Boyle, Robert

(b. Lismore, Ireland, 25 January 1627; d. London, England, 30 December 1691)

natural philosophy, physics, chemistry.

The son of Richard Boyle, first earl of Cork and a great Elizabethan adventurer, and his second wife, Katherine Fenton, Robert Boyle was born to considerable affluence and was related, by blood or marriage, to all the great Anglo-Irish families of his day. He was the youngest son in a family of fourteen children. At the age of eight, after private tuition at home, he was sent for several years to Eton, which the sons of gentlemen were just beginning to attend, and then, at the age of twelve, to the Continent with his next older brother, Francis, later Lord Shannon. There a citizen of Geneva tutored him privately in the polite arts, the conventional subjects of a liberal education, and practical mathematics; then, or in the course of his subsequent travels, he was introduced to the new science, including Galileo’s Dialogue on the Two Chief World Systems, which he read in Florence in 1642.

The outbreak of the Anglo-Irish wars, as well as the Civil War in England, led to his return home. Although his father was a Royalist, Boyle was persuaded by his elder sister, Katherine, Lady Ranelagh, a strong Parliamentarian (as befitted a friend of John Milton), to look favorably on the Parliamentary side. Lady Ranelagh also introduced him to Samuel Hartlib, who seems to have turned his interests to medicine and such practical matters as agriculture. Medicine led him to chemistry, at first for the preparation of drugs; but he soon became not only a skillful chemical experimenter but also an original chemical thinker. He read the chemists who wrote in English, French, or Latin, as well as the most important writers on other sciences. His early interest in astronomy persisted for a time but, under the combined influence of Bacon and Descartes, he soon turned to wider problems. Soon his point of view, except for his belief that chemistry was an important physical science (not merely a practical art or a mystic science), coincided with that of the leaders of the English scientific movement (such as John Wilkins, John Wallis, and Seth Ward), whom he joined at Oxford about 1656.

After the Restoration, Boyle was frequently in London, finally settling there in 1668. He was one of the founders of the Royal Society and throughout his life was its most notable and influential fellow. He was active in Irish affairs, was (from 1661) governor of the Society for the Propagation of the Gospel in New England, and had some connection with the Court. His lodgings (in his sister’s house) were always open to visitors, and his laboratory became a center for research. In spite of frequent ill health he was continuously active in scientific endeavors, and with the aid of assistants (many of whom later became famous scientists) he experimented until his final illness. He was a prolific author, writing on science, philosophy, and theology.

Although Boyle’s first scientific interest was chemistry, his first published scientific book, the one that established his fame, was on pneumatics: New Experiments Physico-Mechanicall, Touching the Spring of the Air and its Effects (1660). Three years earlier he had learned of Guericke’s invention of an air pump and, immediately perceiving the scientific potentialities of the instrument, set his laboratory assistants to work designing one that had a glass receiver and was so constructed that objects could be easily inserted. Robert Hooke’s successful design permitted Boyle to devise and carry out a brilliant series of experiments upon the physical nature of air: he proved that the phenomena of Torricelli’s experiment were indeed caused by the air, that sound was impossible in a vacuum, that air was truly necessary for life and flame, and that air was permanently elastic. In an appendix to the second edition of New Experiments (1662), he developed this last discovery into a quantitative relationship (that volume varies inversely with pressure), rightly called Boyle’s law; here he also endeavored to refute several critics (including Hobbes and the English Jesuit Francis Linus) who tried to defend and uphold the old. Scholastic view that there was no such thing as a vacuum and that some mysterious force, rather than atmospheric pressure, was responsible for the phenomena associated with suction pumps and syphoning.

