtile bodies, that in respect of them, even surfaces that are sensibly smooth, are not exactly so, have their own degree of roughness, consisting of little protuberances and depressions; and though consequently such inequalities may suffice to give bodies differing colours, as we see in marble that appears white or black, or red or blue, even when the most carefully polished; yet it is plain, by the late instance of red marble, and many others, that even bigger protuberances and greater shades may likewise so diversify the roughness of a body's superficies, as manifestly to concur to the varying of its colour, whereby such examples appear to be proper enough to be employed in such a subject as we have now in hand. And having hinted thus much on this occasion, I now proceed.

8. THE situation also of the superficial particles is considerable, which I distinguish into the posture of the single corpuscles, in respect of the light, and of the eye, and the order of them in reference also to one another; for a body may otherwise reflect the light, when its superficial particles are more erected upon the plane, that may be conceived to pass, along their basis, and when the points or extremes of such articles are obverted to the eye, than when those particles are so inclined, that their sides are in great part discernible; as the colour of plush or velvet will appear varied to you, if you carefully stroke part of it one way, and part of it another; the posture of the particular thrids, in reference to the light, or the eye, becoming thereby different. And you may observe in a field of ripe corn blown upon by the wind, that there will appear as it were waves of a colour (at least gradually) differing from that of the rest of the field the wind, by depressing some of the ears, and not at the same time others, making the one reflect more from the lateral and strawy parts than do the rest. And so, when dogs are so angry as to erect the hairs upon their necks, and upon some other parts of their bodies, those parts seem to acquire a colour varied from that which the same hairs made, when in their usual posture they did far more stoop. And that the order wherein the superficial corpuscles are ranged, is not to be neglected, we may guess by turning of water into froth, the beating of glass, and the scraping, of horns, in which cases the corpuscles that were before so marshalled as to be perspicuous, do by the troubling of that order become disposed to terminate and reflect more light, and thereby to appear whitish. And there are other ways in which the order of the protuberant parts, in reference to the eye, may much contribute to the appearing of a particular colour , for I have often observed, that when peas are planted, or set in parallel lines, and are shot up about half a foot above the surface of the ground, by looking on the field or plot of ground from that part towards which the parallel lines tended, the greater part of the ground by far, would appear of its own dirty colour; but if I looked upon it transversely, the plot would appear very green, the upper parts of the peas hindering the intercepted parts of the ground, which, as I said, retained their wonted colour from being discovered by the eye. And I know not, Pyrophilus, whether I might not add, that even the motion of the small parts of a visible object may in some cases contribute, though it be not so easy to say how, to the producing, or the varying of a colour: for I have several times made a liquor which, when it has well settled in a close phial, is transparent and colourless; but as soon as the glass is unstopped, begins to fly away very plentifully in a white and opacous fume. And there are other bodies, whose fumes, when they fill a receiver, would make one suspect it contains milk; and yet when these fumes settle into a liquor, that liquor is not white, but transparent and such white fumes I have seen afforded by unstopping a liquor I know, which yet is itself diaphanous and red: nor are these the only instances of this kind, that our trials can supply us with. And if the superficial corpuscles be of the grosser sort, and be so framed, that their differing sides or faces may exhibit differing colours, then the motion or rest of those corpuscles may be considerable, as to the colour of the superficies they compose; upon this account, that sometimes more, sometimes fewer of the sides disposed to exhibit such a colour may by this means become or continue more obverted to the eye than the rest, and compose a physical surface, that will be more or less sensibly interrupted. As, to explain my meaning, by proposing a gross example, I remember, that in some sorts of leafy plants thick set by one another, the two sides of whose leaves were of somewhat differing colours, there would be a notable disparity as to colour, if you looked upon them both, when the leaves, being at rest, had their upper and commonly exposed sides obverted to the eye, and when a breath of wind passing thorough them, made great numbers of the usually hidden sides of the leaves become conspicuous. And though the little bodies we were lately speaking of, may singly and apart seem almost colourless; yet when many of them are placed other, so near that the eye does not easily discern an interruption, within a sensible space, they may exhibit a colour: as we see, that though the slenderest thrid of dyed silk does whilst looked on single, seem. almost quite devoid of redness (for instance) yet when numbers of these thrids are brought together into one skein, their colour becomes notorious.

9. BUT the same occasion that invited me to say what I have mentioned concerning the leaves of trees, invites me also to give you some account of what happens in changeable taffaties, where we see differing colours, as it were, emerge and vanish upon the ruffling of the same piece of silk; as I have divers times with pleasure observed, by the help of such a microscope, as though it do not very much magnify the object, has in recompence this great conveniency, that you may easily, as fast as you please, remove it from one part to another of a large object, of which the glass taking a great part at once, you. may thereby presently survey the whole. Now by the help of such a microscope I could easily (as I began to say) discern, that in a piece of changeable taffaty (that appeared, for instance, sometimes red, and sometimes green) the stuff was composed of red thrids and green, passing under and over each other, and crossing one another in almost innumerable points: and if I looked through the glass upon any considerable portion of the stuff that (for example sake) to the naked eye appeared to be red, I could plainly see, that in that position, the red thrids were conspicuous, and reflected a vivid light. And though I could also perceive, that there were green ones, yet by reason of their disadvantageous position in the physical surface of the taffaty, they were in part hid by the more protuberant thrids of the other colour: and for the same cause, the reflection from as much of the green as was discovered, was comparatively but dim and faint. And if, on the contrary, I looked through the microscope upon any part that appeared green, I could plainly see that the red thrids were left fully exposed to the eye, and obscured by the green ones, which therefore made up the predominant colour. And by observing the texture of the silken stuff, I could easily so expose the thrids either of the one colour or of the other, to my eye, as at pleasure to exhibit an apparition of red or green, or make those colours succeed one another: so that, when I observed their succession by the help of the glass, I could mark how the predominant colour did as it were start out, when the thrids that exhibited it came to be advantageously placed; and by making little folds in the stuff after a certain manner, the sides that met and terminated in those folds, would appear to the naked eye, one of them red, and the other green. When thrids of more than two differing colours chance to be interwoven, the resulting changeableness of the taffaty may be also somewhat different, but I chuse to give an instance in the stuff I have been speaking of, because the mixture being more simple, the way whereby the changeableness is produced, may be the more easily apprehended: and though reason alone might readily enough lead a considering man to guess at the explication, in case he knew how changeable taffaties are made; yet I thought it not impertinent to mention it, because both scholars and gentlemen are wont to look upon the inquiry into manufactures, as a mechanic employment, and consequently below them; and because also with such a microscope as have been mentioning, the discovery is as well pleasant as satisfactory, and may afford hints of the solution of other phænomena of colours. And it were not amiss that some diligent inquiry were made, whether the microscope would give us an account of the variableness of colour, that is so conspicuous and so delightful in mother of pearl, in opals, and some other resembling bodies. For though I remember I did formerly attempt something of that kind (fruitlessly enough) upon mother of pearl, yet not having then the advantage of my best microscope, nor some conveniencies that might have been wished, I leave it to you, who have better eyes, to try what you can do further; since it will be same discovery to find, that in this case the best eyes and microscopes themselves can make none.

