by Robert Hooke
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The reader of this text file should understand that words or phrases between underscores should be imagined to be set in italics.

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

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

Novem. 23. 1664.


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Physiological Descriptions







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By R. HOOKE, Fellow of the ROYAL SOCIETY.

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Non possis oculo quantum contendere Linceus, Non tamen idcirco contemnas Lippus inungi. Horat. Ep. lib. 1.

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

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

Your Majesties most humble and most obedient Subject and Servant,


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

YOUR most humble and most faithful Servant


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The Instrument is this. I prepare a pretty capaceous Bolt-head AB, with a small stem about two foot and a half long DC; upon the end of this D I put on a small bended Glass, or brazen syphon DEF (open at D, E and F, but to be closed with cement at F and E, as occasion serves) whose stem F should be about six or eight inches long, but the bore of it not above half an inch diameter, and very even; these I fix very strongly together by the help of very hard Cement, and then fit the whole Glass ABCDEF into a long Board, or Frame, in such manner, that almost half the head AB may lye buried in a concave Hemisphere cut into the Board RS; then I place it so on the Board RS, as is exprest in the first figure of the first Scheme; and fix it very firm and steady in that posture, so as that the weight of the Mercury that is afterwards to be put into it, may not in the least shake or stir it; then drawing a line XY on the Frame RT, so that it may divide the ball into two equal parts, or that it may pass, as 'twere, through the center of the ball. I begin from that, and divide all the rest of the Board towards UT into inches, and the inches between the 25 and the end E (which need not be above two or three and thirty inches distant from the line XY) I subdivide into Decimals; then stopping the end F with soft Cement, or soft Wax, I invert the Frame, placing the head downwards, and the Orifice E upwards; and by it, with a small Funnel, I fill the whole Glass with Quicksilver; then by stopping the small Orifice E with my finger, I oftentimes erect and invert the whole Glass and Frame, and thereby free the Quicksilver and Glass from all the bubbles or parcels of lurking Air; then inverting it as before, I fill it top full with clear and well strain'd Quicksilver, and having made ready a small ball of pretty hard Cement, by heat made very soft, I press it into the hole E, and thereby stop it very fast; and to secure this Cement from flying out afterward, I bind over it a piece of Leather, that is spread over in the inside with Cement, and wound about it while the Cement is hot: Having thus softned it, I gently erect again the Glass after this manner: I first let the Frame down edge-wayes, till the edge RV touch the Floor, or ly horizontal; and then in that edging posture raise the end RS; this I do, that if there chance to be any Air hidden in the small Pipe E, it may ascend into the Pipe F, and not into the Pipe DC: Having thus erected it, and hung it by the hole Q, or fixt it perpendicularly by any other means, I open the end F, and by a small Syphon I draw out the Mercury so long, till I find the surface of it AB in the head to touch exactly the line XY; at which time I immediately take away the Syphon, and if by chance it be run somewhat below the line XY, by pouring in gently a little Mercury at F, I raise it again to its desired height, by this contrivance I make all the sensible rising and falling of the Mercury to be visible in the surface of the Mercury in the Pipe F, and scarce any in the head AB. But because there really is some small change of the upper surface also, I find by several Observations how much it rises in the Ball, and falls in the Pipe F, to make the distance between the two surfaces an inch greater then it was before; and the measure that it falls in the Pipe is the length of the inch by which I am to mark the parts of the Tube F, or the Board on which it lyes, into inches and Decimals: Having thus justned and divided it, I have a large Wheel MNOP, whose outmost limb is divided into two hundred equal parts; this by certain small Pillars is fixt on the Frame RT, in the manner exprest in the Figure. In the middle of this, on the back side, in a convenient frame, is placed a small Cylinder, whose circumference is equal to twice the length of one of those divisions, which I find answer to an inch of ascent, or descent, of Mercury: This Cylinder I, is movable on a very small Needle, on the end of which is fixt a very light Index KL, all which are so pois'd on the Axis, or Needle, that no part is heavier then another: Then about this Cylinder is wound a small Clew of Silk, with two small steel Bullets at each end of it GH; one of these, which is somewhat the heavier, ought to be so big, as freely to move to and fro in the Pipe F; by means of which contrivance, every the least variation of the height of the Mercury will be made exceeding visible by the motion to and fro of the small Index KL.