At intervals throughout his life, Boyle published further accounts of the experiments in vacuo that he never tired of devising and that he alone, among the scientists of his day, was capable of devising without cessation. Perhaps the most influential of these experiments were those showing that many fruits and vegetables contain air (actually carbon dioxide), which they give off during fermentation—the eighteenth-century chemist’s “fixed air.” Although Boyle’s reputation in experimental physics rests on his pneumatic experiments, he also worked in the related field of hydrostatics. His Hydrostatical Paradoxes (1666) is both a penetrating critique of Pascal’s work on hydrostatics, full of acute observations upon Pascal’s experimental method, and a presentation of a series of important and ingenious experiments upon fluid pressure.

The air pump experiments showed Boyle to be a confirmed opponent of Aristotelian and Scholastic physics, as well as an able and original experimental physicist. His scientific associates knew him better as a profound believer in the need to establish an empirically based, mechanistic theory of matter and in the possibility of establishing a scientific, rational, theoretical chemistry by means of just such a theory of matter. In 1660 he had already partially prepared a series of treatises upon both subjects, and he occupied himself for the rest of his life with experiments and arguments furthering these beliefs. His first published declaration of his positions appeared in 1661 in Certain Physiological Essays, a work whose arguments were somewhat obscurely supported by the now better known Sceptical Chymist, which was published later in the same year; both had circulated among scientists in earlier, manuscript versions.

Certain Physiological Essays made plain Boyle’s decided support for the particulate theories of matter then slowly displacing the Aristotelian view of the joint role of matter and form. Boyle was long remembered as “the restorer of the mechanical philosophy’s in England, and he regarded his corpuscularian philosophy as an original and useful theory of matter. He had been familiar with Epicurean atomism since boyhood, when he read Diogenes Laertius’ Lives of the Philosophers; he now read the extant writings of his contemporaries, like Gassendi’s brief Epicuri philosophiae Syntagma (1649) and Walter Charleton’s Physiologia Epicuro-Gassendo-Charletoniana (1654). He was, however, too devout to be a true Epicurean and too aware of the developments of contemporary science—to which he was, moreover, contributing fully—to accept any attempt to apply literal Epicureanism to the current scientific scene. Like all his contemporaries, he was familiar with Democritean atomism as confuted by Aristotle, but it had the same disadvantages as Epicureanism.

What really influenced him first were Bacon’s suggestive outlines of the possibilities of an empirically based particulate theory of matter (principally in Novum organum, 1620), and Descartes’s ambitious outline of a completely mechanistic and logical particulate view of the universe (in Principia philosophiae, 1644). From Bacon, he learned to regard heat as a mode of motion of the least particles of matter; he also learned to believe that experiment could lead one to demonstrate, and possibly to prove, the existence of such particles, and that it could further aid in the deduction of how the shape and motion of the particles could provide an explanation of the observed properties of bodies.

Similarly, Boyle took many specific explanations of the properties of matter from Descartes—for example, the view that solidity and fluidity depend upon the amount of relative motion of the constituent particles, the particles of solids being relatively quiescent—although he rejected Descartes’s detailed structure of particles, particularly the omnipresent Cartesian ether, for which he could find no experimental justification. He was also enormously influenced by the commanding scope of Descartes’s great system of the world, built logically from a few definitions of matter and laws of motion.

Boyle was an eclectic; what mattered most to him was destroying all Aristotelian forms and qualities—semantic explanations at best, such as the “form of heat” or “the dormitive virtue of opium”—and substituting for them rational, mechanical explanations in terms of what he called “those two grand and most catholic principles, matter and motion”.

