The words "element" and "principle" are used by him as equivalent terms, and signify those primitive and simple bodies of which compounds may be said to be composed, and into which these compounds are ultimately resolvable.

He concludes... that the Paracelsian elements—their "salt," "sulphur," and "mercury"—are not the first and most simple principles of bodies; but that these consist, at most, of concretions of corpuscles or particles more simple than they, and possessing the radical and universal properties of volume, shape, and motion.

He became a member of what was known as the , a small association of men interested in the new philosophy, who met at each other's houses in London, and occasionally at Gresham College, "to discourse and consider of philosophical inquiries and such as related thereunto." The meetings were subsequently held in , and Boyle took up his residence there in 1654. Here—in association with Wilkins; John Wallis and Seth Ward, the two Savilian Professors of Geometry and Astronomy; , the physician, then student of Christ Church; Christopher Wren, then Fellow of All Souls' College; Goddard, Warden of Merton; and , Fellow of Trinity, and afterwards its President—they sought to cultivate the new philosophy, "being satisfied that there was no certain way of arriving at any competent knowledge unless they made a variety of experiments upon natural bodies. In order to discover what phenomena they would produce, they pursued that method by themselves with great industry, and then communicated their discoveries to each other." The Invisible College eventually grew into the ...

He introduced the air-pump into England, and his "pneumatical engine" enabled him to discover many of the fundamental properties of a gas, notably the relation of its volume to pressure.

He... discovered the dependence of the of a liquid upon , explained the action of the , the effect of the air on the vibration of a pendulum and on the propagation of sound, and made experiments on the nature of , and on the relation of air to and .

His published works contain many well-authenticated chemical facts, which are commonly held to be the discovery of a later time.

Google Books (public domain)

I need not tell you, what complaints the more candid and judicious of the Chymists themselves are wont to make of those boasters, that confidently pretend, that they have extracted the salt or sulphur of quicksilver, when they have disguised it by additaments, wherewith it resembles the concretes, whose names are given it; whereas by a skilful and rigid examen, it may be easily enough stripped of its disguises, and made to appear again in the pristine form of running mercury. The pretended salts and sulphurs being so far from being elementary parts extracted out of the body of mercury, that they are rather... de-compound bodies, made up of the whole metal and the menstruum, or other additaments employed to disguise it.

There are some mixt bodies, from which it has not been yet made appear, that any degree of fire can separate either salt, or sulphur, or mercury, much less all the three. The most obvious instance of this truth is gold, which is a body so fixed, and wherein the elementary ingredients (if it have any) are so firmly united to each other, that we find not in the operations, wherein gold is exposed to the fire, how violent soever, that it does discernably so much as lose of its fixedness or weight, so far is it from being dissipated into those principles, whereof one at least is acknowledged to be fugitive enough.

I remember, that being once at Leyden, I was brought to the top of a tower, where, in a darkened room (such as is now used in many places to bring in the species of external object) a convex glass, applied to the only hole, by which light was permitted to enter, did project upon a large white sheet of paper, held at a just distance from it, a lively representation of divers of the chief buildings in the town; all which, upon the admission of more light into the room, by opening the window, did immediately disappear, And methinks... that in divers of the philosophical theories, that have been formerly applauded, something not unlike this may be easily observed. for though, whilst they are looked on with such a weak and determinate degree of light, they may appear very artificial and well-proportioned fabrics, yet they appear so but in that twilight, as it were, which is requisite to their conspicuousness. For if but a full light of new experiments and observations be freely let in upon them, the beauty of those (delightful, but fantastical) structures does immediately vanish.

For it very rarely otherwise happens, than that theories, that are grounded but upon few and obvious experiments, are subject to be contradicted by some such instances, as more free and diligent inquiries into what of nature is more abstruse, or even into the less obvious qualities of things, are wont to bring to light.

But of such writers the number is yet (and will I fear always be so) small, that I shall not need to make many exceptions, when I treat of the usefulness of writing books of essays, in comparison of that of writing systematically: or, at least... whilst I presume not to judge of other men's abilities, I hope it may be lawful for me to confess freely to you concerning myself, that I am very sensible of my being far from having such a stock of experiments and observations, as I judge requisite to write systematically; and I am apt to impute many of the deficiencies to be met with in the theories and reasonings of such great wits as Aristotle, Campanella, and some other celebrated philosophers, chiefly to this very thing, that they have too hastily, and either upon a few observations, or at least without a competent number of experiments, presumed to establish principles, and deliver axioms.