10. I CONFESS, Pyrophilus, that a great part of what I have delivered (or proposed rather) concerning the differing forms of asperity in bodies, by which differences, the incident light either comes to be reflected with more or less of shade, and with that shade more or less interrupted, or else happens to be also otherwise modified or troubled, is but conjectural. But I am not sure, that if it were not for the dulness of our senses, either these or some other notions of kin to them, might be better countenanced; for I am apt to suspect, that if we were sharp-sighted enough, or had such perfect microscopes, as I fear are more to be wished than hoped for, our promoted sense might discern in the physical surfaces of bodies, both a great many latent ruggednesses, and the particular sizes, shapes, and situations of the extremely little bodies that cause them, and perhaps might perceive among other varieties that we now can but imagine, how those little protuberances and cavities do interrupt and dilate the light, by mingling with it a multitude of little and singly undiscernable shades, though some of them more, and some of them less minute, some less, and some more numerous, according to the nature and degree of the particular colour we attribute to the visible object. As we see, that in the moon we can with excellent telescopes discern many hills and valleys, and as it were pits and other parts, whereof some are more, and some less vividly illustrated, and others have a fainter, others a deeper shade, though the naked eye can discern no such matter in that planet. And with an excellent microscope, where the naked eye did see but a green powder, the affected eye, as we noted above, could discern particular granules, some of them of a blue, and some of them of a yellow colour, which corpuscles we had beforehand caused to be exquisitely mixed to compound the green.

11. AND Pyrophilus, that you may not think me altogether extravagant in what I have said of the possibility (for I speak of no more) of discerning the differing forms of asperity in the surfaces of bodies of several colours, I'll here set down a memorable particular that chanced to come to my knowledge, since I writ a good part of this essay; and it is this. Meeting casually the other day with the deservedly famous Dr. F. Finch, (Since for his excellent qualities and loyalty, graced by his Majesty with the honour of knighthood.) extraordinary anatomist to that great patron of the Virtuosi, the now Great Duke of Tuscany, and inquiring of this ingenious person, what might be the chief rarity he had seen in his late return out of Italy into England, he told me, it was a man at Maestricht in the Low-Countries, who at certain times can discern and distinguish colours by the touch with his fingers. You will easily conclude, that this is far more strange than what I proposed but as not impossible; since the sense of the retina seeming to be much more tender and quick than that of those grosser filaments, nerves or membranes of our fingers, wherewith we use to handle gross and hard bodies, it seems scarce credible, that any accustomance, or diet, or peculiarity of constitution, should enable a man to distinguish, with such gross and unsuitable organs, such nice and subtile differences as those of the forms of asperity, that belong to differing colours; to receive whose languid and delicate impressions by the intervention of light, nature seems to have appointed and contexed into the retina the tender and delicate pith of the optic nerve. Wherefore I confess, I proposed divers scruples, and particularly whether the doctor had taken care to bind a napkin or handkerchief over his eyes so carefully, as to be sure he could make no use of his sight, though he had but counterfeited the want of it; to which I added divers other questions, to satisfy myself, whether there were any likelihood of collusion or other tricks. But I found that the judicious doctor having gone far out of his way, purposely to satisfy himself and his learned prince about this wonder, had been very watchful and circumspect to keep himself from being imposed upon. And that he might not through any mistake in point of memory misinform me, he did me the favour, at my request, to look out the notes he had written for his own and his prince's information, the sum of which memorials, as far as we shall mention them here, was this, that the doctor having been informed at Utrecht, that there lived one at some miles distance from Maestricht, who could distinguish colours by the touch; when he came to the last named town, he sent a messenger for him, and having examined him, was told upon inquiry these particulars.

THAT the man's name was John Vermaasen, at that time about 33 years of age that when he was but two years old, he had the small-pox, which rendered him absolutely blind; that at this present he is an, organist, and serves that office in a public choir.

THAT the doctor discoursing with him over night, the blind man affirmed, that he could distinguish colours by the touch, but that he could not do it, unless he were fasting; any quantity of drink taking from him that exquisiteness of touch, which is requisite to so nice a sensation.

THAT hereupon the doctor provided against the next morning seven pieces of ribbon, of these seven colours, black, white, red, blue, green, yellow, and grey but as for mingled colours, this Verinaasen would not undertake to discern them, though if offered, he would tell that they were mixed.

THAT to discern the colour of the ribbon, he places it betwixt the thumb and the forefinger, but his most exquisite perception was in his thumb, and much better in the right thumb than in the left.

THAT after the blind man had four or five times told the doctor the several colours (though blinded with a napkin for fear he might have some sight) the doctor found he was twice mistaken, for he called the white black, and the red blue; but still, he, before his error, would lay them by in pairs, saving, that though he could easily distinguish them from all others, yet those two pairs were not easily distinguished amongst themselves. Whereupon the doctor desired to be told by him what kind of discrimination he had of colours by his touch, to which he gave a reply, for whose sake chiefly I insert all this narrative in this place I namely, that all the difference was more or less asperity, for says he (I give you the doctor's own words) black feels as if you were feeling needles points, or some harsh sand, and red feels very smooth.

THAT the doctor having desired him to tell in order the difference of colours to his touch, he did as follows.

BLACK and white are the most asperous or unequal of all colours, and so like, that it is very hard to distinguish them; but black is the most rough of the two; green is next in asperity, grey next to green in asperity, yellow is the fifth in degree of asperity: red and blue are so like, that they are as hard to distinguish as black and white; but red is somewhat more asperous than blue, so that red has the sixth place, and blue the seventh in asperity.