“Mechanical”, to Boyle and his contemporaries, was always in opposition to both “Aristotelian” and “mystical”, mechanical explanations were rational and also, inasmuch as they dealt with particles of matter and their motion, consonant with the newly formulated laws of mechanics. It was, Boyle insisted, no derogation of God’s majesty to compare His creative power to that of a watchmaker, the creator of the most elaborate mechanism known to the seventeenth century. Boyle’s first aim in Certain Physiological Essays; in the more elaborate Origine of Formes and Qualities (According to the Corpuscular Philosophy), published in 1666; in the detailed and specific Experiments, Notes &c. About the Mechanical Origine or Production of Divers Particular Qualities, published in 1675; and in numerous other minor treatises was to refute the older Scholastic or Aristotelian view and establish the mechanical one in its place. His second aim was to show that this was best done by the use of experiment, and he devoted great care and ingenuity to devising (and conducting) experiments that should demonstrate the nonexistence of the supposed “substantial forms” and “real qualities” and the positive existence of particles whose size, shape, and motion could easily and rationally account for the observed behavior and properties of matter. The many experiments with which his works are filled made them useful even to those who did not accept his conclusions, and such experiments as those demonstrating the mechanical production of heat and magnetism can still command admiration. Since Boyle rejected both the atoms of the Epicureans and the complex hierarchy of particles of Descartes, preferring the neutral word “corpuscle”, his discussions were, as he hoped, acceptable and convincing to all mechanical philosophers, whatever theory of matter they chose to espouse.

No one except a dedicated Aristotelian could fail to find Boyle’s arguments powerful and convincing; the only question was whether the immense labor of the experimental approach was worthwhile or not. Such rationalists as Huygens and Leibniz were inclined to doubt the value of demonstrating by experiment what they (and all “rational” thinkers) knew to be true by logical resonating. In 1662 and 1663 Boyle conducted (through Henry Oldenburg, who often acted as his editor and literary agent) a long dispute with Spinoza on the question of whether experiment could provide proof: to Spinoza, only logical thought could provide the conviction that Descartes had taught the philosophical world to regard as proof, while experiment could only confirm or (possibly) refute; to Boyle, experiment was an essential ingredient of proof, and logical argument merely meant the employment of a priori hypotheses. This was an important difference in scientific method in the seventeenth century; although Boyle at first had few disciples, his eventual influence in this respect was very great—one of his firmest followers was Isaac Newton, a careful and impressionable student of Boyle’s works.

Boyle’s recognition of the complexities of the experimental approach was very rare in his day. Few before him had realized that empiricism required technique and the working out of methodical procedure. One reason for the now tedious length of most of his treatises was his desire to describe his expriments faithfully and in such a way that others could follow. He also was always careful to describe experiments that did not succeed, a procedure he defended in two of Certain Physiological Essays as essential to progress in experimental philosophy. Nonempiricists might very reasonably find all this tiresomely prolix, but heuristically it was important and influential. Through his writing on his experiments, Boyle helped establish the experimental method in many branches of physics and chemistry.

Successful though Boyle’s empirically based corpuscular philosophy was, it was not without its weaknesses and failures. He was always reluctant to antagonize those with fixed convictions, and therefore was often inclined to avoid committing himself to a definite and limiting view. Thus, he never satisfactorily described his own explanation of the cause of air’s elasticity, although he wrote about the problem on many occasions; indeed, he went so far in his first book on the air pump as to cite the analogy, originated by the anatomist Jean Pecquet, between air particles and coils of raw wool, an analogy that he almost certainly did not accept as an explanation. Yet readers of only this book cannot know of his later doubts, hesitations, and tentative suggestions for a more satisfactory explanation. (In fact, he seems to have held that the elasticity was caused by a combination of the shape of the particles and their motion.)

Again, although he made it very clear that he regarded the cause of heat as nothing more than the vibratory motion of particles, he never clearly defined cold as mere absence of motion, even in the special treatise he wrote on the subject, New Experiments and Observations Touching Cold (1665), which has very valuable discussions of thermometry and of freezing mixtures. He also spoke ambiguously on the nature of light and fire; and his conviction that all properties must ultimately reside in the properties of particles gave him curiously mixed results when, in his Experiments and Considerations Touching Colours (1664) he tried to understand what made matter appear colored. Whiteness and blackness (the nearly total reflection and nearly total absorption of light, respectively) he understood thoroughly and illustrated brilliantly with what came to be considered classic experiments, such as noting the effects of white and black cloths laid on snow on a sunny day. He also observed the colors on soap bubbles and thin glass surfaces (“Newton’s rings”). But he did not understand the relation of light and color, nor did he try to explain this relation or the prismatic colors in terms of modification of light; rather, he thought of light as having a physical constancy and color as being the result of an action by the material particles of bodies. In fairness, however, it must be noted that Boyle appreciated the treatment accorded light by Hooke in his Micrographia (1665) and by Newton in his papers on light and colors (1672, 1675), and recognized their superiority to him in optics.

