Robert Boyle

Boyle, Robert (1627–91)

Boyle is often remembered for the contributions that he made to the sciences of chemistry and pneumatics. Like other natural philosophers in seventeenth-century England, however, he was a synthetic thinker who sought to advance knowledge in all areas of human concern. An early advocate of experimental methods, he argued that experimentation would not only reveal the hidden processes operative in the world but would also advance the cause of religion. Through the study of nature, experimentalists would come to understand that the intricacy of design manifest in the world must be the result of an omniscient and omnipotent creator.

Boyle’s experimental investigations and theological beliefs led him to a conception of the world as a ’cosmic mechanism’ comprised of a harmonious set of interrelated processes. He agreed with the leading mechanical philosophers of his day that the corpuscular hypothesis, which explains the causal powers of bodies by reference to the motions of the least parts (corpuscles) of matter, provided the best means for understanding nature. He insisted, however, that these motions and powers could not be known by reasoning alone, but would have to be discovered experimentally.

1 Life and works

Robert Boyle, born 1627 at Lismore Castle, Ireland, was the youngest son of the first Earl of Cork, one of the wealthiest members of the English aristocracy. Boyle’s formal schooling was limited to four years at Eton (1635–9) after which he embarked upon a tour of Europe. He read the works of Galileo while visiting Florence, and studied the classics, languages, Calvinist theology and Epicurean philosophy during an extended stay in Geneva. Upon the death of his father in 1644 he returned to England and resided in London with his sister Katherine, Lady Ranelagh, through whom he met a number of leading educational theorists, mechanical philosophers and chemists such as Samuel Hartlib, John Milton, Kenelm Digby and Benjamin Worseley.

In 1646 Boyle retired to his inherited estate at Stalbridge where he wrote moral and theological essays, compiled catalogues of medicinal remedies, and began experimental studies in chemistry and anatomy. He moved to Oxford in 1655 in order to work with an informal group of experimentalists meeting there that included Robert Hooke, John Locke and Christopher Wren. While at Oxford he also associated with theologians and linguists such as Thomas Hyde, Samuel Clarke and Thomas Barlow, and he became involved in a number of business ventures including the Hudson’s Bay Company and the East India Trading Company. In 1665 he received an honorary medical degree from Oxford. In 1668 he returned to London and lived there with his sister until both of them died, a week apart, in December 1691.

Boyle gained international recognition with the publication of his first major scientific work, New Experiments Physico-Mechanical, Touching the Spring of the Air (1660), in which he reported a series of experiments performed with an air-pump designed to support the notion of the weight of the air developed by Pascal and Torricelli and his own conception of the spring (elasticity) of the air. His work was seen by many as a significant improvement upon earlier Aristotelian speculations, yet it was also severely criticized, by Henry More and Thomas Hobbes among others. In 1662 he published responses to his critics in a second edition of New Experiments that also contained the first formulation of Boyle’s law, which describes the inverse proportion between the pressure and volume of a gas.

Boyle’s interests were broad and eclectic and his inherited wealth provided him with the leisure to pursue many areas of study. During his lifetime he published over forty works ranging from comprehensive experimental histories to defences of the Christian religion and the new corpuscular philosophy. In one of his last books, The Christian Virtuoso (1690), he explained that such eclecticism was warranted because ‘true philosophy’ is ’of greater extent, than the hypothesis of any one sect of philosophers, being indeed a comprehension of all the sciences, arts, disciplines, and other considerable parts of useful knowledge’.

2 Experimental philosophy

Boyle first became acquainted with the Baconian concept of useful knowledge through his association with the Hartlib group in London, and his own laboratory investigations, particularly in chemistry, increased his conviction that experimental practices would be required to improve upon what he perceived to be the ’barrenness’ of the natural philosophy taught in the schools. He agreed with Bacon that the Aristotelian distinction between natural and artificial processes was not tenable and that the experimental manipulation of natural bodies could yield more than immediate utilitarian benefits (see Bacon, F.). As Boyle explained in his Usefulness of Experimental Philosophy (1670), the production of effects under the controlled conditions of a laboratory may ’either hint to us the causes of them, or at least acquaint us with some of the properties or qualities of things concurring to the production of such effects’.