12. To these informations the obliging doctor was pleased to add the welcome present of three of those very pieces of ribbon, whose colours in his presence the blind man had distinguished, pronouncing the one grey, the other red, and the third green I which I keep by me as rarities, and the rather, because he feared the rest were miscarried.

13. BEFORE I saw the notes that afforded me the precedent narrative, I confess I suspected this man might have thus discriminated colours rather by the smell than by the touch; for some of the ingredients imployed by dyers to colour things, have scents, that are not so languid, nor so near of kin: but that I thought it not impossible that a very critical nose might distinguish them, and this I the rather suspected, because he required, that the ribbons, whose colours he was to name, should be offered him fasting in the morning; for I have observed in setting dogs, that the feeding of them (especially with some sorts of aliments) does very much impair the exquisite scent of their noses. And though some of the foregoing particulars would have prevented that conjecture, yet I confess to you (Pyrophilus) that I would gladly have had the opportunity of examining this man myself, and of questioning him about divers particulars which I do not find to have been yet thought upon. And though it be not incredible to me, that since the liquours that dyers employ to tinge, are qualified to do so by multitudes of little corpuscles of the pigment or dying stuff, which are dissolved and extracted by the liquor, and swim to and fro in it, those corpuscles of colour (as the Atomists call them) insinuating themselves into, and filling all the pores of the body to be dyed, may asperate its superficies more or less according to the bigness and texture of the corpuscles of the pigment; yet I can scarce believe, that our blind man could distinguish all the colours he did, meerly by the ribbons having more or less of asperity; so that I cannot but think, notwithstanding this history, that the blind man distinguished colours not only by the degrees of asperity in the bodies offered to him, but by forms of it, though this (latter) would perhaps have been very difficult for him to make an intelligible mention of, because those minute disparities having not been taken notice of by men for want of touch as exquisite as our blind man's, are thin as he could not have intelligibly expressed; which will easily seem probable, if you confider, that under the name of sharp, and sweet, and sour, there are abundance of, as it were, immediate peculiar relishes or tastes in differing sorts of wine, which, though critical and experienced palates can easily discern themselves, cannot make them be understood by others such minute differences not having hitherto any distinct names assigned them. And it seems that there was something in the forms of asperity that was requisite to the distinction of colours, besides the degree of it, since he found it so difficult to distinguish black and white from one another, though not from other colours. For I might urge, that he seems not consonant to himself about the red, which, as you have seen in one place, he represents as somewhat more asperous than the blue; and in another, very smooth but because he speaks of this smoothness in that place, where he mentions the roughness of black, we may favourably presume that he might mean but a comparative smoothness; and therefore I shall not insist on this, but rather countenance my conjecture by this, that he found it so difficult, not only to discriminate red and blue (though the first of our promiscuous experiments will inform you, that the red reflects by great odds more light than the other) but also to distinguish black and white from one another, though not from other colours. And indeed, though in the ribbons that were offered him, they might be almost equally rough, yet in such slender corpuscles, as those of colour, there may easily enough be conceived, not only a greater closeness of parts, or else paucity of protuberant corpuscles, and the little extant particles may be otherwise figured, and ranged in the white than in the black, but the cavities may be much deeper in the one than the other.

14. AND perhaps (Pyrophilus) it may prove some illustration of what I mean, and help you to conceive how this may be, if I represent, that where the particles are so exceeding slender, we may allow the parts exposed to the sight and touch to be a little convex in comparison of the erected particles of black bodies, as if there were wires I know not how many times slenderer than a hair: whether you suppose them to be figured like needles, or cylindrically, like the hairs of a brush, with hemispherical (or at least convex) tops, they will be so very slender, and consequently the points both of the one sort and the other so very sharp, that even an exquisite touch will be able to distinguish no greater difference between them, than that which our blind man allowed, when comparing black and white bodies, he said, that the latter was the less rough of the two. Nor is every kind of roughness, though sensible enough, inconsistent with whiteness, there being cases, wherein the physical superficies of a body is made by the same operation both rough and white; as when the level surface of clear water being by agitation asperated with a multitude of unequal bubbles, does thereby acquire a whiteness; and as a smooth piece of glass, by being scratched with a diamond, does in the asperated part of its face disclose the same colour. But more (perchance) of this elsewhere.

15. AND therefore, we shall here pass by the question, whether any thing might be considered about the opacity of the corpuscles of black pigments, and the comparative diaphaneity of the of many white bodies, applied to our present case; and proceed to represent, that the newly mentioned exiguity and shape of the extant particles being supposed, it will then be considerable what we lately but hinted (and therefore must now somewhat explain) that the depth of the little cavities, intercepted between the extant particles, without being so much greater in black bodies than in white ones, as to be perceptibly so to the gross organs of touch, may be very much greater in reference to their disposition of reflecting the imaginary subtile beams of light. For in black bodies, those little intercepted cavities, and other depressions, may be so figured, so narrow and so deep, that the incident beams of light, which the more extant parts of the physical superficies are disposed to reflect inwards, may be detained there, and prove unable to emerge; whilst, in a white body, the slender particles may not only by their figure be fitted to reflect the light copiously outwards, but the intercepted cavities being not deep, nor perhaps very narrow, the bottoms of them may be so constituted, as to be fit to reflect outwards much of the light that falls even upon them; as you may possibly better apprehend, when we shall come to treat of whiteness and blackness. In the mean time, it may suffice, that you take notice with me, that the blind man's relations import no necessity of concluding, that though, because, according to the judgment of his touch, black was the roughest, as it is the darkest of colours, therefore white, which (according to us) is the lightest, should be also the smoothest: since I observe, that he makes yellow to be two degrees more asperous than blue, and as much less asperous than green; whereas, indeed, yellow does not only appear to the eye a lighter colour than blue, but (by our first experiment hereafter to be mentioned) it will appear, that yellow reflected much more light than blue, and manifestly more than green; which we need not much wonder at, since in this colour, and the two others (blue and yellow) it is not only the reflected light that is to be considered, since to produce both these, refraction seems to intervene, which by its varieties may much alter the case: which both seems to strengthen the conjecture I was formerly proposing, that there was something else in the kinds of asperity, as well as in the degrees of it, which enabled our blind man to discriminate colours, and does at least show, that we cannot, in all cases, from the bare difference in the degrees of asperity betwixt colours, safely conclude, that the rougher of any two always reflects the least light.