It was not surprising that Boyle regarded extraordinary effects such as optical phenomena as the result of the configuration of particles, for he was, after all, a chemist as well as a physicist; and chemistry had been the first science he thoroughly mastered. He was a practiced and devoted technical chemist in his twenties, whereas he came to experimental physics (in the form of pneumatics) only at the age of thirty. It is true that many of his ideas on the nature and structure of matter were formulated before he began work on the air pump, but it becomes apparent, if one studies his work chronologically, that his first approaches to this subject were chemical. Indeed, his first specific publication on the corpuscular theory of matter, Certain Physiological Essays, also contains his first published account of chemical experiments. This is the complexly titled third essay: “Some Specimens of an Attempt to Make Chymical Experiment Usefull to Illustrate the Notions of the Corpuscular Philosophy”, with the subtitle “A Physico-chemical Essay, Containing an Experiment Touching the Differing Parts and Redintegration of Salt-Petre”; the body of the essay was subsequently referred to by Boyle as “The Essay on Nitre”. This, as he indicated, was an attempt to use a purely chemical experiment (the conversion of niter—KNO₃—to its seemingly component parts by means of a glowing lump of charcoal and its subsequent reconstitution from the fixed and volatile parts) to demonstrate the strong probability of the existence of particles that could persist through physical and chemical changes. Boyle recognized this as a novel approach, and also saw it as an attempt to show chemists that the physicist’s approach, the employment of the mechanical philosophy, might be useful to chemistry; for he considered that it contributed much to an understanding of the reaction involved if one thought in terms of particles (whether simple or complex). He expressly stated in the preliminary discussion that he hoped “to beget a good understanding ’twixt the chymists and the natural philosophers”, a lifelong desire only partially achieved.

It is difficult to realize how confused and confusing chemical reactions appeared before chemists thought in corpuscular terms. Chemistry in Boyle’s day still applied a sort of Aristotelian plenum: the only possibility of breaking down such a substance as niter was to resolve it into its component elements. Seventeenth-century elements, like the Greek elements but unlike nineteenth-century elements, were not merely the simplest bodies into which chemical substances could be analyzed or resolved; they were also the necessary ingredients of all bodies, the substances into which all bodies were analyzable. Thus, if salt was taken to be an element, then salt was present in all bodies and would appear as a product of rigorous analysis. Boyle not only thought that corpuscles were the only things universally present in all bodies; but he also suspected that none of the n accepted elements—whether the earth, air, fire, and water of the Aristotelians; the salt, sulfur, and mercury of the Paracelsans; the phlegm, oil, spirit, acid, and alkali of later chemists—was truly elementary, as the term was then understood. He tried to explain all this in the Sceptical Chymist, a curiously literary piece of polemic that is much misunderstood in modern times. Here, in spite of what is commonly said, Boyle did not give a modern definition of an element, but (specifically and intentionally) a clear definition of an element as it was understood in his day. The work is cast in a decidedly turgid dialogue form, perhaps in imitation of Galileo, perhaps merely as a relic of Boyle’s youthful literary proclivities; its chief value in its day, aside from its main message, was the wealth of chemical experiment that, like the “Essay on Nitre” showed the chemist how to employ corpuscular terms in chemical explanation and also presented new chemical facts. For, prolific experimenter that he was, Boyle almost always found new chemical combinations and reactions, as well as a few new chemical substances; the best-known of these is hydrogen, which he prepared from steel filings and strong mineral acid, but there were also various copper and mercury compounds. Unlike other chemists of his day, he never stressed the novelty of such preparations, for it was the reactions and their interpretation that interested him.