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

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

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

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

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

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

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

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

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

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

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

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

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

First, for Microscopes (where the Object we view is near and within our power) the best way of making it appear bright in the Glass, is to cast a great quantity of light on it by means of convex glasses, for thereby, though the aperture be very small, yet there will throng in through it such multitudes, that an Object will by this means indure to be magnifi'd as much again as it would be without it. The way for doing which is this. I make choice of some Room that has only one window open to the South, and at about three or four foot distance from this Window, on a Table, I place my Microscope, and then so place either a round Globe of Water, or a very deep clear plano convex Glass (whose convex side is turn'd towards the Window) that there is a great quantity of Rayes collected and thrown upon the Object: Or if the Sun shine, I place a small piece of oyly Paper very near the Object, between that and the light; then with a good large Burning-Glass I so collect and throw the Rayes on the Paper, that there may be a very great quantity of light pass through it to the Object; yet I so proportion that light, that it may not singe or burn the Paper. Instead of which Paper there may be made use of a small piece of Looking-glass plate, one of whose sides is made rough by being rubb'd on a flat Tool with very find sand, this will, if the heat be leisurely cast on it, indure a much greater degree of heat, and consequently very much augment a convenient light. By all which means the light of the Sun, or of a Window, may be so cast on an Object, as to make it twice as light as it would otherwise be without it, and that without any inconvenience of glaring, which the immediate light of the Sun is very apt to create in most Objects; for by this means the light is so equally diffused, that all parts are alike inlightned; but when the immediate light of the Sun falls on it, the reflexions from some few parts are so vivid, that they drown the appearance of all the other, and are themselves also, by reason of the inequality of light, indistinct, and appear only radiant spots.

But because the light of the Sun, and also that of a Window, is in a continual variation, and so many Objects cannot be view'd long enough by them to be throughly examin'd; besides that, oftentimes the Weather is so dark and cloudy, that for many dayes together nothing can be view'd: And because also there are many Objects to be met with in the night, which cannot so conveniently be kept perhaps till the day, therefore to procure and cast a sufficient quantity of light on an Object in the night, I thought of, and often used this, Expedient.

I procur'd me a small Pedestal, such as is describ'd in the fifth Figure of the first Scheme on the small Pillar AB, of which were two movable Armes CD, which by means of the Screws EF, I could fix in any part of the Pillar; on the undermost of these I plac'd a pretty large Globe of Glass G, fill'd with exceeding clear Brine, stopt, inverted, and fixt in the manner visible in the Figure; out of the side of which Arm proceeded another Arm H, with many joynts; to the end of which was fastned a deep plain Convex glass I, which by means of this Arm could be moved too and fro, and fixt in any posture. On the upper Arm was placed a small Lamp K, which could be to mov'd upon the end of the Arm, as to be set in a fit posture to give light through the Ball: By means of this Instrument duly plac'd, as is exprest in the Figure, with the small flame of a Lamp may be cast as great and convenient a light on the Object as it will well indure; and being always constant, and to be had at any time, I found most proper for drawing the representations of those small Objects I had occasion to observe.

None of all which ways (though much beyond any other hitherto made use of by any I know) do afford a sufficient help, but after a certain degree of magnifying, they leave us again in the lurch. Hence it were very desirable, that some way were thought of for making the Object-glass of such a Figure as would conveniently bear a large Aperture.