16. BUT this notwithstanding (Pyrophilus) and whatever curiosity I may have had to move some questions to our sagacious blind man; yet thus much I think you will admit us to have gained by his testimony, that since many colours may be felt with the circumstances above related, the surfaces of such coloured bodies must certainly have differing degrees, and in all probability have differing forms or kinds of asperity belonging to them, which is all the use that my present attempt obliges me to make of the history above delivered ; that being sufficient to prove, that colour does much depend upon the disposition of the superficial parts of bodies, and to shew in general, wherein it is probable that such a disposition does (principally at least) consist.

17. BUT to return to what I was saying, before I began to make mention of our blind organist; what we have delivered touching the causes of the several forms of asperity that may diversify the surfaces of coloured bodies, may perchance somewhat assist us to make some conjectures in the general, at several of the ways whereby it is possible for the experiments, hereafter to be mentioned, to produce the sudden changes of colours; that are wont to be consequent upon them: for most of these phænomena being produced by the intervention of liquors, and these for the most part abounding with very minute, active, and variously figured saline corpuscles, liquors so qualified may well enough very nimbly alter the texture of the body they are employed to work upon, and so may change the form of asperity, and thereby make them remit to the eye the light that falls on them after another manner than they did before, and by that means vary the colour, so far forth as it depends upon the texture or disposition of the seen parts of the object; which I say, Pyrophilus, that you may not think I would absolutely exclude all other ways of modifying the beams of light between their parting from the lucid body, and their reception into the common sensory.

18. NOW there seem to me divers ways, by which we may conceive that liquors may nimbly alter the colour of one another, and of other bodies, upon which they act; but my present haste will allow me to mention but some of them, without insisting so much as upon those I shall name.

19. AND first, the minute corpuscles that compose a liquor may easily insinuate themselves, into those pores of bodies, whereto their size and figure makes them congruous; and these pores they may either exactly fill, or but inadequately: and in this latter case they will for the most part alter the number and figure, and always the bigness of the former pores. And in what capacity soever these corpuscles of a liquor come to be lodged or harboured in the pores that admit them, surface of the body will for the most part have its asperity altered, and the incident light that meets with a grosser liquor in the little cavities that before contained nothing but air, or some yet subtiler fluid, will have its beams either refracted, or imbibed, or else reflected more or less interruptedly than they would be, if the body had been unmoistened: as we see, that even fair water falling on white paper, or linen, and divers other bodies apt to soak it in, will for some such reasons as those newly mentioned, immediately alter the colour of them, and for the most part make it sadder than that of the unwetted parts of the same bodies. And so you may see, that when in the summer the highways are dry and dusty, if there falls store of rain, they will quickly appear of a much darker colour than they did before; and if a drop of oil be let fall upon a sheet of white paper, that part of it, which by the imbibition of the liquor, acquires a greater continuity, and some transparency, will appear much darker than the rest, many of the incident beams of light being now transmitted, that otherwise would be reflected towards the beholder's eyes.

20. SECONDLY, A liquor may alter the colour of a body, by freeing it from those things that hindered it from appearing in its genuine colour; and though, this may be said to be rather a restoration of a body to its own colour, or a retection of its native colour, than a change, yet still there intervenes in it a change of the colour which the body appeared to be of before this operation. And such a change a liquor may work, either by dissolving, or corroding, or by some such way of carrying off that matter, which either veiled or disguised the colour that afterwards appears, Thus we restore old pieces of dirty gold to a clean and nitid yellow, by putting them into the fire, and into aqua-fortis, which take off the adventitious filth that made that pure metal look of a dirty colour: and there is also an easy way to restore silver coins to their due lustre, by fetching off that which discoloured them. And I know a chymical liquor, which I employed to restore pieces of cloth spotted with grease to their proper colour, by imbibing the spotted part with this liquor, which incorporating with the grease, and yet being of a very volatile nature, does easily carry it away with itself. And I have sometimes tried, that by rubbing upon a good touch-stone a certain metalline mixture so compounded, that the impression it left upon the stone appeared of a very differing colour from that of gold, yet a little of aqua-fortis would in a trice make the golden colour disclose itself, by dissolving the other metalline corpuscles that concealed those of the gold, which you know that menstruum will leave untouched.

21. THIRDLY, A liquor may alter the colour of a body by making a comminution of its parts, and that principally two ways; the first by disjoining and dissipating those clusters of particles, if I may so call them, which stuck more loosely together, being fastened only by some more easily dissoluble cement, which seems to be the case of some of the following experiments, where you will find the colour of many corpuscles brought to cohere by having been precipitated together, destroyed by the affusion of very piercing and incisive liquors. The other of the two ways I was speaking of, is, by dividing the grosser and more solid particles into minute ones, which will be always lesser, and for the most part otherwise shaped than the entire corpuscle so divided, as it will happen in a piece of wood reduced into splinters or chips, or as when a piece of crystal heated red-hot and quenched in cold water is cracked into a multitude of little fragments, which, though they fall not asunder, alter the disposition of a body of the crystal, as to its manner of reflecting the light, as we shall have occasion to shew hereafter.

22. THERE is a fourth way contrary to the third, whereby a liquor may change the colour of another body, especially of another fluid; and that is, by procuring the coalition of several particles that before lay too scattered and dispersed to exhibit the colour that afterwards appears. Thus sometimes when I have had the solution of gold so dilated, that I doubted whether the liquor had really imbibed any true gold or no, by pouring in a little mercury, I have been quickly able to satisfy myself, that the liquor contained gold; that metal after a little while cloathing the surface of the quicksilver with a thin film of its own livery. And chiefly, though not only by this way of bringing the minute parts of bodies together in such numbers, as to make them become notorious, to the eye, many of these colours seem to be generated which are produced by precipitations, especially by such as are wont to be made with fair water; as when resinous gums dissolved in spirit of wine, are let fall again, if the spirit be copiously diluted with that weakening liquor. And so out of the rectified and transparent butter of antimony, by the bare mixture of fair water, there will be plentifully precipitated that milk-white substance, which by having its looser salts well washed off, is turned into that medicine, which vulgar chymists are pleased to call Mercurius Vitæ.