Although he designed his experimental method as a way by which to learn about the causal processes operative in nature, he opposed what he found to be the premature theoretical systems of many of his contemporaries. In The Sceptical Chymist (1661), for example, he produced experimental refutations of the prevalent Aristotelian and alchemical theories of elements, but he offered no theoretical account of his own with which to replace them (see Alchemy; Natural philosophy, medieval §1). In other works where he did speculate about the causal powers of bodies, his discussions were tentative and hesitant. Boyle’s caution was in part a result of the many practical problems that he encountered in his laboratory. His reflection upon the epistemological significance of these ’contingencies of experiment’ led him to write one of the earliest and most complete accounts of the systematic errors associated with experimental practice.

In his Certain Physiological Essays (1661), Boyle discussed how the use of impure ingredients, imperfect instruments or inappropriate techniques could lead to experimental failure. To mitigate the effects of systematic error, he designed a number of methodological strategies. Some were meant for specific areas of investigation, such as the indicator tests that he developed for the identification of acids and alkalies. Others, such as repetition and variation, were offered as general strategies to be used for all areas of investigation. In order to establish that an experimental result provides reliable evidence about a natural process, one has to ensure that it is not an artefact of the particular materials or instruments used in its production. Not only is it necessary to repeat experimental trials and vary their circumstances, it is also necessary to publish complete accounts of experiments so that others will be able to repeat the trials for themselves or at least judge the appropriateness of the experimental conditions and the soundness of any inferences drawn from them. Boyle’s practical implementation of his programmatic methodological statements can be seen in the experimental histories that he wrote on Colours (1664), Cold (1665), Blood (1684) and Air (1692).

Unlike the stress upon individual reasoning found in the Scholastic and Cartesian philosophical traditions, Boyle insisted that collaboration and cooperation among naturalists were necessary for the advancement of knowledge. This belief was a product of his methodological dictates as well as a consequence of his view concerning the justification of theoretical speculations. According to Boyle, a theory is acceptable only after a ’concurrence of probabilities’ has been produced whereby all of the relevant and available evidence supports a particular conclusion.

Experimentation should ’beget a confederacy, and an union between parts of learning’, because often more than one area of investigation would be required to learn about a natural process. A full understanding of the circulation of the blood, for example, had required the efforts of workers whose areas of expertise were in physiology, anatomy, chemistry and mechanics. As he explained in his Usefulness of Natural Philosophy (1664), there is a ’dependency, continuation, and confederacy of causes’ in nature that results from the ’secret correspondencies and alliances’ between things. This ontological conception was supported by his experimental work as well as by his theological worldview.

3 Theology

In addition to being an experimentalist, Boyle was also a lay theologian who emphasized the importance of revealed religion. In The Excellency of Theology (1674) he argued for the intellectual superiority of scriptural studies over natural philosophy and early in his career he published a work on what we would today call biblical hermeneutics, The Style of the Holy Scriptures (1661), that is significant for understanding his views on interpretation. According to Boyle, the ’seeming contradictions’ identified by critics of the Bible are the product not of its divine author but ’of our ignorance’. The Bible is a complex interrelated whole that must be ‘coherent’ because God would not require humans to believe inconsistencies. The proper method of interpretation, therefore, would require that readers attempt to eliminate apparent contradictions by a gradual process of reconciliation.

In A Free Inquiry into the Received Notion of Nature (1686), Boyle discussed how nature could also be described as a divine text because it is composed of a complex set of interrelated parts all of which were designed by God to produce one coherent whole. The relations that obtain in nature are the ’result of the universal matter, or corporeal substance of the universe, considered as it is contrived in the present structure and constitution of the world, whereby all bodies, that compose it, are enabled to act upon, and fitted to suffer from one another’. In anticipation of Leibniz, Boyle discussed the perfection of the world and maintained that there is an ‘intercourse and harmony between truths’. Naturalists must attempt to discover the ‘connection of physical truths, and the relations that material bodies have to one another’ and thus the interpretation of nature would require the same type of reconciliation process that he had recommended for the Scriptures.