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

The contrivance of the Engine is, only to make the ends of two large Mandrils so to move, that the Centers of them may be at any convenient distance asunder, and that the Axis of the Mandrils lying both in the same plain produc'd, may meet each other in any assignable Angle; both which requisites may be very well perform'd by the Engine describ'd in the third Figure of the first Scheme: where AB signifies the Beam of a Lath fixt perpendicularly or Horizontally, CD the two Poppet heads, fixt at about two foot distance, EF an Iron Mandril, whose tapering neck F runs in an adapted tapering brass Collar; the other end E runs on the point of a Screw G; in a convenient place of this is fastned H a pully Wheel, and into the end of it, that comes through the Poppet head C, is screwed a Ring of a hollow Cylinder K, or some other conveniently shap'd Tool, of what wideness shall be thought most proper for the cize of Glasses, about which it is to be imploy'd: As, for Object glasses, between twelve foot and an hundred foot long, the Ring may be about six inches over, or indeed somewhat more for those longer Glasses. It would be convenient also and not very chargeable, to have four or five several Tools; as one for all Glasses between an inch and a foot, one for all Glasses between a foot and ten foot long, another for all between ten and an hundred, a fourth for all between a hundred and a thousand foot long; and if Curiosity shall ever proceed so far, one for all lengths between a thousand and ten thousand foot long; for indeed the principle is such, that supposing the Mandrils well made, and of a good length, and supposing great care be used in working and polishing them, I see no reason, but that a Glass of a thousand, nay of ten thousand foot long, may be as well made as one of ten; for the reason is the same, supposing the Mandrils and Tools be made sufficiently strong, so that they cannot bend; and supposing the Glass, out of which they are wrought, be capable of so great a regularity in its parts as to refraction: this hollow Cylinder K is to contain the Sand, and by being drove round very quick to and fro by means of a small Wheel, which may be mov'd with ones foot, serves to grind the Glass: The other Mandril is shap'd like this, but it has an even neck instead of a taper one, and runs in a Collar, that by the help of a Screw and a joynt made like M in the Figure, it can be still adjustned to the wearing or wasting neck: into the end of this Mandril is screwed a Chock N on which with Cement or Glew is fastned the piece of Glass Q that is to be form'd; the middle of which Glass is to be plac'd just on the edge of the Ring and the Lath OP is to be set and fixt (by means of certain pieces and screws the manner whereof will be sufficiently evidenc'd by the Figure) in such an Angle as is requisite to the forming of such a Sphere as the Glass is design'd to be of; the geometrical ground of which being sufficiently plain, though not heeded before, I shall, for brevities sake, pass over. This last Mandril to be made (by means of the former, or some other Wheel) to run round very swift also, by which two cross motions the Glass cannot chuse (if care be us'd) but be wrought into a most exactly spherical Surface.