23. A FIFTH way, by which a liquor may change the colour of a body, is, by dislocating the parts, and putting them out of their former order into another, and perhaps also altering the posture of the single corpuscles as well as their order or situation in respect of one another. What certain kinds of commotion or dislocation of the parts of a body may do towards the changing its colour, is not only evident in the mutations of colour observable in quicksilver, and some other concretes long kept by chymists in a convenient heat, though in close vessels, but in the obvious degenerations of colour, which every body may take notice of in bruised cherries, and other fruit, by comparing after a while the colour of the injured with that of the sound part of the same fruit. And that also such liquors, as we have been speaking of, may greatly discompose the textures of many bodies, and thereby alter the disposition of their superficial parts, the great commotion made in metals, and several other bodies by aqua-fortis, oil of vitriol, and other saline menstruums, may easily persuade us; and what such varied situations of parts may do towards the diversifying of the manner of their reflecting the light, may be guessed in some measure by the beating of transparent glass into a white powder, but far better by the experiments lately pointed at, and hereafter delivered, as the producing and destroying colours by the means of subtile saline liquors, by whose affusion the parts of other liquors are manifestly both agitated, and likewise disposed after another manner than they were before such affusion. And in some chymical oils, as particularly that of lemon peels, by barely shaking the glass that holds it into bubbles, that transposition of the parts which is consequent to the shaking, will shew you on the surfaces of the bubbles exceeding orient and lively colours, which, when the bubbles relapse into the rest of the oil, do immediately vanish.

24. I KNOW not, Pyrophilus, whether I should mention as a distinct way, because it is of a somewhat more general nature, that power whereby a liquor may alter the colour of another body, by putting the parts of it into motion; for though possibly the motion so produced does, as such, seldom suddenly change the colour of the body whose parts are agitated, yet this seems to be one of the most general, however not immediate causes of the quick change of colours in bodies. For the parts being put into motion by the adventitious liquor, divers of them that were before united, may become thereby disjoined, and when that motion ceases or decays, others of them may stick together, and that in a new order, by which means the motion may sometimes produce permanent changes of colours, as in the experiment you will meet with hereafter, of presently turning a snowy white body into a yellow, by the bare affusion of fair water, which probably so dissolves the saline corpuscles that remained in the calx, and sets them at liberty to act upon one another, and the metal, far more powerfully than the water without the assistance of such saline corpuscles could do. And though you rub blue vitriol, how venereal and unsophisticated soever it be, upon the whetted blade of a knife, it will not impart to the iron its latent colour; but if you moisten the vitriol with your spittle, or common water, the particles of the liquor disjoining those of the vitriol, and thereby giving them the various agitation requisite to fluid bodies, the metalline corpuscles of the thus dissolved vitriol will lodge themselves in throngs in the small and congruous pores of the iron they are rubbed on, and so give the surface of it the genuine colour of the copper.

25. THERE remains yet a way, Pyrophilus, to be mentioned, by which a liquor may alter the colour of another body, and this seems the most important of all, because though it be named but as one, yet it may indeed comprehend many; and that is, by associating the saline corpuscles, or any other sort of the more rigid ones of the liquor, with the particles of the body that it is employed to work upon. For these adventitious corpuscles associating themselves with the protuberant particles of the surface of a coloured body, must necessarily alter their bigness, and will most commonly alter their shape. And how much the colours of bodies depend upon the bulk and figure of their superficial particles, you may guess by this, that eminent antient philosophers, and divers moderns, have thought that all colours might, in a general way, be made out by these two; whose being diversified will, in our case, be attended with these two circumstances; the one, that the protuberant particles being increased in bulk, they will oftentimes be varied as to the closeness or laxity of their order, fewer of them being contained within the same sensible (though minute) space than before; or else by approaching to one another, they must straiten the pores, and it may be too they will, by their manner of associating themselves with the protuberant particles, intercept new pores. And this invites me to confider farther, that the adventitious corpuscles I have been speaking of, may likewise produce a great change, as well in the little cavities or pores, as in the protuberances of a coloured body; for, besides what we have just now taken notice of, they may, by lodging themselves in those little cavities, fill them up, and it may well happen, that they may not only fill the pores they insinuate themselves into, but likewise have their upper parts extant above them; and partly by these new protuberances, partly by increasing the bulk of the former, these extraneous corpuscles may much alter the number and bigness of the surface's pores, changing the old and intercepting new ones. And then it is odds, but the order of the little extancies, and consequently that of the little depressions in point of situation will be altered likewise: as if you dissolve quicksilver in some kind of aqua-fortis, the saline particles of the menstruum, associating themselves with the mercurial corpuscles, will make a green solution, which afterwards easily enough degenerates. And red lead, or minium, being dissolved in spirit of vinegar, yields not a red, but a clear solution, the redness of the lead being by the liquor destroyed. But a better instance may be taken from copper; for I have tried, that if upon a copper-plate, you let some drops of weak aqua-fortis rest for a while, the corpuscles of the menstruum joining with those of the metal, will produce a very sensible asperity upon the surface of the plate, and will coagulate that way into very minute grains of a pale blue vitriol whereas, if upon another of it of the same plate you suffer a little strong spirit of urine to rest a competent time, you shall find the asperated surface adorned with a deeper and richer blue. And the same aqua sortis, that will quickly change the redness of red lead into a darker colour, will, being put upon crude lead, produce a whitish substance, as with copper it did a blueish. And as with iron it will produce a reddish, and on white quills a yellowish, so, much may the coalition of the parts of the same liquor, with the differingly figured particles of stable bodies, divers ways asperate the differingly disposed surfaces, and so diversify the colour of those bodies. And you will easily believe, that in many changes of colour, that happen upon the dissolutions of metals, and precipitations made with oil of tartar, and the like fixed salts, there may intervene a coalition of saline corpuscles with the particles of the body dissolved or precipitated, if you examine how much the vitriol of a metal may be heavier than the metalline part of it alone, upon the score of the saline parts concoagulated therewith; and, that in several precipitations the weight of the calx does for the same reason much exceed that of the metal, when it was first put in to be dissolved.