And that you may know... what kind of writings I mean, I shall name to you the learned Gassendus his little Syntagma of Epicuruss philosophy, and that most ingenious gentleman Monsieur Descartes his principles of philosophy. For though I purposely refrained, though not altogether from transiently consulting about a few particulars, yet from seriously and orderly reading over those excellent (though disagreeing) books, or so much as Sir Francis Bacon's Novum Organum, that I might not be prepossessed with any theory or principles, till I had spent some time in trying what things themselves would incline me to think; yet beginning now to allow myself to read those excellent books, I find by the little I have read in them already, that if I had read them before I began to write, I might have enriched the ensuing essays with divers truths, which they now want, and have explicated divers things much better than I fear I have done.

The phaenomena afforded by trades, are a part of the history of nature, and therefore may both challenge the naturalist's curiosity and add to his knowledge, Nor will it suffice to justify learned men in the neglect and contempt of this part of natural history, that the men, from whom it must be learned, are illiterate mechanicks... is indeed childish, and too unworthy of a philosopher, to be worthy of an honest answer.

Those hypotheses do not a little hinder the progress of Humane knowledge, that introduce Morals and Politicks into the Explications of Corporeal Nature, where all things are indeed transacted according to Laws Mechanical.

I shall take leave to think the worse, rather of the practice of the men than of the book of God.

He was one of the earliest to insist on the necessity of studying the forms of crystals. He saw in their formation proof that the internal motions, configuration, and position of the integral parts are all that is necessary to account for alterations and diversities in outward character.

And truly... if men could be persuaded to mind more the advancement of natural philosophy than that of their own reputations, it were not, methinks, very uneasy to make them sensible, that one of the considerablest services, that they could do mankind, were to set themselves diligently and industriously to make experiments and collect observations, without being over-forward to establish principles and axioms, believing it uneasy to erect such theories, as are capable to explicate all the phænomena of nature, before they have been able to take notice of the tenth part of those phænomena, that are to be explicated.

Not that I at all disallow the use of reasoning upon experiments, or the endeavouring to discern as early as we can the confederations, and differences, and tendencies of things: for such an absolute suspension of the exercise of reasoning were exceeding troublesome, if not impossible. And, as in that rule of arithmetic, which is commonly called ' by proceeding upon a conjecturally-supposed number, as if it were that, which we inquire after, we are wont to come to the knowledge of the true number sought for; so in physiology it is sometimes conducive to the discovery of truth, to permit the understanding to make an hypothesis, in order to the explication of this or that difficulty, that by examining how far the phænomena are, or are not, capable of being solved by that hypothesis, the understanding may, even by its own errors, be instructed.

For it has been truly observed by a great philosopher, that truth does more easily emerge out of error than confusion.

Those distinct substances, which concretes generally either afford, or are made up of, may, without very much inconvenience, be called the elements or principles of them.

Epicurus... supposes not only all mixt bodies, but all others to be produced by the various and casual occursions of atoms, moving themselves to and fro by an internal principle in the immense or rather infinite vacuum.

It seems not absurd to conceive, that at first production of mixt bodies, the universal matter, whereof they among other parts of the universe consisted, was actually divided, into little particles, of several sizes and shapes, variously moved.

Being Gentlemen and very far from the litigious humour of loving to wrangle about words or terms or notions as empty; they had before his coming in, readily agreed promiscuously to use when they pleased Elements and Principles as terms equivalent: and to understand both by the one and the other, those primitive and simple bodies of which the mixt ones are said to be composed, and into which they are ultimately resolved.

And therefore I think you have done very wisely to make it your business to consider the Phœnomena relating to the present question, which have been afforded by experiments, especially since it might seem injurious to our senses, by whose mediation we acquire so much of the knowledge we have of things corporal, to have recourse to far-fetched and abstracted Ratiocination, to know what are the sensible ingredients of those sensible things that we daily see and handle, and are supposed to have the liberty to untwist (if I may so speak) into the primitive bodies they consist of.

A Person any Thing vers’d in the Writings of Chymists cannot but Discern by their obscure, Ambiguous, and almost Ænigmatical Way of expressing what they pretend to Teach, that they have no Mind, to be understood at all, but by the Sons of Art (as they call them) nor to be Understood even by these without Difficulty And Hazardous Tryalls.

I observe, that of late Chymistry begins, as indeed it deserves, to be cultivated by Learned Men who before despis’d it; and to be pretended to by many who never cultivated it, that they may be thought not to ignore it: Whence it is come to passe, that divers Chymical Notions about Matters Philosophical are taken for granted and employ’d, and so adopted by very eminent Writers both Naturalists and Physitians. Now this I fear may prove somewhat prejudicial to the Advancement of solid Philosophy: For though I am a great Lover of Chymical Experiments, and though I have no mean esteem of divers Chymical Remedies, yet I distinguish these from their Notions about the causes of things, and their manner of Generation.

