philosophy was like Galileo’s claim that the book of Nature was written in mathematical terms. Boyle’s book was ‘a well-contrived romance’ of which every part was ‘written in the stenography of God’s omnipotent hand’, i.e. in corpuscular, rather than geometrical, characters. By revealing its design, like Gassendi and Charleton earlier, Boyle reconciled what had formerly been perceived as an atheistical system with religion and, indeed, with the tenets of the Anglican church that had become the re-established Church of England following the Civil War.
Boyle demonstrated the usefulness of chemistry not merely to medicine and technology (where it had long been accepted) but also to the natural philosopher, who had long despised it as the dubious activity of alchemists and workers by fire. Boyle aimed to show natural philosophers that it was essential that they took note of chemical phenomena, for the mechanical philosophy could not be properly understood otherwise. It was true, he admitted, that the theories of ordinary spagyrical chemists were false and useless; nevertheless, their experimental findings deserved attention, for if they could be disentangled from false interpretations, much would be found that would illustrate and support the corpuscular theory of matter.
In this way, Boyle strove to ‘begat a good understanding betwixt the chymists and the mechanical philosophers’. Chemists recognized him as a fellow chemist, even though he was a natural philosopher; while the natural philosophers recognized him as a respectable chemist because he was also a member of their company. By advocating a mechanical philosophy, Boyle would raise the social and intellectual status of ‘workers by fire’, reduce their proneness to secrecy and mysterious language, and make them into natural philosophers. As he wrote in another essay of 16612:
I hope it may conduce to the advancement of natural philosophy, if,… I be so happy, as, by any endeavours of mine, to possess both chymists and corpuscularians of the advantages, that may redound to each party by the confederacy I am mediating between them, and excite them both to enquire more into one another’s philosophy, by manifesting, that as many chymical experiments may be happily explicated by corpuscularian notions, so many of the corpuscularian notions may be commodiously either illustrated or confirmed by chymical experiments.
Boyle may be said to have united the proto-disciplines of chemistry and physics. But the partnership proved premature, for Boyle succumbed to the danger of not replacing the elements and principles of the chemists with a mechanical philosophy that was useful to the working chemist. This criticism can be most clearly made when discussing Boyle’s definition of the element in the sixth part of The Sceptical Chymist.
I now mean by elements, as those chymists that speak plainest do by their principles, certain primitive and simple, or perfectly unmingled bodies; which not being made of any other bodies, or of one another, are the ingredients of which all those called perfectly mixt bodies are immediately compounded, and into which they are ultimately resolved.
Leaving aside the fact that Boyle made no claim to be defining an element for the first time (as so many modern chemistry textbooks claim), in his next sentence he went on to deny that the concept served any useful function:
… now whether there be any one such body to be constantly met with in all, and each, of those that are said to be elemented bodies, is the thing I now question.
A modern analogy will make Boyle’s scepticism clear. If matter is composed ultimately of protons, neutrons and electrons, or, more simply still, of quarks, this, according to Boyle, should be the level of analysis and explanation for the chemist, not the so-called ‘elements’ that are deduced from chemical reactivity. To Boyle, materials such as gold, iron and copper were not elements, but aggregates of a common matter differentiated by the number, size, shape and structural pattern of their agglomerations. Although he clearly accepted that such entities had an independent existence as minima, he was unable to foresee the benefit of defining them pragmatically as chemical elements. For Boyle an ‘element’ had been irreversibly defined by the ancients and by his contemporaries as an omnipresent substance.
The seventeenth-century corpuscular, physical philosophy was all very well. It might explain chemical reactions, but it did not predict them, nor did it differentiate between simple and complex substances, the elementary and the compound. Nor, at this stage, did it align the supposed particles with weight and the chemical balance. Hence, although corpuscularianism was not overtly denied by later chemists, who were often content to accept it as an explanation of the physical character of matter, in chemical practice it was ignored. Chemists still needed the concept of an element and blithely returned to the four elements or to some other elementary concept. One thing had changed, however, as a result of Boyle’s criticisms. It was no longer possible to argue seriously that all of the possible elements, however many a chemist might postulate, were ubiquitously present in a particular material. Boyle’s scepticism suggested the possibility that some substances might contain less than the total number of elements; this made it possible for later chemists to be pragmatic about elements and to increase their number slowly and stealthily throughout the eighteenth century.
This more pragmatic view is seen clearly in Nicholas Lemery’s Cours de chymie (1675; English trans. 1686)3:
The word Principle in Chymistry must not be understood in too nice a sense: for the substances which are so-called, are Principles in respect to us, and as we can advance no further in the division of bodies; but we well know that they may be still further divided in abundance of other parts which may more justly claim, in propriety of speech, the name of Principles: wherefore such substances are to be understood as Chymical Principles, as are separated and divided, so far as we are capable of doing it by our imperfect powers.
This comes pretty close to Lavoisier’s operational definition of an element (Chapter 3).
It would be wrong to leave the impression that Boyle was a modern physical chemist, or, rather, chemical physicist. As a corpuscularian, Boyle had no difficulty in accepting the plausibility of transmutation of metals; indeed, a particle theory made ‘the alchymists’ hopes of turning other materials into gold less wild’. We know that Boyle took stories of magical events and of successful transmutations extremely seriously. In 1689 Boyle helped to secure the repeal of Henry IV’s Act against the multiplication of silver and gold, on the grounds that it was inhibiting possibly useful metallurgical researches. Throughout his life he investigated alchemists’ claims, albeit privately and cautiously and even secretly since, as recent research has shown, he clearly identified transmutation with the intervention of supernatural forces.
THE VACUUM BOYLIANUM AND ITS AFTERMATH
Boyle’s other principal contribution to natural philosophy was his investigation of the air, made possible by the invention of the air pump. The vacuum pump was first developed in Germany by Otto von Guericke, who demonstrated at Magdeburg in the 1650s how air could be pumped laboriously out of a copper globe to leave a vacuum. He then found that the atmosphere exerted a tremendous compressing force upon the globe. This was demonstrated theatrically in the famous Magdeburg experiment, which involved sixteen horses in trying to tear two evacuated hemispheres apart. Details of Guericke’s pumping system, which were published in 1657, rapidly awakened interest throughout Europe; for if a vacuum really was formed, this was prima facie evidence for the fallibility of Aristotelian physics and evidence in favour of the corpuscular philosophy.
Assisted by a young and talented laboratory assistant, Robert Hooke, Boyle built his own air pump in 1658 and began to investigate the nature of combustion and respiration with its aid. Some forty-three of his experimental findings, most of which he had had carefully witnessed by reputable friends and colleagues, were published