26. BUT, Pyrophilus, to consider these matters more particularly would be to forget that I declared against adventuring, at least for this time, at particular theories of colours, and that accordingly you may justly expect from me rather experiments than speculations: and therefore I shall dismiss this subject of the forms of superficial asperity in coloured bodies, as soon as I shall but have named to you, by way of supplement to what we have hitherto discoursed in this short section, a couple of particulars (which you will easily grant me); the one, that there are divers other ways for the speedy production even of true and permanent colours in bodies, besides, those practicable by the help of liquors: for proof of which advertisement, though several examples might be alledged, yet I shall need but remind you of what I mentioned to you above, touching the change of colours suddenly made on tempered steel, and on lead, by the operation of heat, without the intervention of a liquor. But the other particular I am to observe to you, is of more importance to our present subject; and it is, that though nature and art may in some cases so, change the asperity of the superficial parts of a body, as to change its colour by either of the ways I have proposed, single or unassisted; yet for the most part it is by two or three, or perhaps by more of the forementioned ways associated together, that the effect is produced. And if you confider how variously these several ways and some others allied unto them, which I have left unmentioned, may be compounded and applied, you will not much wonder that such fruitful, whether principles (or manners of diversification) should be fitted to change or generate no small store of differing colours.

27. HITHERTO, Pyrophilus, we have in discoursing of the asperity of bodies considered the little protuberances of other superficial particles which make up that toughness, as if we took it for granted, that they must be perfectly opacous and impenetrable by the beams of light, and so, must contribute to the variety of colours, as they terminate more or less light, and reflect it to the eye mixed with more or less of thus or thus mingled shades. But to deal ingenuously with you, Pyrophilus, before I proceed any further, I must not conceal from you, that I have often thought it worth a serious inquiry, whether or no particles of matter, each of them singly insensible, and therefore small enough to be capable of being such minute particles, as the Atomists both of old and of late have (not absurdly) called Corpuscula Coloris, may not yet consist each of them of divers yet minuter particles, betwixt which we may conceive little commissures where they adhere to one another, and, however, may not be porous enough to be, at least in some degree, pervious to the unimaginably subtile corpuscles that make up the beams of light, and consequently to be in such a degree diaphanous. For, Pyrophilus, that the proposed inquiry may be of moment to him that searches after the nature of colour, you will easily grant, if you consider, that whereas perfectly opacous bodies can but reflect the incident beams of light, those that are diaphanous are qualified to refract them too; and that refraction has such a stroke in the production of colours, as you cannot but have taken notice of, and perhaps admired in the colours generated by the trajection of light through drops of water that exhibit a rainbow, through prismatical glasses, and through divers other transparent bodies. But 'tis like, Pyrophilus, you will more easily allow that about this matter it is rather important to have a certainty, than that it is rational to entertain a doubt; wherefore I must mention to you some of the reasons that make me think it may need a further inquiry: for I find that in a darkened room, where the light is permitted to enter but at one hole, the little wandering particles of dust, that are commonly called motes, and, unless in the sun-beams, are not taken notice of by the unassisted sight; I have, I say, often observed that these roving corpuscles being looked on by an eye placed on the one side of the beams that entered the little hole, and by the darkness having its pupil much enlarged, I could discern that these motes as soon as they came within the compass of the luminous, whether cylinder or inverted cone, if I may so call it, that was made up by the unclouded beams of the sun, did in certain positions appear adorned with very vivid colours, like those of the rainbow, or rather like those of very minute, but sparkling fragments of diamonds: and as soon as the continuance of their motion had brought them to an inconvenient position in reference to the light and the eye, they were only visible without darting any lively colours as before. Which seems to argue, that these little motes, or minute fragments of several sorts of bodies reputed opacous, and only crumbled as to their exterior and looser parts into dust, did not barely reflect the beams that fell upon them, but remit them to the eye refracted too. We may also observe, that several bodies (as well some of a vegetable, as others of an animal nature) which are wont to pass for opacous, appear in great part transparent, when they are reduced into thin parts, and held against a powerful light. This I have not only taken notice of in pieces of ivory reduced into thick leaves, as also in divers considerable thick shells of fishes and in shaving of wood; but I have also sound that a piece of deal, far thicker than one would easily imagine, being purposely interposed betwixt my eye placed in a room, and the clear day-light, was not only somewhat transparent, but (perhaps by reason of its gummous nature) appeared quite through of a lovely red. And in the darkened room above mentioned, bodies held against the hole at which the light entered, appeared far less opacous than they would elsewhere have done insomuch that I could easily and plainly see, through the whole thickness of my hand, the motions of a body placed (at a very near distance indeed, but yet) beyond it. And even in minerals, the opacity is not always so great as many think, if the body be made thin: for white marble, though of a pretty thickness, being within a due distance placed betwixt the eye and a convenient light, will suffer the motions of one's finger to be well discerned through it, and so will pieces, thick enough, of many common flints. But above all, that instance is remarkable, that is afforded us by Muscovy glass (which some call Selenites, others Lapis Specularis;) for though plates of this mineral, though but of a moderate thickness, do often appear opacous, yet if one of these be dexterously split into the thinnest leaves it is made up of, it will yield such a number of them, as scarce any thing but experience could have persuaded me; and these leaves will afford the most transparent sort of consistent bodies, that, for aught I have observed, are yet unknown; and a single leaf or plate will be so far from being opacous, that it will scarce be so much as visible. And multitudes of bodies there are, whose fragments seem opacous to the naked eye, which yet, when I have included them in good microscopes, appeared transparent; but, Pyrophilus, on the other side I am not yet sure that there are no bodies, whose minute particles even in such a microscope as that of mine, which I was lately mentioning, will not appear diaphanous. For having considered mercury precipitated per se, the little granules that made up the powder, looked like little fragments of coral beheld by the naked eye at a distance (for very near at hand coral will sometimes, especially if it be good, shew some transparency). Filings likewise of steel and copper, though in an excellent microscope, and a fair day, they showed like pretty big fragments of those metals, and had considerable brightness on some of their surfaces, yet I was not satisfied, that I perceived any reflection from the inner parts of any of the filings. Nay, having looked in my best microscope upon the red calx of lead (commonly called Minium) neither I, nor any I shewed it to, could discern it to be other than opacous, though the day were clear, and the object strongly enlightened. And the deeply red colour of vitriol appeared in the same microscope (notwithstanding the great comminution effected by the fire) but like grossy beaten brick. so that, Pyrophilus, I shall willingly resign you the care of making same further inquiries into the subject we have now been consider; for I confess, as I told you before, that I think that the matter may need a further scrutiny, nor would I be forward to determine how far or in what cases the transparency or semi-diaphaneity of the superficial corpuscles of bigger bodies may have an interest in the production of their colours; especially because that even in divers white bodies, as beaten glass, snow and froth, where it seems manifest that the superficial parts are singly diaphanous (being either water, or air, or glass) we see not that such variety of colours are produced as usually are by the refraction of light even in those bodies, when by their bigness, shape, &c. they are conveniently qualified to exhibit such various and lively colours as those of the rainbow, and of prismatical glasses.