Convinced as he was that the term element, as used in his day, was an erroneous and misleading concept, Boyle never approached the modern definition, which emerged during the eighteenth century as the influence of his teaching helped to weaken the older view. He seems not to have felt the need of any elements other than corpuscles; in this he was perhaps, as some of his contemporaries complained, too much a physicist and too little a chemist in his mode of thought. But this skepticism did not prevent him from recognizing at least some classes of substances by a method and in a fashion far more useful to chemistry than the old notion of element had been. Characteristically, he arrived at this classification empirically and as an outgrowth of a combination of physical and chemical investigations.

The color changes observed in the course of chemical reactions had always interested Boyle, especially since he thought they showed how evanescent and unreal Aristotelian forms really were; in the Sceptical Chymist he described many reactions involving color changes. He went further in Experiments and Considerations Touching Colours, for here he not only described various ways of producing color changes, such as the conversion of a blue vegetable solution to red or green, but he also emphatically indicated a use for these color changes: chemical classification and identification. It had long been known that some acids turned the blue syrup of violets red; Boyle claimed to be the first to realize that all acids did so and that those substances that did not do so were not acids—a bold but useful distinction. Similarly, he claimed to be the first to note that alkalies—all alkalies—turned syrup of violets green. This left him with three classes of salts: acid, alkali, and those that were neither. He reinforced this empirically derived classification by observing that the blue opalescence of the yellow solution of lignum nephriticum (a South American wood with supposed medical virtues and of considerable optical interest) was destroyed when the solution was acidified and could be restored by the addition of alkali; he also used this reaction to determine the relative strength of acidic and alkaline solutions.

These tests also allowed Boyle to determine the purity of chemicals bought from apothecary shops. He discovered a further useful color change when he demonstrated (what he claimed to have deduced) that different alkalies give differently colored precipitates with mercury sublimate (mercuric chloride); “vegetable alkalis” (potassium carbonate and possibly sodium carbonate) give an orange precipitate (a form of mercuric oxide), while “animal alkalis” (ammonia compounds) give a white precipitate (ammonium-mercury chloride). Since limewater was already known to turn cloudy when a solution of niter was added, Boyle now had the ability to distinguish among all the common alkalies.

The importance of these tests, upon which Boyle placed absolute reliance, was very great, for in the late seventeenth century there was still great confusion over the identity, not to mention the composition, of various simple substances. He found it necessary on the one hand to insist that all salts were not common salt, but on the other that salt of tartar, hartshorn, and vegetable alkali were all one salt—a point not always appreciated by his contemporaries. Many chemists of his day insisted upon sweeping generalizations like that of the acid-alkali hypothesis (which claimed that all substances were either acids or alkalies, and all reactions therefore were neutralizations), or carelessly confused end products with starting materials.

Boyle was unique in realizing the continual need for meticulous care in examining purity, testing composition, and searching for chemical differences and similarities. How methodical he could be is amply demonstrated in his two investigations into the nature of phosphorus, The Aerial Noctiluca (1680) and New Experiments and Observations Made Upon the Icy Noctiluca (1682), in the course of which he discovered the chief chemical and physical properties of phosphorus and phosphoric acid, and in Short Memoirs for the Natural Experimental History of Mineral Waters (1685), an admirable set of analytical directions. Few other chemists of his day seem to have been sufficiently patient to elaborate an analytical procedure, although it became commonplace in the next century.