That then, that I wish for, as to systems, is this, that men, in the first place, would forbear to establish any theory, till they have consulted with (though not a fully competent number of experiments, such as may afford them all the phænomena to be explicated by that theory, yet) a considerable number of experiments, in proportion to the comprehensiveness of the theory to be erected on them. And, in the next place, I would have such kind of supestructures looked upon only as temporary ones; which though they may be preferred before any others, as being the least imperfect, or, if you please, the best in their kind that we yet have, yet are they not entirely to be acquiesced in, as absolutely perfect, or uncapable of improving alterations.

I observe, that of late Chymistry begins, as indeed it deserves, to be cultivated by Learned Men who before despis'd it; and to be pretended to by many who never cultivated it, that they may be thought not to ignore it: Whence it is come to passe, that divers Chymical Notions about Matters Philosophical are taken for granted and employ'd, and so adopted by very eminent Writers both Naturalists and Physitians. Now this I fear may prove somewhat prejudicial to the Advancement of solid Philosophy: For though I am a great Lover of Chymical Experiments, and though I have no mean esteem of divers Chymical Remedies, yet I distinguish these from their Notions about the causes of things, and their manner of Generation.

And therefore I think you have done very wisely to make it your business to consider the Phœnomena relating to the present question, which have been afforded by experiments, especially since it might seem injurious to our senses, by whose mediation we acquire so much of the knowledge we have of things corporal, to have recourse to far-fetched and abstracted Ratiocination, to know what are the sensible ingredients of those sensible things that we daily see and handle, and are supposed to have the liberty to untwist (if I may so speak) into the primitive bodies they consist of.

Being Gentlemen and very far from the litigious humour of loving to wrangle about words or terms or notions as empty; they had before his coming in, readily agreed promiscuously to use when they pleased Elements and Principles as terms equivalent: and to understand both by the one and the other, those primitive and simple bodies of which the mixt ones are said to be composed, and into which they are ultimately resolved.

It seems not absurd to conceive, that at first production of mixt bodies, the universal matter, whereof they among other parts of the universe consisted, was actually divided, into little particles, of several sizes and shapes, variously moved.

Epicurus... supposes not only all mixt bodies, but all others to be produced by the various and casual occursions of atoms, moving themselves to and fro by an internal principle in the immense or rather infinite vacuum.

Those distinct substances, which concretes generally either afford, or are made up of, may, without very much inconvenience, be called the elements or principles of them.

There are some mixt bodies, from which it has not been yet made appear, that any degree of fire can separate either salt, or sulphur, or mercury, much less all the three. The most obvious instance of this truth is gold, which is a body so fixed, and wherein the elementary ingredients (if it have any) are so firmly united to each other, that we find not in the operations, wherein gold is exposed to the fire, how violent soever, that it does discernably so much as lose of its fixedness or weight, so far is it from being dissipated into those principles, whereof one at least is acknowledged to be fugitive enough.

That then, that I wish for, as to systems, is this, that men, in the first place, would forbear to establish any theory, till they have consulted with (though not a fully competent number of experiments, such as may afford them all the phænomena to be explicated by that theory, yet) a considerable number of experiments, in proportion to the comprehensiveness of the theory to be erected on them. And, in the next place, I would have such kind of supestructures looked upon only as temporary ones; which though they may be preferred before any others, as being the least imperfect, or, if you please, the best in their kind that we yet have, yet are they not entirely to be acquiesced in, as absolutely perfect, or uncapable of improving alterations.

For it has been truly observed by a great philosopher, that truth does more easily emerge out of error than confusion.

I shall take leave to think the worse, rather of the practice of the men than of the book of God.

Those hypotheses do not a little hinder the progress of Humane knowledge, that introduce Morals and Politicks into the Explications of Corporeal Nature, where all things are indeed transacted according to Laws Mechanical.

The phaenomena afforded by trades, are a part of the history of nature, and therefore may both challenge the naturalist's curiosity and add to his knowledge, Nor will it suffice to justify learned men in the neglect and contempt of this part of natural history, that the men, from whom it must be learned, are illiterate mechanicks... is indeed childish, and too unworthy of a philosopher, to be worthy of an honest answer.