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

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

The Instrument consisted of five Rulers, or long pieces placed together, after the manner exprest in the second Figure of the first Scheme, where AB denotes a straight piece of wood about six foot and two inches long, about three inches over, and an inch and half thick, on the back side of which was hung a small plummet by a line stretcht from top to bottom, by which this piece was set exactly upright, and so very firmly fixt; in the middle of this was made a hole or center, into which one end of a hollow cylindrical brass Box CC, fashion'd as I shall by and by describe, was plac'd, and could very easily and truly be mov'd to and fro; the other end of this Box being put into, and moving in, a hole made in a small arm DD; into this box was fastned the long Ruler EF, about three foot and three or four inches long, and at three foot from the above mention'd Centers PP was a hole E, cut through, and cross'd with two small threads, and at the end of it was fixt a small sight G, and on the back side of it was fixt a small Arm H, with a Screw to fix it in any place on the Ruler LM; this Ruler LM was mov'd on the Center B (which was exactly three foot distance from the middle Center P) and a line drawn through the middle of it LM, was divided by a Line of cords into some sixty degrees, and each degree was subdivided into minutes, so that putting the cross of the threads in E upon any part of this divided line, I presently knew what Angle the two Rules AB and EF made with each other, and by turning the Screw in H, I could fix them in any position. The other Ruler also RS was made much after the same manner, only it was not fixt to the hollow cylindrical Box, but, by means of two small brass Armes or Ears, it mov'd on the Centers of it; this also, by means of the cross threads in the hole S, and by a Screw in K, could be fastned on any division of another line of cords of the same radius drawn on NO. And so by that means, the Angle made by the two Rulers, AB and RS, was also known. The Brass box CC in the middle was shap'd very much like the Figure X, that is, it was a cylindrical Box stopp'd close at either end, off of which a part both of the sides and bottomes was cut out, so that the Box, when the Pipe and that was joyned to it, would contain the Water when fill'd half full, and would likewise, without running over, indure to be inclin'd to an Angle, equal to that of the greatest refraction of Water, and no more, without running over. The Ruler EF was fixt very fast to the Pipe V, so that the Pipe V directed the length of the Ruler EF, and the Box and Ruler were mov'd on the Pin TT, so as to make any desirable Angle with the Ruler AB. The bottom of this Pipe V was stop'd with a small piece of exactly plain Glass, which was plac'd exactly perpendicular to the Line of direction, or Axis of the Ruler EF. The Pins also TT were drill'd with small holes through the Axis, and through those holes was stretcht and fastned a small Wire. There was likewise a small Pipe of Tin loosly put on upon the end of V, and reaching down to the sight G; the use of which was only to keep any false Rayes of light from passing through the bottom of V, and only admitting such to pass as pierced through the sight G: All things being placed together in the manner describ'd in the Figure; that is, the Ruler AB being fixt perpendicular, I fill'd the Box CC with Water, or any other Liquor, whose refraction I intended to try, till the Wire passing through the middle of it were just covered: then I moved and fixt the Ruler FE at any assignable Angle, and placed the flame of a Candle just against the sight G; and looking through the sight I, I moved the Ruler RS to and fro, till I perceived the light passing through G to be covered, as 'twere, or divided by the dark Wire passing through PP: then turning the Screw in K, I fixt it in that posture: And through the hole S, I observed what degree and part of it was cut by the cross threads in S. And this gave me the Angle of Inclination, APS answering to the Angle of Refraction BPE: for the surface of the Liquor in the Box will be alwayes horizontal, and consequently AB will be a perpendicular to it; the Angle therefore APS will measure, or be the Angle of Inclination in the Liquor; next EPB must be the Angle of Refraction, for the Ray that passes through the sight G, passes also perpendicularly through the Glass Diaphragme at F, and consequently also perpendicularly through the lower surface of the Liquor contiguous to the Glass, and therefore suffers no refraction till it meet with the horizontal surface of the Liquor in CC, which is determined by the two Angles.

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

My way for measuring how much a Glass magnifies an Object, plac'd at a convenient distance from my eye, is this. Having rectifi'd the Microscope, to see the desir'd Object through it very distinctly, at the same time that I look upon the Object through the Glass with one eye, I look upon other Objects at the same distance with my other bare eye; by which means I am able, by the help of a Ruler divided into inches and small parts, and laid on the Pedestal of the Microscope, to cast, as it were, the magnifi'd appearance of the Object upon the Ruler, and thereby exactly to measure the Diameter it appears of through the Glass, which being compar'd with the Diameter it appears of to the naked eye, will easily afford the quantity of its magnifying.