Boyle criticized the Cartesians and atomists who excluded considerations of final causality from their philosophical systems because he believed that the investigation of nature provided one of the best means for learning about its creator. In his Disquisition about the Final Causes of Natural Things (1688), he argued that God may ’declare truths to men, and instruct them, by his creatures and his actions, as well as by his words’. The study of nature could thus lead an experimentalist to the ‘acknowledgement of the divine Architect’s power, wisdom and beneficence’. He did agree with his contemporaries’ criticisms of Aristotelian teleology, however, and he maintained that it was not legitimate to refer to God’s purposes when explaining physical processes. Yet some appeal to God’s initial act of creation could provide a valuable heuristic for natural investigations. Indeed, his conception of the coherence of the world guided his specific formulation of the corpuscular hypothesis and his belief in the omniscience of the creator led him to insist that corpuscular explanations could not be justified by a priori reasoning, but would require experimental proof.

4 Corpuscular hypothesis

In his ‘Excellency and Grounds of the Mechanical or Corpuscular Hypothesis’ (1674) Boyle argued that corpuscularianism was simpler and more intelligible than the alternative Aristotelian doctrine that appealed to the occult qualities and substantial forms of bodies. In his Origin of Forms and Qualities (1666) he also defended a mechanical account of nature by which physical phenomena were to be explained by considering ’only the size, shape, motion (or want of it), texture, and the resulting qualities and attributes of the small particles of matter’. These arguments were similar to those of other mechanical philosophers. Boyle’s extensive experimental practice and his interest in the chemical composition of bodies led him to reject what he saw to be the purely quantitative and mathematical analysis of Descartes, however, and to advocate a more qualitative approach to the study of nature. According to Boyle, it is the set of qualities possessed by a body that defines its essence and gives it the causal power to produce changes in other bodies. He developed an account of the primary and secondary qualities of bodies, which would receive further elaboration and refinement in the philosophical writings of John Locke, in order to describe how corpuscular explanations would allow for a qualitative understanding of physical phenomena (see Locke, J. §4; Primary–secondary distinction §1).

Primary qualities are those ’affections’, such as size and shape, that must belong to all parts of matter. Secondary qualities, on the other hand, are those properties of bodies such as colour and temperature that result from the internal configuration of the parts of matter of which they are composed as well as the external relations that they have to other bodies. Boyle maintained that these secondary qualities ’do as well seem to belong to natural bodies generally considered, as place, time, motion and those other things… treated of in the general part of natural philosophy’. Although the secondary qualities of bodies are causally responsible for human sensations, they are not ’like to the ideas they occasion in us’. Heat, for example, is a product of the rapid motion of the particles composing a body, such as the sun. The sun has the secondary quality of heat that gives it the power to produce the sensation of heat in a human, but even if all ’sensitive beings in the world were annihilated’ the sun would retain its secondary quality and thus continue to have the power to affect other bodies such as ice and wax.

In The Mechanical Origin or Production of Divers Particular Qualities (1675), Boyle reported experiments that he had performed to show how secondary qualities could be added to or taken away from bodies simply by a mechanical alteration of their structure. Repeatedly striking a metallic body with a hammer will cause it to become hot, for example, whereas a piece of glass operated upon in the same way will lose its transparent quality and be reduced to a white powder. Although this work helped to establish the feasibility and intelligibility of mechanical explanations, Boyle was never able to specify the ultimate causal mechanisms responsible for the effects that he produced in his laboratory. His lack of theoretical success may be attributed to his overly cautious attitude that resulted from his appreciation of the fallibility of experimental practice and the complexity of natural processes, as well as to his eclectic and comprehensive approach whereby he sought to combine researches in physics, chemistry and biology. His works are of lasting historical significance not so much because of the specific theories that he developed but because of his successful promotion of a new way of thinking about nature and a new method for investigating physical processes. A self-proclaimed ’underbuilder’, he provided the materials and methods that later thinkers such as Newton and Lavoisier would use to great advantage (see Newton, I.; Chemistry, philosophical aspects of §3).