And that you may know... what kind of writings I mean, I shall name to you the learned Gassendus his little Syntagma of Epicurus's philosophy, and that most ingenious gentleman Monsieur Descartes his principles of philosophy. For though I purposely refrained, though not altogether from transiently consulting about a few particulars, yet from seriously and orderly reading over those excellent (though disagreeing) books, or so much as Sir Francis Bacon's Novum Organum, that I might not be prepossessed with any theory or principles, till I had spent some time in trying what things themselves would incline me to think; yet beginning now to allow myself to read those excellent books, I find by the little I have read in them already, that if I had read them before I began to write, I might have enriched the ensuing essays with divers truths, which they now want, and have explicated divers things much better than I fear I have done.

But of such writers the number is yet (and will I fear always be so) small, that I shall not need to make many exceptions, when I treat of the usefulness of writing books of essays, in comparison of that of writing systematically: or, at least... whilst I presume not to judge of other men's abilities, I hope it may be lawful for me to confess freely to you concerning myself, that I am very sensible of my being far from having such a stock of experiments and observations, as I judge requisite to write systematically; and I am apt to impute many of the deficiencies to be met with in the theories and reasonings of such great wits as Aristotle, Campanella, and some other celebrated philosophers, chiefly to this very thing, that they have too hastily, and either upon a few observations, or at least without a competent number of experiments, presumed to establish principles, and deliver axioms.

For it very rarely otherwise happens, than that theories, that are grounded but upon few and obvious experiments, are subject to be contradicted by some such instances, as more free and diligent inquiries into what of nature is more abstruse, or even into the less obvious qualities of things, are wont to bring to light.

And truly... if men could be persuaded to mind more the advancement of natural philosophy than that of their own reputations, it were not, methinks, very uneasy to make them sensible, that one of the considerablest services, that they could do mankind, were to set themselves diligently and industriously to make experiments and collect observations, without being over-forward to establish principles and axioms, believing it uneasy to erect such theories, as are capable to explicate all the phænomena of nature, before they have been able to take notice of the tenth part of those phænomena, that are to be explicated.

Not that I at all disallow the use of reasoning upon experiments, or the endeavouring to discern as early as we can the confederations, and differences, and tendencies of things: for such an absolute suspension of the exercise of reasoning were exceeding troublesome, if not impossible. And, as in that rule of arithmetic, which is commonly called regula falsi by proceeding upon a conjecturally-supposed number, as if it were that, which we inquire after, we are wont to come to the knowledge of the true number sought for; so in physiology it is sometimes conducive to the discovery of truth, to permit the understanding to make an hypothesis, in order to the explication of this or that difficulty, that by examining how far the phænomena are, or are not, capable of being solved by that hypothesis, the understanding may, even by its own errors, be instructed.

I need not tell you, what complaints the more candid and judicious of the Chymists themselves are wont to make of those boasters, that confidently pretend, that they have extracted the salt or sulphur of quicksilver, when they have disguised it by additaments, wherewith it resembles the concretes, whose names are given it; whereas by a skilful and rigid examen, it may be easily enough stripped of its disguises, and made to appear again in the pristine form of running mercury. The pretended salts and sulphurs being so far from being elementary parts extracted out of the body of mercury, that they are rather... de-compound bodies, made up of the whole metal and the menstruum, or other additaments employed to disguise it.

As for silver, I never could see any degree of fire make it part with any of its three principles. ...But admitting, that some parts of the silver were driven away by the violence of the fire, what proof is there, that it was either the salt, the sulphur, or the mercury of the metal, and not rather a part of it homogeneous to what remained? for besides that the silver, that was left, seemed not sensibly altered, which probably would have appeared, had so much of any one of its principles been separated from it.

I find that even Eminent Writers (such as Raymund Lully, Paracelsus, and others) do so abuse the termes they employ, that as they will now and then give divers things one name, so they will oftentimes give one thing, many Names; and some of them (perhaps) such, as do much more properly signifie some Distinct Body of another kind; nay even in Technical Words or Termes of Art, they refrain not from this Confounding Liberty; but will, as I have Observ'd call the same Substance, sometimes the Sulphur, and Sometimes the Mercury, of a Body.

I cannot conceive, how a body, destitute of understanding and sense, truly so called, can moderate and determine its own motions; especially so as to make them conformable to laws that it has no knowledge of.

Among Latin writers, the acceptations of the word nature are so many, that I remember, one author reckons up no less than fourteen or fifteen. Hence we see how easy 'tis for the generality of men, without excepting those who write of natural things, to impose upon others and themselves, in the use of a word so apt to be mis-employ'd. ..the very great ambiguity of this term, and the promiscuous use made of it, without sufficiently attending to its different significations, render many of the expressions wherein 'tis employ'd either unintelligible, improper, or false.