The Microscope, which for the most part I made use of, was shap'd much like that in the sixth Figure of the first Scheme, the Tube being for the most part not above six or seven inches long, though, by reason it had four Drawers, it could very much be lengthened, as occasion required; this was contriv'd with three Glasses; a small Object Glass at A, a thinner Eye Glass about B, and a very deep one about C: this I made use of only when I had occasion to see much of an Object at once; the middle Glass conveying a very great company of radiating Pencils, which would go another way, and throwing them upon the deep Eye Glass. But when ever I had occasion to examine the small parts of a Body more accurately, I took out the middle Glass, and only made use of one Eye Glass with the Object Glass, for always the fewer the Refractions are, the more bright and clear the Object appears. And therefore 'tis not to be doubted, but could we make a Microscope to have one only refraction, it would, caeteris paribus, far excel any other that had a greater number. And hence it is, that if you take a very clear piece of a broken Venice Glass, and in a Lamp draw it out into very small hairs or threads, then holding the ends of these threads in the flame, till they melt and run into a small round Globul, or drop, which will hang at the end of the thread; and if further you stick several of these upon the end of a stick with a little sealing Wax, so as that the threads stand upwards, and then on a Whetstone first grind off a good part of them, and afterward on a smooth Metal plate, with a little Tripoly, rub them till they come to be very smooth; if one of these be fixt with a little soft Wax against a small needle hole, prick'd through a thin Plate of Brass, Lead, Pewter, or any other Metal, and an Object, plac'd very near, be look'd at through it, it will both magnifie and make some Objects more distinct then any of the great Microscopes. But because these, though exceeding easily made, are yet very troublesome to be us'd, because of their smallness, and the nearness of the Object; therefore to prevent both these, and yet have only two Refractions, I provided me a Tube of Brass, shap'd much like that in the fourth Figure of the first Scheme; into the smaller end of this I fixt with Wax a good plano convex Object Glass, with the convex side towards the Object, and into the bigger end I fixt also with wax a pretty large plano Convex Glass, with the convex side towards my eye, then by means of the small hole by the side, I fill'd the intermediate space between these two Glasses with very clear Water, and with a Screw stopp'd it in; then putting on a Cell for the Eye, I could perceive an Object more bright then I could when the intermediate space was only fill'd with Air, but this, for other inconveniences, I made but little use of.

My way for fixing both the Glass and Object to the Pedestal most conveniently was thus: Upon one side of a round Pedestal AB, in the sixth Figure of the first Scheme, was fixt a small Pillar CC, on this was fitted a small Iron Arm D, which could be mov'd up and down, and fixt in any part of the Pillar, by means of a small Screw E; on the end of this Arm was a small Ball fitted into a kind of socket F, made in the side of the Brass Ring G, through which the small end of the Tube was screw'd; by means of which contrivance I could place and fix the Tube in what posture I desir'd (which for many Observations was exceeding necessary) and adjusten it most exactly to any Object.

For placing the Object, I made this contrivance; upon the end of a small brass Link or Staple HH, I so fastned a round Plate II, that it might be turn'd round upon its Center K, and going pretty stiff, would stand fixt in any posture it was set; on the side of this was fixt a small Pillar P, about three quarters of an inch high, and through the top of this was thrust a small Iron pin M, whose top just stood over the Center of the Plate; on this top I fixt a small Object, and by means of these contrivances I was able to turn it into all kind of positions, both to my Eye and the Light; for by moving round the small Plate on its center, could move it one way, and by turning the Pin M, I could move it another way, and this without stirring the Glass at all, or at least but very little; the Plate likewise I could move to and fro to any part of the Pedestal (which in many cases was very convenient) and fix it also in any Position, by means of a Nut N, which was screw'd on upon the lower part of the Pillar CC. All the other Contrivances are obvious enough from the draught, and will need no description.

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

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

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

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

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

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

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

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

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

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Physiological Descriptions







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

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

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

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

But to proceed: The Image we have here exhibited in the first Figure[1], was the top of a small and very sharp Needle, whose point aa nevertheless appear'd through the Microscope above a quarter of an inch broad, not round nor flat, but irregular and uneven; so that it seem'd to have been big enough to have afforded a hundred armed Mites room enough to be rang'd by each other without endangering the breaking one anothers necks, by being thrust off on either side. The surface of which, though appearing to the naked eye very smooth, could not nevertheless hide a multitude of holes and scratches and ruggednesses from being discover'd by the Microscope to invest it, several of which inequalities (as A, B, C, seem'd holes made by some small specks of Rust; and D some adventitious body, that stuck very close to it) were casual. All the rest that roughen the surface, were onely so many marks of the rudeness and bungling of Art. So unaccurate is it, in all its productions, even in those which seem most neat, that if examin'd with an organ more acute then that by which they were made, the more we see of their shape, the less appearance will there be of their beauty: whereas in the works of Nature, the deepest Discoveries shew us the greatest Excellencies. An evident Argument, that he that was the Author of all these things, was no other then Omnipotent; being able to include as great a variety of parts and contrivances in the yet smallest Discernable Point, as in those vaster bodies (which comparatively are called also Points) such as the Earth, Sun, or Planets. Nor need it seem strange that the Earth it self may be by Analogie call'd a Physical Point: For as its body, though now so near us as to fill our eys and fancies with a sense of the vastness of it, may by a little Distance, and some convenient Diminishing Glasses, be made vanish into a scarce visible Speck, or Point (as I have often try'd on the Moon, and (when not too bright) on the Sun it self.) So, could a Mechanical contrivance succesfully answer our Theory, we might see the least spot as big as the Earth it self; and Discover, as Des Cartes[2] also conjectures, as great a variety of bodies in the Moon, or Planets, as in the Earth.