28. By what has been hitherto discoursed, Pyrophilus, we may be assisted to judge of that famous controversy which was of old disputed betwixt the Epicureans and other Atomists on one side, and most other philosophers on the other side; the former denying bodies to be coloured in the dark, and the latter making colour to be an inherent quality, as well as figure, hardness, weight, or the like. For though this controversy be revived, and hotly agitated among the moderns, yet I doubt whether it be not in great part a nominal dispute; and therefore let us, according to the doctrine formerly delivered, distinguish the acceptations of the word colour, and say, that if it be taken in the stricter sense, the Epicureans seem to be in the right; for if colour be indeed, though not according to, them, but light modified, how can we conceive that it can subsist in the dark, that is, where it must be supposed there is no light: but, on the other side, if colour be considered as a certain constant disposition of the superficial parts of the object to trouble the light they reflect after such and such a determinate manner, this constant, and if I may so speak, modifying disposition persevering in the object, whether it be shined upon or no, there seems no just reason to deny, but that in this sense, bodies retain their colour as well, in the night as day; or, to speak a little otherwise, it may be said, that bodies are potentially coloured in the dark, and actually in the light. But of this matter discoursing more fully elsewhere, as it is a difficulty that concerns qualities in general, I shall forbear to insist on it here.

1. OF greater moment in the investigation of the nature of colours is the controversy, whether those of the rainbow, and those that are often seen in clouds, before the rising, or after the setting of the sun; and in a word, whether those other colours, that are wont to be called emphatical, ought or ought not to be accounted true colours. I need not tell you that the negative is the common opinion, especially in the schools, as may appear by that vulgar distinction of colours, whereby these under consideration are termed apparent, by way of opposition to those that in the other member of the distinction are called true or genuine. This question I say seems to me of importance, upon this account, that it being commonly granted (or however, easy enough to be proved) that emphatical colours are light itself modified by refractions chiefly, with a concurrence sometimes of reflections, and perhaps some other accidents depending on these two; if these emphatical colours be resolved to be genuine, it will seem consequent, that colours, or at least divers of them, are but diversified light, and not such real and inherent qualities as they are commonly thought to be.

2. NOW since we are wont to esteem the echoes and other sounds of bodies, to be true sounds, all their odours to be true odours, and (to be short) since we judge other sensible qualities to be true ones, because they are the proper objects of some or other of our senses; I see not why emphatical colours, being the proper and peculiar objects of the organ of sight, and capable to affect it as truly and as powerfully as other colours, should be reputed but imaginary ones.

AND if we have (which perchance you will allow) formerly evinced colour (when the word is taken in its more proper sense) to be but modified light, there will be small reason to deny these to be true colours, which more manifestly than others disclose themselves to be produced by diversifications of the light.

3. THERE is indeed taken notice of, a difference betwixt these apparent colours, and those that are wont to be esteemed genuine, as to the duration, which has induced some learned men to call the former rather evanid than fantastical. But as the ingenious Gassendus does somewhere judiciously observe, is this way of arguing were good, the greenness of a leaf ought to pass for apparent, because, soon fading into a yellow, it scarce lasts at all, in comparison of the greenness of an emerald. I shall add, that if the sun-beams be in a convenient manner trajected through a glass prism, and thrown upon some well shaded object within a room, the rainbow thereby painted on the surface of the body that terminates the beams, may oftentimes last longer than some colours I have produced in certain bodies, which would justly, and without scruple be accounted genuine colours, and yet suddenly degenerate, and lose their nature.

4. A GREATER disparity betwixt emphatical colours, and others, may perhaps be taken from this, that genuine colours seem to be produced in opacous bodies by reflection, but apparent ones in diaphanous bodies, and principally by refraction; I say principally, rather than solely, because in some cases reflection also may concur: but still this seems not to conclude these latter colours not to be true ones. Nor must what has been newly said of the differences of true and apparent colours, be interpreted in too unlimited a sense, and therefore it may perhaps somewhat assist you, both to repect upon the two foregoing objections, and to judge of some other passages which you will meet with in this tract, if I take this occasion to observe to you, that if water be agitated into froth, it exhibits, you know, a white colour, which soon after it loses upon the resolution of the bubbles into air and water. Now in this case either the whiteness of the froth is a true colour, or not; if it be, then true colours, supposing the water pure and free from mixtures of any thing tenacious, may be as short-lived as those of the rainbow; also the matter, wherein the whiteness did reside, may in a few moments perfectly lose all footsteps or remains of it. And besides, even diaphanous bodies may be capable of exhibiting true colours by reflection; for that whiteness is so produced, we shall anon make it probable. But if on the other side it be said, that the whiteness of froth is an emphatical colour, then it must no longer be said, that fantastical colours require a certain position of the luminary and the eye, and must be varied or destroyed by the change thereof, since froth appears white, whether the sun be rising or setting, or in the meridian, or any where between it and the horizon, and from what (neighbouring) place soever the beholder's eye looks upon it. And since by making a liquor tenacious enough, yet without destroying its transparency, or staining it with any colour, you may give the little films, whereof the bubbles consist, such a texture as may make the froth last very many hours, if not some days, or even weeks, it will render it somewhat improper to assign duration for the distinguishing character to discriminate genuine from fantastical colours. For such froth may much outlast the undoubtedly true colours of some of nature's productions, as in that gaudy plant, not undeservedly called the Marvel of Peru, the flowers do often fade the same day they are blown; and I have often seen, a Virginian flower, which usually withers within the compass of a day; and I am credibly informed, that not far from hence, a curious herborist has a plant, whose flowers perish in about an hour. But, if the whiteness of water turned into froth must therefore be reputed emphatical, because it appears not that the nature of the body is altered, but only that the disposition of its parts, in reference to the incident light, is changed, why may not the whiteness be accounted emphatical too; which I shall shew anon to be producible, barely by such another change in black horn: and yet this so easily acquired whiteness seems to be as truly its colour as the blackness was before, and at least is more permanent than the greenness of leaves, the redness of roses, and in short, than the genuine colours of the most part of nature's productions. It may indeed be further objected, that according as the sun or other luminous body changes place, these emphatical colours alter or vanish. But not to repeat what I have just now said, I shall add, that if a piece of cloth in a draper's shop (in such the light being seldom primary) be variously folded, it will appear of differing colours, as the parts happen to be more illuminated, or more shaded; and if you stretch it flat, it will commonly exhibit some one uniform colour: and yet these are not wont to be reputed emphatical, so that the difference seems to be chiefly this, that in the case of the rainbow, and the like, the position of the luminary varies the colour, and in the cloth I have been mentioning, the position of the object does it. Nor am I forward to allow, that in all cases, the apparition of emphatical colours requires a determinate position of the eye; for if men will have the whiteness of froth emphatical, you know what we have already inferred from thence. Besides, the sunbeams trajected through a triangular glass, after the manner lately mentioned, will, upon the body that terminates them, paint a rainbow, that may be seen, whether the eye be placed on the right hand of it, or the left, or above, or beneath it, or before or behind it: and though there may appear some little variation in the colours of the rainbow beheld from differing parts of the room, yet such a diversity may be also observed by an attentive eye in real colours, looked upon under the like circumstances. Nor will it follow, that because there remain no footsteps of the colour upon the object, when the prism is removed, that therefore the colour was not real, since the light was truly modified by the refraction and reflection it suffered in its trajection through the prism; and the object in our case served for a specular body, to reflect that colour to the eye. And that you may not be startled, Pyrophilus, that I should venture to say, that a rough and coloured object may serve for a speculum to reflect the artificial rainbow I have been mentioning, consider what usually happens in darkened rooms, where a wall, or other body conveniently situated within, may so reflect the colours of bodies without the room, that they may very clearly be discerned and distinguished and yet it is taken for granted, that the colours seen in a darkened room, though they leave no traces of themselves upon the wall or body that receives them, are the true colours of the external objects, together with which the colours of the images are moved, or do rest. And the error is not in the eye, whose office is only to perceive the appearances of things, and which does truly so; but in the judging, or estimative faculty, which mistakingly concludes that colour to belong, to the wall, which does indeed belong to the object, because the wall is that from whence the beams of light, that carry the visible species, do come in strait lines directly to the eye: as for the same reason we are wont, at a certain distance from concave spherical glasses, to persuade ourselves, that we see the image come forth to meet us, and hang in the air betwixt the glass and us, because the reflected beams, that compose the image cross in that place where the image seems to be, and thence, and not from the glass, do in direct lines take their course to the eye. And upon the like cause it is, that divers deceptions in sounds and other sensible objects do depend, as we elsewhere declare.