To his work on acids and alkalies Boyle added a host of other specific tests: for copper by the blue color of its solutions; for silver by its ability to form silver chloride, with its characteristic blackening over time; for sulfur and various mineral acids by their characteristic reactions. Some of these were new, others had been known for years or even centuries. These tests enabled him to discuss the composition of substances in what can only be called positivistic terms—that is, in terms of empirically determined components rather than in terms of metaphysical, a priori “elements.” This was perhaps Boyle’s greatest contribution to chemistry, for while few chemists followed him in altogether dispensing with elements, most chemist saw the utility of distinguishing in analysis between empirically verifiable components and a priori elements. When this occurred generally, the way lay open for the immense strides to be made in analytical chemistry in the eighteenth century. And although it was quite possible to practice this sort of chemistry without paying more than lip service to the corpuscular philosophy (a physicist’s theory, after all), there is no doubt that Boyle was helped by his adherence to the corpuscular philosophy, and perhaps would never have formulated his new chemical method without his habit of thinking in corpuscular terms. And it is not without significance that this more physical way of approaching chemistry was introduced into France by William Homberg, who worked for some time in Boyle’s laboratory.

In his lifetime Boyle was honored not only as an original chemist and physicist, a great exponent of English experimental philosophy, and a pillar of the Royal Society, but also as a prolific writer on natural theology, the point where religion and science met. He was a truly devout man and scrupulous to the point of having a tender conscience where oaths were concerned, as he explained in declining to serve as president of the Royal Society in 1680—presumably because he thought he might be subject to the provisions of the Test Act, as a public officer. Yet he was not dogmatic, and he was a devoted scientific investigator. Fortunately, he experienced no conflicts of conscience; for him a God who could create a mechanical universe—who could create matter in motion, obeying certain laws out of which the universe as we know it could come into being in an orderly fashion—was far more to be admired and worshiped than a God who created a universe without scientific law.

Boyle’s God stands in the same relation to the watchmaker as the watchmaker might to an untutored savage who thinks a watch is a living creature because its hands move. Boyle never tired of writing on this subject, finding his thoughts becoming more devout the more he studied the wonders of nature. Not all his numerous books on religious subjects were an offshoot of his scientific endeavors, but many were, and it was these that were influential. At his death Boyle left a sum of money to found the Boyle lectures (really sermons), intended for the confutation of atheism; and his contemporaries immediately concluded that he meant the arguments against atheism to be drawn from the scientific advances of his day. Hence the first and most famous series of Boyle lectures, by Robert Bentley, was filled with arguments and illustrations drawn from Bentley’s discussions with Newton. Subsequent Boyle lectures (by Clarke, Whiston, Woodward, Derham, and others) followed this pattern to produce what is thought of as a characteristically eighteenth-century form of “natural” religion, much less formal and theological than anything usual in Boyle’s day.

In this, as in so much else, Boyle set the tone and inspired the methods of thought widely accepted by the next two generations. In large part this was so because eighteenth-century Newtonians found that Boyle’s opinions, discoveries, and scientific method usefully supplemented those of Newton. Modern historians see this as a sign of Boyle’s very real influence upon Newton; Newtonians saw it as a proof that the “new science” was a product of the English methods proclaimed in the charter of the Royal Society.

BIBLIOGRAPHY

The standard edition of Boyle’s works is Thomas Birch, ed., The Works of the Honourable Robert Boyle, 5 vols. (London, 1744), 2nd ed., 6 vols. (London, 1772); available in a facs. repr. Separate works are The Sceptical Chymist (London–New York, 1911, and later eds.) and Experiments and Considerations Touching Colours (repr. New York, 1964). John Fulton, A Bibliography of the Honourable Robert Boyle, 2nd ed. (Oxford, 1961), is a complete bibliography of works by Boyle and of secondary sources to 1960. M. B. Hall, ed., Robert Boyle on Natural Philosophy (Bloomington, Ind., 1965), contains an introductory discussion of his work and long illustrative excerpts from his writings. Boyle’s manuscripts are preserved chiefly in the archives of the Royal Society. Many letters to Boyle are published in Birch’s edition cited above; his letters to Oldenburg are published in A. R. and M. B. Hall, eds., The Correspondence of Henry Oldenburg (Madison, Wis., 1965– ).

Marie Boas Hall