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

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Observ. II. Of the Edge of a Razor.

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

Now for the drawing this second Figure[3] (which represents a part of the Edge about half a quarter of an inch long of a Razor well set) I so plac'd it between the Object-glass & the light, that there appear'd a reflection from the very Edge, represented by the white line abcdef. In which you may perceive it to be somewhat sharper then elsewhere about d, to be indented or pitted about b, to be broader and thicker about c, and unequal and rugged about e, and pretty even between ab and ef. Nor was that part of the Edge ghik so smooth as one would imagine so smooth bodies as a Hone and Oyl should leave it; for besides those multitudes of scratches, which appear to have raz'd the surface ghik, and to cross each other every way which are not half of them exprest in the Figure, there were several great and deep scratches, or furrows, such as gh and ik, which made the surface yet more rugged, caus'd perhaps by some small Dust casually falling on the Hone, or some harder or more flinty part of the Hone it self. The other part of the Razor ll, which is polish'd on a grinding-stone, appear'd much rougher then the other, looking almost like a plow'd field, with many parallels, ridges, and furrows, and a cloddy, as 'twere, or an uneven surface: nor shall we wonder at the roughnesses of those surfaces, since even in the most curious wrought Glasses for Microscopes, and other Optical uses, I have, when the Sun has shone well on them, discover'd their surface to be variously raz'd or scratched, and to consist of an infinite of small broken surfaces, which reflect the light of very various and differing colours. And indeed it seems impossible by Art to cut the surface of any hard and brittle body smooth, since Putte, or even the most curious Powder that can be made use of, to polish such a body, must consist of little hard rough particles, and each of them must cut its way, and consequently leave some kind of gutter or furrow behind it. And though Nature does seem to do it very readily in all kinds of fluid bodies, yet perhaps future observators may discover even these also rugged; it being very probable, as I elsewhere shew, that fluid bodies are made up of small solid particles variously and strongly mov'd, and may find reason to think there is scarce a surface in rerum natura perfectly smooth. The black spot mn, I ghess to be some small speck of rust, for that I have oft observ'd to be the manner of the working of Corrosive Juyces. To conclude, this Edge and piece of a Razor, if it had been really such as it appear'd through the Microscope, would scarcely have serv'd to cleave wood, much less to have cut off the hair of beards, unless it were after the manner that Lucian merrily relates Charon to have made use of, when with a Carpenters Axe he chop'd off the beard of a sage Philosopher, whose gravity he very cautiously fear'd would indanger the oversetting of his Wherry.

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

This is another product of Art, A piece of the finest Lawn I was able to get, so curious that the threads were scarce discernable by the naked eye, and yet through an ordinary Microscope you may perceive[4] what a goodly piece of coarse Matting it is; what proportionable cords each of its threads are, being not unlike, both in shape and size, the bigger and coarser kind of single Rope-yarn, wherewith they usually make Cables. That which makes the Lawn so transparent, is by the Microscope, nay by the naked eye, if attentively viewed, plainly enough evidenced to be the multitude of square holes which are left between the threads, appearing to have much more hole in respect of the intercurrent parts then is for the most part left in a lattice-window, which it does a little resemble, onely the crossing parts are round and not flat.

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

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

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