5. I KNOW not whether I need add, that I have purposely tried (as you will find some pages hence, and will perhaps think somewhat strange) that colours, that are called emphatical, because not inherent in the bodies in which they appear, may be compounded with one another, as those that are confessedly genuine may. But when all this is said, Pyrophilus, I must advertise you, that it is but problematically spoken; and that though I think the opinion I have endeavoured to fortify probable, yet a great part of our discourse concerning colours may be true, whether that opinion be so or not.

1. THERE are, you know, Pyrophilus, besides those obsolete opinions about colours, which have been long since rejected, very various theories, that have each of them, even at this day, eminent men for their abettors: for the Peripatetic schools, though they dispute amongst themselves divers particulars concerning colours, yet in this they seem unanimously enough to agree, that colours are inherent and real qualities, which the light doth but disclose, and not concur to produce. Besides, there are moderns, who with a slight variation adopt the opinion of Plato; and as he would have colour to be nothing but a kind of flame consisting of minute corpuscles, as it were darted by the object against the eye, to whose pores their littleness and figure made them congruous; so these would have colour to be an internal light of the more lucid parts of the object, darkened, and consequently altered by the various mixtures of the less luminous parts. There are also others, who, imitation of some of the antient Atomists, make colour not to be lucid steam but yet a corporeal effluvium issuing out of the coloured body; but the knowingest of these have of late reformed their hypothesis, by acknowledging and adding, that some external light is necessary to excite, and, as they speak, solicit these corpuscles of colour, as they call them, and bring them to the eye. Another and more principal opinion of the modern philosophers, to which this last named may by a favourable explication be reconciled, is that, which derives colours from the mixture of light and darkness, or rather light and shadows. And as for the Chymists, it is known, that the generality of them ascribe the origin of colours to the sulphureous principle in bodies; though I find, as I elsewhere largely shew, that some of the chiefest of them derive colours rather from salt than sulphur, and others from the third hypostatical principle, mercury. And as for the Cartesians, I need not tell you, that they, supposing the sensation of light to be produced by the impulse made upon the organs of sight, by certain extremely minute and solid globules, to which the pores of the air and other diaphanous bodies are pervious, endeavour to derive the varieties of colours from the various proportion of the direct progress or motion of these globules to their circumvolution or motion about their own center, by which varying proportion they are by this hypothesis supposed qualified to strike the optic nerve after several distinct manners, so as to produce the perception of differing colours.

2. BESIDES these six principal hypotheses, Pyrophilus, there may be some others, which though less known, may perhaps as well as these deserve to be taken into consideration by you; but that I should copiously debate any of them at present, I presume you will not expect, if you confider the scope of these papers, and the brevity I have designed in them; and therefore I shall at this time only take notice to you in the general of two or three things, that do more peculiarly concern the treatise you have now in your hands.

3. AND first, though the embracers of the several hypotheses I have been naming to you, by undertaking each sect of them to explicate colours indefinitely by the particular hypotheses they maintain, seem to hold it forth as the only needful theory about that subject; yet for my part I doubt, whether any one of all these hypotheses have a right to be admitted exclusively to all others: for I think it probable, that whiteness and blackness may be explicated by reflection alone without refraction, as you will find endeavoured in the discourse you will meet with ere long, of the origin of whiteness and blackness; and on the other side, since I have not found, that by any mixture of white and true black (for there is a blueish black, which many misstake for a genuine) there can be a blue, a yellow, or a red, to name no other colours, produced; and since we do find, that these colours may be produced in the glass prism and other transparent bodies, by the help of refractions, it seems, that refraction is to be taken in, into the explication of some colours, to whose generation they seem to concur, either by making a further or other commixture of shades with the refracted light, or by some other way not now to be discoursed. And as it seems not improbable, that in case the pores of the air, and other diaphanous bodies be every where almost filled with such globuli, as the Cartesians suppose, the various kinds of motion of these globuli may in many cases have no small stroke in varying our perception of colour; So without the supposition of these globuli, which it is not so easy to evince, I think we may probably enough conceive in general, that the eye may b